Steam cracking Pyrolysis gasoline

The feedstocks will t3 ically be low value refinery or petrochemical streams, such as steam cracker by-products rich in C4 s, which have poor propylene selectivity when recycled to the steam cracker. The feedstock can include raffinates, catalytic cracked naphtha, coker naphtha, steam cracker pyrolysis gasoline, as well as synthetic chemical streams containing sufficient amounts of C4-C7 olefins. Dienes, sulfur, nitrogen and oxygenates in the feeds are preferably selectively hydrotreated prior to the conversion process. However, feeds with low levels of dienes, sulfur, nitrogen, metal compounds and oxygenates can be processed directly from FCC units, cokers or steam crackers without any pretreatment. 

Pyrolysis gasoline is a by-product of the steam cracking of hydrocarbon feeds in ethylene crackers (see Ethylene). Pyrolysis gasoline typically contains about 50—70 wt % aromatics, of which roughly 50% is benzene, 30% is toluene, and 20% is mixed xylenes (which includes EB). 

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). 

Significant products from a typical steam cracker are ethylene, propylene, butadiene, and pyrolysis gasoline. Typical wt % yields for butylenes from a steam cracker for different feedstocks are ethane, 0.3 propane, 1.2 50% ethane/50% propane mixture, 0.8 butane, 2.8 hill-range naphtha, 7.3 light gas oil, 4.3. A typical steam cracking plant cracks a mixture of feedstocks that results in butylenes yields of about 1% to 4%. These yields can be increased by almost 50% if cracking severity is lowered to maximize propylene production instead of ethylene. 

Raw materials for obtaining benzene, which is needed for the production of alkylbenzenes, are pyrolysis gasoline, a byproduct of the ethylene production in the steam cracking process, and coke oven gas. Reforming gasoline contains only small amounts of benzene. Large amounts of benzene are further produced by hydrodealkylation of toluene, a surplus product in industry. 

The other source of aromatics is the pyrolysis gasoline (pygas) which is a byproduct of naphtha or gas oil steam cracking. This presents an excellent synergistic opportunity between refinery, BTX complex and stream cracking for olefins production. 

Other sources of benzene include processes for steam cracking heavy naphtha or light hydrocarbons such as propane or butane to produce a liquid product (pyrolysis gasoline) rich in aromatics that contains up to about 65 percent aromatics, about 50 percent of which is benzene. Benzene can be recovered by solvent extraction and subsequent distillation. 

Application To directly recover styrene from raw pyrolysis gasoline derived from steam cracking of naphtha, gas oils and NGLs using the GT-Styrene process. 

Dicyclopentadiene (DCPD) is usually recovered as a high value product from the byproduct pyrolysis gasoline stream that is generated in steam cracking furnaces (see Ethylene and Propylene by Steam Cracking ). U.S. 6,258,989 (to Phillips Petroleum) gives a typical pyrolysis gasoline composition and describes a suitable... 

Application Advanced Pygas Upgrading (APU) is a catalytic process technology developed by SK Corp. and is exclusively offered by Axens to convert pyrolysis (ex steam cracking) gasoline to a superior steam-cracker feed (LPG), and benzene, toluene and xylene (BTX) aromatics. 

Application GT-Styrene is an extractive distillation process that directly recovers styrene from the raw pyrolysis gasoline derived from the steam cracking of naphtha, gasoils and natural gas liquids (NGLs). The produced styrene is high purity and suitable for polymerization at a very attractive cost compared to conventional styrene production routes. The process is economically attractive for pygas feeds containing more than 15,000 tpy of styrene. 

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