Recent advances in sulfur removal from gasoline by pervaporation

Pervaporation (PV) is today considered as a promising unit operation for separation of organic-organic liquid mixtures and is being investigated extensively in chemical and petrochemical industries. Recently, PV applications in environment cleanup operations, especially in the removal of sulfur compounds from gasoline have attracted increasing attention worldwide. Gasoline desulphurization by PV is a newly emerged technology in which sulfur components can be preferentially removed from the gasoline feed due to its higher affinity with, and/or quicker diffusivity in the membrane. A considerable amount of background information, current state and trends of the new PV application in gasoline desulphurization are dealt with. The article focuses on the PV membranes development, interactions between gasoline components and membranes, the improvement in process engineering, techoeconomical analysis and the technology scale up. Finally, some suggestions for further research were presented with the aim of reducing the cost in introducing the PV process into refineries for desulphurization.     

A characterization of pdms pervaporation membranes for the removal of trace organic from water

A new silicone pervaporation membrane for the removal of one of trace organies, 1,2-dichloroethane from water has been developed using polydimethylsiloxane (PDMS) and oligomeric silylstyrene as a crosslinking agent of PDMS. Optimal conditions for fabricating the best membrane were determined from swelling measurements ard pervaporation experiments and then the membrane was characterized at different membrane thickness and operating conditions. In the pervaporation separation of 55–70 ppm of l,2-dichlorocthanc aqueous mixtures, the developed membrane has flux of 2.5–330 g/(m².h) and selectivity of 230–1750 depending on membrane thickness, permeate pressure and operating Temperature. Water permeation through thin membrane was found to be subjected to significant desorption resistance, while the desorption resistance and thermodynamic factors as well as the concentration polarization of the organic at the boundary layer in feed can affect the organic permeation, depending on membrane thickness. Selectivity change with permcaic pressure depends on membrane thickness: at small membrane thickness range, selectivity increases with permeate pressure and at large thickness region it decreases. From the Arrhenius plots of each component fluxes, the permeation activation energies were determined. Through an analysis of the permeation activation energies of each components, the desorption resistance as well as the effects of the thermodynamic factors on permeation was qualitatively characterized.     

Membrane materials in the pervaporation separation of aromatic/aliphatic hydrocarbon mixtures—A review

The separation of aromatic/aliphatic hydrocarbon mixtures is a significant process in chemical industry,but challenged in some cases.Compared with conventional separation technologies,pervaporation is quite promising in terms of its economical,energy-saving,and eco-ffiendly advantages.However,this technique has not been used in industry for separating aromatic/aliphatic mixtures yet.One of the main reasons is that the separation performance of existed pervaporation membranes is unsatisfactory.Membrane material is an important factor that affects the separation performance.This review provides an overview on the advances in studying membrane materials for the pervaporation separation of aromatic/aliphatic mixtures over the past decade.Explored pristine polymers and their hybrid materials (as hybrid membranes) are summarized to highlight their nature and separation performance.We anticipate that this review could provide some guidance in the development of new materials for the aromatic/aliphatic pervaporation separation.     

Application of microwave heating to pervaporation: A case study for separation of ethanol–water mixtures

Membrane pervaporation experiments for dewatering of water–ethanol mixtures were conducted, using a polymeric hydrophilic membrane, under microwave and conventional heating in a multimode microwave oven and a convection oven, respectively. Three feed temperatures (33.5, 45.5 and 51.5 °C) and two feed compositions (5.5 wt% and 20 wt% water in the feed) were considered. At 20 wt% water content, higher water fluxes through the membrane were obtained in the convection oven. At lower water content in the feed (5.5 wt%), the opposite effect was observed; the water fluxes were higher under microwave heating over the considered temperature range. These differences may arise from the different dielectric properties and consequently thermal behaviour of the feed mixtures under microwave heating. Microwave coupling with ethanol is stronger than with water. Moreover, unlike water, the dielectric loss factor of ethanol increases with temperature, which makes microwave dissipation preponderant in hot areas. Hence, high ethanol concentrations in the feed can easily induce thermal gradients.     

n-Butyl acrylate production by esterification of acrylic acid with n-butanol combined with pervaporation

In this study, the esterification reaction of acrylic acid and n-butanol to produce n-butyl acrylate and water was studied using the pervaporation–esterification hybrid process to perform the separation and reaction simultaneously to increase the conversion of limiting reactant. A Pervap 2201 polymeric membrane was used to separate water and also to shift the equilibrium. The Pervap 2201 membrane showed high selectivity to water in the n-butanol, acrylic acid, n-butyl acrylate, and water reaction system. The effects of temperature, the initial molar ratio of n-butanol to acrylic acid, catalyst loading, and the ratio of membrane area to reaction volume (S/V) were studied. The maximum conversion of acrylic acid was calculated as 96.3% at a temperature of 358 K, a molar ratio of 8, with a catalyst loading of 10 g/L and an S/V ratio of 70 m⁻¹.     

Modification of Hβ zeolite by fluorine and its influence on olefin alkylation thiophenic sulfur in gasoline

By modifying the Hβ zeolite with proper amount HF, the catalytic performance of fluorinated Hβ was obviously improved for the olefin alkylation thiophenic sulfur process. Particularly, the acid sites of the fluorinated Hβ catalysts were increased, especially its distribution of medium and stronger Lewis and Brönsted acid sites was optimized, and its thiophene alkylation activity and stability are thus promoted as well as its coking behavior is suppressed during OATS process.     

催化裂化汽油吸附法脱硫技术开发

以氧化锌和过渡金属M为活性组分,以硅藻土为载体,采用浸渍法制备了双组分吸附脱硫剂。以中国石油独山子石化分公司催化裂化汽油为原料,对吸附剂的脱硫深度和硫容等性能进行了评价,在反应温度360 ℃、压力2.0 MPa、V(氢)∶V(油)=1.3和空速7.0 h^-1的条件下,将汽油中硫含量从153.86 μg·g^－1降至14.36 μg·g^－1,汽油抗爆指数损失控制在0.2个单位左右,精制汽油收率保持在99.3％以上。     

Manipulation of confined structure in alcohol-permselective pervaporation membranes

Alcohol-permselectivity pervaporation has been arousing increasingly more attention in bioalcohol production due to the advantages of environmental friendliness, lowenergy consumption and easy couplingwith fermentation process. With the intrinsic feature of larger molecules preferentially permeating and the consequent inferiority in selective diffusion, the development of alcohol-permselectivemembrane is relatively retarded compared with water-permselective membrane. This review presents the prevalent membrane materials utilized for alcohol-permselective pervaporation and emphatically expatiates the representative and important developments in the past five years fromthe aspect of tuning confined structure in membranes. In particular, the diverse structure tuningmethods are described with the classifications of physical structure and chemical structure. The corresponding structure-performance relationships in alcohol-permselective pervaporationmembranes are also analyzed to identify the objective of structure optimization. Furthermore, the tentative perspective on the possible future directions of alcohol-permselective pervaporation membrane is briefly presented.     

Polyvinyl Butyral/Modified SiO2 Nanoparticle Membrane for Gasoline Desulfurization by Pervaporation

Pervaporation (PV) has many potential advantages in fluid catalytic cracking (FCC) gasoline desulfurization. The PV membrane performance was improved by incorporating SiO₂ nanoparticles in polyvinyl butyral (PVB). The coupling agent was used to enhance the compatibility between the inorganic phase and the organic phase to avoid the occurrence of film defects. Polyurethane membranes were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, and atomic force microscopy. To evaluate the PV performance, the real FCC gasoline was tested. The effects of the SiO₂ content, the operating temperature, and the active layer thickness on the PV performance of the PVB/SiO₂ membranes were investigated.     

汽油深度脱硫的技术进展

介绍了加氢脱硫和非加氢脱硫2种汽油脱硫技术。综述了近年来汽油深度脱硫机理方面的研究和技术进展。     

Plasticization of chitosan membrane for pervaporation of aqueous ethanol solution

The process of pervaporation in which two components diffuse through a nonporous polymer membrane was modelled when one of the penetrants can exert a plasticization action to the membrane material. Thereat a phenomenological model was employed for describing the plasticization effect on the diffusivities for penetrants in the membrane. The sorption equilibria and permeation fluxes for aqueous ethanol solutions in a chitosan membrane were measured, and the permeation fluxes for water were compared with those predicted by the proposed model. The concentration of sorbed water was linear with its weight fraction (x₄) in the feed solution, whereas the permeation flux of water was. affected by the plasticization action of sorbed water to the polymer. This plasticization effect on the diffusion process can be simulated in terms of the proposed phenomenological model.     

Experimental study on physical properties and pervaporation performances of polyimide membranes

Five kinds of polyimide membranes have been synthesized from two dianhydrides (including pyromellitic dianhydride (PMDA) and 3, 3^′4, 4^′-benzophenonetetracarboxylic dianhydride (BTDA)) and three diamines (including 4,4^′-diaminodiphenylether (ODA), 4,4^′-diaminodiphenylmethane (MDA) and phenylenediamine (PDA)) via a two-step method, and the properties of polyimide membranes have been characterized by experimental techniques. The permeation experiments of water/ethanol mixtures through the polyimide membranes were carried out at 318, 328, 338 and 348 K. All polyimide membranes in this paper are water selectivity, and the flux of mixtures through MDA-based polyimide membranes is higher than that of solvents through PDA-based polyimide membranes with the same diahydrides, while the separation factor exhibits the opposite variation order at the same temperature. The total flux and the partial water flux through all the membranes increase with the operating temperature rising, and the relationships between the flux and temperature can be described by Arrhenius equation. According to the Arrhenius equation, the active energies of water/ethanol in PMDA-ODA, PMDA-MDA, BTDA-PDA, BTDA-ODA and BTDA-MDA membranes are 35.1, 52.6, 16.4, 19.8 and 27.1 kJ/mol, respectively, and those for partial water flux in PMDA-ODA, PMDA-MDA, BTDA-ODA and BTDA-MDA are 36.1, 46.8, 19.9 and 27.9 kJ/mol, respectively. The separation factors of mixtures in the polyimide membranes but no PMDA-MDA show the trend of increase with the operating temperature. The partial flux of ethanol increases while the separation factor of mixtures in PMDA-MDA decreases with the operating temperature, and the activation energy for partial ethanol flux in PMDA-MDA is 75.2 kJ/mol. In addition, pervaporation performances were attempted to correlate independently with the fractional free volume (FFV) and mean interchain distance (d-spacing) of polymers. It is shown that lnJ increases with d-spacing, while there is no clear relationship between the flux and FFV.     

改性褐煤半焦用于脱除汽油中含硫化合物的研究

以廉价的煤制气副产半焦为载体,经改性后在固定床进行FCC汽油吸附脱硫实验,考察了活化因素、氧化物负载种类及负载量、床层温度、空速等对脱硫效果的影响,得出最佳脱硫工艺条件。经过改性后的活性半焦,用于汽油脱硫具有很好的效果,对于苯并噻吩(BT)脱除的效果尤为明显。     

A review of membrane selection for the dehydration of aqueous ethanol by pervaporation

Four broad types of membranes are categorised: organic polymers generally, crosslinked poly(vinyl alcohol), organic-inorganic hybrids and charged polymers. The best performers in terms of flux, which reaches a maximum of 5 kg/m²h, are anionic or cationic polymers, including polysalts. Polyanion and polysalt membranes are superior. Two examples are thin layers of the active polysalt membrane on a supporting membrane. The best combination for flux and selectivity is a polyethyleneimine/poly (acrylic acid) polysalt deposited on a reverse osmosis membrane, at 4 kg/m²h and 1075 respectively. It is noticeable that hybrid poly(vinyl alcohol)/inorganic membranes do not show enhanced fluxes. Very high separation factors were observed, covering a range of polymers, of neutral, anionic or cationic character. The top results (>10,000) were for charged membranes, either cationic or anionic, but not polysalts. The fluxes encountered here were miniscule, the best being caesium alginate at about 1 kg/m²h. The ideal structure for high fluxes would appear to be one containing discrete domains of oppositely charged species of optimal size. Fresh approaches are being actively studied, such as layer-by-layer deposition of oppositely charged polyelectrolytes, with due attention to appropriate separation of the sites of opposite character.     

Potentials of pervaporation to assist VOCs’ recovery by liquid absorption

Gas treatment by liquid absorption is a well-known process to remove volatile organic compounds (VOCs) from industrial waste gases. Usually the liquid is an organic solvent of high boiling point; however, after VOCs’ absorption it must be regenerated for the possible reuse and this step is classically achieved by heating the liquid. The paper presents the work directed to investigate an alternative regeneration step based on a liquid-vapour membrane separation, i.e. pervaporation. Because most of the energy required in pervaporation processes is consumed to remove the minor component from the initial mixture by selective permeation through the membrane, one can expect a significant energy cut in the operational costs linked to the regeneration of the liquid if the pervaporation step can substitute the heating one. The results reported here show that the technological possibility to use pervaporation is first governed by the stability of the membrane in the absorption liquid. The viability of the overall process is actually controlled by the mutual affinity between the VOCs, the solvent phase and the polymeric material. As a matter of fact, whereas VOCs have to exhibit strong affinities to both the solvent and the membrane material, the polymer has to be well resistant and even repellent to the solvent to avoid the possible sorption in the membrane that would drastically depress the pervaporation efficiency. In other words the membrane transport properties must be specific for the VOCs. This goal was reached following several experimental approaches, going from membrane modifications to the selection of suitable heavy protic solvents. Hence it has been shown for the case of dichloromethane (DCM) that low molecular weights polyalcohols (e.g. glycols) appeared to be suitable media to allow in particular the specific transport of DCM. On the other hand, polydimethylsiloxane (PDMS) based membranes were selected for their stability in these polyglycols and for their marked affinity for DCM. The simulation of the hybrid gas treatment process at pilot-scale was also achieved by a simple model relying on experimental data for both vapour liquid equilibria and permeation flux. A simple comparison of the energy needed to regenerate the heavy solvent by each possible step has also been made.     

A bio-inspired algorithm based on membrane computing and its application to gasoline blending scheduling

For the purpose of applying membrane computing as a global optimization technique, a bio-inspired algorithm based on membrane computing (BIAMC) is proposed to solve both constrained and unconstrained problems. The membrane structure used in BIAMC is a network of membranes that is inspired by the Golgi apparatus. In the process of approaching to the optimum solution, the objects containing a tentative solution are evolved by the rewriting rule in the parallel identical membranes and synthesized by the novel rules of target indication, transition and abstraction in the membrane of quasi-Golgi. The information transfers according to directions defined by the communication rule. Eight well-known unconstrained and constrained functions are used for performance testing. Then we apply the proposed algorithm with two schemes to solving a typical nonlinear optimization of gasoline blending and scheduling problem. The results show that the proposed approach can find optimal or close-to-optimal solutions efficiently.     

高温煅烧脱除磷酸铁中硫的研究

磷酸铁是合成磷酸铁锂电池正极材料的主要原料,目前多采用硫酸亚铁和磷酸盐共沉淀方法制备。硫酸体系内共沉淀获得的磷酸铁中硫杂质含量较高,目前采用水洗方式脱除,吨磷酸铁洗水用量需60~100吨,硫酸盐废水处理成本高。为从源头削减磷酸铁脱硫过程产生的大量废水,根据硫酸盐高温分解的性质,提出磷酸铁高温煅烧脱硫新方法,开展了热力学可行性计算与高温煅烧脱硫动力学研究。结果表明,磷酸铁中硫元素主要以硫酸根形式存在,高温煅烧可有效促进含硫杂质分解,温度越高,脱硫效果越好。高温煅烧脱硫过程反应动力学级数为2,活化能为88.075 kJ/mol,属于化学反应控制。在温度1173 K、煅烧时间10 min的条件下,磷酸铁中硫杂质含量可降至0.01wt%以下。     

Separation by pervaporation of ethanol from aqueous solutions and effect of other components present in fermentation broths

BACKGROUND: In this work, the selective extraction of ethanol by pervaporation through a POMS (polyoctylmethyl siloxane) hydrophobic membrane supplied by GKKS (Germany) was investigated. First, binary ethanol aqueous solutions were studied considering the effect of ethanol feed concentration (0–11 wt%) and operating temperature (307.55–326.35 K). The effect of some by‐products of the ethanol fermentation, such as glycerol, succinic acid, butanol and acetone, on the pervaporation performance has been analyzed. RESULTS: For binary ethanol aqueous solutions, it was found that water permeation flux remained more or less constant while ethanol permeation flux increased continuously when increasing ethanol feed concentration. However, water and ethanol permeances did not change much in the concentration and temperature range studied. It was observed that the addition of glycerol and succinic acid sharply decreased the total permeation flux while ethanol concentration in the permeate was hardly affected. The addition of butanol and acetone resulted in a lower separation factor for ethanol through the POMS membrane. CONCLUSIONS: For ethanol aqueous solutions the POMS membrane was found to be selective towards ethanol, although it does not present higher separation factors than distillation in the concentration range covered in this work. The presence of other components of the fermentation broth has a great influence in the pervaporation behavior. Further work must be done on the study of multicomponent and real mixtures. Copyright © 2009 Society of Chemical Industry     

A model for alkaline removal of sulfur from a low-rank coal

A low-rank coal cleaned by heavy-liquids separation was treated by 1 M KOH solution at room conditions for a maximum of 2 h. The desulfurization mechanism in terms of total sulfur was well described by the model of unreacted-shrinking core in a homogeneous coal particle of unchanging size during process development. The external diffusion stage might be omitted when modeling this process. A chemical reaction component was considered during diffusive flow of KOH through particle pores, too. It was possible to remove 50% of total sulfur after 2 h of treatment, although three-quarters of achieved conversion happened at first 30 min.     

Permselectivities of aromatic polyamide membranes for aqueous alcohol mixtures in pervaporation

The separation of water/alcohol mixtures was carried out using a series of fluorine-containing aromatic polyamide membranes. Aromatic polyamides were prepared by direct polycondensation of fluorine-containing diamine (2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, BAPPH) and various aromatic diacids. The separation factor toward water increased when the feed ethanol concentration was increased. The solubility of ethanol in aromatic polyamide membrane is higher than that of the water, but the diffusivity of water across the membrane is higher than that of alcohols. A separation factor of 83 and a permeation rate of 262 g/m²h with a 90 wt% feed ethanol concentration at 25 °C was obtained.