Cellulosic ethanol

Cellulosic ethanol
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Mitigation
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Renewable energy
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Asian Institute of Technology
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ClimateTechWiki
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Bioenergy
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Ethanol fuel
Definition
Cellulosic ethanol is an alcohol produced from the feedstock available in wide variety of plant materials and agricultural residues.

Cellulosic ethanol is an alcohol produced from the feedstock available in wide variety of plant materials and agricultural residues. Although chemically identical with the first generation bioethanol, it differs in the use of raw material. Hence cellulosic ethanol differs from the conventional ethanol in its use of feedstock and the process implied at the different stages of production. The production of ethanol from an acre of grass or other crops is twice the quantity produced from an acre of corn grown because the in the former the whole plant is used unlike only grains in case of corn (Biocycle, 2005).

Introduction

Identified as a more potent in its net energy content which is three times more than the corn ethanol, and emission of low net level of greenhouse gases, cellulose ethanol exhibits a net energy content three times higher than corn ethanol and emits a low net level of greenhouse gases, R&D in cellulosic ethanol is relentlessly moving towards developing a low cost and efficient and domestically produced substitute to the fossil fuel.

Unlike the first generation bioethanol in which the sugar and starch derived from the crops like corn, sugar beet, sugar cane, wheat is used to produce alcohol, in cellulosic ethanol, agricultural plant wastes like straw, corn stover, lignocellulosic raw materials like wood chips and energy crops like miscanthus, switchgrass, as well as other by-products of lawn and tree maintenance, etc. are used. Hence, this makes cellulosic ethanol cheaper than other bioethanol (Greene 2004).

The bulk of the cellulosic biomass contains cellulose and hemicellulose and some lignin. The sugars are not easily retrievable because they exist within these cellulose and hemicelluloses as polysaccharides. The most challenging part is the breaking down of the complex polymer -polysaccharides for extracting fermentable sugars for efficient and economically viable production of cellulosic ethanol. The sugar thus extracted then can be made available to the microorganisms for fermentation process.

There are several technologies that can be used in conversion of biomass to ethanol. The technologies can be broadly categorized in two path ways:

  1. Biochemical conversion (fermentation) through pretreatment and hydrolysis and
  2. Thermo-chemical conversion through gasification.

1. Biochemical conversion

The first step is to break down cellulose which requires pretreatment. In pretreatment process, hemicelluloses and lignin that surround cellulose are broken down under a moderately high-temperature, high-pressure and through use of dilute acid. This process which is called hydrolysis breaks down hemicelluloses and dissolves lignin. The lignin thus produced forms and important source of heat and electricity, hence, limiting the use of fossil fuel in the conversion process. However, the problem with lignin is that it can under certain conditions during the pretreatment, redeposit onto cellulose which ultimately reduces the yield of sugar. Also this dilute acid treatment makes the process expensive as it requires costly equipment.

It has been proven that a milder pretreatment process whereby an appropriate mixture of enzyme to the hydrolysis of hemicellulose can curb degradation of sugar and ultimately the cost of processing.

Another way of enhancing the pretreatment process has been identified as the Ammonia Fiber Explosion (AFEX) process in which the lignocellulosic biomass is treated with high-pressure liquid ammonia leading to the explosive release of the pressure and thereby rendering the lignocellulosic biomass more susceptible to the enzymatic hydrolysis (Biocycle, 2005).

The simple sugars broken down from the cellulosic materials are fermented using yeast or bacteria under ideal conditions. These microorganisms convert the sugar into ethanol and water which is called the ethanol recovery process. The water is removed through distillation. The process is similar to that of bioethanol.

2. Thermo-chemical conversion

In thermo-chemical conversion of cellulose into ethanol, the ligno-cellulosic raw material is broken into syngas i.e., carbon monoxide and hydrogen first applying heat and chemicals. This process is mostly appropriate when forest products and mill residues that are rich in lignin are used as feedstock and which cannot be converted by biochemical process. This process is however, complex and is similar to that of petrol refining in which contaminants (tar, sulphur, etc.) are also produced along with the syngas. The syngas are converted into ethanol which then undergoes distillation.

Feasibility of technology and operational necessities

Production of cellulosic ethanol for large scale commercial use also requires cultivation of energy crops besides collection of waste as feedstocks. Therefore this requires adequate land, suitable soil and adequate water. Recent studies suggest of world’s 13.5 billion hectares of surface lands, approximately 1.6 billion hectares of land is used as cropland. Therefore, availability of land besides forest land, protected areas and cultivated food cropland that could be used for producing energy crops is estimated between 250-800 million hectares and most of which lies in the tropical regions of Latin America and Africa.

The very first logistics for producing ethanol from cellulose requires producing biomass which can be obtained from forest resources and/or agricultural resources. The produced biomass has to be harvested and then stored before it is finally transported to the conversion plant. These steps comprise theupstream logistics.

Before the biomass is introduced to the bio-refinery, the size in which they’ve been harvested needs to be reduced to the level where it is easy to handle and the process becomes more efficient. So if it is agricultural residue they need to be grinded and if wooden residue then these has to be taken through the chipping process so that the size of the materials are uniform.

However, as summarized in the IEA Bioenergy (2009), there are some critical issues that have to be catered to in biomass logistics that are related with the specific properties of biomass such as low energy density, need for drying and densification, seasonal availability and problems in storing resulting in additional pre-treatment process as well as factors that limit the supply of the mechanized equipment and infrastructures required for market penetration. The solutions to these problems have been proposed as the “development of advanced densification and other pre-treatment technologies, diversifying procurement geographically and in terms of biomass types, and the optimization of fuel supply chains from field to plant gate including the development of specialized harvesting and handling equipment” so that the product can be delivered at the lowest cost possible.

Development of bio-refineries

The biomass is converted into ethanol in a bio-refinery which is similar to oil refinery in terms of operation. However, given the categories of feedstocks with varying compositions, bio-refinery needs more advanced processing technologies. A bio-refinery has to be located close to the source of feedstock to ease transportation of the bulky feedstock both from logistical and economical point of view. A bio-refinery has to be improvised constantly to make the process of conversion more economic thereby using all the components of the collected biomass, obtain increased yield and recycling/reusing all the by-products/co-products obtained during the process. Accurate composition of biomass is vital to the quality and cost of the ethanol produced.

Status of the technology and its future market potential

Ethanol is not yet produced at a commercial scale in the United States. Public and private efforts continue to support research on cellulosic ethanol, and technological advances are expected to reduce costs and improve production methods. As of early 2009, no commercial-size cellulosic ethanol facilities were in operation in the United States. However a number of demonstration plants are in operation and a number of commercial-size facilities are expected to begin production by 2011. In 2007, the DOE funded six facilities with annual plant production goals ranging from 11.4 million to 40 million gallons of cellulosic ethanol.

As of March 2010, there are total 34 cellulosic ethanol projects worldwide following the biochemical pathway. Of these 5 are planned, one under construction and one operational under the commercial scale. The rest are either in the demonstration stage or in a pilot stage. A total of 15 plants are in the United States of America, 6 in Denmark, 4 in Sweden, 2 in Norway and Italy each, 3 in Canada and 1 each in Spain, Austria, Australia and France. Of the five projects producing ethanol from thermo-chemical pathway, four are in Canada of which 2 are operational and one under construction and one is planned and 1 is in the United States of America which is under construction to operate at a commercial scale. Also there are four projects that are applying hybrid technology of which 1 is planned for a commercial scale. Besides these, there are Brazil, China, India and South Africa who are looking into the production of cellulosic ethanol as a potential option to cut down their energy dependence by utilizing locally available raw materials which do not compete with food crops.

According to analysis by the Abengoa bioenergy, up to 2016, the market in the US and UE will be predominantly occupied by the starch technology because of the limitations in the cellulosic ethanol production specifically the availability of raw materials.  However, it is projected that the biomass plants in the US will start operating from 2012 producing up to 5 B/gallon per year and in EU it is expected to produce up to 2-3 ml/year in 2017. Only after 2017, plants operating exclusively on biomass are expected to be feasible owing to the technological and energy crops market development. And in this context, the South East Asian region will potentially be a significant producer of raw material (Abengoa bioenergy, 2007).

Several innovations are going on to make cellulosic bioethanol more cost competitive with other bioethanol. Although very few biorefineries worldwide are producing it at a commercial scale, many companies are coming forward to plan and invest in this technology not only across the developed countries of Europe and America but also in the Asian region including India and China. BC International is one such company that is focusing on innovative ways to produce ethanol at a lower cost and is developing the processing facilities in Asia too. Also a Japanese company has started to produce ethanol from cellulose after receiving license from Arkenol and Masada Corporation (Biocycle, 2005).  

The technology is advancing at the commercial scale in Asia through Verenium corporation which is considered as a pioneering company developing the second generation cellulosic ethanol. Utilizing its technology, a Japanese company called Marubeni and Tsukishima Kikai Co., Ltd. has developed a cellulosic plant in Osaka that produces 1.4 million-litre/year utilizing the construction wood waste as the feedstock. Verenium Corporation itself is establishing a three million litre/ year cellulosic ethanol plant in Saraburi, Thailand (Vereneum Corporation, 2008). Likewise, an ethanol company called Qteros Inc. in collaboration with major Indian ethanol firm called Praj which already has built around 450 ethanol plants in Asian region as well as Africa for commercializing cellulosic ethanol. Over the period of 18-24 months these two companies will be working together for developing the “Process Design Packages” in the course of commercializing the technology. This package will be licensed to the companies willing to produce cellulosic ethanol (MHT,2011).

How the technology could contribute to socio-economic development and environmental protection

Some of the key barriers to the commercialization of cellulosic ethanol as as under:

  • Infrastructure barriers:Infrastructure for the distribution of cellulosic ethanol might be a barrier because it cannot be transported through pipes but has to be carried through vehicles by road. Georgraphical locations suitable for production of feedstock and the area of demand for the ethanol may vary thus requiring extensive investment in infrastructure development like road/railway networks. Also greater investment required for storing and processing especially in the pre-treatment stage.
  • Market barriers:Lack of distribution infrastructure for market penetration, availability of a limited number of vehicle models that can run with the given type of fuel combination that uses high ethanol blend percentage and lack of awareness about the benefits of the cellulosic ethanol among the industry participants as well as the consumers are barriers related with the market place.
  • Feedstock logistical and technical barriers:At present there is lack of efficiency in meeting the requirements related with sustainable harvesting of the feedstock and development of bio-refineries, harvest equipment and technology which can deal with the large yield of biomass. Production of cellulosic ethanol requires adequate land, water and suitable soil.
  • Financial barriers:Expensive process and requires costly equipment, a high cost of cellulose enzyme is a barrier for economic production.  

To promote cellulosic ethanol and remove the barriers there has to be certain policy framework favorable to the promoters and the users. Some such policy may already be in place while some others may be required to be formulated. Some of the key issues that the policies should address are:

  • The governments should have mandates for the use of biofuel
  • The national crop database needs to be expanded to accommodate cellulosic feedstock as well.
  • The financing systems should promote and encourage development of more efficient feedstock supply systems including funding of pilot plants.
  • Subsidies and tax systems have to be favourable for promoting the use of cellulosic ethanol.

Contribution of the technology to social development

  • Employment creation and enterprise development opportunities in the agriculture, forestry and industrial sector (e.g. total 6 million jobs creation by 2020 in China).
  • Lignin which is a non-fermentable co-product in the hydrolysis process has its characteristics similar to that of coal and hence can be used to generate power. The surplus can be used in making additional ethanol or for producing electricity.

Contribution of the technology to economic development (including energy market support)

  • Use of locally available feedstock reduces dependence on fossil fuel
  • Decrease in import of fossil fuel helps to reduce trade deficit  and fiscal deficit
  • Prospects for earning foreign currency through export of cellulosic ethanol
  • Need for infrastructure development creates more business opportunities in the engineering and construction as well as industrial sectors (e.g. in China, 37 million tons of cellulosic ethanol could also create a RMB 90 billion of engineering and construction business opportunity)
  • Farmers can have additional source of income through collection and sale of agri-residues

Contribution of the technology to protection of the environment

Unlike other energy crops the feedstock (eg. trees and switch grass) used for producing cellulosic ethanol for commercial purpose usually require lower input in terms of field equipment, pesticides and fertilizers and can be grown even in marginal lands which are not suitable for growing other crops and do not need to be replanted for as long as 20 years. Other environmental advantages also include soil conservation, enhancement of fertility and optimum use of water and fertilizers (Biocycle, 2005).

Climate

Researchers have proven that cellulosic ethanol has GHG emission reduction potential upto 80% as compared to gasoline based on the WTW model created by Michael Wang of Argonne National Laboratories (Biocycle, 2005). Further to this other analyses suggest that it might even be carbon negative (more carbon dioxide removed from the atmosphere than produced during the lifecycle of the product) based on the use of specific feedstock. It should be noted however, that emission of carbon dioxide due to land use change has not been considered here. Table 1 given hereunder shows emission reduction from cellulosic ethanol compared to gasoline.

As cellulosic feedstock have better energy conversion ratio, emission of carbon dioxide is less compared to corn or cane hence less detrimental impact on land and water.

Financial requirements and costs

The cost of production of cellulosic ethanol depends on two key factors:

  • High capital cost
  • Uncertain cost of feedstock

According to a research finding from the U.S Department of Energy (DOE) in 2006 at the production cost of $2.25 per gallon, the cellulosic ethanol was competitive with the petroleum-based gasoline which was around $120 per barrel.

The initial investment cost of establishing a cellulosic ethanol plant is 6 times as high as the cost for the corn ethanol plant. It is estimated that a cellulosic ethanol plant of 50 million gallons per year capacity costs around US$ 375 million. For a new technology, high capital cost imposes greater risk of investment but later when the technology matures, deployment of the technology and market penetration will become easier and financial risks may reduce.

The cost of biomass production also depends on the price of the feedstock at that particular time. Since the cost of feedstock is not certain and has to be assumed depending upon the demand supply scenario, it may increase with intense competition for low-cost waste products or may decrease as the technology matures and a larger market is created. However, cost of production of cellulosic ethanol is expected to decrease with the advancement in the technology specifically for pretreatment; however, the cost of feedstock will then be the determinant of the overall cost and its competitiveness with other energy/transportation fuels.

References