Holzforschung, Vol. 62, pp. 409–416, 2008 • Copyright  by Walter de Gruyter • Berlin • New York. DOI 10.1515/HF.2008.068 Article in press - uncorrected proof Wood solubilization and depolymerization by supercritical methanol. Part 2: Analysis of methanol soluble compounds Andres J. Soria 1 , Armando G. McDonald 1, * and Bingjun B. He 2 1 Department of Forest Products, University of Idaho, Moscow, ID, USA 2 Department of Biological and Agricultural Engineering, University of Idaho, Moscow, ID, USA *Corresponding author. Department of Forest Products, University of Idaho, Moscow, ID 83844-1132, USA E-mail: armandm@uidaho.edu Abstract Methanol treatment of ponderosa pine wood was per- formed in a batch reactor at temperatures close to and above the critical points of methanol (2388C and 8.3 MPa) to induce wood degradation into its monomeric and oligomeric components. The resultant methanol sol- uble and insoluble residues and gases were collected. The volatile components of the liquid and gaseous frac- tions were analyzed by GC-MS. The gases consisted mostly of carbon dioxide and simple aliphatic hydrocar- bons. The non-volatile methanol soluble components were analyzed by HPLC and size exclusion chromato- graphy. The mixture was found to be promising as a source of raw materials for fuel and chemical manufac- turing. It consists of a blend of carbohydrate and lignin derived compounds and extractives in varying concen- trations depending on the reaction conditions. More extractive compounds were found in the subcritical runs. In mild supercritical conditions the yield of lignin mono- mers and oligomers was increased, while under severe supercritical treatment, lignin and carbohydrate derived compounds were prevalent. Keywords: bio-oil; ponderosa pine; supercritical metha- nol; wood depolymerization; wood liquefaction. Introduction A supercritical fluid (SCF) is defined as a substance above its critical temperature (T C ) and critical pressure (P C ). The critical point is the highest temperature and pressure at which the substance can exist as a vapor and liquid in equilibrium. As temperature increases, the liquid density decreases as a result of thermal expansion, and the viscosity of the gaseous phase increases as a result of an increase in pressure. At the critical point, the den- sities, as well as specific weights, polarity, and viscosity of both phases equilibrate, and any distinction between liquid and gaseous phases disappears (Clifford 1998). Based on SCF technology, fermentable sugars, ali- phatic and phenolic hydrocarbons, furans and other chemicals can be produced from biomass. SFC can also be designated as a single process technology to produce a liquid matrix (the so-called ‘‘bio-oil’’). From the bio-oil, individual chemicals can be easily obtained by extraction or by conventional distillation. Nowadays, such process- es are subsumed as biorefinery (Kabyemela et al. 1999; Saka and Ueno 1999; Kucuk 2001; Kusdiana and Saka 2001; Soria et al. 2005). SCF has several advantages over alternative techniques of thermochemical conver- sion (such as pyrolysis) or of simple extraction: it is less time consuming, solvents are readily recovered, and pressure and temperature variables can be tuned to selectively produce desired compounds (Clifford 1998). The main limitation of SFC technology is its high com- plexity concerning the reactors which should withstand the elevated temperatures and pressures. In the course of SCF experiments for transformation of biomass, water (Savage 1999; Ehara et al. 2002; Kruse et al. 2002; Hao et al. 2003), methanol (Poirier et al. 1987; Miller et al. 1999; Kucuk 2001; Kusdiana and Saka 2001; Minami and Saka 2003; Soria et al. 2005), phenol (Lee and Ohkita 2003) and CO 2 (Ritter and Campbell 1991; McDonald et al. 1997) have been preferably applied. Varying degrees of liquefaction and chemical recovery were obtained depending on the reaction conditions. Supercritical methanol (SCM) shows promise for the conversion of biomass to oligomeric building block com- ponents. Cellulose depolymerizes under SCM conditions and forms stable glycosides at temperatures between 2208C and 4508C and pressures between 14 and 72 MPa (Ishikawa and Saka 2001). The main products from cel- lulose decomposition were methylglycosides of cello- triose, cellobiose, glucose, levo-glucosan and 5-hydroxy- methylfurfural. In SCM, monomeric compounds were found to be stable and the concentrations of methyl a- and b-D-glucosides were higher (Ishikawa and Saka 2001). The mild conditions of SCM processing overcome the shortcomings of other thermochemical processes, e.g., pyrolysis byproducts arise only in low amounts (Antal et al. 1985; Moldoveanu 1998; Saka and Ueno 1999). Lignin also depolymerized in a SCM process into phe- nolic chemicals and carbon fuels (Miller et al. 1999). The decomposition of lignin is believed to be the major con- tributor to the liquefaction of cedar (Cryptomeria japoni- ca) and beech (Fagus creanata) at 3508C and 43 MPa, with overall liquid yields of 53% and 89%, respectively (Minami and Saka 2003). The main lignin derived prod- ucts soluble in methanol after SCM treatment were mon- omeric guaiacol, coniferyl alcohol, and its g-methyl ester Brought to you by | University of Georgia Libraries Authenticated Download Date | 5/24/15 4:05 PM