Effect of ball milling on the hydrolysis of microcrystalline cellulose in hot‐compressed water

Ball milling leads to a considerable reduction in cellulose particle size and crystallinity, as well as a significant increase in the specific reactivity of cellulose during hydrolysis in hot‐compressed water (HCW). Cryogenic ball milling for 2 min also results in a significant size reduction but only little change in cellulose crystallinity and specific reactivity during hydrolysis. Therefore, crystallinity is the dominant factor in determining the hydrolysis reactivity of cellulose in HCW while particle size only plays a minor role. Ball milling also significantly influences the distribution of glucose oligomers in the primary liquid products of cellulose hydrolysis. It increases the selectivities of glucose oligomers at low conversions. At high conversions, the reduction in chain length plays an important role in glucose oligomer formation as cellulose samples become more crystalline. An extensive ball milling completely converts the crystalline cellulose into amorphous cellulose, substantially enhancing the formation of glucose oligomers with high degrees of polymerization. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Structural changes in carbon nanofibers induced by ball milling

A nested cones type carbon nanofiber (CNF) was exposed to ball milling with different milling times. Ball milled CNFs were investigated by transmission electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and thermogravimetric analysis. It was suggested that the milling energy could be consumed by CNF grinding and aggregating. The effect of mechanical stress causes a “flattening” of the CNFs with the loss of the nanofibrous structure, and the amount of carbon layers in crystallite decreases. Multiple structural changes induced by ball milling lead to fluctuations of sp³/sp² and O/C ratios.     

CO_2活化生物质水解残渣制备活性炭的正交实验

以玉米秸秆酸水解残渣为原料、CO2为活化剂,制备了一系列活性炭,采用正交试验方法分析了原料颗粒大小、CO2/N2体积比、活化温度、活化时间4个因素对生物质水解残渣原料活性炭的比表面积、孔径和得率的影响。正交试验结果表明,活化温度和CO2/N2体积比是影响该类活性炭吸附性能的主要因素。制备的活性炭产品最大比表面积达到845.4m2/g,对应的制备工艺:原料颗粒50目、CO2/N2体积比1∶1、活化温度1000℃、活化时间210min。     

木质纤维素水解制取燃料乙醇研究进展

以木质纤维素生产燃料乙醇具有原料可再生性和环境友好的优点而备受重视.本文介绍了国内外木质纤维素制取燃料乙醇中的水解工艺过程,包括浓酸水解、稀酸水解和酶水解工艺,分析了各工艺的技术特点,同时指出稀酸预处理-酶水解工艺将成为近几年国内外研究和开发的重点.     

Progress in the hydrolysis of lignocellulosic biomass for fuel-thanol production

以木质纤维素生产燃料乙醇具有原料可再生性和环境友好的优点而备受重视。本文介绍了国内外木质纤维素制取燃料乙醇中的水解工艺过程,包括浓酸水解、稀酸水解和酶水解工艺,分析了各工艺的技术特点,同时指出稀酸预处理-酶水解工艺将成为近几年国内外研究和开发的重点。     

Ball milling promoted direct liquefaction of lignocellulosic biomass in supercritical ethanol

In the present work, ball milling was applied for the pretreatment of lignocellulose to obtain high conversion and bio-oil yield in supercritical ethanol. Ball milling substantially decreased the crystallinity and particle size of lignocellulose, thereby improving its accessibility in ethanol solvent. An increased bio-oil yield of 59.2% was obtained for the ball milled camphorwood sawdust at 300°C, compared with 39.6% for the original lignocellulose. Decreased crystallinity significantly benefited the conversion of the cellulose component from 60.8% to 91.7%, and decreased particle size was beneficial for the conversion of all components. The obtained bio-oil had a high phenolic content, as analyzed by gas chromatography-mass spectrometry. Methoxylation and retro-aldol condensation were observed during alcoholysis, and the reaction pathways of lignocellulose in supercritical ethanol were attributed to the action of free radicals.     

离子液体预处理油料作物木质纤维素

选取了3种离子液体：氯化1-丁基-3-甲基咪唑([Bmim]Cl)、溴化1-丁基-3-甲基咪唑([Bmim]Br)以及氯化1-辛基-3-甲基咪唑([Omim]Cl),对油料作物木质纤维素部分：花生秸秆、花生壳以及油菜秸秆进行了预处理。对处理前后的物料进行了组分、酶解产糖以及结构分析。原料经酶解后,花生秸秆的产糖率最高(54.31%),且木质素含量最低,表明其更利于生物燃料的生产。3种离子液体中[Bmim]Cl预处理效果最好,产糖率最高可达85.43%(花生秸秆)。采用扫描电镜(SEM)和红外光谱(FT-IR)分析,花生秸秆表面最不完整,结构松散,结晶区域少。经离子液体处理后,所有物料均变得疏松多孔,表面粗糙,提高了物料的可及度。在此基础上,分析阴阳离子对于木质纤维素的溶解过程,发现氯离子和[Bmim]⁺对于纤维素的溶解影响最显著。     

二氧化碳对高温液态水中苯乙腈水解反应的影响研究

为探讨添加了二氧化碳的高温液态水中腈类物质的水解规律,考察了不同的二氧化碳添加量对高温液态水中苯乙腈水解的影响,计算了不同二氧化碳添加量和不同温度对高温液态水反应体系的pH的影响。结果表明：在473.15 K,0、0.2、0.4 MPa二氧化碳压力下的水解反应速率常数分别为6.2 × 10-4、4.1 × 10-4、3.0 × 10-4 min-1,而相对应的pH值分别为5.6、4.1、3.9。对于碱催化机理为主导的苯乙腈水解反应,二氧化碳并不能有效地促进反应进行。     

Simultaneous wet ball milling and mild acid hydrolysis of rice hull

BACKGROUND: Rice hull, an abundant residue but a big issue for the rice processing industry, has the potential to serve as a feedstock for production of ethanol because of its lignocellulosic composition. Simultaneous wet ball milling and mild acid hydrolysis of rice hull was studied in this work. RESULTS: Ball milling with 150 small stainless steel beads and rotation speed of 600 rpm in citrate solvent of pH 4 was the optimal condition for hydrolysis, and the yield of sugar increased with increased milling time. Corresponding structure transformations before and after milling analyzed by X‐ray diffraction (XRD), environmental scanning electron microscopy (ESEM) and transmission fourier transform infrared spectroscopy (FT‐IR) clearly indicate that this hydrolysis could be attributed to the crystalline and chemical structure changes of cellulose in rice hull during ball milling in mild acid solvent. CONCLUSION: This combined treatment of ball milling and citrate solvent greatly changed the crystalline and chemical structure and continuously generated sites accessible to citrate solvent, thus enabling hydrolysis of the rice hull. Copyright © 2009 Society of Chemical Industry     

Emerging role of nanobiocatalysts in hydrolysis of lignocellulosic biomass leading to sustainable bioethanol production

Catalytic conversion (hydrolysis) of carbohydrate polymers present in the lignocellulosic biomass into fermentable sugars is a key step in the production of bioethanol. Although, acid and enzymatic catalysts are conventionally used for the catalysis of various lignocellulosic biomass, recently application of immobilized enzymes (biocatalysts) have been considered as the most promising approach. Immobilization of different biocatalysts such as cellulase, β-glucosidase, cellobiose, xylanase, laccase, etc. on support materials including nanomaterials to form nanobiocatalyst increases catalytic efficacy and stability of enzymes. Moreover, immobilization of biocatalysts on magnetic nanoparticles (magnetic nanobiocatalysts) facilitates easy recovery and reuse of biocatalysts. Therefore, utilization of nanobiocatalysts for catalysis of lignocellulosic biomass is helpful for the development of cost-effective and ecofriendly approach. In this review, we have discussed various conventional methods of hydrolysis and their limitations. Special emphasis has been made on nanobiocatalysts used for hydrolysis of lignocellulosic biomass. Moreover, the other most important aspects, like nanofiltration of biomass, conversion of lignocellulose to nanocellulose, and toxicological issues associated with application of nanomaterials are also discussed.     

Effects of plasticization and hydrostatic pressure on tensile properties of PMMA under compressed carbon dioxide and nitrogen

We investigated the stress?strain behavior of PMMA films under compressed CO₂ and N₂. The elongation at break increased and the stress decreased with increasing CO₂ pressure at pressures above 3 MPa, indicating that the tensile property changed from brittle to ductile under compressed CO₂. In contrast, the material property became more brittle under compressed CO₂ at pressures below 2 MPa and under compressed N₂. By depressurizing the compressed gas and excluding the hydrostatic pressure, the property of the gas‐absorbed specimen changed from brittle to ductile. These results suggest that deformability by molecular orientation is enhanced by the plasticizing effect caused by a large amount of absorbed gas while it is suppressed by the effect of hydrostatic pressure caused by a small amount of absorbed gas. Conversely, the elastic modulus decreased under both compressed CO₂ and N₂, but the decrease under CO₂ was much larger than that under N₂, suggesting that distortion in the elastic region is dominated by the plasticization effect. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43431.     

Catalytic asymmetric hydroformylation in the presence of compressed carbon dioxide

The asymmetric hydroformylation of styrene using [(CO)₂Rh(acac)]/(R,S)‐BINAPHOS as catalyst precursor occurs smoothly in the presence of compressed CO₂ to give appreciable asymmetric induction (ee = 66% (R)) under conditions close to the critical data of pure CO₂, but very low ees are obtained at high CO₂ densities. The phase behaviour of the reaction medium and the different solubilities of the unmodified and ligand‐modified catalytically active species in the supercritical phase provide a possible rationalisation of the results. This revised version was published online in July 2006 with corrections to the Cover Date.     

Lipase-catalysed hydrolysis of blackcurrant oil in supercritical carbon dioxide

The effect of reaction conditions on the extent of conversion in hydrolysis of blackcurrant oil was investigated. The enzyme used was Lipozyme, a lipase from Mucor miehei immobilised on macroporous anionic resin. The reaction was carried out in a continuous flow reactor at 10- and 30-50°C with carbon dioxide saturated with oil and water (55-100%) flowing up through the enzyme bed. Analysis of product composition indicated unfavourable hydrodynamics with significant mixing in the reactor when solvent interstitial velocity was lower than , while above this velocity value the flow pattern was near to plug flow. Lipase stability was very good with no activity reduction observed during a long-term experiment. The reaction rate was a function of the ratio of enzyme load to solvent volumetric flow rate. A complete hydrolysis of oil was achieved in the experiments carried out with the enzyme load of and CO₂ flow rate of 0.4-. The effects of pressure (10-) and temperature (30-40°C) on the reaction rate were small, and the effects of CO₂ saturation with water and of enzyme distribution in the reactor were negligible. Lipozyme displayed specificity towards linolenic acids; the release of α-linolenic acid was faster and that of γ-linolenic acid slower than the release of other constituent acids present in blackcurrant oil.     

Lipase-catalyzed hydrolysis of canola oil in supercritical carbon dioxide

The effect of pressure, temperature, and CO₂ flow rale on the extent of conversion and the product composition in the enzyme-catalyzed hydrolysis of canola oil in supercritical carbon dioxide (SCCO₂) was investigated using lipase from Mucor miehei immobilized on macroporous anionic resin (Lipozyme IM). Reactions were carried out in a continuous flow reactor at 10, 24, and 38 MPa and 35 and 55°C. Supercritical fluid chromatography was used to analyze the reaction products. A conversion of 63–67% (triglyceride disappearance) was obtained at 24–38 MPa. Mono-and diglyceride production was minimum at 10 MPa and 35°C. Monoglyceride production was favored at 24 MPa. The amount of product obtained was higher at 24–38 MPa due to enhanced solubility in SCCO₂. Complete hydrolysis of oil should be possible by increasing the enzyme load and/or decreasing the quantity of the oil substrate. There was a drop in triglyceride conversion over a 24-h reaction time at 38 MPa and 55°C, which may be an indication of loss of enzyme activity. Pressure, temperature, and CO₂ flow rate are important parameters to be optimized in the enzyme-catalyzed hydrolysis of canola oil in SCCO₂ to maximize its conversion to high-value products.     

Effects of compressed carbon dioxide treatment on the specificity of oxidase enzymatic complexes from mate tea leaves

This work evaluates the enzymatic activity of peroxidase (POD) and polyphenoloxidase (PPO) present in the crude extract of mate tea leaves (Ilex paraguariensis St. Hill) submitted to compressed CO₂. The effects of temperature, exposure time, solvent reduced density, pressure, and depressurization rate on the activity of peroxidase and polyphenoloxidase were evaluated through a fractionated factorial experimental planning. Results show that temperature of 30 °C, pressure of 70.5 bar, exposure time of 1 h, depressurization rate of 10 kg m⁻³ min⁻¹ and carbon dioxide reduced density of 0.60 led to an enhancement of around 25% in the peroxidase activity and a polyphenoloxidase activity loss of 50%. Using this experimental condition, thermal stability at low temperature (−4 °C) and the influence of successive pressurization/depressurization cycles were determined. Results suggest that it is possible to increase the specificity of the enzymatic extract towards enhancing POD or PPO activity depending on the experimental condition employed, and that the processing of enzymatic complexes with compressed CO₂ may be a promising route to increase the specificity of enzymatic extracts.     

Thermal conductivity of the ionic liquid [HMIm][Tf2N] with compressed carbon dioxide

The liquid thermal conductivity of the ionic liquid (IL), 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf₂N]), saturated with compressed vapor and supercritical carbon dioxide was measured over three isotherms (298.15, 323.15, and 348.15 K) and pressures up to approximately 20 MPa using a transient hot-wire technique. Pure [HMIm][Tf₂N] thermal conductivity was also measured over a temperature range of 293.15–353.15 K at ambient pressure and with hydrostatic pressure to approximately 20 MPa. Literature vapor–liquid equilibrium data were used to predict the liquid CO₂ composition at the conditions investigated. Initially, the liquid thermal conductivity slightly decreased with pressure/composition of CO₂ followed by a gradual increase that is mainly attributed to hydrostatic pressure effects. Simple composition-based mixing rules for mixture properties are not qualitatively nor quantitatively accurate. These data could be used to engineer heat transfer equipment required for a variety of proposed IL applications in CO₂ capture, absorption refrigeration, biphasic CO₂/IL reaction platforms, etc.     

Application of compressed carbon dioxide in the incorporation of additives into polymers

It has been found that carbon dioxide remarkably accelerates the absorption of many low molecular weight additives into a number of glassy polymers. This effect is due to the high diffusivity, solubility, and plasticizing action of compressed CO₂ in polymers. The transport of CO₂ and the effects of CO₂ pressure on the transport of other low molecular weight compounds in polymers have been studied by a simple gravimetric method: Polymer film samples were contacted in a pressure vessel with compressed CO₂, or with CO₂ plus various organic liquids or solids, and the sample weight was followed with a fast-response electronic balance during subsequent desorption at atmospheric pressure. Upon release of the pressure, absorbed CO₂ rapidly diffuses from the polymer, while the other compounds desorb much more slowly. The amount of additive absorbed can be determined from the plateau weight of the sample after most of the CO₂ has escaped. Extensive kinetic and equilibrium data are reported for the model system poly(vinyl chloride)/dimethyl phthalate/CO₂, and a number of other examples of CO₂-assisted additive absorption are given. This “infusion” process, in effect, amounts to the partitioning of the additive between the CO₂- and polymer-rich phases; consequently, the relative solubility of the additive in CO₂ and in the polymer is a major factor governing the amount of additive absorbed. Data reported here illustrate the generality and potentially broad applicability of CO₂-assisted polymer impregnation.     

Further studies of ball and powder filling effects in ball milling

The specific rates of breakage of quartz have been studied in three tumbling ball mills, two of 195 mm i.d. and one of 0.6 m i. d., as a function of fractional ball and powder loading. It was found that power results from a small mill with small lifters were anomalous, probably due to slippage, so that results reported previously from tests in this mill were not correct as a function of ball load. New results are presented for both wet and dry grinding.