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News and Trends
http://www.ornl.gov/ornlhome/print/press_release_print.cfm?ReleaseNumber=mr20110307-00 Scientists from the University of California, Los Angeles and the Bioenergy Research Center, Oak Ridge National Laboratory (United States) report the direct conversion of cellulose into an advanced biofuel, isobutanol. This is considered to be an important development in the quest for more cost-effective technologies for biofuel production from lignocellulosic biomass. Conventionally, biofuel production from lignocellulosic biomass involves a series of steps which break down the cellulose molecules before they could be further processed by microorganisms to biofuels. Presently, ethanol is the main biofuel produced from lignocellulosic biomass. However, the biofuel of the future is seen to be butanol or isobutanol because their fuel properties are better than ethanol. The new method is seen to significantly reduce the cost of advanced biofuel production from lignocellulosic biomass, because the pretreatment step is made unnecessary. The new direct bacterial conversion process of cellulose to isobutanol involves the use of a bacterium, Clostridium cellulolyticum, which has been ‘metabolically engineered" to divert a metabolic pathway toward isobutanol production. The full results of the study are published in the journal, Applied and Environmental Microbiology (URL above).
(open access journal article during time of access) The role of metabolic engineering and synthetic biology as enabling technologies for the production of alcohol biofuels (i.e. ethanol and butanol) was reviewed by Ramon Gonzalez of Rice University (United States) and colleagues. Advances in synthetic biology, metabolic engineering, and systems biology have resulted in the harnessing of biofuel-producing microorganisms for new pathways of redirecting carbon metabolism into desired products. Some of the new pathways that were reviewed are: (1) expression of pentose catabolic pathways in conventional ethanol-fermenting strains of Saccharomyces cerevisiae and Zymomonas mobilis (wild strains do not usually have the capability to metabolize pentoses, only hexoses) ,(2) conversion of sugars from lignocellulosic biomass to butanol (butanol is considered an ‘advanced biofuel" with better fuel properties than ethanol), (3) sugar conversion to advanced biofuel (particularly those that are similar to gasoline hydrocarbons). (4) efficient co-metabolism of sugar mixtures (i.e. simultaneous, not sequential utilization of sugar mixtures in saccharified/pretreated biomass), and (5) conversion of glycerol-rich feedstocks to biofuels (glycerol is a by-product in biodiesel production). In the review, the authors found "recurring themes" related to (1) strategies for heterologous gene expression, (2) evolutionary selection, and (3) "reverse" metabolic engineering. Advances in the "-omics" sciences have also increased new knowledge "by probing cellular changes associated with new phenotypes and driving the construction of efficient microorganisms for biofuels production." The full review is published in the journal, Microbial Cell Factories (URL above). Biofuels Processing
(full access to journal article may require subscription or payment) A team of Japanese and Korean researchers investigated the low temperature alkali (LTA) pretreatment of sweet sorghum bagasse. Pretreatment is the first step in the production of cellulose from lignocellulosic biomass, where the lignin fraction of the biomass is removed to expose the carbohydrate (cellulose, hemicellulose) fraction. The carbohydrate fraction is then converted to simple sugars for ethanol fermentation. Bagasse from "brown midrib (BMR) mutants" of sweet sorghum was used; this variety is reported to have reduced lignin and high fiber digestibility as silage. Compared to high temperature pretreatment processes, low temperature alkali pretreatment reportedly consumes less energy and improves cellulose-to-ethanol conversion ratio. The LTA conditions tested were: (1) sodium hydroxide concentrations from 0.5 M to 5M, (2) solid to liquid ratios of 5%, 10% and 15%, (3) temperatures of 25oC and 50oC, and (4) pretreatment times of 0.5 hours to 24 hours. Results showed that "the pretreated bagasse exhibited greatly improved enzymatic digestibility, with 24-hour glucan saccharification yields of about 98% (using commercially available cellulose and b-glucosidase). The disruption of the lignin-carbohydrate matrix of the sweet sorghum bagasse was thought to be a factor in digestibility improvement. The BMR (i.e. low-lignin) mutants were also shown to be more susceptible to pretreatment compared to the non-BMR mutants. The full results are published in the journal, Bioresource Technology (URL above).
(full access to journal article may require subscription or payment) Pyrolysis is a thermochemical process for conversion of biomass to biofuels. The biomass is usually heated at high temperatures in the absence of air. Depending on operating conditions, the products are either a gaseous fuel, a liquid mixture of hydrocarbons, a solid fuel, or combinations of the three. In many biomass pyrolysis processes, liquid biofuels are often the target. In microwave-assisted pyrolysis, heating is supplied by microwave technology, and this is reported to have the following advantages: "Uniform internal heating of large biomass particles, ease of control, and less ash in the bio-oil (due to elimination of fluidization/agitation)." Although many studies have been made on the pyrolysis of many types of lignocellulosic biomass for liquid biofuels, little has been done so far on microalgae. Scientists from the University of Minnesota (United States, Nanchang University (China) and Fuzhou University (China) investigated the production of "bio-oil" from the microwave-assisted pyrolysis of the microalgae, Chlorella sp. With a microwave power of 750 watts, they were able to obtain a maximum bio-oil yield of 28.6%. Based on certain physic-chemical properties, the microalgal bio-oil exhibited better quality compared to lignocellulosic bio-oil. About 22.18% of the oil were identified as "aliphatic hydrocarbons, aromatic hydrocarbons, phenols, long chain fatty acids and nitrogenated compounds, among which aliphatic and aromatic hydrocarbons. The full results are published in the journal, Bioresource Technology (URL above).
(open access journal article during time of access) Scientists from the University of Florence and ENEA (Laboratory of Technology and Equipment for Bioenergy) (Italy) investigated the use of torrefaction as a pretreatment method of olive pruning debris (lignocellulosic biomass) for bioethanol production. Torrefaction is a process of heating the biomass in an oxygen-free environment between 200oC and 300oC. It is sometimes called, "mild pyrolysis", "wood cooking" or "roasting". The experiments showed that torrefaction can yield materials "which can be enzymatically hydrolyzed and fermented into ethanol with yields comparable to raw biomass." Within the range of experimental conditions studied, the best conditions were identified at 220°C, with treatment time of 60 min. However further studies are recommended. Treatment conditions need to be determined in order to minimize loss of pentose sugars and minimize formation of products which inhibit ethanol production, The full results are published in the journal, Biomass Conversion and Refinery (URL above). Related information on torrefaction: http://newenergyandfuel.com/http:/newenergyandfuel/com/2008/11/19/torrefaction-%E2%80%93-a-new-process-in-biomass-and-biofuels/ http://news.mongabay.com/bioenergy/2008/07/torrefaction-gives-biomass-20-energy.html
(open access journal article) An international scientific research team from the United States and China (Michigan State University, Lucigen Corporation, and JiLin Rorgoo Renewable Energy Development Company) report the successful use of auxiliary hemicellulase enzymes with core cellulose enzymes to increase sugar yields in the saccharification of AFEX (Ammonia Fiber Explosion) pretreated corn stover. Hemicellulases are enzymes which catalyze the conversion (sometimes called "saccharification") of hemicelluloses in plant biomass, into their component 5-carbon sugars (or pentoses). Cellulases, on the other hand, catalyze the saccharification of celluloses into their component 6-carbon sugars (hexoses). Both sugars are subsequently fermented to ethanol. According to the researchers, AFEX- pretreatment of lignocellulosic plant biomass "cleaves lignin-carbohydrate complexes without physically extracting hemicellulose or lignin into separate process streams; hence, efficient hydrolysis of AFEX treated biomass to achieve both high glucose and xylose yields requires supplementing the cellulases with hemicellulases and other accessory enzymes." Results showed that supplementing 'core fungal cellulases' with auxiliary hemicellulase enzymes in the 'enzyme cocktail' synergistically improved the saccharification of AFEX pretreated corn. Higher glucose and xylose yields (80% and 70%, respectively) were obtained at moderate enzyme loadings, when compared to commercially available enzymes. The full results of the study are published in the open-access journal, Biotechnology for Biofuels. Biofuels Policy and Economics
(full access to journal article may require subscription or payment) Researchers from Utrecht University (Netherlands) and United Nations Agencies (UNIDO, UNCTAD) obtained an overview of 'market actors' currently perceived as major opportunities and barriers for the current (and future) development of international bioenergy trade. The overview was made for three biofuel commodities: bioethanol, biodiesel and wood pellets. In their review, the researchers mention that international trade of certain biofuel commodities have grown in recent years, but some barriers have hampered this growth. They cite examples for the case of palm oil (biodiesel feedstock) exports from Southeast Asia and biodiesel production in Western Europe which have received criticism from some sectors. Using an internet-based stakeholder input survey, they sought to identify and analyze these opportunities and barriers. Majority of the respondents were reported to have an "industrial backround", and more than half were from Western Europe. Among the highlights of the study results are: (1) import tariffs and the implementation of sustainability certification systems are perceived as (potentially) major barriers for the trade of bioethanol and biodiesel, (2) logistics are seen as the main obstacle in the trade of wood pellets, (3) development of technical standards was seen more as an opportunity rather than a barrier for all commodities, (4) high fossil fuel prices and climate change mitigation policies are seen as "most important drivers", (5) specific actions will be required by market parties and policy makers in order to overcome some of the barriers. The complete review is published in the journal, Energy Policy (URL above). |
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