Iron oxides are useful adsorbents for the alternating removal of H2S and O2 from natural gas and biogas. In this context, the present paper aims to elucidate the mechanisms behind the consecutive adsorption of both gases. Three different types of iron oxides/hydroxides were investigated using in-situ infrared and Raman spectroscopy as well as ex-situ X-ray diffraction.The spectroscopic studies confirm that H2S is adsorbed on all kinds of surface sites, particularly at Brønsted and Lewis acid sites. However, on the Brønsted acid sites, H2S undergoes dissociation, leading to the formation of SH−, S2− and H2O. This mechanism substantiates the high H2S uptake capacity of the OH-containing adsorbents. Prolonged H2S adsorption provokes an increasing consumption of the adsorbent, yielding amorphous FeS and elemental sulfur, with hydrogen sulfate and sulfate species also forming as by-products.Furthermore, the subsequent O2 adsorption on the sulfidized samples causes some re-formation of the initial adsorbent with the simultaneous production of elemental sulfur and sulfate entities. As a result of the mechanistic understanding gained in this study, it is concluded that the complete regeneration of the iron substrates is almost impossible due to their substantial degradation, associated with partial conversion into sulfates and the deposition of sulfur.

This study deals with the development of iron oxide/hydroxide adsorbents for the alternating removal of H2S and O2 from natural gas and biogas. The considered procedure initially implies the chemisorption of H2S. In the second step, O2 is removed by reaction with the H2S-treated substrate accompanied by regeneration of the adsorbent. 35 different iron-based samples were physical-chemically characterized and tested towards H2S/O2 break through behavior and adsorption capacity to evaluate structure-performance correlations. It was derived that high BET surface area, high proportion of meso and micro pores, small average pore diameter, low crystallinity and high number of Bronsted acid sites are crucial properties of the adsorbents. As a consequence, Fe(OH)3 and α-FeOOH revealed highest efficiency for the successive adsorption of H2S and O2, while α-Fe2O3 provided rather low performance.Mechanistic investigations were carried out with α -FeOOH and α -Fe2O3 indicating rapid dissociation of H2S on α -FeOOH, while slow molecular adsorption prevailed on α -Fe2O3. With proceeding H2S exposure, the adsorbents were partially transformed into sulfide and sulfate species with some formation of elemental sulfur. In subsequent reaction with O2, the H2S-exposed samples were re-oxidized under partial restructuring, whereas elemental sulfur and sulfate entities were additionally produced.Finally, the concept of the alternating adsorption of H2S and O2 on best α -FeOOH substrate was technically evaluated in a biogas pilot plant. The investigations showed efficient conversion of H2S for 40–100 h, while subsequent O2 conversion was achieved for ca. 5.5 h.

Biogas is a renewable resource with prospects in production of commodity chemicals or for power generation. The latter implies co-usage of biogas and natural gas in gas distribution nets but puts a restriction on the higher heating value (HHV) of all gases pumped into the net. In this contribution, we analyzed and experimentally validated the potential of the oxidative coupling of methane (OCM) as a method for upgrading biogas HHV. The effects of the reaction conditions, i.e., reaction temperature, feed CH4/O2 ratio, and co-feeding of CO2 or H2O, on HHV of the resulting gas mixtures were studied. The highest HHV of 11.48 kW·h·m–3 after water condensation was obtained when performing the OCM reaction over Mn–Na–WOx/SiO2 catalyst at 800 °C using a feed with CH4/O2 ratio of 12 and 30 vol% water. This performance was possible thanks to 86% selectivity to C2 hydrocarbons (C2H4 and C2H6) at 15.2% methane conversion. It was also possible to increase the selectivity to 100% when carbon oxides formed in the OCM re...

AbstractDie Einspeisung von Biogas in das Erdgasnetz kann einen entscheidenden Anteil zum Gelingen der Energiewende beitragen, da Biogas hierdurch für verschiedene Sektoren (Mobilität, Industrie und Gaskraftwerke) nutzbar wird. Die in der Regel vor der Einspeisung durchgeführte Brennwertanhebung mit Flüssiggas verursacht jedoch hohe Kosten und Abhängigkeiten von fossilen Energieträgern. Um eine unabhängige Brennwertanhebung zu ermöglichen wird derzeit das Verfahren der oxidativen Kopplung von Methan zur Erzeugung höherer Kohlenwasserstoffe aus Biogas untersucht.

Membrane separation and gas condensation are combined to reveal an advanced method for the separation of alkanes. First, the applicability of MFI membranes for alkane separation is principally demonstrated by means of realistic adsorption isotherms computed by configurational biased Monte Carlo (CBM) simulations. Next, dew point curves of mixtures comprising different ratios of n-butane (C4) and methane (C1) were calculated according to the thermodynamic methods of Soave–Redlich–Kwong (SRK) and Peng Robinson (PR). From that, isothermal phase boundaries in dependence on the composition of the gas mixture were derived and process parameters under which condensation of the alkane mixture occurs were predetermined. Experimentally, the separation performance of MFI membranes was recorded during separation of n-butane from methane. It was found that liquefied n-butane in the feed and a further liquefaction in the permeate enhance the separation selectivity of MFI zeolite membranes under sweeping conditions tremendously. At the dew point of the feed mixture a sudden rise of the separation factor α is observed. At a temperature of 258K a mixture with χC4=0.5 can be separated with a separation factor αC4/C1=174 due to liquefaction. Experiments without sweeping show a similar behaviour. When forming a two phase mixture in the feed an increase in overall condensation efficiency ηC4 is detected in the permeate. At 258K and pfeed=2bar and ppermeate=1bar 29.6% liquefied n-butane was isolated in the permeate from a mixture comprising χC4=0.5.

CLEAN was a scientific programme in support of a pilot Enhanced Gas Recovery (EGR) project and it was planned to inject nearly 100,000 t of carbon dioxide (CO2) into the Altmark natural gas field. Due to delays in the permitting process, injection did not occur within the time frame of the project. Therefore a test case was studied of the theoretical injection of CO2.Modelling CO2 injection in the Altensalzwedel segment of the Altmark depleted gas field shows that effective injection can be carried out at a tubing head pressure as low as 3.5 MPa and at tubing head temperature of 10 °C.The history matching of the simulation model and the injection prediction were successfully conducted with a volume ratio of injected CO2 to the gas in place of approximately 0.06 which did not show any enhancement in the gas recovery (no EGR effect). Within the pilot project period of 2 years there would be no CO2 arrival at the production well located at about 1,600 m from the injector. Penetration of the CO2 into the reservoir was maximum approximately 800 m and minimum around 250 m depending on the permeability of the formation layer. The gas mixing zone reaches the observation well which is located at about 660 m from the injector already before 1 year of injection.Under the simulated conditions direct monitoring of the CO2 front with active seismic measurements will not be feasible as the reservoir layers are too thin and the effects of CO2 gas replacing reservoir gas are too small. Seismic monitoring has to concentrate on the detection of possible leakages in shallower aquifers where larger velocity and density changes would occur.

This paper presents an innovative well abandonment concept developed for the long-term containment of CO2 in depleted Rotliegend gas reservoirs. The new concept aims at amending the conventional standard well abandonment procedure, taking advantage of the natural creeping ability of the thick, homogeneous Zechstein rock salt formation located around 3,000 m in depth (Altmark area) and consists of four main sealing units: (1) a standard sealing element with cement from the reservoir to the impermeable caprock, (2) a salt plug created in the formerly reamed section of casing within the plastic Zechstein (Upper Permian) rock salt formation, (3) two bridge plugs at the bottom and top of the salt plug and (4) a standard sealing element with cement from the top bridge plug until the ground surface. This site-specific study mainly lays emphasis on the development and field testing of the naturally created salt plug, as a key component of the long-term wellbore sealing concept. Comprehensive numerical simulations conducted prior to and during the field test in 2010 and 2011 successfully predicted the evolution of convergence using downhole measurement data. Preliminary results comprise (1) proven convergence of the rock salt formation, (2) a successful coring and (3) restored integrity of Zechstein salt formation, as proven by the formation integrity test. Based on these results, the new long-term sealing concept has been successfully tested at the Altmark natural gas field and successful application of the concept on other sites with similar geological conditions is foreseen to be likely.

The separation of higher alkanes from methane is a key aspect for conditioning natural gases and accompanying gases. Against this background, a systematic study on related separation performances of several MFI membranes in dependence on their synthetic origin is presented with this contribution. Basically, MFI slurry was used for the activation of inert Al 2O 3 supports for heterogeneous crystallization. The resulting MFI seed layer acts both as heterogeneous nucleation side and as flexible distance holder between support and MFI membrane suppressing defect formations during thermal template removal. For the purpose of further optimization, synthesis parameters like temperature, reaction time, pore size of the support and reactant ratios were varied. Characterization of the membranes via permporometry and single gas permeation using methane and n-butane gave first results on the characteristic properties of the membranes obtained. Also, the non isobar performed separations of C 4/C 1 binary 1:1 mixtures ( p feed = 1 bar, p permeate = 2 bar) are discussed with respect to membrane synthesis. It was found that either selectivity (M10, α = 11.3; J = 128 l m −2 h −1 bar −1 at 75 °C) or permeation flux (M16, α = 3.6; J = 477 l m −2 h −1 bar −1) optimized membranes can be generated via different synthetic routes. Both archetypes were tested in a simulated cascade like separation experiment for the isolation of n-butane from C 4/C 1 = 95:5 mixtures. Under elevated feed pressures ( p feed = 2–11 bar, p permeate = 1 bar) only separation optimized membranes showed a promising applicability due to an increased separation performance also at a lower n-butane content of 6.8%. Increasing feed pressures induced an increase in separation factors from 2.0 to 13.9 at nearly constant permeances of 93–136 l m −2 h −1 bar −1 making customized MFI membranes attractive for technological applications.