Modeling, simulation, and kinetic analysis of a heterogeneous reaction system for the enzymatic conversion of poorly soluble substrate.

We developed a kinetic model that describes a heterogeneous reaction system consisting of a solid substrate suspension for the production of D-amino acid using D-hydantoinase. As a biocatalyst, mass-produced free and whole cell enzymes were used. The heterogeneous reaction system involves dissolution of a solid substrate, enzymatic conversion of the dissolved D-form substrate, spontaneous racemization of an L-form substrate to D-form, and deactivation of the enzyme. In the case of using whole cell enzymes, transfer of the dissolved substrate and product through the cell membrane was considered. The kinetic parameters were determined from experiments, literature data, and by using Marquardt's method of nonlinear regression analysis. The model was simulated using the kinetic parameters and compared with experimental data, and a good agreement was observed between the experimental results and the simulation ones. Factors affecting the kinetics of the heterogeneous reaction system were analyzed on the basis of the kinetic model, and the efficiency of the reaction systems using free and whole cell enzymes was also compared.     

One-step production of D-p-hydroxyphenylglycine by recombinant Escherichia coli strains

The gene encoding D-hydantoinase from Agrobacterium radiobacter NRRL B11291 was successfully cloned by use of polymerase chain reaction. A positive clone was scored, and its nucleotide sequence was further analyzed. The analysis by deleting various lengths of nucleotides from the amino terminus of the open reading frame revealed the putative regions for promoter and RBS site. By highly expressing both D-hydantoinase and carbamoylase, recombinant Escherichia coli strains were able to convert DL-hydroxyphenyl hydantoin (DL-HPH) to D-p-hydroxyphenylglycine (D-HPG) with a conversion yield of 97%, accounting for productivity 5 times higher than that obtained by A. radiobacter NRRL B11291. Immobilizing the recombinant cells with kappa-carrageenan could also achieve a conversion of 93%, while A. radiobacter NRRL B11291 attained 20% within the same period of reaction time. These results illustrate the feasibility in employing recombinant E. coli to accomplish one-step conversion of DL-HPH to D-HPG. In the process of improving D-HPG production, D-hydantoinase activity was increased 2.57-fold but carbamoylase activity remained constant, which resulted in only a 30% increase in the reaction rate. It suggests that carbamoylase is the step setting the pace of the reaction. Since the reaction substrate is highly insoluble, achieving sufficient agitation appears to be an important issue in this heterogeneous system. This view is further supported by the study on repeated use of cells, which shows that to reach a conversion of more than 90% free cells can be recycled six times, whereas immobilized cells can be used only twice. In conclusion, the poor reusability of immobilized cells is due to the fouling on the gel surface.     

基因工程酶法生产N-氨基甲酰-D-对羟基苯甘氨酸反应条件的优化(英文)

为了实现利用生物酶转化法生产D 对羟基苯甘氨酸 ,以工程菌E .coliBL2 1 pMD T7 dht细胞作酶源 ,对底物对羟基苯海因到中间体N 氨基甲酰 D 对羟基苯甘氨酸的酶转化条件进行了优化 .酶转化的最适温度为 37℃ ,最适pH为 9 0 .在Tris HCl、磷酸盐、碳酸盐和硼酸盐 4种缓冲体系中 ,底物对羟基苯海因的转化率相近 .菌体细胞经适当冻融后 ,底物对羟基苯海因的转化率被提高 .水溶性有机溶剂DMSF、DMF和Tween 80使对羟基苯海因的转化率降低 .转化时底物和菌体的合适比例为 30g L对羟基苯海因和 10g L湿菌体 .经工程菌E .coliBL2 1 pMD T7 dht细胞催化 ,底物的转化率在 13h内可达到 96 % .所制备的产物熔点、旋光性和红外光谱等与标准品一致     

Tagatose production by immobilized recombinant Escherichia coli cells containing Geobacillus stearothermophilus l-arabinose isomerase mutant in a packed-bed bioreactor

Using immobilized recombinant Escherichia coli cells containing Geobacillus stearothermophilus l-arabinose isomerase mutant (Gali 152), we found that the galactose isomerization reaction was maximal at 70 degrees C and pH 7.0. Manganese ion enhanced galactose isomerization to tagatose. The immobilized cells were most stable at 60 degrees C and pH 7.0. The cell and substrate concentrations and dilution rate were optimal at 34 g/L, 300 g/L, and 0.05 h(-1), respectively. Under the optimum conditions, the immobilized cell reactor with Mn2+ produced an average of 59 g/L tagatose with a productivity of 2.9 g/L.h and a conversion yield of 19.5% for the first 20 days. The operational stability of immobilized cells with Mn2+ was demonstrated, and their half-life for tagatose production was 34 days. Tagatose production was compared for free and immobilized enzymes and free and immobilized cells using the same mass of cells. Immobilized cells produced the highest tagatose concentration, indicating that cell immobilization was more efficient for tagatose production than enzyme immobilization.     

用基因工程菌酶法和化学法制备-D-对羟基苯甘氨酸(英文)

D 对羟基苯甘氨酸 (D p HPG)是制备羟氨苄青霉素、羟氨苄头孢菌素和羟氨唑头孢菌素等β 内酰胺类抗生素的重要中间体 ,同时它也用于多种多肽类激素及农药的合成 .在D 对羟基苯甘氨酸的多种制备方法中 ,生物酶转化法具有原料易得、工艺简单、耗能少、产率高、成本低、光学纯度好、三废污染少等优势 .为利用生物酶转化法制备D 对羟基苯甘氨酸 ,首先用尿素、乙醛酸和苯酚合成底物D ,L 对羟基苯海因 ,然后利用D 海因酶基因工程菌E .coliBL2 1 pMD T7 dht细胞作酶源 ,进行底物D ,L 对羟基苯海因到中间体N 氨基甲酰 D 对羟基苯甘氨酸的酶法转化 ,最后用化学法将N 氨基甲酰 D 对羟基苯甘氨酸进一步转化为D 对羟基苯甘氨酸 .结果表明 ,底物D ,L 对羟基苯海因的收率为 60 % .8L体积的发酵小试实验表明 ,发酵 12h ,工程菌E .coliBL2 1 pMD T7 dht的海因酶活力为 30 0 0U L ,SDS 聚丙烯酰胺凝胶电泳薄层扫描结果显示海因酶表达量约占菌体总可溶性蛋白质的 60 % ,菌体收率为 6% .8L体积的海因酶转化实验表明 ,在 4 %底物D ,L 对羟基苯海因和 1%菌体 (湿重 )pH 9 0情况下 ,反应 5h ,D ,L 对羟基苯海因的转化率可达 96% .在酸性条件下 ,用NaNO2 将N 氨基甲酰 D 对羟基苯甘氨酸转化为D 对羟基苯甘氨酸 ,反应 2h ,转     

High production of D-tagatose by the addition of boric acid

An L-arabinose isomerase mutant enzyme from Geobacillus thermodenitrificans was used to catalyze the isomerization of D-galactose to D-tagatose with boric acid. Maximum production of D-tagatose occurred at pH 8.5-9.0, 60 degrees C, and 0.4 molar ratio of boric acid to D-galactose, and the production increased with increasing enzyme concentration. Under the optimum conditions, the enzyme (10.8 units/mL) converted 300 g/L D-galactose to 230 g/L D-tagatose for 20 h with a yield of 77% (w/w); the production and conversion yield with boric acid were 1.5-fold and 24% higher than without boric acid, respectively. In 24 h, the enzyme produced 370 g/L D-tagatose from 500 g/L D-galactose with boric acid, corresponding to a conversion yield of 74% (w/w) and a production rate of 15.4 g/L.h. The production and yield of D-tagatose obtained in this study are unprecedented.     

A feasible enzymatic process for D-tagatose production by an immobilized thermostable L-arabinose isomerase in a packed-bed bioreactor

To develop a feasible enzymatic process for d-tagatose production, a thermostable l-arabinose isomerase, Gali152, was immobilized in alginate, and the galactose isomerization reaction conditions were optimized. The pH and temperature for the maximal galactose isomerization reaction were pH 8.0 and 65 degrees C in the immobilized enzyme system and pH 7.5 and 60 degrees C in the free enzyme system. The presence of manganese ion enhanced galactose isomerization to tagatose in both the free and immobilized enzyme systems. The immobilized enzyme was more stable than the free enzyme at the same pH and temperature. Under stable conditions of pH 8.0 and 60 degrees C, the immobilized enzyme produced 58 g/L of tagatose from 100 g/L galactose in 90 h by batch reaction, whereas the free enzyme produced 37 g/L tagatose due to its lower stability. A packed-bed bioreactor with immobilized Gali152 in alginate beads produced 50 g/L tagatose from 100 g/L galactose in 168 h, with a productivity of 13.3 (g of tagatose)/(L-reactor.h) in continuous mode. The bioreactor produced 230 g/L tagatose from 500 g/L galactose in continuous recycling mode, with a productivity of 9.6 g/(L.h) and a conversion yield of 46%.     

Ethanol production from nonsterilized carob pod extract by free and immobilized Saccharomyces cerevisiae cells using fed-batch culture

The production of ethanol from carob pod extract by free and immobilized Saccharomyces cerevisiae cells in batch and fed-batch culture was investigated. Fed-batch culture proved to be a better fermentation system for the production of ethanol than batch culture. In fed-batch culture, both free and immobilized S. cerevisiae cells gave the same maximum concentration (62 g/L) of final ethanol at an initial sugar concentration of 300 g/L and F = 167 mL/h. The maximum ethanol productivity (4.4 g/L h) was obtained with both free and immobilized cells at a substrate concentration of 300 g/L and F = 334 mL/h. In repeated fed-batch culture, immobilized S. cerevisiae cells gave a higher overall ethanol concentration compared with the free cells. The immobilized S. cerevisiae cells in Ca-alginate beads retained their ability to produce ethanol for 10 days. (c) 1994 John Wiley & Sons, Inc.     

Mass production of thermostable D-hydantoinase by batch culture of recombinant Escherichia coli with a constitutive expression system

D-Hydantoinase is an industrial enzyme widely used for the synthesis of optically active D-amino acids. A gene encoding thermostable D-hydantoinase of Bacillus stearothermophilus SD-1 has previously been cloned and constitutively expressed by its native promoter in Escherichia coli XL1-Blue (Lee et al., 1996b). In this work, we attempted mass production of the D-hydantoinase by batch culture of the recombinant E. coli using glycerol as a carbon source. The plasmid content in cells increased in proportion to the culture temperature, which resulted in a two- or three-fold increase of the specific D-hydantoinase activity at 37 degrees C compared with that at 30 degrees C. The plasmid was stably maintained over 80 generations. When glycerol was initially added to a concentration of 100 g/L, the final biomass concentration reached about 50 g-dry cell weight/L in a 50 L-scale fermentation, resulting in the specific enzyme production of 3.8 x 10(4) unit/g-dry cell weight in a soluble form. Glycerol-using batch cultivation of recombinant E. coli was found to be a cost-effective process for the mass production of industrially useful D-hydantoinase. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 449-455, 1997.     

Complete conversion of D,L-5-monosubstituted hydantoins with a low velocity of chemical racemization into D-amino acids using whole cells of recombinant Escherichia coli

A reaction system was developed for the production of D-amino acids from D,L-5-monosubstituted hydantoins with a very slow rate of spontaneous racemization. For this purpose the D-hydantoinase and D-carbamoylase from Agrobacterium radiobacter NRRL B11291 were cloned in separate plasmids and expressed in Escherichia coli. The third enzyme, hydantoin racemase, was cloned from Agrobacterium tumefaciens C58. The hydantoin racemase amino acid sequence was significantly similar to those previously described. A reaction system consisting of recombinant Escherichia coli whole cell biocatalysts containing separately expressed D-hydantoinase, D-carbamoylase, and hydantoin recemase showed high substrate specificity and was effective toward both aliphatic and aromatic D,L-5-monosubstituted hydantoins. After optimizing reaction conditions (pH 8 and 50 degrees C), 100% conversion of D,L-5-(2-methylthioethyl)-hydantoin (15 mM) into D-methionine was obtained in 30 min.     

Bioconversion of D-galactose to D-tagatose: continuous packed bed reaction with an immobilized thermostable L-arabinose isomerase and efficient purification by selective microbial degradation

The continuous enzymatic conversion of D-galactose to D-tagatose with an immobilized thermostable L-arabinose isomerase in packed-bed reactor and a novel method for D-tagatose purification were studied. L-arabinose isomerase from Thermoanaerobacter mathranii (TMAI) was recombinantly overexpressed and immobilized in calcium alginate. The effects of pH and temperature on D-tagatose production reaction catalyzed by free and immobilized TMAI were investigated. The optimal condition for free enzyme was pH 8.0, 60°C, 5 mM MnCl(2). However, that for immobilized enzyme was pH 7.5, 75°C, 5 mM MnCl(2). In addition, the catalytic activity of immobilized enzyme at high temperature and low pH was significantly improved compared with free enzyme. The optimum reaction yield with immobilized TMAI increased by four percentage points to 43.9% compared with that of free TMAI. The highest productivity of 10 g/L h was achieved with the yield of 23.3%. Continuous production was performed at 70°C; after 168 h, the reaction yield was still above 30%. The resultant syrup was then incubated with Saccharomyces cerevisiae L1 cells. The selective degradation of D-galactose was achieved, obtaining D-tagatose with the purity above 95%. The established production and separation methods further potentiate the industrial production of D-tagatose via bioconversion and biopurification processes.     

Coupled fermentation-bioconversion process for production of chiral α-chlorohydrin with recombinant ketoreductase

Enzymatic production of chemicals typically includes fermentation of engineered bacteria, preparation of enzymes, and bioconversion processes. Here coupled fermentation-bioconversion process for production of chiral atazanavir intermediate α-chlorohydrin was established. In the fermentation step, the ketoreductase was released from recombinant E. coli cells into medium after high-temperature induction, and the enzyme activity reached 5960 U/mL in the fermentation supernatant. In the bioconversion step, the fermentation supernatant was used directly for conversion of 200 g/L α-chloroketone in heterogeneous reaction mixture, and the residual amount of chloroketone reached less than 0.1% after 24 h of reaction. After filtration and drying, powder α-chlorohydrin was obtained with total yield of 95.7%. Finally, the filtrate of the reaction mixture was used for 2nd batch conversion, and powder α-chlorohydrin was obtained with yield of 95.6%. The above coupled process simplified enzyme preparation procedure, allowed the bioproduction of α-chlorohydrin to be carried out smoothly with reduced waste water discharge, and was advantageous for industrial scale-up.     

Recombinant polycistronic structure of hydantoinase process genes in Escherichia coli for the production of optically pure D-amino acids

Two recombinant reaction systems for the production of optically pure D-amino acids from different D,L-5-monosubstituted hydantoins were constructed. Each system contained three enzymes, two of which were D-hydantoinase and D-carbamoylase from Agrobacterium tumefaciens BQL9. The third enzyme was hydantoin racemase 1 for the first system and hydantoin racemase 2 for the second system, both from A. tumefaciens C58. Each system was formed by using a recombinant Escherichia coli strain with one plasmid harboring three genes coexpressed with one promoter in a polycistronic structure. The D-carbamoylase gene was cloned closest to the promoter in order to obtain the highest level of synthesis of the enzyme, thus avoiding intermediate accumulation, which decreases the reaction rate. Both systems were able to produce 100% conversion and 100% optically pure D-methionine, D-leucine, D-norleucine, D-norvaline, D-aminobutyric acid, D-valine, D-phenylalanine, D-tyrosine, and D-tryptophan from the corresponding hydantoin racemic mixture. For the production of almost all D-amino acids studied in this work, system 1 hydrolyzed the 5-monosubstituted hydantoins faster than system 2.     

Modeling and kinetic analysis of the reaction system using whole cells with separately and co-expressed D-hydantoinase and N-carbamoylase

We developed a kinetic model that describes a heterogeneous reaction system for the production of D-p-hydroxyphenylglycine from D,L-p-hydroxyphenyl-hydantoin using D-hydantoinase of Bacillus stearothermophilus SD1 and N-carbamoylase of Agrobacterium tumefaciens NRRL B11291. As a biocatalyst, whole cells with separately or co-expressed enzymes were used. The reaction system involves dissolution of substrate particles, enzymatic conversion, racemization of the L-form substrate, and transfer of the dissolved substrate, intermediate, and product through the cell membrane. Because the two enzymes have different pH optimum, kinetic parameters were evaluated at different pH for the reaction systems. The model was simulated using the kinetic parameters and compared with experimental data, and it was found that the kinetic model well describes the behavior of the reaction systems using whole cells with separately and co-expressed enzymes. Factors affecting the kinetics of the reaction systems were analyzed on the basis of the kinetic model. In the reaction system with separately expressed enzymes, racemization rate and transport of the reaction intermediate (N-carbamoyl-D-p-hydroxyphenylglycine) were revealed to be the limiting factors at neutral pH, resulting in accumulation of intermediate in the reaction medium. At alkaline condition, on the other hand, inhibition of N-carbamoylase by ammonia was severe, and thereby the reaction rate significantly reduced. In the co-expressed enzyme system, accumulation of intermediate was negligible in the reaction medium, and the improved performance was observed compared to that with separately expressed enzymes. The present model might be applied for the optimization and development of the reaction system using two sequential enzymes.     

Immobilization of beta-galactosidase on fibrous matrix by polyethyleneimine for production of galacto-oligosaccharides from lactose

The production of galacto-oligosaccharides (GOS) from lactose by Aspergillus oryzae beta-galactosidase immobilized on cotton cloth was studied. A novel method of enzyme immobilization involving PEI-enzyme aggregate formation and growth of aggregates on individual fibrils of cotton cloth leading to multilayer immobilization of the enzyme was developed. A large amount of enzyme was immobilized (250 mg/g support) with about 90-95% efficiency. A maximum GOS production of 25-26% (w/w) was achieved at near 50% lactose conversion from 400 g/L of lactose at pH 4.5 and 40 degrees C. Tri- and tetrasaccharides were the major types of GOS formed, accounting for about 70% and 25% of the total GOS produced in the reactions, respectively. Temperature and pH affected not only the reaction rate but also GOS yield to some extend. A reaction pH of 6.0 increased GOS yield by as much as 10% compared with that of pH 4.5 while decreased the reaction rate of immobilized enzyme. The cotton cloth as the support matrix for enzyme immobilization did not affect the GOS formation characteristics of the enzyme under the same reaction conditions, suggesting diffusion limitation was negligible in the packed bed reactor and the enzyme carrier. Increase in the thermal stability of PEI-immobilized enzyme was also observed. The half-life for the immobilized enzyme on cotton cloth was close to 1 year at 40 degrees C and 21 days at 50 degrees C. Stable, continuous operation in a plug-flow reactor was demonstrated for about 3 days without any apparent problem. A maximum GOS production of 26% (w/w) of total sugars was attained at 50% lactose conversion with a feed containing 400 g/L of lactose at pH 4.5 and 40 degrees C. The corresponding reactor productivity was 6 kg/L/h, which is several-hundred-fold higher than those previously reported.     

Synthesis of galacto-oligosaccharides by β-galactosidase from Aspergillus oryzae using partially dissolved and supersaturated solution of lactose

The effect of enzyme to substrate ratio, initial lactose concentration and temperature has been studied for the kinetically controlled reaction of lactose transgalactosylation with Aspergillus oryzae β-galactosidase, to produce prebiotic galacto-oligosaccharides (GOS). Enzyme to substrate ratio had no significant effect on maximum yield and specific productivity. Galacto-oligosaccharide syntheses at very high lactose concentrations (40, 50 and 60%, w/w, lactose monohydrate) were evaluated at different temperatures (40, 47.5 and 55°C). Within these ranges, lactose could be found as a supersaturated solution or a heterogeneous system with precipitated lactose, resulting in significant effect on GOS synthesis. An increase in initial lactose concentration produced a slight increase in maximum yield as long as lactose remained dissolved. Increase in temperature produced a slight decrease in maximum yield and an increase in specific productivity when supersaturation of lactose occurred during reaction. Highest yield of 29 g GOS/100 g lactose added was obtained at a lactose monohydrate initial concentration of 50% (w/w) and 47.5°C. Highest specific productivity of 0.38 g GOSh(-1) mg enzyme(-1) was obtained at lactose monohydrate initial concentration of 40% (w/w) and 55°C, where a maximum yield of 27 g GOS/100 g lactose added was reached. This reflects the complex interplay between temperature and initial lactose concentration on the reaction of synthesis. When lactose precipitation occurred, values of yields and specific productivities lower than 22 g GOS/100 g lactose added and 0.03 gGOSh(-1) mg enzyme(-1) were obtained, respectively.     

Importance of solute partitioning in biphasic oxidation of benzyl alcohol by free and immobilized whole cells of pichia pastoris

Using free and immobilized whole cells of Pichia pastoris, the biocatalytic oxidation of benzyl alcohol was investigated in different two-phase systems. This reaction was strongly influenced by both the substrate and product inhibitions, and the production rate of benzaldehyde in the aqueous system became maximum at the initial substrate concentration of ca. 29 g/L with the aldehyde formation less than 4 to 5 g/L even after a longer reaction period. The reaction rates in the two-liquid phase systems were predominantly determined by the partitioning behaviors of the substrate and product between the two phases rather than by enzyme deactivation by the organic solvents. In the two-liquid phase systems, consequently, the organic solvent acted as a reservior to reduce these inhibitory effects, and it was essential to select the organic solvent providing the optimal partitioning of the substrate into the aqueous phase as well as the preferential extraction of the product into the organic phase. The whole cells immobilized in a mixed matrix composed of silicone polymer [>50% (v/v)] and Ca alginate gel (<50%) worked well in the xylene and decane media, providing comparable activities with the free cells. The production rate of aldehyde was also influenced by the solute partitioning into the hydrophilic alginate phase where the cells existed. (c) 1994 John Wiley & Sons, Inc.     

假单胞菌海因酶基因在大肠杆菌中的高效表达(英文)

为实现利用生物酶转化法进行D 对羟基苯甘氨酸的工业化生产 ,构建了 3株海因酶基因工程菌 .利用PCR技术从恶臭假单胞菌 (Pseudomonasputida)CPU 980 1染色体DNA中扩增得到长约1.8kb的含编码区和自身启动子的海因酶全基因 .通过将海因酶全基因插入pMD18 T质粒、海因酶基因的编码区与pET 17 b质粒重组、海因酶基因编码区和T7强启动子一起插入pMD18 T质粒分别得到重组质粒pMD dht、pET dht和pMD T7 dht.将上述重组质粒分别转化大肠杆菌 (Escherichiacoli) ,通过地高辛标记菌落原位杂交和海因酶活力测定两种方法 ,筛选出具有海因酶活力的阳性转化子 .结果表明 ,大肠杆菌的RNA聚合酶能够识别和结合来自恶臭假单胞菌海因酶基因的自身启动子 ,该启动子在大肠杆菌中能够工作 .基因工程菌E .coliBL2 1 pMD dht、E .coliBL2 1 pET dht和E .coliBL2 1 pMD T7 dht的海因酶活力分别为 170 0U L、190 0U L和 2 5 0 0U L ,比野生菌P .putidaCPU 980 1的海因酶活力分别提高了 8倍、9倍和 12倍 .薄层扫描结果显示 ,这些工程菌的海因酶表达量分别约占菌体总可溶性蛋白质的 2 0 %、31%和 5 7%.SDS PAGE显示 ,海因酶的单体分子量约为 5 0kD .经工程菌E .coliBL2 1 pMD T7 dht催化 ,底物对羟基苯海因的转化率在 13h内可达到 9     

天蓝色链霉菌海藻糖合酶的异源表达、活性分析及重组菌全细胞转化合成海藻糖的条件优化

从天蓝色链霉菌Streptomyces coelicolor克隆得到海藻糖合酶基因 (ScTreS),在大肠杆菌Escherichia coli BL21(DE3) 中进行了异源表达,通过 Ni-NTA 亲和柱对表达产物进行分离纯化得到纯酶,经 SDS-PAGE 测定其分子量约为62.3 kDa。研究其酶学性质发现该酶最适温度35 ℃;最适pH 7.0,对酸性条件比较敏感。通过同源建模和序列比对分析,对该基因进行定点突变。突变酶K246A比酶活比野生酶提高了1.43倍,突变酶A165T相对提高了1.39倍,海藻糖转化率分别提高了14%和10%。利用突变体重组菌K246A进行全细胞转化优化海藻糖的合成条件并放大进行5 L罐发酵,结果表明：在麦芽糖浓度300 g/L、初始反应温度和pH分别为35 ℃和7.0的条件下,转化率最高达到71.3%,产量为213.93 g/L;当底物浓度增加到700 g/L时,海藻糖产量仍可达到465.98 g/L。     

Hydrolysis of sorghum straw using phosphoric acid: evaluation of furfural production

Sorghum straw is a waste that has been studied scarcely. The main application is its use as raw material for xylose production. Xylose is a hemicellulosic sugar mainly used for its bioconversion toward xylitol. An alternative use could be its conversion toward furfural. The objective of this work was to study the furfural production by hydrolysis of sorghum straw with phosphoric acid at 134 degrees C. Several concentrations of H(3)PO(4) in the range 2-6% and reaction time (range 0-300 min) were evaluated. Kinetic parameters of mathematical models for predicting the concentration of xylose, glucose, arabinose, acetic acid and furfural in the hydrolysates were found. Optimal conditions for furfural production by acid hydrolysis were 6% H(3)PO(4) at 134 degrees C for 300 min, which yielded a solution with 13.7 g furfural/L, 4.0 g xylose/L, 2.9 g glucose/L, 1.1g arabinose/L and 1.2g acetic acid/L. The furfural yield of the process was 0.1336 g furfural/g initial dry matter was obtained. The results confirmed that sorghum straw can be used for furfural production when it is hydrolyzed using phosphoric acid.