Various lignocellulosic raw materials pretreatment processes utilizable for increasing holocellulose accessibility for hydrolytic enzymes: Part II. Effect of steam explosion temperature on beech enzymatic hydrolysis (original) (raw)
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Steam explosion is a well-known process to pretreat lignocellulosic biomass in order to enhance sugar yields in enzymatic hydrolysis, but pretreatment conditions have to be optimized individually for each material. In this study, we investigated how the results of a pretreatment optimization procedure are influenced by the chosen reaction conditions in the enzymatic hydrolysis. Beechwood was pretreated by steam explosion and the resulting biomass was subjected to enzymatic hydrolysis at glucan loadings of 1% and 5% employing either washed solids or the whole pretreatment slurry. For enzymatic hydrolysis in both reaction modes at a glucan loading of 1%, the glucose yields markedly increased with increasing severity and with increasing pretreatment temperature at identical severities and maximal values were reached at a pretreatment temperature of 230 °C. However, the optimal severity was 5.0 for washed solids enzymatic hydrolysis, but only 4.75 for whole slurry enzymatic hydrolysis. ...
Enzymatic Hydrolysis of Fast-Growing Poplar Wood After Pretreatment by Steam Explosion
Cellulose Chemistry and Technology, 2021
The aim of the present study was to investigate the effect of steam explosion pretreatment, without maintaining the heating temperature, on the yield of enzymatic hydrolysis of wood biomass. Genetically modified poplar wood was used for the investigation. The pretreatment process was conducted at temperatures of 160 °C, 175 °C, 190 °C and 205 °C. Then, the system was rapidly decompressed. The heating medium was water. The chemical composition of biomass was determined before and after the steam explosion and then enzymatic hydrolysis was performed. The results of the chemical composition analysis showed a change in the holocellulose content in the analyzed biomass (about 80% for the native sample and 72% for the biomass sample treated at 205 °C), a decrease in the hemicelluloses content from about 40% (native sample) to 16% for the sample treated at 205 °C. The results of enzymatic hydrolysis showed the lowest glucose extraction efficiency for biomass hydrolysis after the treatment ...
Enhancement in enzymatic hydrolysis by mechanical refining for pretreated hardwood lignocellulosics
Bioresource Technology, 2013
Mechanical refining improved the enzymatic hydrolysis sugar recovery. The increase in sugar recovery correlated with the water retention value. Mechanical refiners with different mechanisms affected the biomass digestibility differently. A maximum in absolute enzymatic hydrolysis improvement due to refining was observed. The maximum occurred at conditions that produced intermediate hydrolysis conversions.
2018
Effects were compared for three low-cost pretreatment methods (dilute acid, alkali, and steam explosion) relative to the effectiveness of environmentally friendly enzymatic hydrolysis and ethanol fermentation of aspen, birch, and oak chips. The highest monomeric sugar yield was achieved with the alkali pretreatment of the aspen chips (22 g/L of glucose and 6 g/L of xylose). Additionally, the concentration of lignocellulose degradation products formed during this pretreatment was relatively low, and so the hydrolysis and fermentation efficiencies were 80% and 85%, respectively. The application of dilute acid pretreatment led to lower yield of enzymatic hydrolysis in comparison with alkali pretreatment, resulting in 41% to 62% of theoretical yield for aspen and birch chips, respectively. Increasing the NaOH concentration led to an increase in the monomeric sugar yield, and consequently increased the hydrolysis and fermentation yields. By contrast, increasing the acid concentration res...
Study of enzymatic hydrolysis of mild pretreated lignocellulosic biomasses
Bioresources
The effect of mild acidic and alkaline pretreatments of various plant biomasses on their enzymatic hydrolysis has been studied. The yield of reducing sugars and utilization rate of the biomass were used as reliable characteristics of enzymatic digestibility of the biomasses. The experiments showed that alkaline pretreatment was more efficient than acidic pretreatment. As a result of alkaline pretreatment, a more efficient delignification of the biomasses and considerable improvement of the digestibility parameters were observed. It was found that residual lignin content in the biomass after alkaline pretreatment was related to initial lignin content in untreated biomass. Moreover, residual lignin showed an evident negative effect on enzymatic hydrolysis of pretreated biomass samples, and its removal contributed to higher enzymatic digestibility. It is more preferred to select a mild alkaline pretreatment for biomass that has low content of initial lignin. Such treatment yielded high...
Enhanced Enzymatic Hydrolysis of Steam-Exploded Douglas Fir Wood by Alkali-Oxygen Post-treatment
Applied Biochemistry and Biotechnology, 2004
Good enzymatic hydrolysis of steam-exploded Douglas fir wood (SEDW) cannot be achieved owing to the very high lignin content (>40%) that remains associated with this substrate. Thus, in this study, we investigated the use of alkali-oxygen treatment as a posttreatment to delignify SEDW and also considered the enzymatic hydrolyzability of the delignified SEDW. The results showed that under optimized conditions of 15% NaOH, 5% consistency, 110°C, and 3 h, approx 84% of the lignin in SEDW could be removed. The resulting delignified SEDW had good hydrolyzability, and cellulose-to-glucose conversion yields of over 90 and 100% could be achieved within 48 h with 20 and 40 filter paper units/g of cellulose enzyme loadings, respectively. It was also indicated that severe conditions, such as high NaOH concentration and high temperature, should not be utilized in oxygen delignification of SEDW in order to avoid extensive condensation of lignin and significant degradation of cellulose.
This Account of Bio/Chemical Research∗ records the research developed by the author while at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) of Australia within the Divisions of: Chemical Technology (1982), Chemical and Wood Technology (1983-86) and Biotechnology (1987-1990). The author developed methods on the pretreatment of lignocellulosic residues (sugarcane bagasse, sunflower seed hulls, hardwood (Eucalyptus regnans) and softwood (Pinus radiata)) by autohydrolysis-steam explosion, and the quantitation of saccharification of the pretreated residues by enzymes of the cellulase complex (exo- and endo- cellulases and β-glucosidases). Steam-explosion as pretreatment for enzymatic saccharification of lignocellulosic residues resulted in high conversion yields of cellulose-to-glucose, and esp., when the cellulase digests were supplemented with exogenous β-glucosidase, resulting in glucose yields of >80% within 24 h at 50 °C and pH 5.0. Softwood residues required prior treatment with sulfur dioxide before steam-explosion to produce a deconstructed pulp that was as amenable to enzymatic hydrolysis as bagasse and hardwood residues. Detailed studies on a commercial β-glucosidase preparation (Novozym 188) derived from Aspergillus niger, demonstrated that this enzyme was a “perfect match” for Trichoderma reesei C-30 cellulases in saccharifying steam-exploded lignocellulosic resides. The β-glucosidase preparation was immobilized onto an encapsulated magnetic support coated with an organic polymer, and used to hydrolyze solids-suspensions of pretreated hardwood. The immobilized enzyme was recovered by application of a magnetic field force and recycled for reuse. The efficacy of the magnetic immobilized β-glucosidase was as good as the free enzyme, but more stable to the saccharification environment. A magnetic immobilized β-galactosidase (lactase) preparation was also produced and used to hydrolyze cheese whey lactose. The author documents and comments on the organizational changes that occurred while at the CSIRO during 1982-1990; the Review of the CSIRO, and the changes in the Divisions of Chemical and Wood Technology, and Biotechnology; the redundancy program at the CSIRO in 1990, and the retrenchment of scientific staff. The author took a one-year period of leave from CSIRO in 1989, and spent a sabbatical at Universidade Federal de Rio de Janeiro – COPPE, in Brazil. The author took on a Specialist Consultancy for the United Nations Development Fund on Bioconversion of Lignocellulosic Residues in Chile during 1989. A list of invitations the author received at CSIRO is appended, as well as the publications authored. The author was retrenched from his position as Principal Research Scientist at the CSIRO in 1990, and a period of 20 years lapsed before he could re-immerge in his field of research specialty. The author has now retired after a 47-year research career, most of which was spent investigating the biodegradation and bioconversion of lignocellulosic materials; an interest that commenced in 1969.
Two-stage steam explosion pretreatment of softwood with 2-naphthol as carbocation scavenger
Biotechnology for Biofuels
Background: Lignocellulosic biomass is considered as a potential source for sustainable biofuels. In the conversion process, a pretreatment step is necessary in order to overcome the biomass recalcitrance and allow for sufficient fermentable sugar yields in enzymatic hydrolysis. Steam explosion is a well known pretreatment method working without additional chemicals and allowing for efficient particle size reduction. However, it is not effective for the pretreatment of softwood and the harsh conditions necessary to achieve a highly digestible cellulose fraction lead to the partial degradation of the hemicellulosic sugars. Previous studies showed that the autohydrolysis pretreatreatment of softwood can benefit from the addition of 2-naphthol. This carbocation scavenger prevents lignin repolymerisation leading to an enhanced glucose yield in the subsequent enzymatic hydrolysis. Results: In order to prevent the degradation of the hemicellulose, we investigated in this study a two-stage 2-naphthol steam explosion pretreatment. In the first stage, spruce wood is pretreated at a severity which is optimal for the autocatalytic hydrolysis of the hemicellulose. The hydrolyzate containing the solubilized sugars is withdrawn from the reactor and the remaining solids are pretreated with different amounts of 2-naphthol in a second stage at a severity that allows for high glucose yields in enzymatic hydrolysis. The pretreated spruce was subjected to enzymatic hydrolysis and to simultaneous saccharification and fermentation (SSF). In the first stage, the maximal yield of hemicellulosic sugars was 47.5% at a pretreatment severity of log R 0 = 3.75 at 180 °C. In the second stage, a 2-naphthol dosage of 0.205 mol/mol lignin C 9-unit increased the ethanol yield in SSF with a cellulose loading of 1% using the whole second stage pretreatment slurry by 17% from 73.6% for the control without 2-naphthol to 90.4%. At a higher solid loading corresponding to 5% w/w cellulose, the yields decreased due to higher concentrations of residual 2-naphthol in the biomass and the pretreatment liquor, but also due to higher concentrations of potential inhibitors like HMF, furfural and acetic acid. Experiments with washed solids, vacuum filtered solids and the whole slurry showed that residual 2-naphthol can inhibit the fermentation as a single inhibitor but also synergistically together with HMF, furfural and acetic acid. Conclusions: This work shows that a two-stage pretreatment greatly enhances the recovery of hemicellulosic sugars from spruce wood. The presence of 2-naphthol in the second pretreatment stage can enhance the ethanol yield in SSF of steam explosion pretreated softwood at low cellulose concentrations of 1% w/w. However, with higher solid loadings of 5% w/w cellulose, the ethanol yields were in general lower due to the solid effect and a synergistic inhibition of HMF, furfural, acetic acid with residual 2-naphthol. The concentration of residual 2-naphthol tolerated by the yeast decreased with increasing concentrations of HMF, furfural, and acetic acid.
Optimization of operating conditions in enzymatic hydrolysis of pretreated lignocellulosic materials
2010
This work studies the influence of dry solids load, enzymes ratio and reaction time in sugars concentration and yield of enzymatic hydrolysis of different steam exploded grain straw. Enzymatic hydrolysis was performed using a mixture of cellulase, glucosidade and xylanase, enzymes kindly donated by Novozymes, in test flasks shaken in a rotary incubator at 300 rpm, 50 ºC and pH of 4.8. After 24 h of reaction time, the higher sugars concentration in the hydrolizates was obtained when a 10 % DS was tested (24 g/L for rye straw and 28.1 g/L for wheat straw). When a 10 % DS was tested, maximum glucose and xylose relase after 24 h (84.9 and 19.1 % respectively) were obtained for 1.5:0.5:1.5 enzyme ratio for rye straw, whereas for wheat straw, maximum yield for glucose and xylose (78 % and 29.5 % respectively) were obtained for 1.5:1:1.5, after 24 h of hydrolysis.
Characterization of the Acid Pretreatement for the Enzymatic Hydrolysis of Wood
Holzforschung, 1988
Ground mixed hardwood samples were hydrolyzed with cellulase before and after a short-term pretreatment with sulfuric acid in a plug flow reactor at 180, 200 and 220°C. SEM observations of the Substrates indicate that the enhancement of enzymatic hydrolysis can be attributed mainly to the increment in surface area. Lignin has an inhibiting effect on the enzyme äs it impedes physical contact between cellulose and enzyme. After delignification and alkali extraction alpha-cellulose can be converted by the enzyme almost completely into monomeric sugars.