Residence time, isobutane oxidation

Figure 2. Oxidation of isobutane over (NH4)3PMoj204o reaction conditions residence time 3.6 s, feed composition 26% isobutane, 12% water, 13% oxygen, rest helium.

Dependence of isobutane oxidation on temperature and the residence time in a CSTR was discussed by Caprio et al. (1981). Different oscillations were detected. Jensen and Ray (1980-1, 2) studied horatian oscillations, see Section E.ll... 

The effect of residence time on isobutane conversion and on selectivity to the various products at the temperature of 320°C, under isobutane-rich conditions, is illustrated in Figure 3. The data indicate that methacrolein, methacrylic acid, and carbon dioxide are all formed through direct, parallel reactions acetic acid and possibly carbon monoxide are instead formed through consecutive reactions. Methacrolein undergoes consecutive reactions of transformation to acetic acid, to carbon oxides and possibly in part also to methaciylic acid. Indeed the selectivity to the latter product seems to increase slightly with increasing isobutane conversion. 

The loop reactors, which are recycled tubular reactors, are used by the Phillips Petroleum Co. and Solvay et Cie. The Phillips process is characterized by the use of a light hydrocarbon diluent such as isopentane or isobutane in loop reactors which consist of four jacketed vertical pipes. Figure 1 shows the schematic flow diagram for the loop reactor polyethylene process. The use of high-activity supported chromium oxide catalyst eliminates the need to deash the product. This reactor is operated at about 35 atm and 85-110° C with an average polymer residence time of 1.5 hr. Solid concentrations in the reactor and effluent are reported as 18 and 50 wt %, respectively. The reactor diameter is 30 in. (O.D.) and the length of the reactor loop is about 450 ft. 

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