DEPARTMENT OF CHEMICAL ENGINEERING

By A.V. Baloyi

Subject : Chemical Process Design

Project : Methane Oxidation to Acetic Acid

ABSTRACT

The main objective of this project is to produce acetic acid from methane. This project will show

the industrialization or commercializing of this process by using Unisim design software.

The objective of the development of new acetic acid processes has been to reduce raw material

consumption, energy requirements, and investment costs. Significant cost advantages resulted

from the use of carbon monoxide and of low-priced methanol as feedstock’s. At present,

industrial processes for the production of acetic acid are dominated by methanol carbonylation.

The kinetic reactor has therefore been efficient for the operation. Material and energy balances

were constructed effectively using the data generated from the simulated unit operations. The

commercialization the production acetic acid from methane oxidation it is a success. The

production occurs in three major steps. In the process another method is introduced to maximize

the production without any loss of the raw material. The carbonylation stage makes sure that no

byproducts are discharged everything is converted to acetic acid.

The scope of work covered in the project includes:

Designing a simulation of the plant using UniSIM

Constructing a process flow diagram of the entire process

Calculating mass and energy balances

Equipment design and sizing

Project investment and costs

Carry out HAZOP study on the process

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Table of Contents

Abstract 1

1. Introduction 3

2. Literature Review 4

2.1 Theoretical Background 4-5

2.2 Experimental 6-8

3. Technical 9

3.1 Process Flow Diagram 9

3.2 Material and Energy Balance 10-11

3.3 Process Description 12-13

3.4 Design and Description of each Unit 14

4. Hazards & Safety Considerations 20

5. Economic Analysis 21-22

6. Conclusions and Recommendations 23

7. References 24

8. Appendix 25-28

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1. INTRODUCTION

Acetic acid is an important commodity used in chemical industries, with about 9 million tons of

world demands per year. The primary use of this chemical is in the manufacture of assorted

acetate esters, fungicide, organic compounds, organic solvents and the preparation of

pharmaceuticals, cellulose acetate that is important in making film and plastic wares, perfumes

and synthetic fiber. Methane is the most abundant reactive trace gas in the atmosphere and arises

from both natural and anthropogenic sources. It is a valuable gas and is usable at a wide range of

concentrations, down to 5%. The main objective of this process is to produce acetic acid from

methane. Methane oxidation to acetic acid catalyzed by Pd2+ cations in the presence of oxygen

is the objective of this project but for total conversion other methods will be used because the are

some byproduct in the reaction, which is methanol. This project will show the industrialization or

commercializing of this process by using Unisim design software. This method it inverted in the

lab by Mark Zerella, Argyris Kahros and Alexis T.Bell

The conversion of methane to acetic acid is currently carried out in a three-step process. Methane

is first reformed in a heterogeneously catalyzed process that is energy and capital-intensive to

produce synthesis gas, a mixture of CO and H2. The CO and H2 then react at high pressure in a

second step to produce methanol, and finally, in the third step, acetic acid is produced by

homogeneous-phase carbonylation of methanol. This process is also carried in three major

stapes. The present method to the liquid phase oxidation of methane with an oxidant in a strong

acid in the presence of a catalyst comprising palladium combined with a promoter. However, this

process displayed a serious drawback. During the reaction particles of palladium black were

formed due to the reduction of Pd (II) to Pd. This invention comprises a process for the

production of acetic acid, or derivatives such as methyl acetate and acetyl sulphate, from

methane, by contacting a methane-containing feed with an oxidant in the presence of a

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palladium- containing catalyst, a promoter, and an acid selected from concentrated sulfuric acid

and fuming sulfuric acid.

2. LITERATURE REVIEW

2.1. Theoretical Background

This invention relates in general to an improved process for the production of acetic acid or a

derivative thereof by liquid phase oxidation of methane. In particular the present invention

relates to the liquid phase oxidation of methane with an oxidant in a strong acid in the presence

of a catalyst comprising palladium combined with a promoter. The primary process route used

today for production of acetic acid is by catalytic reaction of methanol and carbon monoxide.

Such a process, typically termed “carbonylation”, is described in a number of patents and

publications. Rhodium, palladium or iridium-containing catalysts have been found especially

useful for conducting this reaction. The approach for the direct synthesis of acetic acid from

methane has been reported by Periana et al., who describe the oxidation of methane to acetic acid

catalyzed by Pd2+ cations in 96 wt% sulfuric acid.

The only other products observed are methyl bisulfate and carbon dioxide. Whereas the

selectivity to the liquid-phase products is reported to be as high at 90%, Pd2+ is observed to

precipitate from solution as Pd-black, causing the reaction to stop. According to the invention,

acetic acid is produced from methane by contacting the methane, in a feed comprising methane

and optionally other components, With an oxygen containing gas in the presence of a palladium-

containing catalyst, a promoter, and an acid selected from concentrated sulfuric acid and fuming

sulfuric acid. The inclusion of a promoter, for example a copper (II) salt, increases the rate of

acetic acid formation from methane by more than a factor of five as compared With the Periana

et al. Work and, in addition, inhibits the precipitation of Pd black, it reduced the production of

the sulfur products and carbon dioxide.

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The methane that is introduced into the process may be an essentially pure methane stream, a

methane stream that contains various impurities, or a stream that contains methane as one of

several components, for example, a methane containing stream that emanates from a chemical

process unit, a natural gas stream, a methane-containing stream produced by a gas generator, a

methane-containing off-gas, a biogenic methane stream, and the like. The methane feed to the

process may also contain other materials that may be oxidized under the process conditions to

form acetic acid. Methanol, dimethyl ether, methyl acetate and methyl bisul fate may also be fed

to the process. The palladium-containing catalyst may be any palladium containing material that

possesses the necessary catalytic activity for this reaction. Preferred palladium-containing

catalysts are palladium salts such as palladium (II) and palladium (IV) sulfates, chlorides,

nitrates, acetates, acety lacetonates, amines, oxides, and ligand-modified palladium systems, for

example systems containing ligands such as phosphines, nitriles, and amines. Promoters suitable

for use in the process of this invention include materials that have a demonstrated REDOX

couple with palladium, such as salts of copper, silver, gold, vanadium, niobium, tantalum, iron,

chromates, and organic sys tems such as hydroquinone or anthraquinone complexes with such

metals. Preferred promoters for the process are salts of copper and iron, most preferably cupric

salts. Other preferred promoters include cupric and cuprous nitrate, sulfate, phosphate, acetate,

acetylacetonate, and oxide, ferric chloride and ferric sulfate.

For metals that have multiple valences, e.g. copper and iron, the promoter can be introduced as a

salt of the lower valence which becomes oxidized in situ When in contact With the oxygen-

containing gas or With H2SO4 or S03. In addition to its primary function, the promoter may also

serve to catalyze regeneration of the acid. Additionally, a salt of platinum or mercury may be

included in the process, to assist in conversion of methane to methanol and/or methyl bisulfate,

which may then be converted to acetic acid by the Catalyst/promote

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6

2.2. Experimental

2.2.1. Method 1

The effects of CH4 and O2 partial pressures were explored to determine the influence of these

variables on the yields of acetic acid and methyl bisulfate, the selectivity of methane conversion

to these products, and the retention of Pd2+ in solution. Unless specified otherwise, all reactions

were carried out in 96 wt% H2SO4 containing 20 mM of PdSO4 at 453 K. The initial partial

pressures of CH4 and O2 were chosen to avoid compositions that would result in an explosive

mixture during any part of the reaction. The results of these experiments are given in Tables 1

shows that for an initial CH4 partial pressure of 200 psi, the yield of acetic acid rose from 65.7 to

181 mM as the initial partial pressure of O2 increased from 0 to 125 psi. Over the same range of

O2 partial pressures, the yield of methyl bisulfate increased from 2.5 to 4.8 mM, whereas the

production of methanesulfonic acid increased from 3.0 to 29.4 mM. The are other two sulfur-

containing byproducts, sulfoacetic acid and methane disulfonic acid.

Figure 1: method 1 results

7

2.2.2. Method 2 (preferred method)

In this example CH4 and 02 Were reacted at 180° C. in a high pressure, glass-lined autoclave

containing catalytic amounts of PdSO4 and CuCl2 added to concentrated sulfuric acid (96%

W/W). Reactions were carried out for 4 h, after which an equal volume of Water Was added to

the product solution in order to hydrolyze any anhydrides. Reaction products were analyzed by

1H NMR. More specially, using a 50 mL glass autoclave liner, 0.0121 g (20 mM) of PdSO4, and

0.0081 g (20 mM) of CuCl2 Were dissolved in 3 mL (5.67 g) of 96% sulfuric acid. A small

Teflon-coated stir bar Was added prior to sealing the autoclave. The reactor was purged With Ar

and then pressurized With 400 psig of CH4 and 30 psig of O2.

Figure 2: lab results

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2.3. Carbonylation of methanol to acetic acid

Novel acetic acid processes and catalysts have been introduced, commercialized, and improved

continuously sincethe1950s.The objective of the development of new acetic acid processes has

been to reduce raw material consumption, energy requirements, and investment costs. Significant

cost advantages resulted from the use of carbon monoxide and of low-priced methanol as

feedstock’s. At present, industrial processes for the production of acetic acid are dominated by

methanol carbonylation.

The carbonylation of methanol is catalyzed by Group VIII transition metal complexes, especially

by rhodium, iridium, cobalt, and nickel. All methanol carbonylation processes need iodine

compounds as essential co-catalysts, the reaction proceeding via methyl iodide, which alkylates

the transition metal involved. Apart from acetic acid, the carbonylation of methanol also gives

rise to the formation of methyl acetate, . In some carbonylation processes methyl acetate is also

used as a solvent. The determination of reaction rate parameters, equilibrium constants, CO

solubility and rate constant, can give rise to develop a reaction rate expression that could be used

to design and to scale up the process. So can the study of the determined parameters in the

reaction modeling and simulation by commercial simulators such as HYSYS.Plant. Because of

the lack of information on homogeneous catalysts in this field, this study focuses on the kinetics

of the homogeneous Rh-catalyzed methanol carbonylation (CH3I: promoter; water content: ~ 11

wt. %) using experimental tests and applying theoretical methods such as ab initio method with

the help of Gaussian-98 program. In the following section, the experimental apparatus of the

research are discussed. Then, the kinetics, modeling and simulation of the carbonylation of

methanol are developed

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3. TECHNICAL

3.1. Process Flow diagram

Figure 3; flow diagram from unisim

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3.2 Material and Energy Balance

3.1.1 Overall Mass Balance

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3.2.2 Energy Balance

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3.3 Process Description

The design models a process based on a three-part system containing the following systems: The

methane oxidation reactor, flash distillation system and the carbonylation reactor.

The reaction requires high pressure and temperatures, from the lab report it required 180 0C and

400Psi of pressure. A compressor and heater were introduced to system. The system consists of

a kinetic reactor containing palladium sulphate as catalyst. The reactor feed is 900 kmol of

methane and 1490 kmol of air. The methane to oxygen ration is 0.3. The methane conversion is

100% (calculated value). The reaction is highly exothermic and therefore water will be used as a

cooling medium, which would then be used as a steam utility.

A separator was introduced to remove the excess of air to make the flash distillation column to

converge faster. The product where cooled down to -500C for the separator. The liquid products

were transferred to the flash distillation column where only the two components had to be

separated, methanol the byproduct and acetic acid the required product. They feed at temperature

of -500C and pressure of 1atm.Them boiling points where very low, high pressure and low

temperatures were used at the flash distillation column. The top came out methanol and bottom

was acetic acid.

Realizing that a lot of methanol is produced another method was found to convert methanol to

acetic acid. This method was introduced to maximize production of acetic acid to make sure no

raw material goes to waste. The new reaction was called carbonylation of methanol.

Carbonylation of methanol is when methanol reacts with carbon monoxide to produce acetic

acid. It is a homogenous reaction where rhodium is used as catalyst. A packed bed reactor was

used for this reaction. The 98kmol of was converted to acetic acid (97.37% conversion). The

reaction occurs in 20MPa and temperature of 2510c. A compressor was introduced to system. the

reaction was endothermic no cooler was required .

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Carbonylation of methanol

Kinetics of reaction

CO+CH 3OH K⃗ CH 3COOH

−r=Keq C

Kmethane=2 .5×1010 exp(9 . 2×104 /RT )

There is only one reaction in the reactor which carbonylation of methanol to acetic acid and

methanol. The E and A for the arrinhius equation were found in one of references of the

research. All the assumptions were in UNIFAC and 97.3% conversion was achieved

Catalyst

The production of acetic acid by the Monsanto process utilizes a rhodium catalyst and operates at

a pressure of 30 to 60 atmospheres and at temperatures of 150 to 200°C. During the methanol

carbonylation, methyl iodide is generated by the reaction of added methanol with hydrogen

iodide. The infrared spectroscopic studies have shown that the major rhodium catalyst species

present is [Rh (CO)2I2]

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3.3 Design and Description of each Unit

3.4.1 Mixer

Function: A mixer is used to manipulate a heterogeneous physical system, with the intent to

make it more homogeneous.

Figure 4 mixer

A mixer was introduced to the system to combine the in feed streams to so they can be heated

and compressed for reactor.

3.4.2 Heater

Figure 5 heater

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From the lab results the reaction required a high pressures and temperatures. The mixed feed was

heated to 1800c and 400Psi of pressure that was the feed to the reactor. The energy required was

1.17e7 kj/hr

3.4.3 Methane oxidation reactor

Function: A reactor is a vessel in which chemical reactions take place. Conditions of operation

are based on the nature of the reaction system and its behavior as a function of temperature,

pressure, catalyst properties, and other factors.

Kinetics of the reaction

CH 4+O2 K⃗eq CH 3COOH +CH 2 OH

−r=Kmethane C

Kmethane=1 . 07×1022 exp(1 .7×105 / RT )

There is only one reaction in the reactor which is methane oxidation to acetic acid and methanol.

The E and A for the arrinhius equation were found in one of references of the research. All the

assumptions were in UNIFAC and 100% conversion was achieved.

Catalyst

Palladium catalyzed cross-coupling reactions have revolutionized the way in which molecules

are constructed. The field of cross-coupling has grown to include numerous strategies for C-C,

C-N, and C-O bond formation. While a range of palladium catalysts have been developed for

each transformation, it is often difficult to determine which catalyst is best for your desired

cross-coupling application. This reaction between CH4 and 02 is reacted at 180° C. in a high

pressure, catalytic amounts of PdSO4 and CuCl2 added to concentrated sulfuric acid (96%

W/W).

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3.4.4 Cooler

Function: A cooler is a heat removal devices used to cool the working fluid.

Figure 6 cooler

The product stream was at high temperatures and pressure. It required to be cooled for

separation. It was cooled from 4000c to -500c at that temperature air is still in gaseous phase. The

pressure was also decreased from 2809 kPa to 1atm. It required energy of 4.5e7kj/hr

3.4.5 Separator

Function: A separator is used to separate dispersed liquid in a gas stream. It is important that the

dimension of the separator is large enough so that liquid can settle in the bottom of the tank.

Figure 7 separator

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The separator was the first stage of separation where excess of air is removed from the main

product. The excess of was emitted to atmosphere where it still safe for the environment. The

emissions contained high amounts of nitrogen.

3.4.6 Distillation column

Function: A distillation column is used to separate different components in a fluid, by using their

difference in boiling point.

The design

Figure 8 distillation column

The column has 10 stages and the feed stage is no 5. It is full reflux and the operational pressures

are between 1000kPa and 1015kPa.

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Worksheet (Distillation Column)

Figure 9 worksheet

The worksheet results show that methanol exits at the top and acetic acid at the bottom. The

UNIFAC models it is advantageous because the VLE can be predicted for a large number of

systems without introducing new model parameters that must be fitted to experimental VLE data.

The binary coefficients of acetic acid were displayed by the UNIFAC only. The first batch of

acetic acid is produced and the methanol continues to produce the second batch.

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3.4.7 Compressor

Function: A compressor converts power into kinetic energy to increase the pressure of gases.

Compressors are used for high operation from 200 kPa - 400MPa.

Figure 10; compressor

The compressor was installed because of the knowledge that was obtain from research that

carbonylation occurs in at high pressures. The compressor was compressing the methanol so the

inlet of the reactor can have high pressures.

3.4.8 Mixer 2

Figure 11 mixer

The mixer is there to combine both the reactants so they could feed to the reactor. The feed to the

reactor is at a pressure of 20MPa and temperature of 2510C .

4. HAZARDS AND SAFETY CONSIDERATIONS

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Hazards Identification

Very hazardous in case of skin contact, of eye contact , of ingestion, of inhalation. Hazardous in case of skin contact (corrosive, permeator), of eye contact (corrosive). Liquid or spray mist may produce tissue damage particularly on mucous membranes of

eyes, mouth and respiratory tract. Inhalation of the spray mist may produce severe irritation of respiratory tract,

characterized by coughing, choking, or shortness of breath. Reacts with metals to produce flammable hydrogen gas.

First Aid Measures

Eye Contact: immediately flush eyes with plenty of water for at least 15 minutes. Skin Contact: immediately flush skin with plenty of water for at least 15 minutes while

removing contaminated clothing and shoes. Cover the irritated skin with an emollient. Inhalation: remove to fresh air. If not breathing, give artificial respiration. If breathing is

difficult, give oxygen. Ingestion: Do not induce vomiting unless directed to do so by medical personnel.

Fire Fighting Measures

Dry chemical powder. Alcohol foam. Water spray or fog

Accidental Release Measures (Spillage)

Absorb with dry earth, sand or other non-combustible material. Absorb with an inert material and put in an appropriate waste disposal. Use water spray curtain to divert vapor drift. Neutralize the residue with a dilute solution of sodium carbonate.

Handling and Storage

Keep away from heat. Keep away from sources of ignition. Do not ingest. Do not breathe gas/fumes/ vapor/spray. Store in a segregated and approved area.

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5. ECONOMIC ANALYSIS

Chemical plants are built to make profit, and an estimate of the investment required and the cost

of production, are needed before the profitability of a project can be assessed. In the economic

analysis of a chemical plant, the costs for the plant are divided into investment cost and operating

cost.

The fixed capital investment is the total cost of the plant ready for start-up. The fixed capital

investment can be subdivided into manufacturing fixed-capital also known as direct cost, and

nonmanufacturing fixed capital or indirect cost. The working capital for an industrial plant

consist of the total amount of money invested in raw materials and supplies carried in stock, cash

for monthly payment of operating expenses, accounts payable, and taxes payable, etc.

The total capital investment (TCI) is the sum of the fixed capital investment end the working

capital. The ratio of working capital to total capital investment used by most chemical plants is

10-20 percent of the total capital investment. In our analysis the working capital was estimated to

be 15 percent of the total capital cost.

Estimation of Total Capital Investment

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S. No. DescriptionDirect Costs

1 Purchased Equipment R 88 000,002 Purchased Equipment Installation R 30 000,003 Instrumentation and Controls R 54 700,004 Piping R 39 990,005 Electrical Equipment and Materials R 36 499,006 Buildings (Including services) R 59 999,007 Yard Improvements R 10 141,008 Service Facilities R 21 500,009 Land R 525 000,00

Total Direct Costs (D) R 865 829,00Indirect Costs

10 Engineering and Supervision R 68 000,0011 Construction Expenses R 54 600,0012 Contractors Fee R 46 533,00

Total Indirect Costs (I) R 169 133,00Fixed Capital Investment (FCI), D + I R 1 034 962,00Working Capital (WC), 15% R 155 244,30Total Capital Investment (TCI) R 1 190 206,30

Cost in R.

Estimation of Total Product Cost

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S. No. DescriptionManufacturing CostsDirect Production Costs

1 Raw Materials R 42 114,002 Operating Labor R 229 588,003 Operating Supervision R 120 411,004 Power and Utilities R 52 000,005 Maintenance and Repairs R 21 899,006 Operating Supplies R 18 577,007 Laboratory Charges R 38 999,008 Patents & Royalties R 0,009 Catalysts and Solvents R 0,00

Total Direct Production Costs R 523 588,00Fixed Charges

10 Depreciation R 80 000,0011 Taxes R 58 000,0012 Insurance R 515 011,0013 Rent R 0,00

Total Fixed Charges R 653 011,00Plant Overhead Costs

14 Plant Overhead Costs R 205 161,00Total Plant Overhead Costs R 205 161,00Total Manufacturing Costs (M) R 1 381 760,00General Expenses

15 Administrative Expenses R 6 500,0016 Distribution & Marketing Expenses R 8 500,0017 Research & Development R 0,0018 Financing (Interest) R 0,00

Total General Expenses (G) R 15 000,00Total Product Cost, M + G R 1 396 760,00

Cost in R.

6. CONCLUSSION AND RECOMMENDATIONS

The commercialization the production acetic acid from methane oxidation it is a success. The

production occurs in three major steps. In the process another method is introduced to maximize

the production without any loss of the raw material. The carbonylation stage makes sure that no

byproducts are discharged everything is converted to acetic acid. The yield of acetic acid, the

primary product of methane oxidation, increases with increasing O2/CH4 ratio for a fixed CH4

partial pressure and with increasing total reactant pressure for a fixed O2/CH4 ratio. Using the

Pd/Cu/O2 mixture, the effect of reaction conditions is evaluated with the aim of maximizing the

acetic acid yield. The increase in acetic acid yield as a consequence of increasing O2/CH4 ratio

is accompanied by only a modest loss in selectivity to oxygen containing organic products, and

the increase in total pressure of CH4 and O2 at a fixed O2/CH4 ratio results in a slight rise in the

yield of acetic acid. This study leads to an efficient and simultaneous estimation of the effects of

pressure, temperature, and the thermodynamic restrictions on kinetic investigation of the

homogeneously rhodium catalyzed carbonylation process. The kinetic reactor has therefore been

efficient for the operation. Material and energy balances were constructed effectively using the

data generated from the simulated unit operations.

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7. REFERENCES

1. Mohammadrezaei, Ali Reza; Jafari Nasr, Mohammad Reza. Iran. J. Chem. Chem. Eng.

Vol. 31, No. 1, 2012

2. Paulik F.E., Roth J.F., Novel Catalysts for the LowPressure Carbonylation of Methanol to

Acetic Acid,Chem. Commun, 1578a (1968).

3. . Mark Zerella, ArgyrisKahros, Alexis T.Bell. Methane oxidation to acetic acid catalyzed

by Pd2+ cations in the presence of oxygen ∗. 2005

4. WANG Ye*, AN DongLi & ZHANG QingHong. Catalytic selective oxidation or

oxidative functionalization of methane and ethane to organic oxygenates. Vol.53 No.2:

337–350.2010

5. Roy A. Periana, Marina Del Rey. process for converting methane to acetic acid. us

7,368,598 b2 .2008.\

6. Abdulwahab GIWA. methyl acetate reactive distillation process modeling, simulation and

optimization using aspen plus. vol. 8, no. 5, 2013

7. Christophe M. Thomas*, Georg Su¨ss-Fink. Ligand effects in the rhodium-catalyzed

carbonylation of methanol. 2003

8. Lødeng, R.: “A Kinetic Model for Methane Directly to Methanol”, Ph.D. Thesis, NTNU, 1991

9. Meyers, R.A.: “Handbook of Petrochemicals Production Processes”, RR Donneley, USA, 2005

10. Olah, G.A., Goeppert, A. and Prakash, G.K.: Beyond Oil and Gas: The Methanol Economy, Wiley-VCH, Darmstad, 2006

11. Peters, M.S., Timmerhaus, K.D. and West, RE.: Plant Design and Economics for Chemical Engineers”, 5th ed., McGraw-Hill, New York, 2003

12. Sinnot, R. and Towler, G.: Chemical Engineering Design, 5th ed., Elsevier Ltd., UK, 2009

13. Smith, R.: “Chemical Process Design and Integration”, John Wiley and Sons Ltd., Chippenham, 2005

14. Tijm, P.J.A., Waller, F. J. and Brown, D.M.: Methanol technology developments for the new millnium. Applied Catalysis A: General, 221, 275-282, 2001

15. Trimm, D.L. and Wainwright, M.S.: “Steam Reforming and Methanol Synthesis”, Catalysis today, 6, 261-278, 1996

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8. APPENDIX

Simulation Parameters

8.1 Stream 1

8.2 Oxygen stream

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8.3 Mixed stream

8.4 Reactor stream

27

8.5 Prod stream

8.6 Separator stream

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8.7 Products

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