Lignin
Background
Lignin is a complex and heterogeneous polymer found in wood. It composed of aromatics crosslinked with carbohydrates. If is the second largest component of biomass on Earth and has many applications. Lignin is difficult to decompose in the wild and a dense source of energy when combusted. Lignin may be an a source of aromatic compounds for OSE.
OSE context
Aromatics from lignin
Phenols and benzenes can be produced from lignin using catalytic hydrocracking, high heat with a hydrogen feed. A variety of valuable chemicals are produced by the decomposition of lignin but the challenge lies in purification.
US patent 4,647,704 issued to Engel et al on March 3, 1987 describes a method of hydrocracking lignin using a tungsten/nickel catalyst supported on a mildly acidic base, notably alumina, silica, alumina phosphate or a combination. The catalyst has superior due to the combination of a cracking catalyst tungsten and a hydrogenating catalyst nickel. The products are phenol or cresols, a methyl phenol, a benzene with a hydroxyl and methyl substitution. The process is conducted in a reactor under a hydrogen atmosphere at pressures of 500 - 3500 psig and temperatures of 300-450 C. Yield is improved with the use of a low weight aliphatic alcohol, namely methanol, in a percentage of up 25% but usually between 7-15%. Inclusion of methanol increases the yield of cresols. A water content of up to 25% wt lignin is found to have optimal yields and additional process improvements include the inclusion of a lewis acid/friedel-crafts (alkylates and acylates benzene) catalyst, namely AlCl3. Lignin from the kraft process or any nonbasic form is suspended in a nonreactive solvent but phenol was found to have the best performance.
The catalyst consists of 2-20% weight tungsten component preferably the zerovalent metal but tungsten sulfide may be used. Tungsten by itself may be used (has both cracking and hydrogenation activity) but a second hydrogenating catalyst enhances action. Preferably nickel (but also palladium) is an effective cocatalyst in the zerovalent metal state and should be combined with the tungsten in a molar ratio nickel:tungsten of 5:1-20:1. Friedel craft catalysts used include iron, antimony, zinc, tin, and aluminium as particularly bromides or chlorides but also fluorides and phosphates and are included in 0.5-5.0% wt lignin. A Fluidized bed reactor has superior performance compared to fixed bed reactors.
After further R&D the examples should be reviewed for optimal performance and adherence to OSE product ecologies.
Basic Studies on the Pyrolysis Products of Lignin by Hwang and Obst utilized model lignin compounds for pyrolysis and analyzed the products by GC-MS. Arylglycerol-ß-arylether (substituted aromatics linked through two carbons one as a C-C bond with hydroxyl group and one ether linkage) linked compounds served as model lignin structures and were pyrolysized at 250-500 C. Pyrolysis at 315 C was found to be optimal. Products were dimethoxyacetonophenone (DMAP), trimethoxyacetonphenone (TMAP), and dimethoxyphenol (DMP) and their exact yields were dependent on the starting material. The yield of aromatic products were higher in veratryl than trimethoxyphenol possibly due to pyrolysis being easier.
http://www.google.com/patents/US3105095
http://www.cellulosechemtechnol.ro/pdf/CCT9(2010)/P.353-363.pdf