Thermal steam cracking

Alkenes or olefins (ethylene, propylene, butenes, and butadiene) are mainly produced via thermal steam cracking. Here, a petroleum fraction is mixed with water and heated briefly (for about 1 second) at 800 to 900C (1,472— 1,652°F), which breaks C-C bonds to yield shorter chains and splits out adjacent hydrogen atoms to form double bonds. The distribution of products obtained is given in Table 1. 

THERMAL STEAM CRACKING PRODUCTS (WEIGHT PERCENT)... 

Table 1. Thermal steam cracking products (weight percent).

KTI Propylene/isobutylene Butanes (field) Thermal steam cracking yields 79 mol% of products for MTBE units NA NA... 

Technip Isobutylene/butacracking Butanes (field) Co-production of propylene and iso-butylene by thermal steam cracking of butane at elevated temperatures NA NA... 

In this chapter we consider other commercially important routes to the production of olefins other than hy thermal steam cracking. Alternative processes generally involve catalytic processes rather than homogeneous gas-phase cracking. Although there have been proposals to develop catalytic processes for the production of ethylene, most of these alternative processes aim to produce propylene rather than ethylene. Some process economics of some of these routes have been compared by Houdek and Anderson and Nextant Inc. ... 

Cycloaliphatic Diene CPD—DCPD. Cycloatiphatic diene-based hydrocarbon resias are typically produced from the thermal or catalytic polymerization of cyclopeatadieae (CPD) and dicyclopentadiene (DCPD). Upon controlled heating, CPD may be dimerized to DCPD or cracked back to the monomer. The heat of cracking for DCPD is 24.6 kJ / mol (5.88 kcal/mol). In steam cracking processes, CPD is removed from C-5 and... 

Gyclopentadiene/Dicyclopentadiene-Based Petroleum Resins. 1,3-Cyclopentadiene (CPD) is just one of the numerous compounds produced by the steam cracking of petroleum distillates. Due to the fact that DCPD is polymerized relatively easily under thermal conditions without added catalyst, resins produced from cycloaHphatic dienes have become a significant focus of the hydrocarbon resin industry. 

In order to increase the solubiUty parameter of CPD-based resins, vinyl aromatic compounds, as well as other polar monomers, have been copolymerized with CPD. Indene and styrene are two common aromatic streams used to modify cyclodiene-based resins. They may be used as pure monomers or contained in aromatic steam cracked petroleum fractions. Addition of indene at the expense of DCPD in a thermal polymerization has been found to lower the yield and softening point of the resin (55). CompatibiUty of a resin with ethylene—vinyl acetate (EVA) copolymers, which are used in hot melt adhesive appHcations, may be improved by the copolymerization of aromatic monomers with CPD. As with other thermally polymerized CPD-based resins, aromatic modified thermal resins may be hydrogenated. 

Petroleum-derived benzene is commercially produced by reforming and separation, thermal or catalytic dealkylation of toluene, and disproportionation. Benzene is also obtained from pyrolysis gasoline formed ia the steam cracking of olefins (35). 

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. 

The major industrial source of ethylene and propylene is the pyrolysis (thermal cracking) of hydrocarbons.137-139 Since there is an increase in the number of moles during cracking, low partial pressure favors alkene formation. Pyrolysis, therefore, is carried out in the presence of steam (steam cracking), which also reduces coke formation. Cracking temperature and residence time are used to control product distribution. 

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