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Potential for large scale ethanol production essay

Cost is an important factor for large scale expansion of bioethanol production. The green gold fuel from lignocellulosic wastes avoids the existing competi- tion of food versus fuel caused by grain based bioethanol production Bjerre et al.

It has been estimated that 442 billion liters of bioethanol can be produced from lignocellulosic biomass and that total crop residues and wasted crops can produce 491 billion liters of bio- ethanol per year, about 16 times higher than the actual world bioethanol production Kim S.

Lignocellulosic materials are renewable, low cost and are abundantly available. It includes crop resi- dues, grasses, sawdust, wood chips, etc. Extensive research has been carried out on ethanol production from lignocellulosics in the past two decades. Hence bioethanol production could be the route to the effective utilization of agricultural wastes. Rice straw, wheat straw, corn straw, and sugarcane bagasse are the major agricultural wastes in terms of quantity of biomass available Kim S. Raw material Current industrial processes for bioethanol production use sugarcane Southern hemisphere or cereal grain Nothern Hemisphere as feedstocks; but they have to compete directly with food sector Wheals et al, 1999.

Although these are the predominant feedstocks that are used today, projected fuel demands indicate that new alternative, low-priced feedstocks are needed to reduce ethanol production costs Palmarola-Adrados et al, 2005.

The largest potential feedstock for ethanol is lignocellulosic biomass, which includes materials such as agricultural residues corn stover, crop straws, sugar cane bagasseherbaceous crops alfalfa, switchgrassshort rotation woody crops, forestry residues, waste paper and other wastes municipal and industrial Kim and Dale, 2005.

Bioethanol production from these feedstocks could be an attractive alternative for disposal of these residues Wymam, 2001. Importantly, lignocellulosic feedstocks do not interfere with potential for large scale ethanol production essay 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.

To avoid conflicts between food use and industrial use of crops, only wasted crops are assumed to be available for producing ethanol. Wasted crops potential for large scale ethanol production essay defined as crops lost during the year at all stages between the farm and households level during handling, storage and transport. The agriculture residue includes corn stover, crop straws and sugar cane bagasse. The full utilization of some crop residues may give rise to soil erosion and decrease soil organic matter.

Most wasted biomass comes from rice, corn, and wheat. The US, Asia and the European Union are leading producers of agricultural by-products, such as straw from rice, corn and cereal crops. Surplus straw offers an ideal feedstock for the manufacture of cellulosic ethanol, presenting no competition to the production of food or animal feed. Nor is any additional land use required to produce bioethanol based on these types of feedstock, as they are automatically created as a by-product during existing production of rice, maize and cereals.

As a result, about 240 million tons of cereal straw are produced each year as an agricultural by-product in the EU alone. Only a small part of this is currently utilized. This means that cellulosic ethanol can play a key role along Europe?? Lignocellulosic feedstocks of different regions worldwide 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. 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.

Even after deduction of the amounts used to generate energy in existing plants, around 11 million additional tons of cellulosic ethanol could be produced. Pretreatment The most important processing challenge in the production of biofuel is pretreatment of the biomass. Lignocellulosic biomass is composed of three main constituents namely hemicellulose, lignin and cellulose.

Pretreatment methods refer to the solubilization and separation of one or more of these components of biomass.

It makes the remaining solid biomass more accessible to further chemical or biological treatment Demirbas, 2005. The lignocellulosic complex is made up of a matrix of cellulose and lignin bound by hemicellulose chains. The pretreatment is done to break the matrix in order to reduce the degree of crystallinity of the cellulose and increase the fraction of amorphous cellulose, the most suitable form for enzymatic attack.

Pretreatment is undertaken to bring about a change in the macroscopic and microscopic size and structure of biomass as well as submicroscopic structure and chemical composition. It makes the lignocellulosic biomass susceptible to quick hydrolysis with increased yields of monomeric sugars Mosier et al, 2005. Physical, chemical, physicochemical and biological treatments are the four fundamental types of pretreatment techniques employed.

In general a combination of these processes is used in the pretreatment step. Physical pretreatment Physical pretreatment can increase the accessible surface area and potential for large scale ethanol production essay of pores, and decrease the crystallinity and degrees of polymerization of cellulose.

Different types of physical processes such as milling e. Milling Milling can be employed to alter the inherent ultrastructure of lignocelluloses and degree of crystallinity, and consequently make it more amenable to cellulase Mais et al, 2002. Milling and size reduction have been applied prior to enzymatic hydrolysis, or even other pretreatment processes with dilute acid, steam or ammonia, on several lignocellulosic waste materials, MSW and activated sludge Muller et al, 2007.

Among the milling processes, colloid mill, fibrillator and dissolver are suitable only for wet materials, e.

The ball mill can be used for either dry or wet materials. Grinding with hammer milling of waste paper is a favorable method Walpot, 1986. Milling can improve susceptibility to enzymatic hydrolysis by reducing the size of the materials, and degree of crystallinity of lignocelluloses Fan et al, 1980which improves enzymatic degradation of these materials toward ethanol or biogas. Irradiation Irradiation by e. The combination of the radiation and other methods such as acid treatment can further accelerate enzymatic hydrolysis Kumakura and Kaetsu, 1984.

Irradiation has enhanced enzymatic degradation of cellulose into glucose.

  1. The two most common types of biofuels in use today are ethanol and biodiesel.
  2. The on-the-site handling of the feedstock raw materials before the enzyme hydrolysis process would help in optimizing the designed enzyme.
  3. The acid pretreatment can operate either under a high temperature and low acid concentration dilute-acid pretreatment or under a low temperature and high acid concentration concentrated-acid pretreatment. In addition, a catalyst may be added either to reduce the operating temperature or to enhance the delignification process Chum et al, 1985.

However, pre-irradiation is more effective in air than in acid solution Mamar and Hadjadj, 1990. Physico-chemical pretreatment Pretreatments that combine both chemical and physical processes are referred to as physico-chemical processes Chandra et al, 2007. Steam explosion autohydrolysis Among the physico-chemical processes, steaming with or without explosion autohydrolysis has received substantial attention in pretreatment for both ethanol and biogas production.

The pretreatment removes most of the hemicellulose, thus improving the enzymatic digestion. In steam explosion, the pressure is suddenly reduced and makes the materials undergo an explosive decompression.

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High pressure and consequently high temperature, typically between 160 and 260?? C, for a few seconds e. The steam explosion process is well documented and was tested in lab-and pilot processes by several research groups and companies. Its energy cost is relatively moderate, and it satisfies all the requirements of the pretreatment process.

The process of steam explosion was demonstrated on a commercial scale at the Masonite plants. Increase in temperature up to a certain level can effectively release hemicellulosic sugars. However, the sugars loss steadily increases by further increasing the temperature, resulting in a decrease in total sugar recovery Ruiz et al, 2008. Special care should be taken in selecting the steam explosion conditions in order to avoid excessive degradation of the physical and chemical properties of the cellulose.

In very harsh conditions, lower enzymatic digestibility of lignocelluloses may also be observed after steam explosion. For instance, generation of condensation substances between the polymers in steam explosion of wheat straw may lead to a more recalcitrant residue Sun et al, 2005. Steam explosion with addition of SO2 Steam pretreatment can be performed with addition of sulfur dioxide SO2while the aim of adding this chemical is to improve recovering both cellulose and hemicellulose fractions.

C, for a period of e. Here the biomass is exposed to liquid ammonia at relatively high temperature e.

Biofuel essay

C for a period of e. The effective parameters in the AFEX process are ammonia loading, temperature, water loading, blowdown pressure, time, and number of treatments Holtzapple et al, 1991. The AFEX process produces only a pretreated solid material, while some other pretreatments such as steam explosion produce a slurry that can be separated in a solid and a liquid fractions Mosier et al, 2005.

The AFEX process can either modify or effectively reduce the lignin fraction of the lignocellulosic materials, while the hemicellulose and cellulose fractions may remain intact. At optimum conditions, AFEX can significantly improve the enzymatic hydrolysis. The optimum conditions for AFEX depend on the lignocellulosic materials. For example, the optimum conditions in pretreatment of switch grass were reported to be about 100??

C, ammonia loading of 1: One of the major advantages of AFEX pretreatment is no formation of some types of inhibitory by-products, which are produced during the other pretreatment methods, such as furans in dilute-acid and steam explosion pretreatment. However, part of phenolic potential for large scale ethanol production essay of lignin and other cell wall extractives may remain on the cellulosic surface.

Therefore, washing with water might be necessary to remove part of these inhibitory components, although increasing the amount of wastewater from the process Chundawat et al, 2007. However, there are some disadvantages in using the AFEX process compared to some other processes. AFEX is more effective on the biomass that contains less lignin, and the AFEX pretreatment does not significantly solubilize hemicellulose compared to other pretreatment processes such as dilute-acid pretreatment.

Furthermore, ammonia must be recycled after the pretreatment to reduce the cost and protect the environment Eggeman and Elander, 2005Sun and Cheng, 2002. CO2 explosion Supercritical carbon dioxide has been considered as an extraction solvent for non-extractive purposes, due to several advantages such as availability at relatively low cost, non-toxicity, non-flammability, easy recovery after extraction, and environmental acceptability Zheng and Tsao, 1996.

Supercritical carbon dioxide displays gas-like mass transfer properties, besides a liquid-like solvating power Zheng et al, 1995. It was shown that in the presence of water, supercritical CO2 can efficiently improve the enzymatic digestibility of aspen hardwood and southern yellow pine softwood Kim and Hong, 2001.

Carbon dioxide molecules should be comparable in size to those of water and ammonia, and should be able to penetrate small pores accessible to water and ammonia molecules. Liquid hot-water pretreatment Cooking of lignocellulosic materials in liquid hot water LHW is one of the hydrothermal pretreatment methods applied for pretreatment of lignocellulosic materials since several decades ago in e.

Water under high pressure can penetrate into the biomass, hydrate cellulose, and remove hemicellulose and part of lignin.

  1. However, high acid concentration e.
  2. Biofuels are transportation fuels such as ethanol and biodiesel that are made from biomass materials. Arguments For And Against Biofuels.
  3. Biofuel June 11, 2018 College essay writing service Question description I will upload the picture of the assignment.
  4. Microwave treatment utilizes thermal and non-thermal effects generated by microwaves in aqueous environments. CO2 explosion Supercritical carbon dioxide has been considered as an extraction solvent for non-extractive purposes, due to several advantages such as availability at relatively low cost, non-toxicity, non-flammability, easy recovery after extraction, and environmental acceptability Zheng and Tsao, 1996.

The major advantages are no addition of chemicals and no requirement of corrosion-resistant materials for hydrolysis reactors in this process. The feedstock size reduction is a highly energy-demanding operation for the huge bulk of materials on a commercial scale; there could be no need for size reduction in LHW pretreatment.

In addition, the process has a much lower need of chemicals for neutralization of the produced hydrolyzate, and produces lower amounts of neutralization residues compared to many processes such as dilute-acid pretreatment.

LHW can enlarge the accessible and susceptible surface area of the cellulose and make it more accessible to hydrolytic enzymes Zeng et al, 2007. Pretreatments with steam and LHW are both hydrothermal pretreatments. Higher pentosan recovery and lower formation of inhibitory components are the main advantages of LHW pretreatment compared to steam explosion.

For instance, treating of de-starched corn fiber with hot water at 160?? At higher temperatures, e. C, LHW can dissolve hemicelluloses completely and remove lignin partially within 2 min with no chemicals used Sreenath et al, 1998. Xylan removal via percolation reactor, or by base addition adjusting the pH during the process, has been suggested to reduce the formation of inhibitors such as furfural and degradation of xylose Laser et al, 2002. The pH, processing temperature, and time should be controlled in order to optimize the enzymatic digestibility by LHW pretreatment.