Isobutane flammability limits

Key points that limit the industrialization of the process were recently illustrated by researchers from Sumitomo. Since the selectivity to methacryhc acid plus methacrolein typically decreases with temperature as the conversion increases, this implies that the rate of production of useful products increases only until the higher conversion compensates for the fall of selectivity. As a consequence of this, the maximum productivity value is reached at a specified temperature. For instance, when a selectivity of 45% is reached at 22% isobutane conversion, with a residence time of 5.4 s, a temperature of 370°C, and a feed containing 25% isobutane, 25% oxygen, and 15% steam, a productivity equal to 0.72 mmol/h/gcat is obtained, which is one order of magnitude lower than the one needed to make the process industrially viable. However, the productivity is limited by the oxygen conversion, the maximum concentration of which is dictated by the flammability limits (see Figure 14.1), and by temperature, since the POM decomposes above 380°C. 

There are two composition limits of flammability for air and a gaseous fuel under specified conditions [76]. The lower limit is the minimum concentration of combustible gas that will support combustion, while the higher limit is the maximum concentration. Table 5.1 shows the lower and higher limits for pure hydrocarbons in air at room temperature and atmospheric pressure (RTP) [76]. For methane in air, the flammability limit is 5—15 mol%. For ethane in air, the limits are 2.9—13.0 mol%. The limits become lower with increasing molecular weight. It also is interesting to note that the limits are the same for n-pentane and isopentane, and also for -butane and isobutane. 

The make-up and recycle oxygen are introduced into the reactor with fresh and recycled isobutane in a proportion such that the oxygen concentration is kept at less than 8 per cent volume. It is essential to ensure that this concentration remains below the lower flammability limit. Make-up inert gas may be required to control this concentration. j... 

PETROLEUM GAS, LIQUIFIED, COMPRESSED (68476-85-7) Highly flammable gas a mixture ofpropane, butane, isobutane, propylene, butylenes, and other flammable hydrocarbon gases of low molecular weight refined from petroleum [explosion limits in air (vol %) 2.2 to 9.5... 

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