For this, three ionic liquids were taken: 1-methylimidazolium bis(trifluoromethylsulfonyl)imide (), 1-ethylimidazolium bis(trifluoromethylsulfonyl)imide (), 1,2-dimethylimidazolium bis(trifluoromethylsulfonyl)imide (), the sorption capacity of ammonia in which practically does not change. Absorbents ScreeningĪ study of the sorption capacity of NH 3 in protic ionic liquids showed that the length of the cation chain has little effect on the solubility of NH 3. Taking into account the mixed gas preparation method, there is no source of moisture in the experimental setup, so the influence of water on separation efficiency was not conducted 2.2. In this way, there was no contact of prepared DES with the room atmosphere. No additional measurements devoted to the moisture content in the prepared DES were performed, as it was prepared under the dry nitrogen environment, further it was sealed in the flask and then was placed in the membrane-assisted gas separation cell connecting the flask to one container and the vacuum pump connected to another container. No additional purification of reagents was used and the standard gravimetric method was used. In the preparation of specific deep eutectic solvent, the following hydrogen-bond acceptor and donor were used: ammonium thiocyanate (≥99.99%) and urea (≥99.5%). All reagents needed for the preparations of DES were purchased from Sigma Aldrich Group (Taufkirchen, Germany). The deep eutectic solvent was used as liquid absorbent in the ammonia capturing process using a membrane-assisted gas absorption unit. The preparation of gas mixtures was performed using single gases of high purity: NH 3 (≥99.9999 vol.%) was purchased from Firm HORST Ltd. That gas mixture is almost equal in composition to the gas stream moving toward the refrigeration block except for the low content of methane and argon (1.03 and 0.27 mol%, respectively). The second mixture contains 75 mol% of hydrogen and 25 mol% of nitrogen. It mainly consists of hydrogen and nitrogen, with a small portion of methane, ammonia, and argon, and the proportion is as follows: H 2/N 2/CH 4/NH 3/Ar = 62.53/23.1/7.49/2.38/4.5 mol%. The first one, which contains ammonia to be captured, is identical to the stream leaving the refrigeration block and is recycled to the reactor. Nevertheless, there is a product purity–recovery rate trade-off, which is a typical issue for separation processes.Īccording to the purpose of the current study-to evaluate the efficiency of a novel membrane-assisted gas separation unit in the ammonia recovery step of the synthesis technological route-the specific gas mixtures were prepared and sealed in the stainless-steel cylinders. For both cases, the membrane-assisted gas absorption cell demonstrated high separation efficiency, and the ammonia concentration in the permeate was never lower than 81 mol% meanwhile, under the hydrogen-nitrogen bore sweep conditions, the ammonia concentration in the permeate reached 97.5 mol% in a single-step process. The separation performance tests were implemented under two sets of conditions, sweeping the bore (permeate) side of a cell with helium and hydrogen-nitrogen mix. In order to minimize the absorbent volume to membrane area ratio, the special separation cell was designed based on a combination of two types of hollow fiber membranes, dense gas separation membrane and porous pervaporation membrane. The present study continues the development and enhancement of a highly efficient unique hybrid technique-membrane-assisted gas absorption in designing the separation unit, which provides the improvement in mass-transfer of a target component during the ammonia capture process from a process loop of the Haber–Bosch technological route.
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