The effect of particle size on hydrolysis reaction rates and rheological properties in cellulosic slurries

The effect of varying initial particle sizes on enzymatic hydrolysis rates and rheological properties of sawdust slurries is investigated. Slurries with four particle size ranges (33 microm < x < or = 75 microm, 150 microm < x < or = 180 microm, 295 microm < x < or = 425 microm, and 590 microm < x < or = 850 microm) were subjected to enzymatic hydrolysis using an enzyme dosage of 15 filter paper units per gram of cellulose at 50 degrees C and 250 rpm in shaker flasks. At lower initial particle sizes, higher enzymatic reaction rates and conversions of cellulose to glucose were observed. After 72 h 50 and 55% more glucose was produced from the smallest size particles than the largest size ones, for initial solids concentration of 10 and 13% (w/w), respectively. The effect of initial particle size on viscosity over a range of shear was also investigated. For equivalent initial solids concentration, smaller particle sizes result in lower viscosities such that at a concentration of 10% (w/w), the viscosity decreased from 3000 cP for 150 microm < x < or = 180 microm particle size slurries to 61.4 cP for 33 microm < x < or = 75 microm particle size slurries. Results indicate particle size reduction may provide a means for reducing the long residence time required for the enzymatic hydrolysis step in the conversion of biomass to ethanol. Furthermore, the corresponding reduction in viscosity may allow for higher solids loading and reduced reactor sizes during large-scale processing.     

Rheology of Dilute Acid Hydrolyzed Corn Stover at High Solids Concentration

The rheological properties of acid hydrolyzed corn stover at high solids concentration (20–35 wt.%) were investigated using torque rheometry. These materials are yield stress fluids whose rheological properties can be well represented by the Bingham model. Yield stresses increase with increasing solids concentration and decrease with increasing hydrolysis reaction temperature, acid concentration, and rheometer temperature. Plastic viscosities increase with increasing solids concentration and tend to decrease with increasing reaction temperature and acid concentration. The solids concentration dependence of the yield stress is consistent with that reported for other fibrous systems. The changes in yield stress with reaction conditions are consistent with observed changes in particle size. This study illustrates that torque rheometry can be used effectively to measure rheological properties of concentrated biomass.     

Computational fluid dynamics simulation and redesign of a screw conveyor reactor

National Renewable Energy Laboratory (NREL) designed a shrinking-bed reactor to maintain a constant bulk packing density of cellulosic biomass. The high solid-to-liquid ratio in the pretreatment process allows a high sugar yield and avoids the need to flush large volumes of solution through the reactor. To scale up the shrinking-bed reactor, NREL investigated a pilot-scale screw conveyor reactor in which an interrupted flight between screws was employed to mimic the “shrinking-bed” effect. In the experiments with the screw conveyor reactor, overmixing and uneven flow occurred. These phenomena produce negative effects on biomass hydrolysis. The flow behavior inside the reactor was analyzed to allow redesign of the screw to achieve adequate mixing and even flow. In the present study, computational fluid dynamics (CFD) was utilized to simulate the fluid flow in the porous media, and a new screw design was proposed. CFD analysis performed on the redesigned reactor indicated that an even flow pattern was achieved.     

Use of computational fluid dynamics simulations for design of a pretreatment screw conveyor reactor

Computational fluid dynamics simulations were employed to compare performance of various designs of a pretreatment screw conveyor reactor. The reactor consisted of a vertical screw used to create cross flow between the upward conveying solids and the downward flow of acid. Simulations were performed with the original screw design and a modified design in which the upper flights of the screw were removed. Results of the simulations show visually that the modified design provided favorable plug flow behavior within the reactor. Pressure drop across the length of the reactor without the upper screws in place was predicted by the simulations to be 5 vs 40 kPa for the original design.     

固体酸改质生物油的研究

利用乙酸和乙醇生成乙酸乙酯的酯化反应为模型反应，筛选得到催化活性最好的固体酸催化剂40％SiO2/TiO2SO42－。 在一定的反应条件下，添加固体酸催化剂和溶剂，生物油的品质得到提高，热值提高了50.7％，运动黏度降低到原来的10％，密度降低了22.6％。生物油改质前后的GC MS分析表明，固体酸可以将生物油中含有的有机羧酸转化为酯类，如甲酸酯、乙酸酯等，使生物油中的羧酸组分发生了催化酯化反应，改善了生物油的品质，生物油物理化学性能得到明显的提高。3A分子筛对生物油的脱水作用不显著，对酸性、密度、黏度等方面影响较小。     

酸化油固定床酶法合成生物柴油研究

酸化油是油脂工作中以皂脚、油脚经酸化处理得到的产品.它的主要成份是游离脂肪酸及中性油,是生产脂肪酸的重要原料,但生产过程中有水解废水的产生,若将其直接排放,既污染了环境又浪费了资源.     

Online upgrading of organic vapors from the fast pyrolysis of biomass

The online upgrading process that combined the fast pyrolysis of biomass and catalytic cracking of bio-oil was developed to produce a high quality liquid product from the biomass. The installation consisted of a fluidized bed reactor for pyrolysis and a packed bed reactor for upgrading. The proper pyrolysis processing conditions with a temperature of 500℃ and a flow rate of 4m3·h-1 were determined in advance. Under such conditions, the effects of temperature and weight hourly space velocity (WHSV) on both the liquid yields and the oil qualities of the online catalytic cracking process were investigated. The results showed that such a combined process had the superiority of increasing the liquid yield and improving the product quality over the separate processes. Furthermore, when the temperature was 500℃, with a WHSV of 3h-1, the liquid yield reached the maximum and the oxygenic compounds also decreased obviously.     

Dilute-acid pretreatment of corn stover using a high-solids percolation reactor

Pretreatment of corn stover by dilute sulfuric acid was investigated using a laboratory percolation (flowthrough) reactor operated under high-solids conditions. The effects of reaction conditions and operating parameters on the performance of the percolation reactor were investigated seeking the optimal range in which acceptable levels of yield and sugar concentration could be attained. It was demonstrated that 70–75% recovery of xylose and 6 to 7% (w/w) xylose concentration were attainable. The high sugar concentration was obtained as a result of dense packing of dry corn stover and the low liquid throughput. Xylose was mostly unreacted, rather than decomposed. The cellulose and the unreacted xylan of treated corn stover were both effectively hydrolyzed by a “cellulase” enzyme preparation that also exhibits some activity on xylan. The xylose yield was affected significantly by the flow rate under the same reaction time and conditions. This behavior appears to be related to sugar decomposition, mass transfer resistance, and the fact that acid is neutralized by the buffering components of the biomass.     

Conversion of municipal solid waste into carboxylic acids by anaerobic countercurrent fermentation

Municipal solid waste (MSW) and sewage sludge (SS) were combined and anaerobically converted into carboxylate salts by using a mixed culture of acid-forming microorganisms. MSW is an energy source and SS is a source of nutrients. In this study, MSW and SS were combined, so they complemented each other. Four fermentors were arranged in series for a countercurrent fermentation process. In this process, the solids and liquid were transferred in opposite directions, with the addition of fresh biomass to fermentor 1 and fresh liquid media to fermentor 4. An intermediate lime treatment of solids exiting fermentor 3 before entering fermentor 4 was applied to improve the product acid concentration from the untreated MSW/SS fermentations. All fermentations were performed under anaerobic conditions at 40°C. Calcium carbonate was added to neutralize the carboxylic acids and to control the pH. Iodoform was used as a methanogen inhibitor. Carboxylic acid concentration and gas composition were determined by gas chromatography. Substrate conversion was measured by volatile solids loss, and carboxylic acid productivity was calculated as the function of the total carboxylic acids produced, the amount of liquid in all fermentors, and time. The addition of intermediate lime treatment increased product concentration and conversion by approx 30 and 15%, respectively. The highest carboxylic acid concentrations for untreated MSW/SS fermentations with and without intermediate lime treatment were 22.2 and 17.7 g of carboxylic acid/L of liquid, respectively. These results confirm that adding a treatment step between fermentor 3 and fermentor 4 will increase the digestibility and acid productivity of the fermentation.     

Production of bio-oil via fast pyrolysis of agricultural residues from cassava plantations in a fluidised-bed reactor with a hot vapour filtration unit

This article reports experimental results on fast pyrolysis of agricultural residues from cassava plantations, namely cassava rhizome (CR) and cassava stalk (CS), in a fluidised-bed fast pyrolysis reactor unit incorporated with a hot vapour filter. The objective of this research was to investigate the effects of reaction temperatures, biomass particle size and the use of simple hot vapour filtration on pyrolysis product yields and properties. Results showed that the optimum pyrolysis temperatures for CR and CS were 475 °C and 469 °C, which gave maximum bio-oil yields of 69.1 wt% and 61.4 wt% on dry biomass basis, respectively. The optimum particle size for bio-oil production in this study was 250–425 μm. The use of the hot filter led to a reduction of 6–7 wt% of bio-oil yield. Nevertheless, the filtered bio-oils appeared to have a better quality in terms of initial viscosity, solids content, ash content and stability.     

Conversion of municipal solid waste into carboxylic acids by anaerobic countercurrent fermentation: effect of using intermediate lime treatment

Municipal solid waste (MSW) and sewage sludge (SS) were combined and anaerobically converted into carboxylate salts by using a mixed culture of acid-forming microorganisms. MSW is an energy source and SS is a source of nutrients. In this study, MSW and SS were combined, so they complemented each other. Four fermentors were arranged in series for a countercurrent fermentation process. In this process, the solids and liquid were transferred in opposite directions, with the addition of fresh biomass to fermentor 1 and fresh liquid media to fermentor 4. An intermediate lime treatment of solids exiting fermentor 3 before entering fermentor 4 was applied to improve the product acid concentration from the untreated MSW/SS fermentations. All fermentations were performed under anaerobic conditions at 40 degrees C. Calcium carbonate was added to neutralize the carboxylic acids and to control the pH. Iodoform was used as a methanogen inhibitor. Carboxylic acid concentration and gas composition were determined by gas chromatography. Substrate conversion was measured by volatile solids loss, and carboxylic acid productivity was calculated as the function of the total carboxylic acids produced, the amount of liquid in all fermentors, and time. The addition of intermediate lime treatment increased product concentration and conversion by approx 30 and 15%, respectively. The highest carboxylic acid concentrations for untreated MSW/SS fermentations with and without intermediate lime treatment were 22.2 and 17.7 g of carboxylic acid/L of liquid, respectively. These results confirm that adding a treatment step between fermentor 3 and fermentor 4 will increase the digestibility and acid productivity of the fermentation.     

One-pot catalytic conversion of cellulose and of woody biomass solids to liquid fuels

Efficient methodologies for converting biomass solids to liquid fuels have the potential to reduce dependence on imported petroleum while easing the atmospheric carbon dioxide burden. Here, we report quantitative catalytic conversions of wood and cellulosic solids to liquid and gaseous products in a single stage reactor operating at 300-320 °C and 160-220 bar. Little or no char is formed during this process. The reaction medium is supercritical methanol (sc-MeOH) and the catalyst, a copper-doped porous metal oxide, is composed of earth-abundant materials. The major liquid product is a mixture of C(2)-C(6) aliphatic alcohols and methylated derivatives thereof that are, in principle, suitable for applications as liquid fuels.     

Modeling of carbonic acid pretreatment process using ASPEN-plusŖ

ASPEN-Plus^Ŗ process modeling software is used to model carbonic acid pretreatment of biomass. ASPEN-Plus was used because of the thorough treatment of thermodynamic interactions and its status as a widely accepted process simulator. Because most of the physical property data for many of the key components used in the simulation of pretreatment processes are not available in the standard ASPEN-Plus property databases, values from an in-house database (INHSPCD) developed by the National Renewable Energy Laboratory were used. The standard non-random-two-liquid (NRTL) or renon route was used as the main property method because of the need to distill ethanol and to handle dissolved gases. The pretreatment reactor was modeled as a “black box” stoichiometric reactor owing to the unavailability of reaction kinetics. The ASPEN-Plus model was used to calculate the process equipment costs, power requirements, and heating and cooling loads. Equipment costs were derived from published modeling studies. Wall thickness calculations were used to predict construction costs for the high-pressure pretreatment reactor. Published laboratory data were used to determine a suitable severity range for the operation of the carbonic acid reactor. The results indicate that combined capital and operating costs of the carbonic acid system are slightly higher than on H₂SO₄-based system and highly sensitive to reactor pressure and solids concentration.     

Production of propionic acid using a xylose utilizingPropionibacterium

The kinetics ofP. acidipropionici (ATCC25562), a xylose-utilizing rumen microorganism, was studied to assess its use for propionic acid production from wood hydrolyzates. Propionic acid has been shown to have a stronger inhibitory effect than acetic acid, with the undissociated acid form being responsible for the majority of the inhibitory effect. Thus, in batch tests with pH controlled at 6.0, the propionic acid concentration reaches 25 g/L and the acetic acid 7 g/L. Xylose uptake rate is dependent on the specific growth rate and glucose concentration. An immobilized cell columnar reactor at very high product yields (80%) proved adequate for propionic production. At cell concentrations of 95 g/L with high product concentration, volumetric productivities of 2.7 g/L·h were obtained in ultrafiltration cell recycle systems.     

Kinetic Study of Empty Fruit Bunch Using Hot Liquid Water and Dilute Acid

Empty fruit bunch (EFB), a residual product of the palm plantation, is an attractive biomass for biorefinery. As xylan is susceptible to high temperature pretreatment, it is important to setup a proper pretreatment condition to maximize the sugar recovery from EFB. Kinetic parameters of mathematical models were obtained in order to predict the concentration of xylose, glucose, furfural, and acetic acid in the hydrolysate and to find production conditions of xylose. We investigated the kinetics of hot liquid water and dilute sulfuric acid hydrolysis over a 40-min period using a self-designed setup by measuring the concentrations of released sugars (xylose, glucose) and degradation products (acetic acid and furfural). The reaction was performed within the range 160～180 °C, under reaction conditions of various concentration of sulfuric acid (0.1～0.2%) and 1:7 solid-liquid ratio in a batch reactor. The kinetic constants can be expressed by the Arrhenius equation with the activation energy for the hydrolysis of sugar and decomposition of sugar. The activation energy of xylose was determined to be 136.2187 kJ mol(-1).     

Laboratory method for high-solids countercurrent fermentations

Equipment and procedures were developed to study the conversion of lignocellulosic biomass to carboxylic acids using high-solids countercurrent fermentations. Countercurrent fermentations of cattle manure yielded a rapid fermentation (maximum 2.98 g of total acid/[L x d]) with high acid concentrations (maximum of 32.5 g of total acid/L), but the acid yield tended to be low (maximum of 0.24 g of total acid/g of volatile solids). Countercurrent fermentations of a mixture of 80% municipal solid waste/20% sewage sludge fermented more slowly (maximum of 1.98 g of total acid/[L x d]) with a lower acid concentration (maximum of 26.5 g of total acids/L), but higher acid yields were achieved (maximum of 0.34 g of total acid/g of volatile solids).     

Flow field in a shrinking-bed reactor for pretreatment of cellulosic biomass

A shrinking-bed reactor was designed by the National Renewable Energy Laboratory to maintain a constant bulk packing density of cellulosic biomass. The high solid-to-liquid ratio in the pretreatment process allows a high sugar yield and avoids the need to flush large volumes of solution through the reactor. The shrinking-bed reactor is a promising pretreatment reactor with the potential for scale-up for commercial applications. To scale up the shrinking-bed reactor, it is necessary to understand the flow pattern in the reactor. In this study, flow field is simulated with computational fluid dynamics using a porous medium model. Different discrete “snapshots” and multiple steady states are utilized. The bulk flow pattern, velocity distribution, and pressure drop are determined from the simulation and can be used to guide reactor design and scale-up.     

Development of a novel laboratory scale high solids reactor for anaerobic digestion of processed municipal solid wastes for the production of methane

Economic evaluations of the capital costs for anaerobic digestion systems for gas production show that the reactor is a significant cost component. The successful application of high solids digestion of processed MSW (e.g., greater than 10% solids within the digester) would allow a decrease in reactor volume with maintenance of relatively high gas production rates. However, high solids slurries do not mix well in conventional stirred tank reactors. A horizontal shaft, hydraulically driven reactor was designed and fabricated to test the anaerobic digestion of high solids concentrations. Digester performance was evaluated as a function of experimental parameters such as nutrient requirements, feeding rates, pH control, and agitator design/ rotation speed; horsepower of mixing was also evaluated for the reactor. Several startup protocols were examined to obtain a biologically stable anaerobic fermentation at high solids levels.     

Model-based fed-batch for high-solids enzymatic cellulose hydrolysis

While many kinetic models have been developed for the enzymatic hydrolysis of cellulose, few have been extensively applied for process design, optimization, or control. High-solids operation of the enzymatic hydrolysis of lignocellulose is motivated by both its operation decreasing capital costs and increasing product concentration and hence separation costs. This work utilizes both insights obtained from experimental work and kinetic modeling to develop an optimization strategy for cellulose saccharification at insoluble solids levels greater than 15% (w/w), where mixing in stirred tank reactors (STRs) becomes problematic. A previously developed model for batch enzymatic hydrolysis of cellulose was modified to consider the effects of feeding in the context of fed-batch operation. By solving the set of model differential equations, a feeding profile was developed to maintain the insoluble solids concentration at a constant or manageable level throughout the course of the reaction. Using this approach, a stream of relatively concentrated solids (and cellulase enzymes) can be used to increase the final sugar concentration within the reactor without requiring the high initial levels of insoluble solids that would be required if the operation were performed in batch mode. Experimental application in bench-scale STRs using a feed stream of dilute acid-pretreated corn stover solids and cellulase enzymes resulted in similar cellulose conversion profiles to those achieved in batch shake-flask reactors where temperature control issues are mitigated. Final cellulose conversions reached approximately 80% of theoretical for fed-batch STRs fed to reach a cumulative solids level of 25% (w/w) initial insoluble solids.     

Fast pyrolysis (ultrapyrolysis) of cellulose

A fast pyrolysis process, termed ultrapyrolysis, has been developed at the University of Western Ontario in order to exploit the high heating rates, short residence times high temperatures and rapid quenching, which are required to produce valuable non-equilibrium intermediates (i.e. ethylene and acetylene) from finely divided biomass. Hot solids(Thermo-for) are used to carry and transfer heat to the biomass particles in a very turbulent vortical contactor (Thermovortactor). This turbulence creates an ideal environment for fast thorough mixing and extremely rapid heat transfer. Cold solids (Cryofor) are then used to quickly quench the products. Trials with cellulose were conducted at temperatures between 750 and 900°C and residence times between 250 and 450 ms. Ethylene yields, expressed as a mass fraction of the product gas, varied from 6.8 to 8.2% for temperatures ranging from 750 to 900°C. The total hydrocarbon yield, also expressed as amass fraction of the product gas, was 18.8% at 900°C. The conversion of cellulose to a permanent non-condensible gaseous product was estimated to be 98% by mass at 900°C.