Magnetic core–shell Fe3O4@C-SO3H nanoparticle catalyst for hydrolysis of cellulose

Catalytic hydrolysis of cellulose over solid acid catalysts is one of efficient pathways for the conversion of biomass into fuels and chemicals. High catalytic activity and easy separation from reaction media are two important factors for evaluating the performance of the solid acid catalysts for the cellulose hydrolysis. In this study, we report a core–shell Fe₃O₄@C-SO₃H nanoparticle with a magnetic Fe₃O₄ core encapsulated in a sulfonated carbon shell, as recyclable catalyst for the hydrolysis of cellulose. The sulfonated carbon shell shows a good activity, presenting 48.6 % cellulose conversion with 52.1 % glucose selectivity under the moderate conditions of 140 °C after 12 h reaction. Importantly, the magnetic Fe₃O₄ core makes the catalysts easily separated from reaction mixtures by using the externally applied magnetic field. In addition, the Fe₃O₄@C-SO₃H nanoparticle catalyst shows a high stability in the activity and magnetization during recycling tests, suggesting it a promising solid acid catalyst for the hydrolysis of cellulose.     

磁性碳基磺酸化固体酸催化剂的制备及其催化水解纤维素

以纤维素和硝酸铁为原料,发烟硫酸为磺酸化试剂,采用热解法合成了磁性碳基磺酸化固体酸催化剂(Fe/C-SO3H).利用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、傅里叶变换红外(FT-IR)光谱仪和振动样品磁强计(VSM)等手段对催化剂进行了表征,评价了催化剂在纤维素水解反应中的催化活性.结果表明,Fe是以γ-Fe2O3的形式存在于碳本体中,催化剂呈现超顺磁性.对于纤维素的水解反应,在优化条件下,纤维素的转化率可达40.6%.此外,催化剂可稳定分散于反应体系中,并在外加磁场作用下可快速与反应体系分离.但催化剂重复使用时催化活性有所下降,其失活原因经初步认定是由于表面部分磺酸基团在反应过程中脱落.     

Well defined thermostable cellulose nanocrystals via two-step ionic liquid swelling-hydrolysis extraction

Cellulose nanocrystals were prepared from cotton fibers by a two-stage method involving ionic liquid swelling treatment followed by hydrolysis under mild acid conditions. Controlled swelling of cellulosic fibers was achieved in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) at 80 °C, while avoiding extensive dissolution of crystalline regions. Since the accessibility of the substrate was considerably enhanced, the hydrolysis occurred even under mild conditions, using up to 60 times less sulfuric acid than the traditional extraction methods based on concentrated sulfuric acid. The effects of process parameters on nanoparticle morphology, composition and stability were investigated. The individual rod-like nanocrystals, observed under field emission gun scanning electron microscopy, exhibited an average diameter of around 20 nm and a length ranging from 150 to 350 nm. According to X-ray photoelectron spectroscopy and thermogravimetric analysis, the surface of the so-extracted nanoparticles proved to be deprived of contaminating sulfate groups leading to significantly higher thermal stability with respect to cellulose nanocrystals extracted by traditional method in concentrated sulfuric acid.     

生物质炭基固体酸催化剂的制备

 以生物质木粉为原料, 采用炭化-磺化法制备了炭基固体酸催化剂, 并用于油酸与甲醇的酯化反应, 考察了制备条件对炭基固体酸催化剂活性的影响. 采用 X 射线衍射、红外光谱、热重分析、高分辨透射电子显微镜及元素分析等手段对催化剂进行了表征. 结果表明, 由生物质木粉制备的炭基固体酸催化剂具有较高催化酯化反应活性, 在 400 oC 下炭化 0.5 h, 135 oC 下磺化 1 h 制备的炭基固体酸催化剂在精馏分水连续酯化装置中催化油酸与甲醇的酯化反应 2 h 时, 酯化转化率达到 96%. 采用炭化-磺化法制备的生物质炭基固体酸催化剂具有蠕虫状的无序乱层炭结构, 磺酸基 (－SO3H) 含量高达 13.25%, 并且在 220 oC 以下时具有良好的热稳定性.     

Preparation of cellulose I nanowhiskers with a mildly acidic aqueous ionic liquid: reaction efficiency and whiskers attributes

Cellulose I nanowhiskers were prepared in relatively high yield (48 ± 2 %) by single-stage hydrolysis of microcrystalline cellulose with an aqueous solution of 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO₄). This reaction occurred under mildly acidic reaction conditions with an [H⁺]/[AGU] ratio of 0.24 mol/mol, i.e., 2 orders of magnitude lower than with concentrated sulfuric acid. The nanowhiskers exhibited small width and width distribution and also smaller length than nanowhiskers obtained with concentrated acid. With a relatively low content of sulfur they also exhibited higher thermal stability than whiskers obtained with concentrated sulfuric acid. The lower solvating power of the aqueous ionic liquid compared to that of concentrated sulfuric acid likely contributes to the greater hydrolysis efficiency in the present system.     

Selective hydrolysis of cellulose for the preparation of microcrystalline cellulose by phosphotungstic acid

Microcrystalline cellulose (MCC), prepared from natural cellulose through acid hydrolysis, has been widely used in the food, chemical and pharmaceutical industries because of its high degree of crystallinity, small particle size and other characteristics. Being different from conventional mineral acids, phosphotungstic acid (H₃PW₁₂O₄₀, HPW) was explored for hydrolyzing cellulose selectively for the preparation of MCC in this study. Various reaction parameters, such as the acid concentration, reaction time, temperature and solid-liquid ratio, were optimized. Rod-like MCC was obtained with a high yield of 93.62 % and also exhibited higher crystallinity and narrower particle diameter distribution (76.37 %, 13.77–26.17 μm) compared with the raw material (56.47 %, 32.41–49.74 μm) at 90 °C for 2 h with 58 % (w/w) HPW catalyst and a solid-liquid radio of 1:40. Furthermore, HPW can easily be extracted and recycled with diethyl ether for four runs without affecting the quality of the MCC products. The technology of protecting the crystalline region while selectively hydrolyzing the amorphous region of cellulose as much as possible by using HPW is of great significance. Due to the strong Brønsted acid sites and highest activity in solid heteropoly acid, the use of effective homogeneous HPW may offer an eco-friendly and sustainable way to selectively convert fiber resources into chemicals in the future.     

Synthesis and acid catalysis of cellulose-derived carbon-based solid acid

SO₃H-bearing amorphous carbon, prepared by partial carbonization of cellulose followed by sulfonation in fuming H₂SO₄, was applied as a solid catalyst for the acid-catalyzed hydrolysis of β-1,4 glucan, including cellobiose and crystalline cellulose. Structural analyses revealed that the resulting carbon material consists of graphene sheets with 1.5 mmol g^?1 of SO₃H groups, 0.4 mmol g^?1 of COOH, and 5.6 mmol g^?1 of phenolic OH groups. The carbon catalyst showed high catalytic activity for the hydrolysis of β-1,4 glycosidic bonds in both cellobiose and crystalline cellulose. Pure crystalline cellulose was not hydrolyzed by conventional strong solid Brønsted acid catalysts such as niobic acid, Nafion^® NR-50, and Amberlyst-15, whereas the carbon catalyst efficiently hydrolyzes cellulose into water-soluble saccharides. The catalytic performance of the carbon catalyst is due to the large adsorption capacity for hydrophilic reactants and the adsorption ability of β-1,4 glucan, which is not adsorbed to other solid acids.     

煤化程度对煤基固体酸结构及其水解纤维素性能的影响

利用煤具有缩合芳环、脂肪侧链及含氧官能团的结构特点，采用不同煤化程度的煤为碳源，在不同炭化温度下制备了煤基固体酸催化剂（CSA）。通过XRD、FT-IR、¹³C NMR对催化剂结构进行了表征。以还原糖和葡萄糖的产率为考察指标，探讨了煤化程度和炭化温度对煤基固体酸非均相催化水解纤维素的影响。结果表明，煤作为碳源具有传统碳源所不具备的结构优势，煤基固体酸碳层片上除含有磺酸基、酚羟基和羧基外，还含有传统碳基固体酸不具备的桥键（-O-、-CH₂-）和侧链（-CH₃、-OCH₃、-CH₂CH₃）。除磺酸基外，其余均由煤的结构演化而来。随着炭化温度的升高，催化剂的芳香度增大、活性基团的种类和数量减少、磺酸基密度逐渐下降，且随着煤化程度增加，煤基固体酸结构可调性降低，所需要的最佳炭化温度也逐渐降低。不同种类的煤基固体酸在水解纤维素过程中表现出了较高的活性，其中，霍林河煤基固体酸的活性最高。水解活性受催化剂芳香片层大小及堆叠高度、片层之间桥键和磺酸基密度等因素的影响，是众多活性基团协同作用的结果。     

Cellulose hydrolysis catalyzed by highly acidic lignin-derived carbonaceous catalyst synthesized via hydrothermal carbonization

Acidic carbonaceous solids were synthesized from mass pine alkali lignin via hydrothermal carbonization followed by sulfonation. Hydrothermal carbonization of lignin in the presence of acrylic acid (LAHC-SO₃H) provided many more carboxylic groups than that in the absence of acrylic acid, allowing subsequent sulfonation to produce a highly active and stable catalyst for cellulose hydrolysis in the [BMIM]Cl-H₂O solvent system. The hydrochar and catalyst were characterized using field emission scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, thermal gravimetric analysis, Fourier transform infrared spectrometer, Brunauer–Emmett–Teller and acid–base titration. Results showed that a high acid content of 5.48 mmol/g, including carboxylic group (2.85 mmol/g), phenolic hydroxyl group (1.05 mmol/g) and sulfonic acid group (1.58 mmol/g), contributed significantly to the highly efficient hydrolysis of cellulose. Further, it was found that addition of trace water in [BMIM]Cl was favorable to cellulose hydrolysis. The highest yield (75.4%) of total reducing sugar (TRS) obtained in [BMIM]Cl-H₂O at a mass ratio of 100:1 was more than twice that (36.1%) achieved in [BMIM]Cl without water; the corresponding reaction conditions were 50 mg of microcrystalline cellulose, 30 mg of catalyst, 1.0 g of [BMIM]Cl, 10 mg of H₂O, reaction temperature of 130 °C and reaction time of 2 h. Furthermore, the TRS yield with 5 cycles for LAHC-SO₃H was higher than 68.1%, and the catalytic activity of catalyst could be fully recovered (74.0% of TRS yield) easily by regeneration.     

Influence of ionic-liquid incubation temperature on changes in cellulose structure,biomass composition,and enzymatic digestibility

Varying ionic liquid, 1-ethyl 3-methyl imidazolium acetate, pretreatment incubation temperature on lignocellulosic biomass substrates, corn stover, switchgrass and poplar, can have dramatic effects on the enzymatic digestibility of the resultant regenerated biomass. In order to delineate the chemical and physical changes resulting from the pretreatment process and correlate changes with enzymatic digestibility, X-ray powder and fiber diffraction, ¹³C cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy, and compositional analysis was completed on poplar, corn stover and switchgrass samples. Optimal pretreatment incubation temperatures were most closely associated with the retention of amorphous substrates upon drying of regenerated biomass. Maximal glucan to glucose conversion for 24 h enzyme hydrolysis was observed for corn stover, switchgrass and poplar at ionic liquid incubation temperatures of 100, 110 and 120 °C, respectively. We hypothesize that effective pretreatment temperatures must attain lignin redistribution and retention of xylan for optimal enzyme digestibility.     

Enzymatic Hydrolysis and Succinic Acid Fermentation from Steam-Exploded Corn Stalk at High Solid Concentration by Recombinant Escherichia coli

Steam-exploded corn stalk biomass was used as the substrate for succinic acid production via lignocellulose enzymatic hydrolysis and fermentation. Succinic acid fermentation was investigated in Escherichia coli strains overexpressing cyanobacterium Anabaena sp. 7120 ecaA gene encoding carbonic anhydrase (CA). For the washed steam-exploded corn stalk at 30 % substrate concentration, i.e., 30 % water-insoluble solids (WIS), enzymatic hydrolysis yielded 97.5 g/l glucose solution and a cellulose conversion of 73.6 %, thus a high succinic acid level up to 38.6 g/l. With the unwashed steam-exploded corn stalk, though a cellulose conversion of 71.2 % was obtained in hydrolysis at 30 % solid concentration (27.9 % WIS), its hydrolysate did not ferment at all, and the hydrolysate of 25 % solid loading containing 3.8 g/l acetic acid and 168.2 mg/l furfural exerted a strong inhibition on succinic acid production.     

磺化水热碳催化乙酰丙酸酯化生成戊酮酸乙酯(英文)

The synthesis of carbon-based, heterogeneous sulphonic catalysts for the production of levulinate esters. Hydrothermal treatment at moderated temperatures was employed to generate highly functional carbonaceous materials, referred to as hydrothermal carbons (HTCs), from both glucose, cellulose and rye straw. The products were sulfonated to generate solid acid-catalysts. Characterisation of the as-synthesised materials as well as catalyst activity tests were performed. SEM images indicate the micrometre-sized particles present in both HTCs were largely unaffected by sulfonation, although cellulose-derived HTC displayed signs of inadequate hydrolysis. FT-IR spectroscopy and elemental analysis confirmed successful incorporation of sulphonic groups. 13C solid state NMR, in addition to TGA, elucidated the carbons’ structural composition and supported the common-ly-proposed hydrothermal carbonisation mechanism. Finally, the catalysts were tested via levulinic acid-ethanol esterification and gave high conversion and ester-selectivities ( 90%).     

Isolation and characterization of cellulose nanocrystals from cloth hairs and evaluation of their compatibility with PLLA

Cellulose nanocrystals were successfully isolated from cloth hairs using phosphoric acid. The yields, degree of polymerization, morphology, average particle size, crystallinity, chemical structure, and thermal stability of the prepared nanocrystals were investigated. The results demonstrated that yields and degree of polymerization decreased with the increase of concentration of phosphoric acid due to preferential degradation of amorphous cellulose, resulting in high thermal stability and crystallinity. Morphological analysis revealed that hydrolysis was more homogeneous with increasing acid concentration. In comparison with the cellulose nanocrystals prepared with 6.5, 8.0, and 9.5 M H₃PO₄, those prepared with 11.0 M H₃PO₄ had the most uniform particle sizes. Moreover, the nanocrystals had important influence on the crystallization of semicrystalline polymer.     

Catalytic conversion of lignocellulosic biomass to fine chemicals and fuels

Lignocellulosic biomass is the most abundant and bio-renewable resource with great potential for sustainable production of chemicals and fuels. This critical review provides insights into the state-of the-art accomplishments in the chemocatalytic technologies to generate fuels and value-added chemicals from lignocellulosic biomass, with an emphasis on its major component, cellulose. Catalytic hydrolysis, solvolysis, liquefaction, pyrolysis, gasification, hydrogenolysis and hydrogenation are the major processes presently studied. Regarding catalytic hydrolysis, the acid catalysts cover inorganic or organic acids and various solid acids such as sulfonated carbon, zeolites, heteropolyacids and oxides. Liquefaction and fast pyrolysis of cellulose are primarily conducted over catalysts with proper acidity/basicity. Gasification is typically conducted over supported noble metal catalysts. Reaction conditions, solvents and catalysts are the prime factors that affect the yield and composition of the target products. Most of processes yield a complex mixture, leading to problematic upgrading and separation. An emerging technique is to integrate hydrolysis, liquefaction or pyrolysis with hydrogenation over multifunctional solid catalysts to convert lignocellulosic biomass to value-added fine chemicals and bio-hydrocarbon fuels. And the promising catalysts might be supported transition metal catalysts and zeolite-related materials. There still exist technological barriers that need to be overcome (229 references).     

Poly(Amic Acid)-Modified Biomass of Baker’s Yeast for Enhancement Adsorption of Methylene Blue and Basic Magenta

In this study, poly(amic acid)-modified biomass was prepared to improve the adsorption capacities for two cationic dyes, methylene blue and basic magenta. X-ray photoelectron spectroscopy and potentiometric titration demonstrated that a large number of imide, amine, and carboxyl groups were introduced on the biomass surface, and the concentrations of these functional groups were calculated to be 0.27, 1.08, and 1.08 mmol g^?1 by using the first derivative method. According to the Langmuir equation, the maximum uptake capacities (q _m) for methylene blue and basic magenta were 680.3 and 353.4 mg g^?1, respectively, which were 13- and sevenfold than that obtained on the unmodified biomass. Adsorption kinetics study showed that the completion of the adsorption process needed only 40 min, which is faster than the common sorbent such as activated carbon and resin. Experimental results showed that pH and ionic strength had little effect on the capacity of the modified biomass, indicating that the modified biomass had good potential for practical use.     

Nanocomposite films based on cellulose reinforced with nano-SiO2: microstructure, hydrophilicity, thermal stability, and mechanical properties

Microcrystalline cellulose/nano-SiO₂ composite films have been successfully prepared from solutions in ionic liquid 1-allyl-3-methylimidazolium chloride by a facile and economic method. The microstructure and properties were investigated by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy, transmission electron microscopy, water contact angle, thermal gravimetric analyses, and tensile testing. The results revealed that the well-dispersed nanoparticles exhibit strong interfacial interactions with cellulose matrix. The thermal stability and tensile strength of the cellulose nanocomposite films were significantly improved over those of pure regenerated cellulose film. Furthermore, the cellulose nanocomposite films exhibited better hydrophobicity and a lower degree of swelling than pure cellulose. This method is believed to have potential application in the field of fabricating cellulose-based nanocomposite film with high performance, thus enlarging the scope of commercial application of cellulose-based materials.     

Sol–gel preparation and characterization of Ag and Mg co-doped nano TiO<Subscript>2</Subscript>: efficient photocatalytic degradation of C.I. Acid Red 27

In this study, we successfully prepared pure, mono-doped, and Ag, Mg co-doped TiO₂ nanoparticles using the sol–gel method, with titanium tetraisopropoxide as the Ti source. The prepared samples were characterized by X-ray powder diffraction (XRD), specific surface area and porosity (BET and BJH) measurement, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence, and energy dispersive X-ray spectroscopy techniques. The XRD data showed that the prepared nanoparticles had the same crystals structures as the pure TiO₂. Also, DRS results indicated that the band gap of co-doped photocatalyst was smaller than that of the monometallic and undoped TiO₂ and that there was a shift in the absorption band towards the visible light region. Furthermore, the photocatalytic activity of the prepared catalysts was evaluated by the degradation of C.I. Acid Red 27 in aqueous solution under visible light irradiation. The results showed that Ag (0.08 mol%), Mg (0.2 mol%) co-doped TiO₂ had the highest photoactivity among all samples under visible light. It was concluded that co-doping of the Ag and Mg can significantly improve the photocatalytic activity of the prepared photocatalysts, due to the efficient inhibition of the recombination of photogenerated electron–hole pairs. The optimum calcination temperature and time were 450 °C and 3 h, respectively.     

Proton Conductor of Propylene Carbonate–Plasticized Carboxyl Methylcellulose–Based Solid Polymer Electrolyte

Carboxyl methylcellulose (CMC) solid polymer electrolytes were prepared by utilizing oleic acid (OA) and different wt.% of propylene carbonate (PC) by using the solution casting technique. An ionic conductivity study of the films was done by using impedance spectroscopy. The highest ionic conductivity gained is 2.52 × 10^?7 S cm^?1 at ambient temperature for sample CMC-OA-PC 10 wt.%. From transference number measurement (TNM), the value of cation diffusion coefficient, D₊, and ionic mobility, μ₊, was higher than the value of anion diffusion coefficient, D_?, and ionic mobility, μ_?. Thus, the results prove that the present samples were proton conductors.     

Consecutive preparation of hydrochar catalyst functionalized in situ with sulfonic groups for efficient cellulose hydrolysis

Hydrochars in situ functionalized with –SO₃H groups were generated from kenaf core via a low-temperature hydrothermal carbonization process of 105 °C with a consecutive catalysis of H₂SO₄. The micro-morphology of the hydrochars was strongly affected by the sulfuric acid concentration. Sphere-like particles with size varying between 200 nm and 1 μm were obtained when the acid concentration was 52 wt%. Acid density of the hydrochar increased with the H₂SO₄ concentration increasing. The presence of considerable acidic groups of –SO₃H, –COOH, and –OH on the surface of hydrochars was evidenced by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The hydrochar obtained can be used directly for effective catalytic hydrolysis of cellulose without any post-modification. This study proposed a promising sustainable and cost-effective route for facile production of acidic hydrochar from crude plant with tunable properties.     

Effects of Liquid Hot Water Pretreatment on Enzymatic Hydrolysis and Physicochemical Changes of Corncobs

Liquid hot water (LHW) pretreatment is an efficient chemical-free strategy for enhancing enzymatic digestibility of lignocellulosic biomass for conversion to fuels and chemicals in biorefinery. In this study, effects of LHW on removals of hemicelluloses and lignin from corncobs were studied under varying reaction conditions. LHW pretreatment at 160 °C for 10 min promoted the highest levels of hemicellulose solubilization into the liquid phase, resulting into the maximized pentose yield of 58.8% in the liquid and more than 60% removal of lignin from the solid, with 73.1% glucose recovery from enzymatic hydrolysis of the pretreated biomass using 10 FPU/g Celluclast?. This led to the maximal glucose and pentose recoveries of 81.9 and 71.2%, respectively, when combining sugars from the liquid phase from LHW and hydrolysis of the solid. Scanning electron microscopy revealed disruption of the intact biomass structure allowing increasing enzyme’s accessibility to the cellulose microfibers which showed higher crystallinity index compared to the native biomass as shown by x-ray diffraction with a marked increase in surface area as revealed by BET measurement. The work provides an insight into effects of LHW on modification of physicochemical properties of corncobs and an efficient approach for its processing in biorefinery industry.