Volume 9 Issue 4

Pretreatment is a prerequisite step for increasing the enzymatic digestibility of agricultural residues for conversion to fuels and chemicals in biorefineries. In this study, a sequential acid and alkaline process was developed for pretreatment of rice straw for ethanol fermentation. Effects of key parameters in acid pretreatment were studied using a full factorial design model, which showed the higher influence of time compared to acid concentration and temperature on reducing sugar yields. The combined sequential process involved an initial hemicellulose solubilization by dilute acid using 1% (w/v) H2SO4 at 125 °C for 10 min, followed by alkaline delignification using 1.25% NaOH at 90 °C for 10 min. Under these conditions, a glucose recovery yield of 70.9% from saccharification of the cellulose enriched fraction was obtained with 2- to 4-fold savings in chemical usage as compared with single-step processes. Scanning electron microscopy revealed modification of biomass micro-structure and increases in reactive surface area. Simultaneous saccharification and fermentation of the solid residues by Saccharomyces cerevisiae, using 25 FPU/g Accellerase® 1500, led to a final ethanol concentration of 21.0 g/L with the productivity of 0.27 g/L/h, equivalent to 84.6% theoretical yield. The results indicate the potential of the sequential process for increasing pretreatment efficiency and allowing stepwise separation of lignocellulose components for multi-product biorefineries.

Ionic liquids are of potential interest in the processing of lignocellulosic biomass. In this study, the ionic liquid co-solvent system of 1-methylimidazole (MIM) and 1-ethyl-3-methyl-imidazolium acetate (EMIMAc) was used to solvate LignoBoost lignin fractionated from black liquor obtained from a kraft paper mill. Lignin ethanol-precipitated (LEP) and ethanol-soluble (LES) fractions were characterized via gel permeation chromatography (GPC) and 13C- and 31P-nuclear magnetic resonance spectroscopy (NMR) to determine structural characteristics and their relationship to polymer solubility in the system. Polymer integrity and solubility were optimal at ~20% lignin loading (w/w). Results showed that LEPs were generally of higher apparent molecular weight (Mw) and enriched with condensed/aliphatic ether linkages and aliphatic hydroxyls. The LESs had a lower apparent Mw and were enriched with carboxylic and phenolic groups. This newly gained knowledge on lignin fractionation and aggregation in the present solvent system provides future opportunities for tuning fractionation/extraction to suit a specific biomass-derived product, e.g., carbon fibers.

In recent years, the alkaline peroxide mechanical pulping performed with refiner-chemical preconditioning (P-RC APMP) has obtained a wide application in many paper grades in China. This is due to such desirable pulp characteristics as its high bulk, opacity, and light scattering coefficient. However, compared with its bleached chemical pulps, the poplar P-RC APMP has weak bonding strength, which limits its application in value-added products. Usually, the interfiber bonding abilities of different fiber fractions are quite different. In this study, the page bonding strength index (B) and the interfiber bonding abilities (shear bond strength per unit area (b) and relative bonding area (RBA)) of different P-RC APMP fiber fractions were extrapolated by the traditional Page Equation. The results show that the higher B could be obtained when the fiber fraction was shorter or smaller. The same trend was observed for b and RBA. Wet pressing was used to improve the bonding ability, and higher pressure of wet pressing or shorter fiber fraction can lead to obviously higher tensile strength.

Wood/polymer nanocomposites were prepared by vacuum impregnation of furfuryl alcohol (FA) and nano-SiO2 into fast-growing poplar wood. The nano-SiO2 was mixed with FA solution, followed by in-situ polymerization of FA. The properties of nanocomposites and the effects of nanoparticles on these properties were investigated. Wood physico-mechanical properties, such as dimensional stability, density, water uptake, and surface hardness, were significantly improved. Moreover, the addition of nano-SiO2 improved the surface hardness and dimensional stability of wood and kept the excellent properties of FA-treated wood. Thermogravimetric analysis indicated that the effect of nano-SiO2 on thermostability was hindered. X-ray photoelectron spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy showed that nano-SiO2 was successfully incorporated into wood via the action of FA, and diffused into the wood lumen and cell wall. X-ray diffraction results indicated the weakening of the crystallinity in the treated wood was due to the polymerization of FA.

In a previous paper, conceptual process design, simulation, and mass and energy balances were presented for an organosolv process with a hardwood feed of 2350 metric tons (MT) per day and ethanol, lignin, furfural, and acetic acid production rates of 459, 310, 6.6, and 30.3 MT/day, respectively. In this paper, the investment and operating costs of the process and the minimum ethanol selling price (MESP) to make the process economically feasible were estimated. The total capital investment of the plant was approximately 720 million USD. Lignin price was found to affect the MESP considerably. With a base case lignin price of 450 USD/MT, the MESP was approximately 3.1 USD per gallon (gal). Higher lignin price of 1000 USD/MT was required to equal the MESP with the December 2013 ethanol market price (2.0 USD/gal). In addition to lignin price, the MESP was found to be strongly affected by feedstock, enzyme, and investment costs. Variations in feedstock and investment costs affected the MESP by approximately 0.2 and 0.5 USD/gal, respectively. Changing the enzyme dosage and price from base case estimate of 5270 USD/MT and 0.02 g/g cellulose to more conservative 3700 USD/MT and 0.06 g/g cellulose, respectively, increased the MESP by 0.59 USD/gal.

Biomass content greatly affects the properties of wood-plastic composites (WPCs). Determination of the biomass in WPCs is important for the development of WPCs. In this study, transmission Fourier transform infrared (FTIR) spectroscopy was used for biomass quantification in the following WPCs: Moso bamboo/polypropylene (PP) composites, Chinese fir/PP composites, and poplar/PP composites. The bands in the region of 1060 to 1030 cm-1 were considered characteristic of biomass. The peak at 1377 cm-1 was typical of PP. The peak intensities ratios (PIRs) of biomass to PP were determined, and the biomass contents were plotted against the PIRs. The achieved coefficients of determination (R2) of the calibration fits exceeded 0.96. The results of validation showed that the range of the relative prediction deviations for biomass within WPC species was lower than ± 5.0%. Additionally, all three WPC species were combined into one data set, and a mixed model was constructed that had a slight decrease in the quality of the correlation (R2 = 0.93). The range of the relative prediction deviations for biomass between WPC species did not exceed ± 9.0%.

Hydroxyapatite/poly(vinyl alcohol) (Hap/PVA) composites have been proposed as a promising biomaterial for use in articular cartilage repair. In this study, HAp/PVA composite gels reinforced with cellulose nanocrystals (CNC) were prepared using the freeze/thaw method. The influence of CNC as a reinforcement on the structure of composite gels was investigated via Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). The mechanical properties and thermal stability of the composite gels were also studied. The FT-IR and XRD results indicated that the HAp/PVA/CNC composite gels were formed by hydrogen bonding. SEM morphology showed that the CNC served as an enhancement phase that interpenetrated the network of the HAp/PVA composite gels. The tensile strength and tensile modulus of the composites improved with increasing dosage of CNC. The thermal stability measurements indicated that the thermal stability of the HAp/PVA composites was slightly improved with the addition of the CNC.

An integrated process of lignocellulosic biomass conversion was set up involving pretreatment by an ionic liquid (IL) and hydrolysis of cellulose using cellulase immobilised by the sol-gel method, with recovery and reuse of both the IL and biocatalyst. As all investigated ILs, regardless of the nature of the anion and the cation, led to the loss of at least 50% of the hydrolytic activity of cellulase, the preferred solution involved reprecipitation of cellulose and lignin after the pretreatment, instead of performing the enzymatic hydrolysis in the same reaction system. The cellulose recovered after pretreatment with 1-ethyl-3-methylimidazolium acetate ([Emim][Ac]) and dimethylsulfoxide (DMSO) (1:1 ratio, v/v) was hydrolysed with almost double yield after 8 h of reaction time with the immobilised cellulase, compared to the reference microcrystalline cellulose. The dissolution capacity of the pretreatment mixture was maintained at satisfactory level during five reuse cycles. The immobilised cellulase was recycled in nine reaction cycles, preserving about 30% of the initial activity.

Starch adhesive was prepared utilizing corn starch, polyvinyl alcohol, and borax as raw materials. A certain amount of water-soluble carboxymethyl cellulose (CMC) was added in the preparation process, and a certain percentage of polymethylene polyphenylene isocyanate pre-polymer as cross-linking agent was used to improve its water resistance. To evaluate the water resistance, three-layer plywood was fabricated by hot pressing, and bonding strength was measured using a mechanical testing machine according to the National Standard of the People’s Republic of China GB/T 17657-2013. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were used to characterize curing of the adhesion. The results showed that the initial viscosity, solids content, and bonding strength of the starch adhesive, as well as the interface compatibility between starch adhesive and pre-polymer, were all improved. The curing temperature of the adhesive decreased, and the optimal addition of CMC was 0.375%.

Native microalgal species may offer a favorable combination of both wastewater treatment and biofuel production. In this research, a green microalgae, Chlamydomonas debaryana, was isolated from a local lagoon, screened for its lipid content using flow cytometry, and further identified with microscopic observations and DNA sequence analysis. When using swine wastewater as a medium, the biomass yields were between 0.6 and 1.62 g/L, giving a median value of 1.11 g/L. By increasing mass transfer rates and providing sufficient light intensity, the microalgal growth was intrinsically enhanced. The growth of C. debaryana reduced most nutritional contents of the wastewater except iron. When combining the microalgal growth and nutrient removal, C. debaryana was able to utilize 1.3 to 1.6×103 mg COD (chemical oxygen demand)/g biomass, 55 to 90 ppm ammonia/g biomass, and 48 to 89 ppm phosphorous/g biomass, The lipid content of C. debaryana was 19.9 ± 4.3% of cell dry weight. The transesterified microalgal oil mostly consisted of 14 kinds of fatty acids, ranging from C5 to C22, which can be refined into renewable jet fuel or used as sources of omega-3 and omega-6 fatty acids.