乙醇催化脱水制乙烯反应条件及飞温现象

以HZSM-5分子筛为乙醇脱水催化剂,考察了催化剂的硅铝摩尔比和反应工艺条件对乙醇转化率及生成乙烯选择性的影响,分析了反应初期的飞温现象,用X射线衍射（XRD）、环境扫描电镜（SEM）和热分析（TG-DTA）对其催化剂进行了表征。结果表明：硅铝摩尔比为50∶1的HZSM-5催化乙醇脱水制乙烯反应在温度300℃、液体质量空速7h-1时,乙醇转化率大于99.8%,乙烯选择性达99.1%。HZSM-5催化乙醇脱水反应初期的飞温过程生成的聚合物堵塞和覆盖部分催化剂孔道,导致催化剂活性下降和乙烯选择性显著降低,适当降低进料温度可有效控制飞温现象发生。     

响应面法优化Zn-Mn-Co/HZSM-5催化乙醇脱水制乙烯

采用响应面法研究温度、乙醇浓度、质量空速对锌、锰、钴改性的HZSM-5催化乙醇脱水制备乙烯过程中乙烯收率的影响。结果表明反应温度对乙烯收率影响最大,并且各因素之间存在交互作用。用响应面方法确定乙醇脱水制备乙烯的最佳工艺条件是：温度261.3 ℃,乙醇浓度34.4％,质量空速1.18 h?1,在该条件下乙烯收率达到98.69％。     

生物乙烯研究进展

介绍了生物乙烯的背景和发展概况,总结了乙醇脱水反应的机理和所用的各类催化剂,分析了生物乙烯产业化中需要解决的关键技术问题,并指出发展生物乙烯有着光明的前景,对石油路线代替战略有着重要的意义.     

NKC-9干氢型树脂催化合成油酸甲酯

采用强酸性阳离子交换树脂作催化剂,对油酸和甲醇反应合成油酸甲酯的工艺进行研究。分别筛选了4种型号的树脂,其中以NKC-9干氢型树脂催化效果最好。考察了酸醇摩尔比、反应温度、催化剂用量、脱水剂用量、反应时间和催化剂重复使用性等因素对转化率的影响。结果表明:反应的适宜条件为酸醇摩尔比1∶2,反应温度70℃,催化剂用量为油酸质量的50%,脱水剂无水CaCl2用量为催化剂用量的10%,反应时间2 h。在此条件下,转化率可达93.85%。催化剂重复使用6次后转换率仍保持在90%以上。研究显示,采用NKC-9干氢型树脂催化合成油酸甲酯具有良好的工业应用潜力。     

枯草芽胞杆菌PnbA酯酶选择性拆分制备l-薄荷醇

利用重组大肠杆菌表达来源于枯草芽胞杆菌CICC 20034中的PnbA酯酶,不对称催化水解dl-薄荷醇丙酸酯制备l-薄荷醇。考察助溶剂种类、助溶剂添加浓度、温度、催化剂用量、底物浓度以及p H等对反应的影响。结果表明:添加25%(体积分数)助溶剂乙醇可显著提升该酯酶对l-薄荷醇的立体选择性,对映选择率(E)由2.4提高到99.43,为不加乙醇条件下的40倍。酶催化最佳条件:25%乙醇作为助溶剂,反应温度37℃,缓冲液为0.1 mol/L Tris-HCl(p H 8.0)并保持p H 8.0反应条件,底物量50 mmol/L,反应体系中酶的添加量750 U/m L,在此条件下,酶促反应30 min后,l-薄荷醇转化率可达34%,产物光学纯度对映体过量值(e.e._p)达95%。     

固体酸S_2O_2~(-8)/ZrO_2/USY催化废报纸制备乙酰丙酸乙酯

以废报纸为原料,S2O2-8/Zr O2/USY为固体酸催化剂,在乙醇中直接制备高价值化学品乙酰丙酸乙酯。利用红外光谱(FT-IR)和BET比表面积分析对催化剂进行表征,结果显示S2O2-8和Zr O2成功负载在USY分子筛上。首先用0.25%H3PO4对废报纸进行预处理,然后考察反应温度、反应时间、催化剂量和液固比对乙酰丙酸乙酯得率的影响。结果表明:在反应温度230℃、反应时间60 min、催化剂1.0 g、液固比45 m L/g条件下,乙酰丙酸乙酯的得率达到28.21%,催化剂使用3次后,催化活性有所下降。     

Au/C催化剂的制备及其对木质素模型化合物的催化氧化研究

以酸处理后的活性炭为载体,采用浸渍法制备了活性炭负载的Au催化剂,研究了该催化剂对木质素模型化合物2-(2-甲氧基苯氧基)-1-苯基乙醇的催化氧化降解反应。结果表明,以甲醇为溶剂,氧气做氧化剂,当反应温度为150℃,反应压力为1.0 MP时,Au/C催化剂能较好的降解木质素模型化合物,转化率达到88%,所得主要产物为愈创木酚,并给出了其可能的催化氧化机理。     

豆甾醇与琥珀酸酐单酯化反应工艺及动力学研究

研究了甲苯为溶剂,吡啶为催化剂,豆甾醇与琥珀酸酐的酯化反应工艺和反应动力学。探讨了反应温度、催化剂吡啶用量、反应物的摩尔配比和反应时间对酯化反应结果的影响。实验结果表明:豆甾醇与琥珀酸酐的反应产物为豆甾醇琥珀酸单酯;当吡啶的体积分数为1.5%,反应物的摩尔比为1.0∶1.6,回流下反应20 h后,豆甾醇的酯化率大于97%,反应后的溶液经蒸发回收溶剂甲苯,固体产物分别经乙醇和水洗涤除杂,所得固体在60℃下真空干燥至恒重,得到的豆甾醇琥珀酸单酯的单程收率大于86%。单酯化反应满足二级不可逆反应动力学规律,反应的活化能为85 kJ/mol。     

间溴苯乙醚的合成研究

以间溴苯酚、金属钠和溴乙烷为原料,乙醇为溶剂,碘化钾为催化剂合成了间溴苯乙醚。考察了反应物的摩尔比、反应温度及反应时间对产物收率的影响。实验结果表明:当n(间溴苯酚):n(金属钠):n(溴乙烷):n(碘化钾)=1:1:1.5:0.18,无水乙醇35mL,反应温度70℃,反应时间为5h时,间溴苯乙醚收率为82.6%。     

酸性功能性离子液体催化合成二甘醇二苯甲酸酯

选用6种酸性功能化离子液体作为催化剂,催化苯甲酸和二甘醇酯化合成增塑剂二甘醇二苯甲酸酯(DEDB),通过实验考察反应温度、时间、催化剂种类及用量、原料投料比等工艺因素对合成收率的影响,确定了最佳反应条件:优选1-丁基磺酸-3-甲基咪唑对甲基苯磺酸盐([(CH_2)_4SO_3HMIm]TS)为催化剂,反应温度160℃,时间4.0 h,苯甲酸与二甘醇的摩尔比为2.2∶1,催化剂用量为二甘醇质量的10%,最终发现DEDB产率可达99.1%,且产品具有较高的品质。产物可以通过简单倾倒与离子液体催化剂分离,离子液体具有优异的重复使用性,使用10次后DEDB的产率仍有95.2%。     

Systematic errors in data evaluation due to ethanol stripping and water vaporization

Systematic errors due to the neglect of water and/or ethanol partition between liquid and gaseous phases are discussed for bioreactors equipped with or without a condenser. Both water vapor and ethanol vapor are present in the off-gas leaving the condenser. Presence of residual water vapor largely influences the gas measurements by dilution. As a consequence, the oxygen consumption rate can be overestimated by a factor of 3 if calculations are not corrected for water vapor content or if no additional device is implemented after the condenser to completely dry the off-gases. The mass balance and partition equations predict that the condenser has only a small effect on reduction of the ethanol vapor content of the off-gas. The reason is the high ethanol concentration of the condensate droplets on the condenser wall in contact with the off-gases. Model predictions as well as experimental results show that ethanol evaporation represents a large fraction of the ethanol production rate and influences greatly the elemental recoveries. For a reactor working at 30 degrees C without condensation of the vapors and for a volumetric aeration rate of 0.63vvm, stripping of ethanol resulted in a gaseous dilution rate of 0.016 h-1 for ethanol. The dilution rate by stripping was reduced to 0.014 h-1 when a condenser at 12 degrees C was implemented. The fraction of ethanol that is stripped is mainly dependent on the ratio D/vvm (liquid to gaseous flow rates), and the effect is only slightly influenced by low condenser temperature. The evaporation of ethanol may account for more than 20% of the ethanol formation rate. Therefore, the condenser does not succeed to reflux all ethanol to the reactor broth. In terms of a unit operation, ethanol vapor can be efficiently reduced by absorption instead of condensation. To demonstrate the feasibility, a simple modification of the reactor was tested for continuous cultures: the feed port was changed from the top-plate to the top of the condenser, which was used as an absorption column. Ethanol stripping was reduced by a factor of 4 as compared to the condensation setup (at 12 degrees C): it accounted for 2% of the ethanol production rate as compared to 8.2% at D = 0.19 h-1 and 0.63vvm.     

Rapid ethanol fermentation of cellulose hydrolysate. I. Batch versus continuous systems

Rapid fermentation of bagasse hydrolysate to ethanol under anaerobic conditions by a strain of Saccharomyces cerevisiae has been studied in batch and continuous cultures at pH 4.0 and 30°C temperature with cell recycle. By using a 23.6 g/liter cell concentration, a concentation of 9.7% (w/v)ethanol was developed in a period of 6 hr. The rate of fermentation was found to increase with supplementation of yeast vitamins in the hydrolysate. In continuous culture employing cell recycle and a 0.127 v/v/m air flow rate, a cell mass concentration of 48.5 g/liter has been achieved. The maximum fermentor productivity of ethanol obtained under these conditions was 32.0 g/liter/hr, which is nearly 7.5 times higher than the normal continuous process without cell recycle and air sparging. The ethanol productivity was found to decrease linearly with ethanol concentration. Conversion of glucose in the hydrolysate to ethanol was achieved with a yield of 95 to 97% of theoretical.     

青橄榄浸膏的提取及其抗氧化活性研究

为优化青橄榄浸膏提取工艺,并探讨其抗氧化性。以茂名盛产的青橄榄为原料,采用超声波辅助乙醇提取法,以总黄酮和总多酚得率为评价指标,考察各因素对青橄榄浸膏提取效果的影响。采用邻苯三酚自氧化法、结晶紫法和DPPH清除能力评价青橄榄浸膏的抗氧化活性。结果显示,浸膏的最佳提取工艺为:乙醇体积分数70%,料液比1∶18 (g∶mL),超声提取温度50℃,时间6 min(超声提取阶段);单纯有机溶剂提取温度60℃,时间45 min(有机溶剂浸提阶段);此条件下总黄酮得率为1. 76%,总多酚得率为15. 53%。终产物浸膏在0. 3 mg/mL浓度下对超氧阴离子自由基抑制率为22. 74%,相当于同等质量浓度的抗坏血酸抑制效果的23. 47%;在0. 02 mg/mL浓度下对羟基自由基的清除率为67. 32%,相当于同等质量浓度的抗坏血酸清除效果的112. 58%;在0. 2 mmol/mL的DPPH溶液体系中,0. 15 mg/mL的浸膏对DPPH的清除率为95. 40%,相当于同等质量浓度的抗坏血酸清除效果的140. 83%;总体来讲,浸膏具有良好的抗氧化能力,虽然对超氧阴离子自由基抑制率弱于抗坏血酸,但羟基自由基的清除率及DPPH清除率均优于抗坏血酸。     

Modeling high-biomass-density cell recycle fermentors

Since intrinsic models, which take into account cell volume fraction, follow from proper application of the law of conservation of mass to a multiphase system, the intrinsic modeling approach should be used whenever biomass occupies a significant volume fraction of the culture. A recent report(11) offers the first comparison of intrinsic and nonintrinsic model predictions to actual experimental data gathered from a high-density yeast recycle fermentor. Here, the analysis of Jarzebski et al.(11) has been carried further to show that the improper nonintrinsic model predicts a steady-state culture glucose concentration that differs from that given by the fundamentally correct intrinsic model by over 60% at the optimal, bleed stream flow rate. In addition, a revised formulation for an intrinsic ethanol mass balance is presented.     

Balancing the Ethanol Formation in Continuous Bioreactors with Ethanol Stripping

Ethanol microbially produced in continuously operated aerated bioreactors is partly discharged with the liquid flow and is partly stripped off with the gas phase. The calculation of ethanol formation rates – as required, for example, in data evaluation by Metabolic Flux Analysis – solely based on the liquid‐borne ethanol, while neglecting the ethanol stripping, inevitably results in defective data interpretation. The proportion of stripped ethanol can be measured or, alternatively, calculated. The developed structured model describes the ethanol stripping as a two‐step process while differentiating between the phase transition from the liquid into the gas and the discharge of the evaporated ethanol with the off‐gas. As shown by model analysis as well as stripping experiments, the stripping rate is mainly determined by the ethanol discharge rather than by the phase transition. Consequently, the ethanol‐stripping rate depends on the specific gas flow rate and the partition coefficient for ethanol (at 30 °C, K_L/G = 3125 L/L), but not on the mass transfer coefficient. As shown by model simulations, the lower the dilution rate and the larger the gas flow rate of an aerated chemostat with a microbial ethanol formation, the higher the proportion of stripped ethanol. Under practically relevant conditions, more than 30 % of the produced ethanol may be stripped off. Exhaust‐gas coolers, actually used to reduce water losses by evaporation, do not prevent but slightly affect ethanol stripping.     

Cell growth and death rates as factors in the long-term performance, modeling, and design of immobilized cell reactors

The viable fraction of immobilized cells in a bioreactor may be critical in predicting long-term or steady-state reactor performance. The assumption of near 100% viable cells in a bioreactor may not be valid for portions of immobilized cell reactors (ICRs) characterized by conditions resulting in appreciable death rates. A mathematical model of an adsorbed cell type ICR is presented in which a steady-state viable cell fraction is predicted, based on the assumptions of no cell accumulation in the reactor and a random loss of cells from the reactor. Data on cell death rates, cell growth rates, and productivity rates as functions of temperature, substrate, and ethanol concentration for the lactose utilizing yeast K. fragillis were incorporated into this model. The steady-state reactor viable cell fraction as predicted by this model is a strong function of both temperature and ethanol concentration. For example, a stable 20% viable fraction of the immobilized cells is predicted in ICR locations experiencing continuous conditions of either 30 g/L ethanol at 40 degrees C, or 95 g/L ethanol at 25 degrees C. Steady-state ICR "plug flow" concentration profiles and column productivities are predicted at three operating temperatures, 20, 30, and 40 degrees C using two different models for ethanol inhibition of productivity. These profiles suggest that the reactor operating temperature should be low if higher outlet ethanol concentrations are desired. Three reactor design strategies are presented to maximize the viable cell fraction and improve long-term ethanol productivity in ICR's: (1) reducing outlet ethanol concentrations, (2) rotating segments of an ICR between high and low ethanol environments, and (3) simultaneous removal of the ethanol produced from the reactor as it is formed.     

The denaturation transition of DNA in mixed solvents

The helix-to-coil denaturation transition in DNA has been investigated in mixed solvents at high concentration using ultraviolet light absorption spectroscopy and small-angle neutron scattering. Two solvents have been used: water and ethylene glycol. The "melting" transition temperature was found to be 94 degrees C for 4% mass fraction DNA/d-water and 38 degrees C for 4% mass fraction DNA/d-ethylene glycol. The DNA melting transition temperature was found to vary linearly with the solvent fraction in the mixed solvents case. Deuterated solvents (d-water and d-ethylene glycol) were used to enhance the small-angle neutron scattering signal and 0.1M NaCl (or 0.0058 g/g mass fraction) salt concentration was added to screen charge interactions in all cases. DNA structural information was obtained by small-angle neutron scattering, including a correlation length characteristic of the inter-distance between the hydrogen-containing (desoxyribose sugar-amine base) groups. This correlation length was found to increase from 8.5 to 12.3 A across the melting transition. Ethylene glycol and water mixed solvents were found to mix randomly in the solvation region in the helix phase, but nonideal solvent mixing was found in the melted coil phase. In the coil phase, solvent mixtures are more effective solvating agents than either of the individual solvents. Once melted, DNA coils behave like swollen water-soluble synthetic polymer chains.     

Ethanol reduces sensitivity to ethylene and delays petal senescence in cut Tweedia caerulea flowers

Tweedia caerulea flowers are sensitive to ethylene and the closing of the flowers, a characteristic of senescence, is accelerated by exposure to ethylene. T. caerulea flowers were continuously treated with ethanol at concentrations of 0, 2, 4, 6, 8, 10 or 12 %, and treatment levels at 4 % and above showed delayed closing. Ethanol accelerated climacteric increase in ethylene production from flowers. Although ethylene production was higher in gynoecium than in petals, ethanol treatment accelerated ethylene production by both organs. Exposure to ethylene increased autocatalytic ethylene production, and production was further accelerated by ethanol treatment. When flowers treated with ethanol were exposed to ethylene, senescence was delayed compared to that for untreated flowers, suggesting that ethanol reduces the sensitivity of flowers to ethylene. These results indicate that treatment with ethanol delays petal senescence in cut T. caerulea flowers, possibly through reduced sensitivity to ethylene.     

A tale of two fluids: does storing specimens together in liquid preservative cause DNA cross‐contamination in molecular gut‐content studies?

The study of food webs and trophic interactions increasingly relies on PCR‐based molecular gut‐content analysis. However, this technique may be prone to error from contamination of minute quantities of DNA; i.e., simply storing specimens together in a liquid medium may lead to cross‐contamination. In this study, we used PCR to determine the contamination rate when (1) specimens were stored together in 95% ethanol for various time periods, and (2) predators fall into ethylene glycol‐filled pitfall traps where the dying predator may inadvertently consume prey DNA‐contaminated liquid. We designed experiments and PCR primers to quantify the risk of contamination for both situations and found no contamination by storing specimens together in 95% ethanol. Furthermore, zero predators contained prey DNA in their gut contents from imbibing prey DNA‐contaminated ethylene glycol. These results support the use of mass sampling techniques, like wet pitfall traps, for molecular gut‐content analysis.