Vapor-phase cracking

The feedstocks used ia the production of petroleum resias are obtaiaed mainly from the low pressure vapor-phase cracking (steam cracking) and subsequent fractionation of petroleum distillates ranging from light naphthas to gas oil fractions, which typically boil ia the 20—450°C range (16). Obtaiaed from this process are feedstreams composed of atiphatic, aromatic, and cycloatiphatic olefins and diolefins, which are subsequently polymerized to yield resias of various compositioas and physical properties. Typically, feedstocks are divided iato atiphatic, cycloatiphatic, and aromatic streams. Table 2 illustrates the predominant olefinic hydrocarbons obtained from steam cracking processes for petroleum resia synthesis (18). 

Thermal polymerization is not as effective as catalytic polymerization but has the advantage that it can be used to polymerize saturated materials that caimot be induced to react by catalysts. The process consists of the vapor-phase cracking of, for example, propane and butane, followed by prolonged periods at high temperature (510—595°C) for the reactions to proceed to near completion. Olefins can also be conveniendy polymerized by means of an acid catalyst. Thus, the treated olefin-rich feed stream is contacted with a catalyst, such as sulfuric acid, copper pyrophosphate, or phosphoric acid, at 150—220°C and 1035—8275 kPa (150—1200 psi), depending on feedstock and product requirement. 

The catalytic reactions occur in the vapor phase. Cracking reactions begin as soon as the feed is vaporized. The expanding volume of the vapors that are generated are the main driving force to carry the catalyst up the riser. 

Chapter 4.1 deals with an important industrial problem, the vapor-phase cracking of acetone. Here the material- and energy-balance design equations are developed. We advise the students to try and develop the design equations independently before consulting the book s derivations. Numerical solutions and MATLAB codes are developed and explained for this problem and sample results are given that need to be checked against those of the students codes. 

Our specific example involves the vapor-phase cracking of acetone into ketone and methane, described by the endothermic reaction... 

Vapor-phase cracking a high-temperature, low-pressure conversion process. 

Vapor-phase cracking produces considerable quantities of unsaturated gases suitable as feedstocks for polymerization units. 

Jeffreys, in a treatment of the design of an acetic anhydride manufacturing facility, states that one of the key steps is the vapor-phase cracking of acetone to ketene and methane ... 

P8-23b The vapor-phase cracking of acetone is to be carried out adiabatically in a bank cf 10001 -in. schedule 40 tubes 10 m in length. The molar feed rate of acetone is 6000 kg/h at a pressure of 500 kPa. The maximum feed temperature is 1050K, Nitrogen is to be fed together with the acetone to provide the sensible heafof reaction. Determine the conversion as a function of nitrogen feed rate (in terms of ) for (a) Fixed total molar flowrate. 

P10-21a The vapor-phase cracking of gas-oil in Example 10-7 is earried out over a different eatalyst, for which the rate law is... 

One-pass catalytic (clay) cracking at 45% gasoline yield Vapor-phase cracking... 

Mixed-phase cracking Reforming Vapor-phase cracking Polyforming Cat cracking... 

An abundant and relatively cheap raw material is almost sure to find in time a use to which it can be economically put. The cracking of petroleum, especially vapor-phase cracking, produces tremendous volumes of olefin gases, which are now extensively used as raw materials for alcohol production. The alcohols made by this procedure are ethyl from ethylene, isopropyl from propylene, normal butyl indirectly from ethylene, secondary butyl from normal butylene, tertiary butyl from isobutylene, and secondary and tertiary amyl from amylenes. 

Likewise, the yield by vapor-phase cracking (1050 to 1150 F) of a 24 API distilled straight-run feed would be large [Eq. (19-3)], but the gas loss would be very large ... 

The tubestill process has been used for vapor-phase cracking without fundamentally changing the process. However, the outlet temperature is much higher (1050 to 1250 F), and the outlet pressure must be reduced to 30 to 50 psi so that substantially a pure vapor phase exists in the cracking tubes. Likewise the best known continuous coking processes are like the tubestill process except that coke drums are introduced before the evaporator vessel of the tubestill process (Fig. 19-15). 

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