Cracking alkylation and catalytic

Here we will describe the main aspects of the chemistry involved in selected zeolite-catalyzed processes in the field of oil refining and petrochemistry, such as short paraffin aromatization, skeletal isomerization of n-paraffins and n-olefins, isoparaffin/olefin alkylation, and catalytic cracking. 

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. 

Refinery alkylation processes utilize either sulfuric acid or hydrofluoric acid as reaction catalysts. The feedstock for both alkylation processes originates primarily from hydrocracking and catalytic cracking operations. Coker gas oils also serve as feedstock in some applications. The differences and similarities between sulfuric acid alkylation and hydrofluoric acid alkylation are shown in TABLE 2-5. Typical alkylation reactions are shown in FIGURE 2-9. A sulfuric acid alkylation unit is illustrated in FIGURE 2-10. 

Thermal and catalytically cracked gasoline fractions can contain significant concentrations of phenols, low-molecular-weight organic acids, and alkyl and aryl mercaptans. All of these compounds can initiate gum formation in gasoline. Caustic treatment readily removes these compounds. 

The use of thermal and catalytic cracking processes for the production of high-octane motor gasolines is accompanied by the production of quantities of light hydrocarbons such as ethylene, propylene, butene, and isobutane. These materials are satisfactory gasoline components octane-wise, but their vapor pressures are so high that only a portion of butanes can actually be blended into gasoline. Alkylation is one of several processes available for the utilization of these excess hydrocarbons. 

Other interesting products that can be obtained from waste plastics using combined thermal and catalytic processes are alkylaromatic compounds, which possess industrial applications as automatic transmission fluids (ATF), detergents (linear alkyl benzenes, LAB), and improvers of cetane number in diesel fuels [104]. The process uses as raw material the olefins generated in a previous step of thermal and catalytic cracking, which represent a cheaper source of olefins alternative to the currently existing ones. No special details about the conditions applied for the olefin production are indicated, the emphasis being focused on the alkylation step. Alkylation catalysts comprise conventional Lewis... 

Principal uses of anti-foulants are in hydrodesulfurizers (for naphtha, gas, and lubricating oUs), in naphtha reformers, in crude and catalytic cracking units. Other units include cokers, visbreakers, alkylation units, ethylene units, deethanizers, solvent recovery units, etc. While fouled equipment consists primarily of heat exchangers, furnace tubes, piping, and distillation towers can also be affected. 

Catalytic cracking is a key refining process along with catalytic reforming and alkylation for the production of gasoline. Operating at low pressure and in the gas phase, it uses the catalyst as a solid heat transfer medium. The reaction temperature is 500-540°C and residence time is on the order of one second. 

Furthermore, the major problem of reducing aromatics is focused around gasoline production. Catalytic reforming could decrease in capacity and severity. Catalytic cracking will have to be oriented towards light olefins production. Etherification, alkylation and oligomerization units will undergo capacity increases. 

Catalysis. As of mid-1995, zeoHte-based catalysts are employed in catalytic cracking, hydrocracking, isomerization of paraffins and substituted aromatics, disproportionation and alkylation of aromatics, dewaxing of distillate fuels and lube basestocks, and in a process for converting methanol to hydrocarbons (54). 

Toxicity and Environmental Fate Information for Propylene CAS 115-07-1 Sourtes. Propylene (propene) is one of the light ends formed during catalytic and thermal cracking and coking operations, it is usually collected and used as a feedstock to the alkylation unit. Propylene is volatile and soluble in water making releases to both air and water significant. 

Seasonal chances in gasoline sales and heating oil sales compel some modifications to be made in conversion level. Therefore, the conversion pattern of a given catalytic cracking unit can vary from season to season. In summer operations, for instance, higher yields of motor gasoline are desired, both from direct production of 5/430° FVT catalytic naphtha and also from conversion of butylenes and isobutane to alkylate. 

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