Lignin, an aromatic renewable resource, is a low-cost byproduct from industrial streams such as cellulosic ethanol and paper and pulping industries. These streams of lignin have varying solvent solubility depending on the industrial processes used to remove the cellulose and hemicellulose from the biomass. Our research approach towards the utilization of these lignin streams is to first dissolve the lignin stream (acetosolv in this case) directly into solvent or utilize pretreatment steps to enhance solubility. Secondly, the dissolved lignin streams are subjected to low temperature, low pressure-hydrogenation (LTLP-H) to liquefy the dissolved lignin into stable oil that can be further upgraded into higher-end products such as thermoset plastics, biofuels, and resins. LTLP-H was performed on soluble lignin streams at room temperature and 1 atm pressure using 10% Pd/C catalyst for 16 hours. Preliminary work has shown that the organosolv industrial stream resulted in a maximum liquid oil yield of 57 wt%. Other industrial lignin streams subjected to LTLP-H included supercritical and enzymatic hydrolysis lignins. These lignins contained higher molecular weight species; therefore, they required pretreatment steps. Pretreatments utilized were 5% ammonium hydroxide solution and 5% calcium hydroxide solution, refluxed with the lignin for 6 hours at 125°C. The yields were lower for the supercritical lignin stream at 22 wt% liquid oil using calcium hydroxide pretreatment while the enzymatic lignin stream produced 23 wt% with an identical pretreatment. <sup>1</sup>H NMR revealed complex polymeric spectra of the lignins prior to LTLP-H with unresolved functionalities. After LTLP-H the spectra indicated resolvable peaks suggesting the breakage of polymeric ether bonds yielding smaller molecular weight chemical species. Resolvable functionalities included methyl and methylene groups at 0.0-1.6 ppm, methylene groups and aliphatic alcohols at 1.6-2.2.0 ppm, methyl and benzyl aromatics and alpha carbonyls at 2.2-3.0 ppm and lastly aliphatic protons adjacent to oxygen at 3.0-4.2 ppm.

Application of low temperature, low pressure hydrogenation to liquefy and stabilize lignin streams

251st National Meeting (2016)

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