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In environmental remediation research, there is a need for gases to participate in reactions in a flowing manner. This mainly includes photocatalytic CO₂ hydrogenation reactions, photocatalytic methane reforming reactions, and photocatalytic degradation reactions of gaseous pollutants.
During flow reactions, due to the constant flow state of the reactive gases, precise adjustment of gas flow rate is required to stably participate in the reaction during the experimental process.
Currently, Perfectlight Technology offers three main products related to gas-involved flow reactions:
1. PLR-PTSR Ⅱ Photothermal Catalytic Reaction Apparatus, mainly suitable for gas-solid photocatalytic reactions in a flowing phase, such as photocatalytic CO₂ hydrogenation, photocatalytic methane reforming, and photocatalytic CO₂ reduction;
2. PLR-GSPR Atmospheric Gas-Solid Phase Photocatalytic Reaction System, mainly suitable for flow reactions of gaseous pollutant degradation, such as photocatalytic degradation of NOx, photocatalytic degradation of VOCs;
3. PLD-DGCS05 Multi-Component Dynamic Gas Mixing System, mainly suitable for mixing multiple gases and accurately controlling gas flow rates.
Figure 1. Flowing Phase Photocatalytic Reaction Apparatus
PLR-PTSR Ⅱ Photothermal Catalytic Reaction Apparatus, PLR-GSPR Atmospheric Gas-Solid Phase Photocatalytic Reaction System, and PLD-DGCS05 Multi-Component Dynamic Gas Mixing System all utilize mass flow controllers for flow control.
A mass flow controller (MFC) is a device that can accurately measure and control gas flow rates. It not only has the flow measurement function of a mass flow meter but also can automatically control gas flow rates based on flow settings, without the need for temperature and pressure compensation of the measured values.
The flow units of a mass flow controller are generally expressed in sccm (Standard Cubic Centimeter Per Minute) and slm (Standard Liter per Minute), which refer to standard milliliters or liters per minute. The indicated flow rates are typically at 0°C and 101.325 kPa.
Mass flow controllers are calibrated before leaving the factory, usually using N₂ as the calibration gas. However, in the experimental process, the raw gas may be different from the calibration gas, resulting in deviations between the set flow rate and the actual flow rate, which can affect the experimental results.
For example, if the experimental raw gas is CO₂ and the mass flow controller is calibrated with N₂, and the desired flow rate is 100 sccm, if the flow rate is still set to 100 sccm, the actual CO₂ flow rate will be 73.7 sccm, which is lower than the desired flow rate.
You can use the formula (1) to convert between the set flow rate and the actual flow rate:
Common gas correction factors are shown in Table 1.
Prior to the experiment, it is essential to check the calibration gas type of the mass flow meter, refer to Table 1, input the experiment's desired flow rate into formula (1), and calculate the set flow rate.
If the raw gas in the experiment is pure gas, you can use formula (1) to calculate. If the raw gas is a mixed gas, you need to use formula (2) to calculate the correction factor of the mixed gas and then input it into formula (1) for calculation.
Where C1, C₂, C₃ represent the volume percentage of gases in the mixed gas.
For example, if the mixed gas is 20% H₂ and 80% CO₂, the mass flow controller is calibrated with Ar, and the desired flow rate is 200 sccm, the calculation for the set flow rate is as follows:
The set flow rate is 361.2 sccm.
Note: The section explaining series catalytic reactions is translated and summarized by the author based on reference materials. The author's proficiency is limited, so if there are any errors, please kindly point them out!
