Pure Gas CO Research Articles

Solubilities of CO2, CH4, C2H6, CO, H2, N2, N2O, and H2S in commercial physical solvents from Monte Carlo simulations

ABSTRACT The removal of acid gas impurities from synthesis gas or natural gas can be achieved using several physical solvents. Examples of solvents applied on a commercial scale include methanol (Rectisol), poly(ethylene glycol) dimethyl ethers (Selexol), n-methyl-2-pyrrolidone (Purisol), and propylene carbonate (Fluor solvent). Continuous Fractional Component Monte Carlo (CFCMC) simulations in the osmotic ensemble were used to compute the Henry coefficients of the pure gases CO, CH, CH, CO, H, N, NO, and HS in the aforementioned solvents. The predicted Henry coefficients are in good agreement with the experimental results. The Monte Carlo method correctly predicts the gas solubility trend in these physical solvents, which obeys the following order: HS > CO > CH > CH > CO > N > H. The gas separation selectivities for the precombustion process and the natural gas sweetening process are calculated from the pure gas Henry coefficients. The CO/NO analogy is verified for the solubility in these solvents.

Conversion of Syngas from Entrained Flow Gasification of Biogenic Residues with Clostridium carboxidivorans and Clostridium autoethanogenum

Synthesis gas fermentation is a microbial process, which uses anaerobic bacteria to convert CO-rich gases to organic acids and alcohols and thus presents a promising technology for the sustainable production of fuels and platform chemicals from renewable sources. Clostridium carboxidivorans and Clostridium autoethanogenum are two acetogenic bacteria, which have shown their high potential for these processes by their high tolerance toward CO and in the production of industrially relevant products such as ethanol, 1-butanol, 1-hexanol, and 2,3-butanediol. A promising approach is the coupling of gasification of biogenic residues with a syngas fermentation process. This study investigated batch processes with C. carboxidivorans and C. autoethanogenum in fully controlled stirred-tank bioreactors and continuous gassing with biogenic syngas produced by an autothermal entrained flow gasifier on a pilot scale >1200 °C. They were then compared to the results of artificial gas mixtures of pure gases. Because the biogenic syngas contained 2459 ppm O2 from the bottling process after gasification of torrefied wood and subsequent syngas cleaning for reducing CH4, NH3, H2S, NOX, and HCN concentrations, the oxygen in the syngas was reduced to 259 ppm O2 with a Pd catalyst before entering the bioreactor. The batch process performance of C. carboxidivorans in a stirred-tank bioreactor with continuous gassing of purified biogenic syngas was identical to an artificial syngas mixture of the pure gases CO, CO2, H2, and N2 within the estimation error. The alcohol production by C. autoethanogenum was even improved with the purified biogenic syngas compared to reference batch processes with the corresponding artificial syngas mixture. Both acetogens have proven their potential for successful fermentation processes with biogenic syngas, but full carbon conversion to ethanol is challenging with the investigated biogenic syngas.

Gas permeability, diffusivity, and free volume of thermally rearranged polymers based on 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)

Abstract HAB-6FDA polyimide was synthesized from 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) by a two-step polycondensation method with chemical imidization. This polyimide was used as the precursor to prepare thermally rearranged (TR) polymers. The rearrangement reaction was performed at temperatures from 350 to 450 °C. Based on mass loss during the TR process, TR conversion levels as high as 76% were observed. CO 2 permeability increased from 12 Barrer in the precursor polyimide (HAB-6FDA) to 410 Barrer in the TR polymer prepared at 450 °C, while pure gas CO 2 /CH 4 selectivity decreased from 42 to 24. Both diffusivity and solubility increased following the rearrangement process, but the change in gas diffusivity was the largest contribution to the increase in permeability. From the polyimide to the sample heated at 450 for 30 min, CO 2 diffusivity increased by approximately a factor of 20 while solubility increased by a factor of 1.7. Similar changes were observed for other gases. Fractional free volume increased from 15% in the polyimide precursor to 20% in the TR polymer rearranged at 450 °C. The HAB-6FDA TR polymers exhibited higher CO 2 permeability than other classes of polymers with similar free volume, suggesting a free volume distribution in these TR polymers that favors high permeability.

Poly(ethylene glycol) and poly(dimethyl siloxane): Combining their advantages into efficient CO 2 gas separation membranes

Polymer blending is a versatile tool to combine the beneficial properties of two or more components in one single material. Here, we present the preparation, thermal- and mass transport properties of a series of blend membranes made from the commercially available PEBAX ® MH 1657 and a poly(ethylene glycol) (PEG) based additive. The additive (PDMS–PEG) consists for 80 wt.% of PEG and the remaining 20 wt.% is poly(dimethyl siloxane) (PDMS), which is highly flexible and permeable. As such, we combine the high selectivity of PEG for CO 2 with the high permeability of PDMS. We extensively study the gas transport properties, and in particular the CO 2/light gas separation performance, using pure and mixed gases. The pure gas CO 2 permeability in the PEBAX ®1657/PDMS–PEG blend membranes increased by a factor 5 to approximately 530 Barrer at 50 wt.% PDMS–PEG loading. CO 2 sorption measurements revealed only a 50% increase in CO 2 solubility and the increase in permeability could be mainly attributed to an increase in diffusivity. Remarkably, the CO 2/H 2 selectivity is enhanced (∼10%) at 50 wt.% loading, while the CO 2/N 2 and CO 2/CH 4 selectivity only slightly decreases. Mixed gas CO 2/H 2 and CO 2/CH 4 permeation measurements up to CO 2 partial pressures of 25 bar reveal that the CO 2 permeability is slightly reduced when gas mixtures are used. The CO 2/H 2 selectivity was found to be independent of the PDMS–PEG loading and feed pressure at a value of approximately 9–10. CO 2/CH 4 mixed gas selectivity decreased slightly with PDMS–PEG loading and pressure, but always remained above 10.

Characterization of silicone rubber membrane materials at low temperature and low pressure conditions

This paper will describe the identification and characterization of synthetic membranes for the separation and purification of CO 2 from the Martian atmosphere for in situ resource utilization (ISRU) applications. An ISRU application is the production of propellant (methane) on the surface of Mars from CO 2. Candidate materials should have high selectivity for carbon dioxide over nitrogen and argon, and a glass transition temperature of −40 °C or less to remain in rubbery state at low temperature for high permeances. Membrane materials we identified include the rubbery polymers poly(dimethyl siloxane) (PDMS) and the copolymer poly(dimethyl, methylphenyl siloxane) (PMPS). Pure and mixed gas permeation experiments with CO 2, N 2 and Ar were performed with these membrane materials at below ambient temperatures. In experiments with commercially obtained PDMS membranes, the pure gas CO 2 permeability increases from 2645 to 2792 Barrers as the temperature decreases from 22 to −20 °C and differential pressure of 1033 mbar (15 psi). The CO 2/N 2 ideal separation factor increases from 10.8 to 19.5 over the same temperature range. However, in pure gas experiments at low pressures (50–500 mbar) for the PDMS membrane, the CO 2/N 2 ideal separation factor decreases as feed pressure decreases which is primarily due to decrease in CO 2 permeability with pressure. Pure gas permeation results with PMPS membranes also showed an increase in CO 2 permeability from 1450 to 1650 Barrers as the temperature decreases from 21 to −10 °C for differential feed pressure of 1378 mbar (20 psi). The CO 2/N 2 ideal separation factor increased from 12 to 27 over the same range of temperature. The ideal separation factors measured at lower feed pressures are closely related to the values at higher feed pressures for the PMPS membrane. This article includes transport data for simulated Martian atmosphere temperature and pressure conditions performed at Lockheed Martin, Denver. An interesting behavior in CO 2 permeance is observed at low feed pressures for both PDMS and PMPS membranes. The trend in CO 2 permeance with temperature changes with variation in feed pressure. A hypothesis is presented for this observation.