Lecture: A Novel Phenolation Process of Residual Lignin for Adhesive Applications to Improve Economics of Bio-Based Conversion Processes 

Lecturer: Prof. Hou-min Chang, Forest Biomaterials, North Carolina State University, USA 

Time: 9:00 am, Jun 16, 2015 

Location: Meeting Room 205 of Administration Building 

Introduction of Lecturer 

Hou-min Chang, Rueben B. Robertson Distinguished Professor Emeritus of the Dept. of Forest Biomaterials (formerly of Wood and Paper Science), obtained his B.S. in Forestry from National Taiwan University in 1962. He obtained his M.S. (1966) in Chemistry and his Ph.D. (1968) in Wood Chemistry from the University of Washington. During his post-graduate studies, he worked as a research assistant in the area of Wood Chemistry at the University of Washington. Upon receiving his Ph.D., Dr. Chang joined the Department of Wood and Paper Science at North Carolina State University (NCSU) until his retirement in 2005. He received Outstanding Research Award in 1985 and the Outstanding Graduate Teaching Award in both 1993 and 1994 from the North Carolina State Alumni Association. He was a visiting Professor at the University of Tokyo in 1981, at Kyoto University in 1998 and a visiting scientist at Weyerhaeuser Company in 1976 and at Taiwan Forestry Research Institute in 2002. Dr. Chang is a Fellow of Technical Association of Pulp and Paper Industry (TAPPI), a member of the American Chemical Society and a Fellow of the International Academy of Wood Science. His research interests are in the chemistry of lignin, chemical processing of wood, chemistry of pulping and bleaching processes and pollution abatement in pulp and paper mills. After his retirement from NCSU in 2005, he continues his research work at NCSU, mainly on bioethanol and lignin structure. He also serves as a Special Professor at Nanjing Forestry University in China, spending 3 months every year there from 2006-2011. He received the Notable Achievement Award at the International Symposium on Wood and Pulping Chemistry in 2007 the Watauga Medal from NCSU in 2010 and the Outstanding Alumni from University of Washington Pulp and Paper Foundation in 2011. Dr. Chang has 8 US patents and 3 pending US patents. He co-edited 3 books, wrote 19 book chapters and published over 150 research articles in peer-reviewed journals. 

Chang’s Homepage: http://cnr.ncsu.edu/fb/people/hou-min-chang/ 

Lecture Abstract 

Conversion of biomass to useful products has been receiving great research attention during the past decades. A good example is ethanol fermentation of bio-sugars, which is efficient and product recovery is well-established. While much research effort has been focused on conversion of bio-sugars to other useful products, relatively little research attention has been given to improving the economics of bio-conversion processes by upgrading the portion of biomass that cannot be converted to the primary product.  With woody biomass feedstock, the residue may constitute ~35-50% of the original feedstock. Traditional techno economic analyses logically consider burning the residue in a biomass boiler to generate process steam and power.  While useful, and may be valuable to claim a “Green” product label, combustion is the least economic route for residue utilization - $90-100 per tonne. With low natural gas prices in the United States, residue, which contains mainly lignin, may be better upgraded in value to other products. Using a southern pine kraft lignin (BCL, BioChoice lignin from Domtar Paper company), we have developed a novel phenolation process that can be applied to residual lignin of any bio-conversion processes.  

In order to improve the reactivity and to decrease the average molecular weight and polydispersity, softwood kraft lignin was dissolved in phenol (up to 40% by weight) and phenolated with a catalytic amount of sulfuric acid (3-5% based on lignin),  without any additional solvent at less than 100 OC. This novel and simple phenolation protocol results in the addition of around 30 weight per cent of phenol onto the lignin macromolecule.  Gel permeation chromatography indicates substantial decrease in both the average molecular weight and molecular weight distribution. Phenolated lignin was characterized by elemental composition and  methoxyl content analysis, ？εi and ？εr UV spectroscopy, FT-IR spectroscopy, 13C and 31P NMR and 13C/1H HMQC correlation 2D NMR. These analyses indicate that: 1) almost all ether bonds remained in lignin including all α- and β-ethers in lignin-carbohydrate complex (LCC), pinoresinol, cyclic β-5, and β-O-4, dibenzodioxocin and vinyl ethers are cleaved, 2) α-carbonyl, stilbene and vinyl ether structures disappear, 3) phenolic hydroxyl content increases substantially and methoxyl content decreases, and 4) phenol is incorporated in the lignin structure. The incorporation of phenol in lignin structure presumably occurs at the benzylic carbon of lignin where stable benzylic carbocations are formed from many substructures in lignin such as LCC, pinoresinol and cyclic β-5, α-carbonyl, stilbene and vinyl ether. This results in the disappearance of these substructures and the formation of diphenyl substituted side-chain structures. The incorporation of phenol in the lignin structure should results in a slight increase in the average molecular weight since no nuclear exchange reaction was observed under the reaction conditions. Thus, the observed decrease in average molecular weight of the phenolated lignin must result from the hydrolysis of β-O-4 structure as well as LCC, dibenzodioxocin and vinyl ethers. All these structures were found in kraft lignin as indicated by 2-D NMR. 

Phenolated lignin was tested for replacement of a portion of phenol in the phenol formaldehyde resin formulation for plywood adhesive in laboratory scale. Up to 40% phenol may be replaced without affecting the properties of plywood and the processibility of the resin. This is in contrast with un-phenolated kraft lignin, in which only less than 25% can be replaced. 

Residual lignin of mixed southern hardwood isolated by auto-hydrolysis followed by enzymatic hydrolysis was subjected to phenolation. The residual lignin has a much higher molecular weight than the softwood kraft lignin. Phenolation results in incorporation of 20% phenol into lignin and the molecular weight is greatly reduced. Chemical and spectral characterization clearly indicates results similar to those of phenolation of kraft lignin.