Detailed characterization of sulfur compounds in fast pyrolysis bio-oils using GC x GC-SCD and GC-MS

Only trace amounts of sulfur (tens to thousands of ppm) are present in bio-oils produced from fast pyrolysis of lignocellulosic biomass. However, even such small amounts of sulfur-containing compounds can act as catalytic poisons during bio-oil upgrading. To improve the knowledge of sulfur speciation in bio-oils for process design and development, e.g. by hydrotreatment, comprehensive two-dimensional gas chromatography (GC x GC) coupled with selective sulfur chemiluminescence detector (SCD) and headspace gas chromatography coupled to a quadrupole mass spectrometry (GC-MS) were combined. This allowed to quantify sulfur-containing compounds present in crude bio-oils produced from different types of biomass (beech wood, miscanthus, and straw) and straw bio-oil after hydrotreatment. Hydrogen sulfide, methanethiol, dimethyl disulfide, and several thiophenes were identified and quantified as the most abundant sulfur compounds. The detailed analysis of the hydrotreated bio-oil prepared at 360 degrees C and 8 MPa showed that most GC-detectable sulfur was related to hydrogen sulfide not sufficiently removed in the product separator. Used analytical methods brought an unprecedented level of details about bio-oil sulfur speciation and acquired data can help to drive further R&D in bio-oil upgrading.

Automated summary

This study used various gas chromatography techniques to quantitatively analyze the sulfur content in crude bio-oils produced from different biomasses and after hydrotreatment, identifying the most abundant sulfur compounds and finding that hydrogen sulfide was not sufficiently removed during the hydrotreatment process. The analytical methods employed provided unprecedented details about the sulfur speciation in bio-oils, which can further drive research and development in bio-oil upgrading.