DDR-type zeolite membrane: A novel CO2 separation technology for enhanced oil recovery

Abstract

JGC Corporation (JGC) and NGK Insulators, Ltd. (NGK) have been developing the world’s largest DDR-type zeolite membrane to meet the practical needs of CO2/hydrocarbon separation in the natural gas and CO2 Enhanced Oil Recovery (CO2-EOR) industries.DDR-type zeolite has desirable nano-size pores for CO2/hydrocarbon separation. NGK has developed a thin, defect-free DDR-type zeolite membrane with a monolithic structure. This membrane is prepared onto the inner surface of a cylindrical monolithic alumina substrate having 30 channels with a diameter and length of 30 mm and 160 mm, respectively. CO2 permselectivity over CH4 of the monolithic membrane was investigated using the binary gas mixture of 61–67 mol% CO2 and 33–39 mol% CH4 at 44–46 °C with up to 8.0 MPa G as the feed pressure. The CO2 permeability reached 1973 Barrer (6.6 × 10−13 mol m m−2 s−1 Pa−1) while the separation factor of CO2/CH4 exceeded 140 at the transmembrane pressure difference of 2.5 MPa. This CO2 permeability decreased to 1154 Barrer (3.9 × 10−13 mol m m−2 s−1 Pa−1) at the transmembrane pressure difference of 7.0 MPa; however, the separation factor of CO2/CH4 was still as high as 90. In order to understand the stability of the monolithic membrane, the change in the permeability of CO2 and CH4 with time was measured at 58–60 °C with transmembrane pressure difference of 7.4–7.7 MPa using the binary gas mixture of 65–71 mol% CO2 and 29–35 mol% CH4 for 140 h. During the gas permeation test, the CO2 permeability was almost constant while CH4 permeability slightly decreased. As a result, the separation factor of CO2/CH4 was maintained at the initial value.Based on the experimental results, we evaluated the potential applicability of the DDR-type zeolite membrane compared to the conventional polymer membrane for a CO2 recovery process in a CO2-EOR project where CO2 is often separated from the associated gas for re-use. We assumed that the associated gas contains 70 mol% CO2 and 30 mol% CH4 at a pressure of 4.0 MPa G while the specification of CO2 purity in the permeate gas was 95 mol% at a pressure of 0.3 MPa G. When this associated gas is treated using a single-stage membrane process, only 49% of CO2 was recovered by a membrane having a CO2/CH4 separation factor of 12.5 like a typical polymer membrane. On the other hand, membranes having CO2/CH4 separation factors of 80–100 could recover 98–99% of CO2 while more than 96 mol% purity of CH4 was obtained at the retentate side. This simulation study indicated that the highly selective membrane like the DDR-type zeolite membrane can recover not only high purity CO2 for CO2-EOR projects, but also make available CH4 for use or sale. This high purity CH4 brings additional benefit to the CO2-EOR operators.