麦草碱性沸石催化制浆及其酶水解

采用过氧化氢进行预浸渍,以固体沸石A和B为催化剂,研究麦草氧碱法制浆对其酶水解的影响。结果表明,当制浆黑液中乙酰丙酸和甲酸的浓度分别达5.1442,6.7096mg/ml时,采用固体沸石A和B蒸煮成浆的水解得率分别为18.38%和23.16%。AMF分析表明,与表面物理结构相比,成浆纤维化学结构的改变对酶水解的影响更大。     

Screening of steam explosion conditions for glucose production from non-impregnated wheat straw

The conversion of wheat straw to fermentable sugar for bioethanol production typically involves a thermal pretreatment step, followed by enzymatic hydrolysis. In this study we have investigated the effect of steam explosion parameters on wheat straw digestibility using a newly designed steam explosion unit and a process without acid impregnation. The wheat straw was steam pretreated using 18 different conditions in the temperature range of 170-220 °C and the resulting material was used directly (i.e. without washing) for enzymatic hydrolysis and fermentation in either a separate hydrolysis and fermentation (SHF)-type or a simultaneous saccharification and fermentation (SSF)-type set-up. Maximum glucose yields upon enzymatic hydrolysis were obtained after pretreatment at 210 °C for 10 min and yields were similar at harsher conditions. Xylose yields increased with temperature and residence time up to 190 °C, but decreased at harsher pretreatment conditions since these led to xylan degradation and concomitant production of furfural. In an SHF-type set-up ethanol formation did not follow enzymatic glucose release and was inversely correlated with furfural levels. An SFF-type set-up displayed a straightforward correlation between the expected amount of released glucose and the ethanol yields. The highest saccharification yields corresponded to about 90% of the cellulose in the substrate. Overall, this study shows that steam explosion without an acid catalyst is a good pretreatment method for saccharification of wheat straw. Optimal steam explosion conditions need to be a compromise between sugar accessibility and sugar degradation.     

Optimization of dilute acid and hot water pretreatment of different lignocellulosic biomass: A comparative study

Pretreatment of biomass to alter their recalcitrant structures is an essential step to obtain high yield of products via bioconversion processes. In this study, main emphasis was to compare the results evaluated in terms of total reducing sugars (TRS) yield after acid and hot water pre-treatment process performed with laboratory scale equipment using different lignocellulosic biomass. The biomass chosen for this purpose i.e. sugarcane bagasse and bamboo were collected from Guwahati, Assam and their physico-chemical characteristics were examined using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and thermo gravimetric analysis (TGA) including proximate and ultimate analysis. Crystalinity of the biomass used was observed to be 33.15% and 31.29% for sugarcane bagasse and bamboo respectively. Hot water and dilute acid pretreatment allows selective solubility of hemicellulose which improves the accessibility of enzymes for cellulose hydrolysis. The highest yield of TRS was observed at run order 8 for both acid and hot water pretreatment (23.49 and 26.50 gL⁻¹) with respect to sugarcane bagasse. But, the pretreatment results obtained for bamboo was slightly different to that of sugarcane bagasse. The highest yield of TRS was obtained at run order 8 for acid (15.6 gL⁻¹) and run order 10 for hot water (17.98 gL⁻¹) pretreatment respectively. Irrespective of biomass type, hot water pretreatment process produced more TRS than acid pretreatment process.     

The effect of sequentially electrodeposited Pd and Pt metal-supported graphene oxide on enhanced oxidation of mixed acids from biomass production

This work aims to use mixed acids from biomass production as fuel for low-temperature fuel cells. Graphene oxide (GO) carrying Pt and Pd nanoparticles homogeneously dispersed by electrodeposition was selected as a carbon support for catalyst fabrication for various electrodes to enhance the oxidation of various components of mixed acids (such as formic acid (FA) and acetic acid (AA)). The structure, surface morphology, and elemental composition of the prepared catalysts were also broadly characterized. In all cases, both noble Pt and Pd in bimetallic catalyst demonstrated that the catalytic ability of them for acid oxidation can be strongly promoted by the appropriate ratio of alloying metal, and the outer layer of Pd and Pt on the electrode affected the oxidation ability of different acid compositions. The results indicate that GO/2Pt2Pd catalysts exhibited high activity with high stability toward formic acid and the mixed acids in the biomass product containing FA and AA at a 12.5:87.5 ratio.     

Insights into biological delignification of rice straw by Trametes hirsuta and Myrothecium roridum and comparison of saccharification yields with dilute acid pretreatment

Rice straw is the most abundant agricultural residue on a global scale and is widely available as feedstock for cellulosic fuel production. However, it is highly recalcitrant to biochemical deconstruction and also generates inhibitors that affect enzymatic saccharification. Rice straw from eastern Arkansas was subjected to dilute acid pretreatment (160 °C, 48 min and 1.0% sulfuric acid) and solid-state fermentation with two lignocellulolytic fungi, Trametes hirsuta and Myrothecium roridum, and their saccharification efficacies were compared. T. hirsuta and M. roridum were tested separately; pretreatment of rice straw with either strain for seven days resulted in 19 and 70% enrichment of its holocellulose content, respectively. However, liquid chromatography analysis of the alkali extracts showed significant differences in cell wall degradation by T. hirsuta and M. roridum. T. hirsuta removed 15% more phenolic compounds and 38% more glucan than M. roridum, while M. roridum removed 77% more xylan than T. hirsuta. Fungal and dilute acid pretreated biomass was then hydrolyzed using Accellerase^® 1500, a saccharification cocktail. Saccharification efficiency of M. roridum was 37% higher than that of dilute acid pretreatment of rice straw, requiring 8% lower enzyme loading and 50% shorter enzymatic hydrolysis duration. Alkali extraction of fungal pretreated biomass also yielded 10–15 g kg⁻¹ of acid precipitable polymeric lignin (APPL), which is a valuable co-product for biorefineries. In comparison to dilute acid pretreatment, fungal pretreatment could be a cost-effective alternative for the degradation of recalcitrant biomass, such as rice straw.     

Solid acid mediated hydrolysis of biomass for producing biofuels

Solid acid catalysts, which have favorable characteristics such as efficient activity, high selectivity, long catalyst life and ease in recovery and reuse, have great potential for efficiently transforming lignocellulosic biomass into biofuels and can replace many conventional liquid acids for hydrolysis and pretreatment. This work briefly introduces conventional biomass pretreatment and hydrolysis techniques, and reviews in detail the characteristics of biomass hydrolysis for five types of solid acid catalysts grouped as H-form zeolites, transition-metal oxides, cation-exchange resins, supported solid acids and heteropoly compounds. Carbonaceous solid acid (CSA) catalysts are considered as the most promising catalyst for cellulose hydrolysis, since they provide good access of reactants to the acidic sites of SO₃H groups. High glucose yields of up to 75% with 80% selectivity have been achieved at 150 °C for 24 h with CSA. However, separation of CSA from un-hydrolyzed cellulose residues after hydrolysis needs further research since these catalysts have similar physical and chemical properties to the residues. Use of functionalized CSA catalysts that contain paramagnetic groups is one method to improve CSA separation and reuse. Suggestions are given for promoting catalytic efficiency for each kind of solid acid catalysts. Methods to promote reactions or increase selectivities such as microwave, ultrasonication and nanotechnology are introduced. Finally, we highlight a recent strategy that exploits acid-functionalized paramagnetic nanoparticles suitable for cellulose hydrolysis, and address new opportunities for the use of solid acid catalysts.     

Rapid fabrication of Cu/Pd nano/micro-particles porous-structured catalyst using hydrogen bubbles dynamic template and their enhanced catalytic performance for formic acid electrooxidation

In this work, a self-supporting Pd–Cu bimetallic film with 3D porous structure was electrodeposited at the surface of glassy carbon electrode (GCE) using a facile double-template fabrication process, including hydrogen bubble templating method and galvanic replacement reaction, and its performance investigated as a catalyst for formic acid oxidation (FAO). The structure of the Cu/Pd porous film was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The electrocatalytic activity of the as-prepared catalysts with high surface areas were evaluated in sulfuric acid solution containing 1 M formic acid using cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The Cu/Pd porous structure exhibited significantly high current densities of formic acid oxidation compared to the Cu/Pd particles film catalyst. The effects of galvanic replacement time and concentration of formic acid on the catalytic activity of as-prepared electrode for FAO were comparatively investigated.     

Enhanced enzymatic conversion with freeze pretreatment of rice straw

Production of bioethanol by the conversion of lignocellulosic waste has attracted much interest in recent years, because of its low cost and great potential availability. The pretreatment process is important for increasing the enzymatic digestibility of lignocellulosic materials. Enzymatic conversion with freeze pretreatment of rice straw was evaluated in this study. The freeze pretreatment was found to significantly increase the enzyme digestibility of rice straw from 48% to 84%. According to the results, enzymatic hydrolysis of unpretreated rice straw with 150 U cellulase and 100 U xylanase for 48 h yielded 226.77 g kg⁻¹ and 93.84 g kg⁻¹ substrate-reducing sugars respectively. However, the reducing sugar yields from freeze pretreatment under the same conditions were 417.27 g kg⁻¹ and 138.77 g kg⁻¹ substrate, respectively. In addition, hydrolyzates analysis showed that the highest glucose yield obtained during the enzymatic hydrolysis step in the present study was 371.91 g kg⁻¹ of dry rice straw, following pretreatment. Therefore, the enhanced enzymatic conversion with freeze pretreatment of rice straw was observed in this study. This indicated that freeze pretreatment was highly effective for enzymatic hydrolysis and low environmental impact.     

Sugarcane hybrids with original low lignin contents and high field productivity are useful to reach high glucose yields from bagasse

Five sugarcane hybrids plus a reference material were evaluated according to the glucose yields obtained after alkaline-sulfite pretreatment and enzymatic hydrolysis. Sugarcane hybrids with varied original chemical compositions were used to assess how contrasting samples might influence the integrated pretreatment and hydrolysis process. The hydrolysis efficiency of six samples treated at three different chemical loads, suggested that lignin and hemicellulose removals during the pretreatment were not the single factor necessary to reach high cellulose conversion levels in the enzymatic hydrolysis step. Pretreated samples with the highest total acid contents (mainly sulfonic acids) were also the most digestible materials. The glucose yields were heavily dependent not only on the digestibility of the pretreated materials but also on the field productivity of the plants. One of the hybrids, presenting high glucan yields after pretreatment and high digestibility, produced low glucose yields because it presented very low biomass productivity. In contrast, one of the hybrids that presented low glucan yield after pretreatment, but was highly digestible and presented high biomass productivity, provided the highest glucose yields in the data set, producing 4192 and 5629 kg of glucose per hectare after enzymatic hydrolysis for 24 h and 72 h, respectively.     

Effect of reaction parameters on the catalytic transesterification of cottonseed oil using silica sulfuric acid

Transesterification of refined cottonseed oil was studied in the presence of silica sulfuric acid as a new heterogeneous solid acid catalyst to overcome the drawbacks of homogeneous alkali and acid catalysts. The effect of various reaction parameters, such as oil to methanol ratio, reaction temperature, reaction time, and catalyst amount, was investigated. The highest methyl ester conversion was obtained at 373 K using 5% catalyst amount and 1:20 methanol ratio within 8 h. Silica sulfuric acid was found to be a promising catalyst for cleaner biodiesel production without tedious post treatments for the product purification.     

Effect of phosphoric acid and acetic acid addition on the hydrogen evolution using Ni based catalyst prepared in ethanol,methanol, and water solvents

Ni-based catalysts were synthesized in water, methanol and ethanol solvents by chemical reduction with sodium borohydride (NaBH₄). The obtained catalyst for the first time was used to catalyze the NaBH₄ hydrolysis reaction with phosphoric acid and acetic acid including different concentrations. The maximum hydrogen production rates obtained in the hydrolysis reaction including 0.5 M phosphoric acid and 0.1 M acetic acid of the Ni-based catalyst prepared in ethanol solvent were 5214 and 3650 ml g^?1 min^?1, respectively.     

Bioethanol production using genetically modified and mutant wheat and barley straws

To improve the performance of wheat and barley straws as feedstocks for ethanol biorefining, the genetic modifications of down regulating Cinnamoyl-CoA reductase and low phytic acid mutation have been introduced into wheat and barley respectively. In this study, total 252 straw samples with different genetic background and location were collected from the field experiment based on a randomized complete block design. The fiber analysis (neutral detergent fiber, acid detergent fiber, and acid detergent lignin) indicated that there were no significant differences between modified and wild type straw lines in terms of straw compositions. However, the difference did exist among straw lines on fiber utilization. 16 straw samples were further selected to conduct diluted acid pretreatment, enzymatic hydrolysis and fermentation. The data indicated that the phytic acid mutant and transgenic straws have changed the fiber structure, which significantly influences their hydrolysibility. These results may lead to a possible solution of mutant or genetic modified plant species that is capable to increase the hydrolysibility of biomass without changing their compositions and sacrificing their agronomy performance.     

Catalytic activity,stability and impedance behavior of PtRu/C,PtPd/C and PtSn/C bimetallic catalysts toward methanol and formic acid oxidation

PtRu, PtPd and PtSn with weight ratios of (2:1) on carbon black (Vulcan XC-72) supported bimetallic catalysts were prepared by using microwave method via chemically reduction of H₂PtCl₆·6H₂O, RuCl₃, PdCl₂ and SnCl₂·2H₂O precursors with ethylene glycol (EG). These prepared catalysts were systematically investigated and obtained results were compared with commercial Pt black, PtRu black catalysts and with each other. The catalysts were characterized with XRD, ICP-MS, EDS and TEM. The electrocatalytic activities, stability and impedance of the catalysts were investigated in sulfuric acid/methanol and sulfuric acid/formic acid mixtures using electrochemical measurements. The results showed that PtSn/C catalyst showed comparable activity and durability with commercial Pt/C catalyst toward methanol oxidation. The synthesized PtRu/C catalyst was found to completely oxidize methanol and it showed more catalytic activity than commercial PtRu catalyst. Bimetallic PtPd/C catalyst gave better activity than both commercial Pt black and synthesized Pt/C catalyst for oxidation of formic acid. Higher electrochemical active surface areas were obtained with supported bimetallic catalysts.     

吸附树脂在秸秆稀酸水解液脱毒中的应用研究进展

秸秆稀酸水解过程会产生甲酸、乙酸、乙酰丙酸、糠醛、酸溶木质素等副产物,其存在会对后续微生物发酵过程产生严重的负面影响。因此,秸秆稀酸水解液的脱毒处理是必不可少且重要的环节。本文从秸秆稀酸水解液中发酵抑制物的产生、类型、抑制机理和稀酸水解液脱毒方法进行综述,重点介绍了最具有工业应用前景的脱毒技术——吸附树脂在秸秆稀酸水解液脱毒中的应用进展。     

Synthesis of low-cost catalyst NiO(111) for CO2 hydrogenation into short-chain carboxylic acids

Reducing gaseous carbon dioxide to valuable chemicals and fuels by using gaseous hydrogen can decrease the concentration of greenhouse gases that contribute to global warming. Carbon dioxide conversion into fuels such as methane, methanol, and formic acid is a good hydrogen-storage method. In this paper, a comparative study of CO₂ conversion into formic and acetic acids on alumina-supported nickel oxide with and without the presence of carbon is reported. NiO (111) with high surface area was synthesized through a simple and one-pot fusion solid-state method at 550 °C and 700 °C. The synthesized catalysts were tested in carbon dioxide hydrogenation reaction in a batch slurry reactor at 130 °C and under mild pressure. Interestingly, the optimum condition of the reaction also successfully produced C₂ carboxylic acid in significant amounts. The highest levels of formic acid and acetic acid production were 8.13 and 7.63 mmol/L, respectively.     

A thermodynamic equilibrium analysis of hydrogen and synthesis gas production from steam reforming of acetic acid and acetone blends as bio-oil model compounds

Thermodynamic analysis of steam reforming of blends of two model oxygenates, acetic acid and acetone, representing carboxylic acids and ketones in bio-oil is performed to investigate the effects of their potential interactions on hydrogen yield, synthesis gas composition and progress of reaction network. The results show that both acetic acid and acetone reach complete conversion at all operating conditions. Higher S/C molar ratio results in higher H₂ and CO₂ yields for both acetic acid and acetone. With the increase in pressure, H₂ and CO yields are diminished whereas CH₄ and CO₂ yields are enhanced. H₂ and CO₂ yields increase with the decrease in acetone concentration in the feed blend. CO and CH₄ production are affected adversely for acetic acid rich blends. The maximum H₂ yield values are 75.54%, 78.34%, 80.09%, 81.78% and 84.17% at 700 °C for acetic acid/acetone blends of 0.0/1.0, 0.3/0.7, 0.5/0.5, 0.7/0.3 and 1.0/0.0, respectively.     

Evaluation of dilute acid and alkaline pretreatments,enzymatic hydrolysis and fermentation of napiergrass for fuel ethanol production

Napiergrass (Pennisetum purpureum Schum.) is a promising low cost raw material which does not compete with food prices, has attractive yields and an environmentally friendly farming. Dilute sulfuric acid pretreatment of napiergrass was effective to obtain high yields of sugars and low level of degradation by-products from hemicellulose. Detoxification with Ca(OH)₂ removed inhibitors but showed sugars loss. An ethanol concentration of 21 g/L after 176 h was found from the hydrolyzate using Pichia stipitis NBRC 10063 (fermentation efficiency 66%). An additional alkaline pretreatment applied to the solid fraction remaining from the diluted acid pretreatment improved the lignin removal. The highest cellulose hydrolysis values were found with the addition of β-glucosidase and PEG 6000. The simultaneous hydrolysis and fermentation of the cellulosic fraction with Saccharomyces cerevisiae, 10% (w/v) solid concentration, β-glucosidase and PEG 6000, showed the highest ethanol concentration (24 g/L), and cellulose hydrolysis values (81%). 162 L ethanol/t of dry napiergrass were produced (overall efficiency of 52%): 128 L/t from the cellulosic fraction and 34 L/t from the hemicellulosic fraction.     

Influence of alkali metal modification and reaction conditions on the catalytic activity and stability of Ni containing smectite-type material for steam reforming of acetic acid

A Ni incorporated mesoporous smectite-like material, SM(Ni), was modified by various alkali metals, such as, Li, Na, K, Rb or Cs, and tested for the steam reforming of acetic acid as a model compound of aqueous phase of bio-oil derived from biomass pyrolysis. Initial conversion of acetic acid and concentration of H₂ produced are drastically enhanced by the modification with these alkali metals. 1.0 wt% K-modified SM(Ni) catalyst exhibits the highest activity among the modified SM(Ni) materials tested. Addition of K promotes the reduction of Ni species incorporated in the smectite, yielding more metallic Ni species than in the original SM(Ni) sample. Therefore, the K-modified SM(Ni) catalyst gives higher initial activity compared with the original smectite catalyst. However, these modified materials lose their activities due to carbon deposition on their surface during the course of reaction, similar to the original SM(Ni). The influence of reaction conditions, such as O₂ or H₂ addition, steam to carbon ratio (S/C) and reaction temperature, was also investigated. Higher and more stable activity was obtained with unmodified SM(Ni) catalyst at a high reaction temperature of 973 K and at an S/C ratio of 3.3.     

Dilute mixed-acid pretreatment of sugarcane bagasse for ethanol production

Integral utilisation of bagasse is a high priority for the diversification of the sugarcane industry. The application of a biorefinery philosophy to bagasse utilisation requires its fractionation into its main components: cellulose, hemicelluloses and lignin. The first stage in that process is the pretreatment, in which a considerable part of hemicelluloses is solubilised, and cellulose is activated towards enzymatic hydrolysis. In this work, a pretreatment method using a mixture of sulfuric and acetic acid is investigated. Two different solid-to-liquid ratios (1.5:10 and 1:10) were used in the pretreatment. Both conditions efficiently hydrolysed the hemicelluloses giving removals above 90%. The extractive components were also effectively solubilised, and lignin was only slightly affected. Cellulose degradation was below 15%, which corresponded to the low crystallinity fraction. The analysis of the morphology of pretreated bagasse confirmed the results obtained in the chemical characterization.     

Characterization of cell wall structure in dilute acid-pretreated biomass by confocal Raman microscopy and enzymatic hydrolysis

The chemical and ultrastructural properties of cell walls were investigated to determine the effect of dilute acid pretreatment on the hydrolysis of lignocellulosic biomass. Confocal Raman microscopy was used to gain a clear understanding of how dilute acid pretreatments destroy lignocellulosic cell walls. Total fermentable sugar (glucose and xylose) was high in oxalic acid hydrolysate (26.18 g/L) compared to that in sulfuric acid hydrolysate (24.34 g/L). Chemical composition of the pretreated biomass differed slightly according to the acid catalyst used. Oxalic acid pretreatment was effective for enzymatic hydrolysis, with 29.46 g/L of total fermentable sugar after 96 h. Optical microscopy showed that dilute acid pretreatment significantly changed cell wall structure, and broken and crushed cell walls could be clearly seen during pretreatment. Based on confocal Raman peak intensity, the ratio of lignin/cellulose [I(1600)/I(900)] was low for oxalic acid-pretreated biomass compared to sulfuric acid-pretreated biomass.