Hydrogen recycle

C, 0.356—1.069 m H2/L (2000—6000 fU/bbl) of Hquid feed, and a space velocity (wt feed per wt catalyst) of 1—5 h. Operation of reformers at low pressure, high temperature, and low hydrogen recycle rates favors the kinetics and the thermodynamics for aromatics production and reduces operating costs. However, all three of these factors, which tend to increase coking, increase the deactivation rate of the catalyst therefore, operating conditions are a compromise. More detailed treatment of the catalysis and chemistry of catalytic reforming is available (33—35). Typical reformate compositions are shown in Table 6. 

HARP [Hybrid argon recovery process] A process for extracting argon from the hydrogen recycle stream in ammonia synthesis. Both PSA and a cryogenic process are used. Krishnamurthy, R., Lemer, S. L., and MacLean, D. M., Gas Sep. Purif, 1987,1, 16. 

Evans, H.J., F.J. Hanus, R.A. Haugland, M.A. Cantrell, L.S. Xu, S.A. Russell, G.R. Lambert and A.R. Harker Hydrogen recycling in nodules affects nitrogen fixation and growth of soybeans. Proceedings of the World Soybean Conference III, R. Shibles, Ed., Westview Press, Boulder, CO, pp. 935-942 (1985). 

Bascones, E., Imperial, J., Ruiz-Argueso, T. and Palacios, J. M. (2000) Generation of new hydrogen-recycling rhizobiaceae strains by introduction of a novel hup minitransposon [In Process Citation]. Appl. Environ. Microbiol., 66, 4292-9. 

Evans, H. J., Russell, S. A., Hanus, F. j. and Ruiz-Argiieso, T. (1988) The importance of hydrogen recycling in nitrogen fixation by legumes. In R. J. Summerfield (ed.). World Crops Cool Season Food Legumes. Boston Kluwer Academic Publishei pp. 777-91. 

Hydrogen recycle line for a reformer unit, to cool the catalyst... 

As discussed in a later section, H2S is an inhibitor for the catalytic site responsible for direct sulfur extraction. Thus, if the H2S partial pressure could be lowered in the reactor, the desulfurization rate could be increased. The simplest means to achieve this goal is through increased hydrogen recycle rates or increasing the hydrogen/feed ratio. Such changes are expensive and can in some instances lower the overall thoughput of the feed. 

The major process variables are (1) reactor temperature (2) hydrogen pressure (3) liquid hourly space velocity and (4) hydrogen recycle rate. Other variables such as reactor type and catalyst type have been discussed in an earlier part of this chapter, while the influence of the feedstock type will be discussed in a later chapter (Chapter 6). 

In the inner loop, the composition of the hydrogen recycle gas is determined by successive substitution. If a target reformate octane is specified, an outer loop adjusts the inlet temperatures to all the reactors by equal increments until the target is reached. 

The impurities can be grouped into two categories lights (water, cyclohexene, cyclohexadiene) and heavies (phenol, dicyclohexyl-ether, cyclohexenyl- cyclohexanone). To limit their amount, the conversion is kept around 80% with a selectivity of about 98%. The hot reactor effluent is cooled in countercurrent with the feed in FEHE, and finally for phase separation in the heat exchanger (E-2) at 33 °C. The simple flash (S-2) can ensure a sharp split between hydrogen, recycled to hydrogenation reactor, and a liquid phase sent to separation. 

Figu re 5.24 CS2 Production rate by phenol fresh feed and fixed hydrogen recycle. At t = 2h, fresh phenol increases from 149.5 to 165kmol/h hydrogen on makeup. 

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