EFFECT OF PRETREATMENT CONDITIONS ON STRUCTURAL CHARACTERISTICS OF WHEAT STRAW

Structural characteristics of lignocellulosic biomass such as surface area, pore volume, crystallinity, hemicellulose, and lignin content significantly affect the yield of fermentable sugars for bioethanol production. In the present work, the effect of dilute acid pretreatment was studied on structural characteristics of wheat straw, using different combinations of process variables (temperature, time, and acid concentration). Pretreated wheat straw (PWS) exhibited higher available surface area and pore volume along with low hemicellulose and lignin content. Crystallinity index (CrI) of biomass at different pretreatment conditions showed an increased trend followed by sharp decrease at high temperature (190°C) conditions. Maximum increase in surface area (7.1 m²/g compared to 4.0 m²/g for untreated wheat straw) was obtained at pretreatment conditions of 180°C temperature, 0.5% (v/v) acid, and 7 min time. SEM imaging of biomass revealed that pore breaking, compression of pores, and partial pore blocking in the case of high temperature (190°C) pretreatment conditions may be the reason behind decreased surface area of biomass. FT-IR analysis showed almost complete hemicellulose removal and acid-soluble lignin removal after dilute acid pretreatment but insufficient removal of acid insoluble lignin.

[Supplementary material is available for this article. Go to the publisher's online edition of Chemical Engineering Communications for the following free supplemental resource: figure showing XRD pattern of biomass with respect to different pretreatment conditions.]     

Study of the characteristics of the ashing process of straw/coal combustion

An experimental study was performed to examine the ashing process during straw/coal co-combustion to determine the effect of the blending ratio on ash products. A total of eleven blending samples with coal contents varying from 5 wt.% to 90 wt.% along with pure wheat straw and pure coal samples were tested to determine the ash fusion points, oxide contents and mineral contents. Blends with coal contents between 5 wt.% and 15 wt.% were able to inhibit ash and reduced ash quantity. Blends with coal contents greater than 20 wt.% promoted ash and increased ash quantity. Thermal decomposition processes during the combustion and ash pyrolysis of the blends with 10 wt.% and 40 wt.% and the samples of pure coal and pure wheat straw were simulated using a Thermal Gravity Analyser. The results indicated that the ashing processes of the blends were influenced by the coupling reactions of the minerals in the straw and coal. When using a blend of 10 wt.% coal, more potassium (K) was accelerated into gaseous products during the volatile releasing and firing stage, which caused an ash quantity reduction effect. K₂O content was lowest in this sample, and a minimum amount of K compounds was detected. With a blend of 40 wt.% coal, because the coupling reactions of Ca and Al produced stable minerals of CaAl₈Fe₄O₁₉ and KSi₃AlO₈, less CaCO₃ and CaSO₄ were produced. Thermal decomposition at the ash pyrolysis stage was very weak and resulted in much less gaseous products than what would be expected at high temperatures; therefore, more ash residues remained.     

Optimization of melt blending process of nylon 6‐POSS: Improving mechanical properties of spun fibers

Blends of nylon 6 and a silsesquioxane additive, aminopropyl isobutyl POSS containing 2.5% POSS by weight, were melt‐compounded with different process conditions in order to test a previously proposed mechanism for reinforcement of PA6 by POSS. In this work, we proposed that above the POSS melting temperature of 267°C POSS becomes partially soluble in the nylon 6 matrix, leading to smaller domains upon cooling, and the remaining nondiffused POSS agglomerates need to have an acceptable size distribution, typically 16 µm² or less in area. In this work, we test this hypothesis by producing blends with POSS existing as phase‐separated aggregates of even smaller size than before and processing them under various thermomechanical conditions. Although there were no significant differences in the morphology and mechanical properties between the different extruded samples, the results from the spun fibers present significant improvements in tensile properties relative to previous reports. Our results suggest that in order to maximize the tensile strength of melt spun fibers, the extruded blends should be processed at temperatures above the POSS melting temperature and at intermediate shear rates, since these conditions lead to lower debonding between POSS particles and the matrix, and smaller average particle size. POLYM. ENG. SCI., 55:1580–1588, 2015. © 2015 Society of Plastics Engineers     

Development of dispersed phase size and its dependence on processing parameters

Through measurement of phase dimension via laser scattering, phase morphology development in immiscible blends of polyamide 12/poly(ethylene glycol) (PEG) with an extremely high viscosity ratio was investigated. The blends were prepared by melt blending in a batch mixer. The objective was to examine the influence of mixing time, rotor speed, as well as blending temperature on the size distribution of the minor phase. It is of interest that the breakup process of the dispersed PA 12 phase was observed for the blend systems even for extremely high viscosity ratios of ≤ 10²–10³. Mixing time had a significant effect on the development of dispersed phase size distribution. It was found that the bulk of particle size reduction took place very early in the mixing process, and very small droplets with a diameter of 0.1–10 μm were produced. The number of small particles then decreased, resulting in a larger average particle size. With further prolonged mixing, the particle size levels off. The particle size and its distribution were also found to be sensitive to the rotor speed. The average particle size decreased with increased rotor speed. The effect of blending temperature on size and size distribution, which has seldom been studied, was also examined in this work. When the blending temperature altered from 190°C to 220°C, the size and its distribution of the dispersed phase varied considerably, and the change of viscosity ratio was found to be the key factor affecting the dispersed phase size. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3201–3211, 2006     

Effect of process variables on liquid hot water pretreatment of wheat straw for bioconversion to fuel‐ethanol in a batch reactor

BACKGROUND: Crop residues as wheat straw are potential sources for fuel‐ethanol production as an alternative to current production based on starch‐ or sugar‐containing feedstocks. In this work, the effect of liquid hot water (LHW) process parameters, i.e. temperature (170 and 200 °C), residence time (0 and 40 min), solid concentration (5% and 10% (w/v)) and overpressure applied in the reactor (30 bar and no overpressure), on pretreatment of wheat straw was studied using a full factorial experimental design. Pretreatment effectiveness was evaluated based on the composition of the solid and liquid fractions obtained after filtration of pretreated material, and the susceptibility of the solid fraction to enzymatic hydrolysis (EH) using commercial cellulases. RESULTS: Statistical analysis showed that only temperature and time, within the limits of the experimental range, have a significant effect on the responses studied. While the effect of pretreatment time in hemicellulose‐derived sugar recovery in prehydrolyzate depends on temperature, EH yield was enhanced as both temperature and time were increased. Maximum EH yield was 96 g glucose per 100 g potential glucose in pretreated residue. Xylan and acetyl groups content remaining in solid residue after pretretament, which were found to be directly correlated, had a marked effect on pretreated substrate degradability. CONCLUSIONS: LHW is an effective pretreatment to enhance the potential of wheat straw as substrate for ethanol production. Maximum hemicellulose‐derived sugar recovery (53% of content in raw material) and EH yield (96% of theoretical) fall within different temperature and time intervals, suggesting separate optimization designs for these responses. Copyright © 2007 Society of Chemical Industry     

麦秸纤维素酶解法制糖研究

对麦秸纤维素预处理过程的影响因素进行了探索,着重对酶解产糖工艺过程进行了讨论分析。结果表明：粉碎至１２０～１５０目并经１％ＮａＯＨ溶液浸渍的麦秸是一种理想的制糖原料;当该原料在５０～５５℃,ｐＨ为４．４,时间为１５ｈ以及适宜的酶与底物配比条件下,可获得理想的产糖率。     

秸秆-粉煤灰纤维陶粒制备方法研究

以小麦秸秆和电厂粉煤灰为原料,辅以外加药剂(水泥、石灰、石膏及水玻璃),经混合、成球、陈化和养护工序,制得小麦秸秆-粉煤灰纤维陶粒(以下简称纤维陶粒).以比表面积(SSA)为主要考察指标,通过单因素实验和正交实验,考察了秸秆用量、秸秆粒径及外加药剂对秸秆-粉煤灰纤维陶粒性能的影响.结果表明,外加药剂对秸秆-粉煤灰纤维陶粒SSA的影响主次顺序为:石灰>水玻璃>水泥>石膏;最佳制备方案为:选用经2次粉碎后的小麦秸秆,秸秆的用量为10%,即秸秆与粉煤灰的质量配比为1∶9,外加药剂:石灰8%,水玻璃2%,水泥3%及石膏2.5%,在优组合下制得的纤维陶粒的SSA为7.925m2/g.     

Successive centrifugal grinding and sieving of wheat straw

Grinding plant biomass may allow the lignocellulosic assembly to become more reactive/accessible by providing energy for polymer dissociation, increasing contact surface (particle size reduction) and reducing cellulose crystallinity. Moreover lignocellulosic composition varies considerably affecting biomass processability as resource for bio-based energies, composite materials and chemicals. The aims of this work were: (i) to analyse composition of wheat anatomic parts present into wheat straw, (ii) to characterize the behaviour of major components upon successive centrifugal grinding steps (2 mm-screen cutting milling followed by 4-step centrifugal grinding) and (iii) to relate particle size distribution and component concentrations into the finest sized product (0.12 mm-screen ground). The powders from successive centrifugal grindings were sieved and their chemical compositions were determined. Ground straw powders were heterogeneous according to different particle aspects: size, shapes and roughness. In general fractions with lower particle size had higher ash and protein contents whereas cellulose contents are higher in the larger fractions. Wheat straw exhibited a non homogeneous reduction behaviour when finely ground. Fraction compositions were only slightly distinct suggesting that although sieving can constitute a preliminary fractionation step, it is necessary to reduce still more the particle size to reach more effective dissociation of macromolecules assembly.     

Production of titania nanoparticles by a green process route

The manufacture of heterogeneous catalysts and catalyst supports produces substantial amounts of nitrate containing aqueous effluent. The use of nitrate free precursors and an environmentally friendly process would change the manufacture so that the entire process of catalyst synthesis and use can be considered green. In this work the precipitation of titania acetylacetonate nanoparticles for use as catalytic supports using a supercritical carbon dioxide anti-solvent process was investigated over a range of conditions. The effects of 1) pressure, 2) temperature, 3) solution flowrate, 4) solution concentration of TiO(acac)₂ in methanol, 5) nozzle diameter and 6) CO₂/methanol flow ratio on the mean particle size and morphology were studied. Particle sizes between 27 and 78 nm were obtained and were generally string and branch-like with an amorphous nature. Pressure and temperature had little effect on the mean particle size. A decrease in the velocity of the solution flow rate led to an increase in mean particle size and to particles that exhibited greater interconnectivity. It was also observed that an increase in concentration of TiO(acac)₂ in methanol led to an increase in mean particle size. The process shows promise for the production of catalysts by an environmentally acceptable route.     

Application of a microassay method to study enzymatic hydrolysis of pretreated wheat straw

BACKGROUND: The conversion of lignocellulosic biomass to ethanol includes a disruptive pretreatment process followed by enzyme‐catalyzed hydrolysis of the cellulose and hemicellulose components to fermentable sugars. As the cost and hydrolytic efficiency of enzymes are major factors that restrict the commercialization of biomass conversion processes, significant efforts are made nowadays to improve the enzymatic mixtures and make the process cost‐effective. RESULTS: In this work, enzymatic microassays have been developed and validated to test new different enzymatic formulations on real lignocellulosic substrates. Homogeneous handsheets from steam pretreated wheat straw were elaborated to be used as substrate. The microassay was adapted to test both water‐insoluble solids and the whole slurry as substrates. Results in hydrolysis microassays were comparable with those obtained in standard flask assays using pretreated wheat straw. Moreover, using the enzymatic microassays, two novel preparations have been evaluated, demonstrating the ability of microassays to discriminate between different enzymatic mixtures. CONCLUSIONS: This enzymatic microassay represents a rapid method to test the performance of new selected cellulase enzymes on real pretreated lignocellulosic substrates. This microassay will enable evaluation of enzyme components separately, or optimized mixtures. Copyright © 2010 Society of Chemical Industry     

Rubber phase dispersion in polypropylene

Impact properties of rubber-modified blends are significantly dependent on particle size and size distribution (dispersion). Past work has shown strong variations in these particle parameters with different processing conditions and these variations reflect, in part, different shear fields developed during melt extrusion and moulding. A major problem ensues involving property variability because of process variability. It is neither practical nor economical to place stringent controls on process variability in a plant. Instead, our current research has indicated that lightly crosslinking the rubber reduced drastically the sensitivity of dispersion to processing conditions, and, with the correct rheology between the rubber and the resin, the same dispersion could be maintained through both the extrusion and moulding stages resulting in finished parts with increased chance of dispersion and property consistency. Four rubbers of different degrees of crosslinking and three polypropylenes of different melt flow and structure were blended at six rubber levels. Mixing was carried out with two twin-screw configurations and the blends were cast or injection moulded using a ram or a screw moulder representing six different processing shear histories. Dispersion was quantitatively characterized by scanning electron microscopy (SEM). Spherical rubber particles revealed on the fracture surface were counted and measured to determine particle size and size distribution for the individual blends. Correlation of the results indicated how particle size and size distribution was influenced by crosslinking and the rubber/resin rheology. This provided some understanding of the mechanics of soft-phase dispersion in these blends.     

麦秆液化物环氧树脂的制备与表征

以苯酚为溶剂,浓硫酸为催化剂液化麦秆得到麦秆液化产物,并以其为原料与环氧氯丙烷反应制备出以麦秆液化物为基材的环氧树脂。考察了液比(苯酚与麦秆质量比)、反应温度和反应时间对液化反应的影响。采用凝胶渗透色谱(GPC)对比分析了麦秆液化物及其环氧树脂的相对分子量分布。以聚酰胺为固化剂进行固化并进行力学测试。结果表明:在液比为4∶1,反应温度为150℃,反应那个时间为60min时,麦秆液化效果最佳,此时,麦秆液化物环氧树脂固化物的剪切强度可达4.1MPa。     

Modeling and analysis of HVOF thermal spray process accounting for powder size distribution

This work focuses on the high velocity oxygen–fuel (HVOF) thermal spray processing of coatings and presents a fundamental model for the process which explicitly accounts for the effect of powder size distribution. The model describes the evolution of the gas thermal and velocity fields, as well as the motion and temperature of agglomerate particles of different sizes. In addition to providing useful insight into the in-flight behavior of particles with different sizes, the model is used to make a control-relevant parametric analysis of the HVOF thermal spray process. This analysis allows us to systematically characterize the influence of controllable process variables such as combustion chamber pressure, oxygen/fuel ratio, as well as the effect of powder size distribution, on the values of particle velocity and temperature at the point of impact on substrate. Specifically, the study shows that particle velocity is primarily influenced by the combustion chamber pressure, and particle temperature is strongly dependent on the fuel/oxygen ratio. Furthermore, it shows that the particle velocity and temperature at the point of impact depend strongly on particle size. These findings are consistent with available experimental observations and set the basis for the formulation of the control problem for the HVOF process.     

PET和关中麦秆共热解特性及其动力学研究

利用TG-FTIR技术研究陕西关中地区小麦秸秆（麦秆）、聚对苯二甲酸乙二醇酯（PET）及其两者混合物麦秆-PET（质量比1：1）在20 K/min的升温速率下的热解行为、主要热解产物、协同效应和动力学。研究结果表明：PET热解初始温度为375℃,最大热失重速率处的温度为454.9℃,失重率为62.87%,其热解残余质量为19.42%;麦秆-PET的热解DTG曲线表现为麦秆和PET主失重峰（339.9和444℃）的叠加,且混合试样在两个强峰处的失重率分别为22.9%和73.9%,最终热解残余质量为23.52%;PET和麦秆共热解过程中会出现两个协同效应（339.9和444℃）,这使得共热解产物中的CO、CH₄以及芳香族、酸类、酮类、醛类、醇类、烷烃、酚类和醚类等轻质焦油组分含量高于麦秆和PET单独热解,共热解提高了热解产物的热值,改善了热解产物组成,提升了热解产物的稳定性和燃料品质;采用Coats-Redfern积分法计算得到PET在主热解区的表观活化能为355.48 kJ/mol,远高于麦秆的表观活化能（86.5 kJ/mol）,麦秆-PET在低温区（258~363℃）的表观活化能为53.6 kJ/mol,在高温区（393~463℃）的表观活化能为81.6 kJ/mol。     

Comparison of different procedures for the detoxification of eucalyptus hemicellulosic hydrolysate for use in fermentative processes

Eucalyptus (Eucalyptus grandis) shavings were submitted to an acid hydrolysis process with the aim of obtaining a hemicellulosic hydrolysate rich in fermentable sugars. However, the hydrolysate obtained contained, in addition to sugars, several compounds that are toxic to microorganisms, namely furfural, hydroxymethylfurfural, acetic acid and phenolics. In order to produce a hydrolysate suitable for use in fermentative processes, several procedures were evaluated for hydrolysate detoxification, including concentration by vacuum evaporation and adsorption on activated charcoal, diatomaceous earths, ion‐exchange resin or adsorbent resin. Hydrolysate concentration was especially effective for furfural removal, whereas the adsorbent resin was efficient in removing hydroxymethylfurfural, phenolics and acetic acid. Combination of this resin with activated charcoal was better than with diatomaceous earths for removal of acetic acid and phenolics. The best detoxification procedure evaluated was based on hydrolysate concentration followed by adsorption on activated charcoal and adsorbent resin. By this treatment, removal rates of 82.5, 100, 100 and 94% were attained for acetic acid, furfural, hydroxymethylfurfural and phenolics, respectively. Copyright © 2005 Society of Chemical Industry     

Investigation of the effect of temperature and alkaline concentration on the solubilization of phenolic acids from dilute acid-pretreated wheat straw

This work deals with the investigation of the effect of alkaline concentration and temperature on the solubilization of phenolic materials from wheat straw, an abundant agricultural waste found in Turkey. The solid residue obtained after dilute acid pretreatment of wheat straw (SPWS) was treated by alkaline to solubilize the lignin to phenolic acids. Four different alkaline concentrations at 120 °C and seven different temperatures with 2 M NaOH were evaluated for the degree of solubilization of the phenolic materials, and the antioxidant activities of the soluble phenolic materials were determined. It was found that coumaric and ferulic acids were the major phenolic acids in all of the conditions tested. The highest antioxidant capacity of the hydrolysate of SPWS was obtained with 2 M NaOH at 150 °C where DPPH*, FRAP and TEAC values were found to be 3.23, 10.27 and 13.70 μmol/g WS, respectively.     

Effect of dynamic vulcanization on properties and morphology of nylon/SAN/NBR blends: A new compatibilization method of nylon/ABS blends

Dynamically vulcanized blends of nylon, styrene–acrylonitrile copolymer (SAN), and nitrile–butadiene rubber (NBR) were examined for mechanical properties, Shore D hardness, Vicat softening temperature, impact process, and phase morphology. The effect of a curing system such as phenolic formaldehyde resins (PF), dicumylperoxide (DCP), and a sulfur system on the mechanical properties of the nylon/SAN/NBR blends was studied, and dynamic vulcanization with a PF system was found to lead to outstanding toughness of the blends. The effect of PF content on the mechanical properties, Shore D hardness, and heat resistance of the nylon/SAN/NBR blends was also investigated. With increasing PF content the notched‐impact strength and Vicat softening temperature (VST) of the nylon/SAN/NBR (50/25/25) blends evidently improved, but tensile strength and Shore D hardness of the blends changed slightly. It can be concluded that the nylon/SAN/NBR (50/25/25) blends dynamically vulcanized by high‐content PF can attain excellent comprehensive mechanical properties, especially supertoughness, at room temperature. SEM was used to investigate the effect of dynamic vulcanization on disperse‐phase particle size, particle size distribution, and phase morphology. It was obvious that disperse‐phase particle size decreased with an increasing PF content. Thermal behavior and miscibility of dynamically vulcanized nylon/SAN/NBR with PF were investigated by DMTA. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2057–2062, 2003     

阿司匹林结晶过程的在线分析

晶体的颗粒尺寸分布和形状是结晶产品的两个关键质量指标,不仅影响结晶产品的性质,还影响下游的过滤、干燥及运输存储等过程。利用超声粒度分析仪、衰减全反射傅里叶红外光谱仪、浊度仪与二维成像系统等分析仪器在线测量了不同搅拌速率和不同降温速率下阿司匹林乙醇溶液结晶过程中温度、浓度、颗粒尺寸分布和形状的变化情况。实验结果表明：较低的降温速率或者较大的搅拌速率条件下得到含有大量细晶的阿司匹林结晶产品;较高的降温速率下得到长宽比较大的阿司匹林结晶产品。调节降温速率和搅拌速率是一种有效控制阿司匹林结晶产品尺寸分布与形状的方法。     

电场强化纤维素酶超滤过程研究

将电场强化膜技术应用于纤维素酶超滤过程,在截留相对分子质量为10 000的聚醚砜(PES)超滤膜上分别考察了电场对粗酶粉配制的纤维素酶模拟溶液以及秸秆酶解液的超滤过程的影响.实验结果表明,在2种情况下,电场均可以有效提高超滤过程的渗透通量.当电流强度为150 mA时,相对于无电场(0 mA)的条件下,纤维素酶模拟溶液通...     

小麦秸秆水热预处理半纤维素降解动力学研究

水热预处理是木质纤维素原料高效能源转化的主要工艺流程之一，但是以小麦秸秆为原料的水热预处理的反应路径与反应机理仍有研究不足之处, 制约该预处理过程的优化及实际生产应用。本文以小麦秸秆为研究对象，实验研究了木质纤维素水热预处理过程反应动力学。研究发现，在水热预处理过程中，小麦秸秆的主要降解过程是半纤维素降解产生低聚木糖、木糖以及糠醛的过程，半纤维素在水热过程中几乎完全降解。随着预处理温度的升高，水解液中低聚木糖和木糖的浓度降低，而糠醛的浓度增加；随着保温时间的延长，低聚木糖与木糖的浓度先增加后减小，糠醛的浓度会趋于稳定。根据实验结果提出反应路径并拟合获得动力学速率常数和反应活化能，所获的动力学模型可以很好地解释反应物浓度的变化，与实验数据吻合良好。该模型可以为小麦秸秆水解预处理系统的设计提供参考。