Major Compelling Reasons for Thrust on Cellulosic Ethanol

Energy Matters

I have been asked by some friends regarding the compulsions for focusing so much on Cellulose when we can do the same in a much simpler manner at a much lower cost with other renewable materials like Sugar cane or corn grains. The reasons may be fairly obvious to many but I will try to capture all arguments together to drive home the point in this post.

1. Food versus Fuel Controversy:

This is the first and foremost reason for pursuing cellulose for ethanol over food based feedstocks like sugar cane or Corn grains. Carbohydrates present in Cellulose ( present mainly in wood, straw, and much of non-edible portions of plant kingdom) cannot be digested by humans. Therefore it doesn’t compete or interfere with food production.

2.Cost of feedstock:

There are two factors that bring down the cost of cellulosic feedstock. They are discussed below:

A. Yield Factor:

This is…

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Cellulosic Ethanol

Energy Matters

Current commercial processes for ethanol use sugar cane or Corn kernel which is a kind of starchy biomass. There are two major problems with these popular processes: One is that it competes with food crops which has led to controversial Food versus Fuel debate. Secondly, the cost of production is not competitive vis-a- vis gasoline. These are the reasons for shifting of attention to Cellulosic ethanol.

Challenges with Cellulose processing:

Breaking down plant biomass(cellulosic) is no easy task. Nature has taken millions of years to evolve to make them hard and recalcitrant. This means they have tremendous resistance to natural forces like attacks from bacteria, fungi, insects, extreme weather etc. Therefore breaking cellulose to fermentable sugars is the primary challenge for the researchers in this area. In any bio process to make ethanol, one has to make easily fermentable sugars as the critical step. Cellulosic biomass also contains sugars but…

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Next Generation Biofuels

Environmental Engineering Engenharia do Ambiente

May 18 (Reuters) – After a decade of promise, advanced biofuels makers are entering a crucial make-or-break period with the first of a new generation of production facilities about to come on line.

The new facilities are designed to take biofuels beyond corn-based ethanol and begin to shift the industry to “advanced” fuels made with a lower carbon footprint derived from products that will not compete with demand for food.

Many of the companies are turning to cellulosic plant materials, animal waste and plant oils to churn out millions of gallons of ethanol, diesel, jet fuel or components for gasoline.

Driving the industry are U.S. government targets stretching out a decade that call for fuel suppliers to blend billions of gallons of the new biofuels into the U.S. gasoline and diesel pools, on top of the corn ethanol that already makes up about 10 percent of the gasoline market.

The…

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Syngas as Feedstock for Biofuels

An attractive approach to converting biomass into liquid or gaseous fuels is direct gasification, followed by conversion of the gas to final fuel. NKGE98YUDMEC Ethanol can be produced this way, but other fuels can be produced more easily and potentially at lower cost, though none of the approaches is currently inexpensive. The choice of which process to use is influenced by the fact that lignin cannot easily be converted into a gas through biochemical conversion. Lignin can, however, be gasified through a heat process. The lignin components of plants can range from near 0% to 35%. For those plants at the lower end of this range, the chemical conversion approach is better suited. For plants that have more lignin, the heat-dominated approach is more effective. Once the gasification of biomass is complete, the resulting gases can be used in a variety of ways to produce liquid fuels discussed, in brief, below

Fischer-Tropsch (F-T) fuels

The Fischer-Tropsch process converts “syngas” (mainly carbon monoxide and hydrogen) into diesel fuel and naphtha (basic gasoline) by building polymer chains out of these basic building blocks. Typically a variety of co-products (various chemicals) are also produced.  Figure 2.1 shows the production of diesel fuel from bio-syngas by Fisher-Tropsch synthesis (FTS).

The Fisher-Tropsch process is an established technology and has been proven on a large scale but adoption has been limited by high capital and O&M costs. According to Choren Industries, a German based developer of the technology, it takes 5 tons of biomass to produce 1 ton of biodiesel, and 1 hectare generates 4 tons of biodiesel.

Methanol

Syngas can also be converted into methanol through dehydration or other techniques, and in fact methanol is an intermediate product of the F-T process (and is therefore cheaper to produce than F-T gasoline and diesel). Methanol is somewhat out of favour as a transportation fuel due to its relatively low energy content and high toxicity, but might be a preferred fuel if fuel cell vehicles are developed with on-board reforming of hydrogen.

Dimethyl ether

DME also can be produced from syngas, in a manner similar to methanol. It is a promising fuel for diesel engines, due to its good combustion and emissions properties. However, like LPG, it requires special fuel handling and storage equipment and some modifications of diesel engines, and is still at an experimental phase. If diesel vehicles were designed and produced to run on DME, they would become inherently very low pollutant emitting vehicles; with DME produced from biomass, they would also become very low GHG vehicles.

Rationale for Decentralized Production of Biogas and Bioethanol

Clean Energy Diary

We live in a technological world where fuel and power play a critical role in shaping our lives and building our nations. The growth of a nation is measured in terms of fuel and power usage; yet there are many challenges and uncertainties in fuel supply and power generation technologies in recent past due to environmental implications. Fossil fuels accelerated our industrial growth and the civilization . But diminishing supply of oil and gas, global warming, nuclear disasters, social upheavals in the Arabian countries, financial problems, and high cost of renewable energy have created an uncertainty in the energy supply of the future. The future cost of energy is likely to increase many folds yet nobody knows for certain what will be the costs of energy for the next decade or what will be the fuel for our cars.  Renewable energy sources like solar and wind seem to be…

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Biochemical Conversion of Wastes

Advanced waste-to-energy technologies can be used to produce biogas (methane and carbon dioxide), syngas (hydrogen and carbon monoxide), liquid biofuels (ethanol and biodiesel), or pure hydrogen. The most famous (and most important) biochemical conversion technologies are anaerobic digestion and alcohol fermentation. Anaerobic digestion is a series of chemical reactions during which organic material is decomposed through the metabolic pathways of naturally occurring microorganisms in an oxygen depleted environment. Alcohol fermentation is the transformation of organic fraction of biomass to ethanol by a series of biochemical reactions using specialized microorganisms. It finds good deal of application in the transformation of woody biomass into cellulosic ethanol.

Anaerobic Digestion

Anaerobic digestion is the natural biological process which stabilizes organic waste in the absence of air and transforms it into biofertilizer and biogas. Anaerobic digestion is a reliable technology for the treatment of wet, organic waste.  Organic waste from various sources is biochemically degraded in highly controlled, oxygen-free conditions circumstances resulting in the production of biogas which can be used to produce both electricity and heat. Almost any organic material can be processed with anaerobic digestion. This includes biodegradable waste materials such as municipal solid waste, animal manure, poultry litter, food wastes, sewage and industrial wastes.

An anaerobic digestion plant produces two outputs, biogas and digestate, both can be further processed or utilized to produce secondary outputs. Biogas can be used for producing electricity and heat, as a natural gas substitute and also a transportation fuel. A combined heat and power plant system (CHP) not only generates power but also produces heat for in-house requirements to maintain desired temperature level in the digester during cold season. In Sweden, the compressed biogas is used as a transportation fuel for cars and buses. Biogas can also be upgraded and used in gas supply networks.

Digestate can be further processed to produce liquor and a fibrous material. The fiber, which can be processed into compost, is a bulky material with low levels of nutrients and can be used as a soil conditioner or a low level fertilizer. A high proportion of the nutrients remain in the liquor, which can be used as a liquid fertilizer.

Biofuels Production

A variety of fuels can be produced from waste resources including liquid fuels, such as ethanol, methanol, biodiesel, Fischer-Tropsch diesel, and gaseous fuels, such as hydrogen and methane. The resource base for biofuel production is composed of a wide variety of forestry and agricultural resources, industrial processing residues, and municipal solid and urban wood residues. Globally, biofuels are most commonly used to power vehicles, heat homes, and for cooking.

The largest potential feedstock for ethanol is lignocellulosic biomass wastes, which includes materials such as agricultural residues (corn stover, crop straws and bagasse), herbaceous crops (alfalfa, switchgrass), short rotation woody crops, forestry residues, waste paper and other wastes (municipal and industrial). Bioethanol production from these feedstocks could be an attractive alternative for disposal of these residues. Importantly, lignocellulosic feedstocks do not interfere with food security.

Ethanol from lignocellulosic biomass is produced mainly via biochemical routes. The three major steps involved are pretreatment, enzymatic hydrolysis, and fermentation. Biomass is pretreated to improve the accessibility of enzymes. After pretreatment, biomass undergoes enzymatic hydrolysis for conversion of polysaccharides into monomer sugars, such as glucose and xylose. Subsequently, sugars are fermented to ethanol by the use of different microorganisms.

Future Perspectives for Biofuel Production

ImageFuels produced from biomass provide unique environmental, economic and social benefits and can be considered as a safe and clean liquid fuel alternative to fossil fuels. The biomass resource base is composed of a wide variety of biomass wastes, such as forestry resources, agricultural wastes, industrial processing residues, municipal solid wastes and marine resources.

Significant progress has been made in the past several years in all aspects of cellulosic and lignocellulosic biomass conversion to ethanol. The areas of focus include low-cost thermochemical pretreatment, highly effective enzymes and efficient and robust fermentative microorganisms. Innovation in industrial biotechnology, especially in the development of enzymes and genetically engineered microorganisms, is the key to the success of biofuel programs at commercial scale.  A good deal of research efforts are focused on exploring combinations of thermal, chemical and biological processes to develop the most efficient and economical route for the commercial production of cellulosic ethanol.

A biorefinery takes advantage of the various components in biomass and their intermediates by producing several products, therefore maximizing the value derived from the biomass feedstock. A biorefinery could produce high-value chemicals and transportation fuels, such as biodiesel or bioethanol. At the same time, it can generate electricity and process heat, through CHP technology, for its own use and perhaps enough for sale of electricity to the local utility.

Algae-based technologies could provide a key tool for reducing greenhouse gas emissions from coal-fired power plants and other carbon intensive industrial processes. In addition, algae production has great promise because algae generate higher energy yields and require much less space to grow than conventional feedstocks.

Concept of Biorefinery

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A biorefinery is a facility that integrates biomass conversion processes and equipment to produce fuels, power, and value-added chemicals from biomass. The biorefinery concept is analogous to today’s petroleum refinery, which produces multiple fuels and products from petroleum.By producing several products, a biorefinery takes advantage of the various components in biomass and their intermediates, therefore maximizing the value derived from the biomass feedstock. A biorefinery could, for example, produce one or several low-volume, but high-value, chemical products and a low-value, but high-volume liquid transportation fuel such as biodiesel or bioethanol. At the same time, it can generate electricity and process heat, through CHP technology, for its own use and perhaps enough for sale of electricity to the local utility. The high value products increase profitability, the high-volume fuel helps meet energy needs, and the power production helps to lower energy costs and reduce GHG emissions from traditional power plant facilities.

There are several platforms which can be employed in biorefineries with the major ones being the sugar platform and the thermochemical platform (also known as syngas platform). Sugar platform biorefineries breaks down biomass into different types of component sugars for fermentation or other biological processing into various fuels and chemicals. On the other hand, thermochemical biorefineries transform biomass into synthesis gas (hydrogen and carbon monoxide) or pyrolysis oil.

The thermochemical biomass conversion process is complex, and uses components, configurations, and operating conditions that are more typical of petroleum refining. Biomass is converted into syngas, and syngas is converted into an ethanol-rich mixture. However, syngas created from biomass contains contaminants such as tar and sulphur that interfere with the conversion of the syngas into products. These contaminants can be removed by tar-reforming catalysts and catalytic reforming processes. This not only cleans the syngas, it also creates more of it, improving process economics and ultimately cutting the cost of the resulting ethanol.

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Ethanol Production via Biochemical Route

Ethanol from lignocellulosic biomass is produced mainly via biochemical routes. The three major steps involved are pretreatment, enzymatic hydrolysis, and fermentation as shown in Figure. Biomass is pretreated to improve the accessibility of enzymes. After pretreatment, biomass undergoes enzymatic hydrolysis for conversion of polysaccharides into monomer sugars, such as glucose and xylose. Subsequently, sugars are fermented to ethanol by the use of different microorganisms.

Pretreated biomass can directly be converted to ethanol by using the process called simultaneous saccharification and cofermentation (SSCF). Pretreatment is a critical step which enhances the enzymatic hydrolysis of biomass. Basically, it alters the physical and chemical properties of biomass and improves the enzyme access and effectiveness which may also lead to a change in crystallinity and degree of polymerization of cellulose. The internal surface area and pore volume of pretreated biomass are increased which facilitates substantial improvement in accessibility of enzymes. The process also helps in enhancing the rate and yield of monomeric sugars during enzymatic hydrolysis steps.

Pretreatment methods can be broadly classified into four groups – physical, chemical, physio-chemical and biological. Physical pretreatment processes employ the mechanical comminution or irradiation processes to change only the physical characteristics of biomass. The physio-chemical process utilizes steam or steam and gases, like SO2 and CO2. The chemical processes employs acids (H2SO4, HCl, organic acids etc) or alkalis (NaOH, Na2CO3, Ca(OH)2, NH3 etc). The acid treatment typically shows the selectivity towards hydrolyzing the hemicelluloses components, whereas alkalis have better selectivity for the lignin. The fractionation of biomass components after such processes help in improving the enzymes accessibility which is also important to the efficient utilization of enzymes.

The pretreated biomass is subjected to enzymatic hydrolysis using cellulase enzymes to convert the cellulose to fermentable sugars. Cellulase refers to a class of enzymes produced chiefly by fungi and bacteria which catalyzes the hydrolysis of cellulose by attacking the glycosidic linkages. Cellulase is mixture of mainly three different functional protein groups: exo-glucanase (Exo-G), endo-glucanase(Endo-G) and β-glucosidase (β-G). The functional proteins work synergistically in hydrolyzing the cellulose into the glucose. These sugars are further fermented using microorganism and are converted to ethanol. The microorganisms are selected based on their efficiency for ethanol productivity and higher product and inhibitors tolerance. Yeast Saccharomyces cerevisiae is used commercially to produce the ethanol from starch and sucrose.

Escherichia coli strain has also been developed recently for ethanol production by the first successful application of metabolic engineering. E. coli can consume variety of sugars and does not require the complex growth media but has very narrow operable range of pH. E. coli has higher optimal temperature than other known strains of bacteria.

The major cost components in bioethanol production from lignocellulosic biomass are the pretreatment and the enzymatic hydrolysis steps. In fact, these two process are someway interrelated too where an efficient pretreatment strategy can save substantial enzyme consumption. Pretreatment step can also affect the cost of other operations such as size reduction prior to pretreatment. Therefore, optimization of these two important steps, which collectively contributes about 70% of the total processing cost, are the major challenges in the commercialization of bioethanol from 2nd generation feedstock.

Enzyme cost is the prime concern in full scale commercialization. The trend in enzyme cost is encouraging because of enormous research focus in this area and the cost is expected to go downward in future, which will make bioethanol an attractive option considering the benefits derived its lower greenhouse gas emissions and the empowerment of rural economy.

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Biomass Resources from Sugar Industry

Venezuelan sugar cane (Saccharum) harvested fo...
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Sugarcane is one of the most promising agricultural sources of biomass energy in the world. It is the most appropriate agricultural energy crop in most Cane producing countries due to its resistance to cyclonic winds, drought, pests and diseases, and its geographically widespread cultivation. Due to its high energy-to-volume ratio, it is considered one of nature’s most effective storage devices for solar energy and the most economically significant energy crop. The climatic and physiological factors that limit its cultivation to tropical and sub-tropical regions have resulted in its concentration in developing countries, and this, in turn, gives these countries a particular role in the world’s transition to sustainable use of natural resources.

 According to the International Sugar Organization (ISO), Sugarcane is a highly efficient converter of solar energy, and has the highest energy-to-volume ratio among energy crops. Indeed, it gives the highest annual yield of biomass of all species. Roughly, 1 ton of Sugarcane biomass-based on Bagasse, foliage and ethanol output – has an energy content equivalent to one barrel of crude oil.   Sugarcane produces mainly two types of biomass, Cane Trash and Bagasse. Cane Trash is the field residue remaining after harvesting the Cane stalk and Bagasse is the milling by-product which remains after extracting the Sugar from the stalk. The potential energy value of these residues has traditionally been ignored by policy-makers and masses in developing countries. However, with rising fossil fuel prices and dwindling firewood supplies, this material is increasingly viewed as a valuable Renewable Energy resource.

Sugar mills have been using Bagasse to generate steam and electricity for internal plant requirements while Cane Trash remains underutilized to a great extent. Cane Trash and Bagasse are produced during the harvesting and milling process of Sugar Cane which normally lasts 6 to 7 months.

Around the world, a portion of the Cane Trash is collected for sale to feed mills, while freshly cut green tops are sometimes collected for farm animals. In most cases, however, the residues are burned or left in the fields to decompose. Cane Trash, consisting of Sugarcane tops and leaves can potentially be converted into around 1kWh/kg, but is mostly burned in the field due to its bulkiness and its related high cost for collection/transportation.

 On the other hand, Bagasse has been traditionally used as a fuel in the Sugar mill itself, to produce steam for the process and electricity for its own use. In general, for every ton of Sugarcane processed in the mill, around 190 kg Bagasse is produced. Low pressure boilers and low efficiency steam turbines are commonly used in developing countries. It would be a good business proposition to upgrade the present cogeneration systems to highly efficient, high pressure systems with higher capacities to ensure utilization of surplus Bagasse.

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What is Lignocellulosic Biomass?

Farmer plowing in Fahrenwalde, Mecklenburg-Vor...
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First-generation biofuels (produced primarily from food crops such as grains, sugar beet and oil seeds) are limited in their ability to achieve targets for oil-product substitution, climate change mitigation, and economic growth. Their sustainable production is under scanner, as is the possibility of creating undue competition for land and water used for food and fibre production.

The cumulative impacts of these concerns have increased the interest in developing biofuels produced from non-food biomass. Feedstocks from ligno-cellulosic materials include cereal straw, bagasse, forest residues, and purpose-grown energy crops such as vegetative grasses and short rotation forests. These second-generation biofuels could avoid many of the concerns facing first-generation biofuels and potentially offer greater cost reduction potential in the longer term.

The largest potential feedstock for ethanol is lignocellulosic biomass, which includes materials such as agricultural residues (corn stover, crop straws and bagasse), herbaceous crops (alfalfa, switchgrass), short rotation woody crops, forestry residues, waste paper and other wastes (municipal and industrial). Bioethanol production from these feedstocks could be an attractive alternative for disposal of these residues. Importantlylignocellulosic feedstocks do not interfere with food security. Moreover, bioethanol is very important for both rural and urban areas in terms of energy security reason, environmental concern, employment opportunities, agricultural development, foreign exchange saving, socioeconomic issues etc.

Economically, lignocellulosic biomass has an advantage over other agriculturally important biofuels feedstocks such as corn starch, soybeans, and sugar cane, because it can be produced quickly and at significantly lower cost than food crops. Lignocellulosic biomass is an important component of the major food crops; it is the non-edible portion of the plant, which is currently underutilized, but could be used for biofuel production. In short, lignocellulosic biomass holds the key to supplying society’s basic needs for sustainable production of liquid transportation fuels without impacting the nation’s food supply.

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