Chemical looping steam reforming of acetic acid in a packed bed reactor

Abstract

Chemical looping steam reforming of acetic acid (CLSR-HAc) was carried out in a packed bed reactor at 650 °C and 1 atm using two nickel-based catalysts (‘A’ with alumina support and ‘B’ with calcium aluminate support) to study the effect of the temperature of oxidation (TOX) on the efficiency of the process and the materials properties of the catalysts upon cycling. CLSR-HAc could not be sustained with steady outputs with TOX of 600 °C for catalyst A, but it was conducted successfully at temperatures up to 800 °C, whereas with B it could be operated reaching close to equilibrium conditions over five cycles with TOX of 600 °C. CLSR-HAc can run efficiently for further cycles at the right operating conditions (S/C of 3, WHSV of 2.5 h−1, TOX 800 °C, TSR 650 °C) even in the presence of the side reactions of acetic acid decomposition and coking. The yield of hydrogen produced had a minimum efficiency of 89% compared to equilibrium values, and the acetic acid conversion was in excess of 95% across 10 chemical looping steam reforming cycles. High purity hydrogen (>90% compared to equilibrium values) was also produced in this study. Chemigrams obtained from TGA-FTIR analysis indicates that two forms of carbon were formed on the catalyst during CLSR-HAc; TEM images and diffraction patterns indicate that poly graphitic carbon and amorphous carbon were formed while SEM images of the oxidised catalyst showed that the carbon was eliminated during the oxidation step of CLSR. A full carbon elemental balance of the process confers that majority of the carbon share (ca 90%) was utilised for efficient steam reforming of acetic acid with ca 10% of the carbon input deposited during the reduction step and subsequently burned during oxidation over the CLSR cycles.