Characteristics of Char produced by means of Slow Pyrolysis of Residual Lignin from Bio-ethanol Production Chain

The production of ethanol from lignocellulose is growing rapidly, and by looking at the industrial activities in this field steam explosion is by far the most applied pre-treatment technology allowing the delignification of the lignocellulosic feedstock. Formed sugars are further converted by simultaneous saccharification and fermentation to ethanol, and residual lignin is used as energy source. Lignin is a racemic, heteropolymer consisting of three hydroxycinnamyl alcohol monomers differing in their degree of methoxylation: p-coumaryl, coniferyl and sinapyl alcohols. The distribution of the three alcohols in lignin is dependent on the source feedstock. Moreover, lignin chemistry and structure can be modified on dependence of the extraction method from the biomass matrix. The residual lignin from ethanol production is underutilized with about 60 % more lignin generated than is needed to meet internal energy use. The exploitation of this residue for the combined production of biofuels and added value chemicals and materials present a key factor for the increase of the efficiency of the overall ethanol production chain. Pyrolysis can be explored as a possible thermal treatment capable of producing, in the absence of molecular oxygen, a solid residue (char) suitable for application in several fields and a liquid (bio-oil) and gaseous products that can be exploited for energy applications or as a chemicals' source. Review of the literature suggests many possibilities for valorizing char potential for diverse applications such as fuel in traditional and advanced power generation facilities, fertilizer and carbon sink, contaminant adsorbent in wastewater and soil, adsorbent or catalyst for gas cleaning, catalyst for syngas conversion to liquid hydrocarbons and biodiesel production, raw material for supercapacitors and filler in wood and polymer composites. The data from previous studies show that pyrolysis chars vary greatly in structure and chemistry due, in part, to the large degree of chemical heterogeneity of the feedstock. At our knowledge char deriving from pyrolysis of residual lignin from ethanol production has received less attention with respect to the liquid product. It has been tested as growth enhancer and as substitute for carbon-black in rubber. In this paper a preliminary study on the solid residue obtained from the thermal treatment of residual lignin spanning from torrefaction to pyrolysis temperature range has been conducted. Torrefaction and pyrolysis tests were performed under slow pyrolysis conditions. Chemical physical analyses were carried out on the solid residues in order to investigate changes in the elemental composition, volatile matter content and porosity characteristics (BET pore volume and pore size distribution) as a function of the temperature.