GB1384916A - Reacation zone control - Google Patents

Abstract

1384916 Dehydrogenating ethylbenzene; reforming naphtha UNIVERSAL OIL PRODUCTS CO 23 May 1972 [24 May 1971] 24083/72 Heading C5E [Also in Division G3] In a conversion process wherein a reactant stream passes through at least two reactors in series the reactors are automatically controlled in response to an analysis of the final effluent so as to maintain a given conversion specification and to optimize a performance characteristic, e.g. maximize or minimize a ratio of substances in the effluent. (See Division G3). Fig. 3 shows a three stage reactor 51 having catalyst zones A, B, C for the dehydrogenation of ethylbenzene (EB) to styrene. The catalyst is preferably an alkali-promoted iron catalyst. Reactor pressure may be sub- or super-atmospheric, preferably 1À3 to 2À4 atm. Superheated steam at 760‹ C. is introduced from 85 into at a ratio of 0À65 to 1 steam to EB, and also into zones B and C at higher temperatures and ratios. The effluent 53 is analysed by a chromatograph 68 for quantities of benzene (B), toluene (T), styrene (S), and EB. The peak or average values of these quantities are supplied to amplifiers 35 ... 38. The ratio of S to EB is determined at 45 and supplied as a "conversion" signal to a controller 71. The sum of B and T, obtained at 46, is compared with S at 47 and this ratio is a "performance index" signal and this is optimized at 80. The output of 80 is combined with that from 71 to form the set point of temperature controllers 64 which regulate the flow of steam. The arrangement is such that S is kept at 80% of EB while the "performance index" ratio is kept at a minimum consistent with this. Fig. 4 shows catalytic reforming units using the invention. A low octane naphtha on line 100 is combined with a recycle gas stream of hydrogen, with some methane, ethane, and propane and traces of heavier hydrocarbons from line 99 and fed to a heater 104, which it leaves at 900‹ to 1000‹ F. It enters a reactor 101 at a pressure of 21À4 atm. The reactor has a noble metal catalyst and the mixture is converted to hydrocarbons having a higher octane number. This leaves the reactor at 20‹ to 150‹ F. cooler than the inlet temperature and is reheated at 154‹ to 900‹ to 1000‹ F. again. Further cooling occurs in a second catalytic reactor 151 and in a heat exchanger 135, which the mixture leaves at 60‹ to 120‹ F. A vapour phase is separated at 136 on line 99 from which a net hydrogen rich gas is withdrawn at 140. A liquid phase is withdrawn on line 141 for fractionation. Control is effected by regulating the fuel supply to heaters 104, 154. For this purpose the octane value of the liquid phase is measured at 118 and the signal from this is supplied to controller 121 as a "conversion signal". A "performance index" signal is obtained by measurement at 143 of the flow of liquid from 136 and this is optimized by device 130. The output signals from 121 and 130 are combined to from the set point of temperature controllers 114. The arrangement is such that the liquid flow is maximized, consistent with maintaining the required octane value. Modifications.-Control may be effected other than by temperature adjustment, e.g. adjustment of feed components or catalyst circulation. In HF alkylation, circulation of isobutane reactant may be controlled. The system may include a computer which modifies the set specification to compensate for the interaction between conversion and performance index, or time delays may be incorporated for the same purpose. Alternatively, temperature adjustment may be made subject to maintainance of an average for all the reactors. The optimizer may "look" at the cross product of two related variables, e.g. yield and octane. The performance index could be established by measuring recycle gas density. A specific system similar to Fig. 4, but using four reactors is described, with performance figures given.