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Studies in Surface Science and Catalysis 164

BIOCATALYSIS IN OIL REFINING

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Studies in Surface Science and Catalysis 164

Advisory Editors: B. Delmon and J. T. Yates Series Editor: G. Centi

Vol. 164

BIOCATALYSIS IN OIL REFINING

M. M. Ramírez-Corredores Strategic Options-Refining Technology, B.P. International Ltd., Sudbury on Thames, UK.

Abhijeet P. Borole Oak Ridge National Laboratory, Oak Ridge, Knoxville, USA.

Amsterdam • Boston • Heidelberg • London • New York • Oxford

Paris • San Diego • San Francisco • Singapore • Sydney • Tokyo

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Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, The Netherlands Linacre House, Jordan Hill, Oxford OX2 8DP, UK

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Dedication

To Alejandro and Susana, who are the source of my inspiration in life. Magdalena Ramírez,

To my parents, who taught me that perseverance and dedication are key to success in life,

Abhijeet P. Borole

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FOREWORD

The oil industry is experiencing unexpected changes, some derived from the volatility of the prices, while others originating from the market situation. Demand is growing steadily but the supply is not able to cope up with the demand. The supply profile is itself changing, since the average slate is becoming heavier and increasingly sour. Geographically, the largest exploration is taking place in the North and South American continents, where the largest reserves of heavy oil exist. The heavier oils are being characterized to identify the higher molecular weight compounds present in these crudes and to determine the extent of heteroatom molecules or contaminants. There is a definite need to develop new technologies or optimize existing ones for conversion of the heavy molecules (known as the heavy end or the bottom of the barrel) and for the removal of the contaminants in a cost-effective way.

Clean production and energy efficient processes constitute the fundamental principles governing new technology developments. The R&D activities on biological transformation of organic molecules, which started some 40 years ago, showed promise for some industrial sectors. Biotechnologies have found their way in different economy sectors, for which biotechnology-based solutions have been implemented. The extent of application of biotechnological solutions has been limited. Over the next few years, however, this will change and such technologies are expected to take over traditional chemical technologies.

Within the oil industry itself, the biological solutions have been investigated for various upstream and downstream operations, although commercialization has not been observed. This book is focused on downstream or refining bioprocess applications. Its intent is to build a bridge between science and technology, by analyzing the open literature as well as the information buried within the patent literature. The multi-disciplinary nature of this technology requires biologists, chemists and engineers ‘speaking’ a common language and understanding the complexity of biological-chemical-engineering issues. The lack of a commercial process in this area indicates the complexity of this problem and the need for thinking out of the box.

The bridge we are intending to offer through this book would make it clear that the alternative approach needs to be strongly collaborative between different branches of science and engineering and establishing the connections and alliances to complete the whole set of skills, competences, and infrastructure and maximizing the intellectual capital. The collected information and knowledge is presented together with the identification of the stakeholders involved (people and companies). The reader will have the chance to structure and complement his/her team with the information provided or search in the presented references. Open knowledge could also be complemented with a suitable proprietary intellectual property by subscribing to appropriate joint ventures, partnerships

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viii Foreword

or licensing contracts. The implementation of a bioprocess in the oil refining industry may seem far away; however, identifying a niche and implementing multi-disciplinary resources can put this on a fast track. Although, it is evident that significant more work and alternate approaches are needed, the vast existing knowledge can provide significant insight into identifying the right target and a potential development path to enable successful implementation of bioprocessing technologies in the future. The reader is invited to accept the challenge.

M. M. Ramírez-Corredores and Abhijeet P. Borole

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PREFACE

Biotechnology is a powerful enabling technology to achieve clean industrial products and processes while promoting industrial sustainability. Biotechnology has been penetrating industrial operations in many sectors, because of its ability to reduce the number of manufacturing steps, thereby reducing material and energy consumption, and reduction in pollution and waste generation, for the same level of industrial production. Numerous applications of biotechnology can be found in Pharmaceuticals, Fine Chemicals, Life Science Research, Agriculture, Food & Beverage, and Cosmetics industries but not in the Oil industry. The potential of biotechnology in the oil refining industry is the subject of this book. Significant research has been done in one major area, biodesulfurization, although commercialization has not taken place. This book describes the efforts in biodesulfurization and other areas of oil refining.

The need for this book was realized due to the large gap in the knowledge of a typical researcher in a petroleum or petrochemical industry in investigating or developing a biotechnology-based solution to a refinery problem. Secondly, there was a need to compile all the findings in the petroleum biorefining and bioupgrading area to facilitate future research in this area. Thus, this book is geared towards helping researchers and technologists catch up on previous and current research in this field.

Chapter 1 describes the current scenario and the need for biotechnological solutions. In the first Chapter, we have also provided definitions of some general biology terms to bring the petroleum industry researcher up to speed and referred to the particular application where the terms may be useful. Chapter 2 gives an overview of the conventional hydroprocessing schemes currently in use in refining operations. This Chapter is included for the biotechnology researcher who has little knowledge of the refinery operations. Chapter 3 provides the details of the biocatalyst and bioprocess developments to date. This includes the widely studied biodesulfurization (BDS) as well as the less studied biodenitrogenation (BDN), biodemetallization (BDM), and bioconversion or bioupgrading (BCK). Chapter 4 is included to provide the reader with an information resource to help with research and development activities. This Chapter lists companies actively involved in the biotechnology arena, both for R&D and for commercial operations, which can be used to find molecular biology and enzyme supplies, or to find companies offering services in the biotechnology area. Chapter 5 describes the technological results, in the form of awarded patents and analyzes their chronology and implications for refining operations.

Developing a bioprocess for removing heteroatoms from petroleum or for upgrading heavy crudes involves two main components. The first is biocatalyst development and second is bioprocess development. Both of these topics are discussed in this book,

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x Preface

although there has been much more work done in biocatalyst development compared to the processing aspects. The complexity of finding a suitable biocatalyst for say, biodesulfurization or any other refining operation, is enormous. This is because of two reasons. First reason is related to the complexity of the material to be converted and second, is related to the multi-phase bioprocess involving, an oil, aqueous, gas (usually air), and a solid (biocatalyst) phase. The effort needed to find the solution is no doubt a multi-disciplinary one, involving petroleum chemistry, analytical chemistry, microbiology, molecular biology, enzymology, and chemical engineering. The first problem is that petroleum or any refined stream contains numerous species of molecules on which the biocatalyst needs to act on. Thus, the substrate specificity needed is very broad. Unfortunately, biocatalysts, by design are supposed to be very specific. This is what enables the biocatalysts to overcome reaction energy barriers at low temperatures and pressures, unlike chemical catalysts. To develop suitably broad and highly active biocatalysts, newly developed genetic engineering and molecular biology techniques have to be employed. These techniques are discussed in the book as well, with reference to their application. Companies involved in providing services in these areas are listed in Chapter 4 and cover expertise in gene identification, sequencing, strain development and bioprocess engineering needs. In addition, several Universities and research organizations are also discussed with reference to screening of microorganisms, enzyme characterization, and pathway identification.

In addition to the bioprocessing of petroleum, the book also contains a small section on bioremoval of hydrogen sulfide from gaseous streams. This applies to removal of hydrogen sulfide from effluents from hydrotreatment operations. It forms an essential part of the biotechnology portfolio for the petroleum refining industry. Chapter 3 as well as Chapter 5 includes discussion on bioprocesses capable of removing hydrogen sulfide.

The Chapter 5 provides an integrated list of companies and research organizations involved in petroleum biorefining research. The background of each company and its efforts leading to its patent portfolio in this area are discussed. We have tried to include all known companies that have participated to date in this area; however, the list is not strictly exhaustive.

Finally, hoping that this book provides every reader with the information he/she is looking for. If you do not, you may contact us the address provided and we will make every effort to respond. You may reach us to provide your feedback or tell us about the deficiencies in this book. We wish you an informative and pleasant reading.

Abhijeet P. Borole and Maria Magdalena Ramírez-Corredores September 2006.

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CONTENTS

Foreword vii

Preface ix

Chapter 1 Introduction 1

1. Refining Scenarios 1

2. Biocatalysis 3

Chapter 2 Conventional refining processes 9

1. Introduction 9

2. Hydrotreating Processes 14

2.1. Chemistry 15

2.1.1. Reactions 15

2.1.2. Catalysts 18

2.2. Process 22

3. Gasoline Hydrotreating 24

3.1. Chemistry 25

3.2. Process 26

4. Diesel Hydrotreating 28

4.1. Chemistry 29

4.2. Process 35

5. Vacuum Gas Oil Hydroprocessing 40

5.1. Vacuum Gas Oil Hydrotreating 41

5.2. Vacuum Gas Oil Hydrocracking 43

6. Residue Hydroprocessing 46

6.1. Residue Hydrotreating 48

6.2. Residue Hydrocracking 51

References 56

Chapter 3 Emerging biocatalytic processes 65

1. Preamble 65

2. BDS 67

2.1. General 67

2.2. Biocatalytic Technologies (Microorganisms and Derivations) 68

2.2.1. Initial biodesulfurization efforts 68

2.2.2. Anaerobic Pathways 70

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2.2.3. Aerobic sulfur-specific pathways 71

2.2.4. Aerobic Destructive and Ring Opening Pathways 88

2.2.5. Genetics of desulfurizing organisms 91

2.2.6. Purification and characterization of desulfurization

enzymes 93

2.2.7. Specificity of desulfurization enzymes 101

2.2.8. Enzymatic desulfurization 102

2.2.9. Biocatalyst production, recycle, and regeneration 103

2.2.10. Engineered strains for desulfurization 107

2.2.11. Strategies for further microbial catalyst

improvement 115

2.3. Process Aspects 116

2.3.1. Overall process designs and patented technologies 116 2.3.2. Process parameters and operating conditions 126 2.3.3. Bioreactor design and development 128 2.3.4. Separation of oil-water-biocatalyst mixtures 130 2.3.5. Other process options 134 2.3.6. Diesel biodesulfurization 135 2.3.7. Biodesulfurization of gasoline 141

2.4. Desulfurization of Gaseous Streams 141

2.5. Summary 144

2.5.1. Pioneering biocatalytic work 144

2.5.3. Biocatalytic enzymes 145 2.5.4. Activity improvement 145 2.5.5. Specificity improvement 146 2.5.6. Biocatalyst production and regenerability 147 2.5.7. Bioreactor and process schemes 147 2.5.8. Product separation 148

3. BDN 149 3.1. General 149

2.5.2. Biocatalyst concept and BDS-active Microorganisms 144

3.2. Metabolic Pathways 151

3.2.1. Acridine 152

3.2.2. Carbazole and derivatives 152

3.2.3. Quinoline and derivatives 154

3.2.4. Isoquinoline 160

3.2.5. Indole 161

3.2.6. Pyridine and derivatives 163

3.3. Enzymes 165

3.3.1. Quinoline and related compounds 166

3.3.2. Carbazole 171

3.3.3. Indole 172

3.3.4. General 172

3.4. Microorganisms 172

3.5. Process Aspects 179

3.6. Summary of BDN Advances 183

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Contents xiii

4. BDM 184

4.1. General 184

4.2. Technical findings 186

4.2.1. Enzymatic work 186

4.2.2. Microbial work 187

5. Bio-Upgrading 189

5.1. General 189

5.1.1. Heavy oil characteristics 190

5.1.2. Pathways for upgrading heavy crudes 191

5.2. Viscosity and MW reduction 192

5.2.1. Structural splitting 192

5.2.2. Oxygen introduction 194

5.2.3. Aromatic ring saturation 199

5.3. Processes 199

5.3.1. Viscosity reduction processes 199

5.3.2. Chemical conversion processes 200

References 204

Chapter 4 Biotechnology and supporting companies 227

1. General 227

2. Biology-Based Organizations 231

2.1. Introduction 231

2.2. Molecular Biology Companies 232

2.2.1. 454 Corporation 232 2.2.2. Advance ChemTech 232 2.2.3. Agowa 233 2.2.4. AlphaGene 233 2.2.5. Alpha Innotech 233 2.2.6. Amplicon Express 233 2.2.7. Ana-Gen 234 2.2.8. Anaspec, Inc. 234 2.2.9. Applera 234 2.2.10. Aurora Biomolecules 234 2.2.11. Biacore 234 2.2.12. Biopro International, Inc. 235 2.2.13. Bioserve Biotechnologies, Ltd. 235 2.2.14. BioVentures 235 2.2.15. BioWorld Products 236 2.2.16. Caliper Life Sciences 236 2.2.17. ChemGenes Corporation 236 2.2.18. Commonwealth Biotechnologies, Inc. 236 2.2.19. DGT Digital Gene Technologies 237 2.2.20. European Molecular Biology Laboratory’s 237 2.2.21. GATC Biotech 237 2.2.22. Miltenyi Biotec 238 2.2.23. Proteinlabs, Inc. 238

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2.2.24. Structural Genomics Consortium 238

2.2.25. Structural Genomics Centers 239

2.2.26. Zyomyx, Inc. 239

2.3. Genetic Engineering Companies 239

2.3.1. Aptagen Gene 239 2.3.2. Biotage 239 2.3.3. Cambio 240 2.3.4. Entelechon 240 2.3.5. Geneart 241 2.3.6. Invitrogen 241 2.3.7. Joint Center for Structural Genomics 242 2.3.8. Operon Technologies, Inc. 242 2.3.9. Orchid Cellmark 243 2.3.10. Oxford Gene Technologies 243

2.4. (Microbiology) Depositary Agencies 243

2.4.1. American Type Culture Collection (ATCC) 243

2.4.2. German Collection of Microorganisms and Cell Culture 246

2.4.3. Ferm 246

3. Biocatalyst (Enzyme/Protein) Companies 247

3.1. Altus Biologics, Inc. 249

3.2. Applied Enzyme Technology Ltd. 249

3.3. Bachem 250

3.4. Biocatalysts Ltd. 250

3.5. BioCatalytics, Inc. 251

3.6. Biopract 251

3.7. BioResearch Products, Inc. 251

3.8. Diversa Corporation 251

3.9. Enzyme Services and Consultancy 252

3.10. Iogen Corporation 253

3.11. Maps (India) Ltd. 253

3.12. Novozymes A/S 254

3.13. N-Zyme BioTec GmbH 255

3.14. Worthington Biochemical Corporation 255

4. Biotechnology-Based Companies 256

4.1. Acacia Research Corp. 256

4.2. Affymetrix 257

4.3. Apocom Genomics 257

4.4. Aurora Biosciences Corporation 258

4.5. Avecia Biotechnology 258

4.6. AVIVA Biosciences Corporation 258

4.7. Ben Venue Laboratories 259

4.8. Beyond Genomics, Inc. 259

4.9. Bio-Concept Laboratories Inc. 260

4.10. BioZone Laboratories 260

4.11. Biologics Process Development, Inc. 260

4.12. Bio Science Contract Production 260

4.13. BioMetics 261

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Contents xv

4.14. Cedra Corporation 261

4.15. Cell & Molecular Technologies, Inc. (CMT) 261

4.16. ChemOvation Ltd. 262

4.17. Ciphergen Biosystems 262

4.18. Cogenics 262

4.19. deCODE Genetics 263

4.20. Delaware Biotechnology Institute 264

4.21. DiscoveRX Corporation 264

4.22. Dyadic International, Inc. 265

4.23. Enchira Biotechnology 265

4.24. Genencor International, Inc. 266

4.25. Goodwin Biotechnology, Inc. 266

4.26. GPC Biotech’s 267

4.27. HyClone 267

4.28. Illumina, Inc. 267

4.29. Integrated Genomics 268

4.30. Large Scale Biology Corporation 269

4.31. Maxygen, Inc. 269

4.32. MediChem International 271

4.33. Millipore 271

4.34. Molecular Machines & Industries GmbH 272

4.35. Nanogen, Inc. 272

4.36. Novagen, Inc. 273

4.37. Organix, Inc. 273

4.38. PerkinElmer Life Sciences (Formerly: NEN Life Science Products) 274

4.39. Prior Separation Technology 274

4.40. Proteus 274

4.41. Sangamo BioSciences, Inc. 275

4.42. The Center for Biotechnology 276

4.43. Xencor 276

References 277

Chapter 5 R&D technological results 279

Overview 279

1. Agip Petroli (Italy); Enichem Anic Spa (Italy), and Eni Tecnologie

Spa (Italy) 281

2. Archaeus Technology Group Ltd. (Great Britain) 285

3. Arctech Inc/Atlantic Research Corporation (United States) 286

4. ASS Universities Inc/Brookhaven Science (United States) 287

5. Atlantic Richfield Co (United States) 291

6. Atlas, Ronald/Southern Pacific Petroleum (United States) 291

7. Babcock & Wilcox Co (United States) 292

8. BHP Minerals International Inc. (United States) 293

9. Biostar BV (Netherlands) 294

10. BWN Live Oil (Australia) 295

11. Clean Diesel Technologies, Inc. (United States & International) 296

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xvi Contents

12. Combustion Engineering (United States) 297

13. Environmental Bioscience Corporation/Energy Biosystems Corp./Enchira

Biotechnology Corp. (United States) 298

13.1. Environmental Bioscience Corp (EBC1) 306

13.2. Energy Biosystems Corporation (EBC2) 307

13.3. Enchira Biotechnology Corporation (EBC3) 322

14. Exxon Research and Engineering (ER&E) Co (United States) 323

15. Gas Research Institute (United States) 326

16. Houston Industries Inc. (United States) 328

17. Imperatrix (United States) 329

18. Institute Francais Du Petrol (France) 330

19. Instituto Mexicano De Petroleo/Universidad Nacional Autonoma

De Mexico (Mexico) 331

20. Institute of Gas Technology (United States) 332

21. Institute of Process Engineering (China) 337

22. Intevep S. A. (Venezuela) 337

23. Japanese Cooperating Organizations (Japan) 338

23.1. Agency of Industrial Science & Technology/National Institute

of Advanced Industrial Science & Technology 339

23.2. Japan Cooperation Center, Petroleum (JCCP) 341

23.3. Petroleum Energy Center (PEC) 342

24. Kansai Electric Power (Japan) 345

25. Korea Advanced Institute of Science and Technology (Korea) 346

26. Kurashov, Viktor Mikhajlovich (Russia) 347

27. Kyushu Kankyo Kanri Kyokai (Japan) 348

28. Lambda Group Inc. (United States) 348

29. Marine Biotechnology Institute Co Ltd (Japan) 349

30. Microbes Inc. (United States) 349

31. Ni Aoot; Vatel Skij Inst Neftepromyslov (Russia) 350

32. Nippon Oil Co Ltd (Japan) 351

33. Oldfield, Christopher, Court of Napier University 351

34. Paques Biological Systems BV (Netherlands) 352

35. Petroleo Brasileiro SA (Brazil) 353

36. Petrozyme Technologies Inc (Canada) 354

37. Petroleum Industry Development Center (Sekiyu Sangyo Kasseika

Center); Mitsubishi Oil Co Ltd (Japan) 355

38. Plummer, Mark A (United States) 356

39. Shell Oil Co (Netherlands) 356

40. Standard Oil Co (United States) 357

41. Technology Licensing Organization 358

42. Tonen Corp (Japan) 359

43. Unitika Ltd (Japan) 360

44. Universidad De Alcalá, Universidad Complutense De Madrid, and

Consejo Superior De Investigaciones Científicas (Spain) 361

45. University of Osaka (Japan) 361

46. University of Shandong (China) 362

47. University of Waseda (Japan) 362

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Contents xvii

48. UOP LLC (United States)/Paques Biological Systems BV

(Netherlands) 362

49. Valentine, James M (United States) 363

General Discussion 364

References 366

Chapter 6 Research needs and future directions 375

1. Research Needs 375

1.1. Biodesulfurization 375

1.1.1. Over-expression of DszB 379

1.1.2. Substrate specificity of Dsz enzymes 379

1.1.3. Thermostability 380

1.1.4. Benzothiophene desulfurization 380

1.1.5. Desulfurization of highly substituted alkyl and aryl DBTs 380

1.1.6. Process Development 381

1.2. Biodenitrogenation 382

1.3. Biodemetallization 383

1.4. Bioupgrading 383

2. Future Directions 384

2.1. Future scenario 384

2.2. Technology needs 386

References 387

Subject Index 389

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Chapter 1

INTRODUCTION

1. REFINING SCENARIOS

Catalytic processes form the majority of unit operations in the oil industry. Catalysis, therefore, becomes a significant factor in the economic viability and, nowadays, a strong factor in the environmental viability of the industry. Catalyst development and understanding is essential to the majority of refining and petrochemical advances. New technical improvements and breakthroughs depend on catalysis and are expected to come through a molecular-level understanding of the processes. The oil industry would need continued catalysis support to change its product portfolio with environment friendly technologies.

Environmental regulations have moved towards more extreme levels. In terms of sulfur, for instance, the Environmental Protection Agency (EPA) has proceeded with a tough rule to slash the current average sulfur in gasoline to 30 ppm, which has been phased in from 2004 to 2006. Beginning 2004, refiners and importers had to make or sell gasoline with the average production capped at 300 ppm and corporate sulfur levels averaging 120 ppm. In 2005, the refinery average was set at 30 ppm, with a production cap of 300 ppm and a corporate average of 90 ppm. In 2006, refiners are expected to meet the 30 ppm average sulfur level, with a cap of 80 ppm. It is clear, that the trend is converging to zero sulfur.

The environmental regulations and product quality standards in USA and Europe are being copied by different countries propagating through integrated market blocks or market agreements between larger oil companies. This can also lead to collaborations for development and sharing of environmentally benign technologies needed to achieve those cleaner fuel specifications.

We are currently facing an evolution of the fuel market conditions, from continuous refining to the emergence of new concepts for combustion systems and even for the energy conversion mechanisms (e.g. hybrid cars, fuel cell (FC) vehicles, etc.). A close extrapolation of the present might be enough for working out fuel quality specifications of both, conventional and alternative fuels. The closest approximation, in the short term, shows a wider fuel choice menu for combustion-based vehicles: ‘advanced’ gasoline (ultra-low sulfur, narrow cut, aromatics and olefins content, etc.), reformulated diesel (ultra-low sulfur, high cetane, narrow cut, polyaromatics content, etc.), and reformulated jet fuel (composition, sulfur, etc.). In the mid term, alternative fuels will increase their competence, among them liquefied petroleum gases (LPG), vehicular natural gas (VNG), ethanol, methanol, and biodiesel. The consumption of gas-to-liquid (GTL) fuels will probably grow steadily in the immediate future. Besides, the environmental constraints,



2 Biocatalysis in Oil Refining

the oil prices and the natural gas availability (in certain regions) will bring the GTL-derived fuels into scene. The incorporation of natural gas as a refining feedstock would be the result of the need for cleaner fuels and a preference for building specific molecules instead of cracking the large ones (with less selectivity).

More complex hydrocarbonaceous fuels might materialize in the long term, depending on the alternative vehicle market. The fuel development programs also include hydrocarbonaceous fuels for both, on-board reformers and for liquid hydrocarbon fuel cells. The introduction of hybrid and FC cars would inevitably reduce the share of gasoline in total fuel consumed.

Transportation fuel represents the largest demand share of the oil market, so changes in the transport fleet (type of vehicle, relative proportion of each type, etc.) will certainly affect the refining profile. All these alternatives sum up to an enormous fuel menu, which, by all means, looks unviable. Such complexity and diversity has to be focused to narrow the choices and the number of co-existing fuels, while complying with market requirements at the same time.

The market pattern for oil refining products is evolving and will continue to do so in the future. The trend is towards lighter and cleaner products. The demand for fuel oil and residuals is decreasing consistently, but the consumption of lighter fuels is increasing. In the long term, the residuals market would disappear. The resemblance of a refinery would then be closer to a chemical plant, rather than the landscape exhibited these days. In a contraposition, the market share of the heavy and extra heavy oils might have increased, due to the decline of the light and median reserves. In fact, an increase on heavier feedstocks has already begun and will be a constant factor in the future. Introduction of new, non-oil derived fuels will impact the oil-derived market share. Also, if gasoline use remains where it is or increases, the specifications are bound to be severe. Speciation, well-known in biology, will be a fact in the fuel business.

Keeping in mind the global resources and market scenarios, one might expect that product specifications will have an added dimension. The new dimension made necessary by the very low sulfur- and nitrogen-levels and fuel properties would be in terms of molecular properties of the fuels rather than behavior parameters (octane number, cetane number, etc.). In addition, the H/C ratio will be higher than the current corresponding product. The distribution infrastructure will set limitations, but only in the immediate future, as in the long term, new fuels are bound to appear. The changes in the product portfolio will necessarily leave surplus streams, which will require new applications and uses.

The environmental cost can only be overcome with technology development, with a minor contribution from the quality of the raw material. Important to consider is that technology would be only available to those who generate it. However, the economical situation of the refining industry has shadowed the impact of technology development on competitiveness and we have seen strong budget cuts in R&D because of decrease in profit margins.

The refinery will evolve to meet the market (and so, the environmental) needs. Some characteristics are easy to foresee: versatility, integration from resources to final user (well-to-wheels), intensive incorporation of computing tools (integrated and predictive modeling at all levels: feedstock-process-product), large dynamic incorporation of new catalysts, ‘chemistry driven’, fast incorporation of emerging knowledge and last, but most important, environmental preservation and safe operation.



3 Introduction

The benefits obtained from catalysis can simply be measured from the size of the business (i.e., catalyst manufacturing represents a US$ 10 billion market, including refining, petrochemical, chemical, and environment). An example is the fluid catalytic cracking process. Since the 1950s, yields which were at 4900 octane units per barrel of feed have grown almost to the theoretical (6200) limit of about 6000. With increasing competition, the new catalytic technologies being developed will more than likely be part of individual companies and belong exclusively to those who developed them.

2. BIOCATALYSIS

Industrial biotechnology has emerged into a world where environmental sustainability has become a global concern. Biotechnology is a technology in which living organisms (or their components) are used to manufacture or modify industrial products as well as to modify living species such as plants or animals or to develop microorganisms for specific applications. When considering the refining scenarios, we mentioned the expected impact of the environmental regulations (growing towards more stringent restrictions), the impact of the changes in the fuel consumption patterns, and the increasing use of heavier feedstocks. Thus, barriers and complications to achieving the desired fuel specifications are already visible and will remain a factor in the future. Modern biotechnological processes can address some of these concerns, introducing environmental and economic benefits as well as technical and process advantages over other technologies.

Biotechnology-based processes have been penetrating industrial operations in many sectors, particularly because such processes enable new product development via green technologies, and due to increase in energy efficiency and reduction in material consumption. The pollution and waste minimization achieved is usually realized at the same level of industrial production. The initial paradigm of clean products for a clean environment is now being extended to clean process technologies for the manufacture of those clean products. Biological technologies are emerging as competitive means for achieving this new paradigm. The use of biocatalytic processes in place of chemical catalytic processes dramatically improves product quality while reducing capital costs and production expenses. Separation and disposal steps are significantly simplified. Most of the technologies developed or under development, address a number of multi-billion dollar industries. The target markets include protein-based pharmaceuticals and vaccines, fine chemicals and agricultural products, and more recently, industrial chemicals as well.

Biocatalytic processes have been demonstrated to be superior in industries such as pharmaceuticals, fine chemicals, life science research, agriculture, food & beverage, and cosmetics; however, such processes have not yet been commercialized in the oil and petrochemical industry. It is possible to foresee a growing role for industrial process biotechnology in these areas as well, because of two reasons: (1) they have demonstrated clear economic and environmental benefits in the other sectors and (2) because the power of the biological toolset itself continues to grow. The expectation of developing clean-burning fuels comes from the observation that living systems manage their environment rather efficiently compared to man-made chemical plants, and that their wastes tend to be recyclable and biodegradable. This, along with the increasing ability to manipulate




biological materials and processes, strongly points to a significant impact on the future of manufacturing industries.

The advantages of biocatalysis namely, moderate operating conditions, high selectivity, and the potential of producing specialty chemicals, have not been realized in the refining industry. Biocatalytic routes for refining processes (mostly devoted to desulfurization today) have been examined at academic level and at most the pilot level [Valentine J., Feb.1999, US Patent 5, 874, 294, (references cited therein)]. Therefore, biocatalytic desulfurization could be the first process to reach a refinery application in the near future. Although this technology has advanced significantly towards a practical application, it has not reached commercialization due to an insufficient rate and low stability of the biocatalysts. Effort on engineering scale up, downstream processing, and waste treatment has been minimal and significant effort will be needed in this area for commercialization.

The core of a biocatalytic refining process is the biocatalyst. The availability of new tools in the Molecular biology (MB) and Genetic engineering (GE) areas has opened up new avenues for development of the biocatalyst. Molecular biology essentially implies a study of the biochemical and molecular processes within cells, especially the processes of replication, transcription, and translation. Genetic engineering, on the other hand, concerns the manipulation of an organism’s genetic endowment by introducing or eliminating specific genes through modern molecular biology techniques. A broad definition of genetic engineering also includes selective breeding and other means of artificial selection.

A biocatalyst is defined as a biological material or a material of (non-human) biological origin, which possesses the ability to catalyze one or more reactions, sometimes in the presence of co-factors or co-enzymes. Most of the initial work in biodesulfurization was done with biocatalysts in the form of whole cells (WC). The next step was the study of pure (or mixed) enzymes as biocatalysts. A further step was taken towards enzyme-and gene-engineering and new forms of the biocatalyst were suggested. In intellectual property related to biodesulfurization, one may encounter additional cellular components in the definition of biocatalyst, such as cell-free fraction or extract, a DNA molecule or recombinant DNA molecule or molecular fragments, gene sequences, gene fragments, protein sequences, open reading frames (ORF), plasmids, etc. Whether to use a WC, an enzyme, or any other system as the biocatalyst is a techno-economic decision.

Definition of miscellaneous biochemical terms used in the book: A sequence, in general, is the relative order of base pairs, whether in a fragment of a

protein, DNA, a gene, a chromosome, or an entire genome. DNA is composed of two antiparallel strands of deoxynucleotides held together by hydrogen bonds between purine (adenine, A and guanine, G) and pyrimidine (thymidine, T; uracil, U; and cytosine, C) bases.

An open reading frame (ORF) is a stretch of triplet codons with an initiator codon (in most cases ATG, adenine-thymidine-guanine) at one end, a stop codon at the other as identifiable by nucleotide sequences. An ORF is potentially capable of coding for an as yet unidentified polypeptide. An ORF consists of a long DNA sequence that is uninterrupted by a stop codon (basic unit of the genetic code, comprising three-nucleotide sequences of messenger ribonucleic acid (mRNA), each of which is translated into one amino acid in protein synthesis) and encodes part or all of a protein. The reading frame determines which amino acids will be encoded by a gene and it also decides which nucleotide to start translation, and when to stop.



5 Introduction

A codon is the coding unit formed by any triplet of nucleotides in DNA or RNA. Therefore, they can be considered the carriers of the primary genetic information that codes for a particular amino acid or signals the beginning or end of the message. The term ‘codon’ is also used for the corresponding (and complementary) sequences of three nucleotides in the messenger RNA into which the original DNA sequence is transcribed. Of the 64 possible codons in the genetic code, the RNA triplets UAA, UAG, and UGA serve as terminator codons. AUG and GUG are initiator codons. One should remember that a coding sequence is that part of the gene, which directly specifies the amino acid sequence of its protein product.

A plasmid is an autonomous, covalently closed circular (or linear) double-stranded and self-replicating DNA molecule found in most bacterial species and in some eukaryotes. Although the genetic information contained in a plasmid concerns replication, stability and autonomous transferability, their actual replication relies on the replication apparatus of the host cell.

A primer is a very special sequence, which plays an important role in duplication. (i) In RNA, it is a short sequence that is paired with one strand of DNA and provides a free 3′-OH terminus at which a DNA polymerase starts synthesis of a deoxyribonucleotide chain. (ii) In DNA, it is another short sequence, which is complementary to a sequence of messenger RNA and allows reverse transcriptase to start copying the adjacent sequences of mRNA. (iii) In retroviruses, it is a cellular transfer RNA whose elongation initiates RNA-directed DNA synthesis by the DNA polymerase.

A vector (or cloning vector) is any DNA molecule (or fragment) capable of autonomous replication within a host cell into which other DNA sequences can be inserted and thus amplified.

A recombinant DNA molecule is a novel DNA sequence formed by in vitro combination of two non-homologous DNA molecules (or fragments) giving rise to genetic material.

An enzyme, the most typical biocatalyst, is a protein (or peptide molecular chain), which can be made from living cells and promote, direct or facilitate the occurrence of a specific chemical reaction, without being consumed during the course of such reaction. The term ‘enzyme’ is mostly used to describe proteinaeceous catalysts. However, in some instances it also includes co-enzymes or co-factors as they are supposed to be required to bring about the desired reaction.

In Chapters 3–5, the reader will come across many new concepts. The important ones are described below.

The equivalent to a reaction network, from the chemical point of view, is a metabolic pathway for the biological applications. This means the individual steps, which might take place to achieve the complete process. For each of these steps, one or more enzymes (or biocatalysts) might be required. Of course, each of these steps will exhibit its own kinetic rate. Consequently, optimizing biochemical pathways can enable enhancements in process efficiency. The key to increasing the metabolic flux through the bacteria is to manipulate them by GE. One route to a significant increase in the flux is simply by amplifying the expression of the proteins coded by the genes involved. The biocatalytic rate is limited by the actual concentration of the proteins/enzymes. Further increases in activity may be achieved by modifying the proteins themselves. New metabolic pathways have been reported recently and thus, potential for improvement in biocatalytic rates via genetic and metabolic engineering exists. Another strategy in metabolic engineering is to




change the host bacterial strain, perhaps to take advantage of strains with better growth properties, physical properties (for mixing and separations), cellular transport and/or a higher intrinsic cofactor regeneration/metabolic conversion rate.

If the activity is controlled by the existence of a slowest step, then two different approaches can be considered for optimization. The first approach consists of extraction and purification of the enzymes or proteins, followed by formulation of a new biocatalyst containing the enzyme or protein involved in the slowest step at a higher concentration. A second approach is to over express that enzyme or protein by GE tools in the WC.

Biotechnology embraces a wide range of techniques, and none of these will apply across all industrial sectors. Nonetheless, the technology is so versatile that many industries that have not used biological sciences in the past are now exploring the possibility of doing so. The application of knowledge obtained from life science research has given rise to emergent biotechnological processes. The biological applications in the food and pharmaceutical industries are well substantiated. The maturity of such processes has lead to the development of more sophisticated tools for the R&D activities. Tools associated with improving efficiency of R&D activities to take ideas from the point of discovery to commercialization have exploded. The nature of this research has led to automation of the discovery process. Thus, high throughput experimentation (HTE) and high throughput screening (HTS) tools are now widely applied by biotechnology working teams.

Biotechnology is a powerful enabling technology for achieving clean industrial products and processes that can provide a basis for industrial sustainability. New genomic information from various organisms may help make crude oil resources the preferred energy basis and carbon source for the manufacture of value-added chemicals and materials. Yet genomic information alone is not sufficient to complete the transformation. New tools, such as the ability to manipulate genes and pathways in innovative ways, are critical for the development of enzymes that operate as catalysts under conditions optimal for refining processes, essentially fitting the enzyme to the process rather than the process to the enzyme. The technologies represent powerful means for improving the properties of industrially relevant biocatalysts.

Achieving the goal of developing environmentally benign technologies for biorefining requires joint R&D efforts by academia, government, and industry. The development of biocatalytic refining processes requires a multi-disciplinary effort that addresses key challenges necessary to unleash its commercial potential for that application. Biotechnology, including genetic engineering (recombinant DNA technology and its applications), has become increasingly important as a tool for creating value-added products and for developing biocatalysts making collaborative work imminent.

One of the most important advantages of the bio-based processes is operation under mild conditions; however, this also poses a problem for its integration into conventional refining processes. Another issue is raised by the water solubility of the biocatalysts and the biocatalyst miscibility in oil. The development of new reactor designs, product or by-product recovery schemes and oil-water separation systems is, therefore, quite important in enabling commercialization. Emulsification is thus a necessary step in the process; however, it should be noted that highly emulsified oil can pose significant downstream separation problems.

Typically, a biocatalytic process for oil refining involves several stages beginning with biocatalyst production. This involves growth of the microorganism via fermentation



7 Introduction

in the presence of carbon sources and other nutrients. Biomass is then harvested from the culture medium, typically via centrifugation. If the desired biocatalyst is an enzyme, then the biomass pellet is subjected to isolation or purification of the enzyme and/or desired biomolecules. The biocatalyst is then suspended in aqueous media and contacted with oil (typically at a ratio of 1:1) in stirred reactors or other reactor configurations to provide efficient oil-water contacting. The next step is separation of the oil and water phase. In the case of desulfurization, the sulfate formed in the process can be removed from the aqueous phase by adding calcium salts (lime or hydrated lime) or ammonium salts (or hydroxide ions).

The study of enzymatic processes and the understanding of the related mechanisms are crucial in making progress in the field of catalysis. However, in terms of efficiency and efficacy the optimum process might employ an enzymatic biocatalyst, rather than cells. The final answer would probably demand on an economic evaluation. Nevertheless, continued technical innovation, including that based upon recombinant DNA technology, is vital for the wider utilization of biotechnology by the industry. Whether the biocatalyst is a living cell or any other derived biomolecule, its preparation begins with culturing the cells in a fermenter. The aqueous culture medium should contain assimilative carbon sources, nitrogen sources, as well as various other salts.

Although biotechnology processes may be applicable to many different operations in the oil industry, this book is focused on the refining sector. Another challenging field related to fossil fuel operations is that of carbon dioxide sequestration, where biotechnology may provide a viable solution. Since fossil fuels are currently the single most important raw material for energy generation and chemical production, the concomitant CO2 emissions are source of increasing concern because CO2 is a major greenhouse gas. Biotechnology can contribute to reducing this effect of fossil carbon consumption and hence global warming in various ways: improving industrial processes and energy efficiency, and producing biomass-based materials and clean fuels (biodiesel, bioethanol, etc.). While biofuels may seem as an obvious competition to oil-derived fuels, in an ever-increasing need for energy and fuels, realistically they may be needed to supplement oil-derived fuels. The other two areas where biotechnology has played a role in the oil industry traditionally include bioremediation and microbial enhanced oil recovery (MEOR). Bioremediation and biodegradation technologies have improved the overall efficiency of oil exploitation processes, particularly in the area of pollution control. Oil production has been enhanced by the use of microorganisms in certain oil fields.

The application of biocatalytic technologies in the refining industry will be possible only if it can improve product yields and produce cleaner fuels economically. The hurdle to commercialization of the biodesulfurization process is still the activity of the biocatalyst. The reasons for this will be evident from the discussion in Chapter 3.

Biocatalytic processes may also have utility for generating novel useful materials in the petrochemicals area. This book focuses on biocatalysts and biocatalytic refining processes and does not cover other applications. The companies and R&D groups, which have made important contributions to the development of refining processes, are listed in Chapter 4, along with a discussion of their contributions. So far, most of the effort has been on biodesulfurization (BDS). Very little has been done in the area of biodenitrogenation (BDN) and bioconversion (BCK) and almost nothing on biodemetallization (BDM). Refining processes considered here can potentially be applied at the well-head (surface installations) or within the well (in situ) as well.



Chapter 2

CONVENTIONAL REFINING PROCESSES

1. INTRODUCTION

Refining is a very elaborate operation, by which crude oil is transformed into a series of products such as, gases, fuels, solvents, lube oils, etc. Crude oil is a complex mixture of hydrocarbons (HC) of different C/H ratio and molecular structures. The different classes of HC molecules comprise paraffins, olefins, cycles, aromatics, resins, asphaltenes, and other poly-unsaturated molecules. In addition to hydrocarbons, crude oils also contain some other compounds composed by other atoms (heteroatoms) than carbon and hydrogen. Those moieties consist of sulfur (S), nitrogen (N), oxygen (O), and heavy metals (mainly iron, nickel, and vanadium). Crudes are usually classified in terms of their specific gravity as very light, light, median, heavy, and extra heavy. An empirical set of units for the crude gravity, defined by the American Petroleum Institute (API), is currently used in oil industry. Their appearance varies from transparent liquids to black solids, going from light to heavy. Light oils have lower specific gravity and larger API gravity, while for heavy oils vice versa. Their composition also changes, and so the concentration of those heteroatomic compounds typically increases from light to heavy. The crude oils are also categorized in terms of their chemical composition, as for instance, sour crude oils, those presenting high acidity (in the past associated with the presence of H2S and other sulfur compounds, but more recently directly measured), paraffinic (those mostly composed by paraffins), naphthenic, and aromatic (a high proportion of cyclic or aromatic compounds, respectively).

The number and quality of manufactured products are determined by the market and governmental regulations and policies, at a given moment and this has been changing with time. Hence, refining is not only complex but also a dynamic manufacturing process that requires continuous updating and revamping. Refining technology has evolved from simple distillation processes to a highly sophisticated mixture of processes that cover the separation of the crude into simplified fractions and the chemical modification of their constituents.

Physical separation processes initiate the refining operation, and are meant for removing inorganic materials and separating the crude in less complicated mixtures. Among these processes, we find dehydration, desalting, distillation, and some other pretreatments. Distillation is carried out first at atmospheric pressure and the atmospheric residue is then distilled under vacuum. In figurative terms, distillation cuts the crude into rough mixtures within certain ranges of boiling points that contain compounds within a given range of number of C atoms. Table 1 describes these cuts, in refining terms when the cut is directly derived from the distillation; they are referred as straight run (SR). The cuts from the atmospheric distillation are abbreviated with an A before the




Table 1. Petroleum products

Cut Carbon chain length

Petroleum gases 1–4 Naphtha 5–10 Kerosene 10–16 Gas oil (diesel oil) 14–20 Lubricating oil 20–50 Fuel oil 20–70 Residue >70

Boiling range/�C



11 Conventional refining processes

Fuel Gas

Desalting

Light SR naphtha

SR kerosene

Des

alte

d cr

ude

Atm

osph

ere

resi

due

SR Gas oil

SR middle

distillates

Light vacuum

distillates

Heavy vacuum

distillates

Vacuum

residue

Lube feedstock

Gas

Gas Separator

Catalytic Isomerization

Hydrocracking

Atm

osph

eric

Dis

tille

rV

acuu

m D

istil

ler

Coking

Catalytic Cracking

Solvent Extraction

Solvent Deasphalting

Solvent Dewaxing

Visbreaking

Catalytic Reforming

Alkylation

Gas Plant

Polymerization

Hydrotreating

Hydrotreating

Gasoline Sweetening

Treating and

Blending

Distillates Sweetening

Treating and

Blending

Residual Sweetening

Treating and

Blending

C3

Heavy naphtha

Low-S distillate

Light cracked distillate

Heavy vacuum distillate

Heavy cracked distillate

Decanted oil

Thermal cracked distillate

Asphalt

Raffinate

Deoiled wax

Dewaxed oil

Condensates

LPG

Aviation gasoline

Motor gasoline

Residual fuel oil

Solvents

Kerosene

Jet fuels

Distillates fuel oils

Diesel

Solvents

Lubricants

Greases

Waxes

Hydrocracking

Polygasoline

C4

Alkylate

Isonaphtha

Reformate Hydrocracked naphtha

Light cracked naphtha

Crude oil

Heavy SR naphtha

Hydrotreating

C3 – C4

Hydrotreating and Blending

Figure 1. Refining processes.

of those compounds in the fuels. The ‘Clean Air Act’ in the US created a cascade consequence in some other countries, which soon began regulating the content of noxious compounds in fuels. The discovery of the ‘green house’ effect, caused by the presence of certain compounds in the atmosphere imposed new conditioning on the transportation fuels, from the governmental environmental agencies.

More recently, the fuel manufacturing process has been stressed from two adverse factors. On one side is the increasing strength of environmental rules, which require a severe decrease in the concentration of the so-called contaminants in the final product. On the other side is the change in refinery diet (crude oil mix used as entree feedstock) which is becoming ‘heavier’, implying a larger concentration of contaminants in the feedstock. Consequently, this stress results in an increase in processing costs associated with controlling contaminant concentration, requiring development of new technological solutions.

As a consequence of these changes, the refining product profile also changes. Ultra-low sulfur fuels (10–15 ppm) will be used globally. Addition of oxygenates and biofuels into the product slate seems to be mandatory. Sulfur in off-road diesel would decrease to ultra-low levels and that in marine fuels will be under a certain maximum. The production of heating oil and fuel oil will decrease, while petroleum coke will increase. New lubricating oils have to be modified to perform as high performance synthetic lubes. The sulfur produced as refinery byproduct will accordingly increase.

Consequently, environmental regulations affect each fuel composition in different ways. For gasoline, requirements include a reduction in sulfur, nitrogen, olefins and




aromatics content, increase in oxygen containing compounds (octane enhancers), seasonal volatility control (limits on Reid Vapor Pressure, RVP), and lead-additives elimination. In the case of diesel, reduction of sulfur, nitrogen and polyaromatic compounds, lubricity, and fluidity control. Another issue to be considered regards the toxic compounds completely banned from the fuels, since some of them can be produced during the manufacturing processes. The US Environmental Protection Agency (EPA) lists the air toxic compounds, from which 21 are associated with mobile sources [1]. These are: acetaldehyde, acrolein, arsenic compounds, benzene, 1,3-butadiene, chromium compounds, diesel exhaust (particulate matter), ethylbenzene, dioxin/furans, formaldehyde, lead compounds, manganese compounds, mercury compounds, MTBE, naphthalene, n-hexane, nickel compounds, polycyclic organic matter (POM, include 7 polycyclic aromatic hydrocarbons (PAHs) identified by EPA as probable human carcinogens: benz(a)anthracene, benzo(b)fluoranthene, benzo(k)-fluoranthene, benzo(a)pyrene, chrysene, 7,12-dimethylbenz(a)anthracene, and indeno(1,2,3-cd)pyrene), toluene, styrene, and xylene.

The scope of this book covers refining processes, which could be affected by biocatalytic innovations. Until now, the biological applications considered include the removal of the contaminants with a lesser focus on reduction of the molecular-size or the viscosity (upgrading). Therefore, an introductory background will be given on the related conventional refining processes. As already mentioned in Chapter 1, most of the biocatalytic R&D activities have been focused to removal of sulfur (desulfurization), less on removal of nitrogen (denitrogenation) and almost nothing on the removal of metals (demetallization) or on upgrading.

As already mentioned, hydrogen addition at high temperatures and pressures is commonly referred as hydroprocessing (HDP), and represents a series of processes to deal with contaminant removal and conversion. Consequently, special attention would be given to conventional hydroprocessing, in this chapter. In Table 2, the compounds, which would react under typical operating conditions in a hydroprocessing reactor, are exemplified. Two broad groups of processes can be distinguished, those used for contaminant removal and those addressing conversion.

The first, known as hydrotreatment (HDT), runs at lower temperatures and pressures than those applied for conversion purposes, named hydrocracking (HCK). Although, HDT was originally conceived as a finishing stage of distillated fuels, its advantage for pretreating feedstocks for conversion processes was soon realized. In fact, the increasing proportion of heavy fuels in the refinery diet placed HDT as a necessary pre-step for the conversion process. On the other hand, HCK refers to the action of hydrogen on molecular size reduction via cleavage of C−C bonds. The processing of resids or entire crude oil is also referred to as hydroconversion. Gas oils, both atmospheric and vacuum are also processed through HCK. In some instances, the HDT units are operated at higher temperatures and pressures than usual (but lower than those used in HCK are), to favor moderate conversion. This operating mode is regarded as mild hydrocracking (MHC).

Normally, removal of sulfur, nitrogen, and metals from those steams used in fuel manufacturing is carried out by hydrogen addition reactions. Thus, hydrodesulfurization (HDS) stands for the removal of sulfur, hydrodenitrogenation (HDN) for the removal of nitrogen, hydrodemetallization (HDM) for metals, and finally the hydrogenation of aromatics is referred as aromatic saturation (HDA). In a lesser extent, oxygen is also removed (hydrodeoxygenation, HDO). These processes are referred commonly as




Table 2. Examples of reactive compounds relevant to HDP

Sulfur compounds

S S S

SH

Thiophene Benzothiophene (BT) Dibenzothiophene (DBT) Benzo(a)naphtho(2,3-d)thiophene

Nitrogen compounds

N N H

N H N N

Pyridine Indole Quinoline Carbazole Acridine

Metal compounds

N N

N

N

Ni

Ni-TETMP complex

N N

NN

V

O

Vanadyl-TETMP complex

Aromatic compounds

Anthracene Phenanthrene Fluorene

Fluoranthene Pyrene Coronene



14

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

Biocatalysis in Oil Refining

hydrotreatment processes. Under the high hydrogen pressure, olefins (and some other unsaturated compounds) are also hydrogenated.

2. HYDROTREATING PROCESSES

As mentioned above, two factors are adding to the demand of more severity in the hydrotreatment operations: stringent environmental regulations and the increasing proportion of heavy sour crudes in the refinery diet. As an example, in Fig. 2, we show the trend of the API gravity of the imported crude oils by US during the last 25 years. Data was taken from the Energy Information Administration (EIA) [2]. The percentages of total imported crude oil has been grouped in four ranges of API gravity, to reflect the trend of heavy �40�0�. The effect of declining supply of light oils and the increasing proportion of median and heavy, in recent times, is clearly shown. Market analysis and forecast outlook reported by EIA, forecasted that the average API gravity of the crude oil fed to refining processes in USA will be about 29, by 2010, and this value will keep decreasing continuously, from now on. Although, the shown example corresponds to US, the global situation shows a steady growth in the heavy oil supply, leading to a continuous increase in the average concentration of unwanted contaminants (S, N, and metals).

Manufacturing high quality fuels would require not only more hydroprocessing but also other chemical processing. In the immediate future, most of the refinery investments are made to cope with these requirements and particularly involve hydrotreatment processes. However, commercially available technology does not have all the answers to the market needs. Some niches are open for new technology development.

50

45

40

35

30

25

20

15

10

5

0

40.1

Figure 2. Change in quality (API gravity) of imported crude oils in US.




2.1. Chemistry 2.1.1. Reactions Reactions occurring in hydrotreatment include both hydrogenation and hydrogenolysis reactions.

Aromatics, olefins and in general, unsaturated compounds undergo hydrogenation reactions, usually unwanted due to their detrimental effect on the operating costs, derived from an excessive consumption of hydrogen. Aromatic saturation, however, is used in jet fuel to improve the smoke point and in diesel for cetane enhancement. In the case of gasoline, extreme hydrogenation leads to a deterioration of the fuel performance parameters.

Aromatic saturation reactions are reversible and exothermic, and at typical reaction conditions, do not attain 100% conversion. Furthermore, increasing the temperature to favor conversion of the other concurrent reactions disfavor aromatic hydrogenation. The kinetics studies indicate that they are fast reactions, indicating that equilibrium is reached under HDT conditions.

Cetane number, in the case of diesel and octane number for gasoline, are parameters that measure the tendency of the fuel to ignite spontaneously. For gasoline, a value of 100 octane is the rating assigned to isooctane (2,2,4-trimethylpentane) and 0 is given to n-heptane, for the RON (Research Octane Number) scale. A high value of octane number corresponds to a hydrocarbon with very low tendency to knock and high resistance to spontaneous ignition. Hexadecane (commonly known as cetane) represents a cetane number of 100, while 1-methylnaphthalene or heptamethylnonane represents 0 and 13 (recently amended), respectively, in the cetane number scale. In this case, high values correspond to hydrocarbons that easily ignite. The molecular structures of the compounds used as standards for the measurement of the octane and cetane performance parameters are shown in Table 3.

Table 3. Standard molecules for scale of fuel performance parameters

Value Octane Number (Gasoline) Cetane Number (Diesel)

Hexadecane Isooctane

13

Heptamethylnonane

0 n-heptane

1-Methylnaphthalene

100




However, for the scope of this book, most relevant are the hydrogenolysis reactions, through which the heteroatom moieties are removed from their bearing compounds. These reactions can be schematically represented as:

R −X + H2 → RH + XH� The amount of hydrogen required depends on the chemical nature of the X moiety and

on the relative stability of the remaining R species and the reactivity of the conforming carbon chain. In some instances, such as in the case of polynuclear aromatic species, multiple hydrogenations of the aromatic rings is needed to weaken the C−X bond enough to facilitate its cleavage. Sulfur removal occurs either with or without hydrogenation of the heterocyclic ring, indicating that removal of sulfur is less demanding on hydrogenation than the removal of nitrogen [3]. The reactivity of sulfur compounds has been the subject of numerous studies. In Table 4, the relative reactivity of some of the different

Table 4. Sulfur compounds present in crude oil

Sulfur type Compound Relative Reactivity

RSR’ and RSSR’ Sulfides and Disulfides 10–100

Thiophene (T)

s

s

s

s

1

Benzothiophene (BT) 0.5

Dibenzothiophene (DBT) 0.05

Benzonaphthothiophene 0.1

Substituted DBT 2

1 9

8

3

4

S

6

7

1-Methyl-DBT (1MDBT) 0.05

2 and 3-Methyl-DBT (2MBBT; 3MDBT))

4-Methyl-DBT (4MDBT)

Mono-substituted DBT 0.15

0.03

4,6-Dimethyl-DBT (4,6DMDBT)

Bi-substituted DBT 0.006




types of sulfur compounds present in oil is summarized [4,5]. The reactivity of sulfur containing hydrocarbon molecules depends on the molecular structure, according to the compound family a relative scale of reactivity has been worked out.

The sulfur in paraffins and in aromatics with single rings is relatively easy to desulfurize, essentially due to the molecular flexibility. The sulfur atom would easily reach the surface active sites of the catalyst. This flexibility decreases in naphthenic compounds, though cyclic compounds are somewhat flexible, they only have limited degree of freedom. Flexibility is lost in aromatic rings, and the accessibility of the sulfur atom gets completely inhibited when very bulky substituents occupy the 4 and 6 positions in the 2 aromatic-ring fused moieties, such as DBT. In fact, observing DBT one may point out that the connection between the two benzene rings by a C−C bond and a C−S−C, making the two rings connected through a single S atom, makes this molecule essentially flat. The approach of the S atom to the catalyst surface is greatly limited by this flat structure of the molecule. From this reasoning the relative reactivity of sulfur compounds varies as paraffins > naphthenes > aromatics. The reactivity sequence according to the sulfur compound can be stated as sulfides > Ts > BTs > DBTs. From the previous reasoning on stability and reactivity, we may conclude that hydrogen consumption follows the same order [6].

In addition to the inherent reactivity of the different compounds, an inhibiting effect of H2S was found to affect differently the hydrogenation and the hydrogenolysis reactions [7]. The effect of hydrogen sulfide on the catalytic sites, during reaction, was explained to be due to its capacity for filling the sulfur vacancies and yielding an increase in the number of Bronsted acid sites [8]. The H2S partial pressure is defined by the HDS activity of the catalyst, but in turn the H2S partial pressure defines the relative population of sites (to a given sulfiding degree) and so the HDS activity. Under a given set of hydrotreatment conditions for a particular feedstock, the catalytic surface reaches a steady state in terms of its sulfiding degree. However, preliminary studies of hydrotreatment reactions were carried out in a sulfur deficient atmosphere and those results have to be examined with care. In summary, the reciprocal effect of H2S and HDS has to be considered in depth, particularly for the hydrotreatment of low-sulfur containing streams.

The acidic nature of the active site can be related to its interaction with nitrogen compounds as well [9]. Furthermore, the mutual need for the hydrogenation sites, as well as for the hydrogenolysis sites of both S and N compounds leads to a relative effect between each other, which has been referred as competitive inhibition [10]. A comprehensive discussion on how the sulfiding degree of the catalyst affect acidity and the functionality of the catalyst has been presented [11]. The surface parameters showed interdependence, which determines not only activity but also functionality. At a given set of conditions, a high metal dispersion is associated not only to a high hydrogenation activity but also to a high sulfiding degree. In terms of acidity, the number of acid sites may be associated with activity, while the acid strength distribution affects functionality. Strong acid sites will retain the basic nitrogen compounds at the surface, causing an increase in their competitive inhibition. In this circumstance, basic nitrogen compounds would represent a poisonous effect on HDS, as has been observed [12]. A wide acid strength distribution would favor the handling of a broader range of nitrogen compounds with different basicity [11].

In the case of hydrodenitrogenation, the study of the reaction kinetics on model compounds has shown the lack of the steric inhibiting effect observed in case of the




sulfur-containing compounds. Organonitrogen compounds present in the liquid fuels are mainly cyclic compounds. Nevertheless, aliphatic amines and nitriles are also present at a lesser concentration but their reactivity is much higher and so they denitrogenate rapidly [13]. The cyclic compounds are classified as basic and non-basic. In the first family of compounds, the lone-electron pair of the nitrogen atom acts as a Lewis base. On the other hand, with non-basic compounds, the electrons are delocalized in the aromatic ring, and have no basic character. However, upon hydrogenation of the nitrogen-containing ring, the aromaticity is destroyed and the compound becomes basic. Quinoline is the most studied example of basic compound, while indole and carbazole are examples on the non-basic nitrogen compounds.

The deactivating effect of nitrogen compounds on hydrogenation reactions is well-known and documented. On sulfided catalysts, this effect is aggravated by the acidic nature of the active sites and the basic behavior of the nitrogen compounds (those originally present and those produced upon hydrogenation). In that sense, the nitrogen compounds are regarded as self-poisoning, but the effect impinges along all other hydrogenation-demanding compounds and reactions. Additionally, HDN produces ammonia, which is also a poison for the hydrogenation sites, strongly affecting the aromatic saturation. Basic compounds are found to poison the HDS active sites. To account for all these effects Bindhe [14] proposed a model that separated the active sites in two classes (hydrogenation and hydrogenolysis sites) and assigned the poisoning effect to the basic compounds adsorption. Under this latter assumption, higher temperatures might be recommended to minimize adsorption of the deactivating compounds.

As mentioned above, the cleavage of the C−N bond requires the hydrogenation of the aromatic rings of the molecule prior to nitrogen removal [15]. Since the hydrogenation reactions are thermodynamically controlled, it implies that the position of the hydrogenation equilibrium will affect denitrogenation rates. Mathur et al. evaluated the kinetic rate constants of quinoline, isoquinoline, methyl-substituted quinoline, and of two-, three-and four-rings nitrogen compounds. They evidenced that there is no steric hindrance in HDN reactions, and assigned it to the flexibility of the hydrogenated molecules, which actually undergo C−N bond cleavage [16,17]. The number of studies reporting comparison between the reactivity of basic and non-basic compounds is scarce. A comparison between indole and quinoline indicated no significant difference in their pseudo-first order rate constant (4�19 ×10−5 and 3�18 ×10−5, respectively) [14].

Distillate hydroprocessing has a long R&D history, through which most of the issues have been addressed by the study of the reactions on model compounds, in an effort to simplify the complexity of the process. Real conditions and multi-compound mixtures are hardly seen in these studies. On the other hand, real feedstocks have been also considered at industrial conditions, and phenomenological models are derived from these studies. In summary, the complexity of hydroprocessing has still a long road to transit before complete understanding of its chemistry. The dynamic action of H2S, reaction thermodynamics, mass transfer, and competitive inhibition are only a few of the basic research challenges in this area.

2.1.2. Catalysts HDP catalysts have a long history that accounts for almost a century, yet the basic formulation remains, though an enormous range of improvements have been introduced




through the years. A comprehensive review has been published in 1996 [18], in time to include the closely found steric hindrance, in the group of later-called, refractory S-compounds.

The general formulation of hydrotreatment catalysts consists of a high surface area alumina support, containing an active phase consisting of an oxide of a Group IVB metal (molybdenum or tungsten, preferentially) in a concentration from 10% to about 35%, and between 2% and 8% of a Group VIII transition metal (cobalt or nickel, typically), which acts as an activity promoter. Other promoters are used to enhance other catalytic properties, some are use for activity, stability, or functionality (for instance, to introduce an acid function, e.g., Si, F, Cl, etc., or to increase hydrogenation, e.g., P). The catalysts are prepared in their oxide form, which is considered the precursor of the active species that are actually, the sulfides of the active metals.

The catalysts are subjected to an activation procedure prior to their use in hydrotreatment, for converting the oxide promoters in their corresponding active sulfides. The sulfiding step is carried out with an organic sulfur compound, which either chemically reacts with the metal oxide to form the sulfide or easily decomposes in the presence of hydrogen rendering H2S. Both reactions can also occur simultaneously during activation. The presence of a high hydrogen pressure is thought to induce the decomposition of the sulfur compound and to drive the reduction of the active metals (Mo and W). However, the kinetics of the sulfidation reaction is fast enough to avoid the full reduction of the metals. In fact, the sulfidation state reached by the same metals, by sulfiding from their elemental state results in a very poor activity catalyst. For this reason and for the production of undesirable water, reduction has to be controlled. The sulfidation reactions are exothermic and extreme care has to be taken to prevent development of excessive heat in the bed or formation of hot spots. Since reactions occur on the metal sites, excessive heat may lead to sintering and the agglomerated metal phase becomes less reactive and results in a poor sulfurization. On the other hand, uneven heating of the catalyst particles weaken the mechanical strength of the extrudates. The resulting catalyst could break down easily forming fines and causing an increase in the pressure drop through the bed. Temperature and H2S partial pressure has to be carefully controlled during sulfidation. Temperature is increase in two stages, first at 250–275�C, and in the second stage at 290–350�C. The most commonly used sulfiding agent is dimethyldisulfide (DMDS), due to its readiness towards decomposition at moderate hydrogen pressure (decomposition temperature about 230�C). Catalysts can be also purchased in a presulfided state, for which a straightforward reactivation procedure is followed upon loading the reactor. However, the differential costs between presulfided catalyst or sulfiding in situ does not justify its use, sometimes.

The nature of the active phase is still subject of debate; however, the most widely accepted is the Co–Mo–S model proposed by Topsoe’s group, for the CoMo catalyst, but valid also for the NiMo catalysts. Theoretical calculations carried out using Density Functional Theory (DFT) showed that the promoter effect is to lower the binding energy of the Mo–S bonds at the edges of the crystal structures, creating what could be highly active centers [19]. Physical characterization, has demonstrated the existence of two distinguished Co–Mo–S phases, which has been nominated as I and II, II being more active than I. CoMoS-I is directly linked to the support and it is dispersed as an almost monolayer type of stacking. CoMoS-II has less linkage sites and a thicker stacking [15]. Although, CoMoS (I and II) is a model for the active phase, its quantification has




been related to the observed catalytic activity, but no details of the active sites have been provided, so far. The early studies on supported and unsupported MoS2 led to the hypothesis of geometrically distinct sites, from the edges or the rims, should exhibit different catalytic properties. The morphology of CoMoS-II phase seems to offer more exposed rim sites, which should not exhibit much of steric hindrance. Nevertheless, for decades, sulfur vacancies were thought to be playing an important role in regards to catalytic activity. It was till recently, when they could be observed directly by Scanning Tunneling Microscopy (STM) [20]. Notwithstanding, the need for demonstrating the catalytic activities of these distinctive sites remains.

When the main emphasis is on desulfurization, Co–Mo is primarily used. In the case that high levels of denitrogenation are required, then Ni–Mo is preferred. Finally, when higher requirements of hydrogenation are needed the recommendation falls in Ni–W. At low hydrogen pressure, there is an apparent superior hydrogen uptake with the CoMo catalysts, than that observed for the NiMo or NiW catalysts. In fact, at low pressure, CoMo’s HDS activity is higher than that of NiMo’s and NiW’s, and consequently hydrogen consumption agrees with the S removal [21]. For the same reason (lower hydrogenation capacity), CoMo catalysts are the least active for HDN reactions.

NiMo catalysts though designed for HDS are highly active for hydrogenation reactions and in consequence for HDN. Their hydrogenation capabilities make them most appropriate for the treatment of cracked feeds (FCC and coker feeds, mainly HCK in a lesser extent), and for a top layer in a reactor where coke precursors are suspected to be fed (highly olefinic or unsaturated cuts, gums precursors, etc.). However, their sensitivity to hydrogen pressure results in higher working pressures than CoMo. The HDS activity of NiMo catalysts is especially dependant on their hydrogenation activit

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