System liquid phase processes

Membrane Pervaporation Since 1987, membrane pei vapora-tion has become widely accepted in the CPI as an effective means of separation and recovery of liquid-phase process streams. It is most commonly used to dehydrate hquid hydrocarbons to yield a high-purity ethanol, isopropanol, and ethylene glycol product. The method basically consists of a selec tively-permeable membrane layer separating a liquid feed stream and a gas phase permeate stream as shown in Fig. 25-19. The permeation rate and selectivity is governed bv the physicochemical composition of the membrane. Pei vaporation differs From reverse osmosis systems in that the permeate rate is not a function of osmotic pressure, since the permeate is maintained at saturation pressure (Ref. 24). 

Cyclohexane is oxidized in a liquid-phase process to a mixture of cyclohexanone and cyclohexanol (KA oil). The reaction conditions are 95-120°C at approximately 10 atmospheres in the presence of a cohalt acetate and orthohoric acid catalyst system. About 95% yield can be obtained ... 

The process of direct synthesis of DME includes reactions of methanol synthesis and methanol dehydration, which are catalyzed by two different catalysts. Although the technology for the production of methanol is generally considered mature, most of thran are gas phase process, and the performances of these catalysts are restricted remarkably in liquid phase process. Development of high performance bifunctional catalyst system is very... 

Nippon Steel has developed an interesting liquid-phase process for producing 2-methylpyridine from ethylene and ammonia (74MI1 81MI2, 81MI3). The catalyst is reminiscent of the well-known Wacker process, viz. Pd /Cu redox system [Eq.(5)]. 

The Wacker-Hoechst process has been practised commercially since 1964. In this liquid phase process propylene is oxidized to acetone with air at 110-120°C and 10-14 bar in the presence of a catalyst system containing PdCl2. As in the oxidation of ethylene, Pd(II) oxidizes propylene to acetone and is reduced to Pd(0) in a stoichiometric reaction, and is then reoxidized with the CuCl2/CuCl redox system. The selectivity to acetone is 92% propionaldehyde is also formed with a selectivity of 2-4%. The conversion of propylene is more than 99%. 

Ethylene acetoxylation was also developed as a gas phase process following the liquid phase process and has been in commercial use since 1968. There is a notable difference between the two processes in the liquid phase the presence of palladium salts and redox systems results in the formation of both vinyl acetate and acetaldehyde, whereas in the gas phase process, using palladium metal,... 

The liquid and gas phase catalyst systems for vinyl acetate are based on the same components no coincidence as the latter was developed after the discovery of the former. They differ mainly in the reoxidation of Pd(0), which is carried out by Cu(II) in the liquid phase process and is not necessary in the gas phase process. It therefore seems tempting to suggest that the chemistry is similar in both cases, at least as far as the vinyl acetate formation is concerned. 

The regeneration of activated carbon beds used in gas phase adsorption requires less severe conditions than for liquid phase processes. Regeneration can be conducted in situ by stripping with steam. Newer and more efficient systems use regeneration by hot inert gas, nominally at 350°F, to recover a greater portion of contaminants with their subsequent recovery. This is particularly attractive if the disposal of condensate from steam regeneration becomes a problem [73]. 

Catalytic reactions can take place in either the liquid or vapor phase. Liquid phase reactions can be run in either a continuous manner or as a batch process while vapor phase reactions are run only in a continuous mode. In a batch reaction the catalyst, reactants, and other components of the reaction mixture are placed in an appropriate reaction vessel, the reaction is run and the products removed from the vessel and separated from the catalyst. In a continuous system the reactants are passed through the catalyst and the products removed at the same rate as the reactants are added. The applicability of vapor phase processes is limited by the volatility and thermal stability of the reactants and products so such processes are not commonly involved in the preparation of even moderately complex molecules. Because of this, primary attention will be placed here on liquid phase processes with vapor phase systems of secondary importance. A discussion of the different types of reactors used for each of these processes is found in the following chapter. The present discussion is concerned with the effect that the different reaction parameters can have on the outcome of a catalytic reaction. 

The results obtained show that immobilization of metal complexes in polymer gels allows to prepare physically heterogeneous and chemically homogeneous catalysts and leads to an important increase in their activity, selectivity and stability in the reactions of dimerization of lower olefins. The immobilization of the complexes opens new possibilities of macromolecular design of the catalysts with desired structural organization and will contribute to the development of general principles of synthesis of highly efficient and environmentally friendly catalytic systems for liquid phase processes. 

The catalyst systems employed are based on molybdenum and phosphorus. They also contain Various additives (oxides of bismuth, antimony, thorium, chromium, copper, zirconium, etc.) and occur in the form of complex phosphomolybdates, or preferably heteropolyacids deposited on an inert support (silicon carbide, a-alumina, diatomaceous earths, titanium dioxide, etc.). This makes them quite different from the catalysts used to produce acrylic acid, which do not offer sufficient activity in this case. With residence times of 2 to 5 s, once-through conversion is better than 90 to 95 per cent, and the molar yield of methacrylic acid is up to 85 to 90 per cent The main by-products formed are acetic add, acetone, acrylic add, CO, C02, etc. The major developments in this area were conducted by Asahi Glass, Daicel, Japan Catalytic Chemical, Japanese Gem, Mitsubishi Rayon, Nippon Kayaku, Standard Oil, Sumitomo Chemical, Toyo Soda, Ube, etc. A number of liquid phase processes, operating at about 30°C, in die presence of a catalyst based on silver or cobalt in alkaline medium, have been developed by ARCO (Atlantic Richfield Co,), Asahi, Sumitomo, Union Carbide, etc. 

Efficient treatment of the disparate length and time scales will be the key to the further development of predictive computational models for both plasma and electrochemical engineering. This is not limited to the plasma or liquid-phase processes. It includes the solid materials produced or modified by these technologies from the atomic level, to the microstructure to the bulk material properties. Finally, integration of modeling/simulation with design, sensors, control, optimization, safety and reliability will result in an ultimate integrated system which is based on molecular principles and which extends all the way to the factory scale ... 

There is a growing body of evidence in support of this hypothesis, especially for gas phase systems in channels in the order of 10-100 am. For liquid phase processing it is probably not practical to go to these low dimensions. But can these gains be obtained at... 

Commercial Processes.. The Oxo reaction is carried out in the liquid phase. With gaseous olefins, a suspension medium such as an inert hydrocarbon is used of a boiling range sufiSciently different from the aldehyde product to allow easy separation. No additional medium is required for hydrofonnylation of liquid olefins. Two liquid-phase processes have been developed. In the earlier one the catalyst is slurried in the feedstock or added liquid medium. Less operating difiSculty is claimed for the newer fixed-bed system because the need for filtration and solids handling is eliminated. 

Liquid-Phase Processes. Prior to 1980, commercial Hquid-phase processes were based primarily on an AIQ catalyst. AIQ systems have been developed since the 1930s by a number of companies, including Dow, BASF, Shell Chemical, Monsanto, SocmtH Chimique des Charbonnages, and Union Carbide—Badger. These processes generally involve ethyl chloride or occasionally hydrogen chloride as a catalyst promoter. Recycled alkylated ben2enes are combined with the AIQ. ethyl chloride to form a separate catalyst—complex phase that is heavier than the hydrocarbon phase and can be separated and recycled. 

Vsipor-Phsise Processes. Although vapor-phase alkylation has been practiced since the eady 1940s, it could not compete with liquid-phase processes until the 1970s when the Mobil—Badger vapor-phase ethylbenzene process was introduced (Fig. 4). The process is based on Mobil s ZSM-5 zeohte catalyst (38,52,53). The nonpoUuting and noncorrosive nature of the process is one of its major advantages over the AlQ liquid-phase system... 

Processes which take place within homogeneous liquids phases process are the preferred reaction systems for thermokinetic descriptions. In heterogeneous systems, which can be modelled with the help of macrokinetic formal rate laws, thermokinetic evaluation is possible, too, but only if additional information on the properties of the two phases is obtained in parallel. 

That is why, for fast liquid-phase processes where the volume is within 2-30 m, an intensive mixing and a well-developed heat removal system cannot be considered a successful or an optimal solution for the aforementioned problems when using continuous industrial reactors. Reactor dimensions substantially exceed the volume of a reaction zone and therefore, the duration of reactant flow through a reactor is several times longer than the duration of the chemical process needed for the required degree of conversion of the initial feedstock. It favours side reactions and reduces the selectivity in relation to the desired main process. 

There are several typical oxidation products from alkenes, which can be reached via catalytic routes using molecular oxygen as terminal oxidant. We are only considering liquid phase processes catalyzed by transition metal ions or complexes typically below 100-150 C. Many of these homogeneous catalytic reactions occur at or around room temperature. In addition to a single solvent containing the dissolved catalyst complex, phase-transfer conditions involving liquid-liquid or solid-liquid systems will in some cases be described. Likewise,... 

Cryotropic gel formation is a liquid-phase process occurring in the unfrozen liquid microphase of a macroscopically frozen system. 

A major advantage of vapor phase processes is the easy separation of reaction products from the catalytic system. Selectivity and catalyst deactivation and regeneration procedures, however, appear to be more critical compared to the liquid phase process. 

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