Dehydration water vapor removal

Upon water vapor removal from the stream, only part of the dry gas-catalytic activity is recovered. This partial activity recovery may be mainly attributed to decomposition of the hydrolyzed copper complexes, and bare ion (due to the dehydration of copper complexes on the exterior surface) migration to active sites inside the zeolite cavities. Another contribution may come fi m tiie fine CuO particles on the zeolite surface, i.e., small part of active Cu cations are slowly restored by solid ion exchange with Bronsted acid sites. This hypothesis is drawn from the observation that Cu(H)-ZSM-5 with low Cu ion exchange level can be obtained by solid ion exchange between H-ZSM-5 and CuO in a vacuum at 5(X)°C as reported by Karge, et al (75). The permanent activity loss, however, is not explained. This may be attributed to irreversible CuO particle formation and deactivation, or dealumination if it happened in this study. 

In the first step of refining, the unreacted ammonia is removed from the reactor effluent in the overhead of the ammonia stripper. The tails are fed into an evaporator where sodium chloride is concentrated and removed. The vapor from the evaporator is dehydrated in the three subsequent columns. In the first dehydrator, water is removed until the N2H4-H2O mixture approaches the azeotropic concentration of about 65 percent hydrazine. In the second dehydrator, aniline is used as the extracting agent to break the azeotrope, and the water is removed in the overhead with the aniline, which is subsequently recovered in a decanter for recycle. The final column removes aniline from the hydrazine, producing 98 percent purity N2H4. 

The methyl a-hydroxyisobutyrate produced is dehydrated to MMA and water in two stages. First, the methyl a-hydroxyisobutyrate is vaporized and passed over a modified zeoHte catalyst at ca 240°C. A second reactor containing phosphoric acid is operated at ca 150°C to promote esterification of any methacrylic acid (MAA) formed in the first reactor (74,75). Methanol is co-fed to improve selectivity in each stage. Conversions of methyl a-hydroxyisobutyrate are greater than 99%, with selectivities to MMA near 96%. The reactor effluent is extracted with water to remove methanol and yield cmde MMA. This process has not yet been used on a commercial scale. 

Favor adsorption for processes that require essentially complete removal of water vapor (adsorptive dehydration is capable of achieving dew point depres >45° C (80°F) molecular sieves are favored adsorbents. 

A typical dehydration. specification in the U.S. Gulf Coast is 7 lb of water vapor per MMsef of gas (7 Ib/MMscf). This gives a dew [lomi ot around 32 f for 1,000 psi gas. In the northern areas of the U.S. and Canada the gas contracts require lower dew points or lower water vapor conceniia tions ill (he gas. Water vapor concentrations of 2—4 Ib/MMscf are comnioii II I he g. as is to be proces.sed at very low temperatures, as in a cryogenic gas pl.mi. w ater vapor removal down to 1 ppm may be required. 

To keep water from condensing as the gas is processed, it is necessary to dehydrate the gas (that is, remove water vapor) until the amount of water vapor remaining in the gas is less than that required to fully saturate the gas at all conditions of temperature and pressure. Since the dehydrated gas will have a lower dew point, dehydration is sometimes called dew point depression. For example, if the amount of water vapor in the 3,000 psig gas stream referred to earlier were reduced from 105 Ib/MMscf to 50 Ib/MMscf, the dew point would be reduced from 150°F to 127°F. That is, its dew point will be depressed by 23°F. 

Membranes will also remove some of the water vapor. Depending upon the stream properties, a membrane designed to treat CO2 to pipeline specifications may also reduce water vapor to less than 7 Ib/MMscf. Often, however, it is necessary to dehydrate the gas downstream of the membrane to attain final pipeline water vapor requirements. 

Gas dehydration is the process of removing water vapor from a gas stream to lower the temperature at which water will condense from the stream. This temperature is called the dew point of the gas. Most gas sales contracts specify a maximum value for the amount of water vapor allowable in the gas. Typical values are 7 Ib/MMscf in the Southern U.S., 4 Ib/MMscf in the Northern U.S. and 2 to 4 Ib/MMscf in Canada. These values correspond to dew points of approximately 32°F for 7 lb/ MMscf, 20°F for 4 lb MMscf, and 0°F for 2 Ib/MMscf in a 1,000 psi gas line. 

Makower and Nielsen 21) have described another method that can be used to alter the texture of the dehydrated material in order to increase its permeability to water vapor and to shorten the time required for removal of water. The method, called the lyophilization procedure, involves the following steps ... 

Water is present in the materials of interest as free water or water of crystallization, or as combined water. The process of dehydration refers to the removal of the water of crystallization, while the removal of combined water is called dehydroxylation because hydroxyl groups in the material are broken down to form water vapor. The dehydroxylation process is very often alternately described as calcination. The drying process used in the present text pertains to both dehydration and dehydroxylation. In the processing of ores for metal extraction, drying essentially implies the removal by evaporation of water which a material holds in it in various forms. 

During the dehydration stage (between 450°C and 600°C), hydroxyl (OH ) ions in the clay are dislodged from their molecules, combine with each other to form water vapor, and are thus removed from the clay structure and released into the atmosphere. It is during this stage, as a consequence of the displacement of the hydroxyl ions, that the chemical composition and the structure of the clay are irreversibly altered and converted to fired clay. 

Water stability is a major challenge that has to be overcome before metal organic framework can be used in removing carbon dioxide from flue gas. The core structure of MOF reacts with water vapor content in the flue gas leading to severe distortion of the structure and even failure. As a consequence, the physical structure of MOF is changed, e.g., reduction of porosity and surface area, etc. that decreases the capacity and selectivity for C02. Complete dehydration of flue gas increases the cost of separation. It is therefore essential for MOFs to exhibit stability in the presence of water up to certain extent [91]. 

Zinc bromide, ZnBr2, used as a desiccant Zinc chloride, ZnCl2, used as a dehydrating condensing agent in org synthesis Commercial dehydration operations are best performed on solids by an apparatus that provides air to catty off water vapor on its release Some of the equipment is convertible from heat removal to heat supply by simply changing the temp level of the fluid or air (Ref 3)... 

Gas Dehydration. It has been found that water vapor permeates cellulose acetate membranes at a rate approximately 500 times that of methane (Ref. 2). This exceptionally high selectivity for water vapor make cellulose acetate membrane systems attractive for dehydration of hydrocarbon gas streams to pipeline specifications on either a pure gas stream or while simultaneously removing contaminating acid gases. For these applications the small size, low weight and low maintenance of the SEPAREX system is particularly advantageous for offshore installations. 

Nature furnishes us with a certain number of hydrated silicates which mineralogists call zeolites the dehydration of certain hydrates offers curious peculiarities analcime, for instance, may be completely dehydrated without any sudden variation in form or optical properties of the crystals being observed Georges Friedel has shown that analcime had not, at a given temperature, an invariable dissociation tension let us suppose the temperature constant in a first equilibrium state the tension of the water vapor which exists in equilibrium above the crystals has the value P remove a portion of this water vapor the analcime will undergo a certain dehydration and the tension of the water vapor will increase, but only to a value P, less than P and BO on analcime is therefore not a definite hydrate, but only a solid solution in which water is mixed with an anhydrous silicate. 

Along the line AB, solid is in equilibrium with vapor. If the pressure is decreased below the line AB, the solid will sublime. This relationship is the basis of freeze-drying foods, such as those shown in Figure 25. The food is frozen, and then a vacuum is applied. Water sublimes, which dehydrates the food very quickly. The food breaks down less when water is removed at the low temperature than when water evaporates at normal temperatures. 

Mols liquid water collected on dehydrator tray and removed at that point up tower above where reflux returns below this tray - 777.7 - 268 (water vapor in tower overhead) = 509.7 mols/hr... 

Vapor pressures of DMSO and wafer are shown in Fig. ll-12d. Based on appearances, they could be separated by a single-stage batch distiUation (under vacuum and in a short time to avoid decomposition). Because of the affinity between these two liquids, however, a single-stage water stripper removed too much DMSO in the overhead stream. The solution to this problem was to insert a reflux condenser in the vessel with warm water in the jacket to aUow return of the entrained DMSO in the vapor stream back to the boilup. In accord with Fig. 11 -12d, the dehydration system pressure was maintained at about 50 mm Hg and the condenser jacket temperature was set at about 50-60°C, which successfully removed the water and maintained the freezing point near 18°C in the crystallizer. 

Liquid water and sometimes water vapor are removed from natural gas to prevent corrosion and formation of hydrates in transmission lines and to attain a water dew point requirement of the sales of gas. Many sweetening agents employ an aqueous solution for treating the gas. Therefore dehydrating the natural gas that normally follows the sweetening process involves ... 

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