Reducing the Energy Demand of Cellulosic Ethanol through Salt Extractive Distillation Enabled by Electrodialysis

One of the main challenges when a biochemical conversion technique is employed to produce cellulosic ethanol is the low concentration of ethanol in the fermentation broth, which increases the energy demand for recovering and purifying ethanol to fuel grade. In this study, two design cases implementing salt extractive distillation—with salt recovery enabled by a novel scheme of electrodialysis and spray drying—along with heat integrated distillation techniques of double-effect distillation and direct vapor recompression are investigated through process simulation with Aspen Plus® 2006.5 for reducing the thermal energy demand. Conventional distillation along with molecular sieve based dehydration is considered as the base case. Salt extractive distillation along with direct vapor recompression is found to be the most economical ethanol recovery approach for cellulosic ethanol with a thermal energy demand of 7.1 MJ/L (natural gas energy equivalents, higher heating value), which corresponds to a thermal energy savings of 23% and cost savings of 12% relative to the base case separation train thermal energy demand and total annual cost.     

加盐萃取精馏分离乙醇—水体系的研究进展

乙醇在化工、医药和电子等领域有广泛的应用,燃料乙醇作为可再生能源,已成为世界各国新型能源研发的重点。加盐萃取精馏是在溶盐精馏和萃取精馏的基础上发展起来,目前加盐萃取精馏是分离乙醇—水体系的重要方法。本文将分别介绍溶盐精馏和萃取精馏,以及加盐萃取精馏分离乙醇—水体系的研究现状及发展前景。     

A new process for fuel ethanol dehydration based on modeling the phase equilibria of the anhydrous MgCl2 + ethanol + water system

The use of ethanol as a fuel for motor engines has attracted significant attention because of its possible environmental and economic advantages over fossil fuel. However, the energy demand for the ethanol dehydration process significantly impacts its production cost. A new and energy efficient process is developed on the basis of salt extractive distillation, which uses recycled MgCl₂ granules as a separating agent. Vapor‐liquor‐equilibria (VLE) data for the ternary MgCl₂ + ethanol + water system, and the three constituent binary systems were measured at 30, 60, 90, and 101.3 kPa. A large enhancement of relative volatility of the ethanol + water system in the presence of MgCl₂ is observed throughout the entire ethanol concentration range, which completely broke the azeotrope. The salt effect of MgCl₂ is thought to be the result of energetic interactions and the hydration equilibrium reaction of the Mg²⁺ ion with water molecules. The calculation results by the mixed‐solvent electrolyte model embedded in the OLI platform equipped with new model interaction parameters and equilibrium constant (obtained via the regression of experimental VLE data), provided for a satisfactory means of simulating the MgCl₂ salt extractive distillation process. Finally, the process was proven feasible at the laboratory‐scale resulting in large granules of recovered MgCl₂ and a product of 99.5 wt % ethanol. © 2014 American Institute of Chemical Engineers AIChE J, 61: 664–676, 2015     

Experimental validation of hybrid distillation‐vapor permeation process for energy efficient ethanol–water separation

BACKGROUND: The energy demand of distillation‐based systems for ethanol recovery and dehydration can be significant, particularly for dilute solutions. An alternative separation process integrating vapor stripping with a vapor compression step and a vapor permeation membrane separation step, termed membrane assisted vapor stripping (MAVS), has been proposed. The hydrophilic membrane separates the ethanol–water vapor into water‐rich permeate and ethanol‐enriched retentate vapor streams from which latent and sensible heat can be recovered. The objective of this work was to demonstrate experimentally the performance of a MAVS system and to compare the observed performance with chemical process simulation results using a 5 wt% ethanol aqueous feed stream as the benchmark. RESULTS: Performance of the steam stripping column alone was consistent with chemical process simulations of a stripping tower with six stages of vapor liquid equilibria (VLE). The overhead vapor from the stripper contained about 40 wt% ethanol and required 6.0 MJ of fuel‐equivalent energy per kg of ethanol recovered in the concentrate. Introduction of the vapor compressor and membrane separation unit and recovery of heat from both membrane permeate and retentate streams resulted in a retentate ethanol concentrate containing ca 80 wt% ethanol, but requiring only 2.2 MJ fuel kg^?1 ethanol, significantly less than steam stripping alone. CONCLUSION: Performance of the experimental unit with a 5 wt% ethanol feed liquid corroborated chemical process simulation predictions for the energy requirement of the MAVS system, demonstrating a 63% reduction in the fuel‐equivalent energy requirement for MAVS compared with conventional steam stripping or distillation. Published 2009 by John Wiley & Sons, Ltd.     

Ethanol dehydration by extractive distillation

Experiments and process simulation enable favourable operating conditions to be determined for the extractive distillation of ethanol—water, with ethylene glycol as a solvent. The solvent molar rate to feed molar rate ratio S/F = 0·6 and the reflux ratio R = 0·5 were determined in order to achieve at least 99·5 mole % purity of ethanol. Other parameters examined include feed concentration, purity of solvent, and number of plates. Extractive distillation can be used to achieve high purity of ethanol at low energy consumption and under simple operating conditions.     

盐效应制取无水乙醇的研究现状及发展前景

无水乙醇广泛应用于制药、化工、能源等行业,需求量日益剧增。目前,利用盐效应制取无水乙醇的方法主要有溶盐精馏、加盐萃取精馏。文章对盐效应方法做了分析,对盐的选择和盐效应在分离工艺中的研究进展做了详细的阐述。     

Novel applications of dividing‐wall column technology to biofuel production processes

Biofuels enjoy nowadays increased public and scientific attention, driven by key factors such as volatile oil price, the need for increased energy security, and concerns over greenhouse gas emissions from fossil fuels. However, in order to make biofuels a competitive alternative, the cost of production has to be significantly reduced by using enhanced process technologies. Distillation is heavily involved in the production processes of biofuels—taking the blame for the high energy requirements that have a negative impact on the operating costs. Dividing‐wall column (DWC) is one of the best examples of proven industrial process intensification technology in distillation, as it allows significantly lower investment and operating costs while also reducing the number of equipment units and the carbon footprint. This work presents an overview of novel applications using the DWC technology in the production of the most important biofuels, by employing multi‐component separations, azeotropic, extractive or reactive distillation in a DWC: enhanced methanol recovery and glycerol separation in biodiesel production, synthesis of fatty acid methyl esters and dimethyl ether (DME) by reactive distillation, integrated DME purification and methanol or CO₂ recovery in the dimethyl ether process, as well as bioethanol concentration and dehydration. The industrially relevant case studies presented here show that significant energy savings are possible (ranging from ∼20 to 60%) while simplifying the processes by using less equipment that requires a lower plant footprint. Remarkably, in most cases there is also the possibility of revamping existing plants producing biofuels, and thus reusing the already available equipment. © 2013 Society of Chemical Industry     

生物基燃料乙醇生产工艺的能耗分析与节能技术综述

针对如何高效、经济和可持续发展生物质液体燃料这一问题,考察了淀粉质原料生产燃料乙醇的整个流程,从原料预处理到酒精脱水,尤其针对蒸馏、蒸煮液化等耗能较大的阶段,对不同的生产工艺技术进行了能耗比较,分析了不同的节能技术。通过大量的数据分析评述了最佳的技术路线,为燃料乙醇生产系统的节能降耗提出建议。     

Production of fuel ethanol from softwood by simultaneous saccharification and fermentation at high dry matter content

BACKGROUND: The production of bio‐ethanol from softwood is considered a promising alternative to fossil fuels in Sweden. In order to make fuel ethanol economically competitive with fossil fuels, it is important to reduce the production cost, which can be done by increasing the dry matter content of the fermentation medium, thus reducing the energy demand in the final distillation of the fermentation broth. Running simultaneous saccharification and fermentation (SSF) at higher dry matter content has, however, been found to decrease the ethanol yield. RESULTS: The use of different stirrer types and stirring speeds in the present study has shown to have an influence on the final ethanol yield in SSF with 10% water‐insoluble solids (WIS). Also, higher concentration of pretreatment hydrolysate, i.e., with increased inhibitor concentration, at the same WIS resulted in a decreased ethanol yield. However, despite stirring problems and high inhibitor concentration, ethanol was produced at 12% WIS with an ethanol yield in the SSF step of 81% of the theoretical based on the content of fermentable sugars in the fermentor. CONCLUSION: The decrease in ethanol yield in SSF at high dry matter content has been shown to be a combined effect of increased mass transfer resistance and increased inhibitor concentration in the fermentation broth. Copyright © 2008 Society of Chemical Industry     

Membrane‐assisted vapor stripping: energy efficient hybrid distillation–vapor permeation process for alcohol–water separation

BACKGROUND: Energy efficient alternatives to distillation for alcohol recovery from dilute solution are needed to improve biofuel sustainability. A process integrating steam stripping with a vapor compression step and a vapor permeation membrane separation step is proposed. The objective of this work is to estimate the energy and process costs required to make a fuel grade ethanol (0.5 wt% water) from 1 and 5 wt% ethanol aqueous streams using the proposed process. RESULTS: Using process simulation and spreadsheeting software, the proposed membrane‐assisted vapor stripping process was estimated to require as little as 8.9 MJ of fuel‐equivalent energy per kg of fuel grade ethanol recovered from a 1 wt% ethanol feed stream, 2.5 MJ kg^?1 for a 5 wt% ethanol solution. This represents an energy saving of at least 43% relative to standard distillation producing azeotropic ethanol (6 wt% water). Process costs were also found to be lower than for distillation at the 3.0 × 10⁶ kg‐ethanol year^?1 scale modeled. CONCLUSION: In this hybrid system, the stripping column provides high ethanol recoveries and low effluent concentrations while the vapor compression‐membrane component enables the efficient recovery of latent and sensible heat from both the retentate and permeate streams from the membrane system. Published in 2008 by John Wiley & Sons, Ltd.     

乙醇-水-离子液体三元体系的气液平衡测定及其萃取精馏试验

在101.32 kPa下,用改进的Othmer釜测定了乙醇-水-1,3-二甲基咪唑磷酸二甲酯盐([MMIM]+[DMP]-)物系等压气液平衡数据。实验结果表明,加入[MMIM]+[DMP]-使气液平衡线偏离乙醇-水二组分物系的气液平衡线,[MMIM]+[DMP]-含量越高,偏离程度越大;[MMIM]+[DMP]-表现出盐效应,使乙醇对水的挥发度发生改变,消除了乙醇-水物系的共沸点;并以[MMIM]+[DMP]-作为乙醇-水物系萃取精馏的溶剂,进行了萃取精馏的小型工艺试验,结果塔顶乙醇质量分数达到99.5%,能够满足工业要求。     

Analysis of Energy‐Efficient Complex Distillation Options to Purify Bioethanol

Three complex extractive distillation options were studied for the purification of a dilute mixture of ethanol and water. The first option uses an extractive distillation column and the other two options use thermally coupled extractive distillation sequences. The results indicate that the fully thermally coupled extractive option can reduce energy consumption by ca. 30 % compared to the scheme that uses an extractive distillation column. This fully thermally coupled extractive distillation sequence can produce ethanol as distillate with a mass fraction of 0.995, the entrainer as the bottoms product and a mixture of ethanol and water as the sidestream.     

Extractive distillation with the mixture of ionic liquid and solid inorganic salt as entrainers

The use of the mixture of ionic liquid (IL) and solid inorganic salt in place of the single IL as entrainers for extractive distillation, which integrates the advantages of a liquid solvent, that is, IL (easy operation and nonvolatility) and a solid salt (high separation ability) has been proposed in this work. The vapor–liquid equilibrium experiments indicated that the combination of [EMIM]⁺[Ac]^? and KAc is the most promising for the separation of ethanol and water among all of the entrainers investigated. Based on the thermodynamic study, the conceptual process design was developed to evaluate the competitiveness of the suggested entrainers for the separation of ethanol and water. It was determined that the overall heat duty on reboilers in the extractive distillation process using the new mixed entrainers decreases 19.04% compared with the benchmark entrainer [EMIM]⁺[Ac]^?. Moreover, the density functional theory and COSMO‐RS model were used to achieve theoretical insights at the molecular level. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2994–3004, 2014     

中粮(安徽)非粮乙醇技术改造能量投入/产出分析

中粮(安徽)15万吨/年粮食燃料乙醇的非粮原料技术改造取得了预期效果。本文在概述非粮原料改造基础上,采用能量投入/产出分析方法,对以木薯和玉米为原料的燃料乙醇生产过程的能量效率进行了分析,对原料变化产生的影响进行评价,最后展望今后采用非粮路线发展生物质液体燃料的前景。结果表明,生产环节改造对能量效率变化具有重要影响。玉米乙醇的净能量值为1.77MJ/L,木薯乙醇为7.82MJ/L,以木薯为原料的燃料乙醇具有较高的能量效率。但综合考虑能量效率、碳排放及土地利用等因素,继续拓展生物质原料应以农林废弃物为主,木薯原料的使用规模不宜轻易扩大。     

Economic evaluation of energy saving alternatives in extractive distillation process

Until now, there has not been consensus about the superiority of thermally coupled sequence over the conventional sequence in the extractive distillation process. In this sense, the main goal of this paper is to analyze three approaches for saving energy in the extractive distillation process: optimization, thermal integration and thermal coupling. Three azeotropic mixtures were investigated: ethanol and water (M1); tetrahydrofuran and water (M2); and acetone and methanol (M3). The solvents were ethylene glycol for M1 and M2, and water for M3. The results are shown in terms of the total annual cost (TAC) and specific energy consumption (SEC), and revealed that a thermally coupled extractive distillation sequence with a side rectifier did not always present the best results. Taking the case studies from literature as a starting point (without thermal integration), the optimization procedure used in this work found that TACs are always lower. The inclusion of thermal integration in configurations led to reducing TAC for all mixtures under investigation when compared to the sequences without this integration. When comparing two modifications in the layout of extractive distillation, it can be seen that it is more advantageous to use the preheating of the azeotropic feed with the recycle stream from the recovery column of the conventional sequence than using a thermally coupled sequence.     

淀粉质原料发酵法制燃料乙醇中蒸煮液糖化阶段能耗分析及改进技术的探究

针对如何解决能源的可持续发展这一重要问题,考察了石油替代产品--燃料乙醇的生产流程,从原料预处理到酒精脱水,针对耗能较大的蒸煮液糖化这一原料预处理阶段,对不同的生产工艺技术进行了能耗比较,分析了不同的节能技术。通过大量的数据分析评述了最佳的技术路线,为燃料乙醇生产系统的节能降耗提出建议。     

单(2-羟乙基)铵甲酸盐离子液体用于乙醇水溶液萃取精馏的过程模拟

利用Aspen Plus模拟软件,模拟研究了由乙醇质量分数为95%的工业酒精通过常压萃取精馏制取无水乙醇的工艺过程,并对单(2-羟乙基)铵甲酸盐离子液体和乙二醇传统萃取剂的分离性能进行了比较分析。考察了原料和萃取剂的进料位置、萃取剂用量、回流比等参数对分离效果的影响,获得了优化的操作条件,即精馏塔塔板数28,原料进料板为第17块,萃取剂进料板为第2块,溶剂比为0.6,摩尔回流比为1.6。在优化操作条件下,塔顶产品中乙醇的质量分数可达99.98%,与乙二醇为萃取剂的传统萃取精馏过程相比,再沸器热负荷降低28%,具有明显的节能效果。     

节能型乙醇蒸馏及脱水集成工艺

围绕由生物质发酵醪液生产燃料乙醇过程中精馏与脱水工艺展开研究,提出了精馏塔塔顶部分冷凝技术。通过计算机模拟,着重从能耗方面将该方案与常规工艺以及最近出现的回流段无水乙醇共沸精馏技术进行比较。结果表明,部分冷凝工艺和回流段无水乙醇共沸精馏流程节能效果显著。     

分批萃取精馏回收无水乙醇的新工艺

针对分批萃取精馏法回收无水乙醇原有工艺流程中存在的问题,提出了优化方案。在原有流程的基础上,添加了一个溶剂回收釜,塔的下段液相流体直接流入溶剂回收釜。结果使得塔釜的温度变化降低,加热容易控制,操作时间变短。此方案对分批萃取精馏法回收无水乙醇的工艺改造有参考价值。     

新型分离法回收制药废液中四氢呋喃

为了从制药废液中回收四氢呋喃 ,研究了萃取精馏技术和加盐萃取精馏技术在分离甲醇 四氢呋喃 水体系中的应用 ,选择了萃取精馏及加盐萃取精馏所用溶剂 ,设计了工艺流程 ,确定了操作条件 ,采用以上技术从废液中回收的四氢呋喃 ,纯度可达到 99.5 % (质量 )