Phenols from Lignin

Abstract

Lignin accounts for approximately 25-35 % of the organic matrix of wood and lignocellulosic biomass in itself is the most abundant renewable material on the planet. It has long been recognized as a potential feedstock for producing chemicals, fuels, and materials. Despite this excellent availabilty of lignin it is a low value compound and has so far mainly been used as energy source in combustion applications. Less than 5 % are being processed for other purposes. This article discusses the potential for an increased use of lignin as a renewable raw material, possible conversion routes towards monomeric phenolic compounds, and applications for these products. A brief overview about present state-of-the-art is given and a high-yielding, one-step approach of producing alkylated phenolic compounds from lignin is presented.

Heterogeneously catalyzed lignin depolymerization

“…Additional methods employed to isolate lignin are indicated by the following nomenclatures: milled wood lignin, acidolysis lignin, cellulolytic enzyme lignin, enzymatic mild acidolysis lignin, pyrolysis lignin, and steam explosion lignin [15]. Alkaline lignin or Kraft lignin is produced in large quantities by the pulp and paper industry, which are, hence, the most abundant sources of lignin for the subsequent chemical processing [3]. In the Kraft process, lignocellulose is treated with either sodium hydroxide and/or sodium sulfide at 170°C, facilitating the separation of cellulosic fibers from lignin [16]; however, this approach is energy intensive, and the sulphite route introduces considerable sulfur into the resulting lignin.…”

“…1). Lignin is a highly branched phenolic polymer of high molecular weight, typically between 600 and 1500 kDa [3], with an annual global production of around 40-50 million tons. It occurs primarily in plant cell walls, and the principal components are guaiacyl alcohol, syringyl alcohol, and p-coumaryl alcohol [4].…”

“…Oxidizing routes are generally undesirable due to radical formation which can result in partial repolymerization, whereas hydrogenolysis protocols minimize lignin repolymerization and promote C-O bond cleavage by quenching and recombination of radicals, although the addition of molecular hydrogen can result in fully hydrogenated cyclic hydrocarbons of relatively low commercial value. Hydrogen-donating solvents able to generate/transfer hydrogen have, thus, also shown promise, e.g., Connors et al report hydrogen transfer from ethanol, tetralin, and formic acid during lignin hydrocracking [5], while Kleinert et al reported a novel solvolysis method employing high-pressure thermal treatment of lignin in the presence of ethanol as solvent and formic acid as hydrogen-donor, the latter decomposing to liberate CO 2 and hydrogen [3]. Glycerol [6] and isopropanol [7] are also promising hydrogen-donor solvents.…”

The Influence of Alkali and Alkaline Earth Metals and the Role of Acid Pretreatments in Production of Sugars from Switchgrass Based on Solvent Liquefaction

“…3,4 Depending upon operating conditions, polysaccharides can be converted to sugars 5−12 and lignin can be converted to low-molecular-weight phenolic compounds simultaneously. 13,14 Sugars in the liquid products can be fermented or catalytically upgraded into fuels, and phenolic compounds can also be catalytically upgraded into fuels. Usually, the fast pyrolysis process takes a few seconds, whereas solvent liquefaction takes from seconds up to an hour depending on the reaction temperature, pressure, and the choice of solvent.…”

Screening for potential co-products in a Miscanthus sinensis mapping family by liquid chromatography with mass spectrometry detection

“…and Panicum virgatum, as a source of renewable biomass (Lewandowski et al, 2000). Components of biomass, such as lignin, cellulose and hemicellulose (Kleinert and Barth, 2008), are used to provide bioenergy in the form of heat, electricity and liquid fuels (Cherubini, 2010). There are numerous other chemicals with potential commercial value present in grasses (Heaton, et al, 2008).…”