Chemical Analysis of Impurities in Diverse Bioethanol Samples

Bioethanol has recently become an important resource for chemical industries. The chemical compositions of 17 different types of bioethanol were investigated with a focus on impurities that could affect catalytic performances in the downstream chemical processes. Lignocellulosic ethanol contained higher concentrations and a greater variety of organic impurities compared to sugar- or starch-derived bioethanol. Twenty-nine impurities were identified in lignocellulosic ethanol, whereas 16 impurities were in sugar- or starch-derived bioethanol. Lignocellulosic ethanol contained high concentrations of acetic acid, acetaldehyde, methanol, and furan-related compounds such as furfural. In contrast, with the exception of molasses-derived bioethanol obtained by crude distillation, the concentrations of these components were lower in sugar- or starch-derived bioethanol samples. Lignocellulosic ethanol contained dimethyl disulfide and thiazole, whereas the only organosulfur compounds found in sugar- or starch-derived bioethanol were dimethyl sulfide and dimethyl sulfoxide. These sulfur-containing impurities can cause catalyst deactivation in the bioethanol transformation processes. In lignocellulosic ethanol, more than 0.1 mu g/mL of Si was detected.