Economics membrane reactors

Criscuoli, A., A. Basile, E. Drioli, and O. Loiacono, An economic feasibility study for water gas shift membrane reactor, J. Membr. Sci., 181, 21-27, 2001. 

Sjardin, M., Damen, K.J. and Faaij, A.P.C. (2006) Techno-economic prospects of small-scale membrane reactors in a future hydrogen-fuelled transportation sector. Energy, 31 (14), 2187-2219. 

J. R.H., Koukou, M.K. and Papayannakos, N. (1997) Water gas shift membrane reactor for C02 control in IGCC systems Techno-economic feasibility study. Energy Conversion and Management, 38 (9999), S159-S164. 

In this context photocatalytic processes in membrane reactors represent a technology of great scientific interest because they allow chemical reactions and separation process to be obtained in one step, minimizing environmental and economic impacts. 

In chapter 2, some basic ideas about steam reforming in conventional and membrane reactors are worked out. In this chapter the operation of conventional steam-reformers is compared with possible membrane steam-reformers. In this chapter also a techno-economic evaluation of a membrane reactor compared with the conventional process is provided. The boundary conditions imposed by process technology and the techno-economic evaluation result in the formulation of requirements for the development of the membranes, i.e. selectivity, flux, tube length, operating pressure, etc. 

R. Meijer, D. van der Vlist, F. Janssen, A. Anundskas, T. Pettersen and T. Strom, Membrane Reactor for Cost Effective Environmental-Friendly Production of Hydrogen - Techno-economic Evaluation , Internal Report, (1997). 

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. 

When looking for an economically feasible enzymatic system, retention and reuse of the biocatalyst should be taken into account as potential alternatives [98, 99]. Enzymatic membrane reactors (EMR) result from the coupling of a membrane separation process with an enzymatic reactor. They can be considered as reactors where separation of the enzyme from the reactants and products is performed by means of a semipermeable membrane that acts as a selective barrier [98]. A difference in chemical potential, pressure, or electric field is usually responsible from the movement of solutes across the membrane, by diffusion, convection, or electrophoretic migration. The selective membrane should ensure the complete retention of the enzyme in order to maintain the full activity inside the system. Furthermore, the technique may include the integration of a purification step in the process, as products can be easily separated from the reaction mixture by means of the selective membrane. 

In addition to the above potential process economic benefits, inorganic membrane reactors can also result in a safer operating environment. Some combustion reactions involve rapid release of energy when the reactants are mixed in a batch or bulk mode. Carefully controlled addition of a critical reactant (e.g., oxygen) to the reaction system (e.g., fuel) from opposite sides of the membrane reactor can minimize the potentials for... 

When it is advantageous or necessary for a reactant stream to be concentrated or purified before reaction is initiated from either technical or economical standpoints, a membrane can be a strong candidate for the pretreatment of the reactant However, this need can often be taken care of by directly introducing the reactant to be purified to the other side of a membrane reactor, as will be discussed later. 

Edlund, DJ., W.A. Pledger. B.M. Johnson and D.T. Fricscn, 1992. Toward economical and energy-efficient production of hydrogen from coal using metal-membrane reactors (paper 11. present at 5th NAMS Annual Meeting. Lexington. Kentucky. USA. 

In addition to the end seal issue just described, there is another critical material engineering issue facing membrane reactors. It concerns the connection between the membrane element and module housing or piping. In fact, this is considered to be one of the most critical issues to be addressed to make inorganic membrane reactors technically feasible and economically viable. 

In a simple membrane reactor, basically the membrane divides the reactor into two compartments the feed and the permeate sides. The geometries of the membrane and the reaction vessel can vary. The feed may be introduced at the entrance to the reactor or at intermediate locations and the exiting retentate stream, for process economics, may be recycled back to the reactor. Furthermore, the flow directions of the feed and the sweep (including permeate) streams can be co-current or counter-current or some combinations. It is obvious that there are numerous possible process and equipment configurations even for a geometrically simple membrane reactor. 

As in the case of gas separation discussed in Chapter 7, which reaction component(s) in a membrane reactor permeates through the membrane determines if any gas recompression is required. If the permeate(s) is one of the desirable products and needs to be further processed downstream at a pressure comparable to that before the membrane separation, recompression of the permeate will be required. On the other hand, if the retentate(s) continues to be processed, essentially no recompression will be necessary. Recompressing a gas can be rather expensive and its associated costs can be pivotal in deciding whether a process is economical. 

As indicated in Chapter 7, compression and recompression costs can be very significant in determining if the underlying membrane process, including membrane reactors, is economically comj>etitivc. The compression cost can be considered to be proportional to the compression ratio which is the ratio of the outlet to inlet pressures. 

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. 

Based on the above considerations, the types of reactions that are amenable to inorganic membrane reactors in the first wave of industrial implementation will probably be as follows (1) The reactions are heterogeneous catalytic reactions, particularly dehydrogenation processes (2) The reaction temperature exceeds approximately 200°C (3) When the reactions call for high-purity reactant(s) or produces) and the volume demand is relatively small, dense membrane reactors (e.g., Pd-based) can be used. On the other hand, if high productivity is critical for the process involved, porous membrane reactors are necessary to make the process economically viable. 

Thus, it is not easy to obtain reliable cost data for separation processes, let alone catalytic reaction processes, using inorganic membranes. Some general guidelines, however, have been provided for separation processes in isolated cases and will be summarized in this chapter. Understandably no definitive economics related to inorganic membrane reactors has been presented in the literature due to the evolving nature of the technology. 

Coupling two operations like membrane separation and a catalytic reaction or adsorption in a given process of synthesis, purification, or decontamination of effluents is intrinsically interesting from a general technical-economical point of view. Ceramic membranes are ideal solid-fluid contactors, which can be efficiently used to couple separation and heterogeneous catalysis for membrane reactor applications. ... 

---