Production of Motor Fuel Grade Alcohol by Concentration Swing Adsorption

Abstract

A new cyclic process concept called “concentration swing adsorption” for separation of bulk binary liquid mixtures is described. The process carries out the primary separation by selective liquid-phase adsorption of one of the components of the feed mixture on an adsorbent. The adsorbed component is then desorbed by a desorbent liquid which is equally or more strongly adsorbed than the slectively adsorbed component of the feed mixture. The desorbent liquid is removed from the adsorbent by displacing it with the less strongly adsorbed component of the feed mixture so that the adsorbent can be resused. The process also includes a complementary step where the adsorbent is rinsed with the more strongly adsorbed component of the feed mixture so that two essentially pure products are produced from the feed mixture with high recoveries of both components. At least one simple distillation is also required by the process which separates the desorbent liquid from the less strongly adsorbed component of the feed mixture. The process can be used to separate liquid mixtures with close boiling components or azeotropic mixtures which require energy intensive distillation. A very efficient separation can be achieved in these cases by spending only a fraction of the distillation energy. An example of such an application, viz., separation of a bulk ethanol–water mixture for motor fuel grade alcohol production, is described. A local equilibrium model of the process is used to evaluate the performance of the process for that separation using an activated carbon as the adsorbent and acetone as the desorbent liquid. Experimentally measured equilibrium adsorption characteristics for ethanol–water, acetone–water, and acetone–ethanol binary liquid mixtures on the carbon as well as adsorption column dynamics for the steps of the process are reported.     

Effectiveness factors for reactions between volatile and non-volatile components in partially wetted catalysts

A steady state model is formulated to describe the reactions between one gaseous and two non-volatile components on partially wetted catalysts in a trickle-bed reactor. Unlike previous studies, the model does not assume a gaseous or liquid limiting reactant. The computed results show the effect of intraparticle and interphase mass transfer resistances as well as of wetting efficiency and number and location of wetted zones on catalyst performance. Maximum effectiveness factors are generally obtained with intermediate values of the wetting efficiency. The model is applied to a typical HDS process of heavy gas oil in trickle-bed reactors.     

Trickle-bed reactors: Effect of wetting geometry on overall effectiveness factor

Calculations of the overall effectiveness factor in a trickle-bed reactor are given that take into account liquid distribution on the external catalyst surface. Two cases are examined: nonvolatile limiting reactant (A), and limiting reactant present in both fluid phases (B). Parameters investigated, for first-order, isothermal kinetics, are: number of wetted and nonwetted zones, particle shape, Thiele Modulus, wetting efficiency, and Biot numbers. The calculated results fall within the range of limiting solutions obtained independently. For case A the difference between 2- and 8-zone models may reach 40% within the commercially important range of the Thiele modulus. For case B it probably does not exceed 25%. Comparison is also made with experimental data. It is concluded that a multizone model can be useful in the analysis. A new form of approximate model is proposed for case A.     

Mass transfer accompanied by parallel reversible chemical reactions

Theoretical effects of parallel reversible chemical reactions on the rate of mass transfer are investigated in this paper. On the basis of the film theory, an analytical equation has been derived for gas absorption accompanied by first-order parallel rversible reactions. Analytical approximate equations have been developed and finite difference techniques applied to study the enhancement of mass transfer by second-order complex reactions. Results of this study indicate that when the diffusion is accompanied by second-order parallel reactions, the mass transfer rate increases with the concentration of the liquid reactant in the bulk, and approaches that of diffusion and first-order parallel reactions if the product of the diffusivity and bulk concentration of the liquid reactant is much larger than that of the gas reactant.     

Hurdles and solutions for reactions between gas and liquid in a monolithic reactor

In this paper, proof of principle experiments and exploratory work that solves the problem of ensuring that a gaseous and a liquid reactant are available at the catalytically active site at the same time by separating the reaction and the transport of the gaseous reactant. The equipment consisted of an autoclave in which a feed was saturated with hydrogen, a reactor with a catalyst coated on a monolith, a pump to circulate the feed/product stream, and devices to control and monitor the process.

A lot of information of how the process can be practised was gathered during the work. Conversion per pass should be below the amount of hydrogen that can be dissolved in the liquid to avoid coke deposition (and hence deactivation) of the catalyst. The effectiveness of the catalyst coated on the monolith was found to be 100%.

Several variations of the process design and catalysts used were explored. Integration of the monolith with a heat exchanger will obviously allow for the use of the process for very exothermic reactions like (nitro)benzene hydrogenation. A monolith to which Rh-cyclooctadiene-1,2-bis-diphenylfosfino-ethane (a homogeneous catalyst) was tethered was equally active in hydrogenation of 1-hexene as Rh-cyclooctadiene-1,2-bis-diphenylfosfino-ethane tethered to a standard alumina. This allows (fine)chemical producers to repeatedly use the expensive homogeneous catalysts without the need for separation of the catalyst from the reaction mixture.     

Etching effects of ethanol on multi-walled carbon nanotubes

The morphology and microstructure of multi-walled carbon nanotubes (MWCNTs) were modified using ethanol as a mild gas reactant. The etching by OH radicals and deposition of C radicals on the carbon nanotubes were considered to be responsible for the modification of the MWCNT structures and the formation of new carbon nanostructures. The effects of etching and deposition on the MWCNTs were confirmed by using methanol as another gas reactant; this molecule has a higher ratio of hydroxyl radicals to carbon atoms than ethanol. In addition, water vapor, containing no carbon atoms in the molecule, was also applied to etch the MWCNTs as a weak oxidant which resulted in stronger etching effects on the MWCNTs than methanol and ethanol.     

气相第2组分对水溶解CO2过程界面对流影响的LIF观测

采用激光诱导荧光（LIF）观测方法考察了在气相中分别添加乙醇和二氯甲烷分别对CO₂在水中溶解过程界面对流的影响,得到了液相中CO₂浓度分布及其演化的观测结果,通过物料衡算得到了相应条件下的液相传质系数。CO₂溶解过程会出现由密度梯度引起的Rayleigh对流。实验结果表明,当添加的乙醇含量小于8.47 mg·L^-1时,Rayleigh对流会被增强,进而促进了CO₂的溶解;随着气相中乙醇含量的增大,Rayleigh对流反而被抑制;气相添加二氯甲烷会显著增强Rayleigh对流,提高了CO₂的传质速率,随着气相二氯甲烷含量的增大,CO₂在水中溶解过程的液相传质系数呈现先加强后恒定的趋势。     

Direct production of crystalline boric acid through heterogeneous reaction of solid borax with propionic acid: Operation and simulation

The production of boric acid through reaction of borax crystals with propionic acid was investigated in batch mode. It was found that the product boric acid precipitates on the solid borax reactant. An increase in the coefficient of variation of feed crystals resulted in an increase in the time of completion of the reaction. A sharp interface model with variable bulk fluid concentration of liquid reactant was developed for simulation of the process. The analytical solution of the series of rate equations involving liquid film, solid boric acid layer and chemical reaction resistances was obtained, and a new method for simultaneous determination of kinetic parameters was established. The chemical reaction and diffusion through the solid layer of boric acid were the rate controlling mechanisms. A numerical algorithm was also developed for predicting the fractional conversion of multisize borax crystals using the mono size kinetic parameters determined according to the proposed analytical method.     

利用中孔分子筛Al-MCM-41催化合成农药异戊烯酸乙酯的条件

[方法]利用中孔分子筛Al-MCM-41作催化剂,直接用反应物乙醇作带水剂,以乙醇和异戊烯酸为原料,采用分批补充乙醇的工艺方法合成农药异戊烯酸乙酯。考察了催化剂用量、反应物物质的量比、反应温度和反应时间对反应转化率和选择性的影响。[结果]该反应最佳的合成条件:异戊烯酸和乙醇的物质的量比为1∶8,催化剂的量为异戊烯酸质量的1.8%,反应时间为6 h,反应在剧烈回流温度下进行。在此条件下,异戊烯酸转化率可达89.9%,产品纯度大于99.7%。[结论]中孔分子筛Al-MCM-41可作为合成异戊烯酸乙酯高效而环保的固体酸催化剂。     

A STUDY ON THE PERFORMANCE OF THE CATALYTIC POROUS-WALL THREE-PHASE REACTOR

A theoretical investigation of a catalytic porous-wall reactor in which gaseous and liquid reactants approach each other from opposite sides of the catalyst is undertaken. Equations for the annular liquid-channel are coupled with those for the catalytic wall and solved numerically and analytically using a simplified model. For the model reaction under study, the main design and operation parameters which affect reactor performance are the Thiele modulus, Peclet number, width of the liquid channel and the inlet concentration of the reactant in the liquid phase.

The effect of reactor configuration is peculiar to the cylindrical geometry because the thickness and relative location of the catalytic wall as well as the selection of the liquid and gas channels can influence the reactor performance. Thin-walled catalyst tubes have larger effectiveness factors and as the tube radius approaches that of the reactor, conversion in the reactor increases especially when the liquid is saturated with the gaseous reactant. Concentration of the liquid reactant in the feed has a significant effect if the reactant is depleted at some point inside the catalyst wall. Since the reaction zone width can be adjusted by changing the feed composition, this might have important implications with respect to selectivity.     

Selectivity in gas purification: film theory,semi-infinite medium

A film theory model describing simultaneous transport of two gases into a reactive liquid has been used in an examination of the conditions that optimize selectivity. One component reacts instantaneously, the other at a finite rate. The resulting unstable two point boundary value problem was solved numerically for a range of the dimensionless numbers that characterize an important application for this system. Selectivity is shown to be favored by low interfacial concentrations of both gases but particularly of the component reacting instantaneously; it is also favored by high concentrations of the non-volatile liquid reactant. Selectivity can be high while the rate of transfer of the selective component can also be large. Good mixing can further help the selectivity if this does not significantly reduce the bulk concentrations of the non-volatile reactant. A boundary condition of the film theory often imposed on such systems is shown to be unnecessary.     

PERFORMANCE OF AN ANNULAR CATALYTIC THREE-PHASE REACTOR FOR A SECOND ORDER REACTION

A novel annular catalytic three-phase reactor is theoretically investigated for a second order hydrogenation reaction. The results indicate that the ratio of the gaseous reactant to the liquid reactant within the reaction zone of the annular reactor can be adjusted by changing the reactor dimensions and the concentration of the gaseous reactant in the feed. As a consequence, the annular reactor may have a significant advantage over the trickle-bed reactor with respect to the selectivities that may be achieved in the reactor.     

离子液体催化合成醋酸正丙酯的工业实验

在南京扬子石化精细化工有限责任公司年产1500t醋酸正丙酯工业装置上进行了BILE-3型离子液体催化合成醋酸正丙酯的工业实验。考察了BILE-3型离子液体催化合成醋酸正丙酯工艺中反应体系水、酸度等工艺条件对酯化反应的影响,并与传统硫酸催化酯化工艺进行了比较。工业实验结果表明,酯化反应体系中水小于反应物料质量分数5%,酸度在45～65gKOH/100g,酯化釜液位高度在反应釜容积的50%～70%,酯化反应转化率为95%以上,选择性为99%以上;与传统硫酸催化酯化相比,BILE-3型离子液体催化工艺具有生产成本低、过程清洁、不腐蚀设备、运行周期长等优点。     

催化加氢合成对甲氧基苯甲醇工艺优化

研究了以对甲氧基苯甲醛为底物,通过Pd/C催化氢化合成对甲氧基苯甲醇的工艺。考察了不同溶剂,反应压力,催化剂用量,底物浓度,反应温度,反应时间及催化剂重复使用诸因素对产物对甲氧基苯甲醇收率或产物组成的影响。结果表明:以200mL乙醇为溶剂,原料为0.4mol,5%Pd/C用量为5%(质量分数),反应压力为0.3MPa,反应温度为30℃,反应时间为8h时,经过过滤,常压蒸馏、减压蒸馏,得无色透明的对甲氧基苯甲醇液体,收率可接近95%。     

MASS TRANSFER WITH CHEMICAL REACTION IN PARTIALLY WETTED FLAT PLATE CATALYST PELLETS: RIVULET FLOW ANALYSIS

Mass transfer with chemical reaction is analyzed in a system formed by a flat plate solid catalyst, partially wetted by a flowing rivulet of a liquid in contact with a stagnant pure gas. The paper solves the fluid dynamic problem of the liquid phase first, and afterwards incorporates the mass transfer and the chemical reaction. The system is assumed to be isothermal and at steady state, with a first order kinetics whose limiting reactant is in the gas phase. This work studies the influence of the gas-liquid surface tension, the liquid reactant flow rate, the liquid viscosity and the angle of inclination of the solid, upon the wetting factor. The model proposed also predicts the effect of these parameters and the Thiele modulus on the overall effectiveness factor and the molar flux of the limiting gaseous reactant at the catalytic solid-liquid interface in a direct way. This approach makes the wetting factor a non-manipulated variable.     

On the application of the shrinking core model to liquid—solid reactions

It is shown that the pseudo steady state approximation in the application of the shrinking core model to liquid—solid reactions is valid even when the ratio of liquid reactant concentration to molar density of the solid is high. In this case the pseudo steady state approximation neglects both the accumulation term and the convective mass transfer term in the mass balance. The respective errors thus introduced have different signs and largely cancel each other. It is also shown that the experimental analysis of liquid—solid reactions can be simplified by a suitable design of batchwise experiments, which also increases the accuracy in parameter estimation.     

板式精馏塔实验性能测试

本文对废液中低浓度乙醇的回收再利用进行了研究,主要对低浓度乙醇精馏过程中的不同实验条件进行了初探,得出了塔釜加热电压,塔釜液浓度,回流比等实验条件与塔顶产品浓度之间的关系,并用计算机绘制了图表,确定一组最优的实验条件。     

生料淀粉制乙醇研究及产业化进展

燃料乙醇作为一种高效的液体燃料已在全世界范围推广使用。目前,广泛使用的干法制乙醇工艺已十分成熟。然而,生产过程更为简化、条件更为温和、可实现更高水平浓醪发酵的生料淀粉制乙醇工艺已成为燃料乙醇工业进一步迈向绿色减排、高效节能的重要发展方向。生料淀粉工艺经历了几十年实验室研究,并且也已在产业化方面有巨大发展。尤其以美国POET公司为代表,其BPX生淀粉水解专利技术已在24套燃料乙醇工业装置上得到应用。综述了生料淀粉工艺研究进展,并对已经产业化的案例作了介绍。开发具有自主知识产权的生料淀粉制乙醇工艺、关键技术及装备也是我国未来燃料乙醇产业发展的一个重要方向。     

乙醇溶液液滴降压闪蒸特性

基于液滴低压闪蒸理论,设计了一套悬垂液滴的真空闪蒸可视化实验装置,研究了质量分数为0、5%、10%、20%的乙醇溶液液滴的降压闪蒸特性,记录了液滴的成核结晶过程。液滴在降压条件下会经历液态蒸发、伴随气泡生长的蒸发、稳态蒸发结冰、伴随气泡生长的结冰、外部结冰内部气泡逸出最终爆裂5种形态。研究表明乙醇溶液的浓度越高,液滴的凝固点越低,液滴结晶所需时间越长;同时还发现一定浓度的乙醇溶液可以提高液滴结晶时的闪蒸室压力,降低了对系统真空度的要求。