Membrane-based separation process

By 1960, the elements of modem membrane science had been developed, but membranes were used in only a few laboratory and smaU, specialized industrial appHcations. No significant membrane industry existed, and total annual sales of membranes for aU appHcations probably did not exceed 10 million in 1990 doUars. Membranes suffered from four problems that prohibited their widespread use as a separation process they were too unreHable, too slow, too unselective, and too expensive. Partial solutions to each of these problems have been developed since the 1960s, and in the 1990s membrane-based separation processes are commonplace. 

Reverse Osmosis. This was the first membrane-based separation process to be commercialized on a significant scale. The breakthrough discovery that made reverse osmosis (qv) possible was the development of the Loeb-Sourirajan asymmetric cellulose acetate membrane. This membrane made desalination by reverse osmosis practical within a few years commercial plants were installed. The total worldwide market for reverse osmosis membrane modules is about 200 million /yr, spHt approximately between 25% hoUow-ftber and 75% spiral-wound modules. The general trend of the industry is toward spiral-wound modules for this appHcation, and the market share of the hoUow-ftber products is gradually falling (72). 

Soni, V., Abildskov, J., Jonsson, G., Gani, R., 2006, Structural design of polymers for membrane based separation processes using reverse simulation approach, Computer Aided Chemical Engineering, (in press). 

My knowledge grew at Bend Research, Inc. under Harry Lonsdale, another membrane pioneer who was involved in the theoretical and practical side of membranes since the early 1960 s at Gulf General Atomic (predecessor of Fluid Systems, now Koch Membrane Systems), Alza, and later Bend Research, which he co-founded with Richard Baker. At Bend Research, I had the opportunity to develop novel membranes and membrane-based separation processes, including leading several membrane-based projects for water recovery and reuse aboard the International Space Station. 

Yun CH, Guha AK, Prasad R, and Sirkar KK. Novel microporous membrane-based separation processes for pollution control and waste minimization. In Sawyer DT and Martell AE Eds. Industrial Environmental Chemistry Waste Minimization in Industrial Processes and Remediation of Hazardous Waste. Proceedings of the Texas A M University, lUCCP 10th Annual Symposium on Industrial Environmental Chemistry Waste Minimization in Industrial Processes and Remediation of Hazardous Waste, March 24-26, Plenum, New York 1992 pp. 135-146. 

The process of ED is, by definition, a membrane-based separation process in which ions are driven through an ion-selective membrane under the influence of an electric field [35]. Conversely, in electrofiltration a charged pollutant particle is prevented from moving through a membrane by the influence of an electric field. Electrosorption is an electrically enhanced ion-exchange process and electroremediation is a process developed for the decontamination of polluted soil. Each different process is discussed separately. 

Nano filtration According to the International Union of Pure and Applied Chemistry (lUPAC) recommendations [16] nanofiltration is a pressure-driven membrane-based separation process in which particles and dissolved molecules smaller than about 2 nm are retained. ... 

Membrane-based separation processes to capture either H2 or CO2 from the gasifier are new and less studied methods of CO2 separation and capture. Membranes separate the desired gas component without requiring phase changes or chemical or physical sorption. The cost of membrane separation is generally dictated by the overall pressure drop. Membranes made of various types of materials such as polymers, metals, and rubber composites have been investigated. Palladium and molecular sieves are currently under study. ° ... 

Membrane-based separation processes are recognized as environmentally friendly alternatives to conventional separation techniques such as distillation or extraction. The field of large-scale applications covers the range of drinking water processing, potable water production, waste-water treatment, application in the food and pharmaceutical industries, recovery of aroma and active substances as well as sterile filtration of pharmaceuticals and clarification of beverages. 

Membrane-based separation processes are also used in large-scale applications with closed water recirculation. Examples for such processes are electrophoretic coatings in the automotive industry, or the work-up of detergent solutions and caustic solutions from the beverage industry or water from dye baths. The use of membranes in such processes reduces on the one hand the demand on fresh-water. 

Membrane-based reactive separation (otherwise also known as membrane reactor) processes, which constitute the subject matter of this book, are a special class of the broader field of membrane-based separation processes. In this introduction we will first provide a general and recent overview on membranes and membrane-based separation processes. The goal is to familiarize those of our readers, who are novice in the membrane field, with some of the basic concepts and definitions. A more complete description on this topic, including various aspects of membrane synthesis can be obtained from a number of comprehensive books and reviews that have already been published in this area [1.1, 1.2, 1.3,... 

Membrane-based separation processes are today finding widespread, and ever increasing use in the petrochemical, food and pharmaceutical industries, in biotechnology, and in a variety of environmental applications, including the treatment of contaminated air and water streams. The most direct advantages of membrane separation processes, over their more conventional counterparts (adsorption, absorption, distillation, etc.), are reported to be energy savings, and a reduction in the initial capital investment required. 

The membrane is the heart of any membrane-based separation processes. Initial breakthrough in membrane technology came from the phase inversion technique developed by Loeb and Sourirajan. The membrane prepared by adopting... 

Membrane-based separation processes over the years have emerged as one of the potential players for process intensification in many areas of the nnclear fnel cycle, in both front and back ends. Treatment of radioactive liquid wastes is receiving considerable attention worldwide due to the recognition of its importance for the protection of human health and the environment from the adverse effect of radiation associated with these wastes [4]. 

Since the 1990s, membrane-based separation processes integrated with traditional treatment systems have been successfully deployed in large desalination, wastewater and municipal water treatment plants [1-4]. More than a dozen large seawater RO (SWRO) plants with product water capacities greater than 200,000 m /day have been commissioned in the last decade. 

Desalination of saline water (sea and brackish waters) is a well-established means of water supply in many countries. Basically, desalination processes in this area can be divided into two groups (1) phase-change/thermal, and (2) membrane-based separation processes. Phase-change processes include multi-stage flash,multiple effect boiling, vapour compression,freezing,humidi-fication/dehumidification and solar stills. RO, ED and membrane distillation (MD) are typical membrane separation processes (Charcosset, 2009). 

Today polymeric membranes are widely used to produce potable water from seawater, treat industrial effluents, for controlled drug delivery systems, separate common gases, pesticide release systems, and in prosthetic devices for humans, among others (76). Most of these methods require the separation of two or more components. Membrane-based separation processes are environmentally green, economic, and frequently more efficient than conventional methods. 

For any membrane-based separation process to be successful, the membrane must possess two key attributes high flux and good selectivity. Flux, which depends directly on permeability, was treated in Sections 4.4.2 and 4.4.4. Selectivity depends in part on differences in permeant size and solubility in the membrane (Section 4.4.5). Separation will then occur because of differences in the transport rates of molecules within the membrane. This rate of transport is determined by the mobility and concentration of the individual components as well as the driving force, which is the chemical potential gradient across the membrane. 

Use of membrane-based separation processes represents a promising alternative to traditional processes, since they do not require high energy and chemical consumption, thus significantly improving the sustainable energy approach. In particular, innovative methods based on the carrier facilitated transport across a liquid membrane (LM) show great potential since they do not produce by-products of difficult disposal and they can be operated continuously. 

Table 2. Relevant sections for each membrane based separation process... 

One of them employs membrane-based separation processes connected to the esterification reaction. In this respect, vapor permeation and pervaporation process have been tested and dn-ee different layouts have been reported for ethyl lactate production. In one of them, membrane module is located outside the reactor unit and the retenate is recirculated to the reactor." " In another scheme, the membrane module is placed inside the reactor, but the membrane does not participate in the reaction directly and simply acts as a filter," " and in the third configuration, membrane itself participates in die reaction catalysis (catalytic membrane reactor)." Different hydrophilic membranes, such as polymeric, ceramic, zeolites and organic-inorganic hybrid membranes were tested. ... 

---