1. Hydrogen Production by Microwave Pyrolysis of Glycerol
The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok
Suksun Amornraksa
OBJECTIVE
The objective of this research is to study the potential of hydrogen production from glycerol by microwave pyrolysis. This is done by investigating the influence of operating parameters (i.e. microwave power, cracking temperature, type of glycerol) to the product distribution and yield.
METHODOLOGY
RESULTS & DISCUSSION
The cause of a higher H2 product from crude glycerol may be because the contained water (10.4wt%) took part in glycerol reforming mechanism. Firstly, the glycerol is decomposed to H2 and CO by glycerol decomposition reaction (Eq. 1). Then, the water is reacted with CO to produce the H2 as shown by water-gas shift reaction (Eq. 2). The glycerol decomposition reaction and water-gas shift reaction can be summarized to glycerol reforming reaction, which is represented on Eq. 3.
C3H8O3 → 4H2 + 3CO Eq. 1
CO + H2O ↔ H2 + CO Eq. 2
C3H8O3 + 3H2O → 3CO2 + 7H Eq. 3
In conclusion, the microwave pyrolysis could be potentially used to produce hydrogen from glycerol. In addition, we can produce hydrogen directly from crude glycerol without any purification. This can significantly reduce the production cost.
Crude glycerol (85.0% purity and 10.4wt% of water) and pure glycerol (99.5% purity and 0.5wt% of water) were used as the raw material in this study. The reaction was carried out in a fixed-bed quartz reactor filled with granular activated carbon (as microwave receptor). A 1100-watts pulsed-mode household microwave oven was used as a heat source. Its power level can be adjusted to10%, 30%, 50%, 70%, and 100% of the maximum power. Nitrogen (99.99% purity) was used as carrier gas.
Pyrolysis experiments were performed at different temperatures between 400 and 700°C. After the system was made inert and the temperature of microwave receptor was stabilized, 1 ml of liquid glycerol was fed into the reaction chamber using a medical syringe. The gas products were collected in sample bags (Air bag). Then, the components of gas products including H2, CO, CO2, CH4, C2H4, and C2H6 were analyzed by a Varian 450-GC gas chromatograph.
Pure glycerol
Crude glycerol
Figure 1: Schematic of microwave pyrolysis system
Figure 2: Effect of temperature on H2 and CO concentration (vol%)
RESULTS & DISCUSSION
GUIDELINES FOR THE INNOVATION
For the temperature profile experiment, it was found that the trend of temperature at 10%, 30%, and 50% microwave power level is stable during minutes of heating time while 70% and 100% are stable during minutes. The average temperature at 10%, 30%, and 50% are 437.8, 581.7, and 634.4°C, respectively. Additionally, the 70% and 100% microwave power provided the average temperature of and 700.6°C respectively. However, when considering about temperature profile of 70% and 100%, it was found that the trend of temperature at 70% has been stabilized more than 100%.
For the microwave pyrolysis experiment, the main gas products obtained from microwave pyrolysis of glycerol were H2 and CO. Other gases including CO2, CH4, C2H4, and C2H6 were found at lower concentrations. The highest volume of H2 (45.53 and 45.52vol%) was obtained from microwave cracking of crude glycerol at and 702.4°C. The pyrolysis temperature did have a significant effect on composition of gas products, especially to H2 content. Moreover, crude glycerol was found to provide a slightly higher H2 content when compared with pure glycerol.
Microwave pyrolysis can be applied to many industries, especially in petrochemical. In addition, this technology can be used with other raw materials such as biomass, hydrocarbons to produce high value-added gaseous and liquid products.
Acknowledgement
This research work is financially supported by Office of the Higher Education Commission, and King Mongkut's University of Technology North Bangkok (contract no. 2555A ). The authors are grateful for Thailand institute of scientific and technological research (TISTR) for their support in gas composition analysis. Special thanks also go for Patum Vegetable Oil Co., Ltd. for the supply of crude glycerol used in this work.
Contact
Dr. Suksun Amornraksa