Pilot-Scale Gasification of Corn Stover, Switchgrass, Wheat Straw, and Wood: 2. Identification of Global Chemistry Using Multivirate Curve Resolution Techniques

A pilot-scale study was conducted to examine the effect of the steam-to-biomass ratio, the gasification temperature, and the thermal cracker temperature for Vermont wood, wheat straw, switchgrass, and corn stover on the formation and speciation of tars. This study is divided into two parts; the first paper detailed the processing conditions and gives quantitative information on low-molecular-weight species. This paper, which is the second part of this study, uses multivariate curve resolution techniques to correlate process variables with the mass spectra gathered during the study to (1) identify the global chemistry of the system and (2) to identify differences or similarities of the product gas streams for each feedstock. Three main groups of products were identified statistically: (1) primary and secondary pyrolysis products (e.g., guaiacol, furfural), (2) cracking products (e.g., phenol, cresol), and (3) polynuclear aromatic hydrocarbons (PAHs). Our findings support known global reaction mechanisms that delineate the formation of the more-refractory PAHs, whereby oxygenated pyrolysis products are cracked into smaller fragments that contain less oxygen. These crack further into small hydrocarbons and radicals that undergo molecular weight growth to produce PAHs. The results from this statistical analysis indicate that, at high temperatures, where PAHs dominate, there is little variation observed between the feedstocks.