Separators high-pressure


Separation of low-molecular-weight materials. Low-molecular-weight materials are distilled at high pressure to increase their condensing temperature and to allow, if possible, the use of cooling water or air cooling in the column condenser. Very low  [c.74]

Figure 3.9a shows the temperature-composition diagram for a maximum-boiling azeotrope that is sensitive to changes in pressure. Again, this can be separated using two columns operating at different pressures, as shown in Fig. 3.96. Feed with, say, rpA = 0.8 is fed to the high-pressure column. This produces relatively pure A in the overheads and an azeotrope with xba = 0.2, Xbb = 0.8 in the bottoms. This azeotrope is then fed to a low-pressure column, which produces relatively pure B in the overhead and an azeotrope with 3 ba = 0.5, BB = 0.5 in the bottoms. This azeotrope is added to the feed to the high-pressure column. Figure 3.9a shows the temperature-composition diagram for a maximum-boiling azeotrope that is sensitive to changes in pressure. Again, this can be separated using two columns operating at different pressures, as shown in Fig. 3.96. Feed with, say, rpA = 0.8 is fed to the high-pressure column. This produces relatively pure A in the overheads and an azeotrope with xba = 0.2, Xbb = 0.8 in the bottoms. This azeotrope is then fed to a low-pressure column, which produces relatively pure B in the overhead and an azeotrope with 3 ba = 0.5, BB = 0.5 in the bottoms. This azeotrope is added to the feed to the high-pressure column.
Refrigerated condensation. Separation by condensation relies on differences in volatility between the condensing components. Refrigeration or a combination of high pressure and refrigeration is needed.  [c.108]

Membrane separation. Membranes separate gases by means of a pressure gradient across a membrane, typically 40 bar or greater. Some gases permeate through the membrane faster than others and concentrate on the low-pressure side. Low-molecular-weight gases and strongly polar gases have high permeabilities and are known as fast gases. Slow gases have higher molecular weight and symmetric molecules. Thus membrane gas separators are effective when the gas to be separated is already at a high pressure and only a partial separation is required.  [c.109]

Sometimes it is extremely difficult to avoid vapor recycles without using very high pressures or very low levels of refrigeration, in which case we must accept the expense of a recycle compressor. However, when synthesizing the separation and recycle configuration, vapor recycles should be avoided, if possible, and liquid recycles used instead.  [c.115]

Often, in the feed to a separation train, some components are difficult to condense. Total condensation of these components might require low-temperature refrigeration and/or very high operating pressures. Under these circumstances, the light components are normally removed from the top of the first column to minimize the use of refrigeration and high pressures in the column sequence.  [c.132]

Reverse osmosis is a high-pressure membrane separation process (20 to 100 bar) which can be used to reject dissolved inorganic salt or heavy metals. The concentrated waste material produced by membrane process should be recycled if possible but might require further treatment or disposal.  [c.312]

Gas is sometimes produced at very high pressures which have to be reduced for efficient processing and to reduce the weight and cost of the process facilities. The first pressure reduction is normally made across a choke before the well fluid enters the primary oil / gas separator.  [c.249]

Facilities for the treatment and compression of gas have already been described in earlier sections. However, there are a number of differences in the specifications for injected gas that differ from those of export gas. Generally there are no technical reasons for specifications on hydrocarbon dew point control (injected gas will get hotter not cooler) although it may be attractive to remove heavy hydrocarbons for economic reasons. Basic liquid separation will normally be performed, and due to the high pressures involved it will nearly always be necessary to dehydrate the gas to avoid water drop out.  [c.259]

Capillary Electrochromatography Another approach to separating neutral species is capillary electrochromatography (CEC). In this technique the capillary tubing is packed with 1.5-3-pm silica particles coated with a bonded, nonpolar stationary phase. Neutral species separate based on their ability to partition between the stationary phase and the buffer solution (which, due to electroosmotic flow, is the mobile phase). Separations are similar to the analogous HPLC separation, but without the need for high-pressure pumps, furthermore, efficiency in CEC is better than in HPLC, with shorter analysis times.  [c.607]

High-pressure liquid chromatography (HPLC) is simply a variant on LC in which the moving liquid stream is forced along under high pressure to obtain greater efficiency of separation.  [c.414]

LC, or sometimes HPLC (high-pressure liquid chromatography), is a means of separating components of mixtures by passing them in a solvent through a chromatographic column so that they emerge sequentially.  [c.415]

The column is the site of actual separation, and, of the variables involved in its preparation, the packing material is the most important. Historically, cross-linked polystyrene gel particles were used as the stationary phase. Being only semirigid, these are of limited utility in modern high-performance, high-pressure equipment. These and other cross-linked polymers in the form of spheres with diameters in the range 10-100 jum are commercially available with a range of pore sizes, and are still widely used when pressures less than about 3000 psi are sufficient. More recently, silica particles with dimensions in the 5-10 fim range have also become available with a range of pore dimensions. Being rigid, these can withstand higher pressures. Silica particles are also available with various organic functional groups chemically bonded to their surface to minimize adsorption. If adsorption occurs, then both size exclusion and adsorption mechanisms are involved and the experiment is no longer governed by size exclusion principles alone.  [c.652]

When and loir are widely separated the effect of background aerosol scattering can be taken account of more effectively by employing a third wavelength, X2, between and in a three wavelength DIAL technique. With this technique, two wavelengths sample the absorption within the Hartley band and the third wavelength lies in a region just outside the band where there is little ozone absorption. For ozone detection in the troposphere the third wavelength employed, I2 in Figure 9.35, is provided by Raman shifting of the 266 nm radiation using a cell containing high pressure deuterium gas to produce radiation of wavelength 289 nm.  [c.381]

Small Particle Silica Columns. Process-scale reversed-phase supports can have particle sizes as small as 5—25 p.m. Unlike polymeric reversed-phase sorbents, these smaH-particle siHca-based reversed-phase supports requite high pressure equipment to be properly packed and operated. The introduction of axial compression columns has helped promote the use of high performance siHca supports on a process scale. Resolution approaching that of an analytical-scale separation can be achieved using these columns that can also be quickly packed. These columns consist of a plunger fitted into a stainless steel column. The particles are placed into the column in a slurry. The plunger then squeezes or compacts the bed in an axial direction to give a stable, tightly packed bed. This type of column must be operated at pressures of up to 10 MPa (100 bar), but also gives excellent resolution in mn times of an hour or less (36).  [c.55]

Another alternative to separating commingled plastics is advanced waste recycling. This is the high temperature-high pressure conversion of plastic wastes to form petrochemical process streams. Research is in progress to determine the conditions that will favor conversion of commingled plastic wastes to certain types of chemical feedstocks including synthesis gas (hydrogen + carbon monoxide), hydrogen, cmde pyrolysis oil (containing benzene, toluene, and xylene), olefins, and oxygenates such as methanol, esters, and methyl formate (63). This technology has also been evaluated for producing fuels medium BTU gas for boilers, and Hquid fuels such as diesel oil. None of these processes is currendy economic.  [c.232]

The synthesis recycle loop has the stripped gas going to two high pressure carbamate condensers in series and to a high pressure separator and then back to the reactor. The flow is maintained by using an NH -driven Hquid—Hquid ejector. The reactor is operated at 15 MPa (150 bat) with a NH —CO2 molar feed ratio of 3.5. The stripper is a falling-film type and since high temperatures (200—210°C) ate requited for efficient thermal stripping, stainless steel tubing is not suitable. Titanium was initially used, but it also was not satisfactory because of erosion neat the bottom. At this time a bimetallic tube of zirconium and 25-22-2 stainless steel is used. The zirconium is corrosion-free and the only problem is the difficulty in getting proper welds and separation of the two layers at the bottom ends. Fabrication mistakes have been the only source of problems with this vessel to date.  [c.301]

As mentioned before, because of design and operating conditions (ie, NH /CO2 ratio, pressure, temperature, reactor volume), only one recirculation stage is required (0.4 MPa) (4 bar). On expansion, a large portion of the carbamate left in the urea solution from the stripper decomposes. The remaining solution passes through a rectifying column, heater, and separator. The gases formed go to a carbamate condenser and are pumped via the high pressure carbamate pump (either reciprocating or centrifugal) to the high pressure scmbber.  [c.304]

The urea solution leaving the stripper bottom contains about 12 wt% of NH and is further purified in the 1.8 MPa (18 bar) and 0.2 MPa (2 bar) recovery sections of the plant. The resultant NH and CO2 separated in the decomposers is absorbed and returned to the synthesis section by the high pressure centrifugal carbamate pump.  [c.305]

There are two variations for this commercial production route the two-stage process developed by Wacker-Chemie and the one-stage process developed by Farbwerke Hoechst (91—92). In the two-stage process shown in Figure 1, ethylene is almost completely oxidized by air to acetaldehyde in one pass in a tubular plug-flow reactor made of titanium (93,94). The reaction is conducted at 125—130°C and 1.13 MPa (150 psig) using the palladium and cupric chloride catalysts. Acetaldehyde produced in the first reactor is removed from the reaction loop by adiabatic flashing in a tower. The flash step also removes the heat of reaction. The catalyst solution is recycled from the flash-tower base to the second stage (or oxidation reactor) where the cuprous salt is oxidized to the cupric state with air. The high pressure off-gas from the oxidation reactor, mostly nitrogen, is separated from the Hquid catalyst solution and scmbbed to remove acetaldehyde before venting. A small portion of the catalyst stream is heated in the catalyst regenerator to destroy any undesirable copper oxalate. The flasher overhead is fed to a distillation system where water is removed for recycle to the reactor system and organic impurities, including chlorinated aldehydes, are separated from the purified acetaldehyde product. Synthesis techniques purported to reduce the quantity of chlorinated by-products generated have been patented (95).  [c.51]

One of the key challenges is the separation of secreted soluble fermentation products from the broth. A few products are present at concentrations as low as 0.1%. Even the more typical concentrations of values of 5—15% entail formidable efforts. Then the products often need further purification prior to any form of final inspection or packaging. Numerous physical and chemical methods are employed in a variety of combinations with most fermentations for the isolation and purification steps (21—23). As an example, for the penicillin fermentation, cells are separated from the product containing supernatant by filtration. The filtrate is passed through a series of Podbelniak extractors and the penicillin moves into an organic phase (amyl or butyl acetate). Extraction using phosphate buffer separates the potassium penicillin into the aqueous phase. Crystallization from an / -butanol—water mixture renders a pure product that can be further poHshed or converted into other semisynthetic penicillins. Eor intracellular products, where whole-cell preparations are inappropriate, cells have to be broken open, eg, by high pressure homogenization or bead milling, and the cell debris has to be removed, usually by centriftigation, prior to additional purification steps. The challenge is even tougher for recombinant proteins and peptides. Isolation must be in an intact form appropriate for further purification and refolding into an active form. The elimination of the key contaminants is accompHshed using traditional  [c.182]

In order to make a multipurpose plant even more versatile than module IV, equipment for unit operations such as soHd materials handling, high temperature/high pressure reaction, fractional distillation (qv), Hquid—Hquid extraction (see Extraction, liquid-liquid), soHd—Hquid separation, thin-film evaporation (qv), dryiag (qv), size reduction (qv) of soHds, and adsorption (qv) and absorption (qv), maybe iastalled.  [c.438]

I eon—Helium Separation and Purification. As indicated eadier, neon, heHum, and hydrogen do not Hquefy in the high pressure (nitrogen) column because these condense at much lower temperatures than nitrogen. As withdrawn, the noncondensable stream has a neon—helium content that varies 1—12% in nitrogen, depending on the rate of withdrawal and elements of condenser design and plant operation.  [c.11]

Effect of Temperature on Design. In gas separation processes high pressure equipment is needed to operate at temperatures considerably below atmospheric, whereas some heterogeneous gas reactions have to be carried out at high temperatures to make them economically feasible. Both high and low temperatures have an effect on the mechanical properties of metals. In general, the ductile properties, and in particular the toughness and impact strength, of most low alloy steels, decrease sharply as the temperature is reduced and care has to be taken over the choice of materials if low temperature embrittlement is to be avoided. On the other hand, the yield and tensile strength of steels decrease as the temperature increases and allowance has to be made for this in estimating the static strength of a thick-waHed cylinder at temperatures above ambient. Above about 350°C, creep starts to become an important factor with Ni—Cr—Mo steels of the sort used for high pressure appHcations, and the stresses in the wall of the vessel and its deformation are no longer independent of time. In addition to the effect of temperature on mechanical properties, temperature gradients, generated in the walls of vessels as a result of apphed heat or of heat Hberated by exothermic reactions proceeding within the vessel, cause thermal stresses which may need to be considered when estimating the stresses in a thick-waked cylinder subjected to both internal pressure and heat flux.  [c.85]

The biggest problem associated with high pressure reciprocating pumps is that of satisfactorily sealing the plungers. To avoid excessive rate of wear a hquid film must be maintained between the plunger and the packing and, if this caimot be done by the fluid being handled, separate lubrication must be arranged. The plungers in the intensifiers are usually sealed using stationary chevron or U-type packings in which the Hquid under pressure deflects the limbs of the U to provide the seal. Packing rings are often made of filled polytetrafluoroethylene (PTFE), which has low friction coefficient and good resistance to attack from solvents, such as benzene, toluene, hexane, etc, used to dissolve the organic peroxides. The rings held between suitably shaped steel rings are compressed by a plug being screwed into a recess at the end of the cylinder. Some peroxides deposit soHd material during the compression process, which is difficult to control this has an adverse effect on the life of the packing and the operation of the valves which are usually of the ball or double ball type. The valves may be accommodated in the pump body itself or more usually in a separate head attached to the body.  [c.99]

Basically, a vertical mechanism (Fig. 37a) was adopted from the design of large diesel engines and this, together with a horizontal mechanism (Fig. 37b), was used for some of the earliest secondary compressors. Since there is only one working stroke in two, both mechanisms suffer from large cycHc torque fluctuations. The mechanisms in Figure 37c and d give a more uniform torque diagram and the load on the smaH-end bearing reverses which aids their lubrication. The horizontal machine, unlike the vertical, has excellent accessibility to all parts of the drive mechanism as well as to the valves and glands furthermore, layout of the pipework and auxiliary plant such as coolers, pulsation dampers, and separators is easier. The mechanism in Figure 37c which makes use of a yoke or secondary cross-head to which the plungers of an opposed pair of cylinders are attached, was adopted by Dresser Rand. The inboard cylinders are not as accessible as the outboard, but alignment is good. The arrangement has the added advantage that it is easy to incorporate a distance piece to prevent ethylene entering the crankcase, an important safety consideration, but it suffers because of its great overall length. The most commonly adopted design is that of Figure 37d in which the connecting rod is connected to a cross-head which surrounds the crankshaft. The cross-head is connected to a second cross-head on the opposed high pressure cylinder. With this design the cross-head guides can be arranged in the base of the machine as is done by Burckhardt and GHH or in the plane of the center-line of the plungers which is the design adopted by Nuovo Pignone (175).  [c.104]

The most demanding requirements with respect to water quaUty are in the electronics industry and in very high pressure power plants (see Electronic materials Power generation). Although mixed-bed units are recognized for giving practically complete removal of all ionic constituents, the mixed-bed unit will give off trace amounts if systems are not designed to approach 100% separation of the two resins before regeneration. Any cation-exchange resin remaining with the anion exchanger is converted to the sodium form when the anion exchanger is regenerated with NaOH. Likewise,  [c.382]

Gas Adsorption. There are few commercial installations. Ammonia [7664 1-7] is adsorbed by a cation exchanger in the hydrogen form and eluted with an acid to give ammonium sulfate or ammonium chloride [12125-02-9]. Success has been reported on the removal of sulfur dioxide [7446-09-5] on a weak base anion exchanger (55) (see Adsorption, gas separation). Chemical compounds such as phenol, ethylene dichloride [107-06-2] and benzene [71 3-2] have been successfully removed on polymeric adsorbents (56). The concern with systems for removing impurities from air, or other gaseous streams, is the high pressure drop typical of high velocities through beds of small-diameter resin particles. Other concerns are water content of both the resin and the gaseous stream, temperature, and cost effective regeneration procedures, especially for organic substances.  [c.388]

The most important commercial products of high-pressure science are the extremely hard materials, synthetic diamond [40, 4T and 42] and (c-BN) [43]. At ambient pressure, diamond is less stable than the less dense allotrope, graphite. c-BN also may be less stable than the less dense h-BN isomer with its graphitic stnichire of rings of alternating B and N atoms. Diamond and c-BN with four equivalent sp bonds per atom are denser than graphite and h-BN with tlnee sp bonds, each shorter than an sp bond and one very long intennolecular van der Waals bond per atom. The volume change, AF, for the transfonnations from graphite to diamond is negative. Thus, the A(PF) = PAV contribution to the change of enthalpy or Gibbs free energy is negative and becomes even more negative at higher pressures, so the denser fonns of each material become more stable at higher pressures. Rearranging the bonds around each atom involves high-energy barriers that separate the low and high density fonns (for a historical review of these processes see [44])- Although Yagi and Utsumi [45] showed that the graphite converted to the hexagonal fonn of diamond at  [c.1959]

The role of solid and liquid lubricants at solid-solid interfaces is to reduce friction forces during sliding. Liquid lubrication is commonly described as occurring in tliree regimes that depend upon the nonnal forces and sliding speeds of two surfaces in contact. At low nonnal force and high sliding speeds liquid films can completely separate two surfaces, preventing solid-solid contact. Under these conditions, usually referred to as hydrodynamic lubrication, the frictional forces between two surfaces are detennined by the rheological properties of the thin fluid film that separates them. As the nonnal force is increased and the sliding speed decreased the interface enters the boundary regime of lubrication. The surfaces have defonned under the high nonnal forces and are thought to be separated by monomolecular films of adsorbed molecules. These are typically surfactant-like species that are added to lubricant fluids for just this purjDose. Under even higher nonnal forces the interface enters the extreme pressure regime during which direct solid-solid contact occurs. The surfaces are defonned even further and high rates of wear are observed exposing clean solid surfaces. Lubricant fluids usually contain extreme pressure additives which can react with clean exposed surfaces under high pressure and high temperature conditions to fonn thin solid films with low shear yield strengths. It is these thin solid films that provide lubrication. As implied by the discussion above, lubricant fluids are often very complicated mixtures containing as many as ten or 20 additives, each of which serves a specific purjDose in reducing friction and wear of solid surfaces in sliding contact [2].  [c.2743]

When the pore structure is viewed as an assembly of interconnected channels, the flux vectors are formed by adding contributions from the separate channels, so before a model of this type can be constructed it is necessary to have equations which will predict the fluxes in a single chann< throughout the range from very small to very large diameters. But we have already seen that no such equations are presently available. The classic-Knudsen theory gives the fluxes for very small pores or very low pressures, and the continuum theory developed in Chapter 4 gives the fluxes for large pores or high pressures, but in intermediate cases there is no adequate theory.  [c.67]

Another example is the purification of a P-lactam antibiotic, where process-scale reversed-phase separations began to be used around 1983 when suitable, high pressure process-scale equipment became available. A reversed-phase microparticulate (55—105 p.m particle size) C g siUca column, with a mobile phase of aqueous methanol having 0.1 Af ammonium phosphate at pH 5.3, was able to fractionate out impurities not readily removed by hquid—hquid extraction (37). Optimization of the separation resulted in recovery of product at 93% purity and 95% yield. This type of separation differs markedly from protein purification in feed concentration ( i 50 200 g/L for cefonicid vs 1 to 10 g/L for protein), molecular weight of impurities (<5000 compared to 10,000—100,000 for proteins), and throughputs ( i l-2 mg/(g stationary phasemin) compared to 0.01—0.1 mg/(gmin) for proteins).  [c.55]

Uses. Because of its good solvency and relatively low boiling point, acetonitrile is used widely as a recoverable reaction medium, particularly for the preparation of pharmaceuticals. Its largest use is for the separation of butadiene from hydrocarbons by extractive distillation (see Azeotropic and EXTRACTIVE distillation) (31). It also has been proposed for the separation of other olefins, eg, propylene, isoprene, aHene, and methylacetylene from hydrocarbon streams (32—34). It is a superior solvent for polymers and can be used as a solvent for spinning fibers and for casting and mol ding plastics. It is used widely in spectrophotometry and electrochemistry. Since pure acetonitrile does not absorb uv light, it is commonly used as a solvent in high pressure flquid chromatography (hplc) for the detection of materials, eg, residual pesticides, in the ppb range highly purified hplc grade acetonitrile is routinely available from suppflers.  [c.219]

However, recycling of many other plastics remains uneconomic (1). This is reflected in a number of companies closing plastics recycling operations in the mid-1990s (73). The costs of recycling commingled plastics has been estimated at U.S. 1700 per ton (72). This is ten times more expensive than recycling easily separated homogeneous products such as PET and HDPE. In Germany, federal mandates require recycling of 60% of all plastic packaging. German projects to recycle over one biUion pounds a year of plastics have been aimounced (74,75). These processes will use high temperature—high pressure processes to depolymerize commingled plastics to produce petrochemical feedstocks. These processes are not economic (65,76).  [c.233]

Chromatographic techniques are readily appHed to SAN for molecular weight deterrnination. Size-exclusion chromatography or gel permeation chromatography (gpc) (22) columns and conditions have been described for SAN (23). Chromatographic detector differences have been shown to be of the order of only 2—3% (24). High pressure precipitation chromatography can achieve similar molecular weight separation (25). Liquid chromatography (Ic) can be used with secfractioned samples to determine copolymer composition (26). Thin layer chromatography will also separate SAN by compositional (monomer) variations (25).  [c.192]

Fig. 6. Adsorption capacity of various dessicants vs years of service in dehydrating high pressure natural gas (39). a, Alumin a H-151, gas 27° C and 123 kPa, from oil and water separators b, siUca gel, gas 38° C and 145 kPa, from oil absorption plant c, sorbead, 136-kPa gas from absorption plant Fig. 6. Adsorption capacity of various dessicants vs years of service in dehydrating high pressure natural gas (39). a, Alumin a H-151, gas 27° C and 123 kPa, from oil and water separators b, siUca gel, gas 38° C and 145 kPa, from oil absorption plant c, sorbead, 136-kPa gas from absorption plant
Until separation techniques such as chromatography (28,29) and counter-current extraction had advanced sufficientiy to be of widespread use, the principal alkaloids were isolated from plant extracts and the minor constituents were either discarded or remained uninvestigated. With the advent of, first, column, then preparative thin layer, and now high pressure Hquid chromatography, even very low concentrations of materials of physiological significance can be obtained in commercial quantities. The alkaloid leurocristine (vincristine, 22, R = CHO), one of the more than 90 alkaloids found in Catharanthus roseus G. Don, from which it is isolated and then used in chemotherapy, occurs in concentrations of about 2 mg/100 kg of plant material.  [c.533]

Eig. 8. A power plant for utilizing geopressured resources (32). The high pressure fluid is fed from the well. A, to a turbine, B, where its mechanical energy is utilized to generate electricity. The fluid then proceeds to a separator, C, where the methane is separated and used to generate electricity in a combustion generator, D. The Hquid fraction is deflvered to a heat exchanger, E, of binary plant. The binary plant loop contains a turbine, G, and a cooling heat exchanger, H, which uses water, I, to recondense the working fluid. It also contains an additional heat exchanger, E, to extract the thermal energy from the exhaust gas of the combustion generator. A pilot plant mn for a year included all these elements except the initial turbine, B.  [c.269]

Glycerol from glycerides (natural glycerol) is obtained from three sources soap manufacture, fatty acid production, and fatty ester production. In soap manufacture, fat is boiled with caustic soda solution and salt. Fats react with the caustic to form soap (qv) and glycerol. The presence of salt causes a separation into two layers the upper layer is soap and the lower layer, referred to as spent lye, contains glycerol, water, salt, and excess caustic. Continuous saponification (consap) processes for producing soap are now common and produce a spent lye similar to batch or kettie processes. In producing fatty acids, the most common process is continuous, high pressure hydrolysis where a continuous, upward flow of fat in a column flows countercurrent to water at 250—260°C and 5 MPa (720 psi). The fat is spHt by the water into fatty acids and glycerol. The fatty acids are withdrawn from the top of the column, and the glycerol-containing aqueous phase (called sweet water) falls and is withdrawn from the bottom. Concentration of the sweet water by evaporation results in a product called hydrolysis cmde. The fatty acids from splitting are used to make soap, reduced to the corresponding fatty alcohol, or marketed as fatty acids. A third source of natural glycerol is the esterification of fats with alcohol to produce fatty esters. A fat usually reacts with methanol in the presence of an alkah catalyst such as sodium methoxide to produce methyl ester and glycerol, which is separated from the methyl ester by water washing. Acidulation with hydrochloric acid and removal of residual methanol produces a cmde glycerol with a few percent salt content. The methyl esters are reduced to the corresponding fatty alcohols, marketed as fatty esters, or used as an emission reducing component of diesel fuels.  [c.347]

First, is die removal of impurities. Water, carbon dioxide, and sulfides are removed by scmbbing with monoethanol amine (see Alkanolamines) and diediylene glycol (see Glycols), followed by drying with alumina. Then the natural gas is concentrated in helium as the higher boiling hydrocarbons are liquefied and collected. Cmde helium, concentrated to perhaps 70% and containing nitrogen, argon, neon, and hydrogen, undergoes final purification at pressures up to 18.7 MPa (2700 psi). The crude material is chilled to 77 K in liquid nitrogen-cooled cods of a heat exchanger. Under the high pressure, the low temperature liquefies most of the remaining nitrogen and argon, allowing the helium together with last traces of nitrogen, neon, and hydrogen to separate. Evaporation of nitrogen reduces the temperature and nitrogen content of the helium before it passes into liquid-nitrogen-cooled adsorbers. Activated charcoal operating at liquid nitrogen temperatures or below is capable of adsorbing all nonhelium gases. Hence, passage through these adsorbers yields helium that exceeds 99.9999% in purity. Both concentration and purification steps require nitrogen refrigeration, which is obtained by expansion engines or turbines as well as by expansion valves.  [c.10]

For the high pressure reverse-osmosis units, epoxy resias which can withstand elevated hydrauHc pressures (>10,000 kPa, 1,450 psi) are used as potting agents. Composite polysulfone hoUow fibers have been potted with an epoxy resia sandwiched between two layers of siUcone mbber. The mbber has low adhesion to the fiber, but protects it from epoxy wieking and breakage near the potting fixation spots and permits cutting of the fibers while they are fixed ia the mbbery medium. In large commercial reverse-osmosis (RO) units for desalination of seawater and brackish water (eg, Permasep, HoUosep), the fibers are assembled ia a U shape (Fig. 13) and are epoxy-potted. Winding of RO hoUow-fiber membranes iato a permeator is described ia References 6, 17, and 23. Various types of blood-compatible polyurethanes are available for hemodialysis potting others that resist attack by solvents are available for hquid-mixture separation by per-vaporation. A difficulty sometimes encountered with ion-exchange hoUow fiber is their tendency to undergo dimensional changes when wetted. Siace most potting agents require dry potting conditions, the adhesive bond may faU after several wet-dry cycles. To circumvent this problem, chemical treatment is employed to neutralize the ion-exchange sites at the ends of the bundles.  [c.152]

Polyamide. Nylon hoUow fibers are produced by Du Pont, Berghof GmbH, and many others. The development of hoUow fiber initially from nylon-6 or nylon-6,6 was a natural extension of technology estabUshed in the textile industry (see Polyamides, fibers). These materials were aimed toward the desalination of brackish water employing high pressure reverse osmosis. Fiber dimensions were 50—60 pm OD and 25—30 pm ID. Hydraulic permeabUity through these aUphatic nylon derivatives was very low. The second generation of asymmetric polyamide hoUow-fiber membranes developed for high pressure reverse osmosis consist of derivatives of aromatic polyamides (aramids) with improved water permeabUity and water (brackish and seawaters) separation. They ate the largest consumers of hoUow fibers. The fibers are spun from a solution of inorganic salts and DMA while a nitrogen stream is maintained through the nascent fiber bore. The extmsion is carried into a high temperature nitrogen atmosphere, resulting in solvent evaporation, and skin estabUshment in the outer zone is annealed. These fibers must be stored wet to retain the asymmetric morphology essential for high hydraulic permeabUity.  [c.154]

HoUow-fiber membranes are subjected to extensive studies for gaseous separation (eg, CO2, H2, O2, N2, H2S, CO, CH, where the capiUary configuration has an advantage over the spiral-wound flat film (42) and plate-and-frame devices. Such fibers achieved first niche commercial prominence in such medical purposes as membrane oxygenators. Commerciali2ations and development activities are now occurring rapidly at a number of corporations including A/G Technology, Dow Chemical Co., Du Pont, Monsanto, Perma Pure, Toyobo, Ube Industries, and Union Carbide. For high pressure apphcations it appears glassy rigid polymers as polysulfone, polycarbonate polyaramid, and polyamide are preferred. Sintered inorganics, ie, iron, nickel, aluminas, and carbides are involving much attention. Glassy polymers have an amphorous polymeric material that is below its softening or glass-transition temperature under the conditions of use. This concept is opposed to a mbber polymer which is employed above its glass-transition temperature. The rigidity of the glassy polymers offer better selectivity than the mbbery polymers (24).  [c.155]

A.queous Jilkaline E.kctrolysis. The traditional process employs potassium hydroxide, KOH, added to the water to improve the conductivity through the ceU. Table 9 shows operating parameters for industrial electrolyzers. All of these systems use a diaphragm to separate the cathode and anode, and keep the product oxygen and hydrogen from mixing. There are basically two types of units offered tank type and filter press. In the tank type, many individual cells are coimected in parallel and fed from one low voltage source. This requires large current flows at low voltage, as well as large transformers and rectifiers. Most commercial electrolyzers are of the filter press type, where cells are stacked and coimected in series. The back side of the cathode for one cell is the anode for the next. This is called a bipolar arrangement. The voltage required to mn the whole module is the sum of the voltages for each individual cell, so low voltages are not needed. However, a series arrangement means that if one cell fails, the module fads. Some units operate at high pressures. This is considered an efficient way to compress hydrogen. Much work is being directed toward improving traditional alkaline electrolysis (157,158). New cell geometries that lower resistances, better electrodes to reduce overvoltages, and better diaphragm materials, so that higher temperatures can be used, are ad. being considered. Higher temperatures enable the electrodes to function more efficiently. Improvements in design and materials are manifested in higher ceU current densities.  [c.425]

Stopped-FlowMixing. Instmments that combine fast-acting syringes and good mixers with automated measurements of concentrations in situ are now readily available from several commercial sources. These are called stopped-flow apparatuses. Eigure 1 shows a schematic diagram of the essential elements. Reactants are placed in separate syringes. The plungers are pushed forward very quickly, usually by means of high pressure air discharge. The two reagents are combined in the mixer and then flow into an observation cell, in which the concentration of a reactant or product is measured. A catching syringe is added to recover the sample and provide a controllable means of halting the high speed flow. The probe that measures concentrations as a function of time after mixing is almost always a uv or visible absorption spectrophotometer, although photofluorescence has become an option routinely available in commercial instmments. This latter measurement is actually a fluorescence-detected absorption measurement the fluorescence is directiy proportional to the amount of light absorbed. Conductivity measurement is also fairly common. Because the apparatus is quite compact, the entire  [c.509]


See pages that mention the term Separators high-pressure : [c.79]    [c.126]    [c.2123]    [c.78]    [c.446]    [c.287]   
Surface production operations Ч.2 (1999) -- [ c.356 ]