Cellulosic ethanol research papers

In future, there will be plentiful industrial scale progress in the subject of lignoethanol where the hard part of a plant cellulose will be converted into fermentable sugars and consequently converted to bioethanol. After microbial fermentation, the produce is subjected to distillation, dehydration and then is condensed for quality improvement and water and other impurities removal. However, due to high cost in the form of energy input, this traditional process is replaced with some energy saving processes molecular sieve mainly to avoid distillation completely for dehydration.

This process involves the use of ethanol vapors under pressure and allows these vapors to pass through molecular sieve beads bed. This will be a very important contribution in future to lessen the burdens on Pakistan economy.

Cellulosic Ethanol Research Papers - lacardetab.tk

The government of Pakistan should make policy to endorse the blending of ethanol in transportation fuels as early as it becomes conceivable [ 18 ]. Besides this, other advantages of ethanol usage are good engine performance and better yields; it burns more efficiently and keeps our environment clean and more easily biodegradable, as well as consistent with the global focus on biofuel. The main factor in ethanol production is the content of lignocellulose present in substrates which will be hydrolyzed by different hydrolyzing agents to provide fermentable glucose [ 37 , 38 ].

The nature-inspired enzymes from wood fungus and termite may be used as an extra bonus in the presence of exiting bioethanol production technologies, which can convert the long chains of polysaccharides into monosaccharaides. Different industries like forestry, pulp and paper, agriculture and food processing including municipal solid waste MSW and animal wastes are major producers of lignocellulosic waste materials [ 39 , 40 ].

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Currently, lignocellulolytic enzymes are derived from fungus, gut of termite and certain bacteria [ 41 ]. Established technology for bioethanol in Pakistan is relatively of low-tech approach to meet some needs by employing molasses and some selective biomass. Such limitations with biomass make the process and yield profit limited.

At the same time, the farmers and agribusinesses cannot access recent technologies that may greatly expand the use of bioethanol to meet the demand for power in many applications. The current energy scenario warrants the demand for research and development of biomass-based biofuel production systems. Biomass, due to its renewable nature and abundance, is becoming an increasingly attractive fuel source.

Syngenta Believes in Cellulosic Ethanol

Lignin, the second most abundant biomass constituting aromatic biopolymer on Earth, is highly recalcitrant to depolymerization. Lignin serves as bonding for hemicellulose and cellulose and creates an obstacle for penetration of any solution or enzyme to lignocellulosic structure which is the major structural component of all plants and can be depolymerized to fermentable sugars. Microbes enhance the conversion of lignin into fermentable sugars but there are some hurdles which need to be removed first.


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Recalcitrant nature of lignin could be tackled through different biocatalysts due to their non-hazardous and eco-friendly nature. Therefore, lignocellulolytic microorganisms like fungi and some bacteria are considered as promising biomass degraders especially for large-scale applications due to their potential yields of extracellular synergistically acting enzymes into the environment. These enzymes can contribute significantly in degradation of lignocellulosic material by converting long chain polysaccharides into their 5- and 6-carbon sugar components [ 42 , 43 ].

Although lignin resists attack by most microorganisms, basidiomycetes, white-rot fungi are able to degrade lignin efficiently [ 44 , 45 ]. Lignocellulolytic enzymes-producing fungi are widespread and include species from the ascomycetes e.

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Trichoderma reesei and basidiomycetes phyla such as white-rot e. Phanerochaete chrysosporium and brown-rot fungi e. Fomitopsis palustris [ 46 , 47 ]. Few basidiomycetes, for example, P. Ethanol fermentation requires high concentration of sugar solutions; therefore, biocatalytic conversion of lignocellulosic material into hydrolysate containing high concentration of sugar will be incentive for decreasing production cost. Therefore, variety of lignocellulytic material wheat straw, rice straw and rice husk could be degraded by basidiomycetes and subject to ethanologenic fermentation for ethanol production cost-effectively.

However, some strains of white-rot fungi have promising potential to degrade lignin by simultaneous attack on lignin, hemicellulose and cellulose, whereas few can selectively work just on lignin. It is pertinent here to note that synergistic biocatalytic ability of white rot fungi would be source of efficient depolymerization method and will be helpful in proving that the heteropolymer lignin represents an untapped resource of renewable aromatic chemicals [ 48 , 49 ].

Production of high concentrated cellulosic ethanol by acetone/water oxidized pretreated beech wood

Lignocellulosic biofuel production is not yet economically competitive with fossil fuels; therefore, to ensure successful utilization of all sugars is important for improving the overall economy especially in terms of maximum theoretical yield. Xylose is one of the most abundant sugars in lignocellulosic hydrolysate. Therefore, over expression of xylose isomerase will facilitate complete utilization of xylose present in hydrolysate which otherwise remains to varying extent in spent culture [ 18 , 50 ]. Repolymerization is observed to occur within few hours after onset of lignin volarization.

For this purpose, organization of most effective microbial sink for immediate utilization of low molecular species for bioethanol production is the most appealing option [ 51 , 52 ]. Preventing repolymerization of low molecular weight lignin species into high molecular weight lignin compounds and ensuring the complete utilization and conversion of available sugars into bioethanol can make the bioprocess cost-effective.

Cellulosic Ethanol on the Cheap

The description in this chapter will lead to development of technologies that can be helpful in efficient depolymerization of lignin and its simultaneous conversion into high-valued microbial-assisted advanced biofuel. The chapter represents need for development of road map for advanced level of biofuel production from waste crop residues.

The enzymes convert the long chains of polysaccharides into monosaccharaides. Currently, lignocellulytic enzymes used for ethanol production from cellulosic biomass are obtained from fungus, gut of termite and certain bacteria [ 40 ]. Present restrictions of enzymatic breakdown of lignocellulose-based biomass are mostly due to concern of enzymatic steadiness and vulnerability to inhibitors or by-products [ 53 , 54 ]. Continuous bioengineering efforts and prospecting should provide novel enzymes with lower susceptibility to inhibitors and relatively higher specific activity [ 55 ].

Few insects such as termites have very efficient approaches to break the lignocellulose-based substrates as potential mean of bioenergy [ 56 ]. In case of lower termites, activity cellulolytic is normally dependent on enzymes produced by endosymbiotic, flagellated protists [ 57 ], while in case of higher termites, their guts contain lignocellulytic enzymes which combine with cellulases secreted by certain endosymbiotic gut bacteria [ 58 , 59 ].

Hence, establishment of large-scale bioethanol production plant by treating waste crop residues with such novel enzyme will enhance the production and can successfully provide support to deteriorating economy of Pakistan Figure 2.

Final Report: Using Waste to Clean Up the Environment: Cellulosic Ethanol, the Future of Fuels

The resulting cleaner environment is another benefit that has monetary values that the government may be financially and ethically interested in. Such multiple positive benefits will attract different interested parties to involve in replication of process, each with resources and benefits to sustain and multiply. Additionally, the greenhouse gas emission will be reduced by burning bioethanol, as the net CO 2 emission is zero because the amount of CO 2 emitted on burning is equal to the amount of it, which is absorbed from the atmosphere by the process of plant photosynthesis which will be used for production of bioethanol [ 60 ].

The government of Pakistan should make policy to enforce the blending of ethanol in transportation fuels as early as it becomes conceivable [ 18 ]. Successful implementation of large-scale waste crop residue-based bioethanol production concept will attract private sector investment and company-farm partnership to accelerate the development and commercialization of new bioenergy solution to improve emerging economies and transform the lives of at least small farmers.

The concept is readily adoptable by different agricultural regions as the essential supply of the feedstock is available in the form of agricultural residues that are sustainable and typically available abundantly and locally. Rise in natural gas price 0. Pakistan being an agricultural country produces wheat, sugarcane and potatoes as one of its biggest crops [ 62 — 64 ].

Consequently, large amounts of wheat straw and sugarcane bagasse are obtained as by waste products. Due to high ambient temperature in most part of the year, poor post-harvest processing and storage of thousands of tons of biomass are wasted each year. In short access of promising process for the initiation of sustainable strategies for waste crop residue-based bioethanol production while consuming starch, cellulosic and lignin loads of effluents of respective origins in the country, bestowed with suitable biomass and temperature optima for successful cultivation of ethanologenic microbes, is expected to provide sustainable supplies of biofuels.

Additionally, more than three billion acres worldwide which are not suitable for agriculture purpose due to dryness could be utilized for growing drought-hardy plants for biofuels production. The only disadvantage of using these crops is that they contain lignocellulose, a hard plant material, that needs more treatment than either corn or sugarcane to be converted into alcohol. Therefore, search for ways to make the overall process more efficient by reusing materials, changing the fermenting agent and searching for better and nature-inspired enzymes will be milestone in this regard.

The process development of nature inspired enzyme-assisted conversion of agricultural and food waste into bioethanol that can be used as clean biofuel is demand of time. Adoption of these new dimensions for bioethanol production will definitely reduce pressure on energy and transportation sector, entire dependence on conventional fuels and can triumph fight against climate change. Lignocellulose is a potential resource for biofuel generation because of its low cost and large-scale availability 2. However, the need for high-dosages of costly commercial cellulases in the saccharification process makes it challenging for cellulose-based biofuels to be economically feasible 3.

Although two leading enzyme companies Genencor and Novozymes have significantly reduced cellulase prices to 15—20 cents per gallon of ethanol produced , these prices are still 5- to fold higher than those of the amylases used for starch-based biofuel production 4. Thus, development of a microorganism that is capable of both producing cellulases and fermenting resultant sugars into biofuels is a promising approach to alleviate the economic burden imposed by the need for commercial enzymes 5.


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Saccharomyces cerevisiae has been reported to have a superior capacity for converting glucose into ethanol 6. Several engineered S. This is due to insufficient production or secretion of CBH 11 , as CBHs are responsible for the degradation of crystalline cellulose and have been considered key forces in disrupting the recalcitrant structure of cellulose Up to now, cellulolytic S.

www.hiphopenation.com/mu-plugins/dept/dating-nestler-slide-rules.php Secretion system, which releases enzymes into extracellular environment, is the most common route of cellulase production in recombinant strains. Although free enzymes can easily penetrate into the secondary cell wall of plant cells 14 , they are incapable of being recycled usage during an industrial process In comparison, a cell-surface display system permits immobilization of enzymes on the cell surface through glycosylphosphatidylinositol GPI anchoring of proteins Immobilization of numerous cellulases on a given microbial cell provides an effective increase of local enzyme concentration; facilitates synergistic interactions among enzymes; and, most importantly, enables re-utilization of enzymes in repeated fermentation, improving the economic feasibility of the process The cellulose degradation mechanisms of free-form cellulases and cellulosomes complexed cellulase system have been studied intensively in the last few decades 14 , 17 , however, few investigations have focused on the mechanisms employed by cell-surface-displayed enzymes non-complexed cellulase system.

Cellulosic ethanol production using cellulase-displaying cells is gaining increased attention 16 , but information on how these cells digest cellulose to fermentable sugars is still unclear. To achieve commercial scale, high bioethanol productivity will need to be obtained from lignocellulosic waste e. Here, we report the successful engineering of a cellulose-adherent S.

The interactions between engineered yeast cells and cellulose were imaged by scanning electron microscopy SEM to demonstrate clearly the dynamic mechanisms of cell-to-cellulose adhesion. This work provided valuable information on how to increase cellulose hydrolysis efficiency by enhancing cell-to-cellulose interactions for various types of substrate, and therefore may lead to a feasible path towards the cost-competitive production of cellulosic ethanol. The relevant features of the recombinant yeast strains used in this study are listed in Supplementary Table 1.

Cellulase enzyme encoding genes were all expressed under the control of the SED1 promoter, which is highly induced during the stationary-phase growth The schemes of engineered cellulolytic yeast strains producing enzymes via cell-surface display or secretion are illustrated in Fig. In the strain expressing cell-surface-displayed proteins, the enzymes were encoded fused to the N-terminus of Sed1, a S.


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