Effect of N₂ on Biological Methanation in a Continuous Stirred-Tank Reactor with <i>Methanothermobacter marburgensis</i>

• Main Authors: Marc Philippe Hoffarth, Timo Broeker, Jan Schneider
• Format: Article
• Language: English
• Published: MDPI AG 2019-07-01
• Series: Fermentation
• Subjects: biological methanation; CSTR; <i>Methanothermobacter marburgensis</i>; methane; carbon dioxide; dinitrogen; hydrogen; power-to-gas
• Online Access: https://www.mdpi.com/2311-5637/5/3/56

In this contribution, the effect of the presence of a presumed inert gas like <inline-formula> <math display="inline"> <semantics> <msub> <mi mathvariant="normal">N</mi> <mn>2</mn> </msub> </semantics> </math> </inline-formula> in the feed gas on the biological methanation of hydrogen and carbon dioxide with <i>Methanothermobacter marburgensis</i> was investigated. <inline-formula> <math display="inline"> <semantics> <msub> <mi mathvariant="normal">N</mi> <mn>2</mn> </msub> </semantics> </math> </inline-formula> can be found as a component besides <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>CO</mi> <mn>2</mn> </msub> </mrow> </semantics> </math> </inline-formula> in possible feed gases like mine gas, weak gas, or steel mill gas. To determine whether there is an effect on the biological methanation of <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>CO</mi> <mn>2</mn> </msub> </mrow> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <msub> <mi mathvariant="normal">H</mi> <mn>2</mn> </msub> </semantics> </math> </inline-formula> from renewable sources or not, the process was investigated using feed gases containing <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>CO</mi> <mn>2</mn> </msub> </mrow> </semantics> </math> </inline-formula>, <inline-formula> <math display="inline"> <semantics> <msub> <mi mathvariant="normal">H</mi> <mn>2</mn> </msub> </semantics> </math> </inline-formula>, and <inline-formula> <math display="inline"> <semantics> <msub> <mi mathvariant="normal">N</mi> <mn>2</mn> </msub> </semantics> </math> </inline-formula> in different ratios, depending on the <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>CO</mi> <mn>2</mn> </msub> </mrow> </semantics> </math> </inline-formula> content. A possible effect can be a lowered conversion rate of <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>CO</mi> <mn>2</mn> </msub> </mrow> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <msub> <mi mathvariant="normal">H</mi> <mn>2</mn> </msub> </semantics> </math> </inline-formula> to <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>CH</mi> <mn>4</mn> </msub> </mrow> </semantics> </math> </inline-formula>. Feed gases containing up to 47% <inline-formula> <math display="inline"> <semantics> <msub> <mi mathvariant="normal">N</mi> <mn>2</mn> </msub> </semantics> </math> </inline-formula> were investigated. The conversion of hydrogen and carbon dioxide was possible with a conversion rate of up to 91% but was limited by the amount of <inline-formula> <math display="inline"> <semantics> <msub> <mi mathvariant="normal">H</mi> <mn>2</mn> </msub> </semantics> </math> </inline-formula> when feeding a stoichiometric ratio of 4:1 and not by adding <inline-formula> <math display="inline"> <semantics> <msub> <mi mathvariant="normal">N</mi> <mn>2</mn> </msub> </semantics> </math> </inline-formula> to the feed gas.