Hydrolysis of pentosans in bagasse pith

Work has been conducted on the hydrolysis of pentosans in bagasse pith as the first part of a study of the chemistry of bagasse processing aimed at establishing an integrated industry. Bagasse pith is the fine part screened out and discarded as waste during the preparation of raw material for bagasse pulping plant. By using dilute sulphuric acid at a concentration less than 2% by weight and at a temperature lower than 165°C, pith is hydrolysed to pentoses in a yield of 80–90% based on potential pentoses in pith. Hydrolysis of pentosans in pith, within the scope of experiment, seems to be a first order reaction. However, the semi-logarithmic time plot for the hydrolysis of potential pentoses in the residue consists of two straight lines of different slope. This may be explained on the assumption that bagasse pith contains two major fractions of pentosans that are hydrolysed at different rates. Saeman's equation for hydrolysis of wood with sulphuric acid may be adapted to represent dependence of rate constant K on acid concentration C and reaction temperature T in hydrolysis of the two major parts of pentosans in bagasse pith. K₁ = 6.4 × 10⁵C^1.02 exp (?6378/T) K₂ = 10.7C^0.363 exp (- 2826/T)     

羧基化改性纤维素凝胶球的制备和表征

以微晶纤维素为原料,利用NaOH/尿素体系对微晶纤维素进行溶解,得到再生纤维素溶液。采用滴定悬浮的方法制备纤维素水凝胶球,采用2,2,6,6-四甲基哌啶-1-氧基自由基（TEMPO）/NaBr/NaClO选择性氧化体系对纤维素水凝胶球进行氧化处理,获得羧基化改性纤维素水凝胶球,冷冻干燥得到羧基化改性纤维素气凝胶球。研究结果表明：羧基化改性纤维素水凝胶球的含水量为95.64%,吸附4h,亚甲基蓝的吸附量达到6.97mg/g。对羧基化改性纤维素气凝胶球进行傅里叶变换红外光谱（FT-IR）和扫描电子显微镜（SEM）表征分析,在1600cm^-1处出现了CO的伸缩振动峰,TEMPO的选择性氧化对样品起到羧基化改性作用,羧基化改性纤维素气凝胶增加了球形气凝胶的表面通透性,内部仍呈现网络结构,羧基化改性纤维素气凝胶球的密度为0.038g/cm³。     

Improved oxidation resistance of expanded graphite through nano SiC coating

Expanded graphite with nano SiC and amorphous SiC_xO_y coating was successfully prepared through pyrolysing silane coupling agent (SCA), where the grafting of SCA dominated the final products. The results show that mainly amorphous SiC_xO_y coating covers expanded graphite at 1000 °C, regardless of the SCA concentration. In comparison, nano SiC coating can be synthesized at 1200 °C depending on the good dispersion of SCA (with a SCA concentration of 50 vol%). The formed SiC coating contributes to much higher peak oxidation temperature (812.1 °C) than 678.0 °C of the pure expanded graphite. Meanwhile, the oxidation activation energies of expanded graphite are remarkably improved from 149.15 kJ/mol to 176.16 kJ/mol (based on Kissinger method), attributing to the derived nano SiC and SiC_xO_y coating.     

Wet oxidation pretreatment of lignocellulosic residues of sugarcane,rice, cassava and peanuts for ethanol production

Wet oxidation (WO) pretreatment of sugarcane bagasse, rice hulls, cassava stalks and peanut shells was investigated. WO was performed at 195 °C for 10 min, with 2 g kg^?1 of Na₂CO₃ and under either 3 or 12 bar of oxygen. Oxygen pressure and the type of raw material used had a major effect on the fractionation of the materials, formation of sugars and by‐products, and cellulose enzymatic convertibility. Cellulose content in the solid fraction increased after pretreatment of all materials, except rice hulls. The greatest increase, from 361 g kg^?1 to almost 600 g kg^?1, occurred for bagasse. The solubilisation of individual components was different for each material. Bagasse xylan was solubilised to a large extent, and 45.2% of it was recovered as xylose and xylo‐oligosaccharides in the liquid fraction. In the prehydrolysates of rice hulls around 40% of the original glucan was recovered as gluco‐oligosaccharides, due to hydrolysis of starch contained in grain remains. The formation of by‐products was modest for all the materials, but increased with increasing oxygen pressure. The highest yield of acetic acid (34–36 g kg^?1 of raw material) and furfural (0.7–1.8 g kg^?1) occurred for bagasse. The pretreatment enhanced the enzymatic convertibility of cellulose giving the best result (670.2 g kg^?1) for bagasse pretreated at the highest oxygen pressure. However, for the other materials the pretreatment conditions were not effective in achieving cellulose conversions above 450 g kg^?1. Some enzymatic conversion of xylan was observed. Copyright © 2007 Society of Chemical Industry     

Hydrolysis of pentosans in bagasse pith

Work has been conducted on the hydrolysis of pentosans in bagasse pith as the first part of a study of the chemistry of bagasse processing aimed at establishing an integrated industry. Bagasse pith is the fine part screened out and discarded as waste during the preparation of raw material for bagasse pulping plant. By using dilute sulphuric acid at a concentration less than 2% by weight and at a temperature lower than 165°C, pith is hydrolysed to pentoses in a yield of 80–90% based on potential pentoses in pith. Hydrolysis of pentosans in pith, within the scope of experiment, seems to be a first order reaction. However, the semi-logarithmic time plot for the hydrolysis of potential pentoses in the residue consists of two straight lines of different slope. This may be explained on the assumption that bagasse pith contains two major fractions of pentosans that are hydrolysed at different rates. Saeman's equation for hydrolysis of wood with sulphuric acid may be adapted to represent dependence of rate constant K on acid concentration C and reaction temperature T in hydrolysis of the two major parts of pentosans in bagasse pith.      

Grafting of methacrylic acid to loomastate viscose fabric using KMnO4/NaClO2 system

Graft polymerization of methacrylic acid (MAA) to loomstate viscose fabric (greige fabric) using KMnO₄/NaClO₂ system was studied. Residual thiocarbonate and/or sizing materials on the fabric as well as presence of NaClO₂ act in favor of primary radical formation which, in turn, accelerate formation of cellulose macroradicals capable of initiating grafting. The polymerization reaction was studied with respect to polymer yield, graft yield, homopolymer, total conversion, and graft efficiency. The magnitude of each of these characteristics was found to depend upon parameters such as concentrations of KMnO₄, NaClO₂, and MAA as well as liquor ratio, reaction time, and temperature of polymerization. By and large all these parameters enhance the polymerization process with the exception of the liquor ratio. A reaction mechanism for the polymerization reaction is also reported. © 1995 John Wiley & Sons, Inc.     

蔗渣浆制造黏液纤维的研究

<正>在黏液纤维制造中,用蔗渣浆代替木浆作原料,常被人怀疑甚至否定其可能性,其主要根据为草类纤维的形态结构不同於木材纤维,而以天然纤维的形态结构作为对原料适合与否的判断标准。我们认为:黏液丝浆的良好制备条件均应最大限度地破坏了天然纤维的形态结构,主要是细胞壁的组织。後者的存在影响丝光化与黄酸化的反应     

Hydrothermal Solubilization–Hydrolysis–Dehydration of Cellulose to Glucose and 5-Hydroxymethylfurfural Over Solid Acid Carbon Catalysts

Solid acid catalysts based on graphite-like mesoporous carbon material Sibunit were developed for the one-pot solubilization–hydrolysis–dehydration of cellulose into glucose and 5-hydroxymethylfurfural (5-HMF). The catalysts were produced by treating Sibunit surface with three different procedures to form acidic and sulfo groups on the catalyst surface. The techniques used were: (1) sulfonation by H₂SO₄ at 80–250 °C, (2) oxidation by wet air or 32 v/v% solution of HNO₃, and (3) oxidation-sulfonation what meant additional sulfonating all the oxidized carbons at 200 °C. All the catalysts were characterized by low-temperature N₂ adsorption, titration with NaOH, TEM, XPS. Sulfonation of Sibunit was shown to be accompanied by surface oxidation (formation of acidic groups) and the high amount of acidic groups prevented additional sulfonation of the surface. All the Sibunit treatment methods increased the surface acidity in 3–15 times up to 0.14–0.62 mmol g^?1 compared to pure carbon (0.042 mmol g^?1). The catalysts were tested in the depolymerization of mechanically activated microcrystalline cellulose at 180 °C in pure water. The main products 5-HMF and glucose were produced with the yields in the range of 8–22 wt% and 12–46 wt%, respectively. The maximal yield were achieved over Sibunit sulfonated at 200 °C. An essential difference in the composition of main products obtained with solid acid Sibunit carbon catalysts (glucose, 5-HMF) and soluble in water H₂SO₄ catalysts (formic and levulinic acids) as well as strong dependence of the reaction kinetics on the morphology of carbon catalysts argue for heterogenious mechanism of cellulose depolymerization over Sibunit.     

Grafting of N-methylolacrylamide onto flax/polyester fabric using ferrous cellulose thiocarbonate/H2O2 redox system

Graft copolymerization of N-methylolacrylamide onto flax/polyester blend fabric using ferrous cellulose thiocarbonate/H₂O₂ redox system was investigated under different conditions including hydrogen peroxide concentration (1?60 mmol/l), ferrous ammonium sulphate concentration (1?50 mmol/l), N-methylolacrylamide concentration (5?200%, based on weight of sample), polymerization time (10?90 min), temperature (20?50°C), and pH of the medium (1.1?11). The nitrogen content and/or the methylol content were used for calculation of graft yields. Results obtained indicated that graft yields, derived from nitrogen analysis, are higher the greater the H₂O₂ concentration increases till 40 mmol/l, then level off. On the other hand, graft yields derived from methylol content exhibit maximum value at 10 mmol/l H₂O₂. The results indicate also that grafting was highly favoured when it was carried out using 1 mmol/l ferrous ammonium sulphate and pH 4.4 at 30°C for 60 min. The apparent activation energy of the copolymerization reaction amounts to 9.74 kJ/mol. Furthermore, the graft yield increases by increasing N-methylolacrylamide concentration within the range studied. The work was further extended to include a comparison between the polymerization efficiencies of the ferrous cellulose thiocarbonate/H₂O₂ redox system and the ferrous/H₂O₂ redox system in inducing grafting of N-methylolacrylamide onto flax/polyester blend fabric. For this reason, the two systems were studied with respect to graft yield, homopolymer proportion, total conversion, graft efficiency, and homopolymer efficiency.     

Effects of ozone and chlorine dioxide on the chemical properties of cellulose fibers

The effects of ozone and chlorine dioxide on the structure of hardwood cellulose fibers were studied by chemical methods. Chlorine dioxide had very little effect on the cellulose degree of polymerization (DP_v), although 40–50% of the chlorine dioxide charged was consumed. By contrast, ozonation of the cellulosic fibers resulted in a substantial reduction in the cellulose DP_v. Increasing the ozone charge increased the extent of cellulose degradation. At an ozone charge of approximately 3 wt % (20 mol equiv/100 g of fiber), a 40% reduction in DP_v, as measured by cupriethylenediamine viscosity, was observed. A comparison of the cellulose DP_v values obtained for ozonated cellulose fibers reduced with sodium borohydride before the viscosity measurements increased confirmed that the primary reaction of ozone with the cellulose fibers was glycosidic bond cleavage, with only a small amount of cellulose oxidation taking place. A functional group analysis of the ozonated cellulose fibers revealed a slight increase in the amount of carbonyl groups introduced into the fibers. In addition, carbon dioxide was detected, which combined with the lack of change in the carboxyl group content, indicated that the oxidation mechanism likely occurred in a three‐step process: formation of the carbonyl groups, followed by oxidation to carboxyl groups, and finally, decarboxylation resulting in glycosidic bond cleavage. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1219–1223, 2004     

TEMPO及其衍生物制备纳米纤维素及其智能调节方法的研究进展

2,2,6,6-四甲基哌啶氧自由基(TEMPO)共氧化剂体系被广泛应用于选择性氧化纤维素的C6位伯醇羟基。在氧化过程中,纤维素的聚合度大幅度降低,因此被应用于制备纳米纤维素。随着TEMPO/NaClO/NaBr氧化技术的发展成熟,TEMPO/NaClO/NaClO2和4-乙酰胺基-TEMPO/NaClO/NaClO2体系都得到了广泛关注。随着研究的深入,TEMPO及其衍生物氧化体系已经成为一种高效且全pH范围适用的选择性氧化体系。TEMPO/NaClO/NaBr氧化体系在pH范围9～11活性最高,TEMPO/NaClO/NaClO2体系能够应用于pH中性的条件下,4-乙酰胺基-TEMPO/NaClO/NaClO2体系一般的pH使用范围为3.5～6.8。传统的TEMPO氧化过程需要持续手动控制pH恒定,操作繁琐,可控性差,应用缓冲溶液可控制TEMPO氧化过程中pH在一定范围内恒定,从而实现了TEMPO氧化体系的智能控制。文章综述了TEMPO及其衍生物制备纳米纤维素及其智能调节方法的研究进展。     

Flotation separation of pyrite from arsenopyrite in the presence of oxidants

ABSTRACT

Four oxidants, NaClO, KMnO₄, K₂Cr₂O₇, and H₂O₂, were used to promote the flotation separation of pyrite (FeS₂) from arsenopyrite (FeAsS). Ore flotation results indicate that H₂O₂ has the best selectivity for the As-S separation. When H₂O₂ is used, the As content in pyrite concentrate decreases from 2.27% without addition of H₂O₂ to 1.11% with H₂O₂ dosage of 900 g/t, and the pyrite recovery is still high (86.58%). NaClO, KMnO₄, and K₂Cr₂O₇ have poor selectivity for the As-S separation. Cyclic voltammetry measurements by using mineral microelectrodes indicate that H₂O₂ shows selective oxidation effect on arsenopyrite while other three oxidants have no selective oxidation effects on arsenopyrite and pyrite. In the presence of dixanthogen coating on the mineral surface, all the four kinds of oxidants can oxidize dixanthogen to a certain degree. Moreover, the collector coatings on arsenopyrite surface are oxidized more easily than on pyrite.     

Synthesis and studies of egyptian bagasse pith phenol formaldehyde cationic exchangers

The article is concerned with a simple method for preparing cationic resins from polycondensation of Egyptian bagasse pith (as a source of cheap and renewable material) with phenol and paraformaldehyde as a cross-linking agent. Optimum principal reaction conditions of the preparation and properties are determined and compared with resin without bagasse pith content. The Synthesized resins are stable in water, organic solvents, thermal treatment, and mineral acids (1M). The sample having a cation exchange capacity up to 3.92 meq g^?1 of dry resins are being introduced as new cationic exchangers. The synthesized resins are used in the study of the possible separation of univalent cations. The rational thermodynamic equilibrium constants (In K) are calculated for Li⁺ ?Na⁺ exchanges on the resins having a various amount of bagasse pith. The thermodynamic parameters are computed and suitable explanations are described. © 1994 John Wiley & Sons, Inc.     

Synthesis and characterization of maleylated cellulose-<Emphasis Type="Italic">g</Emphasis>-polyacrylamide hydrogel using TiO<Subscript>2</Subscript> nanoparticles under sunlight

Graft polymerization onto the cellulose is one way to produce semisynthetic copolymers and semiconductors were hardly used as initiators. Maleylated cellulose (MC) with different degree of carboxyl groups was synthesized and degree of carboxyl groups was determined using titration method. Then the graft copolymers of acrylamide (AM) on MC were synthesized by titanium dioxide semiconductor photoinitiator in aqueous suspension under sunlight. The effect of different parameters, such as the degree of carboxyl groups, degassing of atmosphere, reactor type, light source, MC/AM ratio, and initiator concentration, was evaluated in the synthesis of graft copolymers. MC with a high degree of carboxyl groups about 2.8 mmol g^?1 was selected for graft photopolymerization. Maximum monomer conversion (55%) for Maleylated cellulose-g-polyacrylamide (MC-g-PAM) was achieved with 0.5 mg TiO₂, MC/AM = 0.056, argon atmosphere, sunlight source, and double quartz tube reactor. The maximum amount of equilibrium swelling (41 g g^?1) was achieved for MC-g-PAM with 34% monomer conversion. The resulting graft copolymers were characterized by FT-IR, SEM, and TGA. Synthesis of MC-g-PAM using TiO₂ nanoparticles (NPs) as the initiator was done successfully that shows the TiO₂ NPs are useable in graft polymerization of acrylamide monomers onto the MC under sunlight.     

Creation of a new material stream from Japanese cedar resources to cellulose nanofibrils

Japanese cedar is one of the most abundant plantation softwoods in Japan, although it is not effectively utilized as a wood resource. Japanese cedar cellulose was isolated and subjected to one-pot catalytic oxidation and reduction with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and NaBH₄, respectively. The TEMPO-oxidized and NaBH₄-reduced Japanese cedar celluloses (TOCs-NaBH₄) had carboxylate content of up to 1.4 mmol/g and viscosity-average degrees of polymerization from 2000 to 3000. The X-ray diffraction patterns of the TOCs-NaBH₄ showed that the crystal widths were ~ 3 nm, indicating that the C6-OH groups present on the crystalline cellulose microfibril surfaces were selectively oxidized to C6-carboxylate groups. When the TOCs-NaBH₄ with carboxylate content of 0.9–1.4 mmol/g were mechanically disintegrated in water, transparent TEMPO-oxidized cellulose nanofibril (TOCN) dispersions were obtained. The lengths of the TOCNs, determined from their atomic force microscopy images, varied from 800 to 1500 nm, depending on the oxidation conditions. The TOCNs prepared from Japanese cedar cellulose have an average of high aspect ratios (> 300), which is greater than that (~ 150) prepared from wood pulp and thus advantageous.     

Effect of carboxyl content on the physicochemical properties and intramolecular water distribution of 6-carboxyl chitooligomer prepared by laccase-TEMPO

6-carboxyl chitooligomer was prepared by degradation of chitosan with H₂O₂ followed by catalytic oxidation in the laccase-2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) system. The TEMPO was used as a single variable to alter the content of introduced carboxyl groups. The resulting oxidation products were analyzed by ion chromatography, scanning electron microscopy, and ¹H low-field NMR. Moisture absorption-retention ability, antioxidation, and thermal stability also were characterized. The results showed that the carboxyl content in the molecules increased with increasing TEMPO. With the addition of 8% TEMPO (mass fraction relative to chitooligomers), the carboxyl content and the oxidation degree of the product reached 4.90 mmol/g and 96.53%, respectively. Under these conditions, it also had the highest ABTS radical cation scavenging ability of 85.47% and improved thermal stability. When the amount of TEMPO was reduced to 2%, the oxidation product had a degree of oxidation of ~50% and showed a unique molecular structure and supreme moisture absorption-retention ability. A higher associated water content was observed inside the molecules where more bound water was locked in the process of moisture absorption. Furthermore, the physicochemical properties of 6-carboxyl chitooligomer were much higher than chitooligomer and oligomeric sodium hyaluronate (HA-Oligo). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47509.     

The Absorption Kinetics of NO into Weakly Acidic NaClO Solution

NO is a major air pollutant from coal-fired power plants. A combined removal of SO₂ and NO is a prospective process. In this paper, the absorption kinetics of NO into weakly acidic NaClO solution was studied in a stirred tank reactor. It was proven that the absorption process occurred under the fast pseudo-mth reaction regime, and the reaction was found to be first-order with respect to both NO and NaClO. When the initial pH value of NaClO solution is 5.5, it has the best performance for NO absorption. The frequency factor and the average activation energy of this reaction were 7.96 × 10⁸ m³/(mol s) and 28.15 kJ/mol, respectively. The absorption rate of NO increased with increasing reaction temperature.     

Regeneration of 4-Chlorophenol Exhausted GAC with a Microwave Assisted Wet Peroxide Oxidation Process

To improve the performance of wet oxidation for the regeneration of GAC, a microwave assisted wet peroxide oxidation process has been applied for the regeneration of 4-chlorophenol exhausted GAC. The effects of various factors including reaction temperature, H₂O₂ dosage, reaction time, and addition of catalyst have been studied. The regeneration improves with the increase in reaction temperature, H₂O₂ dosage, and reaction time. The addition of Cu²⁺ further promotes the regeneration process. Under the conditions of temperature 150°C, H₂O₂ dosage 15 mmol, reaction time 20 min, Cu²⁺ concentration 20 mg/L, the regenerated GAC recovers 93.5% of its adsorption capacity. A nearly complete degradation of 4-chlorophenol in the aqueous phase is observed based on UV-vis and high-performance liquid chromatography spectra studies.     

Sugarcane Bagasse Drying in a Cyclone: Influence of Device Geometry and Operational Parameters

Sugarcane bagasse is becoming more and more commonly used in generating electrical energy, steam, and bioethanol. Drying is important in sugarcane and other types of biomass because it can be used to improve the calorific value and overall energetic use. In this work, sugarcane bagasse was treated by drying in a cyclonic dryer. The influence of the geometry of the device (the conical part of the cyclone) and process parameters (bagasse mass flow rate and temperature) were tested. The modification on the conical part was related to two different angles and with two different inferior outlets (B). Experimental design was carried out for each geometry. The independent variables were the drying agent temperature (35 to 275°C) and the bagasse mass flow rate (0.1 × 10^?2 to 2.9 × 10^?2 kg s^?1). The air flow rate was kept constant at 7.5 × 10^?2 kg s^?1. The dependent variables were moisture reduction (MR) and average particle residence time (t_res) in the cyclonic dryer. For both cyclonic geometries, it was observed that MR was directly proportional to the temperature and inversely proportional to the bagasse mass flow rate. t_res was also inversely proportional to the bagasse mass flow rate. Decreasing B tended to increase tres and MR.     

Exploring the Redox Behavior of La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Mn<Subscript>1−x</Subscript>Al<Subscript>x</Subscript>O<Subscript>3</Subscript> Perovskites for CO<Subscript>2</Subscript>-Splitting in Thermochemical Cycles

Mixed oxides with perovskite structure have been proposed as promising alternative for the solar fuel production via thermochemical redox cycles. For this work, the system La_0.6Sr_0.4Mn_1?xAl_xO₃ (x?=?0 to 0.8) was selected according to its high thermal stability and rapid oxidation kinetics, and the influence of the Al/Mn ratio on the redox properties was investigated. The characterization of the five oxides samples with different Al content confirmed the high redox capacity and the favorable behavior of these materials in consecutive cycles, as analyzed thermogravimetrically. The results show that following reduction at 1300?°C in inert atmosphere up to 0.32 mmol g^?1 of O₂ are released, while a 10-cycle reaction test confirms the feasibility of long term operation with these perovskites. It was observed that the reduction extent was enhanced with increasing the Al-content, but the oxidation degree is maximum for compositions near x?=?0.5, corresponding to an O₂ release of 0.318 mmol g^?1 (δ?=?0.132). After selecting the compositions with more promising redox properties, additional reactions were performed in a lab-scale fixed bed reactor with injection of CO₂ in the oxidation step at 900?°C in order to generate CO. In these tests, the most interesting results were obtained for the perovskite La_0.6Sr_0.4Mn_0.6Al_0.4O_3, with reduction extent of 0.266 mmol?g^?1, but the production of CO is in comparison significantly lower (0.114 mmol?g^?1). Further studies are required to determine the best operation conditions for thermochemical cycles using those materials.