Dilute Sulfuric Acid Pretreatment Research Articles

Bioethanol production from cotton stalk: A comparative study of various pretreatments

Cotton stalk (CS) is a potential biomass for bioethanol production, but the direct conversion without pretreatment always results in an extremely low yield because of the recalcitrant nature of lignocellulose. In this study, the effects of various methods, i.e. dilute sulfuric acid pretreatment (DSAP), ultrasound-assisted alkali pretreatment (UAAP), and high pressure-assisted alkali pretreatment (HPAP), on chemical composition, physical structure, and subsequent enzymatic hydrolysis and ethanol fermentation for bioethanol production from CS have been explored. It was found that the intact structures of pretreated CS were obviously disrupted. The hemicellulose and lignin of biomass were removed and the crystallinity of cellulose increased after pretreatments. HPAP led to the highest reducing sugar and ethanol yields (271.70mgg−1 and 45.53%, respectively) compared with UAAP and DSAP. HPAP proved to be a potential and effective pretreatment method for ethanol production from CS.

Fermentative production of high titer gluconic and xylonic acids from corn stover feedstock by Gluconobacter oxydans and techno-economic analysis

High titer gluconic acid and xylonic acid were simultaneously fermented by Gluconobacter oxydans DSM 2003 using corn stover feedstock after dry dilute sulfuric acid pretreatment, biodetoxification and high solids content hydrolysis. Maximum sodium gluconate and xylonate were produced at the titer of 132.46g/L and 38.86g/L with the overall yield of 97.12% from glucose and 90.02% from xylose, respectively. The drawbacks of filamentous fungus Aspergillus niger including weak inhibitor tolerance, large pellet formation and no xylose utilization were solved by using the bacterium strain G. oxydans. The obtained sodium gluconate/xylonate product was highly competitive as cement retarder additive to the commercial product from corn feedstock. The techno-economic analysis (TEA) based on the Aspen Plus modeling was performed and the minimum sodium gluconate/xylonate product selling price (MGSP) was calculated as $0.404/kg. This study provided a practical and economic competitive process of lignocellulose utilization for production of value-added biobased chemicals.

Techno-Economic Analysis of Cellulosic Butanol Production from Corn Stover through Acetone–Butanol–Ethanol Fermentation

Biobutanol has fuel properties comparable to those of gasoline; however, its commercial production through acetone–butanol–ethanol (ABE) fermentation from lignocellulosic biomass is still encumbering due to low product yield, energy extensive recovery method, and butanol toxicity to microbes. Recent development of simultaneous saccharification, vacuum fermentation, and recovery technique has the potential to reduce these problems and improve butanol yield, which has gained significant attention as an emerging alternative way for ABE fermentation. Thus, the main objective of this study was to assess the techno-economic feasibility of commercial-scale ABE fermentation for a 113.4 million L/year (30 million gal/year) butanol production and identify operational targets for process improvement. Commercial dilute sulfuric acid pretreatment and corn stover feedstock were used in this study. Experimental data on the pretreatment of corn stover and the ABE fermentation and recovery were gathered from recent public...

Conversion of apple pomace waste to ethanol at industrial relevant conditions.

Apple pomace samples were evaluated for conversion to ethanol at industrial relevant conditions. Biomass degradation efficiency by commercial enzymes was evaluated at 20% solid loading for dilute sulfuric acid, calcium oxide, and autoclave without any chemical (control) apple pomace samples. The control and calcium oxide-pretreated pomace provided similar sugar yields, while dilute sulfuric acid pretreatment resulted in reduced sugar yields. The control and calcium oxide-pretreated pomace hydrolysate were fermented to ethanol using a native Saccharomyces cerevisiae yeast strain, producing 38.8 and 36.9g/L of ethanol, respectively. When control apple pomace sample loading was increased from 20 to 30%, 57.5 and 50.1g/L of glucose and fructose was produced, respectively. Lastly, we found that unhydrolyzed solids (UHS) present during fermentation had little effect on ethanol yield, as 53.6 and 53.8g/L of ethanol were produced with and without UHS, respectively. Overall, ethanol yields were 134g per kg of dry apple pomace. A complete process mass balance for enzyme hydrolysis and ethanol fermentation is provided in this manuscript. These results show that apple pomace is an excellent feedstock for producing ethanol that could be either used as biofuel or as beverage.

Response Surface Optimization of Dilute Sulfuric Acid Pretreatment of Switchgrass (panicum Virgatum L.) for Fermentable Sugars Production

Pretreatment of lignocellulosic materials to disrupt their recalcitrant structures is a crucial step on second generation biofuel production. In this study, response surface methodology (RSM) was used to investigate the effects of dilute sulfuric acid hydrolysis conditions on switchgrass (Panicum virgatum L.). A central composite rotatable design (CCRD) was applied to assess the effect of acid concentration (0.16 – 1.84% (w/w)), solid load (4.9 – 30.1% (w/w)) and hydrolysis time (9.6 – 110.5 min), on glucose, xylose and total sugars (glucose, xylose and arabinose) recovery yields and total inhibitors generated (acetic acid, levulinic acid, 5- hydroxymethylfurfural and furfural) after acid hydrolysis. Afterwards, enzymatic hydrolysis of the solid phase was performed as a second treatment step. Experimental data were fitted to a second order polynomial model to find the optimum acid hydrolysis conditions by multiple regression analysis. The results show a strong dependence of total sugars recovery and total fermentation inhibitors on acid concentration, and a weaker dependence on solid load and acid hydrolysis time. The optimized hydrolysis conditions, predicted by the polynomial model, were 1.72% (w/w) of sulfuric acid concentration and 112.0 min of acid hydrolysis time, for a fixed value of 10.0% (w/w) of solid load, with a total sugars yield of 78.8% for acid hydrolysis combined with a subsequent enzymatic hydrolysis step.

The influence of dilute sulfuric acid pretreatment on biogas production from wheat plant

ABSTRACTDilute sulfuric acid pretreatment was used to improve the biomethane production from wheat plant (WP) via mesophilic anaerobic digestion. The pretreatments were performed at 121°C for different time durations of 10, 30, 60, and 120 min. The maximum methane yield of 302.4 mL/g volatile solids (VS) was obtained after the pretreatment for 120 min, which was 15.5% higher than that of the untreated WP. The highest amounts of lignin removal (15.2%) and xylan degradation (91.5%) were also achieved after this pretreatment. The pretreatment for 60 min enhanced the methane yield by 8.9%, while the pretreatments for 10 and 30 min had no positive effects on the methane yield. All of the pretreatments significantly removed the hemicelluloses. Moreover, the qualitative analysis of the untreated and pretreated WP structure showed significant reduction in the crystallinity index accompanied by the destruction of surface layers of WP structure after pretreatment.

Production of biobutanol from acid-pretreated corncob using Clostridium beijerinckii TISTR 1461: Process optimization studies

ABSTRACTCorncob is a potential feedstock in Thailand that can be used for fermentable sugar production through dilute sulfuric acid pretreatment and enzymatic hydrolysis. To recover high amounts of monomeric sugars from corncob, the sulfuric pretreatment conditions were optimized by using response surface methodology with three independent variables: sulfuric acid concentration, temperature, and time. The highest response of total sugars, 48.84 g/L, was found at 122.78°C, 4.65 min, and 2.82% (v/v) H2SO4. With these conditions, total sugars from the confirmation experiment were 46.29 g/L, with 5.51% error from the predicted value. The hydrolysate was used as a substrate for acetone–butanol–ethanol fermentation to evaluate its potential for microbial growth. The simultaneous saccharification and fermentation (SSF) showed that C. beijerinckii TISTR 1461 can generate acetone–butanol–ethanol products at 11.64 g/L (5.29 g/L acetone, 6.26 g/L butanol, and 0.09 g/L ethanol) instantly using sugars from the hydrolysed corncob with Novozymes 50013 cellulase enzyme without an overliming process.

Effects of fertilizer application and dry/wet processing of Miscanthus x giganteus on bioethanol production

The effects of wet and dry processing of miscanthus on bioethanol production using simultaneous saccharification and fermentation (SSF) process were investigated, with wet samples showing higher ethanol yields than dry samples. Miscanthus grown with no fertilizer, with fertilizer and with swine manure were sampled for analysis. Wet-fractionation was used to separate miscanthus into solid and liquid fractions. Dilute sulfuric acid pretreatment was employed and the SSF process was performed with saccharomyces cerevisiae and a cocktail of enzymes at 35°C. After pretreatment, cellulose compositions of biomass of the wet samples increased from 61.0–67.0% to 77.0–87.0%, which were higher than the compositions of dry samples. The highest theoretical ethanol yield of 88.0% was realized for wet processed pretreated miscanthus, grown with swine manure. Changes to the morphology and chemical composition of the biomass samples after pretreatment, such as crystallinity reduction, were observed using SEM and FTIR. These changes improved ethanol production.

Effect of Drying Method of Corn Stover on Sugar Recovery during Dilute Sulfuric Acid Pretreatment

The effects of drying method on the sugar conversion of corn stover during dilute sulfuric acid pretreatment were studied. Oven-dried corn stover (ODCS) was more sensitive to temperature and time during dilute sulfuric acid pretreatment than air-dried corn stover (ADCS). The yield of the total reducing sugar reached 43.9% when ODCS was pretreated for 50 min at 120°C, which was even higher than the value of the ADCS treated for 90 min. The glucose yield of ODCS was 1.6- to 1.9-fold higher than ADCS. These results indicate that rapidly losing water is a better drying method compared to air drying.

Degradation Profiles of Non-lignin Constituents of Corn Stover from Dilute Sulfuric Acid Pretreatment

Corn stover was separated into four derived streams: ethanol extractives (EE), hot water extractives (HWE), extracted cellulose, and extracted hemicelluloses. They were separately treated with 0.75% dilute sulfuric acid at 180°C for 40 minutes. Over 100 degradation products were separated and identified using gas chromatography-mass spectrometry (GC-MS) and liquid chromatography (LC). These products contained compounds from several chemical classes, including sugars, aromatics, carboxylic acids, furans, alcohols, aldehydes, and cyclenes. Itaconic acid, succinic acid, fumaric acid, azelaic acid, DL-isoborneol, and 3-methyl-2-furoic acid were detected in the dilute sulfuric acid pretreated corn stover for the first time. Potential microbial fermentation inhibitors and valuable chemical building blocks were evaluated. In an effort to identify and develop inhibitors which are useful for controlling and improving the lignocellulosic biorefinery process, how they originated from the corn stover constituents was examined.

Long term storage of dilute acid pretreated corn stover feedstock and ethanol fermentability evaluation

This study reported a new solution of lignocellulose feedstock storage based on the distributed pretreatment concept. The dry dilute sulfuric acid pretreatment (DDAP) was conducted on corn stover feedstock, instead of ammonia fiber explosion pretreatment. Then the dry dilute acid pretreated corn stover was stored for three months during summer season with high temperature and humidity. No negative aspects were found on the physical property, composition, hydrolysis yield and ethanol fermentability of the long term stored pretreated corn stover, plus the additional merits including no chemicals recovery operation, anti-microbial contaminant environment from stronger acid and inhibitor contents, as well as the mild and slow hydrolysis in the storage. The new pretreatment method expanded the distributed pretreatment concept of feedstock storage with potential for practical application.

Physical–chemical–morphological characterization of the whole sugarcane lignocellulosic biomass used for 2G ethanol production by spectroscopy and microscopy techniques

The natural recalcitrance of sugarcane lignocellulosic biomass remains a challenge for second generation (2G) ethanol production. Here, the physical–chemical–morphological characteristics of the whole sugarcane lignocellulosic biomass (including bagasse, straw, and tops) from commercial sugarcane varieties were evaluated before and after dilute sulfuric acid pretreatment, in order to help predict the behaviors of these materials during the 2G ethanol process. Analyses using NMR, FTIR, XRD, and SEM showed that the properties of the sugarcane varieties evaluated here were very similar. The crystallinity index values calculated from the XRD results were also similar for the different residue fractions, and were higher after pretreatment due to the removal of hemicellulose. The lignin and crystalline cellulose FTIR absorption bands were most intense for bagasse, followed by straw and tops. NMR analysis identified the presence of skeletal aromatic and methoxyl groups, attributed to the lignin structure, with the intensity of the signals following the order: bagasse > straw > tops. SEM images showed that structural disruption followed the order: tops > straw > bagasse. The spectral and morphological differences helped to elucidate the characteristics that made the bagasse fraction of the sugarcane residue less susceptible to enzymatic saccharification. Differences between the spectra for straw and tops indicated that the straw was less easily digested by enzymatic action, as also indicated by the morphological analysis. The results demonstrate that the combined use of spectroscopy and microscopy techniques can contribute to understanding the behavior of different biomasses intended to be used for 2G ethanol production.

Supercritical fluids as a green technology for the pretreatment of lignocellulosic biomass

One of the main drawbacks for using lignocellulosic biomass is related to its recalcitrance. The pretreatment of lignocellulosic biomass plays an important role for delignification and crystallinity reduction purposes. In this work rice husk (RH) was submitted to supercritical pretreatment at 80°C and 270bar with the aim to determine the effect on lignin content, crystallinity as well as enzymatic digestibility. The yields obtained were compared with dilute sulfuric acid pretreatment as base case. Additionally a techno-economic and environmental comparison of the both pretreatment technologies was performed. The results show a lignin content reduction up to 90.6% for the sample with 75% moisture content using a water–ethanol mixture. The results for crystallinity and enzymatic digestibility demonstrated that no reductions were reached. Supercritical pretreatment presents the best economical and environmental performance considering the solvents and carbon dioxide recycling.

Production of single cell oil from Lipomyces starkeyi ATCC 56304 using biorefinery by-products

Single cell oil (SCO) is a valuable noncrop-based renewable oil source. Hemicellulose derived sugars can be utilized to produce SCO using the oleaginous yeast Lipomyces starkeyi ATCC 56304. Bran by-products were tested as hemicellulose-rich feedstocks for the production of SCO. Whole and destarched corn and wheat bran hydrolysates were produced using hydrothermal and dilute sulfuric acid (0%, 0.5%, 1.0%, v/v) pretreatment along with enzymatic hydrolysis. Whole bran hydrolysates produced from hydrothermal pretreatment generated the highest average oil yields of 126.7 and 124.3mgoil/g sugar for both wheat and corn bran, respectively. 1.0% acid pretreatment was effective for the destarched bran generating a hemicellulose hydrolysis efficiency of 94% and 84% for wheat and corn bran, respectively, resulting in the highest oil yield of 70.7mgoil/g sugar. The results indicate pretreated corn and wheat bran hydrolysates can serve as viable feedstocks for oleaginous yeast SCO bioconversion.

Chemical Pretreatment and Enzymatic Saccharification of Seaweed Solid Wastes

The technical feasibility of seaweed waste utilization as a resource of renewable energy was investigated in this paper. The production of fermentable sugars from seaweed waste was studied by dilute sulfuric acid and sodium hydroxide pretreatment and further enzymatic hydrolysis. Pretreatment was conducted by using 1.0 and 2.0% dilute sulfuric acid w/v and 4 and 5% sodium hydroxide w/v for 30 min at 121 oC. Pretreated seaweed wastes were analyzed by X­Ray Diffraction (XRD) to examine the crystallinity index of the cellulose and observed using Scanning Electron Microscopy (SEM) to examine the changes in structure of cellulose fiber. Saccharification of pretreated seaweed waste was carried out using crude cellulase enzyme provided by Pulp and Paper Research Center in Bandung. Saccharification was done in shake flask with 20% of substrate in citrate phosphate buffer at 30 oC and 50 oC, agitation of 150 rpm in shaking incubator for 48 h. Samples were collected at 2, 6, 12, 24 and 48 h for further analysis. Enzyme concentrations were varied between 10­50 U/g dry samples. The results showed that dilute acid and base pretreatment of seaweed solid waste can be used to improve the digestibility of seaweed waste. It successfully acted by reducing the lignin content and degrading the structure of cellulose from crystalline into amorphous form which is more susceptible to the enzyme action.The optimum pretreatment condition was shown by 4% NaOH at 121 oC for 30 min, producing the most fermentable sugar concentration. Sugar concentration produced by saccharification was optimum at 50 oC, enzyme concentration of 50 U/g sample for 24 h base pretreatment. The results of the experiment were expected to contribute in the process development of bioconversion of lignocellulosic materials into renewable energy sources.

Furfural production from hydrolysate of barley straw after dilute sulfuric acid pretreatment

Lignocellulosic biomass contains various fermentable sugars and versatile compounds, and should be isolated selectively. In this study, a two step process for furfural production is suggested. Dilute acid pretreatment, which solubilizes hemicellulose, was performed on barley straw at 110–190 °C temperature with 0.1–2% sulfuric acid for 2–20 min and a liquid portion of the hydrolysate was utilized. Using this hydrolysate, furfural production was conducted. Approximately 140–200 °C temperature induced the hydrolysis and pyrolysis of the hydrolysate. The initial reaction rate was found to be 2.84×10−5 mol/L·sec at 180 °C when reacted for 5min, 48.5% of theoretical furfural production was obtained, and it was faster than the generally used one step furfural production methods. In addition, a high temperature gradient for pre-heating showed improvement of temperature control.

Preliminary evaluation of five elephant grass cultivars harvested at different time for sugar production

Five elephant grass cultivars, Pennisetum purpureum. cv. Huanan (Huanan), P. purpureum. cv. N51 (N51), P. purpureum. cv. Sumu No. 2 (Sumu-2), (Pennisetum americanum×P. purpureum)×P. purpureum cv. Guimu No. 1 (Guimu-1) and P. americanum cv. Tift23A×P. purpureum cv. Tift N51 (Hybrid Pennisetum), at three harvest stages were studied. With dilute sulfuric acid pretreatment followed by enzymatic hydrolysis, it is found that cellulose conversion of the five elephant grass cultivars harvested in August and September is higher than that harvested in October. The cellulose conversion for elephant grass cultivars harvested in August and September follows an order of Hybrid Pennisetum>Sumu-2>Huanan>Guimu-1>N51. This may be explained by the fact that lignification is gradually strengthened with time, inhibiting degradation of cellulose and hemicellulose. Moreover, cellulose conversions of Hybrid Pennisetum, Sumu-2 and Huanan harvested in August and September are higher based on hierarchical clustering results.

Comparison of five pretreatments for the production of fermentable sugars obtained from Pinus pseudostrobus L. wood.

To benefit from the use of a waste product such as pine sawdust from a sawmill in Michoacán, Mexico, five different pretreatments for the production of reducing sugars by enzymatic hydrolysis were evaluated (sodium hydroxide, sulfuric acid, steam explosion, organosolv and combined method nitric acid / sodium hydroxide). The main finding of the study was that the pretreatment with 6 % HNO3 and 1 % NaOH led to better yields than those obtained with sodium hydroxide, dilute sulfuric acid, steam explosion, and organosolv pretreatments. Also, HNO3 yields were maximized by the factorial method. With those results the maxima concentration of reducing sugar found was 97.83 ± 1.59, obtained after pretreatment with 7.5 % HNO3 at 120 °C for 30 minutes; followed by 1 % of NaOH at 90 °C for 30 minutes at pH 4.5 for 168 hours with a load enzyme of 25 FPU/g of total carbohydrates. Comparing the results obtained by the authors with those reported in the literature, the combined method was found to be suitable for use in the exploitation of sawdust.

Furfural production from empty fruit bunch – A biorefinery approach

Biofuels production from agriculture residues is gaining much attention in Brazil due to agriculture residue availability, environmental benign properties of the fuel and the capacity to improve rural development. However, for consideration of rational use of biomass resource, a biorefinery approach capable of multiproduct output is desirable. In this context, this study deals with the process optimization of furfural production from oil palm empty fruit bunch using dilute sulfuric acid pretreatment followed by dehydration without any additional catalyst. The reaction conditions were optimized using experimental design. Furfural yield up to 57.6g/kg dry EFB or 16g/L could be produced at optimum dehydration process conditions of temperature 198°C and 11min residence time. Large quantity of water is utilized in washing process that has to be minimized by alkali or ammonia washing and considerable amount of acetic acid is produced that could be recovered as a product.

Impact of Pretreatment Technologies on Saccharification and Isopentenol Fermentation of Mixed Lignocellulosic Feedstocks

In order to enable the large-scale production of biofuels or chemicals from lignocellulosic biomass, a consistent and affordable year-round supply of lignocellulosic feedstocks is essential. Feedstock blending and/or densification offers one promising solution to overcome current challenges on biomass supply, i.e., low energy and bulk densities and significant compositional variations. Therefore, it is imperative to develop conversion technologies that can process mixed pelleted biomass feedstocks with minimal negative impact in terms of overall performance of the relevant biorefinery unit operations: pretreatment, fermentable sugar production, and fuel titers. We processed the mixture of four feedstocks—corn stover, switchgrass, lodgepole pine, and eucalyptus (1:1:1:1 on dry weight basis)—in flour and pellet form using ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate, dilute sulfuric acid (DA), and soaking in aqueous ammonia (SAA) pretreatments. Commercial enzyme mixtures, including cellulases and hemicellulases, were then applied to these pretreated feedstocks at low to moderate enzyme loadings to determine hydrolysis efficiency. Results show significant variations on the chemical composition, crystallinity, and enzymatic digestibility of the pretreated feedstocks across the different pretreatment technologies studied. The advanced biofuel isopentenol was produced during simultaneous saccharification and fermentation (SSF) of pretreated feedstocks using an engineered Escherichia coli strain. Results show that IL pretreatment liberates the most sugar during enzymatic saccharification, and in turn led to the highest isopentenol titer as compared to DA and SAA pretreatments. This study provides insights on developing biorefinery technologies that produce advanced biofuels based on mixed feedstock streams.