Two-stage Pretreatment Research Articles

On Polydispersity of Plant Biomass Recalcitrance and Its Effects on Pretreatment Optimization for Sugar Production

This paper discusses a property associated with plant biomass recalcitrance to enzyme and microbial deconstructions in sugar production from cellulose and hemicelluloses. The hemicelluloses are more readily hydrolyzed to sugars than is cellulose. As a result, optimization to maximize individual glucose and hemicellulose sugar recovery is not possible. This property is an inherent feature of plant biomass and is named polydispersity of plant biomass recalcitrance (PPBR) in this study. A set of pretreatment experiments using eucalyptus and sulfite pretreatment to overcome recalcitrance of lignocelluloses was conducted. The results were used to predict the conditions for individually maximizing enzymatic glucose and xylose yields. The predicted maximal yields were used to quantitatively illustrate the PPBR concept. The effect of PPBR on pretreatment optimization and strategies for maximal sugar recovery using two-stage pretreatment are discussed.

A two-stage pretreatment of seedlings improves adventitious shoot regeneration in sugar beet (Beta vulgaris L.)

The effects of a two-stage pretreatment of seedlings on the subsequent shoot regeneration capacity were investigated. Pretreated seedlings were obtained by germinating seeds on three different germination media and then further culturing on six different growth media. Lamina and petiole explants of two sugar beet (Betavulgaris L.) breeding lines were then excised from the pretreated seedlings and cultured on five different shoot regeneration media. In both breeding lines, petiole explants produced significantly more shoots than lamina explants with higher frequencies of organogenic capacities; petiole explants of the lines M1195 and ELK345 produced a mean of 2.1 and 2.7 shoots per explant while their lamina explants produced 1.5 and 2.2 shoots per explant, respectively. A genotypic variation was evident as the line ELK345 was more productive for shoot development from both types of explants. In overall comparisons of different germination, growth and regeneration media, germination medium was most effective when supplemented with 0.5 mg/l 6-benzyladenine (BA) while both growth and regeneration media were most productive when contained a combination of 0.25 mg/l BA and 0.10 mg/l indole-3-butyric acid (IBA). Of all the treatments tested, the highest mean number of shoots per explant (8.3 shoots) and frequency of organogenic explants (75.6%) were obtained on regeneration medium supplemented with 0.25 mg/l BA and 0.10 mg/l IBA when petiole explants of the line ELK345 were excised from the seedlings that had been germinated on medium containing 0.5 mg/l BA followed by further growth on medium containing 0.25 mg/l BA and 0.10 mg/l IBA.

Methyl Ester Production from Rubber Seed oil Using Two-Step Pretreatment Process

Vegetable oil methyl ester is a very suitable substitute to diesel fuel as green energy or renewable energy in CI engines. A method has been developed to form methyl ester from rubber seed oil, by reducing the acid value of the oil having about 24% free fatty acids (FFAs) to 2 mg KOH/g by a two-stage pretreatment process. The first stage requires about 0.4 v/v of methanol–oil ratio and the second stage 0.35 v/v of methanol, in the presence of an acid catalyst, 1% v/v H2SO4, with continuous stirring at a temperature of 63(±2)°C. The mixture is provided one hour settling time to form the top layer as methanol–water mixture, which is removed. The bottom layer is subjected to transesterification with 0.3 v/v of methanol–oil ratio in the presence of 0.5 w/v KOH as alkaline catalyst to produce rubber seed oil methyl ester. The properties of rubber seed oil methyl ester are comparable with diesel fuel as per the ASTM D6751.

Two-Stage Fungal Pre-Treatment for Improved Biogas Production from Sisal Leaf Decortication Residues

Sisal leaf decortications residue (SLDR) is amongst the most abundant agro-industrial residues in Tanzania and is a good feedstock for biogas production. Pre-treatment of the residue prior to its anaerobic digestion (AD) was investigated using a two-stage pre-treatment approach with two fungal strains, CCHT-1 and Trichoderma reesei in succession in anaerobic batch bioreactors. AD of the pre-treated residue with CCTH-1 at 10% (wet weight inoculum/SLDR) inoculum concentration incubated for four days followed by incubation for eight days with 25% (wet weight inoculum/SLDR) of T. reesei gave a methane yield of 0.292 ± 0.04 m3 CH4/kg volatile solids (VS)added. On reversing the pre-treatment succession of the fungal inocula using the same parameters followed by AD, methane yield decreased by about 55%. Generally, an increment in the range of 30–101% in methane yield in comparison to the un-treated SLDR was obtained. The results confirmed the potential of CCHT-1 followed by Trichoderma reesei fungi pre-treatment prior to AD to achieve significant improvement in biogas production from SLDR.

Deconstructing recalcitrant Miscanthus with alkaline peroxide and electrolyzed water

A two-stage pretreatment method was proposed and tested for deconstruction of recalcitrant Miscanthus. During a 1st pretreatment at 50 °C, 1.0–4.0% alkaline peroxide solutions were used to partially remove hemicellulose and lignin. The remaining solids were subjected to a 2nd pretreatment at 121 °C with electrolyzed water. Using 15 filter paper units of cellulase per gram cellulose, a digestibility of 95% was achieved by the two-stage method, which was higher than 81% obtained from a 1% H 2SO 4 pretreatment (200 °C, 8 min). A mass balance for the two-stage process showed that 63% hemicellulose and 64% lignin were removed from the Miscanthus samples after the 1st pretreatment. The Scanning Electron Microscopy images and Fourier Transform Infrared Spectroscopy spectra revealed that after the 1st pretreatment, crystalline cellulose fibers were partially exposed and the linkages between residual lignin and hemicellulose disappeared. After the 2nd pretreatment, cellulose fibers were completely exposed even with cracks developed.

Two-stage dilute-acid pretreatment of softwoods.

Whole tree chips obtained from softwood forest thinnings were pretreated via single- and two-stage dilute-sulfuric acid pretreatment. Whole-tree chips were impregnated with dilute sulfuric acid and steam treated in a 4-L steam explosion reactor. In single-stage pretreatment, wood chips were treated using a wide range of severity. In two-stage pretreatment, the first stage was carried out at low severity to maximize hemicellulose recovery. Solubilized sugars were recovered from the first-stage prehydrolysate by washing with water. In the second stage, water-insoluble solids from first-stage prehydrolysate were impregnated with dilute sulfuric acid, then steam treated at more severe conditions to hydrolyze a portion of the remaining cellulose to glucose and to improve the enzyme digestibility. The total sugar yields obtained after enzymatic hydrolysis of two-stage dilute acid-pretreated samples were compared with sugar yields from single-stage pretreatment. The overall sugar yield from two-stage dilute-acid pretreatment was approx 10% higher, and the net enzyme requirement was reduced by about 50%. Simultaneous saccharification and fermentation using an adapted Saccharomyces cerevisiae yeast strain further improved cellulose conversion yield and lowered the enzyme requirement.

A process economic approach to develop a dilute-acid cellulose hydrolysis process to produce ethanol from biomass.

Successful deployment of a bioethanol process depends on the integration of technologies that can be economically commercialized. Pretreatment and fermentation operations of the traditional enzymatic bioethanol-production process constitute the largest portion of the capital and operating costs. Cost reduction in these areas, through improved reactions and reduced capital, will improve the economic feasibility of a large-scale plant. A technoeconomic model was developed using the ASPEN Plus modeling software package. This model included a two-stage pretreatment operation with a co-current first stage and countercurrent second stage, a lignin adsorption unit, and a cofermentation unit. Data from kinetic modeling of the pretreatment reactions, verified by bench-scale experiments, were used to create the ASPEN Plus base model. Results from the initial pretreatment and fermentation yields of the two-stage system correlated well to the performance targets established by the model. The ASPEN Plus model determined mass and energy-balance information, which was supplied to an economic module to determine the required selling price of the ethanol. Several pretreatment process variables such as glucose yield, liquid: solid ratio, additional pretreatment stages, and lignin adsorption were varied to determine which parameters had the greatest effect on the process economics. Optimized values for these key variables became target values for the bench-scale research, either to achieve or identify as potential obstacles in the future commercialization process. Results from this modeling and experimentation sequence have led to the design of an advanced two-stage engineering- scale reactor for a dilute-acid hydrolysis process.

Hybrid process for the conversion of lignocellulosic materials.

Because of the recalcitrant nature of lignocellulosic materials, it is important to pretreat the biomass in order to obtain a suitable material for the bioconversion. In this study, two different types of pretreatments were performed. The first experiment used a 2-gal Parr reactor operated at 140, 150, 160, and 170 degrees C with sulfuric acid concentrations varying from 0.5 to 2%. A second pretreatment was performed with a two-stage low-temperature process. The first-stage pretreatment was performed at 100 or 120 degrees C with sulfuric acid concentrations of 0.5, 2, and 5% followed by a second-stage pretreatment at 120 degrees C with 2% acid concentration. The best residues for enzymatic hydrolysis and simultaneous saccharification and fermentations (SSF) came from the higher temperature pretreatment with the Parr reactor. However, a large portion of the xylose fraction was degraded to furfural and glucose was degraded to HMF. On the contrary, the two-stage low temperature pretreatment resulted in a very low percentage of xylose degradation, and no glucose degradation. The residues from this two-stage pretreatment performed satisfactorily toward the production of ethanol by SSFs. This study discusses the results obtained from these experiments.

Stabilization of mercury containing sludge by a combined process of two-stage pretreatment and solidification

The stabilization of a mercury-bearing sludge, which is a typical hazardous waste of the chlor-alkali industry in the southern of Taiwan, has been performed by using a cement-fly ash solidification method. A two-stage pretreatment procedure consisting of using sodium sulfide and ferrous sulfate is employed to stabilize the solid end-product. Both the concentrations of the organic mercury in the extraction leachate ( C o) of the solids matrix, which had not been previously paid much attention to, and of the total mercury ( C t) have been examined. The results indicate that the two-stage pretreatment greatly enhances the stabilization efficiency of the solid matrix. The value of C t can be reduced to a value lower than 1 ppb, which is well below 5 ppb (a Japanese safety regulation on Hg for the in-land sanitary landfill). No organic mercury in the extraction leachate has been detected for the combined process of the two- stage pretreatment and the solidification. Furthermore, within the ranges of experimental conditions of this work, the tendency of C t to increase with curing time in the solidification by the process without two-stage pretreatment is greatly prevented by the two-stage pretreatment process. In addition, the 28-day compressive strength of the solid end-product can reach a value larger than 33 kg/cm 2, which is well above 10 kg/cm 2 (another Japanese regulation)