Some industrial processes require the separation of gas or vapor mixtures. Methods for separating the mixtures vary from separation by diffusion to separation by distillation. Many of the methods, such as distillation, are energy intensive. Membranes can reduce the energy required to produce a desired separation. Because of their corrosion resistance and high temperature applications, engineered inorganic membranes can significantly increase the efficiency of many of these processes. The magnitude of the separation factor, available operating conditions, enrichment, yield, and cost of the membranes play a large role in determining whether membranes can be more economical than other methods of separation. These factors have to be evaluated on a case-by-case basis.Martin Marietta Energy Systems' Office of Technology Transfer conducted a preliminary market survey with the assistance of the University of Tennessee and commercial marketing experts in inorganic membranes. The survey assumed that membranes could be made with permeabilities a factor of 3 larger and with cost per unit area a factor of 3 smaller than is currently available. The results indicated that active implementation of such technology could expect to achieve the following results:• $2 billion dollar per year sales market,• $16.6 billion increase in the national GDP,• $2 billion improvement in the balance of trade, and• 6 quads per year decrease in energy use.

Synthesis gas produced in coal gasification processes contains hydrogen, along with carbon monoxide, carbon dioxide, hydrogen sulfide, water, nitrogen, and other gases, depending on the particular gasification process. Development of membrane technology to separate the hydrogen from the raw gas at the high operating temperatures and pressures near exit gas conditions would improve the efficiency of the process. Tubular porous alumina membranes with mean pore radii ranging from about 9-22 Å have been fabricated and characterized. Based on the results of hydrostatic tests, the burst strength of the membranes ranged from 800-1600 psig, with a mean value of about 1300 psig. These membranes were evaluated for separating hydrogen and other gases. Tests of membrane permeabilities were made with helium, nitrogen, and carbon dioxide. Measurements were made at room temperature in the pressure range of 15-589 psi. In general, the relative gas permeabilities correlated qualitatively with a Knudsen flow mechanism; however, other gas transport mechanisms such as surface adsorption also may be involved. Efforts are under way to fabricate membranes having still smaller pores. At smaller pore sizes, higher separation factors are expected from molecular sieving effects.

No abstract

This report was prepared as an account of work sponsored by an agency e', the United States Government, Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or " implied, or assumes any legal liability or responsibility for the accuracy, com,, pleteness, or usefulness of any information, apparatus, product, or process dis. closed, or represents that Its use would not infringe privately owned rights, ,, Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement,recommendation, or favoring by the Uniteo States Government or any agency thereof, The views and opinions of authors expressed herein do not rlecessarily state or reflect those of the United States Governmentor any agency thereof,

The economic viability of coal gasification could depend on the ability to clean and purify the coal gases at elevated temperatures. Inorganic membranes have the potential for being used for that purpose. Efforts have been undertaken at the Oak Ridge K-25 Site to develop membranes that would be useful for separating hydrogen from the coal gas at the high operating temperatures. This paper will give a brief review of some fundamentals of gas separation with membranes. Also, a brief discussion of the theory derived to guide the development process will be given. The theory can be used to indicate the pore size needed to achieve good separation. In addition, some experimental results that have been obtained with some of the membranes that have been fabricated will be discussed.