Hybrid membrane processes

The use of a combined membrane system of MF/UF plus NF seems to be the most promising innovation (jacangelo et al (1995b)). 

MF and UF have been compared as a pretreatment step for NF in colour removal. MF obtained poor colour removal (80%) and flux reduction is higher for the higher flux membranes (MF) (Chang et al (1995)). Chellam et al (1997) compared MF and UF (10 kDa) as pretreatment for NF and found no difference, but both performed significantly better than conventional pretreatment, which was attributed to coUoid removal. A low flux and high recover operation was recommended for NF. UF has been used as a pretreatment to RO in water treatment (Kamp (1995)). Amy et al. (1993) stated that to guarantee low fouling of NF, pretreatment with MF or UF was required. MF was only moderately 

Rautenbach and Groschl (1990) described NF as a pretreatment step to RO to increase the recover of the RO process, due to the removal of scaling agents by NF. NF also has the advantage that a concentrate of a relatively low salinity is produced which may be used for irrigation, reducing the quantity of concentrate to be disposed (Dal-Cin et al. (1995)). 

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Very low capital and operating cost The separation could be made more economical by using a hybrid membrane process, i.e., a combination of distillation and pervaporation processes. Thus, a part of the total separation employs distillation where it is economical. PV replaces the subsequent separation where distillation becomes expensive. The overall operating cost of such a hybrid process is much lower than that of distillation alone. 

San Roman M.F., Ortiz Gandara I., Ibanez R., and Ortiz I., Hybrid membrane process for the recovery of major components (zinc, iron and HCl) from spent pickling effluents, J. Membr. Sci. 616,415, 2012. 

Membrane processes have been widely adopted over the last 30 years in spite of inherent hmitations such as fouHng, thermal and chemical resistance and maximum achievable purity. One reason for their wide success is the emergence of integrated/hybrid membrane processes for several appHcations, some of which are discussed in Chapter 3. The principal characteristics of membrane processes are Hsted in Table 1.3. AH processes except dialysis, ED and EDI are pressure driven, and aU except PV and MD do not involve a phase change. 

The hybrid systems described below include membrane technologies for processing a wide spectrum of feed streams in various applications. A small sampling of current and potential applications is discussed. The list of examples selected is intentionally Hmited the intention is to illustrate the extent of process alternatives possible with various hybrid membrane processes. 

Figure 3.13 Hybrid membrane process schemes for recovering leaf proteins.

Figure 3.18 Processing of citrus juices by a hybrid membrane process. Source Romicon.

Wine processing by a hybrid membrane process is shown in Figure 3.20. The first UF unit removes microorganisms, coUoids, and high molecular weight materials. The MF step removes yeast used for fermentation. The second UF unit is used for sterifising prior to botding. Membrane pore size plays a crucial part in the retention of colour and aroma compounds. UF membranes with MWCO of between 100,000 and 500,000 Da are best [23]. 

This theoretical study is focused on the process combination of a distillation column and a pervaporation unit located in the side stream of the column. This hybrid membrane process can be applied for the separation of azeotropic mixtures such as acetone, isopropanol and water. Water is removed from the side stream of the column by pervaporation, while pure acetone and isopropanol are obtained at the top and bottom of the column. Detailed simulation studies show the influence of decisive structural parameters like side stream rate and recycle position as well as operational parameters like reflux ratio and mass flow on concentration profiles, membrane area and product compositions. 

Distillation is still the most common unit operation to separate liquid mixtures in chemical and petroleum industry because the treatment of large product streams and high purities with a simple process design is possible. Despite of this the separation of azeotropic mixtures into pure components requires complex distillation steps and/or the use of an entrainer. Industrial applied processes are azeotropic, extractive or pressure swing distillation (Stichlmair and Fair, 1998). Another sophisticated method for the separation of binary or multicomponent azeotropic mixtures is the hybrid membrane process, consisting of a distillation column and a membrane unit. 

In this work the separation of the ternary mixture of acetone, isopropanol and water using a hybrid membrane process is studied. This non-ideal mixture with a minimum-... 

Figure 2 Hybrid membrane process to separate a) close boiling, b) binary azeotropic and c) multicomponent mixtures (Hommerich, 1998a).

Table 9. Cost Comparison Between High-Pressure Distillation and Hybrid Membrane Process for DMC/MeOH Azeotrope Separation (3401...

This chapter examines newly developed hybrid membrane processes for gas separation, which integrate membrane permeation with pressure swing adsorption (PSA) technology. A brief review of the theory underlying membrane and PSA processes is provided. The discussion will focus on the evaluation of the present state of the art of both processes and on the practical application of both technologies into a hybrid membrane/PSA concept. 

For last few years, extensive studies have been carried out on proton conducting inorganic/organic hybrid membranes prepared by sol-gel process for PEMFC operating with either hydrogen or methanol as a fuel [23]. A major motivation for this intense interest on hybrid membranes is high cost, limitation in cell operation temperature, and methanol cross-... 

Sol-gel techniques have been successfidly applied to form fuel cell components with enhanced microstructures for high-temperature fuel cells. The apphcations were recently extended to synthesis of hybrid electrolyte for PEMFC. Although die results look promising, the sol-gel processing needs further development to deposit micro-structured materials in a selective area such as the triple-phase boundary of a fuel cell. That is, in the case of PEMFC, the sol-gel techniques need to be expanded to form membrane-electrode-assembly with improved microstructures in addition to the synthesis of hybrid membranes to get higher fuel cell performance. 

Figure 10. A hybrid hydrate-membrane process for C02 recovery from fuel gas.

The process design principles of SLM, non-dispersive extraction, and hybrid hquid membrane systems need to be understood through bench scale experiments using feed solution of practical relevance. While the economic analysis of an ELM process can be performed from small scale experiments, such an analysis is difficult for other LM systems. In particular, availability and cost of hollow fiber membranes for commercial application are not known apriori. A simple rule of thumb for cost scale-up may not be apphcable in the case of an HE membrane. Yet we feel that the pilot plant tests would be adequate to make realistic cost benefit analysis of a liquid membrane process, since the volume of production in )8-lactam antibiotic industries is usually low. 

Naturally, there exist a variety of membrane separation processes depending on the particular separation task [1]. The successful introduction of a membrane process into the production line therefore relies on understanding the basic separation principles as well as on the knowledge of the application limits. As is the case with any other unit operation, the optimum configuration needs to be found in view of the overall production process, and combination with other separation techniques (hybrid processes) often proves advantageous for large-scale applications. 

On the other hand, a pervaporation membrane can be coupled with a conventional distillation column, resulting in a hybrid membrane/distillation process (228,229). Some of the investigated applications of such hybrid pervaporation membrane/distillation systems are shown in Table 9. In hybrid pervaporation/ distillation systems, the membrane units can be installed on the overhead vapor of the distillation column, as shown in Figure 13a for the case of propylene/ propane splitting (234), or they can be installed on the feed to the distillation column,... 

The above laboratory-based successes show the future of this technology is promising, but they need to be supplemented with novel modification and processing techniques that can be scaled for high production levels. These hybrid membranes show considerable potential, however, they still require extensive research before implementation. Indeed if the number of patents filed recently is any indication, hybrid membranes are attracting industrial attention [64-81],... 

Developing new membrane processes and hybrid processes in order to increase the efficiency of the biochemical reactions and the filtration ... 

The hybrid sulphur process requires electrolysers which are not described in chemical engineering economics literature. A specific approach has been developed by collecting data from literature and constructors of alkaline electrolysers (Mansilla, 2008). Electrolyser characteristics are also considered (catalyst coating, membranes). 

Figure 1 Flowsheet of hybrid membrane-PSA process. Steps pressurization (PR = PRi + PR2). high-pressure adsorption (HPA), co- and counter-current blowdown (CD, BD), Purge (PG) A stream enriched in less adsorbed component, B-. stream enriched in strongly adsorbed component. Pressure histories of the integrated cycle at CSS.

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