Atomically Precise Membranes for Advanced Gas Separations

Every year, the world uses close to 100 trillion standard cubic feet of natural gas, all of which is pre-treated before entering to the pipeline, making natural gas processing by far the largest market for industrial gas separation processes and equipment. A particular need remains in the separation of CH4 and N2 to reduce the high costs involved in the cryogenic distillation based N2 rejection systems. The separation process represents a great challenge due to the inert nature of these species (that makes any adsorptive or chemical separation difficult) and the similarity of their molecular sizes (that prevents molecular sieveing). TDA Research (TDA), in collaboration with Membrane Technology Research (MTR), proposes to develop an ultra-thin, nanoporous polymer membrane with pores size precisely controlled at 3.7A to facilitate the size selective separation of the N2 and CH4 molecules (with 3.6 and 3.8A kinetic diameters, respectively). Our atomically precise polymer is produced in a manner that every atom is at its specified location relative to the other atoms, with no defects (e.g., missing atoms, extra atoms, or incorrect/impurity atoms). The pre-cursor molecules self-assemble into defect-free molecular layers. The membrane’s uniform pore size will also allow size-based separation of other natural gas impurities, CO2, H2O and H2S, that are smaller than N2, presenting a great potential of carrying out multiple natural gas processing steps in a single module. In Phase I, we will synthesize various nanoporous polymers and assess their efficacy in bulk natural gas treatment applications such as CH4/CO2 and CH4/N2 separations to improve the heating value of the gas. We will evaluate the efficacy of these new membranes in a bench-top test unit to determine the separation efficiency (e.g., flux, selectivity). We will assess the impact of key operating parameters on performance (e.g., temperature, pressure) and evaluate the life of the membrane under representative conditions to ensure the absence of any fouling due to irreversible adsorption of natural gas constituents (e.g., heavy hydrocarbons, moisture). Based on the results, we will carry out a detailed engineering design and analysis work to finalize the design of the device (complete with 3-dimensional drawings) to estimate the cost.Natural gas processing is a multi-step process that involves the removal of impurities such as N2, H2O and acid gases (CO2, H2S) and compression of the gas to pipeline standards. The membrane proposed for this application enables the separation of all these impurities from methane and other hydrocarbons in a single-step. Due to the well-defined nanostructures, and myriad chemical functionalities, as well as the ability to rationally molecularly-engineer these properties, our polymer membranes can also be applied in other industrial separation processes and petrochemical applications.