Medium-pressure process

During World War II, nine commercial plants were operated in Germany, five using the normal pressure synthesis, two the medium pressure process, and two having converters of both types. The largest plants had capacities of ca 400 mr / d (2500 bbl/d) of Hquid products. Cobalt catalysts were used exclusively. 

Direct production of select MDCHA isomer mixtures has been accompHshed usiag mthenium dioxide (30), mthenium oa alumiaa (31), alkah-moderated mthenium (32) and rhodium (33). Specific isomer mixtures are commercially available from an improved 5—7 MPa (700—1000 psi) medium pressure process tolerant of oligomer-containing MDA feeds (34). Dimethylenetri(cyclohexylamine) (8) [25131 -42-4] is a coproduct. 

The first commercial Fischer-Tropsch facility was commissioned in 1935, and by the end of the Second World War a total of fourteen plants had been constructed. Of these, nine were in Germany, one in France, three in Japan, and one in China. Both German normal-pressure and medium-pressure processes (Table 18.1) were employed. The cobalt-based low-temperature Fischer-Tropsch (Co-LTFT) syncrude produced in these two processes differed slightly (Table 18.2), with the product from the medium-pressure process being heavier and less olefinic.11 In addition to the hydrocarbon product, the syncrude also contained oxygenates, mostly alcohols and carboxylic acids. 

Anon( Ref 67) and Reidel (Ref 79) describe the Phillips Chemical Co plant near Houston, Texas. It is the NEC (Nitrogen Engineering Corp) medium pressure process utilizing natural gas as starting material. Resen(Ref 70) describes the manuf of ammonia at the Lion Oil Co plant in Louisiana. Frankenburg (Ref 51) studied the relationship between the nature and the effectiveness of ammonia synthesis catalysts. Other studies of synthesis catalysts were made by Odelh6g(Ref 44), Enomoto Horiuchi(Refs 53 54), Nielsen(Ref 60), Emmett(Ref 74) and Faith... 

The commercial production of high-density polyethylene started almost at the same time in late 1956 by Phillips using a chromium-based catalyst in a medium-pressure process and by Hoechst using a Ziegler catalyst in a low-pressure process. Polypropylene production began in Montecatini and Hercules plants in 1957. Poly(l-butene) and poly(4-methyl-1-pentene) have been produced in small commercial quantities since about 1965. The commercial production of ethylene/propylene-based rubbers started in 1960 [241]. 

This type of reactor was used for the cobalt-catalyzed atmospheric or medium-pressure processes in Gennany until 1945. but since then, an improved reactor has been developed for the commercial iron catalyzed ARGb high-load process. This is own in Figure 3 115]. The catalyst is emttained in tubes of 50 mm ID... 

Methanol from synthesis gas Low and medium pressure process... 

The normal synthesis gas required for the Fischer-Tropsch process is a mixture of 2 volumes of hydrogen and 1 volume of carbon monoxide. Recent practice in the Ruhr when using cobalt catalyst showed ratios of from 1.8 to 2.0 for the atmospheric pressure process and ratios as low as 1.5 for the medium-pressure process. In the Ruhrehemie plant at Sterkrade, the medium-pressure process used different ratios for each of the three stages of the synthesis, 1.4, 1.6, and 1.8, respectively, by introducing the requisite amount of "converted water gas before each stage. In all cases, the synthesis gas contained inert constituents which seldom exceeded 20% by volume. 

In atmospheric and some low- to medium-pressure processes, one or more separate oxidation-cooling units are often included prior to gas absorption. These units are built in the form of vertical towers which are cooled with external water curtains, shell-and-tube units, and also drum and cascade coolers. Excess air in the gas promotes initial oxidation, and some of the water vapor also present condenses to form weak nitric acid, which is later concentrated in the absorption section. Additional air for oxidation usually is injected at some point in the process, often in the absorption tower. In some plants, the gas is rapidly cooled to condense the water vapor without forming much weak acid, thereby helping to increase final acid concentration. A special condenseix yclone separator unit designed for this purpose is described by.Graham etal..[10]. 

The Standard Oil process has the longest history. Working with ethylene pressures around 70 bar, it represents a medium-pressure process. The polymerization is started by one of the usual commercial hydroforming catalysts partially reduced M0O3 aluminum oxide, activated by sodium or lithium aluminum hydride. The ethylene is dissolved to 5-10% in xylene and polymerized to practically a 100% yield at temperatures below 200°C but still above the melting point of poly(ethylene). This solution polymerization enables the catalyst surfaces to be kept predominantly free and active. 

The feed gas of ammonia oxidation is a mixture of NH3 with air and contains, typically, 11 vol.% NH3 (the lower flammability limit is 15% at 20 °C). The gas velocity (empty reactor) under reaction conditions (mean gas temperature 600 °C) is in the range 0.7-1.3ms for low- and medium-pressure processes (1-4 bar) and up to 3 m s for high-pressure processes (8-12bar) (Holzmann, 1967). Thus, the residence time (empty reactor) is about 0.2-0.6 ms, if we take the number of gauzes N (3 for 1 bar and 30 for a high pressure of around 10 bar) and the diameter of the wire d (typically 60 p,m) as basis for the reactor length I at = Nd (that is, only the space taken up by the catalyst is counted). 

The conversion reached at the first gauze is 63%. In total, only four gauzes are needed to reach almost full conversion (Table 6.4.2), which is also the number of gauzes used industrially for a medium-pressure process (Holzmaim, 1967). An additional verification of the calculation is the final system temperature of 907 °C, which is exactly the value of AT d (= 757 K) higher than the gas inlet temperature of 150 °C, as required by the overall heat balance. 

Process parameter [related to 11HNO3 (100%)] Medium-pressure process High-pressure process Dual pressure process... 

In a practical industrial process, it is well accepted that the condensing temperature should be controlled to adjust the ammonia content in the recycle gas. Commonly the content of ammonia in the inlet gas is 3%-4% for a low-pressure process, 2.0%-3.0% for a medium-pressure process, and 3.0%-3.8% for a high-pressure process. If the absorption by water is used for the separation of, the content of ammonia in the inlet gas can be reduced to below 0.5%. ... 

Use as Ligand in Ziegler-Natta Polymerization of Ethylene in Solution. A medium pressure process for the polymerization of ethylene has been developed in the presence of a catalytic system involving a monocyclopentadienyl titanium species, containing TIPSthiolate as the heteroligand and two activable ligands (2C1 or 2Me), associated with an ionic activator such as triphenyl-carbenium tetrakis(pentafluorophenyl)borate. ... 

Tertiary butanol is preferred because of its low chain-terminating properties. Three different methods for the production of ethylene vinyl acetate copolymers are known, these being high-pressure process (0%-45% vinyl acetate) low-pressure emulsion process (55%-100% vinyl acetate) and medium-pressure process in solution (30%-100% vinyl acetate). 

At about the same time that news of the Ziegler discovery was released, the Phillips Petroleum Company in the United States atmounced that it had developed a medium-pressure, catalytic process (500 psig) to produce a high-density, crystalline polyethylene. The process was discovered when traces of ethylene in a flue gas had polymerized over conventional cracking catalysts. The Phillips catalyst contained chromic oxide supported on silica. The Standard Oil Company of Indiana (later Amoco) also introduced a medium pressure process using a catalyst comprising molybdenum oxide supported on carbon or alumina, but it did not enjoy the success of the Ziegler or Phillips processes and was only operated in three full-scale plants. ... 

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