2a. Identification and Significance of the Problem, and Technical Approach

There are increased concerns by the natural gas industry over economically upgrading of natural gas containing high levels of contaminants, mostly CO2. This affects 17% of US reserves. The goal is to lower the CO2 content below 2%, a typical pipeline specification. CO2 removal from methane is also of concern where 1) CO2 flooding of oil wells is used for secondary recovery and 2) the upgrade of landfill gas from solid waste-disposal sites.

Presently, carbon dioxide is commercially separated from methane with a non-porous polymer membrane system using bundles of hollow cellulose acetate fibers. These bundles are placed in modules known as permeators. The permeator vessel is provided with an inlet and outlet for the mixed gases (the feed) and the outlets for the product or permeate stream. Gases permeate through the membrane by a solution-diffusion mechanism where the rate of CO2 permeation is much faster than methane Improvements in the economics and performance have been sought and much effort has been focussed on polyimide and polyamide polymeric membranes but commercialization has not occurred with these newer systems.

It is surprising that carbon has rarely been tried as a membrane material since large differences in the rate of adsorption and permeation between CO2 and methane occur with active carbon. Some of the difficulty in making hollow fibers of active carbon with sufficient strength to withstand the pressures of natural gas at the well-head. It is also difficult to fabricate a successful membrane from material in powder form. However some laboratory studies with membranes of carbon molecular sieves have indicated significantly higher permeabilities and selectivities of many of the common gases including CO2 compared with polymer membranes. In the case of carbon molecular sieve membranes, the mechanism for transport is one of adsorption and pore diffusion.

Mega-Carbon Company believes it has the capability to solve the present technical problem of making carbon membranes with the necessary properties for removing CO2 from natural gas and in an economic way. Mega-Carbon has much expertise in the making and molding active carbon systems with different carbons and with different porosities. These are the properties that are going to determine the selectivity and the permeability of any resulting membrane. In terms of different carbons Mega-Carbon approach will include identifying carbons with varied structure, particularly with combination of macropore (diameter > 1000A> feeder pores in combination with smaller mesopores (20A<diameter< 1000A) and modification of existing activated carbons via additional activation. The carbons will then be formulated in the same manner as Mega-Carbon has developed adsorbent carbon blocks to control gasoline vapor emissions with a major automotive company.

The basis of this technology are two patents that will be granted to Mega-Carbon in a few months on a novel bonding technology. This bonding process called Mega-Cast has been developed to bond carbon powders and adsorbent blocks. What makes Mega-Cast bonding unique is that very little of the adsorption capacity is lost due to pore plugging. The illustration of the bonded carbon in Figure is one way to view the process with the carbon particles bonded at various points by a polymer binder.

Carbon particles are shown darker and are bonded by the polymer droplets shown in the lighter shade. Every carbon is different and adjustments are always necessary in the formulation. Blocks can be cast routinely but extrusion is a special challenge and requires additives to impart desired rheological properties and stabilization of the slip.

To prepare a carbon adsorbent block, a carbon slip is first prepared with a polymer binder. There are two types of binders, one suitable for temperatures in the range of 200 C and the other a higher temperature version which retains its strength at temperatures as high as 350 C. The carbon slip can be prepared from either powder or granules and is then extruded, slip-cast, or compression molded to a variety of shapes( blocks, cubes, etc. ). The binder cures at modest temperatures, eliminating the need for high temperature calcination and most of the adsorption capacity is preserved. The use of compression during the forming process translates into higher bulk densities and will frequently lead to higher adsorption capacity per unit volume. Dynamic performance of the carbon blocks depends directly on how the block is formed, flow channels, and type/size of starting material. Most importantly, there are cases where the bonded carbon is noticeably better than a granular bed. Pressure drop of the carbon block depends on the form of the starting carbon and the incorporation of flow channels.

Mega-Carbon Company believes it has the capability to solve the present technical problem by successful application of this new approach for the following reasons: