Production processes medium pressure

Ironically, the high-pressure process produces a low-density product low medium pressure produce a high-density material. You d think it would be just the opposite. But it has to do with branching and crystallinity. The high-pressure leads to less crystalline molecules the less crystalline, the less dense. (Recall the past example in Figure 22—6. Uncooked spaghetti is denser than uncooked macaroni, and the spaghetti-shaped polymers are completely crystalline.)... 

The major process units include an air compressor to provide feed air to the process, and an ammonia vaporizer and superheater for pretreatment of the feed ammonia. A reactor vessel with a fixed platinum/rhodium catalyst bed quickly oxidizes the ammonia at reaction temperatures approaching 950°C. The reaction yield is 95%. A heat exchanger train immediately following the reactor is used to recover reaction heat. Reaction heat is recovered for both gas expansion (to provide shaft power for the air compressors) and for production of medium-pressure steam (at 380°C and 4000 kPa). The high-level energy available in the process is shared approximately equally between gas expansion and steam production. About 40% of all steam production is delegated to in- house process requirements, leaving about 3200 kg/hour available for export. 

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. 

Dual-Pressure Process. Dual-pressure processes have a medium pressure (ca 0.3—0.6 MPa) front end for ammonia oxidation and a high pressure (1.1—1.5 MPa) tail end for absorption. Some older plants still use atmospheric pressure for ammonia conversion. Compared to high monopressure plants, the lower oxidation pressure improves ammonia yield and catalyst performance. Platinum losses are significantiy lower and production mns are extended by a longer catalyst life. Reduced pressure also results in weaker nitric acid condensate from the cooler condenser, which helps to improve absorber performance. Due to the spHt in operating conditions, the dual-pressure process requires a specialized stainless steel NO compressor. 

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. 

Development of SASOL. Over 70% of South Africa s needs for transportation fuels are being suppHed by iadirect Hquefaction of coal. The medium pressure Fischer-Tropsch process was put iato operation at Sasolburgh, South Africa ia 1955 (47). An overall flow schematic for SASOL I is shown ia Figure 12. The product slate from this faciUty is amazingly complex. Materials ranging from hydrocarbons through oxygenates, alcohols, and acids are all produced. 

Complexed arenediazonium salts are stabilized against photochemical degradation (Bartsch et al., 1977). This effect was studied in the former German Democratic Republic in the context of research and development work on diazo copying processes (Israel, 1982 Becker et al., 1984) as well as in China (Liu et al., 1989). The comparison of diazonium ion complexation by 18-crown-6 and dibenzo-18-crown-6 is most interesting. Becker at al. (1984) found mainly the products of heterolytic dediazoniation when 18-crown-6 was present in photolyses with a medium pressure mercury lamp, but products of homolysis appeared in the presence of dibenzo-18-crown-6. The dibenzo host complex exhibited a charge-transfer absorption on the bathochromic slope of the diazonio band. Results on the photo-CIDNP effect in the 15N NMR spectra of isotopically labeled diazonium salts complexed by dibenzo-18-crown-6 indicate that the primary step is a single electron transfer. 

Figure 23.9d shows an induction turbine. Induction turbines work like extraction machines, except in reverse. Steam at a higher pressure than the exhaust is injected into the turbine to increase the flow part way through the machine and to increase the power production. In a situation like the one shown in Figure 23.9d, an excess of medium-pressure (MP) steam generation over and above that for process heating is used to produce power and exhaust into a low-pressure steam, where there is a demand for the low-pressure steam for process heating. 

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. 

The most frequently used lamp for UV curing processes is medium-pressure mercury lamp. Its emission spectrum can be used to excite the commonly used photoinitiators. Moreover, this type of lamp has a relatively simple design, is inexpensive, can be easily retrofitted to a production line, and is available in lengths up to 8 ft (2.5 m). Power levels in common use are in the range 40 to 240 W/cm, and even higher levels are available for special applications. ... 

The continuous photolysis of the acid has also been studied at temperatures between 90-190°C. in a static system 73 the light source was a medium pressure mercury arc and irradiation was continued for 200 min. The major products isolated were C2F6 and C02, with smaller amounts of CO, H2, and CF3H C2F4 was not detected. There was a marked reduction in the yields of CO, C02, and H2 when isobutane or butene-1 were present and it was inferred that COOH radicals were produced in the system. Process (77a) was proposed as the principal process, together with a moderate contribution from process (77d), and a minor contribution from process (77c). 

Medium-pressure steam is produced in this process to provide some plant heating/energy requirements. An economic advantage is the income derived from the export of excess steam. The steam specification corresponds to requirements for in-house application at the steam turbine, and also in response to the needs of the adjacent ammonia plant. The final steam specification is a superheated medium-pressure product at 380°C and 4000 kPa. 

One of today s fastest growing segments of the wood composition board industry is production of medium density fiberboard (MDF) using a dry process similar to that used for particleboard. First mention of the possibility of utilizing bark for MDF came in a presentation by Brooks in 1971 (43). He described a process in which a homogenous board with superior properties could be made from such raw materials as mixed, unbarked hardwood pulp chips unbarked pine chips, if bark content was less than 30% forest thinnings, branches, and so on and hardwood bark. Furnish was prepared by double-disk pressurized refiners. Brooks concluded a plant could be built to operate on 100% hardwood bark. 

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]. 

Methanol synthesis resembles that of ammonia in that high temperatures and pressures are used to obtain high conversions and rates. Improvements in catalysts allow operation at temperatures and pressures much lower than those of the initial commercial processes. Today, low-pressure Cu-Zn-Alminium oxide catalysts are operated at about 1500 psi and 250°C. These catalysts must be protected from trace impurities that the older high-pressure (5000 psi and 350°C) and medium-pressure (3000 psi and 250°C) catalysts tolerate better. Synthesis gas production technology has also evolved so that it is possible to maintain the required low levels of these trace impurities. 

When applied to biomass feedstocks, few steam gasification systems in which oxygen and air are excluded have been described or operated as autother-mal processes since this early work. Wright-Malta Corporation s directly heated, pressurized steam gasification process for the production of medium-energy gas described earlier is one of these (Hooverman and Coffman, 1976 Coffman and Speicher, 1993). An external heat source is needed only during startup, and water is added as a cofeedstock if the biomass feedstock contains insufficient moisture (i.e., less than about 50 wt %). The process was described as follows (Coffman, 1981) ... 

Current pharmaceutical production practice uses substantially three moist-heat sterilization processes 1) pressurized saturated steam 2) superheated water and 3) steam-air mixture. Process 1 is the traditional multipurpose process, which obviously uses pure pressurized saturated steam as sterilizing medium. Processes 2 and 3 are so-called counterpressure processes they were introduced in pharmaceutical production practice approximately 20 years ago and, respectively, use a spray superheated water and a homogeneous... 

The photolysis of tetrahydrofuran with a medium-pressure Hg arc led to carbon monoxide, hydrogen, methane, ethane, ethylene, propylene, cyclopropane, and formaldehyde as major products (196) Quantum yields or absolute yields are not known. The yields of formaldehyde, ethylene, and propane declined with increasing pressure, those of carbon monoxide and cyclopropane increased starting from near zero at very low pressures. In the absence of a material balance mechanistic conclusions cannot be drawn except that the processes 49 to 51 are very likely important. 

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