Obtaining CO2 content of synthetic biogas through pH measurement of dissolved biogas in dilute solution of NaOH

Document Type: Research Article


Department of Chemical and Petroleum Engineering, Sharif University of technology


The feasibility of measuring CO2 content in biogas was evaluated in this research. Firstly, Curtipot pH simulator was used to visualize the titration behaviors of various percentages of dissolved CO2 in a wide range of concentration of NaOH solution. As a general output of those simulations, it was shown that when the titration curves of different CO2 content samples are separated enough, titration can provided precise information about the value of dissolved CO2. In addition, when the ratio of molar concentration of NaOH to the molar concentration of CO2 is in the range of 1 to 2(equivalent to stoichiometric ratio of bi-carbonate and carbonat), the separability of the curves is enough satisfactory to be used for precise determination of CO2; Outside this range, the accuracy of data segregation by titration diminishes. Moreover, when the ratio of molar concentration of NaOH to CO2 is between 1 and 2, by only a one-time probing, it is possible to determine the concentration of CO2 in standard NaOH solution. In this case, titration over a wide range of pH, does not provide more reliable and accurate information. The effects of temperature on CO2 measurement shows that a difference of even 10 °C can only cause less than 1% decrease in CO2 estimation. Finally, a comparison between gas chromatography and pH measurement was performed and the experimental results showed closeness the results of our proposed method with that of GC(less than 0.05% relative error). This method can be used in designing a non-expensive measuring method that would pave down the road for developing countries.


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