Hydrogen-selective membrane reactor process

In the case of C02-selective membranes in precombustion processes, the fuel heating value remains at the high-pressure retentate side (H2 and unconverted fuel) in the WGS separation process. The power-cycle efficiency for natural-gas-fuelled GTCC including C02-selective membranes in the WGS reactor appears less pressure dependent compared to hydrogen-selective membranes, due to the lower amount of C02 produced in the MSR + WGS reactions [24]. A relative simple simulation for precombustion capture made (based on C02/H2 selectivity of 50) [24], suggests that... 

In the present concept of styrene dehydrogenation implementation of inorganic membranes is not feasible. Application of Knudsen diffusion membranes with a low permselectivity to hydrogen leads to a considerable permeation of ethylbenzene and thus, to lower yields. Microporous and palladium membranes give better results, but worse than a conventional case, because the conversion is limited by reaction kinetics. The ratio of permeation rate to reaction rate is very important in selecting membranes in a membrane reactor process in which equilibrium shift is foreseen. 

Natural gas steam reforming process is an ideal candidate for hydrogen selective membrane integration tanks to its high reaction endothermicity and the fast kinetics leading to equilibrium condition inside traditional reactors. 

Many efforts devoted to the development of membrane competitive applications by the most prestigious research centers worldwide attest the strategic importance and the potentiality of membrane reactors for the industry. The scientific production dealing with selective membrane reactors is growing exponentially as reported in Chap. 2, 750 papers on membrane reactors have been published in 2009, of which 220 on Pd-based membranes. The main processes in which R D departments are focusing the attention are those devoted to hydrogen production, for which two configurations are imder study ... 

In configuration 1, the reformer and membrane module (RMM) where hydrogen selective membrane is assembled in separation modules applied downstream to reaction units so that the process scheme is composed by a series of reaction-separation units (staged membrane reactor architecture)... 

Numerous types of materials, for instance, polymers, glasses, ceramics, and metals can be applied for membrane synthesis [180-183], The major step in the preparation of a membrane is to adapt the material through an appropriate methodology to get a membrane structure with a morphology suitable for a particular type of separation process [183], For example, in the special case of membrane reactors (see Section 10.6.2), one of the most important separations is the selective subtraction of hydrogen from the reaction zone therefore, such membranes must be hydrogen selective [184-186],... 

It may be necessary to improve membrane selectivities, so that further purification of the produced hydrogen before re-use in the desulphurisation units can be limited as far as possible. Moreover the membrane reactor can be optimised for various variables, such as H2S conversion, hydrogen recovery, membrane area and temperature. In a techno-economic evaluation combined with advanced process design the impact of different operating parameters on the investment and operating costs should be studied. 

The major inpact of this process is reflected in the reaction selectivity, which is a very inportant indicator of reactor performance. The selectivity increases as the recovery of the hydrogen produced increases. This result is due to the fact that reaction 5 is suppressed as hydrogen is removed. Figure 11 contrasts the packed bed and membrane reactors in terms of selectivity at three different temperatures. As the temperature increases the... 

First of all, hydrocarbons constitute a major force in the very important petroleum and petrochemical industry. Generation or consumption of hydrogen, a very valuable commodity chemical, is one of the key steps in many chemical processes. Even a modest success in the improvement of reaction conversion, yield or selectivity by the use of a membrane reactor can represent a substantial economic benefit due to the volume of streams involved. 

It has been shovm that membranes can enhance the conversion of a water-gas shift membrane reactor and concurrently separate hydrogen from carbon dioxide. The efficiency of CO2 control using the membrane reactor with a H2/CO2 selectivity of 15 is significantly higher compared to a conventioncd technique (i.e. wet washing with a sorbent). It is not necessary to exceed a selectivity of approximately 40 for H2/CO2 for the process under consideration, because further increase in reactor performance seems marginal. Enlargement of the permeation is an important aspect on the other hand, so that the total surface area necessary for the full-scale application can be reduced. 

In recent years, new concepts to produce hydrogen by methane SR have been proposed to improve the performance in terms of capital costs reducing with respect to the conventional process. In particular, different forms of in situ hydrogen separation, coupled to reaction system, have been studied to improve reactant conversion and/or product selectivity by shifting of thermodynamic positions of reversible reactions towards a more favourable equilibrium of the overall reaction under conventional conditions, even at lower temperatures. Several membrane reactors have been investigated for methane SR in particular based on thin palladium membranes [14]. More recently, the sorption-enhanced steam methane reforming (Se-SMR) has been proposed as innovative method able to separate CO2 in situ by addition of selective sorbents and simultaneously enhance the reforming reaction [15]. 

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