Hans E. Grethlein

Effect of steam explosion pretreatment on pore size and enzymatic hydrolysis of poplar

Abstract The purpose of this study was to determine the effect of batch steam explosion pretreatment on the rate of subsequent enzymatic hydrolysis of hybrid poplar wood. This pretreatment was found to be effective as indicated by the fact that for many of the pretreatment conditions studied the glucose yield obtained after 24 h of enzymatic hydrolysis using enzymes from Trichoderma reesei And Aspergillus niger is in excess of 90% of the potential, whereas the corresponding yield from unpretreated substrate is only 15%. The effect of pretreatment is believed to be primarily due to the increase in pore surface area accessible to enzyme molecules. Measurements show a considerable increase in pore volume available to 5–9 nm solute probes. Pretreated wood that was subsequently oven-dried hydrolysed poorly and showed a reduction in available pore volume after drying. Xylans are readily hydrolysed to xylose during pretreatment and owing to decomposition the amount of xylose in solution after steam pretreatment decreases as the severity of the reaction conditions increases; the converse is true for glucose. We conclude that steam explosion pretreatment can be effective on hybrid poplar and that the quantitative results obtained can be used for process design.

Pretreatment for enhanced hydrolysis of cellulosic biomass

This review will cover a number of physical and chemical pretreatment methods for cellulosic substrates which enhance their hydrolysis by cellulase or consumption by microorganisms. While the emphasis is on the literature of the last two years, some earlier work is cited which has influenced the work in the pretreatment field. In order to interpret the effects of a pretreatment method, emphasis in the past has been on crystallinity index (CI) and lignin content. Although these parameters happen often to correlate with the rate or extent of hydrolysis, it is suggested that a more basic parameter is the pore size distribution of the wet substrate and the associated surface area available to the cellulase that is the major factor in determining the effectiveness of a pretreatment method.

Kinetics of acid hydrolysis of corn stover

Abstract A small-scale steam-injection plug-flow reactor was developed and employed to obtain kinetic parameters under experimental conditions of potential commercial interest. Using dilute H 2 SO 4 as a catalyst, glucose yields are maximized at short residence times (e.g. 6 sec) and high temperatures (e.g. 240°C). At such short residence times, glucose decomposition reactions become important and the glucose kinetic parameters were, therefore, determined in a separate study. In this study, these values were imposed in the determination of the kinetic parameters used to represent the hydrolysis of the glucan in corn stover.

Glucose decomposition at high temperature, mild acid, and short residence times

Abstract Glucose is an intermediate product in the conversion of biomass to liquid fuels and chemicals via H2SO4 hydrolysis and subsequent fermentation. Unfortunately, glucose is destroyed as well as formed in this reaction. This study of glucose decomposition kinetics can be used to more accurately determine the kinetics of glucose formation from cellulosic biomass. The results demonstrate the importance of parallel reversion reactions in explaining the higher rates of disappearance of glucose found in this study as compared to earlier studies. An heuristic set of decomposition rate constants, applicable to conditions likely to be found in a flow reactor, are presented.

Improved cellulose acetate membranes for reverse osmosis

Abstract Performance of cellulose acetate membranes in reverse osmosis varies with the conditions under which they are cast. By varying casting solution composition and holding time in a systematic way, improvement in water flux at a given level of salt rejection has been obtained. Statistically designed experiments have been helpful in optimizing these two variables. A phase diagram of the cellulose acetateformamide-acetone casting system has been determined which gives the region of natural solubility of this three component system.

Computer simulation of the dartmouth process for separation of dilute Ethanol/Water mixtures

High energy costs are associated with the recovery of ethanol from fermentation broths. This paper discusses a computer simulation of the Dartmouth Process, which aims to reduce these costs by the use of IHOSR distillation, extensive heat integration, and extractive distillation using a salt.To resolve the uncertainty in modeling alcohol-water-salt vapor-liquid equilibrium, a new and more accurate activity coefficient model was used. An Aspen™ model was used to generate capital and energy costs for a range of ethanol concentrations in the feed. Simulation results show that the Dartmouth Process offers substantial economic advantages over benzene azeotropic distillation, particularly at low feed concentrations.

A study on reproducibility of cellulose acetate membranes

Abstract The variation in flux and rejection of replicate cellulose acetate membranes is measured within a membrane sheet as well as between membranes. Although the casting conditions were carefully controlled and various influences were studied. the source of variation in replicates was not identified. It is shown that the cause of variation is not due to hand or machine casting technique, casting solution composition, heat treatment, dust, overall film thickness or pressure history.

Process design and economic evaluation for the production of glucose from enzymatic hydrolysis of acid pretreated mixed hardwood

Abstract A basic process plant design is presented which has a production capacity of 1060 tons of glucose per day. The processing scheme for converting mixed hardwood to glucose consists of a mild acid hydrolysis pretreatment of the substrate in a continuous plug flow reactor, followed by enzymatic hydrolysis in a batch stirred reactor. As the slurry concentration varies from 10 to 20 percent in the enzymatic hydrolysis, the glucose yields change from 91.4 to 74 percent, respectively. The costs of producing glucose per pound in an aqueous solution with a substrate cost of 2¢/1b are given for each design and range from 13 to 16¢/1b. Since the concentration of glucose is different in each design, an additional cost of bringing each design to at least 10 percent glucose is given. A cost sensitivity study is presented. Also, the cost of straight acid hydrolysis with 56 percent glucose yield is compared to this 2-stage process.

Enhanced hydrolysis of wood in an acetone and acid aqueous system

Abstract The effect of acetone on the dilute acid hydrolysis of mixed hardwood cellulose was studied. By using acetone, glucose yields as high as 83·4% were obtained in a bench-scale percolation reactor. Without acetone, traditional glucose yields from wood cellulose in percolation reactors were limited to 65%. Under normal acid hydrolysis conditions when water was used, the main glucose decomposition product was hydroxymethyl-furfural (HMF). When acetone was used, under mild conditions, the main decomposition product was 1,6-anhydroglucose which could be posthydrolyzed into glucose. This suggests that nearly quantitative yields of glucose can be obtained under proper reaction conditions when acetone, acid and water are used.