Ceramic membranes liquid processing

Ceramic, Metal, and Liquid Membranes. The discussion so far implies that membrane materials are organic polymers and, in fact, the vast majority of membranes used commercially are polymer based. However, interest in membranes formed from less conventional materials has increased. Ceramic membranes, a special class of microporous membranes, are being used in ultrafHtration and microfiltration appHcations, for which solvent resistance and thermal stabHity are required. Dense metal membranes, particularly palladium membranes, are being considered for the separation of hydrogen from gas mixtures, and supported or emulsified Hquid films are being developed for coupled and facHitated transport processes. 

A membrane can be defined as a thin and selective barrier that enables the transport or the retention of compounds between two media. In the case of ceramic membranes, the usual driving force for transport is a pressure gradient between the feed and strip compartments (transmembrane pressure). The treated phases can be liquid or gas. For porous membranes, the pore size mainly manages the cutoff of the membrane. However, for retention of the smallest entities by the smallest pores, the transport mechanisms are more complex than simple sieving. Specific physical and chemical interactions (electrostatic repulsion, physisorp-tion, capillary condensation, etc.) become preponderant and determine the membrane selectivity. Table 25.1 summarizes the characteristics of the main processes in which ceramic membranes are involved. 

This brief overview of mass transfer and separation mechanisms involved in ceramic membrane processes will be useful not only for a better understanding of actual operating conditions of ceramic membranes, but also for anticipating future applications. For example, a same microporous membrane can serve theoretically as liquid or gas separation membrane. However, transport mechanisms and operating conditions being totally different, a good membrane permeability and selectivity in the former case cannot be systematically transposed to the second case. 

Separation of manufactured sohds from process liquids and recycling of these liquids (water or organic solvents) is an interesting way to valorize by-products and to minimize the production of liquid effluents in a number of industries. Microfiltration ceramic membranes have been aheady used for the recovery of particles in the ceramic industry and in drilling operations, of pigments in paint and ink industries, and have potential applications in a wide variety of liquid-solid separation... 

The actual interest for ceramic membranes in many applications dealing with the treatment of liquids results from an increasing demand for secure and reliable membrane processes. In the food and pharmaceutical industries for which sanitary requirements are of the utmost importance, ceramic membranes afford a very good reliability in terms of cleaning and... 

A typical example of the application of ceramic membranes in chemical industry is the cleaning of mono ethanol amine. Mono ethanol amine (MEA) is used for the absorption of H2S from acid gasses but is polluted during this process by various organic compounds. Filtration of the MEA over 0.2 pm HIC ceramic membranes at an average flux of 32 1/m h produces a clean, transparent yellow liquid, free of solids. Filtration temperature is 37°C, pH is about 11.5. Tests lasted successfully for over 700 h. Another example is the filtration of Ti02 from a waste stream in the so-called sulphuric acid process... 

Solid-state electrochemistry is an important and rapidly developing scientific field that integrates many aspects of classical electrochemical science and engineering, materials science, solid-state chemistry and physics, heterogeneous catalysis, and other areas of physical chemistry. This field comprises - but is not limited to - the electrochemistry of solid materials, the thermodynamics and kinetics of electrochemical reactions involving at least one solid phase, and also the transport of ions and electrons in solids and interactions between solid, liquid and/or gaseous phases, whenever these processes are essentially determined by the properties of solids and are relevant to the electrochemical reactions. The range of applications includes many types of batteries and fuel cells, a variety of sensors and analytical appliances, electrochemical pumps and compressors, ceramic membranes with ionic or mixed ionic-electronic conductivity, solid-state electrolyzers and electrocatalytic reactors, the synthesis of new materials with improved properties and corrosion protection, supercapacitors, and electrochromic and memory devices. 

Large-pore" materials are becoming important in some industrial applications catalytic processes for selective oxidation, hydrodesulfurization, steam reforming inorganic ceramic membrane reactors supports for high performance liquid chromatography, etc. 

Recently much attention has been paid to ceramic membranes exhibiting a nanoporous structure with the aim of new membrane processes for the nanofiltration of liquids [26], pervaporation [27], gas separation [27,28], or catalysis... 

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