Olefin production plants

Figure 26.1 Location of a current NH3-SCR (a) and future H2-SCR unit (b) in an industrial furnace used in olefin production plants.

Olefins are produced primarily by thermal cracking of a hydrocarbon feedstock which takes place at low residence time in the presence of steam in the tubes of a furnace. In the United States, natural gas Hquids derived from natural gas processing, primarily ethane [74-84-0] and propane [74-98-6] have been the dominant feedstock for olefins plants, accounting for about 50 to 70% of ethylene production. Most of the remainder has been based on cracking naphtha or gas oil hydrocarbon streams which are derived from cmde oil. Naphtha is a hydrocarbon fraction boiling between 40 and 170°C, whereas the gas oil fraction bods between about 310 and 490°C. These feedstocks, which have been used primarily by producers with refinery affiliations, account for most of the remainder of olefins production. In addition a substantial amount of propylene and a small amount of ethylene ate recovered from waste gases produced in petroleum refineries. 

Molecular sieves have had increasing use in the dehydration of cracked gases in ethylene plants before low temperature fractionation for olefin production. The Type 3A molecular sieve is size-selective for water molecules and does not co-adsorb the olefin molecules. 

Supercondensed Mode A method of operating gas-phase olefin polymerization plants. See High Productivity. 

Computer modeling of hydrocarbon pyrolysis is discussed with respect to industrial applications. Pyrolysis models are classified into four groups mechanistic, stoichiometric, semi-kinetic, and empirical. Selection of modeling schemes to meet minimum development cost must be consistent with constraints imposed by factors such as data quality, kinetic knowledge, and time limitations. Stoichiometric and semi-kinetic modelings are further illustrated by two examples, one for light hydrocarbon feedstocks and the other for naphthas. The applicability of these modeling schemes to olefins production is evidenced by successful prediction of commercial plant data. 

Successful stoichiometric modeling is demonstrated for industrial pyrolysis of light hydrocarbon and their mixtures. A semikinetic approach is more appropriate for naphtha pyrolysis. Although the final form of such a model is simple, its development generally requires more innovations. Applicability of the naphtha model to olefins production is evidenced by the successful prediction of commercial plant performances. 

The Reppe process is based on acetylene as a raw material. These reactions were developed by Reppe et al. [2]. In accordance with the rise of the petrochemical industry, most processes switched from acetylene to olefins as raw material. However, only the 1,4-butanediol production process continued to rely on the Reppe process. Mitsubishi Chemical Corporation developed a totally different production method that uses 1,3-butadiene to produce 1,4-butanediol and THF. Commercial production was launched in 1982 and has been continued ever since. This process ended the over-half-century monopoly of the Reppe method. The Mitsubishi Chemical method has an advantage over the Reppe method with respect to the handling of raw materials and production costs, but in recent years, Chinese companies that can take advantage of inexpensive natural gas and coal have built a new production plant by using the Reppe method and international competition is getting more intense. 

We call this the "Reactor Granule" technology, and it represents a revolution in the development of "Ziegler-Natta" olefin polymerization. This "Reactor Granule" becomes a micropolyolefin production plant in which polyolefin alloys and blends are formed directly from the monomers. ... 

Because of its simple design, employing only two fixed bed reactors, this process is offered for retrofitting H2SO4 or HE alkylation units as well as olefin polymerization and dimerization plants with minor modifications. ExSact is especially suitable to revamp olefin dimerization mills with minimal capital investment, offering a 10-12 higher MON than the dimerization product with a double production capacity (255). ExSact has been chosen to revamp a 3500 bbl/day olefin oligomerization plant in Europe. 

Besides operating our ACR pilot plant, we at Union Carbide are doing extensive research, development and engineering design work, primarily on separations and purifications. Here, because of our long experience in olefins production - we operate plants with about 2,000,000 metric tons of ethylene capacity - we have considerable expertise. A prototype ACR unit -actually a small commercial plant of about 25,000 tons/ year ethylene output - is now in the design phase. We expect to build the unit in one of our existing U.S. plants within the next 4 years. 

As a by-product, hydrogen is also produced by electrolytic processes such as chlorine-sodium hydroxide production, catalytic reforming processes in refineries, olefin production, and recovery from ammonia plant purge gas. 

In the United States alone, there are 23 production plants yielding about 22 billion pounds per year in 2010. The largest producers include ExxonMobil, Dow Chemical, Basell USA, Formosa Plastics, Huntsman, INEOS Olefins and Polymers, Phillips Sumika, Sunoco, and Total Petrochemicals. 

The removal of acetylenes and dienes from steam-cracked olefins is a critical step in purification. Selective hydrogenation processes and catalysts have become more important as worldwide olefin production has increased in 1999 to more than 90 million tormes of ethylene and almost 50 million tonnes of propylene. Demand for better catalysts with improved selectivity and longer operating cycles has grown as larger plants are built. Tighter product specifications have also been imposed now that more of the olefins produced are being converted to polyolefins. 

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