Separation Technologies for the Industries of the Future (1998) / Chapter Skim
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2 Chemical Industry
2 Chemical Industry
Pages 13-27
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From page 13... ...
TRADITIONAL CHEMICAL ENGINEERING SEPARATION PROCESSES Chemical products are made by a combination of processes that include synthesis, separation, and purification. The traditional chemical engineering methods of separation and purification include distillation, crystallization, adsorption, membrane processes, absorption and stripping, and extraction.
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From page 14... ...
Crystallization Crystallization is one of the oldest unit operations in the portfolio of separation techniques used for industrial and laboratory processes. Crystallization is used to achieve several functions: separation, purification, concentration, solidification, and the production of a crystal that can be used to determine molecular structure.
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From page 15... ...
Desorption can be accomplished by increasing the temperature, reducing the pressure, adding another component that competitively adsorbs with the adsorbate, or a combination of these strategies. Membrane Processes Separation processes involving membranes require two bulk phases that are physically separated by a third phase, the membrane.
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From page 16... ...
a typical electrodialysis stack consists of a series of anion-exchange and cation-exchange membranes arranged in an alternating pattern between an anode and a cathode to form individual cells. A reverse osmosis membrane separates the various low-molecular-weight molecules and ions from the solvent by forcing the solvent or major component to pass selectively through the membrane by applying pressure greater than the normal osmotic pressure.
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From page 17... ...
A number of promising technologies under development could produce industrial gases, such as oxygen, nitrogen, and these noble gases, more efficiently and at lower cost. Reactive Metal Complex Sorbents Reactive metal complex sorbents may provide a means for producing oxygen more efficiently and at lower cost (see Chapter 4~.
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From page 18... ...
Specific sorbents could be used to remove contaminants from noble gases and to purify nitrogen for use as a production gas. Production of High Purity Gases With changing technologies, the demands for high-purity and ultra-high purity gases have increased.
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From page 19... ...
Inorganic Membranes Thin, nanostructured, dense metal and metal oxide membranes might be developed for the separation of gases, for example, high purity hydrogen, oxygen, and nitrogen. Indications are that membranes have been developed at Oak Ridge National Laboratories, but the work remains classified, and these membranes are, therefore, not available for commercial testing and exploration.
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From page 20... ...
In general, more novel methods will have to be developed to produce very thin membranes for a high flux of the permeating acid gases. Dishllabon Technologies In spite of the high energy required for distillation, this process is often chosen over other separation processes because of the relatively low initial capital investment required and because it can yield high purity products.
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From page 21... ...
Although most membrane processes cannot produce high-purity products, it may be possible to take advantage of the energy efficiency associated with them to perform part of the separation. In one study, simulations were performed to identify systems with a high probability of using one-third less energy than current distillation operations.
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From page 22... ...
from an existing solid body, is one of the most widely used separation techniques in the production of large-volume and specialty chemicals. For example, drying is used in the devolatilization of polymers, where unreacted monomers and solvents are removed.
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From page 23... ...
Potential separation processes for chiral compounds include high-performance liquid chromatography, crystallization, and selective chiral permeation through membranes. High-Pe~formance Liquid Chromatography High-performance liquid chromatography with chiral stationary phases is used on both an analytical and preparative scale to separate racemic mixtures of chiral compounds.
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From page 24... ...
Promising research for the separation, removal, or recovery of components from dilute streams includes: reactive metal complex sorbents; gas separation membranes; the use of selective reducing/oxidizing agents; electrically aided membrane separation, such as electrodialysis; continuous adsorption processes; air oxidation combined with absorption; and the use of selective absorbents to remove the products from bioprocessing streams. Reactive Metal Complex Sorbents Reactive metal complex sorbents may offer a means of separating out components of dilute effluent streams, such as recovering metals from dilute solutions by extraction with a liquid that contains a metal-ion specific ligand.
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From page 25... ...
Thus, new membranes with higher selectivity, possibly achieved through the control of swelling, would lower costs and increase applications. Reducing Agents It may be possible to detoxify effluent streams containing low levels of valuable metal ions by reduction with a low-cost reducing agent, such as H2.
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From page 26... ...
Membrane pervaporation is an emerging technology for the isolation and recovery of VOCs from aqueous streams. Adsorbent Specificity for Separation of Bioprocessing Streams Affinity-based separation processes have grown more important in recent years because of their application in biological processes or on biologically produced species.
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From page 27... ...
Areas for research include the following: · more efficient and cost effective separation methods for producing oxygen ~ . trom air · more efficient methods of recovering nitrogen and noble gases from cryogenic air separation fractions · more efficient separation technologies for producing gases in high-purity form, particularly nitrogen, hydrogen, and argon · improved methods of separating out and removing unwanted acid gases, principally CO2, H2S, COS, and SO2 from process streams · more energy efficient distillation technologies and practices · more efficient distillation of substances with similar boiling points or when constant boiling azeotropes are formed · more efficient use of energy in drying techniques for the production of large-volume and specialty chemicals separation technologies for the production of single-isomer chiral compounds technologies for the separation of components from dilute product or waste streams, including metal salts, inorganic compounds, and particulate matter from aqueous streams; valuable metal ions, such as copper, silver, mercury, gold, palladium, and platinum, from effluent streams; and VOCs and involatile organic compounds from effluent streams · separation technologies for recycling chemically similar commodity organicpolymer materials
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