Gasoline from steam cracking

Gasolines from steam cracking have a high content of S, benzene and other aromatics. 

About 95% of toluene is obtained from the refinery catalytic reforming of naphtha feedstocks in what are called reformers. About 5% is obtained from pyrolysis gasoline from steam cracking of hydrocarbons associated with ethylene and propylene. 

Besides ethylene and propylene, the steam cracking of naphtha and catalytic cracking in the refinery produce appreciable amounts of C4 compounds. This C4 stream includes butane, isobutane, 1-butene (butylene), cis- and trans-2-hutene, isobutene (isobutylene), and butadiene. The C4 hydrocarbons can be used to alkylate gasoline. Of these, only butadiene and isobutylene appear in the top 50 chemicals as separate pure chemicals. The other C4 hydrocarbons have specific uses but are not as important as butadiene and isobutylene. A typical composition of a C4 stream from steam cracking of naphtha is given in Table 8.3. 

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

The two most important sources of aromatics from steam cracking are pyrolysis gasoline and pyrolysis tar. The composition of typical pyrolysis gasoline from cracking is shown in Table 3.25. 

As the growing demand for some coal-tar constituents for the development of mass-produced plastics, such as phenolic resins and polystyrene, and the increasing production of explosives could not be met by coal tar alone, new sources of aromatics were developed, starting from petroleum. The development of the production of reformate-gasoline and steam cracking of petroleum fractions has made two further feedstock sources for the production of aro-... 

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. 

Following cracking, the spent catalyst and oil descended to a disengager that separated the gasoline from the catalyst. The catalyst, with oil residue entrained on its surface, then moved through a purging section where superheated steam thermally removed oil remnants. The oil-free catalyst, still laden with carbon deposits, was then lifted by elevator from the bottom of the reactor to the top of the regenerator. 

The cracking of isobutane to isobutylene is of special interest because of the high demand for isobutylene as a feed for the production of oxygenates, mainly MTBE, as octane-enhancing gasoline additives. Isobutane separated from the steam cracking C4 cut or produced by butane isomerization is cracked in the presence of steam to yield isobutylene and propylene.148,149... 

Gasoline composition from hexadecane cracking over calcined and steamed AFS and USY zeolites can be represented by general correlations as shown in Figure 5. As these correlations are unique to zeolite Y, they indicate that the Y zeolite framework topology plays an important role in the mechanism of product formation. The method of dealumination and subsequent steam treatment lead to various PONA compositions however, these compositions result from a... 

Figure 7 shows calculated octane numbers from hexadecane cracking as a function of gasoline yield. Calcined and steamed zeolites are represented by open and closed symbols, respectively. The calculated octane number reflects changes in the gasoline molecular weight distribution and, to a lesser extent, composition effects. 

The high temperature process is the only commercially proven process for the production of olefins and liquids from coal. Current developments favour a low temperature process which is commercially proven to produce liquids and wax from coal or gas. The low temperature process produces a waxy synthetic crude oil which is cracked to produce diesel of high cetane and naphtha. The naphtha, which has high level of Unear paraffins, is sold on the petrochemical naphtha market rather than conversion into gasoline. The conversion of this naphtha into olefins by steam cracking has been addressed in previous chapters. 

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