Benzene hydrogenation reactors

Catalytic Activity. An aliquot (20-50 mg) of the sample used for dispersion measurement was reactivated for one hour at 300° C under hydrogen. The rate of benzene hydrogenation was measured in a conventional flow reactor at low conversion (<2%) to avoid heat and mass transfer limitations. The pressure of benzene was 56 torr and that of hydrogen was 704 torr under these conditions the reaction is zero order for benzene. 

Theoretical and experimental results on deactivation have been summarized in two reviews by Butt (.1,2). Previous work of particular interest to the present study has been done by Blaum (3) who used a one-dimensional two-phase model to explore the dynamic behavior of a deactivating catalyst bed. Butt and cowotkers (b,5,6)have performed deactivation studies in a short tubular reactor for benzene hydrogenation for both adiabatic and nonadiabatic arrangements. They experimentally observed both the standing (6) and travelling (4) deactivation wave. Hlavacek... 

Model Reaction. The benzene hydrogenation on nickel-kiesel-guhr has been selected as a model reaction. This reaction is well understood and can serve as a typical representative of hydrogenation reactions. Butt (4 5) and Pexider et al.(11) have studied this reaction in laboratory and pilot plant reactors respectively. Pexiderfs data have been obtained from a nonadiaba-tically operated reactor. The reaction rate expression has ... 

The crude MNB is washed to remove residual acid and the impurities formed during the nitration reaction. The product is then distilled and residual benzene is recovered and recycled. Purified MNB is fed, together with hydrogen, into a liquid phase plug-flow hydrogenation reactor that contains a DuPont proprietary catalyst. The supported noble metal catalyst has a high selectivity and the MNB conversion per pass is 100%. 

Theoretical equations developed in this paper are intended to model benzene hydrogenation in an industrial reactor and account for the loss of catalyst activity due to sulfur poisoning. The approach used to develop the equations results in an analytical solution for the partial differential equations describing hydrogenation, sulfur poisoning, and a catalyst active site balance. The solution, which accounts for thiophene... 

Plow system and reactor The experimental flow system employs a parallel feed arrangement, with one stream containing a pure benzene/hydrogen mixture and another containing thiophene in addition to benzene/hydrogen feed. A four-way valve was used to allow one feed to go through the reactor while another to be diverted to a bypass line. 

The benzene hydrogenation was carried out at atmospheric pressure in a flow system provided with a fixed bed reactor. The activity tests were made under the following conditions T = 773 K, = 0.05 atm, PH2 - 0.95 atm, benzene flow rate = 2 cra h K Conversion was always less than lOX, The feed was doped with thiophene in concentrations between 0 and 50 ppm of S. 

Benzene hydrogenation, used as a model reaction to characterize the metallic active phase before and after poisoning by sulfur, was performed in a conventional fixed-bed reactor. Before reaction the catalyst was treated in a flow of H2 for two hours at 723 K. Benzene was added by saturating hydrogen gas with liquid benzene at 280 K. Benzene hydrogenation was performed at 453 K. 

Benzene hydrogenation was carried out in the flow-type quartz reactor under atmospheric pressure at 150 and 180°C. The reactor was heated by thermostatically controlled vertical furnace. A mixture of benzene (7.4-14.8 hr ) and hydrogen (H2 C6H6 = 6 1) was passed through a layer of catalysts, entered a condenser and analysed chromatographically. Reaction order under these conditions was zero. 

Fig. 11.14. Process flow sheet of cyclohexane/benzene heat pump using hydrogen permeable membranes Rdit and R/rdehydrogenation and hydrogenation reactors C, compressors T, turbine HE, heat exchangers CHE, counter-current heat exchangers P, liquid pump M, hydrogen membranes. Reproduced from Cacciola et al. [133] with permission.

Catalytic measurements. The high pressure reactor for benzene hydrogenation has been previously described (8). The reaction was conducted at 598 K under 4 0 bars total pressure. The benzene feed contained 1.5 % by weight of dimethyldisulfide (DMDS) which was fully decomposed on the catalyst, so that the H2S/H2 and benzene/H2 molar ratios during reaction amounted to 10-4 and 4xl0-3 respectively. The catalyst mass was 0.4 g and the liquid feed rate 1.6 jtl mn . Catalyst sulfidation was performed in the reactor itself but at atmospheric pressure, using a H2-H2S feed. Details of the complete procedure are following ... 

Reactor operation A stream of benzene/hydrogen was introduced to... 

The benzene hydrogenation was carried out at atmospheric pressure in a flow system provided with a fixed bed reactor. The activity tests were made under the... 

Benzene hydrogenation activity evaluation of the catalysts was carried out by a pulse and continuous testing method and the results are indicated in Table-2 and Figure 1. Activity is represented as percentage of benzene converted to cyclohexane. Activity results as per evaluation in pulsed microcatalytic reactor indicated a similar trend as obtained from continuous testing of samples. 

The kinetics of benzene hydrogenation to cyclohexane over a Ni/Si02 catalyst were studied using a small fixed-bed reactor [7]. The bed had 0.87 g of 0.22-mm catalyst particles diluted with 19.2 g of glass beads. 

Metaxas, K., and Papayannakos, N. (2008), Gas-liquid mass transfer in a bench-scale trickle bed reactor used for benzene hydrogenation, Chemical Engineering Technology, 31(10) 1410-1417. 

An example of a liquid-phase process with a fixed-bed reactor (Pt-catalyst) for benzene hydrogenation is the Hydra process developed by UOP, shown by the flow diagram in Figure 5.31. 

The benzene hydrogenation on the Ni catalysts based on the porous glass beads was carried out in a continuous-flow reactor at atmospheric pressure. A gaseous mixture of benzene and hydrogen flowed through the catalyst bed (0.1 or 0.2 g catalyst) at temperatures between 80 and 140°C. The partial pressure of benzene was 0.141 atm. Only cyclohexane was detected as a product under the present conditions. 

A mixture of chlorobenzenes, unreacted benzene, hydrogen chloride and iron catalyst leaves the reactor, and is separated by distillation. 

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