Steam Explosion of Straw in Batch and Continuous Systems (original) (raw)
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Changes in chemical composition of steam-exploded wheat straw during enzymic hydrolysis
Enzyme and Microbial Technology, 1989
Steam-exploded wheat straw was hydrolysed with Trichoderma reesei enzymes for 24 h, The hydrolysis was studied by monitoring the production of reducing sugars and the alteration of the chemical composition of the solid residue. A 90% degree of saccharification was obtained. It was shown that the overall dissolution of substrate can be accurately followed by measuring the ash content of the solid residue from the hydrolysis. Monomeric glucose was found to be adsorbed onto the solid residue daring the hydrolysis. The enzymic hydrolysis released the main polysaccharide components, glucose and xylose, to almost the same rate and extent, whereas the yield of arabinose was not as high. The constituents acetyl, p-coumaryl, and ferulyl, uronic acids and galactose were, however, more resistant to enzymic hydrolysis. Klason lignin was almost quantitatively retained in the solid residue.
Comparison of SHF and SSF processes for the bioconversion of steam-exploded wheat straw
Journal of Industrial Microbiology and Biotechnology, 2000
Two processes for ethanol production from wheat straw have been evaluated Ð separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF). The study compares the ethanol yield for biomass subjected to varying steam explosion pretreatment conditions: temperature and time of pretreatment was 2008C or 2178C and at 3 or 10 min. A rinsing procedure with water and NaOH solutions was employed for removing lignin residues and the products of hemicellulose degradation from the biomass, resulting in a final structure that facilitated enzymatic hydrolysis. Biomass loading in the bioreactor ranged from 25 to 100 g l À 1 (dry weight). The enzyme-to-biomass mass ratio was 0.06. Ethanol yields close to 81% of theoretical were achieved in the two-step process (SHF) at hydrolysis and fermentation temperatures of 458C and 378C, respectively. The broth required addition of nutrients. Sterilisation of the biomass hydrolysate in SHF and of reaction medium in SSF can be avoided as can the use of different buffers in the two stages. The optimum temperature for the single-step process (SSF) was found to be 378C and ethanol yields close to 68% of theoretical were achieved. The SSF process required a much shorter overall process time (%30 h) than the SHF process (96 h) and resulted in a large increase in ethanol productivity (0.837 g l À 1 h À 1 for SSF compared to 0.313 g l À 1 h À 1 for SHF) .
Effect of steam explosion temperature on wheat straw enzymatic hydrolysis
Wood Research, 2016
Wheat straw is an abundant and readily available lignocellulosic material potentially suitable for the second generation bioethanol production. Steam explosion was investigated as a suitable pretreatment method. Effect of steam explosion temperature on wheat straw enzymatic hydrolysis was investigated. Optimum steam explosion temperature at around 200°C was determined based on concentration of monosaccharides in hydrolysates, conversion of cellulose and xylan and yield of monosaccharides from wheat straw. This corresponds to creating conditions resulting in sufficient damage to the lignocellulose structure which leads to higher enzyme accessibility. Lower temperature does not enable sufficient enzyme accessibility while excessively high temperature results in significant breakdown of monosaccharides and lignin and creation of inhibitors. The amount of originated inhibitors was also determined for each studied steam explosion temperature.
Ethanol Production From Steam-Explosion Pretreated Wheat Straw
Bioconversion of cereal straw to bioethanol is becoming an attractive alternative to conventional fuel ethanol production from grains. In this work, the best operational conditions for steam-explosion pretreatment of wheat straw for ethanol production by a simultaneous saccharification and fermentation process were studied, using diluted acid [H 2 SO 4 0.9 % (w/w)] and water as preimpregnation agents. Acid-or water-impregnated biomass was steam-exploded at different temperatures (160-200°C) and residence times (5, 10, and 20 min). Composition of solid and filtrate obtained after pretreatment, enzymatic digestibility and ethanol production of pretreated wheat straw at different experimental conditions was analyzed. The best pretreatment conditions to obtain high conversion yield to ethanol (approx 80% of theoretical) of cellulose-rich residue after steam-explosion were 190°C and 10 min or 200°C and 5 min, in acid-impregnated straw. However, 180°C for 10 min in acid-impregnated biomass provided the highest ethanol yield referred to raw material (140 L/t wheat straw), and sugars recovery yield in the filtrate (300 g/kg wheat straw).
Biomass and Bioenergy, 1998
AbstractÐThe utilization of steam explosion technology for the production of cellulose pulps was evaluated at a bench scale using wheat straw as raw lignocellulosic material. Steam explosion was used either as a pretreatment method to achieve the fractionation of the straw into its constitutive polymers, or as a rapid pulping method for the production of unbleached chemical pulps from alkali-impregnated straw. In the fractionation process straw was pretreated by steam explosion at temperatures comprised between 205 and 2308C, and a reaction time of 2 min. The exploded ®ber was washed three successive times to yield a hemicellulosic sugars-rich solution. The recovered ®ber was deligni®ed by alkali at 1608C for 60 min. The alkali lignin was recovered by ®ltration after acidi®cation of the black liquor. The resulting ®ber was screened to separate the ®nes from the pulp. The latter was bleached and viscose-grade cellulose obtained. By-products of the process were lignin, and molasses rich in hemicellulose-derived oligomers. The optimization of the process led to the following results at a steam explosion severity of log 10 (R 0 ) = 3.80: viscose-grade cellulose pulp yield = 70% of the potential; lignin recovery = 70% of the Klason lignin present in the original straw; hemicellulose sugars = 55% of the potential pentosan, recovered as molasses. The production of chemical pulp from wheat straw was studied using a conventional soda process and a two-stage cooking sequence, consisting of straw impregnation with the caustic liquor followed by rapid (4 min) steam explosion treatment (160±2158C) of the impregnated material following withdrawal of the excess impregnation liquor. The impregnation/steam treatment sequence for wheat straw pulping shortens the total processing time (impregnation + cooking) to less than 15 min. Unbleached IRSP pulps, with yields of 33±34% (screened and ®nes removed) show strength properties comparable both to those of conventional unbleached wheat straw soda pulps and hardwood Kraft pulps, re®ned to similar freeness values (around 300 ml CSF). #
Acetic acid-catalyzed steam explosion pretreatment was applied to wheat straw at temperatures of 190 and 210 °C for 2, 6, and 10 min of residence time. The effects of pretreatment conditions on the total gravimetric recovery, hemicellulose sugars, glucose content, and yield of the enzymatic hydrolysis of cellulose were studied. The results indicated that the total gravimetric recovery decreases while the solubility of hemicellulose and the yield of cellulose enzymatic hydrolysis increase as the pretreatment severity increases. Pretreatment at 190 °C with a 2-min residence time resulted in the highest total gravimetric recovery, 58.9%. The optimum defiberation, glucose content, and enzymatic hydrolysis yields of 70.4 and 79.6%, respectively, occurred following pretreatment at 210 °C with a 10-min residence time. The optimal pretreatment condition was determined to be 190 °C for 10 min. Under the optimum conditions, the recovery yield of all sugars reached 42.7%. This pretreatment resulted in the highest recovery yield of all sugars.
Holzforschung, 1997
Lignin was produced from wheat straw via a fractionation process based on a steam explosion pretreatment followed by an alkali delignification stage. The yield and chemical composition of the resulting lignin samples were related to the conditions of the pretreatment stage. Temperature and time were grouped into a single reaction ordinate, R 0 , by using the reaction severity concept. Increasing the severity of the pretreatment causes the lignin yield to increase in the severity range studied, from logioRo =3.39 to 4.13. The methoxyl and aliphatic alcohol contents decreased as the pretreatment became more severe. The apparent molecular weight distribution (polystyrene-equivalent) was bimodal for all the samples. The yield of the alkali-extracted lignin obtained at the optimum severity for hemicellulose and cellulose recovery (logi 0 Ro = 3.80) was 70.5% of the Klason lignin in wheat straw, while the C-9 structure calculated for this material was: C 9 H7.ü8O2.4üNü.üy(OCH3)ü.8i(OH)i.ü5(COCH3)o.oü5
Pretreatment and fractionation of barley straw using steam explosion at low severity factor
Biomass and Bioenergy, 2014
Agricultural residues represent an abundant, readily available, and inexpensive source of renewable lignocellulosic biomass. However, biomass has complex structural formation that binds cellulose and hemicellulose. This necessitates the initial breakdown of the lignocellulosic matrix. Steam explosion pretreatment was performed on barley straw grind to assist in the deconstruction and disaggregation of the matrix, so as to have access to the cellulose and hemicellulose. The following process and material variables were used: temperature (140e180 C), corresponding saturated pressure (500e1100 kPa), retention time (5e10 min), and mass fraction of water 8e50%. The effect of the pretreatment was assessed through chemical composition analysis. The severity factor R o , which combines the temperature and time of the hydrolytic process into a single reaction ordinate was determined. To further provide detailed chemical composition of the steam exploded and non-treated biomass, ultimate analysis was performed to quantify the elemental components. Data show that steam explosion resulted in the breakdown of biomass matrix with increase in acid soluble lignin. However, there was a considerable thermal degradation of cellulose and hemicellulose with increase in acid insoluble lignin content. The high degradation of the hemicellulose can be accounted for by its amorphous nature which is easily disrupted by external influences unlike the well-arranged crystalline cellulose. The carbon content of the solid steam exploded product increased at higher temperature and longer residence time, while the hydrogen and oxygen content decreased, and the higher heating value (HHV) increased.
Journal of the Science of Food and Agriculture, 2013
BACKGROUND: In recent decades, bioconversion of lignocellulosic biomass to biofuel (ethanol and biodiesel) has been extensively investigated. The three main chemical constituents of biomass are cellulose, hemicellulose and lignin. Cellulose and hemicellulose are polysaccharides of primarily fermentable sugars, glucose and xylose respectively. Hemicellulose also includes small fermentable fractions of arabinose, galactose and mannose. The main issue in converting lignocellulosic biomass to fuel ethanol is the accessibility of the polysaccharides for enzymatic breakdown into monosaccharides. This study focused on the use of steam explosion as the pretreatment method for canola straw as lignocellulosic biomass.
Fermentable sugars production from acid-catalysed steam exploded barley straw
Chemical engineering transactions, 2018
Barley straw is being considered a potential lignocellulosic raw material for fuel-ethanol production. Ethanol production from lignocellulosic biomass consists in three main steps: pretreatment, enzymatic hydrolysis and fermentation. In order to improve the accessibility of the enzymes during enzymatic hydrolysis, a dilute phosphoric acid steam explosion pretreatment was applied. A three factor experimental design with temperature (160-200 oC), residence time (10 – 30 min) and phosphoric acid concentration (1 – 3 % w/v) as relevant factors was performed after a previous stage of overnight soaking. Once the pretreatment was done, both liquid and pretreated solids were separated by filtration and analysed. The pretreated solids were further subjected to enzymatic hydrolysis (S/L= 5 %, 50 oC, 150 rpm, 15 FPU / g substrate, pH = 4.8) and the released glucose was determined. Optimal pretreatment conditions were determined based on highest recovery of hemicellulosic sugars and minimum inh...