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JSM Biotechnology & Biomedical Engineering Special Issue on Industrial Biotechnology-Made in Germany: The path from policies to sustainable energy, commodity and specialty products Edited by: Dr. Thomas Brück Professor of Industrial Biocatalysis, Dept. of Chemistry, Technische Universität München (TUM), Germany Central

JSMBiotechnology & Biomedical Engineering

Special Issue on

Industrial Biotechnology-Made in Germany: The path from policies to sustainable energy, commodity and specialty productsEdited by:Dr. Thomas BrückProfessor of Industrial Biocatalysis, Dept. of Chemistry, Technische Universität München (TUM), Germany


Cite this article: Koltermann A, Kraus M, Rarbach M, Reisinger C, Zavrel M, et al. (2014) Cellulosic Ethanol from Agricultural Residues – An Advanced Biofuel and Biobased Chemical Platform. JSM Biotechnol Bioeng 2(1): 1024.

*Corresponding authorYvonne Söltl, Group Biotechnology, Clariant (Produkte) Deutschland GmbH, Staffelseestraße 6, 81477 Munich, Germany, Tel: 4989710661180; Fax: 4989710661122; Email:

Submitted: 23 March 2014

Accepted: 12 May 2014

Published: 14 May 2014

ISSN: 2333-7117

Copyright© 2014 Söltl et al.


KeywordsCellulosic ethanol; Agricultural residues; Advanced biofuels; Biobased chemicals; Enzymatic hydrolysis, Biocatalysis.

Review Article

Cellulosic Ethanol from Agricultural Residues – An Advanced Biofuel and Biobased Chemical PlatformKoltermann, A., Kettling, U., Kraus, M., Rarbach, R., Reisinger, C., Zavrel, M., Söltl, Y.Group Biotechnology, Clariant (Produkte) Deutschland GmbH, Germany


Cellulosic ethanol made from agricultural residues has been a scientific and commercial interest for decades however the development and commercial deployment of technologies have been limited. It constitutes an almost carbon neutral new energy source using an already existing renewable feedstock that doesn’t compete with food or feed production and land use. The field of application is wide, from second generation biofuel to the chemical industry. A key controversial issue regarding technological developments aimed at the production of cellulosic ethanol is the commercial economic viability of the process. The challenges facing process development include optimization of the ethanol yield while lowering operational and capital costs such as the reduction in enzyme costs and energy efficiency improvements. Recent years have seen great success in the development and deployment of cellulosic ethanol technologies. Now policy makers are asked to facilitate the market entry of such innovative processes by setting a long-term stable framework. Clariant’s sunliquid® technology overcomes the main challenges of competitive conversion of lignocellulosic feedstock into cellulosic sugars for fermentation to cellulosic ethanol. In July 2012 a demonstration plant with an annual output of 1000 tons of ethanol started operation. This is the last step on the way to commercializing a technology platform for second generation biofuels and biobased chemicals. The plant represents the complete production chain, including pretreatment, process-integrated production of feedstock and process specific enzymes, hydrolysis, simultaneous C5 and C6 fermentation and energy saving ethanol separation. The process itself is energy neutral, yielding cellulosic ethanol with about 95% of CO2 emission reductions.

ABBREVIATIONSa: Year; t:Metric Tons; USD: US Dollars

INTRODUCTIONToday the chemical industry is facing the situation that

most of its products are based on fossil resources. Over the last couple of decades the price for oil and fossil derived energy has risen drastically. While a barrel of crude oil was sold at about 20 USD at the end of the last century today the price is stable over 100 USD/barrel (with a peak of almost 140 USD/barrel in 2008) [1,2]. Thus, the fuels and chemical industry is looking for innovations to increase energy and process efficiency as well as to foster the substitution of fossil resources with renewable ones to remain competitive in the long term. Along with this comes an increased demand for more sustainability from the market side. The transition from an entirely fossil based industry to a more and more bio-based one is one of the mega trends seen in the chemical sector today.

Industrial biotechnology is the key enabling technology for the shift towards a sustainable bioeconomy. Today, biobased chemicals and biofuels available in the market are ultimately derived from sugars by means of biotechnological processes. This imposes a new dilemma: Using food or feed for the large scale production of for example fuels and converting land for the production of such feedstock has to be seen controversial, as the priority of agriculture is and should be to feed an ever growing population.

However, sugars can not only be derived from foodstuff.

The structural, so called lognocellulosic part of the plants also contains a substantial amount of sugars, bound in long chain sugar polymers cellulose and hemicellulose, glued together by lignin. One hectare of wheat for example yields about 3-3.5 tonnes of sugars bound in lignocellulosic biomass in addition to the 4-4.5 tonnes of sugars from the grain. Hence straw is an extremely attractive additional source of sugars from the non-edible parts of agricultural crops.

These cellulosic sugars are harder but not impossible to access. By using specific enzymes, the stable structure can efficiently be broken down into the corresponding monomeric sugars which can then be fermented into the desired product. Recently, significant advances have been made in research and process development, with cellulosic ethanol being the first product currently on the brink of commercial deployment (Figure 1).

The technology

A key controversial issue regarding technological developments aimed at the production of cellulosic ethanol is the economic viability of the process. In order to be competitive on the fuel market, the production costs achieved in the medium term must be comparable with the costs of manufacturing conventional bioethanol from plants containing sugar or starch. The challenges facing process development therefore include optimization of the ethanol yield, the lowest possible energy input and a reduction in the cost of enzymes – as yet one of the major cost factors (Figure 2).


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In recent years, Clariant, a global leader in the field of specialty chemicals headquartered in Switzerland, has been developing the sunliquid process for the production of cellulosic ethanol from agricultural residues, which is now ready to market (Figure 3). The biofuel obtained using this process is manufactured on an energy-neutral basis and boasts greenhouse gas savings of some 95%. The remaining 5% being attributable to the use of transport energy in logistics chain which is calculated as fossil-based. The production costs can compete with those of first-generation bioethanol.

Firstly, the feedstock, i.e. wheat straw, undergoes mechanical and thermal pre-treatment. This results in the lignin separating from the cellulose and hemicellulose chains, allowing the enzymes to split into sugar monomers during the next step (Figure 4).

The enzymes used have been optimised to a high degree by the company and specifically modified for each type of feedstock and the relevant process conditions. This ensures particularly efficient hydrolysis, giving rise to high sugar yields.

As a result of process-integrated enzyme production, enzyme costs can be reduced to a minimum. To this end, a small portion of the pre-treated feedstock is channelled off from the main mass to serve as a basic source of nutrients for special microorganisms which produce the enzymes. These are therefore created

whenever and wherever needed, with no costs being incurred for transport, storage or processing and without being dependent on enzyme suppliers.

Following hydrolysis, any remaining solid matter (mainly lignin) is separated out and incinerated to generate energy, leaving a sugar solution containing C5 sugars in addition to glucose, a C6 sugar. The sunliquid process uses a special fermentation organism which simultaneously converts both C6 and C5 sugars into ethanol by way of a one-pot reaction, consequently producing around 50% more ethanol than comparable processes, which are only able to convert C6 sugars.

The final unit process consists of purifying the ethanol produced. This is usually carried out by means of classic distillation which, however, calls for high energy input. Clariant has developed an energy-efficient, adsorption-based separation process which, by comparison, offers energy savings of up to 50%. As a result of optimising this and other process design features, it is possible to generate the energy needed for the entire process from accumulated residue (mostly lignin). No additional fossil energy sources are required.

The products

One of the main features of cellulosic ethanol is its particularly high potential for greenhouse gas emission savings, which can reach up to 100% compared with fossil fuel (Figure 5). If agricultural waste is used as feedstock, cellulosic ethanol does not entail any additional land use, nor does it compete with food and feed production [3-5]. As a result, cellulosic ethanol opens up a new domestic source of energy based on renewable feedstock which can be produced on a regional basis without having to cultivate new land. By utilizing residue, additional value is generated for this waste as it helps to diversify farm income. The concept of decentralised plants generates new green jobs, especially in rural areas.

Cellulosic ethanol used as biofuel is the first product derived from lignocellulosic biomass entering the market. Ethanol itself has however many other applications and serves as an important feedstock for the chemical industry. For example ethylene is currently the most important chemical worldwide for conversion into polyethylene. Today’s production is mainly based on cracking of naphtha, but an alternative route would be the conversion of bioethanol via dehydration. In addition, the sunliquid technology generates access to cellulosic sugars and hence creates a platform for a wide range of biobased chemicals such as organic acids, higher alcohols or other specialty and bulk chemicals [6,7]

The feedstock potential

Many new developments in the field of liquid energy resources focus on the use of so-called second-generation feedstocks, i.e. feedstocks which consist of lignocellulose and are therefore not suitable for use in food production. Above all, agricultural residues such as cereal straw, maize straw and sugarcane bagasse are of particular interest, but also certain energy crops, such as miscanthus and switch grass, are possible candidates [8-10].

Especially agricultural residues already pose a high potential–they are readily available globally in substantial amounts without

Figure 1 Global distribution of structural biomass.

Figure 2 Challenges in process development and sunliquid solutions.


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Figure 3 The sunliquid process creates sustainable and efficient cellulosic ethanol from agricultural residues.

Figure 4 The optimized enzyme mixture splits polymeric sugars into monomers.

Figure 5 Greenhouse gas emissions from various biofuels compared with gasoline.


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interfering with current agricultural practice (Figure 6) [11].

The most important type of agricultural waste in the EU is cereal straw, of which some 240 million tons accumulate across the EU´s 27 member states each year [12]. Several long-term studies have shown that depending on the region and prevailing local conditions, up to 60% of the residual straw can be collected from the fields and made available for recycling [13-15]. Using the sunliquid process, 27 million tons of cellulosic ethanol could be produced from this volume of straw, which is equivalent to the energy content of almost 18 million tons of fossil-based petrol. This means that around 25% of the EU´s demand for gasoline predicted for 2020 could be met by cellulosic ethanol. A study conducted by Bloomberg New Energy Finance includes other types of residue and various scenarios in its calculations and forecasts fossil gasoline substitution potential of up to 62% [16].

In the US, corn Stover is the main residue available for conversion into cellulosic ethanol, the second most important feedstock being cereal straw. The Billion Ton study released by the Department of Energy estimates the volumes of corn stover and cereal straw available in a sustainable way at 190-290 million tons [17]. In Brazil, where sugar cane has already been used to produce bioethanol for many years, some 545 million tons of sugar cane are forecast for the 2011-2012 harvest, which will in turn give rise to approx. 73 million tons of bagasse [18]. Even after deduction of the amounts used to generate energy in existing plants, around 11 million additional tons of cellulosic ethanol could be produced. This is equivalent to about 50% of Brazil´s current ethanol production.

The political framework

The nature of future changes in fuel supplies ultimately depends on the political environment. A striking example has been set by Brazil where, in 1975, the ProAlcool programme was initiated as an answer to the oil crisis. Over the following fourteen years, the government promoted the development of an ethanol industry based on a series of measures which included

blend ratios, adapting vehicle fleets, a petrol-ethanol pricing policy and low-interest loans. In 2011, the percentage of new purchases attributable to flex-fuel vehicles amounted to 83.1% and today, fuel supplied by Brazilian petrol stations contains at least 20% ethanol.

Future developments in each fuel market are therefore largely dependent on the measures instituted by the relevant governments. Today many governments have fuel strategies in place that include ambitious targets for the use of biofuels to secure energy supply or reduce greenhouse gas emissions.

In the European Union, the Renewable Energy Directive is the legislative instrument in place. By 2020 20% of the overall energy consumption and 10% of energy consumed in the transport sector is required to come from renewable resources. Currently, European Parliament and Council are discussing an amendment of the Directive proposed by the European Commission to cap the use of conventional biofuels and to introduce a dedicated blending mandate for advanced biofuels. As a result of ongoing discussions a stable long-term framework needs to be agreed on to facilitate market entry for innovative technologies like cellulosic ethanol production and foster private investments in the sector.

In the US, the Renewable Fuels Standard requires obligated parties to blend increasing volumes of various types of renewable fuel over time. When RFS2 was passed in 2007, Congress divided the 36 billion gallon per year (by 2022) blending standard into two primary categories: conventional biofuels (15 billion gallons per year) and advanced biofuel (21 billion gallons per year). The conventional biofuel requirement increases to 15 billion gallons per year by 2015, then “flat lines” at this level through 2022. The advanced biofuel requirement started with 600 million gallons in 2009 and increases to 21 billion gallons annually in 2022. The RFS is working and must maintain pressure on the marketplace to realize its full potential through 2022 and onwards [19]. To reduce the dependency on fossil imports while at the same time reducing pollution, the Indian government has initiated a biofuels program. In September 2002 the Ministry of Petroleum and Natural Gas has issued a 5% mandatory blending quota for Figure 6 Lignocellulosic feedstock of different regions worldwide.

Figure 7 The sunliquid demonstration plant has been producing cellulosic ethanol from agricultural residues since July 2012.


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ethanol in nine major states and 4 union territories from 2003 on. Due to a supply shortage of ethanol in 2004/2005, the blending was made optional and only resumed mandatory in 20 states in October 2006. Then in 2008, the Government announced its National Biofuels Policy which was approved by the Union Cabinet in December 2009. The program constitutes a three-phase implementation of ethanol blending in petrol across the country, starting at 5% in 2010, increasing it to 10% by 2012 and finally reaching 20% in 2017.

One thing is certain - innovative technology, such as that used to produce cellulosic ethanol, cannot be successfully introduced onto the market unless the prevailing political environment is reliable, thereby providing security for investors. This includes blend ratios, as well as investment support for initial production facilities in order to bridge the specific technical challenges of commissioning the first plants.

DISCUSSION AND CONCLUSIONThe use of lignocellulosic feedstock for cellulosic biofuels or

biobased chemicals production has a lot to offer: the exploitation of a new and renewable resource, high greenhouse gas savings, reduced dependence on fossil imports, economic growth just to name a few. Realization on an industrial scale is no longer merely a dream. The first production plants for cellulosic ethanol are already under construction in the US, one started operation in Italy in 2013, and four demonstration plants are currently located in Europe – one of which is operated by Clariant.

On 20 July, the sunliquid demonstration plant was officially commissioned in the Lower Bavarian town of Straubing (Figure 7). The plant replicates the entire process chain on an industrial scale, from pre-treatment to ethanol purification, serving to verify the viability of the sunliquid technology on an industrial scale. On an annual basis, up to 1,000 tons of cellulosic ethanol can be produced at this plant, using approximately 4,500 tons of wheat straw. Since May 2013 first runs on corn Stover from North America and bagasse from Brazil have been successful. The plant is certified under the European ISCC scheme to prove that the cellulosic ethanol produced here is truly sustainable according to European legislation.

However, to effectively enter the market, a supportive, reliable framework needs to be in place to foster investment and ensure investors’ confidence. In an economy where resource efficiency and sustainability become more and more important, we need to use all available resources in the most rational way. By using agricultural byproducts for the production of bio-based products, both plate and tank can be filled, while at the same time protecting climate and the environment and drive economic growth.

ACKNOWLEDGEMENTWe thank the Bavarian government and the Federal Ministry

for Education and Research for the support of accompanying research regarding the sun liquid demonstration plant.

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Koltermann A, Kraus M, Rarbach M, Reisinger C, Zavrel M, et al. (2014) Cellulosic Ethanol from Agricultural Residues – An Advanced Biofuel and Biobased Chemical Platform. JSM Biotechnol Bioeng 2(1): 1024.

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