Applications of Membrane Separation Processes

Cas Separation In general, a high selectivity is always obtained at the expense of an exponential reduction in gas permeability (It S = const, x It kM)- A highly selective 

Thermal energy (kWh Electrical energy (kWh Typical salt content of raw water in total dissolved solids content (TDS) (mg 1 ) Typical salt content of product water in TDS (mgr ) 12 35 30000-100000 10 0.4-7 1 1000- 100-3000 45000 500 500 

Feedwater and drinking water requirement Salinity in total dissolved solids content (TDS) (mg 1 ) 

Seawater Brackish water River water Pure water (WHO drinking water guidelines) 15 000-50000 1500-15000 500-1500 1000 

if the O2/N2 selectivity increases from 5 to 7 (Drioli and Giomo, 2009). Today s industrial membranes for gas separation therefore have a selectivity of 6-8. 

Your objectives in studying this section are to be able to  

Describe the different types of membrane materials and shapes. 

Define and enumerate applications of dialysis, reverse osmosis, gas permeation, ultrafiltration, and microfiltration. 

Explain and quantify the effect of concentration polarization in reverse osmosis and ultrafiltration. 

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The application of membrane-separation processes in the treatment of wastewater of the leather industry can give a reduction of the environmental impact, a simplification of deaning-up procedures of aqueous effluents, an easy re-use of sludge, a decrease of disposal costs, and a saving of chemicals, water, and energy [22],... 

The development and application of membrane separation processes is one of the most significant advances in chemical and biological process engineering in recent years. Membrane processes are advanced filtration processes which utilise the separation properties of finely porous polymeric or inorganic films [1,2]. Membrane separations are used in a wide range of industrial processes to separate biological macromolecules, colloids, ions, solvents and gases. They also have important medical uses, especially in renal dialysis. The world-wide annual sales of membranes and membrane equipment are worth in excess of 1 billion. 

G. R. Groves, Application of membrane separation processes to the treatment of indnstrial efflnents for water reuse. Desalination 47, 277-284 (1983). 

Cellulose acetate is the material for the first-generation reverse osmosis (RO) membranes. The announcement of cellulose acetate membranes for seawater desalination by Loeb and Sourirajan in 1960 triggered the applications of membrane separation processes in many industrial sectors. Cellulose acetate membranes are prepared by the dry-wet phase inversion technique. 

Ravanchi M. T., Kaghazchi T., Kargari A. 2009. Application of membrane separation processes in petrochemical industry A review. Desalination 235 199-244. 

An RO membrane acts as a barrier to flow, allowing selective passage of a particular species (solvent) while other species (solutes) are retained partially or completely. Solute separation and permeate solvent (water in most cases) flux depend on the material selection, the preparation procedures, and the structure of the membrane barrier layer [5,15]. Cellulose acetate (CA) is the material for the first generation reverse osmosis membrane. The announcement of CA membranes for sea water desalination by Loeb and Sourirajan in 1960 triggered the applications of membrane separation processes in many industrial sectors. CA membranes are prepared by the dry-wet phase inversion technique. Another polymeric material for RO is aromatic polyamide [16]. 

Briischke, H. (1995). Industrial application of membrane separation processes. Pure and Applied Chemistry, 67, 993—1002. 

This book brings together experts from a number of disciplines working within membrane technology all with the same goal of the development and fabrication of new membranes for increased and efficient application of membrane separation processes. The authors of each chapter share their experience and insights in a specific membrane fabrication area. In many cases, this information extends into application of the membrane system as the research uses membrane performance data to improve subsequent membrane fabrication methods. 

Paleologou et al. (1994) discussed membrane applications in the pulp and paper industry with respect to technical feasibility, process integration and the economics of the mill system. The following are some applications of membrane separation processes in the pulp and paper industry. 

In this chapter we will provide an overview of the application of membrane separations for chiral resolutions. As we will focus on physical separations, the use of membranes in kinetic (bio)resolutions will not be discussed. This chapter is intended to provide an impression, though not exhaustive, of the status of the development of membrane processes for chiral separations. The different options will be discussed on the basis of their applicability on a large scale. 

A limitation to the more widespread use of membrane separation processes is membrane fouling, as would be expected in the industrial application of such finely porous materials. Fouling results in a continuous decline in membrane penneation rate, an increased rejection of low molecular weight solutes and eventually blocking of flow channels. On start-up of a process, a reduction in membrane permeation rate to 30-10% of the pure water permeation rate after a few minutes of operation is common for ultrafiltration. Such a rapid decrease may be even more extreme for microfiltration. This is often followed by a more gradual... 

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. 

The development of ab initio methods for the prediction of the performance of membrane separation processes has made substantial developments. Sophisticated methods now exist for such prediction, and these have been experimentally verified in the laboratory. The present challenges are two-fold. Firstly, to continue the fundamental development to more complex separations. Secondly, to apply the verified methods in the design of full-scale industrial processes. The existence of good predictive methods is expected to further expand the application of membrane processes. 

The investigation of Dean vortices and their application to membrane separation processes has been the subject of several experimental and theoretical studies concerning the improvement of microfiltration (ME), ultrafiltration (UF), and nanofiltration (NF),... 

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. 

Transport in dense discriminating layers is most commonly described using the well developed solution-diffusion theory [36]. The theory is based on the assumptions that 1) the driving force for transport is a gradient in chemical potential, 2) at a fluid-membrane interface the chemical potential in the two phases are equal (i.e., equilibrium exists), and 3) the pressure within the membrane is constant and equal to the highest value at either interface. Baker [37] summarizes the application of the theory to a variety of membrane separation processes ranging from dialysis to gas separation. 

Microporous silica hydrogen permselective membranes have been extensively studied as a potentially more practical alternative to Pd membranes. Cutting edge research into silica membranes has shown that they have good hydrogen flux and separation, as well as adequate thermal stability. However, the hydrothermal stability of a silica hydrogen permselective membrane is a key factor in determining its suitability for a commercial application of membrane assisted processes. 

The application of membrane separators and MRs as unit operations in complex processes can provide unique opportunities for capital and operatimial cost reductions. As was the case for development of membrane materials and modules at the device level, entire processes that leverage membrane technology can be designed and optimized for specific techno-economic goals, such as profit margin, environmental emissions, or utility consumption. 

Table 3.3.14 Technically important applications of membrane separation technologies. Partly adapted from Baerns et al. (2006) details of these processes are found in Drioli and Ciorno (2009), Nunes and Peinemann (1915), and Brueschke and Melin (2006).

The field of membrane separations is radically different from processes based on vapor-liquid phase separation. Nevertheless, membrane separations share the same goal as the more traditional separation processes the separation and purification of products. The principles of membrane separation processes and their application to different types of operations are discussed in the last chapter. 

The industrial application of pressure-driven membrane processes has gained significance in recent decades. Several technological innovations addressed to develop highly effective and permeable membranes and to improve efficiency in module design have spread the use of membrane separation processes to (among others) chemical, food, pharmaceutical and biomedical industries. Some important drawbacks of pressure-driven membrane processes, however, are still limiting their wide industrial acceptance. 

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