MEMBRANES FOR CO2 CONTENT ADJUSTMENT IN NATURAL GAS TO SYNGAS PROCESSES
Publication Date: 2009-May-29
The IP.com Prior Art Database
in natural gas to syngas processes
This invention relates to processes for syngas generation and utilization to produce hydrocarbon liquid from natural gas with significant CO2 content. A CO2-selective membrane system is utilized to adjust and control the CO2 content in feed gas to a methane conversion reactor (for SMR, POX and ATR etc) by treating at least a portion of the feed gas so that a syngas with a desired H2/CO ratio is produced, or any constraints related to CO2 down stream can be met. The membrane’s separation performance is controlled by adjusting the permeate side pressure according to feedback signals from the down stream process units regarding CO2 content desired and/or H2/CO ratio needed for the syngas product as well as composition changed in reservoir gas. This process is especially applicable to liquid fuel production project based on remote natural gas reservoirs with high level of CO2 content.
Application of syngas as a chemical feedstock is closely related to its H2/CO ratio. For instance, syngas of H2/CO=2 is needed to produce kerosene and diesel using FT reactions and for the production of methanol. For oxo alcohols and dimethyl ether (DME) production, syngas H2/CO ratio needs to be ~1.
Steam methane reforming (SMR), partial oxidation (POX) and auto thermal reforming (ATR) processes can all be used to produce syngas form natural gas. When a given H2/CO ratio is required for down stream syngas conversion processes, adjustment of CO2 content in the feed gas can be an effective way of achieving the desired H2/CO ratio. For instance, CO2 can be added to the SMR reactors to reduce the product syngas H2/CO ratio through CO2 reforming (CO2+ CH4 = 2CO + 2 H2). However, at a given H2O/CH4 ratio in the feed gas, the CO2 content in the feed gas is limited by carbon formation concern. For example, to obtain a H2/CO ratio of 2.0 using regular Ni catalysts, a CO2/CH4 ratio of about 0.7 is required at a H2O/CH4 ratio of about 2.0.
When POX or ATR is used, a significantly lower H2/CO ratio is resulted for the syngas product compared to SMR. CO2 presence in its natural gas feed could be too high for the desired H2/CO in the product.
Many large natural gas reservoirs produce NG with high CO2 content.
Southeast Asiagas fields have estimated fields having reserves of >400*108 m3. Many of these fields, however, are rich in CO2. For instance, the natural gas field in
Indonesiahas huge reserves of more than 200 TCF, but has high CO2 content (70%).
Building GTL plants at these locations to convert NG to liquid seems to be the best way to bring these natural resources to commercially viable liquid fuel products.
Japex (Japan Petroleum Exploration Co., Ltd.) has claimed the development a new catalyst that can produce syngas of H2/CO=2 in a s...