Steam cracking, naphtha

This table, points out the low production of propylene in comparison with the steam cracking of naphtha, the high coproduction of acetylene ranging up to nearly 150 kg t ofethyiene instead of the 15 kg/t observed in naphtha steam cracking, and the substantial formation of fuel oil and tars. 

Based on the foregoing considerations, it can therefore be infen that a decrease in the tube diameter, which causes a reduction in residence ime, results in a higher ethylene yield (diagram a in Fig. 2.12) in industrial naphtha steam cracking conditions. Simultaneously, a drop in the propylene yield (diagram b in Fig. 2.12) is observed in the normal... 

Table 9 Comparison Between Simulated and Experimental Yields of Naphtha/Steam Cracking in Honeycomb Reactor ...

In practice, tubes,with inside diameter from 65 mm (Stone and Webster) to 120 mm [Lummus, Selas) and 7 to 5 mm thick are employed for naphtha steam cracking Tbe gases flow within these tubes at a linear velocity of about 300 m/s. The pressure drop recorded between the furnace inlet and outlet may reach 0.4 to 0.7.10s Pa in these conditions. The tubes are fabricated by extrusion or centrifugal casting Cast tubes are made of medium alloy steels (25 to 30 per cent chromium and 20 to 30 per cent nickel) containing 0.5 per cent carbon. If they are positioned vertically, their sagging strength allows for metal skin temperatures of 1000 to 1100 C. 

Naphtha steam cracking, quench boiler performwh... 

Tig. 2.17- Cold separation section of a naphtha steam-cracking unit. 

Table 2.12 shows the typical analyses of a Cs- gasoline and of aromatic cuts, obtained by naphtha steam cracking As may be observed, these effluents contain non-negligible amounts of diolefins and alkenylaromatics, which make those employed in the refinery (C3 fraction) unsuitable for direct use as a gasoline. These thermally unstable components cause gumming in motors, and therefore must first be removed. 

Table 3.26 Composition of pyrolysis tar from naphtha steam cracking...

Butenes are usually obtained from Crack C via naphtha steam cracking (Scheme 4.4) [31]. After the removal of butadiene and isobutene from the crude stream, the so-called Raffinate II contains 1-butene, cis/trans-2-hutene, and the isomeric butanes. Alternatively, it has been produced for a subsequent hydroformylation by dehydrogenation of n-butane on a Cr on alumina... 

For its relevance, propene is one of the most important olefins. Propene is obtained mainly from naphtha steam cracking as a coproduct with ethene, and also as a coproduct from fluid catalytic cracking (FCC) units at refineries. Relatively small amounts are produced by propane dehydrogenation and by Fischer-Tropsch synthesis. Because of the strong global demand for polypropene, acrylonitrile, 0x0 alcohol, and acrylic acid products, present propene supply from conventional sources cannot fulfill the market needs. An alternative route to propene is by applying the metathesis reaction for the conversion of a mixture of ethene and 2-butene into propene (Equation [16.2]). 

TABLE 7.2. Petrochemicals From Naphtha Steam Cracking."... 

Butenes are usually derived from Crack-C4 from naphtha steam cracking [27]. After the removal of butadiene (by extraction) and isobutene (by conversion into methyl t-butylether) from the crude stream, the so-called Raffinate II contains 1-butene (50-65%), cis/trons-2-butene, and the isomeric butanes. Raffinate II is the cheapest source of butenes, and their most valuable hydroformylation product is n-pentanal, whereas the isomers 2-methylbutyraldehyde and 3-methylbutyraldehyde are less in demand and lower in value. The main application for -valeraldehyde is its transformation into 2-propylheptanol (2-PH) by aldolcondensation and subsequent hydrogenation of the product (Scheme 14.4) [28, 29]. like 2-EH, 2-PH is also an important plasticizer alcohol. n-Valeraldehyde is also used as an ingredient in flavoring mixtures. w-Valeraldehyde can be converted into -valercarboxylic ester by subsequent oxidation and esterification with tertiary valeric alcohol, providing a useful lubricant and a substitute for Freon. 

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