Commercial plants

Mobil s Low Pressure Isomerization Process (MLPI) was developed in the late 1970s (123,124). Two unique features of this process are that it is Operated at low pressures and no hydrogen is used. In this process, EB is converted to benzene and diethylbenzene via disproportionation. The patent beheved to be the basis for the MLPI process (123) discusses the use of H-ZSM-5 zeoHte with an alumina binder. The reaction conditions described are start-of-mn temperatures of 290—380°C, a pressure of 273 kPa and WHSV of 5—8.5/h. The EB conversion is about 25—40% depending on reaction conditions, with xylene losses of 2.5—4%. The PX approach to equiHbrium is about 99 ndash 101%. The first commercial unit was Hcensed in 1978. A total of four commercial plants have been built. 

These processes use expensive C2 hydrocarbons as feedstocks and thus have higher overall acrylonitrile production costs compared to the propylene-based process technology. The last commercial plants using these process technologies were shut down by 1970. 

The propylene-based process developed by Sohio was able to displace all other commercial production technologies because of its substantial advantage in overall production costs, primarily due to lower raw material costs. Raw material costs less by-product credits account for about 60% of the total acrylonitrile production cost for a world-scale plant. The process has remained economically advantaged over other process technologies since the first commercial plant in 1960 because of the higher acrylonitrile yields resulting from the introduction of improved commercial catalysts. Reported per-pass conversions of propylene to acrylonitrile have increased from about 65% to over 80% (28,68—70). 

Generally, yields on both fluorspar and sulfuric acid are greater than 90% in commercial plants. 

Oxidation of methanol to formaldehyde with vanadium pentoxide catalyst was first patented in 1921 (90), followed in 1933 by a patent for an iron oxide—molybdenum oxide catalyst (91), which is stiU the choice in the 1990s. Catalysts are improved by modification with small amounts of other metal oxides (92), support on inert carriers (93), and methods of preparation (94,95) and activation (96). In 1952, the first commercial plant using an iron—molybdenum oxide catalyst was put into operation (97). It is estimated that 70% of the new formaldehyde installed capacity is the metal oxide process (98). 

In Sasolburg, South Africa, a commercial plant using the Fischer-Tropsch process was completed in 1950 and began producing a variety of Hquid fuels and chemicals. The faciUty has been expanded to produce a considerable portion of South Africa s energy requirements (15,16). 

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. 

Acetylene Recovery Process. A process to recover coproduct acetylene developed by Linde AG (Fig. 11), and reduced to practice in 11 commercial plants, comprises three sections acetylene absorption, ethylene stripper, and acetylene stripper. 

Cmshed stone is conveyed by a mbber-belt conveyor and bucket elevator. Fine stone and dust are conveyed by enclosed screw conveyors, air slides, or pneumatic air systems into storage bins and tank tmcks for shipment. For screening, changeable vibratory screens predominate for all sizes from 23 cm to 0.074 mm (200 mesh). Most stone is stored uncovered on the ground in conical stockpiles, suppHed by radial belt conveyors. Such a conveyor can maintain four stockpiles of different sized stone. Large commercial plants typically stockpile stone in 10 sizes ... 

Reverse Osmosis. This was the first membrane-based separation process to be commercialized on a significant scale. The breakthrough discovery that made reverse osmosis (qv) possible was the development of the Loeb-Sourirajan asymmetric cellulose acetate membrane. This membrane made desalination by reverse osmosis practical within a few years commercial plants were installed. The total worldwide market for reverse osmosis membrane modules is about 200 million /yr, spHt approximately between 25% hoUow-ftber and 75% spiral-wound modules. The general trend of the industry is toward spiral-wound modules for this appHcation, and the market share of the hoUow-ftber products is gradually falling (72). 

The scientific basis of extractive metallurgy is inorganic physical chemistry, mainly chemical thermodynamics and kinetics (see Thermodynamic properties). Metallurgical engineering reties on basic chemical engineering science, material and energy balances, and heat and mass transport. Metallurgical systems, however, are often complex. Scale-up from the bench to the commercial plant is more difficult than for other chemical processes. 

A large use of molecular sieves ia the natural gas industry is LPG sweetening, in which H2S and other sulfur compounds are removed. Sweetening and dehydration are combined in one unit and the problem associated with the disposal of caustic wastes from Hquid treating systems is eliminated. The regeneration medium is typically natural gas. Commercial plants are processing from as Htde as ca 30 m /d (200 bbl/d) to over 8000 m /d (50,000 bbl/d). 

The first commercial plant to use CYANEX 272 became operational in 1985. An additional three plants were constmcted between 1985 and 1989. Of the four, one is in South America and three in Europe. An additional three plants have been built two in Europe (1994) and one in North America (1995). Approximately 50% of the Western world s cobalt is processed using CYANEX 272. Both high purity salts and electrolytic cobalt metal are recovered from solutions ranging in composition from 30 g/L each of cobalt and nickel to 0.2 g/L Co, 95 g/L Ni Operating companies usually regard use of CYANEX 272 as confidential for competitive reasons and identities cannot be disclosed. CYANEX 272 is being evaluated on the pilot-plant scale in many additional projects involving the recovery of cobalt and other metals. 

The design or substantial modification of a new plant or process, its subsequent constmction, and start-up represent a tremendous investment of time and money. The rewards are great if a significant improvement is realized the risks are also great if a costiy commercial plant fails to produce as expected. To reduce the degree of risk, lengthy and expensive research programs are often undertaken. 

The need for a pilot plant is a measure of the degree of uncertainty in developing a process from the research stage to a hiU commercial plant. A modification to a weU-known process may go directiy from basic research work to design of a commercial plant using this approach for a brand new process risks a significant failure. Hence, one or more intermediate size units are usually desirable to demonstrate process feasibiUty as well as to determine safe scale-up factors. 

Scale-up is the process of developing a plant design from experimental data obtained from a unit many orders of magnitude smaller. This activity is considered successful if the commercial plant produces the product at plaimed rates, for plaimed costs, and of desired quaUty. This step from pilot plant to full-scale operation is perhaps the most precarious of all the phases of developing a new process because the highest expenses ate committed at the stages when the greatest risks occur. 

Instrumentation. Pilot plants are usually heavily instmmented compared to commercial plants. It is not uncommon for a pilot plant to have an order of magnitude more control loops and analytical instmments than a commercial plant because of the need for additional information no longer requked at the commercial stage. A discussion of all the specific types of instmmentation used on pilot plants is beyond the scope of this article. Further information on some of the more common instmmentation is available (1,51). 

One of the most vexing aspects of pilot-plant work can be feed and product handling as a pilot plant is neither designed nor operated as a closed-loop system like a commercial plant. Indeed, the problems involved in handling and storing feed and product materials can sometimes seem to rival the pilot-plant process problems in difficulty. 

Production. Production of polycarbonate has steadily iacreased siace the opening of the first commercial plants ia the early 1960s. Worldwide capacity reached 665,000 t ia 1992 (38). Siace the mid-1980s, productioa has iacreased at 8—13% per year. Expected capacity ia 1995 is over oae million metric toas. Plants have opened ia several couatries, including Japan, Chiaa, Korea, and Brazil, although as of this writing (1995) the United States remains the primary producer of polycarbonate. U.S. production is about 47% of that worldwide. 

Researchers at Phillips Petroleum Company developed a commercially viable process for the synthesis of PPS involving the polymerization of /)-dich1orohenzene and a sodium sulfide source in a polar organic compound at elevated temperature and pressure. This Phillips process was patented in 1967 (18). Between 1967 and 1973, Phillips built and operated a pilot plant, estabhshed market demand, and constmcted a hiU-scale commercial plant. In 1973, the world s first PPS plant came on-stream in Phillips faciUty in Borger, Texas. 

Gymene. Methyhsopropylben2ene [25155-15-1] can be produced over a number of different acid catalysts by alkylation of toluene with propylene (63—66). Although the demand for cymene is much lower than for cumene, one commercial plant was started up in 1987 at the Yan Shan Petrochemical Company in the People s RepubHc of China. The operation of this plant is based on SPA technology offered by UOP for cumene. The cymene is an intermediate for the production of y -cresol (3-methylphenol) [108-59-4]. 

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