High selective ethylbenzene obtainment through alkylation of dilute ethene with gas phase-liquid phase benzene and polyethylated benzenes

High selective ethylbenzene obtainment through alkylation of dilute ethene with gas phase-liquid phase benzene and polyethylated benzenes Shenglin Liu, Fucun Chen, Sujuan Xie, Qingxia Wang, Longya Xu Laboratory of Natural Gas Utilization and Applied Catalysis. Dalian Institute of Chemical Physics. The Chinese Academy of Sciences, Dalian 116023, P. R. China E-mail: slliu@dicp.ac.cn; lyxu@dicp.ac.cn Introduction Ethene exothermally reacts with benzene to form ethylebenzene (EB), although undersirable chain and side reactions also takes place to produce as xylene, diethylbenzene (DEB), tri-ethylbenzene (TEB) and heavier aromatics, et al. The heave aromatics, PEB and BEB can be diverted to the fuel oil system via separation, and the DEB and TEB mixture can be transformed into EB via a transalkylation reactor system. Only the xylene isomer trace products show up as an impurity in the subsequent product, and are generally considered undersirable, because its boiling point is very close to that of the EB, thus no practical separation is possible. In the vapor phase reactor system, the EB product typically contains 2000-3000 ppm of xylene isomers. In order to minimize the formation of xylene isomers, DICP adopted vapor phase-liquid phase reactor process that the FCC off-gas vapor phase alkylation combined with DEB and TEB mixture liquid phase transalkylation [1], and the catalytic distillation [2], where the xylene isomers amounts in the EB product are 1000-1500 ppm and 500-1000 ppm, respectively. On the basis of the previous work, we explore a new process, namely, gas phase dilute ethene alkylation with gas phase-liquid phase benzene. In the new process, the xylene isomers amount in the EB product is less 100 ppm, and the EB selectivity can be above 99.9% by addition some of polyethylated benzenes into the benzene feed in the alkylation reactor, thus, the transalkylation reactor can be omitted in comparison with the vapor phase-liquid phase reactor and the catalytic distillation process. Here, we discuss the new process in detail. Results and discussion EB synthesis through alkylation of gas phase dilute ethene with gas phase-liquid phase benzene is put forward. The EB production system comprises a reactor vessel having several sections, namely, an alkylation section 6, an upper heat exchange section 7, and a bottom heat exchange section 5. The alkylation section, a fixed bed catalytic alkylation section, where vapor phase ethene and vapor phase-liquid phase benzene feed stream react to form liquid phase EB and PEBs, is an isothermic reactor. The heat of the reaction is used to vaporize benzene and heat the transalkylation feed. Because of the dilute effect of the methane, nitrogen and hydrogen in the ethene feed, the alkylation reaction is carried out at a temperature that is at least 10 oC lower than the normal boiling temperature of benzene at a given alkylation pressure, so long as the integrated vapor and liquid traffic is maintained between the upper heat exchange section and the bottom heat exchange section. The cool dilute ethene feed is heated to the temperature of the bottom heat exchange section at the heat exchanger 9, and then enters the bottom heat exchange section 5. Benzene and transalkylation feed from the upper of the reactor vessel are heated to the desired reaction temperature via the upper heat exchange section 7. The heating feeds above contact with a zeolite catalyst in the reaction section 6 to produce EB, DEB and DEB (PEBs), et al. Vaporizing benzene and heating the transalkylation feed mostly recover the heat of the reaction. The benzene is recondensed at the reactor vessel overhead 8 and 10. The overhead of the alkylation catalyst bed 6 contains hydrogen, methane, nitrogen, ethane, benzene, unconverted ethene and very small amounts of PEBs, et al. The overhead gas from the alkylation bed proceeds to the upper heat exchange section 7, where PEBs is recondensed by the reflux of benzene. Reactor vessel overhead gas stream from the upper heat exchange section 7 proceeds to condenser 8. The gas is further cooled in reflux drum 10. Liquid and vent gas products are separated in 10. Vent gas 4 proceeds to PSA hydrogen recovery (not shown) or to a fuel gas system. While the cool benzene from 10 and fresh benzene feed from 2, besides some transalkylation feed, are reheated at the heat exchanger 9 and enter the reactor vessel. Liquid bottom products exiting from the reactor vessel contain benzene, ethylbenzene and PEBs. Some of products exchange heat with the dilute ethylene at heat exchange 9, and the remaining products are separated into benzene, EB, TEB, DEB, via PEB column (not shown). Benzene, TEB and DEB recycle to reflux drum 10 from 2 and 11, respectively. In order to demonstrate the novel process rationality and the thermodynamics analysis legibility (not shown), the 3998 catalyst was used for the alkylation of gas phase ethene with gas phase-liquid phase benzene. Under the reaction conditions: temperature: 140-185 oC, pressure:1.6-2.1 Mpa, benzene/ethene mole ratio:3.0-5.5, ethene space velocity: 0.19-0.27 h-1, 3998 catalyst loaded:1000g, during the1010 h-time-on-stream, ethene conversion is above 95%, xylene content in the products is less 100 ppm, iso-PB selectivity is above 99%, EB selectivity is about 80%. If added 4-6 v% transalkylation feed into the benzene feed, EB selectivity can be exceeded 99%, indicating that the transalkylation reactor may be omitted. This demonstrated that the novel process is ration able, and the 3998 catalyst possesses good reaction performance. In the present, the 3998 catalyst and the process has been expended to 3000 ton/a EB product industry process. Table 1 Reaction performance of 3998 catalyst T(℃) P(Mpa) SV(h-1) B/E (mol) TOS (h) E conv.(%) Xylene (ppm) iPB sel (%) EB Sel(%) Ethylation Sel(%) 140-160 1.6 0.27 3.0 1 97.2 40 99.3 88.1 88.1 153-172 2.0 0.26 3.9 151 96.5 0 99.6 89.8 98.7 160-178 2.0 0.20 5.2 424 98.1 18 99.9 83.1 98.1 171-181 1.9 0.20 4.1 658* 96.6 0 99.4 100.7 99.5 178-182 2.0 0.19 4.2 674 98.4 0 99.1 101.3 99.6 170-181 2.1 0.20 4.1 700 97.5 5 99.1 99.7 99.4 174-185 2.1 0.20 4.2 978 96.3 0 99.5 99.5 99.2 174-185 2.1 0.20 4.1 1010 97.4 10 99.5 99.9 99.8 FCC off-gas feed (v%):H2:15-20;N2:15-18;O2:0.30-0.50;COx:3.0-4.0;CH4:27-30;C2H4:15-20; C2H6:14-17;C3H6:0.04~1.0;C3H8:0.50-1.0;H2S:100~500ppm;H2O:1000~1500 ppm. Transalkylation feed (wt%): EB:1.01; DEB:89.78; TEB: 9.21. *: Benzene + 4-6 v% transalkylation feed during the 658-1010 h time-on-stream References [1] L. Y. Xu, J. X. Liu, Q. X. Wang, et al. Appl. Catal. A，2004，258，47-53. [2] X. D. Ph D dissertation, 2004, Dalian Institute of Chemical Physics, CAS, 2004