Olefins from cracking

V. I. Komarewsky and J. R. Coley Polymerization of Olefins from Cracked Gases... 

Activation of Molecular Hydrogen by Homogeneous Catalysts S. W. Weller and G. A. Mills Catalytic Syntheses of Ketones V. I. Komarewsky and J. R. Coley Polymerization of Olefins from Cracked Gases... 

The sulfuric acid alkylation process for making aviation or motor gasoline from isobutane and olefins from cracked gases requires a relatively high isobutane-to-olefin ratio in the reaction zone to insure high octanes, good yields, and low polymer formation in the acid. The sulfuric acid catalyst can make use not only of the relatively pure external isobutane... 

The important process variables in the polymerization of olefins from cracked gases are time, catalyst activity, pressure, hydration, and temperature. All these variables are related to some extent and can be interchanged within certain narrow limits. 

Essentially all the commercial catalysts for the polymerization of olefins from cracked gases contain phosphoric acid and therefore are poisoned by alkaline materials in the reactor feed. The most commonly encountered poisons of this type are ammonia and combined organic nitrogen compounds of a basic nature. 

Polymerization of olefins from cracked gases today covers a broad range of products from motor fuel to petrochemicals. The petrochemical list is expanding rapidly with many of these products being made from propylene. Figure 1 shows a typical chamber type unit for producing the important petrochemicals, tetramer and cumene. 

Propylene-Butylene Motor Polymer This product is the most predominant of those made by polymerization of the olefins from cracked gases. It is a clean-burning fuel having a... 

Commercial polymerization was once used only for converting the olefins from cracked gases into motor fuel. However, it is rapidly becoming very important in the production of such petrochemicals as heptene, propylene dimer, trimer, tetramer and pentamer and the alkylated aromatics such as ethylbenzene, isopropylbenzene, cymene, and butyl-benzenes. This list may be expected to grow as new uses are found for the heavier olefins. 

To combine olefinic gases by polymerization to form heavier fractions, the combining fractions must be unsaturated. Hydrocarbon gases, particularly olefins, from cracking reactors are the major feedstock of polymerization. 

Linear a-olefins were produced by wax cracking from about 1962 to about 1985, and were first commercially produced from ethylene in 1965. More recent developments have been the recovery of pentene and hexene from gasoline fractions (1994) and a revival of an older technology, the production of higher carbon-number olefins from fatty alcohols. 

The feedstock, usuaHy consisting of propylene and butylenes (various isomers of C Hg) from cracking processes, may even consist of selective olefins for dimer, trimer, or tetramer production ... 

The olefins used are propylenes and butylenes ethylene is also produced from cracking operations but is not used in refinery processing. 

Paraffins are relatively inactive compared to olefins, diolefins, and aromatics. Few chemicals could be obtained from the direct reaction of paraffins with other reagents. However, these compounds are the precursors for olefins through cracking processes. The C -Cg paraffins and cycloparaffms are especially important for the production of aromatics through reforming. This section reviews some of the physical and chemical properties of C1-C4 paraffins. Long-chain paraffins normally present as mixtures with other hydrocarbon types in different petroleum fractions are discussed later in this chapter. 

Butadiene is obtained mainly as a coproduct with other light olefins from steam cracking units for ethylene production. Other sources of butadiene are the catalytic dehydrogenation of butanes and butenes, and dehydration of 1,4-butanediol. Butadiene is a colorless gas with a mild aromatic odor. Its specific gravity is 0.6211 at 20°C and its boiling temperature is -4.4°C. The U.S. production of butadiene reached 4.1 billion pounds in 1997 and it was the 36th highest-volume chemical. ... 

Naphthas obtained from cracking units generally contain variable amounts of olefins, higher ratios of aromatics, and branched paraffins. Due to presence of unsaturated compounds, they are less stable than straight-mn naphthas. On the other hand, the absence of olefins increases the stability of naphthas produced by hydrocracking units. In refining operations, however, it is customary to blend one type of naphtha with another to obtain a required product or feedstock. 

Kerosine, a distillate fraction heavier than naphtha, is normally a product from distilling crude oils under atmospheric pressures. It may also he obtained as a product from thermal and catalytic cracking or hydrocracking units. Kerosines from cracking units are usually less stable than those produced from atmospheric distillation and hydrocracking units due to presence of variable amounts of olefinic constituents. 

The feed to a catalytic reformer is normally a heavy naphtha fraction produced from atmospheric distillation units. Naphtha from other sources such as those produced from cracking and delayed coking may also be used. Before using naphtha as feed for a catalytic reforming unit, it must be hydrotreated to saturate the olefins and to hydrodesulfurize... 

The most important olefins and diolefins used to manufacture petrochemicals are ethylene, propylene, butylenes, and hutadiene. Butadiene, a conjugated diolefin, is normally coproduced with C2-C4 olefins from different cracking processes. Separation of these olefins from catalytic and thermal cracking gas streams could he achieved using physical and chemical separation methods. However, the petrochemical demand for olefins is much greater than the amounts these operations produce. Most olefins and hutadienes are produced hy steam cracking hydrocarbons. 

While most isoprene produced today comes from the dehydrogenation of C5 olefin fractions from cracking processes, several schemes are used for its manufacture via synthetic routes. The following reviews the important approaches for isoprene production. 

The classical HCK mechanism on bifunctional catalysts separates the metallic action from that of the acid by assigning the metallic function to the creation of an olefin from paraffin and the isomerization and cracking of the olefins to the acid function. Both reactions are occurring through carbenium ions [102],... 

Solvent, product aldehyde pressure, 500 psi temperature, 107°C catalyst, 3/1 weight ratio of PPh3 to HRh(CO)(PPh3)3. b Chevron cracked-wax o-olefin. c Gulf a-olefin from ethylene polymerization. 

In an olefins plant, the feed is subjected to very high temperatures in cracking furnaces for a few moments and then cooled rapidly to stop the cracking. Elaborate separation facilities are necessary to separate the olefins. from the by-products of the cracking process. 

List all the possible products that could result from cracking butane, CH3-CH2-CH2-CH3, in an olefins plant. Remember, "Anything that can happen. .. ... 

The dominant share of styrene production comes from dehydrogenation of EB in plants like that shown in Figure 8-5. Some comes as a coproduct in propylene oxide/styrene plants. An even smaller amount is recovered from the gasoline fraction of olefins plants cracking heavy liquids. 

Ren, T., Patel, M. and Blok, K. (2006) Olefins from conventional and heavy feedstocks Energy use in steam cracking and alternative processes. Energy, 31, 425. 

Figure 4-1 Flow sheet of a steam cracking plant to produce olefins from alkanes.

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