Dehua Liu

Effects of some inhibitors on the growth and lipid accumulation of oleaginous yeast Rhodosporidium toruloides and preparation of biodiesel by enzymatic transesterification of the lipid.

Microbial lipid produced using yeast fermentation with inexpensive carbon sources such as lignocellulosic hydrolyzate can be an alternative feedstock for biodiesel production. Several inhibitors that can be generated during acid hydrolysis of lignocellulose were added solely or together into the culture medium to study their individual inhibitory actions and their synergistic effects on the growth and lipid accumulation of oleaginous yeast Rhodosporidium toruloides. When the inhibitors were present in isolation in the medium, to obtain a high cell biomass accumulation, the concentrations of formic acid, acetic acid, furfural and vanillin should be lower than 2, 5, 0.5 and 1.5xa0g/L, respectively. However, the synergistic effects of these compounds could dramatically decrease the minimum critical inhibitory concentrations leading to significant growth and lipid production inhibitions. Unlike the above-cited inhibitors, sodium lignosulphonate had no negative influence on biomass accumulation when its concentration was in the range of 0.5–2.0xa0g/L; in effect, it was found to facilitate cell growth and sugar-to-lipid conversion. The fatty acid compositional profile of the yeast lipid was in the compositional range of various plant oils and animal tallow. Finally, the crude yeast lipid from bagasse hydrolyzate could be well converted into fatty acid methyl ester (FAME, biodiesel) by enzymatic transesterification in a tert-butanol system with biodiesel yield of 67.2% and lipid-to-biodiesel conversion of 88.4%.

1,3-Propanediol and its copolymers: Research, development and industrialization

1,3‐Propanediol (PDO), is now taking the transition from a traditional “specialty chemical” to a “commodity chemical”. The market for PDO is growing rapidly as the technology develops. With the advancing PDO production technology, polytrimethylene terephthalate (PTT) as a new type of polyester has been applied in carpet and textile fibers, monofilaments, films, and nonwoven fabrics, and in the engineering thermoplastics area, because PTT has unique properties compared to other polymers such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Responding to the environmental and sustainability factors, one‐ or two‐step fermentation technology for PDO production has attracted peoples attention. A novel flexible process for PDO production by using aerobic fermentation from glycerol or glucose has been developed and demonstrated with a facility capacity of 4000 t/year in a pilot plant. By using engineered Escherichia coli, 135 g/L PDO was obtained with glucose as feedstock. Since the bio‐process of PDO production consumes 40% less energy and reduces greenhouse gas emissions by 20% versus petroleum‐based propanediol, the bio‐based PTT is more environmentally friendly and sustainable compared with the fossil fuel‐based polymers, which made PTT more attractive with good prospects for the future.

Downstream processing of biotechnological produced succinic acid

Succinic acid is a promising chemical which has a wide range of applications and can be biologically produced. The separation of succinic acid from fermentation broth makes more than 50xa0% of the total costs in their microbial production. This review summarizes the present state of methods studied for the recovery and purification of biologically produced succinate. Previous studies on the separation of succinic acid primarily include direct crystallization, precipitation, membrane separation, extraction, chromatography, and in situ separation. No single method has proved to be simple and efficient, and improvements are especially needed with regard to yield, purity, and energy consumption. It is argued that separation technologies coupled with upstream technology, in situ product removal, and biorefining strategy deserve more attentions in the future.

Enzymatic hydrolysis and simultaneous saccharification and fermentation of alkali/peracetic acid-pretreated sugarcane bagasse for ethanol and 2,3-butanediol production

The enzymatic digestibility of alkali/peracetic acid (PAA)-pretreated bagasse was systematically investigated. The effects of initial solid consistency, cellulase loading and addition of supplemental β-glucosidase on the enzymatic conversion of glycan were studied. It was found the alkali-PAA pulp showed excellent enzymatic digestibility. The enzymatic glycan conversion could reach about 80% after 24 h incubation when enzyme loading was 10 FPU/g solid. Simultaneous saccharification and fermentation (SSF) results indicated that the pulp could be well converted to ethanol. Compared with dilute acid pretreated bagasse (DAPB), alkali-PAA pulp could obtain much higher ethanol and xylose concentrations. The fermentation broth still showed some cellulase activity so that the fed pulp could be further converted to sugars and ethanol. After the second batch SSF, the fermentation broth of alkali-PAA pulp still kept about 50% of initial cellulase activity. However, only 21% of initial cellulase activity was kept in the fermentation broth of DAPB. The xylose syrup obtained in SSF of alkali-PAA pulp could be well converted to 2,3-butanediol by Klebsiella pneumoniae CGMCC 1.9131.

Kinetic model for glycan hydrolysis and formation of monosaccharides during dilute acid hydrolysis of sugarcane bagasse

Sugarcane bagasse was hydrolyzed with 0.4-5 wt.% sulfuric acid at 97-126 °C. A novel kinetic model was proposed to describe glycan solubilization and formation of monosaccharides. Based on the multilayered structure of plant cell wall, the concept of potential hydrolysis degree (h(d)) was introduced into kinetic models for the hydrolysis of biomass glycans. It was found that during xylan hydrolysis, xylo-oligomers were apparently present in the liquid phase, particularly at low temperature. Therefore, to accurately determine the rate constants of xylan hydrolysis, residual xylan content in the solid phase, xylo-oligomers and xylose concentrations in liquid phase should be measured. Similarly, the concept of potential hydrolysis degree was applicable for araban and cellulose hydrolysis. The kinetic relationships between rate constant or h(d) and reaction severity (dilute acid concentration and temperature) were determined according to experimental data. The results showed that the model was reliable (determination coefficients (R(2)) in the range of 0.95-0.995) to describe the kinetic behavior of dilute acid hydrolysis of sugarcane bagasse.

Batch and multi-step fed-batch enzymatic saccharification of Formiline-pretreated sugarcane bagasse at high solid loadings for high sugar and ethanol titers

Formiline pretreatment pertains to a biomass fractionation process. In the present work, Formiline-pretreated sugarcane bagasse was hydrolyzed with cellulases by batch and multi-step fed-batch processes at 20% solid loading. For wet pulp, after 144 h incubation with cellulase loading of 10 FPU/g dry solid, fed-batch process obtained ~150 g/L glucose and ~80% glucan conversion, while batch process obtained ~130 g/L glucose with corresponding ~70% glucan conversion. Solid loading could be further increased to 30% for the acetone-dried pulp. By fed-batch hydrolysis of the dried pulp in pH 4.8 buffer solution, glucose concentration could be 247.3±1.6 g/L with corresponding 86.1±0.6% glucan conversion. The enzymatic hydrolyzates could be well converted to ethanol by a subsequent fermentation using Saccharomices cerevisiae with ethanol titer of 60-70 g/L. Batch and fed-batch SSF indicated that Formiline-pretreated substrate showed excellent fermentability. The final ethanol concentration was 80 g/L with corresponding 82.7% of theoretical yield.

Fractionating pretreatment of sugarcane bagasse by aqueous formic acid with direct recycle of spent liquor to increase cellulose digestibility--the Formiline process.

A lignocellulose pretreatment process was developed with formic acid delignification (FAD) followed by alkaline deformylation (AD), which was termed as Formiline process. In FAD, more than 80% of lignin and hemicellulose were removed, but cellulose formylation also happened. Formic acid concentration (FAC) was the most important factor affecting delignification and cellulose formylation. Increasing FAC could enhance degree of delignification but also increased cellulose formylation. The presence of formyl group could inhibit the enzymatic hydrolysis of cellulose; however, removing formyl group with a small loading of alkali well recovered cellulose digestibility. The spent liquor could be directly recycled for delignification thus significantly decreasing energy consumption in solvent recovery. The Formiline-pretreated substrates showed an excellent enzymatic digestibility and could be very well converted to ethanol by simultaneous saccharafication and fermentation (SSF). The final ethanol concentrations were 55.4 and 80.1g/L respectively at initial solid consistencies of 15% and 20%.

Microwave pretreatment of substrates for cellulase production by solid-state fermentation.

The agricultural residues, wheat bran and rice hulls, were used as substrates for cellulase production with Trichoderma sp 3.2942 by solid-state fermentation. Microwave irradiation was employed to pretreat the substrates in order to increase the susceptibility. Although the highest cellulase yield was obtained by the substrates pretreated by 450xa0W microwave for 3xa0min, pretreatment time and microwave power had no significant effect on cellulase production. The initial reducing sugar content (RSC) of substrates was decreased by microwave irradiation, but more reducing sugars were produced in later fermentation. Alkali pretreatment combined with microwave pretreatment (APCMP) of rice hulls could significantly increase cellulase yields and reducing sugar. The maximum filter paper activity, carboximethylcellulase (CMC)ase, and RSC were increased by 35.2%, 21.4%, and 13%, respectively, compared with those of untreated rice hulls. The fermented residues could produce more cellulase and reducing sugars than fresh rice hulls after they were treated by APCMP. The increased accessibility of the substrates by microwave pretreatment was mainly achieved by rupture of the rigid structure of rice hulls. However, for alkali pretreatment and APCMP, delignification and removal of ash played very important roles for increasing the acceptability of substrates.

Dependence on the properties of organic solvent: Study on acyl migration kinetics of partial glycerides

During Rhizopus oryzae-mediated methanolysis of triglycerides for biodiesel production, the amount of 1,2-DG and 2-MG as well as the ratio of 1,2-DG/1,3-DG and 2-MG/1-MG differed significantly in different reaction medium, which indicated that solvent might be a crucial factor that would influence the acyl migration rate, leading to varied biodiesel yield. In this paper, the influence of solvent and their properties on acyl migration kinetics of both 1,2-diglyceride and 2-monoglyceride were investigated systematically. It was found that decreasing solvent polarity would give increasing acyl migration rate constants in general. Solvent polarity influenced the acyl migration rate through the influence of the charge dispersion of the transition state. High polarity of the solvent was unfavorable to the transition state charge dispersion, which would increase its energy state, and thus decreased the acyl migration rate and then led to relatively lower methyl ester yield.

Kinetics of Formic Acid-autocatalyzed Preparation of Performic Acid in Aqueous Phase

Abstract Performic acid (PFA) is an oxidant used in chemical processing, synthesis and bleaching. The macro kinetic models of synthesis, hydrolysis and decomposition of PFA were investigated via formic acid-autocatalyzed reaction. It was found that the intrinsic activation energies of PFA synthesis and hydrolysis were 75.2 kJ·mol −1 and 40.4 kJ·mol −1 respectively. The observed activation energy of PFA decomposition was 95.4 kJ·mol −1 . The experimental results indicated that the decomposition of PFA was liable to occur even at the ambient temperature. Both the spontaneous decomposition and the radical-introduced decomposition contributed to the decomposition of PFA.