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RITTER has developed a CO2 absorption bottle which reliably absorbs more than 99% of CO2 from biogas. Guaranteed! Without any indicator liquid for absorption limit! This absorption bottle combined with the »RITTER Biogas Batch Fermentation System« provides the ideal solution for professional biogas research.

Operating Principle

The biogas generated in the fermentation bottles flows through a dip pipe into the absorption bottle (“bubbler”) containing the absorption solution. Due to the unique dip pipe design RITTER guarantees a CO2 absorption rate of at least 99% up to reaching the absorption capacity limit. This capacity limit will be indicated by the MilliGascounter by measuring the volume of methane remaining in the gas stream after absorbing the CO2.

The high CO2 absorption rate is achieved as a result of …

  • the large wetting surface of the biogas within the absorption liquid.
  • the long holding time of the CO2 inside of dip pipe chamber.

Due to this design, the absorption capacity of the RITTER CO2 absorption bottle is far superior to that of absorption bottles with surface absorption as the following diagram shows:

CO2 absorption of RITTER Absorption Bottles comparison diagram

Technical Specifications

Dimensions absorption bottle (»bubbler«)Volume 250 ml
Wide mouth GL80 with screw cap
ø D 95 mm x H 106 mm
MaterialBorosilicate glass
Dip pipe chamber volume8.3 ml
Holding time of CO2 bubble in dip pipe chamberdependent on gas flow rate
Absorption solution3-molar caustic potash solution (KOH 3 mol/ltr in aqua dest.)
Gas in/outlet portsPVDF screw-type tube connection for tube Ø 4i / 6o mm
RITTER Absorptions-Flasche mit innovativem Tauchrohr-Design

Absorption Capacity


The absorption capacity is the volume of CO2 which is absorbed until the absorption rate is decreased from 100% at start of absorption process to 99%. When the limit of absorption capacity is reached, the gas at the absorption bottle outlet contains 1% of CO2.
Definition of CO2 absorption capacity with RITTER Absorption Bottles

Table of absorption capacities at various flow rates and CO2 concentrations: (1)

Biogas InputFlow Rate (ml/h)
CO2 absorption capacity, approx. (ltr) (2)40% CO2 / 60% CH417.013.412.
60% CO2 / 40% CH417.013.511.
Max. volume of methane, approx. (ltr) (3)40% CO2 / 60% CH425.520.
60% CO2 / 40% CH411.

(1) The table will subsequently be updated with data of additional CO2 concentration values. For determination of the CO2 concentration value the gas analyser »RITTER MultiGas« is recommended. With the dual version, the concentration value for Methane can be determined simultaneously as well. If no determination of the CO2 concentration value is possible, it is recommended to use the smallest amount of CO2 concentrations stated in the above table.
(2) Per bottle filling 250 ml, absorption solution KOH 3 mol
(3) After the CO2 was absorbed from the biogas, the MilliGascounter displays the volume of the pure methane. The CO2 absorption capacity limit is reached when the MilliGascounter indicates the values the stated in the table above.
Please note: The values for the max. volume of methane stated at a specific flow rate were obtained at a constant flow rate of biogas. However, with biogas fermentation processes the flow rate varies in general significantly during a fermentation test run. In order to get a more meaningful value for the remaining CO2 absorption capacity the use of the data acquisition software »RIGAMO« is highly recommended.

Calculation of Absorption Capacity with Data Acquisition Software »RIGAMO«

The table above shows that the absorption capacity with the RITTER absorption bottle …

  • does not vary very much with different concentrations of CO2.
  • varies significantly with increasing flow rates because of the decreasing time the CO2 is in contact with the absorption liquid. However, due to the unique dip pipe design RITTER this time is far higher than with usual surface absorption bottles.

The following diagram shows the CO2 absorption capacity as a function of the flow rate:

CO2 absorption capacity of RITTER Absorption Bottles with flow rate diagram
With the data acquisition software »RIGAMO«, the actual flow rate is taken into account at any time during the fermentation process for calculation of the remaining CO2 absorption capacity individually for each of up to 18 absorption bottles.

Features of the software:

  • Calculation of remaining CO2 absorption capacity by regression curves at actual flow rates and with different CO2 concentrations.
  • Display of remaining CO2 absorption capacity in real time for each absorption bottle.
  • Storage of remaining CO2 absorption capacities for each bottle at the end of the fermentation process so that the remaining absorption capacity can be used for following fermentation processes.
  • Setting of an individual value of remaining CO2 absorption capacity for giving an alarm when approaching the pre-set level of remaining CO2 absorption capacity.

V 2.1 / Rev. 2023-06-19 / Subject to alterations.