Catalytic pyrolysis of lignin by using analytical pyrolysis-GC-MS

Catalytic pyrolysis of Kraft lignin and Scots pine wood over three different catalysts HZSM-5, Y-zeolite and Pd/C was studied. All experiments, with and without a catalyst, were carried out in small scale, using analytical pyrolysis gas chromatography mass spectrometry (Py-GC-MS) at 600 °C. The catalytic pyrolysis result showed that the Kraft lignin was less altered over the tested catalysts in comparison to Scots pine wood (lignin). Over the acidic zeolite catalysts, aromatic hydrocarbons with one to three aromatic rings were formed from both samples, together with deoxygenated phenolic structures. Conversion of Scots pine wood-aromatic hydrocarbons was higher with both zeolites in comparison to Kraft lignin, especially when HZSM-5 was used. Y-zeolite changed the product distribution of Kraft lignin more than HZSM-5. With Y-zeolite, the proportion of benzenediols and p-hydroxypehnyl structures was increased, indicating demethylation and demethoxylation of lignin guaiacyl units. With Pd/C catalyst, deoxygenation of lignin guaiacyl units took place from both Scots pine wood and Kraft lignin. At high temperature pyrolysis with Pd/C, hydrogenation of double bonds was avoided. Conversion of Scots pine wood lignin-guaiacyl-type lignin derivatives with no oxygen-containing side chain structures was higher in comparison to Kraft lignin. Verification of the results with principal component analysis (PCA) revealed that catalytic pyrolysis treatments clearly differ from the non-catalytic treatment of Scots pine wood. In the case of Kraft lignin, only pyrolysis with Y-zeolite clearly changed the product distribution in comparison to non-catalytic pyrolysis. Based on the results, analytical Py-GC-MS proved to be a promising method for testing the behaviour of different catalysts.