Maximum Glucose Yield Research Articles

Pretreatments of cellulose pyrolysate for ethanol production by Saccharomyces cerevisiae, Pichia sp. YZ-1 and Zymomonas mobilis

Cellulosic pyrolysate containing levoglucosan was chemically hydrolyzed and a maximum glucose yield of 17.35% was obtained by the hydrolysis with 0.2 mol/l H 2SO 4 at 121°C for 20 min . The total initial glucose was maintained at 41.9 g/l by diluting the hydrolysate. Ten detoxification methods were employed including either single addition of solid Ca(OH) 2 (to pH 6.0 or 10.4) or its combinations with absorbents. The neutralization+diatomite shaking method gave the hydrolysate which was most completely fermented by Saccharomyces cerevisiae and Pichia sp. YZ-1. The maximal ethanol yield of 0.45 g/g glucose was obtained by S. cerevisiae.

Levulinic acid production based on extrusion and pressurized batch reaction

Levulinic acid is a highly versatile chemical with numerous industrial uses, having the potential to become a commodity chemical. It can be used as a raw material for resins, plasticizers, textiles, animal feed, coatings and antifreeze. Starches and sugars are typically converted to levulinic acid using a batch reactor. Blends of corn starch (70%), sulfuric acid (5%), and water (25%) were extruded using a laboratory-scale, twin-screw extruder equipped with a static mixer and a condenser. The extrudates were further reacted, under pressure, with additional water and sulfuric acid. For any given set of reaction conditions, the levulinic acid yields in high amylose corn starch (HAS) samples were about 3% higher than those in normal corn starch (NS) samples. The levulinic acid yield increased as reaction time increased from 20 to 60 min. However, the yields in the samples containing 25% (w.b.) extruded starch and further reacted at 40 and 60 min of reaction time were not significantly different. The levulinic acid yield increased as the sulfuric acid content of the secondary treatment was increased from 2 to 4%. A sulfuric acid content greater than 0.3% by weight of starch did not increase levulinic acid yield. The levulinic acid yield increased from 7 to 47% as reaction temperature increased from 160 to 200 °C under pressure, whereas the glucose yield decreased from 77 to 0%. The levulinic acid yields from the extruded samples were higher than those from unextruded starch samples. The difference increased from 0.4 to 11.3% as reaction temperature increased from 160 to 200 °C. The maximum yields of glucose, hydroxymethyl furfural (HMF), and levulinic acid were obtained at 160, 180, and 200 °C reaction temperatures, respectively. Glucose and levulinic acid yields increased as extrusion temperature increased and screw speed decreased. The maximum yield of levulinic acid was 47.5% when extruded HAS was reacted at 200 °C after being extruded at 180 °C and 20 rpm screw speed.

Simulation of a cross-flow shrinking-bed reactor for the hydrolysis of lignocellulosics

An idealized model is developed for the case in which biomass slurry is conveyed through an annulus, with water or steam entering through an inner porous wall and liquid product leaving through an outer porous wall. It is assumed that the ratio of occluded liquid to solid in the slurry is a constant, R ws, and that non-occluded water is immediately removed from the reactor. The goal of >90% sugar yield with >10% sugar in the product is almost reached (88% glucose yield, 91% xylose yield, 47 g/l glucose and 45 g/l xylose) at 240 °C, 1% acid, R ws=1 and a radial wash water flow of three times the initial mass flow of solids to the reactor per meter of reactor length per g/l of sugar concentration in the occluded water. If R ws is limited to 3, the yield falls to 85% and the total sugar concentration to 61 g/l. Even without cross-flow wash, the yields can be increased by about 16 percentage points, compared to plug flow, by extracting excess liquid through the outer wall as it is formed. At 200 °C, where one might prefer to operate for ease of control and concern about the possibility of making fermentation inhibitors at higher temperatures, the maximum glucose yield in a plug-flow reactor is low (12–13%) whereas in a cross-flow reactor, at a high cross-flow wash rate, it can still be quite high (60–83%) but at a very low concentration (0.57–1.47%). In these simulations it is assumed that one-half of the inerts is solubilized. The formation of oligomers is neglected.

Enhancing enzymatic hydrolysis of cellulose by ultrasonic pretreatment

Slurries of rice-straw cellulose (obtained by delignification and removal of hemicelluloses from the powdered raw material) were subjected to ultrasonic waves at different intensities for various times (constant temperature). Susceptibility of the samples to cellulose-hydrolysis increased initially with pretreatment time, reaching a maximum or a constant level thereafter. Maximum glucose yield (~21%) was obtained under the following conditions: enzyme/substrate ratio 0.1; amplitude 18mm (peak to peak), and exposure time 30 minutes. This yield is 30X that of the starting raw material, 10X that of the untreated rice-straw cellulose and 12-13X that of the value reported by others regarding pretreatment of wheat-straw cellulose by phenol. Changing the enzyme/substrate ratio to 0.4 raises glucose yield to 42% under the same conditions. Removal of temperature control during pretreatment (50-80 °C) increases the yield up to ~30% without increasing the enzyme/substrate ratio.

A note on the conversion of oil-palm trunks to glucose via acid hydrolysis

Due to replanting activities large quantities of oil-palm trunks will be generated annually in Malaysia starting from this decade. A project was initiated to study the feasibility of converting palm trunks into glucose which could then be used to produce ethanol. The palm trunks were hydrolysed using different concentrations of sulphuric acid. Two sets of experiments were performed. In one set, the palm trunks were hydrolysed without prior treatment with NaOH, while in the second set the sample was treated first with NaOH before being subjected to acid hydrolysis. Glucose yield was found to be dependent on acid concentration as well as NaOH treatment. For samples that were treated with NaOH, yields were generally higher than those not treated. Maximum glucose yield was at a hydrolysing acid concentration of about 1.7%.

The influence of SO 2 and H 2SO 4 impregnation of willow prior to steam pretreatment

In this investigation, steam pretreatment of willow with the addition of SO 2 or H 2SO 4 was studied, the aim being to recover both the cellulose and the hemicellulose fractions. The willow was steamed (1 bar saturated steam) prior to impregnation with 0–3% H 2SO 4 or 1% SO 2 (w/w substrate). The pretreatment experiments were performed at temperatures in the range 160–230°C for 10 min. The highest xylose recovery with H 2SO 4 impregnation was obtained using 3% H 2SO 4 at 190°C, where 80% of the available xylose could be recovered by washing. At these pretreatment conditions, a glucose yield after enzymatic hydrolysis of 67%, based on the glucan available in the raw material, was achieved. The maximum glucose yield, 95%, was obtained when the willow was impregnated with 1% SO 2 and pretreated at 200°C. At these conditions, 62% of the original xylose was solubilized. As glucan is the main constituent of willow, a high yield of glucose is of more importance than a high yield of xylose, leading to the conclusion that impregnation with SO 2 is better than impregnation with H 2SO 4.

Cloning and expression of the Clostridium thermosulfurogenes glucose isomerase gene in Escherichia coli and Bacillus subtilis

The gene that encodes thermostable glucose isomerase in Clostridium thermosulfurogenes was cloned by complementation of glucose isomerase activity in a xylA mutant of Escherichia coli. A new assay method for thermostable glucose isomerase activity on agar plates, using a top agar mixture containing fructose, glucose oxidase, peroxidase, and benzidine, was developed. One positive clone, carrying plasmid pCGI38, was isolated from a cosmid library of C. thermosulfurogenes DNA. The plasmid was further subcloned into a Bacillus cloning vector, pTB523, to generate shuttle plasmid pMLG1, which is able to replicate in both E. coli and Bacillus subtilis. Expression of the thermostable glucose isomerase gene in both species was constitutive, whereas synthesis of the enzyme in C. thermosulfurogenes was inducible by D-xylose. B. subtilis and E. coli produced higher levels of thermostable glucose isomerase (1.54 and 0.46 U/mg of protein, respectively) than did C. thermosulfurogenes (0.29 U/mg of protein). The glucose isomerases synthesized in E. coli and B. subtilis were purified to homogeneity and displayed properties (subunit Mr, 50,000; tetrameric molecular structure; thermostability; metal ion requirement; and apparent temperature and pH optima) identical to those of the native enzyme purified from C. thermosulfurogenes. Simple heat treatment of crude extracts from E. coli and B. subtilis cells carrying the recombinant plasmid at 85 degrees C for 15 min generated 80% pure glucose isomerase. The maximum conversion yield of glucose (35%, wt/wt) to fructose with the thermostable glucose isomerase (10.8 U/g of dry substrate) was 52% at pH 7.0 and 70 degrees C.

One-dimensional model of the acid hydrolysis of cellulosic substrates in a solid-liquid cyclone reactor

The use of rotating flow in an annulus is investigated as a means of enhancing the yield of glucose and xylose in the acid hydrolysis of cellulosic slurries. A one-dimensional model of such a cyclone reactor is developed for flow cases, co-current and counter-current flow. For the case of 250°C, 1% w/w acid, the one-dimensional model indicates an increase in the maximum glucose yield from 48.1% in a plug flow reactor to 69.3% in a co-current cyclone reactor, and up to 81.0% in a countercurrent cyclone reactor. The corresponding xylose yields are 91.6% for co-current operation and 97.7% for countercurrent operation. In the co-current case the maximum glucose and xylose yields do not occur at the same location in the reactor; however, in the countercurrent case they do. Although product yields are dramatically improved over those obtained in a plug flow reactor, the product concentrations are lower than would typically be obtained in a plug flow reactor.

Optimization of physiological factors for direct saccharification of cassava starch to glucose by Rhizopus oligosporus 145f

Direct saccharification of 2.64% cassava starch by Rhizopus oligosporus 145F was attempted under various cultural conditions. Maximum glucose yield of 18.0 g/L culture filtrate was obtained with an initial pH 3.8, 2% (v/v) inoculum of R. oligosporus spores, and an incubation temperature of 45 degrees C in shake flask cultures for 48 h. This concomitantly produced 2.7 g mycelia/100g cassava starch containing 20.2% true protein. The production of glucose and mycelia was accomplished with 92.8% starch saccharification having 67.9% starch to glucose conversion efficiency.

Solvolysis of wood and pure cellulose by anhydrous hydrogen fluoride vapor

The solvolysis of bigtooth aspen wood and pure cellulose (filter paper) by anhydrous hydrogen fluoride (HF) vapor was investigated. Each substrate was exposed to a 100% HF vapor stream at 0·101 MPa and 27°C to 77°C for a given reaction time. The water-soluble reaction products were then post-hydrolyzed in 2 n trifluoroacetic acid for 1 h at 121°C. With this two-step hydrolysis, maximum glucose yields of 85% from wood and 94% from pure cellulose were obtained. HPLC analysis of the water-soluble reaction products obtained before post-hydrolysis revealed that glucose and glucosyl fluoride repolymerized to oligomers during vapor-phase HF solvolysis of cellulose. The oligosaccharide product distribution was dependent on reaction time, temperature and sample water content.

A comparative study of the enzymatic hydrolysis of acid‐pretreated white pine and mixed hardwood

Removal of hemicellulose by acid pretreatment in a flow reactor followed by enzymatic hydrolysis of the neutralized slurry has resulted in glucose yields as high as 95% for mixed hardwood. For white pine, however, the maximum glucose yield is 65%. Although pine has a higher extractives content, removal of the extractives prior to enzymatic hydrolysis does not increases the glucose yield. Pore size measurements reveal that the increase in pore volume, in the size range of the cellulase molecule, following pretreatment for pine is only about one-half the value obtained with mixed hardwood. This suggests that pore volume is an important determinant of substrate-enzyme reactivity.