Highest Ethanol Yield Research Articles

Rational promoter elements and evolutionary engineering approaches for efficient xylose fermentation in Saccharomyces cerevisiae

We screened and identified a set of efficient promoters in Saccharomyces cerevisiae that maintained their relatively strong strengths to regulate the heterologous xylose-assimilating pathway genes XYL1 and XYL2, and native XKS1 and pentose phosphate pathway four genes, irrespective of glucose or xylose fermentation medium. In this study, we developed a rapid and efficient xylose-fermenting S. cerevisiae strain 7-1 based on balanced pathway expression levels driven by our proposed strong promoters. Next, 7-1 was used to initialize the evolutionary engineering, through first aerobic and anaerobic sequential batch cultivation. The finally evolved strain of 7-1E1 displayed a high ethanol yield (0.45 g/g) and low xylitol accumulation (0.13 g/g). Moreover, the evolved strain of 7-1E1 displays great potential for ethanol production from lignocellulosic biomass. This work reveals that efficient xylose assimilation is attributed to the elevated expression levels of xylose utilization genes, which was accomplished through the strong promoter rational regulation in the chromosome of the evolved strain.

ANÁLISE ESTATÍSTICA PARAMÉTRICA DE FATORES DE OPERAÇÃO NO PROCESSO DE FERMENTAÇÃO PARA OBTENÇÃO DE CACHAÇA

Brazilian sugar cane spirit (cachaça) production is traditional among rural producers in Santo Antônio da Patrulha-RS-Brazil. In this work, in similar conditions used by the producers, the effect of different °Brix and nutrients concentration on sugar cane juice fermentation time and ethanol yield was tested. Sixteen experiments were executed, predicted in a statistical planning, in order to identify the effect of eight factors. The results indicate that the increase on manganese sulfate concentration and cornmeal amount, and also the zinc sulfate concentration increase in interaction effect with higher °Brix, cause increase in fermentation time. It was also observed that the ethanol yield was higher at lower °Brix and at higher triple superphosphate amount in interaction effect with higher °Brix. Ammonium sulfate and copper sulfate concentrations, and also rice bran amount had no significant influence on the process. The best parameters determined, at local conditions, to obtain the lowest fermentation time and higher ethanol yield are the following: 14°Brix, triple superphosphate 0.5 g/L, zinc sulfate 0.5 g/L, manganese sulfate 0.2 g/L, cornmeal 5 g/L. It is also indicated the maintenance of ammonium sulfate 0.5 g/L and rice bran 5 g/L.

Simultaneous Saccharification and Fermentation of Low Strength Sodium Hydroxide Pre-treated Rice Straw for Higher Ethanol Yields: Batch and Fed Batch Hybrid Approach

Low strength sodium hydroxide pre-treated rice straw was hydrolysed at two different solid loadings i.e. 10 and 15 % (w/v) with in-house cellulases (IC) produced by Aspergillus terreus along with commercial cellulases (CC) by using batch and fed batch hybrid simultaneous saccharification and fermentation process. Optimization of process parameters enhanced the crude cellulase activities i.e. filter paper, β-glucosidase and endoglucanase by 1.6, 2.7 and 2.2 fold in 6 days as compared to activities obtained on a single substrate i.e. rice straw. Out of four fed batch approaches, approach III (A-III) at 10 % solid loading yielded higher ethanol concentrations of 30.55 and 28.66 g L−1 by using thermo tolerant in-house yeast strain Kluyveromyces marxianus at 42 °C. Combination of 9 FPU g−1 substrate and CC plus 30 CBU of commercial β-glucosidase (Cβ) yielded slightly higher theoretical ethanol yields of 92.24 % as compared to 86.54 % obtained from IC+Cβ. Dunnett’s Post Hoc Annova test also proved that CC+Cβ were found to be significant in batch as well fed batch experiments as compared to other combinations tried. Thus, fed batch A-III seems to be an optimistic one to overcome the problems associated with batch mode to achieve higher ethanol yields.

Analysis of ethanol fermentation mechanism of ethanol producing white-rot fungus Phlebia sp. MG-60 by RNA-seq.

BackgroundThe white-rot fungus Phlebia sp. MG-60 shows valuable properties such as high ethanol yield from several lignocellulosic materials, although white-rot fungi commonly degrade woody components to CO2 and H2O. In order to identify genes involved in ethanol production by Phlebia sp. MG-60, we compared genes differentially expressed by the ethanol producing fungus Phlebia sp. MG-60 and the model white-rot fungus Phanerochaete chrysosporium under ethanol fermenting and non-fermenting conditions using next-generation sequencing technologies.ResultsmRNAs from mycelia of Phlebia sp. MG-60 and P. chrysosporium under fermenting and non-fermenting conditions were sequenced using the MiSeq system. To detect differentially expressed genes, expression levels were measured in fragments per kilobase of exon per million mapped reads (FPKM). Differentially expressed genes were annotated using BLAST searches, Gene Ontology classifications, and KEGG pathway analysis. Functional analyses of differentially expressed genes revealed that genes involved in glucose uptake, glycolysis, and ethanol synthesis were widely upregulated in Phlebia sp. MG-60 under fermenting conditions.ConclusionsIn this study, we provided novel transcriptomic information on Phlebia sp. MG-60, and these RNA-seq data were useful in targeting genes involved in ethanol production for future genetic engineering.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2977-7) contains supplementary material, which is available to authorized users.

Production of second generation ethanol using Eucalyptus dunnii bark residues and ionic liquid pretreatment

The production of ethanol using Eucalyptus dunnii bark pretreated with 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) as ionic liquid (IL) was studied. In the present work high ethanol yields were obtained using the minimal quantity of IL necessary for wetting but not dissolving the lignocellulosic material. The best result obtained was 70% of ethanol yield using an IL:bark ratio of 5:1, with separate hydrolysis and fermentation (SHF) process, and a cellulase load of 50 FPU/gram of pretreated material.

Alkaline Pretreatment of Sweet Sorghum Bagasse for Bioethanol Production

Lignocellulosic material, which consist mainly of cellulose, hemicelluloses and lignin, are among the most promising renewable feedstocks for the production of energy and chemicals. The bagasse residue of sweet sorghum can be utilized as raw material for alternative energy such as bioethanol. Bioethanol production consists of pretreatment, saccharification, fermentation and purification process. The pretreatment process was of great importance to ethanol yield. In the present study, alkaline pretreatment was conducted using a steam explosion reactor at 1300C with concentrations of NaOH 6, and 10% (kg/L) for 10, and 30 min. For ethanol production separated hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) process were conducted with 30 FPU of Ctec2 and Htec2 enzyme and yeast of Saccharomyces cerevisiae. The results showed that maximum cellulose conversion to total glucose plus xylose were showed greatest with NaOH 10% for 30 min. The highest yield of ethanol is 96.26% and high concentration of ethanol 66.88 g/L were obtained at SSF condition during 48 h process. Using SSF process could increase yields and concentration of ethanol with less energy process. Article History: Received January 16th 2016; Received in revised form May 25th 2016; Accepted June 28th 2016; Available onlineHow to Cite This Article: Sudiyani, Y., Triwahyuni, E., Muryanto, Burhani, D., Waluyo, J. Sulaswaty, A. and Abimanyu, H. (2016) Alkaline Pretreatment of Sweet Sorghum Bagasse for Bioethanol Production. Int. Journal of Renewable Energy Development, 5(2), 113-118.http://dx.doi.org/10.14710/ijred.5.2.113-118

In situ detoxification of dry dilute acid pretreated corn stover by co-culture of xylose-utilizing and inhibitor-tolerant Saccharomyces cerevisiae increases ethanol production

Co-culture of xylose-utilizing and inhibitor-tolerant Saccharomyces cerevisiae was developed for bioethanol production from undetoxified pretreated biomass in simultaneously saccharification and co-fermentation (SSCF) process. Glucose accumulation during late fermentation phase in SSCF using xylose-utilizing strain can be eliminated by the introduction of inhibitor-tolerant strain. Effect of different ratios of two strains was investigated and xylose-utilizing strain to inhibitor-tolerant strain ratio of 10:1 (w/w) showed the best xylose consumption and the highest ethanol yield. Inoculating of xylose-utilizing strain at the later stage of SSCF (24–48h) exhibited lower ethanol yield than inoculating at early stage (the beginning 0–12h), probably due to the reduced enzymatic efficiency caused by the unconsumed xylose and oligomeric sugars. Co-culture SSCF increased ethanol concentration by 21.2% and 41.0% comparing to SSCF using individual inhibitor-tolerant and xylose-utilizing strain (increased from 48.5 and 41.7g/L to 58.8g/L), respectively, which suggest this co-culture system was very promising.

Synthesis of 2,3,4,5-tetrasubstituted pyrroles and 1,4-dihydro-tetraarylpyrazines using acidic alumina as a heterogeneous catalyst

Some new 2,3,4,5-tetrasubstituted pyrroles were synthesized via three-component condensation reaction of benzoin derivatives, 1,3-dicarbonyl compounds, and ammonium acetate using acidic Al2O3 as an efficient and reusable heterogeneous catalyst in refluxing ethanol in high yields. Also, acidic alumina was catalyzed 1,4-dihydro-tetraarylpyrazines by the condensation reaction of benzoins and ammonium acetate in refluxing ethanol in high yields. Alumina showed much the same efficiency when used in consecutive reaction runs. Acidic alumina was used as heterogeneous acidic catalyst for the synthesis of tetrasubstituted pyrroles in refluxing ethanol. The catalyst could be recycled for several times.

Candida shehatae and Saccharomyces cerevisiae work synergistically to improve ethanol fermentation from sugarcane bagasse and rice straw hydrolysate in immobilized cell bioreactor

Sugarcane bagasse (SCB) and rice straw (RS), abundant lignocellulosic agro‐industrial residues in South‐East Asia, are potent feedstocks for bioethanol production as they contain significant amount of glucose and xylose monomers after fractionation and subsequent enzymatic hydrolysis. To simultaneously convert glucose and xylose to ethanol, it requires co‐cultivation of Saccharomyces cerevisiae and Candida shehatae which are hexose and pentose‐fermenting yeasts, respectively. Xylose‐fermenting strain grows slower than glucose‐fermenting one, therefore low efficiency of xylose‐to‐ethanol conversion was found. To enhance the efficiency of ethanol fermentation, the present work proposed to improve xylose assimilation by using co‐immobilization of two strains in a packed bed bioreactor and to increase oxygenation of the medium by applying a recycled batch system when the recycle stream was intervened by a mixing system in a naturally aerated vessel. Initially, conversion of glucose and xylose to ethanol using pure culture was investigated. Subsequently, influence of different immobilization techniques was investigated. Cells entrapment in Ca‐alginate beads provided considerably high ethanol yield over cells immobilized on delignified cellulose, and thus it was selected to use as inoculum in an immobilized cell bioreactor (ICB). The results showed that continuous ethanol production yielded 0.38 and 0.40 g/g corresponding to 74.5% and 78.4% theoretical yields from SCB and RS hydrolysate, respectively. However, recycled batch system produced significantly improved ethanol yield to 0.49 g/g and 0.50 g/g corresponding to 96.1% and 98.0% theoretical yields for SCB and RS hydrolysate, respectively. In this study, higher ethanol concentration and less unfermented sugar concentration was successfully achieved in the ICB with recycled batch system when using SCB and RS hydrolysate as the substrate.

Ammonium acetate as a catalyst and/or reactant in the reaction of dimedone, aromatic aldehyde, and malononitrile: synthesis of tetrahydrobenzo[b]pyrans and hexahydroquinolines

The reaction of aromatic aldehydes, dimedone, and malononitrile in the presence of ammonium acetate has afforded tetrahydrobenzo[b]pyrans instead of polyhydroquinolines under both grinding and reflux conditions; thus ammonium acetate acts as a catalyst for this transformation instead of a reactant. Polyhydroquinoline derivatives were also synthesized via a one-pot condensation of aromatic aldehydes, malononitrile and an enaminone, which was prepared by the reaction of dimedone and ammonium acetate, in refluxing ethanol in high yields.

Biorefinery lignosulfonates as a dispersant for coal water slurry

Valorization of lignin from biofuel production is the key to developing biorefinery technologies for sustainable and economic utilization of lignocellulosic biomass. Here we present isolating lignosulfonate from the spent liquors of Sulfite Pretreatment to Overcome the Recalcitrance of Lignocelluloses (SPORL)-pretreated lodgepole pine and Douglas-fir forest residue as a dispersant for coal water slurry. The two SPORL pretreatments were conducted at a pilot scale and resulted in very high ethanol yield from the pretreated biomass. Therefore, demonstrating the commercial utility of these lignosulfonates has practical significance. The two isolated biorefinery lignosulfonates (LSs), Na-LS and Ca-LS, both had a molecular weight of approximately 9000 Da. Fundamental lignin properties such as chemical structure, functional groups were analyzed. The two LSs showed slightly better to equal performance in modifying CWS rheology than a commercial dispersant naphthalene sulfonate formaldehyde condensate (FDN), despite they were less sulfonated than FDN. The practical importance of this study is that the pilot-scale pretreatments that produced the two LSs also produced excellent bioethanol yields at high titer without detoxification and washing. This suggests SPORL pretreatment is a promising technology for economic bioconversion of under-utilized woody biomass.

Simultaneous achievement of high ethanol yield and titer in Clostridium thermocellum.

BackgroundBiofuel production from plant cell walls offers the potential for sustainable and economically attractive alternatives to petroleum-based products. Fuels from cellulosic biomass are particularly promising, but would benefit from lower processing costs. Clostridium thermocellum can rapidly solubilize and ferment cellulosic biomass, making it a promising candidate microorganism for consolidated bioprocessing for biofuel production, but increases in product yield and titer are still needed.ResultsHere, we started with an engineered C. thermocellum strain where the central metabolic pathways to products other than ethanol had been deleted. After two stages of adaptive evolution, an evolved strain was selected with improved yield and titer. On chemically defined medium with crystalline cellulose as substrate, the evolved strain produced 22.4 ± 1.4 g/L ethanol from 60 g/L cellulose. The resulting yield was about 0.39 gETOH/gGluc eq, which is 75 % of the maximum theoretical yield. Genome resequencing, proteomics, and biochemical analysis were used to examine differences between the original and evolved strains.ConclusionsA two step selection method successfully improved the ethanol yield and the titer. This evolved strain has the highest ethanol yield and titer reported to date for C. thermocellum, and is an important step in the development of this microbe for industrial applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0528-8) contains supplementary material, which is available to authorized users.

Ethanol production from a biomass mixture of furfural residues with green liquor-peroxide saccarified cassava liquid.

BackgroundAs the most abundant renewable resources, lignocellulosic materials are ideal candidates as alternative feedstock for bioethanol production. Cassava residues (CR) are byproducts of the cassava starch industry which can be mixed with lignocellulosic materials for ethanol production. The presence of lignin in lignocellulosic substrates can inhibit saccharification by reducing the cellulase activity. Simultaneous saccharification and fermentation (SSF) of furfural residues (FR) pretreated with green liquor and hydrogen peroxide (GL-H2O2) with CR saccharification liquid was investigated. The final ethanol concentration, yield, initial rate, number of live yeast cells, and the dead yeast ratio were compared to evaluate the effectiveness of combining delignificated lignocellulosic substrates and starchy substrates for ethanol production.ResultsOur results indicate that 42.0 % of FR lignin removal was achieved on FR using of 0.06 g H2O2/g-substrate and 9 mL GL/g-substrate at 80 °C. The highest overall ethanol yield was 93.6 % of the theoretical. When the ratio of 0.06 g/g-H2O2-GL-pretreated FR to CR was 5:1, the ethanol concentration was the same with that ratio of untreated FR to CR of 1:1. Using 0.06 g/g-H2O2-GL-pretreated FR with CR at a ratio of 2:1 resulted in 51.9 g/L ethanol concentration. Moreover, FR pretreated with GL-H2O2 decreased the concentration of byproducts in SSF compared with that obtained in the previous study.ConclusionsThe lignin in FR would inhibit enzyme activity and GL-H2O2 is an advantageous pretreatment method to treat FR and high intensity of FR pretreatment increased the final ethanol concentration. The efficiency of ethanol fermentation of was improved when delignification increased. GL-H2O2 is an advantageous pretreatment method to treat FR. As the pretreatment dosage of GL-H2O2 on FR increased, the proportion of lignocellulosic substrates was enhanced in the SSF of the substrate mixture of CR and FR as compared with untreated FR. Moreover, the final ethanol concentration was increased with a high ethanol yield and lower byproduct concentrations.

Anaerobic digestion as a pretreatment to enhance ethanol yield from lignocelluloses

Biogas production process was used as a biological pretreatment for efficient ethanol production. Three types of lignocelluloses, including rice straw, hardwood sycamore, and softwood pine, were pretreated with anaerobic digestion (AD) process. The effects of ultrasonication on AD-treated and untreated lignocelluloses were studied prior to ethanol production by separate hydrolysis and fermentation (SHF). The pretreated and untreated samples were compared using compositional analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. The biological pretreatment significantly reduced the hemicellulose content of samples. Rice straw had the highest conversion of carbohydrate to biogas. Additionally, the highest ethanol yield after SHF of the straw was 69.5% with respect to the theoretical yield. This value was obtained after the pretreatment with AD process followed by 1h ultrasonication at 60°C. As a pretreatment, the application of AD process increased the overall production of biofuels, expressed as gasoline equivalent volume, by 3.6–4.6 fold. The gasoline equivalent volumes were improved from 75, 51 and 29mL for untreated straw, sycamore and pine, respectively, to 260, 204 and 130mL for the pretreated materials. About 35% of these volumes are attributed to methane.

Suitability and availability analysis of tropical forest wood species for ethanol production: a case study in East Kalimantan

Amirta R, Mukhdlor A, Mujiasih D, Septia E, Supriadi, Susanto D. 2016. Suitability and availability analysis of tropical forest wood species for ethanol production: a case study in East Kalimantan. Biodiversitas 17: 544-552. Fifteen species of woody biomass from tropical forest of East Kalimantan, Indonesia and identified as Acacia mangium, Aleurites moluccana, Alstonia scholaris, Anthocephalus cadamba, Artocarpus altilis, Artocarpus elasticus, Cananga odorata, Gmelina arborea, Lagerstroemia speciosa, Leucaena leucocephala, Macaranga gigantea, Macaranga tanarius, Paraserianthes falcataria, Shorea leprosula and Swietenia macrophylla were characterized and studied to find out and discover their potential utilization as suitable feedstocks for biofuel (ethanol) production. Characterization was done by evaluation of lignin, holocellulose and cellulose contents of woody biomass including the yield of reducing sugar (saccharification) after pretreated with alkaline (NaOH) at moderate temperature. Among 15 species of tropical forest wood biomass evaluated, our findings showed that M. gigantea was gave the highest yield of saccharified sugar (42.22%, weight of original wood dry basis) and also yield of theoretical ethanol (± 273 L/ton). We also found growth of M. giganteawas very fast to produce approximately 26,119 kg ha-1 dry biomass within 3 years. In general, the tropical wood biomass such as M. gigantea, A. moluccana, G. arborea, A. cadamba, and P. falcataria are suitable and potentially to be used as feedstocks for ethanol production due to their fast growing ability, availability and attractive chemical composition to produce high saccharified sugar and yield of ethanol.

Nitrogen response of sweet sorghum genotypes during rainy season

Sweet sorghum ( Sorghum bicolor (L.) Moench) is a smart biofuel crop, which can be grown under tropical rainfed conditions without sacrificing food and fodder security. Three sweet sorghum cultivars (viz. ICSA 52 × SPV 1411, CSH 22 SS and ICSV 93046) were grown under six nitrogen levels (0, 30, 60, 90, 120, 150 kg ha -1 ) on Vertisols during two rainy ( kharif ) seasons at ICRISAT, Patancheru, India. The results from two-year trial indicated that out of three sweet sorghum cultivars evaluated, sweet sorghum hybrid CSH 22 SS produced highest green stalk (46.90 t ha -1 ) and ethanol yield (1940 l ha -1 ) compared to other cultivars. The three cultivars responded well to applied N doses up to 150 kg ha -1 , however, application of N beyond 90 kg ha -1 did not result in any significant increase in grain yield and economic returns. Net economic returns of Rs 32,898 ha -1 (US$ 601.21 ha -1 ) were significantly higher with 90 kg N ha -1 application as compared to other levels of fertilization. It is concluded that for obtaining the highest green stalk yield, ethanol yield and thereby maximum economic returns, sweet sorghum cultivar, viz. CSH 22 SS should be fertilized with 90 kg N ha -1 .

Two consecutive step process for ethanol and microbial oil production from sweet sorghum juice

The juice extracted from sweet sorghum stalks has been previously explored to produce ethanol and also to grow oleaginous yeasts and algae with the objective of producing microbial oil. In this paper we propose a different process route in order to produce ethanol and microbial oil in two consecutive fermentation steps. Ethanol is produced first followed by the growth of oleaginous yeast employing the residual carbon and nitrogen left from the first step. Two yeasts were compared for ethanol production. Trichosporon oleaginosus was cultivated for lipid production. The yeast selection for the first step was the most important factor for achieving a high ethanol yield and the effect of inorganic nitrogen addition was not significant. The remaining sugars consisted of a mixture of sucrose and fructose and no residual glucose was detected in any of the runs. In the second step T. oleaginosus DSM 11815 grew in the pooled juices remaining from the first step for 168h and produced biomass with 28% lipid content. Glucose showed the highest uptake rate, sucrose was utilized until low glucose values prevailed, and fructose was slowly metabolized and a substantial amount remained. Although the two step process has flexibility in choosing the proper microorganism for each step, it is necessary to look for a rapid fructose uptake strain for both fermentations.

Fed-batch Saccharomyces cerevisiae fermentation of hydrolysate sugars: A dynamic model-based approach for high yield ethanol production

The efficient fermentation of hydrolyzed sugars from lignocellulosic biomass feedstock to ethanol remains a complex multi-parametric problem. Thus, in the present study, an advanced structured dynamic model for the simulation of the fermentative ethanol production from hydrolysate sugars is developed. The model is combined with a statistical experimental design to determine an optimal operating strategy that maximizes ethanol production and serves for the systematic evaluation of critical process variables. In particular, the effects of various operating conditions and feeding strategies on the dynamic behavior of batch and fed-batch fermentation processes are explored. The deviation from the desired product or the metabolic inhibition of ethanol production are related with the applied environmental conditions and substrate and product inhibition phenomena. The operating strategy, designed with the assistance of the mathematical tools proposed in this study, includes an exponential addition policy of substrate. This strategy is experimentally proved to enhance the final product concentration, raising the ethanol productivity to 2.27 g L−1 h−1 and the ethanol yield to 53.5% of the maximum theoretical value. Moreover, the simulated strategies were in excellent agreement with the experimental results obtained from the real process using low and high glucose initial concentration, under batch and fed-batch conditions, in both flask- and bioreactor-scale cultivations, proving the model's predictive and optimization capabilities. Further improvement of process performance is expected when combining the proposed dynamic model with advanced optimization algorithms to derive the optimal bioprocess operating strategy.

Direct bioconversion of brown algae into ethanol by thermophilic bacterium Defluviitalea phaphyphila.

BackgroundBrown algae are promising feedstocks for biofuel production with inherent advantages of no structural lignin, high growth rate, and no competition for land and fresh water. However, it is difficult for one microorganism to convert all components of brown algae with different oxidoreduction potentials to ethanol. Defluviitalea phaphyphila Alg1 is the first characterized thermophilic bacterium capable of direct utilization of brown algae.ResultsDefluviitalea phaphyphila Alg1 can simultaneously utilize mannitol, glucose, and alginate to produce ethanol, and high ethanol yields of 0.47 g/g-mannitol, 0.44 g/g-glucose, and 0.3 g/g-alginate were obtained. A rational redox balance system under obligate anaerobic condition in fermenting brown algae was revealed in D. phaphyphila Alg1 through genome and redox analysis. The excess reducing equivalents produced from mannitol metabolism were equilibrated by oxidizing forces from alginate assimilation. Furthermore, D. phaphyphila Alg1 can directly utilize unpretreated kelp powder, and 10 g/L of ethanol was accumulated within 72 h with an ethanol yield of 0.25 g/g-kelp. Microscopic observation further demonstrated the deconstruction process of brown algae cell by D. phaphyphila Alg1.ConclusionsThe integrated biomass deconstruction system of D. phaphyphila Alg1, as well as its high ethanol yield, provided us an excellent alternative for brown algae bioconversion at elevated temperature.

N2 explosive decompression pretreatment of biomass for lignocellulosic ethanol production

This paper presents a novel biomass pretreatment method that uses high pressured N2 and temperature to break the hemicellulose and lignin seal around the cellulose macro fibrils in the cell walls of the lignocellulosic biomass in order to open up the biomass structure for more efficient enzymatic hydrolysis. In this method the biomass is exposed to a high pressure using N2 gas, and temperature. Under pressure, cells of the lignocellulosic biomass are filled with a solution saturated with nitrogen. When the pressure is then suddenly released, the feedstock is exposed to an explosive decompression and the dissolved nitrogen is released from the solution. Sudden change in the volume breaks the cell walls and opens the biomass structure resulting in increased surface area of the substrate for enzymatic hydrolysis. No catalysts or chemicals were added in the process thereby, making it economically and environmentally attractive. In this research, a range of different pressures (1–60 bar) and temperatures (25–175 °C) were applied to barley straw to evaluate the efficiency of the pretreatment. The pretreatment was followed by enzymatic hydrolysis and fermentation. Resulting glucose and ethanol concentrations were measured and the yields were considered as an estimate for the most suitable set of pretreatment conditions. The results indicate that the highest glucose yield and hydrolysis efficiency were gained at 150 °C and 10–30 bars. The fermentation efficiency was lower at higher temperatures. Nonetheless, the highest ethanol yield was still gained at the same conditions.