GC–MS analysis of alkylpyrazines in the pyrolysis oils of silica-polyethylenimine CO2 sorbents

Solid sorbents based on silica and polyethyleneimine (PEI) are intensively investigated in the field of carbon capture and storage (CCS). Pyrolysis was proposed as a thermal process to recover the pure silica from exhausted sorbents and convert PEI into potentially useful products, such as alkylated pyrazines. A GC–MS method based on internal standardisation with 2-methoxypyrazine was developed and evaluated to determine the concentration of six pyrazines in the pyrolysis oils of exhausted silica-PEI sorbent pyrolysed at 400, 500, 600 and 650 °C. The most abundant pyrazines were 2-ethyl and 2,3-dimethyl, occurring at concentrations of 5–28 mg g^–1, followed by pyrazine, 2-methyl, 2-ethyl-3-methyl and 2-propylpyrazine. The GC–MS results were compared to those from a HPLC-DAD method using the Welch's test. The 37 % discrepancy of concentrations was attributed to spectral interference in LC-DAD. GC was slightly less precise than HPLC, calibration errors were lower and enabled the identification of highly alkylated pyrazines. Both methods provided comparable values of total pyrazine yields (around 4–7 % by weight).