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The two-stage high-pressure fermentation (HPF) process enables the production of methane at high operating pressure. Pressure significantly reduces the energy needed for injecting the produced biogas into the gas grid by 45–60%. It also allows for incorporating large parts of the necessary biogas upgrading process into the synthesis step. As a result, the two-stage HPF process provides pressurized biogas with methane volume fraction ranging from 0.75 to 0.94. The pressure is not generated by energy intensive gas compression, but in-situ by microbial gas production. In comparison to conventional biomethane production, the overall costs could be reduced up to 20%. HPF is most beneficial when its operating pressure is adapted to that of the gas grid. The article presents briefly the development of the two-stage HPF beginning with tests in batch reactors, followed by experiments on gas solubility, and proof-of-concept in continuously operated methanogenesis reactors (MR) up to 9 bar. It also represents the effect of incorporating microfiltration (MF) of the feed stream, on improving the biogas quality and process stability of a continuously operated lab scale HPF process. By linking the MF with the HPF, methane volume fraction in the MR increases from 0.86 to 0.94 at 25 bar. Finally, the simulation and experimental results show good agreement with each other thereby making them a good basis for further optimization of the HPF process.

In this work, a new CO2 separation process using ionic liquid solvents is proposed. The approach focusses not only on improving the applied solvents or their CO2 absorption chemistry, but also on adapting the separation process itself for exploiting the advantages of ionic liquids. This is achieved by adjusting the operating temperatures of the absorption and the regeneration columns of the upgrading process to the same moderate temperature level and operating the desorption of CO2 under moderate vacuum instead of applying high grade heat from an external source. In this article, the proposed CO2 separation process is described in detail and the results of the development and characterization of appropriate ionic liquid solvents for applying the process to biogas upgrading are presented. The characterization section includes measurements on thermal and chemical stability, physical and chemical CO2 solubility, physical CH4 solubility, effective and intrinsic absorption kinetics, heat of reaction and various additional material properties of ionic liquid solvents. Physical gas solubility is examined for Room Temperature Ionic Liquids with [NTf2], [Tf], [DCA] and [TCM] anions with imidazolium cations in a wide temperature range of 25–125 °C. The applied short chain [Tf] and [TCM] based RTIL feature a high selectivity concerning physical solubility of CO2 and CH4. Furthermore, the applied chemically functionalized IL (CFIL) show almost the double chemical CO2 loading capacity than conventional amines. The measurements on absorption kinetics show that the absorption of CO2 in the applied IL solvent in the desired temperature range is about as fast as when aqueous DEA is applied. Based on the derived experimental results, an energetic evaluation of the process is carried out indicating that the proposed process enables considerable potentials for energetic savings, forming the basis for being close to economic feasibility within relatively short payback periods.

The concept of pressurized two-stage anaerobic digestion integrates biogas production, purification and pressure boosting within one process. The produced methane-rich biogas can be fed into gas grids with considerably less purification effort. To investigate biogas production under high pressures up to 50 bar, a lab scale two-stage anaerobic digestion system was constructed including one continuously operated pressurized methane reactor. This investigation examined the effects of different operating pressures in methane reactor (10, 25, 50 bar) on biogas quantity and quality, pH value and process stability. By increasing operating pressures in methane reactor, the pH value decreased from 6.65 at 10 bar to 6.55 at 50 bar. Simultaneously, methane content increased from 79.08% at 10 bar to 90.45% at 50 bar. The results show that methane reactors can be operated up to 50 bar pressure continuously representing a viable alternative to commonly used gas upgrading methods because of reduced purification effort.

The gas holdup is an important parameter for the design of slurry bubble columns. However, there is no correlation in literature to calculate the gas holdup of such reactors for industrially relevant conditions if the reactor is operated in the homogeneous regime. In this article, a novel correlation for calculating the gas holdup in the homogeneous and in the pseudo-homogeneous regimes is proposed. The correlation takes the relevant parameters into account: gas, liquid, and solid properties, sparger design, reactor diameter, and gas velocity. The correlation is also applicable for systems operated at elevated pressure and temperature. The correlation is based on 1199 data points, and it was developed by using the method of least squares. About two thirds of the data used were taken from literature (more than 20 research papers). The data from literature were carefully checked for confidence before using them for the correlation. > 90 % of the data points are covered by the new correlation with a relative error of less than 30 %, the standard deviation is 17.8 % and the averaged relative error is 9.5 %. Finally, the correlation was successfully validated with measurements which were not used to fit the correlation. An Excel file for using the developed correlation can be found in the Supplementary material.

The publication gives an overview of the production costs of synthetic methane in a Power-to-Gas process. The production costs depend in particularly on the electricity price and the full load hours of the plant sub-systems electrolysis and methanation. The full-load hours of electrolysis are given by the electricity supply concept. In order to increase the full-load hours of methanation, the size of the intermediate hydrogen storage tank and the size of the methanation are optimised on the basis of the availability of hydrogen. The calculation of the production costs for synthetic methane are done with economics for 2030 and 2050 and the expenditures are calculated for one year of operation. The sources of volume of purchased electricity are the short-term market, long-term contracts, direct-coupled renewable energy sources or seasonal use of surpluses. Gas sales are either traded on the short-term market or guaranteed by long-term contracts. The calculations show, that an intermediate storage tank for hydrogen, adjustment of the methanation size and operating electrolysis and methanation separately, increase the workload of the sub-system methanation. The gas production costs can be significantly reduced. With the future expected development of capital expenditures, operational expenditure, electricity prices, gas costs and efficiencies, an economic production of synthetic natural gas for the years 2030, especially for 2050, is feasible. The results show that Power-to-Gas is an option for long-term, large-scale seasonal storage of renewable energy. Especially the cases with high operating hours for the sub-system methanation and low electricity prices show gas production costs below the expected market prices for synthetic gas and biogas.

The European Union overall greenhouse gas (GHG) emission target is an 80 % – 95 % reduction from the GHG emissions emitted in 1990, the German target of 95 % reduction is even tougher.

Es wurde ein Verfahren entwickelt, das die Umwandlung von Reststoffen zu methanbasierten Kraftstoffen unter hochstmoglichem Erhalt des biogenen Kohlenstoffs mithilfe von elektrischer Energie aus erneuerbaren Quellen ermoglicht. Waldrestholz, Stroh und Klarschlamm wurden als besonders relevante Einsatzstoffe identifiziert. Durch die hochintegrierte Kopplung von Vergasung, Hochtemperaturelektrolyse und Methanisierung wird der biogene Kohlenstoff aus den Edukten nahezu vollstandig in das Produkt Methan uberfuhrt. Die Gestehungskosten sind dabei mit denen gegenwartig eingesetzter Technologien vergleichbar und liegen bei Grosanlagen im Bereich ublicher Werte der Biomethanerzeugung.

For evaluation of design specifications for catalytic oxygen removal units, examinations on reaction kinetics of catalytic oxidation of methane at very low O2:CH4 ratios have been performed in the temperature range between 200 For comparison of conversion rates of oxygen with various other reductives, such as ethane, propane and butane, equivalent experiments were performed and kinetic parameters of corresponding power law approaches are given. Finally, the catalytic activity of further noble metals and some transition metal catalysts was tested and compared to the platinum reference catalyst.

This work focuses on the deactivation and in-situ regeneration effects of a commercial PdO/Al2O3 catalyst for removal of oxygen by oxidation of CH4 at low O2:CH4 ratios when hydrogen sulfide and sulfur dioxide are applied to the gas stream. The experimental work is carried out at an operating temperature range of 200 °C SO2 and H2S show a different behavior in the examined range of operating conditions. Due to the low operating temperatures and low oxygen contents applied in this work, it was possible to identify an intermediate species, presumably PdSO3, with an increased activity for the oxidation of methane. This stands in contrast to the literature, where SO2 is typically seen to cause catalyst deactivation. Based on the experimental results, a reaction scheme was derived and kinetic measurements for each of the participating reactions were carried out separately. Furthermore, a deactivation model was derived and validated by experimental data with low contents of H2S, showing that residual activities, as observed by some authors, are a result of rate-equality of deactivation and in-situ regeneration process on the surface of the catalyst.

Three ionic liquids {butyl-trimethyl-ammonium bis(trifluoromethylsulfonyl)imide [N1114][BTA], 1-methyl-1-propyl-piperidinium bis(trifluoromethylsulfonyl)imide [PMPip][BTA], and 1-ethyl-3-methylimid...

To ensure an efficient use of biogas produced by anaerobic digestion, in some cases it would be advisable to upgrade the biogenic gases and inject them into the transnational gas grids. To investigate biogas production under high-pressure conditions up to 100 bar, new pressure batch methane reactors were developed for preliminary lab-scale experiments with a mixture of grass and maize silage hydrolysate. During this investigation, the effects of different initial pressures (1, 50 and 100 bar) on pressure increase, gas production and the specific methane yield using nitrogen as inert gas were determined. Based on the experimental findings increasing initial pressures alter neither significantly, further pressure increases nor pressure increase rates. All supplied organic acids were degraded and no measurable inhibition of the microorganisms was observed. The results show that methane reactors can be operated at operating pressures up to 100 bar without any negative effects on methane production.