![]() ![]() Finally, in section 10 we summarize present and future research directions in membrane materials science. Sections 4, 5, 6, 7, 8, and 9 of this paper review some of the promising new materials that may help membrane gas separation technology break out of its box. It seems likely, therefore, that most of these unsolved applications will require development of new types of advanced membranes. ![]() However, over the past 25 years, hundreds of conventional polymers have been suggested without much success. It is possible that some of these problem applications may be solved with a variant of the conventional polymer membranes already available. These permeance and selectivity targets are for real membranes, used with industrially relevant gas mixtures under the conditions of temperature, pressure, and contaminant composition expected in the industrial application. This description will suggest performance targets that, if achieved, might get the technology off the ground. In section 3, we describe a number of large gas separation applications where development of better membranes could make a difference. This section sets the stage for understanding the membrane materials and application challenges as well as some of the proposed solutions that follow. In section 2, a brief review of the fundamental principles of membrane gas transport is provided. For this reason, industrial membrane producers have focused most of their development efforts on optimizing the production of their current membrane products. Such an improvement would be commercially useful for the company making the breakthrough but is unlikely to significantly expand the overall membrane market against the competitive technologies of cryogenic distillation or pressure swing adsorption. Membranes with increased selectivity at the same permeance will reduce the compressor size, and membranes with increased permeance at the same selectivity will reduce the membrane skid size, but these improvements will require a significant development effort and are likely to only reduce the total process cost by 5–10%. In nitrogen plants, the membrane skid represents about a third of the cost, the air compressor is another half, and balance of the plant components is the remainder. The same polymers-polysulfone, polyimides, substituted polycarbonate, and poly(phenylene oxide)-all with membrane selectivities of 4–7 have been used for more than 20 years. For example, the separation of nitrogen from air represents about half of the current gas separation market. One reason is that the big, and relatively easy, applications shown in Table 1 are mostly solved problems. There are several reasons for this lack of success. The time was then ready for this base technology to be applied to gas separation. By the late 1970s, reverse osmosis and the related membrane water treatment process of ultrafiltration were off the ground, and the market was supplied by established companies. It took another 10 years to develop the technology required to fabricate the membranes on a large scale and package them into large membrane area modules. This breakthrough made desalination by reverse osmosis potentially economical. These membranes had 20 times the permeance of any membrane then known and good water/salt selectivity. The microporous support provided mechanical strength, while the thin dense skin performed the separation. This membrane consisted of a dense, thin selective polymer layer on top of a much thicker microporous support layer. (1) From 1959 to 1962, Sidney Loeb and Sirivasan Sourirajan created the first asymmetric reverse osmosis membrane. Today’s membrane gas separation industry grew out of the development of membrane technology for water treatment. ![]()
0 Comments
Leave a Reply. |