•Pore-broadened Al-SBA-15 was synthesized by tuning the hydrophobic core size.•Template micelle was sensitive to changes of temperature and TMB contents.•40–60 °C assembling temperature got high structure regularity, otherwise order lost.•18 nm highly-ordered pores were obtained at a TMB/P123 ratio of 0.25.•Catalytic acid sites were well reserved when broadened by TMB.A series of pore-broadened Al-SBA-15 samples were synthesized using a direct hydrothermal method. The effects of aluminum incorporation, assembling temperature, and co-solvent (1,3,5-trimethylbenzene (TMB)) content were investigated by low-angle XRD, N2 adsorption and desorption isotherm analysis, SEM, TEM, NH3-TPD, FTIR, pyridine-IR, and 27Al NMR. The results indicated that aluminum incorporation (Si/Al ratio = 10) increased the pore size of SBA-15 from 5.66 to 10.13 nm. A small pore size of 6.55 nm was observed at a low assembling temperature of 30 °C, attributing to the inadequate stretching of the molecular template. An increased pore size of 8.45 nm was obtained at an assembling temperature of 60 °C because of the partial hydrophobization of the hydrophilic groups, whereas a high temperature of 70 °C resulted in the generation of least ordered pores. The hydrophobic co-solvent TMB showed a significant broadening level as a result of its effective fusion into the hydrophobic micelle cores. A highly ordered pore framework with a pore size of 18 nm was obtained at a TMB/P123 ratio of 0.25, which was found to be optimum. More or less TMB led to the generation of mesocellular silica-aluminum foams with a complete loss of regularity. The 27Al NMR results showed that aluminum was mostly tetrahedrally coordinated. The NH3-TPD and pyridine-IR detection results indicated that a number of weak and medium acid sites (as Bronsted and Lewis acid sites) existed in Al-SBA-15 pore-broadened by TMB.

For high caloricity and stability in bio-aviation fuels, a certain content of aromatic hydrocarbons (AHCs, 8–25 wt%) is crucial. Fatty acids, obtained from waste or inedible oils, are a renewable and economic feedstock for AHC production. Considerable amounts of AHCs, up to 64.61 wt%, were produced through the one-step hydroprocessing of fatty acids over Ni/HZSM-5 catalysts. Hydrogenation, hydrocracking, and aromatization constituted the principal AHC formation processes. At a lower temperature, fatty acids were first hydrosaturated and then hydrodeoxygenated at metal sites to form long-chain hydrocarbons. Alternatively, the unsaturated fatty acids could be directly deoxygenated at acid sites without first being saturated. The long-chain hydrocarbons were cracked into gases such as ethane, propane, and C6–C8 olefins over the catalysts' Brønsted acid sites; these underwent Diels–Alder reactions on the catalysts' Lewis acid sites to form AHCs. C6–C8 olefins were determined as critical intermediates for AHC formation. As the Ni content in the catalyst increased, the Brønsted-acid site density was reduced due to coverage by the metal nanoparticles. Good performance was achieved with a loading of 10 wt% Ni, where the Ni nanoparticles exhibited a polyhedral morphology which exposed more active sites for aromatization.

A new vision of using carbon dioxide (CO2) catalytic processing of oleic acid into C8–C15 alkanes over a nano-nickel/zeolite catalyst is reported in this paper. The inherent and essential reasons which make this achievable are clearly resolved by using totally new catalytic reaction pathways of oleic acid transformation in a CO2 atmosphere. The yield of C8–C15 ingredients reaches 73.10 mol% in a CO2 atmosphere, which is much higher than the 49.67 mol% yield obtained in a hydrogen (H2) atmosphere. In the absence of an external H2 source, products which are similar to aviation fuel are generated where aromatization of propene (C3H6) oxidative dehydrogenation (ODH) involving CO2 and propane (C3H8) and hydrogen transfer reactions are found to account for hydrogen liberation in oleic acid and achieve its re-arrangement in the final alkane products. The reaction pathway in the CO2 atmosphere is significantly different from that in the H2 atmosphere, as shown by the presence of 8-heptadecene, γ-stearolactone, and 3-heptadecene as reaction intermediates, as well as a CO formation pathway. Because of the highly dispersed Ni metal center on the zeolite support, H2 spillover is observed in the H2 atmosphere, which inhibits the production of short-chain alkanes and reveals the inherent disadvantage of using H2. The CO2 processing of oleic acid described in this paper will significantly contribute to future CO2 utilization chemistry and provide an economical and promising approach for the production of sustainable alkane products which are similar to aviation fuel.

•Addresses the molecular mechanisms why a long term tolerant algae species can stand high concentrations of CO2•Examines how CO2 enrichment can improve the productivity of microalgae.•A microalgae species is developed for CO2 capture of the industrial flue gasesMicroalgae are the potential choice in diverting carbon emission from industrial plants. Owing to the high CO2 concentrations, industrial flue gas can constrain the growth of most microalgae. A continuous transfer procedure was developed to select a tolerant microalgae species to feed on CO2-rich industrial flue gas. The ability to capture CO2 by the developed microalgae species is verified in a closed gas bag system and the bubble column reactors. A total of 432 metabolic molecules were collected from the microalgae culture subject to the ambient (0.04% CO2) and the CO2-elevated (15%) treatments, 37 of which showed significantly different concentrations. These 37 metabolites were found to enhance the cellular physiology mechanisms of the microalgae to thrive in the high concentrations of CO2. The productivity of microalgae was shown to be improved for industrial applications.Download high-res image (169KB)Download full-size image

•Co-expression of dual enzymes for d-psicose production from D-glucose.•Dual-genes expression plasmid construction by inserting a set of expression elements.•Conversion rate of d-psicose from d-glucose was approximately 10%.•Enzymatic production of d-psicose from sugarcane bagasse and microalgae hydrolysate.d-Psicose has been drawing increasing attention in recent years because of its medical and health applications. The production of d-psicose from d-glucose requires the co-expression and synergistic action of xylose isomerase and d-psicose 3-epimerase. To co-express these genes, vector pET-28a(+)-dual containing two T7 promoters and RBS sites and an Multiple Cloning Sites was constructed using the Escherichia coli expression plasmid pET-28a(+). The xylose isomerase gene from E. coli MG1665 and the d-psicose 3-epimerase gene from Agrobacterium tumefaciens CGMCC 1.1488 were cloned and co-expressed in E. coli BL21(DE3). After 24 h incubation with the dual enzyme system at 40 °C, the sugar conversion ratio from d-glucose to d-psicose reached 10%. The optimal conditions were 50 °C, pH 7.5 with Co2+ and Mg2+. The d-psicose yields from sugarcane bagasse and microalgae hydrolysate were 1.42 and 1.69 g/L, respectively.Download high-res image (76KB)Download full-size image

•Enhanced alkali pretreatment effectively improved enzymatic hydrolysis of cellulose.•AMIC assisted alkali pretreatment was more efficient in dissolving cellulose.•Cellulose I structure was highly disrupted with increased area and porosity.•The glucan and xylan conversion efficiency reached 99.51% and 92.76%, respectively after 72 h hydrolysis.Microwave irradiation (MWI) and ionic liquid (IL) assisted methods were chosen to strengthen the alkali pretreatment process to improve saccharification efficiency of sugarcane bagasse (SCB). Four different pretreatment approaches namely alkali, IL, MWI-alkali and IL-alkali pretreatments were compared. The chemical composition, morphology and crystal performance of the substrates were analyzed by the standardized methods of the National Renewable Energy Laboratory, field emission scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. IL assisted treatment brought the highest lignin removal (78.51%), and the glucan and xylan conversion achieved 99.51% and 92.76%, respectively, after 72 h of enzymatic hydrolysis. The similar effect occurred for MWI assisted alkali-pretreatment approach. SEM and XRD analyses showed that the strengthened process obviously changed the structure and crystallinity of the substrates. Moreover, as a persuasive tool, the fractal-like theory was used to study the enzymatic hydrolysis kinetics.

Higher alcohols, longer chain alcohols, contain more than 3 carbon atoms, showed close energy advantages as gasoline, and were considered as the next generation substitution for chemical fuels. Higher alcohol biosynthesis by native microorganisms mainly needs gene expression of heterologous keto acid decarboxylase and alcohol dehydrogenases. In the present study, branched-chain α-keto acid decarboxylase gene from Lactococcus lactis subsp. lactis CICC 6246 (Kivd) and alcohol dehydrogenases gene from Zymomonas mobilis CICC 41465 (AdhB) were transformed into Escherichia coli for higher alcohol production. SDS-PAGE results showed these two proteins were expressed in the recombinant strains. The resulting strain was incubated in LB medium at 37 °C in Erlenmeyer flasks and much more 3-methyl-1-butanol (104 mg/L) than isobutanol (24 mg/L) was produced. However, in 5 g/L glucose-containing medium, the production of two alcohols was similar, 156 and 161 mg/L for C4 (isobutanol) and C5 (3-methyl-1-butanol) alcohol, respectively. Effects of fermentation factors including temperature, glucose content, and α-keto acid on alcohol production were also investigated. The increase of glucose content and the adding of α-keto acids facilitated the production of C4 and C5 alcohols. The enzyme activities of pure Kivd on α-ketoisovalerate and α-ketoisocaproate were 26.77 and 21.24 μmol min−1 mg−1, respectively. Due to its ability on decarboxylation of α-ketoisovalerate and α-ketoisocaproate, the recombinant E. coli strain showed potential application on isoamyl alcohol and isobutanol production.

Though less attention has been paid to microalgae as a feedstock for bioethanol production, many microalgae seem to have this potential since they contain no lignin, minor hemicellulose, and abundant carbohydrate. The objective of this study was to investigate the effect of nitrogen starvation on carbohydrate and starch accumulation in green microalga Chlorella zofingiensis and assess the feasibility of using this microalga as a bioethanol feedstock. The results showed that the specific growth rate under nitrogen starvation (0.48 day−1) was much lower than that under nitrogen repletion (1.02 day−1). However, nitrogen starvation quickly induced the accumulation of carbohydrate, especially starch. After merely 1 day of nitrogen starvation, carbohydrate and starch increased 37 % and 4.7-fold, respectively. The highest carbohydrate content reached 66.9 % of dry weight (DW), and 66.7 % of this was starch. In order to obtain enough carbohydrate productivities for bioethanol production, two-stage cultivation strategy was implemented and found to be effective for enhancing biomass, carbohydrate, and starch simultaneously. The optimal biomass, carbohydrate, and starch productivities of C. zofingiensis were obtained after 5 days of cultivation, and their values were 699, 407, and 268 mg L−1 day−1, respectively.

Hemicellulose and lignin are the main factors limiting accessibility of hydrolytic enzymes besides the crystallinity of cellulose. The decomposition behavior of hemicellulose and lignin in the step-change flow rate hot water system was investigated. Xylan removal increased from 64.53% for batch system (solid concentration 4.25% w/v, 18 min, 184°C) to 83.78% at high flow rates of 30 ml/min for 8 min, and then 10 ml/min for 10 min. Most of them (80–90%) were recovered as oligosaccharide. It was hypothesized that the flowing water could enhance the mass transfer to improve the sugars recovery. In addition, the solubilization mechanism of lignin in the liquid hot water was proposed according to the results of Fourier transform-infrared spectroscopy and scanning electron microscopy of the water-insoluble fraction and gas chromatography–mass spectrometry of the water-soluble fraction. It was proposed that lignin in the liquid hot water first migrated out of the cell wall in the form of molten bodies, and then flushed out of the reactor. A small quantity of them was further degraded into monomeric products such as vanillin, syringe aldehyde, coniferyl aldehyde, ferulic acid, and p-hydroxy-cinnamic acid. All of these observations would provide important information for the downstream processing, such as purification and concentration of sugars and the enzymatic digestion of residual solid.

According to fractal-like theory in the heterogeneous system, a cellulase-catalyzed kinetic equation that contained two parameters (rate constant k and fractal dimension h) was deduced. The equation described directly the mathematical relationship between reducing sugar concentration and hydrolytic time, and accurately fitted the experimental data of free/immobilized cellulase at 37, 40, 44, 47, and 50 °C (R2 > 0.99). The fitted h value is estimated as a constant (0.6148) in these tested temperatures. The fitted k value increased with temperature increase, and the relationship agreed with Arrhenius equation (R2 > 0.98). The fractal-like equation could predict accurately the experimental data at low temperature 34 °C for free/immobilized cellulase and high temperature 53 °C for immobilized cellulase, but the prediction at 53 °C for free cellulase was not accurate enough due to its lower stability than immobilized cellulase. The application of fractal-like theory in cellulase kinetics is successful.

Performance of cathode electron receivers has direct effect on the voltage and power density of MFC. This paper explored the electrical performance of MFC with potassium permanganate, ferricyanide solution and dissolved oxygen (DO) as cathode electron receivers. The results showed that the internal resistance of MFC with DO depends on catalyst and is higher than that of MFC with potassium permanganate and potassium ferricyanide solution. The maximum volume power density is 4.35 W/m3, and the smallest internal resistance is only about 54 Ω. In case of DO, the internal resistance and power density is different depending on the catalyst and is not too much related to the membranes.

By considering the features of fluidized-bed reactors and the kinetic mechanism of biomass gasification, a steady-state, isothermal, one-dimensional and two-phase mathematical model of biomass gasification kinetics in bubbling fluidized beds was developed. The model assumes the existence of two phases — a bubble and an emulsion phase — with chemical reactions occurring in both phases. The axial gas dispersion in the two phases is accounted for and the pyrolysis of biomass is taken to be instantaneous. The char and gas species CO, CO2, H2, H2O, CH4 and 8 chemical reactions are included in the model. The mathematical model belongs to a typical boundary value problem of ordinary differential equations and its solution is obtained by a Matlab program. Utilizing wood powder as the feedstock, the calculated data show satisfactory agreement with experimental results and proves the effectiveness and reliability of the model.

•Gas-sampling bag was applied as a gas-cultivation system to study CO/syngas bioconversion.•Gas-sampling bag can maintain the headspace atomosphere over a long time.•C. autoethanogenum preferred to use CO other than CO2.•C. autoethanogenum produced the highest level of ethanol with 100% CO as the substrate.•C. autoethanogenum showed a better performance in CO fermentation to ethanol than C. ljungdahlii.Bioconversion of CO/syngas to produce ethanol is a novel route in bioethanol production, which can be accomplished by some acetogens. Specific culture vessels and techniques are needed to cultivate these microorganisms since they are anaerobic and substrates are gaseous. In this work, gas-sampling bag was applied as a gas-cultivation system to study CO/syngas bioconversion by Clostridium autoethanogenum and was demonstrated to be efficient because of its flexibility and excellent ability to maintain the headspace atmosphere. C. autoethanogenum can use CO as the sole carbon and energy source to produce ethanol, acetate as well as CO2. In the experimental range, higher ethanol production was favored by higher yeast extract concentrations, and the maximum ethanol concentration of 3.45 g/L was obtained at 1.0 g/L of yeast extract. Study with various bottled gases showed that C. autoethanogenum preferred to use CO other than CO2 and produced the highest level of ethanol with 100% CO as the substrate. C. autoethanogenum can also utilize biomass-generated syngas (36.2% CO, 23.0% H2, 15.4% CO2, 11.3% N2), but the process proceeded slowly and insufficiently due to the presence of O2 and C2H2. In our study, C. autoethanogenum showed a better performance in the bioconversion of CO to ethanol than Clostridium ljungdahlii, a strain which has been most studied, and for both strains, ethanol production was promoted by supplementing 0.5 g/L of acetate.

•Oleyl alcohols were used to partially substitute the water to investigate its effect.•Insoluble solids was found in batch hydrolysis with diverse ratio of water was replaced.•Fed-batch hydrolysis was carried out with solvent water/oleyl alcohol ratio of 3:1.•Glucose production was found to be less than pure water hydrolysis system.•Solids effect was related to the solvent water content.Solvent water is an essential factor for high solids enzymatic hydrolysis. To investigate its effect on substrate conversion efficiency in high solids hydrolysis of sugarcane bagasse (SCB), oleyl alcohol was used to partially substitute the solvent water. The results in batch hydrolysis tests in which diverse ratio of solvent water was replaced found that the majority of the substrate was insoluble. Then high solids fed-batch hydrolysis with the reaction solution mixed with solvent water and oleyl alcohol in the ratio of 3:1 (solids concentration correspond to 24% (w/v)) was carried out at the final real solids loading of 18% (w/v). The produced sugars were found to be less than pure water system, which indicated that water played a significant role in high solids hydrolysis process, and solids effect was related to the solvent water content.

•The transcription data of Dunaliella parva under nitrogen sufficient and nitrogen limitation conditions was reported.•We identified important pathways and genes involved in biofuel production in D. parva, especially important wri1 gene.•We cloned the full-length cDNA and promoter of wri1, and studied differential expression of wri1.Compared with first generation plant-based biofuels, microalgae have potential advantages as feedstock for biofuel production. However, the genome sequences were insufficient in non-model microalgae with potential for biofuel production, which limited the development of genetic engineering of these microalgae. Here we described the de novo transcriptome sequencing and assembly for the halophilic green alga Dunaliella parva and identified important pathways, genes and transcription factor gene wri1 involved in biofuel production. The Illumina Hiseq 2000 platform was applied to D. parva transcriptome sequencing, which produced 26,304,060 (assembled into 60,883 contigs) and 26,797,446 (assembled into 55,236 contigs) high quality reads in samples SCH-5.0 mMA (control sample) and SCH-0.5 mMA (nitrogen limitation sample) respectively. Assembled contigs were subjected to Blastx search and annotated with NCBI non-redundant protein database, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes orthology identifiers. These analyses obtained the majority of genes involved in the biosynthesis and degradation of lipid and starch in D. parva. In addition, we have identified numerous differentially expressed genes, especially important transcription factor gene wri1 (GenBank KR185335) and studied differential expression of wri1 between control and nitrogen limitation sample, which provided foundation for illuminating the regulation mechanism of lipid biosynthesis induced by nitrogen limitation.

•Biogas production was enhanced by co-digestion of rice straw with other materials.•The optimal ratio of kitchen waste, pig manure and rice straw is 0.4:1.6:1.•The maximum biogas yield of 674.4 L/kg VS was obtained.•VFA inhibition occurred when kitchen waste content was more than 26%.•The dominant VFA were propionate and acetate in successful reactors.In order to investigate the effect of feedstock ratios in biogas production, anaerobic co-digestions of rice straw with kitchen waste and pig manure were carried out. A series of single-stage batch mesophilic (37 ± 1 °C) anaerobic digestions were performed at a substrate concentration of 54 g/L based on volatile solids (VS). The results showed that the optimal ratio of kitchen waste, pig manure, and rice straw was 0.4:1.6:1, for which the C/N ratio was 21.7. The methane content was 45.9–70.0% and rate of VS reduction was 55.8%. The biogas yield of 674.4 L/kg VS was higher than that of the digestion of rice straw or pig manure alone by 71.67% and 10.41%, respectively. Inhibition of biogas production by volatile fatty acids (VFA) occurred when the addition of kitchen waste was greater than 26%. The VFA analysis showed that, in the reactors that successfully produced biogas, the dominant intermediate metabolites were propionate and acetate, while they were lactic acid, acetate, and propionate in the others.

Cellular biochemical composition of the microalga Chlorella zofingiensis was studied under favorable and nitrogen starvation conditions, with special emphasis on lipid classes and fatty acids distribution. When algal cells were grown in nitrogen-free medium (N stress), the increase in the contents of lipid and carbohydrate while a decrease in protein content was detected. Glycolipids were the major lipid fraction (50.7% of total lipids) under control condition, while neutral lipids increased to be predominant (86.7% of total lipids) under N stress condition. Triacylglycerol (TAG) content in N stressed cells was 27.3% dw, which was over three times higher than that obtained under control condition. Within neutral lipids fraction, monounsaturated fatty acids (MUFA) were the main group (40.6%) upon N stress, in which oleic acid was the most representative fatty acids (34.5%). Contrarily, glycolipids and phospholipids showed a higher percentage of polyunsaturated fatty acids (PUFA). Lipid quality assessment indicated the potential of this alga as a biodiesel feedstock when its neutral lipids were a principal lipid fraction. The results demonstrate that the neutral lipids content is key to determine the suitability of the microalga for biodiesel, and the stress cultivation is essential for lipid quality.

•High-solids fed-batch enzymatic hydrolysis of alkali-pretreated SCB was applied.•Fed-batch system viscosity was tested for determing the right operation conditions.•The produced total sugars was more than 230 g/L with 36% solids loading.•The Final glucose concentration reached 134.9 g/L with nearly 60% glucan conversion efficiency.Viscosity trends in alkali-pretreated sugarcane bagasse (SCB) slurries undergoing high solids fed-batch enzymatic hydrolysis were measured for a range of solids loading from 15% to 36%. Solids liquefaction times were related to system viscosity changes. The viscosity decreased quickly for low solids loading, and increased with increasing solids content. Fed-batch hydrolysis was initiated with 15% solids loading, and an additional 8%, 7% and 6% were successively added after the system viscosity decreased to stable values to achieve a final solids content of 36%. Two enzyme-adding modes with 8.5 FPU/g solid were investigated. The batch mode with all enzyme being added at the beginning of the reaction produced the highest yields, with approximately 231.7 g/L total sugars and 134.9 g/L glucose being obtained after 96 h with nearly 60% of the final glucan conversion rate. This finding indicates that under the right conditions, the fed-batch strategy might be a plausible way to produce high sugars under high solids.

For high caloricity and stability in bio-aviation fuels, a certain content of aromatic hydrocarbons (AHCs, 8–25 wt%) is crucial. Fatty acids, obtained from waste or inedible oils, are a renewable and economic feedstock for AHC production. Considerable amounts of AHCs, up to 64.61 wt%, were produced through the one-step hydroprocessing of fatty acids over Ni/HZSM-5 catalysts. Hydrogenation, hydrocracking, and aromatization constituted the principal AHC formation processes. At a lower temperature, fatty acids were first hydrosaturated and then hydrodeoxygenated at metal sites to form long-chain hydrocarbons. Alternatively, the unsaturated fatty acids could be directly deoxygenated at acid sites without first being saturated. The long-chain hydrocarbons were cracked into gases such as ethane, propane, and C6–C8 olefins over the catalysts' Brønsted acid sites; these underwent Diels–Alder reactions on the catalysts' Lewis acid sites to form AHCs. C6–C8 olefins were determined as critical intermediates for AHC formation. As the Ni content in the catalyst increased, the Brønsted-acid site density was reduced due to coverage by the metal nanoparticles. Good performance was achieved with a loading of 10 wt% Ni, where the Ni nanoparticles exhibited a polyhedral morphology which exposed more active sites for aromatization.