Stability Patterns of Methoxy Phenols under Alkaline Hydrolysis Conditions

It has long been recognized that lignin is a potential renewable source of chemicals, however, there has been only limited success in the commercialization of processes for converting lignin into chemicals [1,2]. Alkaline hydrolysis of lignin has received considerable attention because the reagents are relatively inexpensive and the phenolic products obtained are of potential value [1]. The most successful process for commercial production of a low molecular weight chemical from lignin was the alkaline hydrolysis of mostly lignosulfonates into vanillin [3,4]. With addition of air or oxygen yields increase into the 10–30% range. Several groups have studied the production of phenols and methoxy phenols from cooking kraft black liquor at higher temperatures (260–310 C) [5,6]. The main chemicals identified were guaiacol and catechol plus their methyl and ethyl analogs, and phenol. The yield of ether-solubles was reported to reach a maximum of about 30% on a weight basis. The yield of identifiable phenolics was about 10% with catechol the largest product (~5%). Thring and co-workers studied the alkaline hydrolysis of lignins isolated with organic solvents, ethylene glycol [7] and ethanol [8]. At a treatment severity equivalent to a reaction temperature of 300C for 1 hour, 20% of ethylene glycol lignin was recovered as ether-solubles. The yield of identifiable phenolics was about 11% with catechols being the largest components. Similar yields and products were observed when ALCELL lignin was used as the feedstock.