Alvin O. Converse

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.

Common aspects of acid prehydrolysis and steam explosion for pretreating wood

Abstract The initial rate of hydrolysis using cellulase from Trichoderma reesei for various wood samples is directly proportional to the surface area available to the enzyme. Both dilute acid hydrolysis in a continuous flow reactor or autohydrolysis in a steam exploder are similar pretreatment methods in that they increase the pore volume of the wood by removing hemicellulose which increases the surface area available to the enzyme. Thus, pretreated wood samples by either method with the same available surface area give essentially the same initial rate of hydrolysis; and, the increase in rate of hydrolysis is controlled by the severity of the pretreatment.

Kinetics of enzymatic hydrolysis of lignocellulosic materials based on surface area of cellulose accessible to enzyme and enzyme adsorption on lignin and cellulose

ConclusionComparison of the model with experimental data is currently in progress. It appears that more detailed studies of the adsorption dynamics, not just adsorption equilibrium, are needed.

Substrate reactivity as a function of the extent of reaction in the enzymatic hydrolysis of lignocellulose

In an effort to better understand the role of the substrate in the rapid fall off in the rate of enzymatic hydrolysis of cellulose with conversion, substrate reactivity was measured as a function of conversion. These measurements were made by interrupting the hydrolysis of pretreated wood at various degrees of conversion; and, after boiling and washing, restarting the hydrolysis in fresh buffer with fresh enzyme. The comparison of the restart rate per enzyme adsorbed with the initial rate per enzyme adsorbed, both extrapolated back to zero conversion, provides a measurement of the substrate reactivity without the complications of product inhibition or cellulase inactivation. The results indicate that the substrate reactivity falls only modestly as conversion increases. However, the restart rate is still higher than the rate of the uninterrupted hydrolysis, particularly at high conversion. Hence we conclude that the loss of substrate reactivity is not the principal cause for the long residence time required for complete conversion. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 650-655, 1997.

Kinetics of thermochemical pretreatment of lignocellulosic materials

The results of an experimental study of the acid hydrolysis of hardwood are presented in the form of values for the three parameters, activation energy, power on the acid concentration, and pre-exponen-tial factor, of the first order kinetic constants for each of the following reaction participants: xylan remaining, glucan remaining, xylose formed, and xylose decomposed. These are used as a base for a quantitative theory to predict the temperature, time, and acid concentrations needed for effective pretreatment of the substrate for subsequent enzymatic hydrolysis of the glucan. This theory is based on the assumption that successful pretreatment requires >90% removal of the xylan, <10% removal of the glucan, and >80% xylose yield. This theory is compared with selected published data.

Sugar monomer and oligomer solubility: data and predictions for application to biomass hydrolysis.

Oligomer solubility could potentially play an important role in controlling the rates and yields in the thermochemical hydrolysis of hemicellulose as a pretreatment for subsequent enzymatic conversion of cellulose. However, limited data or models are available to describe the aqueous solubility of sugar monomers and oligomers. In this work, we measured the solubilities of sugars common to many biomass feedstocks in the temperature range of 25–30°C. Then we reviewed solubility models for sugars from the open literature. Finally, we applied models to test their ability to describe this and other data reported in the literature. It was found that the solubility of sugar monomers was not well described by the ideal solubility law or other more complex models. However, with an empirical adjustment to the enthalpy of fusion, the ideal solubility law was able to approximately predict the solubility of cello-oligomers. Based on these results, solubilities for low molecular weight xylo-oligomers are predicted to investigate their possible importance in pretreatment and define further experimental measurements needed to improve our understanding of sugar and oligomer solubility.

Surface area of pretreated lignocellulosics as a function of the extent of enzymatic hydrolysis

The distribution of surface area as a function of pore size in the pores of hardwood, pretreated by mild acid hydrolysis, was estimated from the pore volume distribution, as a function of the extent of enzymatic hydrolysis. Pore volume distributions were obtained using the solute exclusion technique. Throughout the reaction, the total surface area of the substrate was mostly in pores too small to be accessible to the enzyme, which has been estimated to be 51–90 Å in diameter. For wood pretreated at 200°C, the surface area of pores large enough to be accessible to cellulase decreases rapidly as the enzymatic hydrolysis proceeds. The surface area in pores too small to be accessible to the enzyme decreases more slowly, presumably because the substrate containing these small pores reacts only at the external surface. In wood pretreated at 220°C, a more gradual decrease in the accessible pore surface area occurs. It is hypothesized that this occurs because of the increase of external surface as the size of the substrate particle decreases by more severe pretreatment. This external surface is thought to adsorb more of the enzyme, leaving less for the surface in the pores. For the more severely pretreated hardwood, more enzyme is adsorbed throughout the course of reaction.

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.

Seasonal Energy Storage in a Renewable Energy System

Because of a concern that in developing transitional energy systems the endpoint system requirements should be kept in mind, this paper focuses on storage in a renewable energy system that uses no fossil fuels. Based largely on the current seasonal patterns of consumption and wind and solar energy generated, it is estimated that the energy storage capacity that would be required to supply the electrical energy for the United States for a year given that the source of the electricity is from solar, wind, or a combination of the two, is in the order of 10%-20% of the total annual demand. While the uncertainty within and between published estimates of biomass availability is quite large, a partial review of the literature indicates that the global biomass primary energy potential could satisfy seasonal energy demands in a sustainable manner. The storage volumes required for biomass and hydrogen, another storage possibility, to meet seasonal storage needs are considerably smaller than that required for compressed air or elevated water.

The effect of enzyme and substrate levels on the specific hydrolysis rate of pretreated poplar wood

The hydrolysis of pretreated poplar wood was carried out with initial concentrations of 1.26, 2.52, 5.04 mg proteinJmL of GC123Trichoderma reesei. cellulase and substrate concentrations of 2.5% wJv, 5% w/v, and 10% wJv at pH 4.8 and 40°C. The concentration of enzyme protein remaining in solution, the glucose concentration, and the total potential glucose concentrations were measured as a function of time during the hydrolysis. The enzyme rapidly adsorbed initially, reaching a maximum in about 30 min. About 55–75% of the cellulase returned to solution as the remaining cellulose was hydrolyzed. Dilution of the unhydrolyzed residue, largely lignin, did not cause additional desorption of the cellulase. The specific hydrolysis rate (i.e., the rateJamount of adsorbed enzyme) declined significantly with increased conversion, even when corrected for glucose inhibition. At a given initial substrate concentration, the specific rate was found to be largely independent of the total enzyme concentration. However, at a given fractional conversion, the specific rate was found to be reduced by increased substrate concentration.