Study On Thermo-Bio-Chemical Biorefinery: Fast Pyrolysis of Lignocellulosic Biomass After Hydrolysis Pre-Treatment

Rene Garrido, Nydia Ruiz-Felix, and Justinus Satrio

Chemical Engineering Department, Villanova University, PA 19085

Abstract

Biomass-based energy is a renewable source of energy from organic and inorganic matter formed in a biological or mechanical process. Although fossil fuels, such as petroleum oil and coal, have their foundation in ancient biomass; they have been “out” of the carbon cycle for a long time. Their combustion consequently disturbs the carbon dioxide content in the atmosphere. Biomass, specifically lignocellulosic biomass, as the only carbon-containing renewable energy source can be classified as natural (without human intervention), residual (byproduct of waste generated by agricultural activities, forestry, and industry wood processing), and energy crops (for the production of biofuels). The complex nature of lignocellulosic biomass poses a substantial challenge to the large-scale biomass utilization. Lignocellulosic materials contain highly valuable carbohydrates (cellulose and hemicelluloses) and lignin. The carbohydrate (sugar) polymers are tightly bound to the lignin, which makes the separation process challenging. While it is technologically viable to exploit lignocellulosic materials and organic wastes into energy, chemicals and fuels, the cost related with it needs to be lowered. It also must be demonstrated that a commercial scale biomass utilization process is environmentally sound.

At present, routes to process lignocellulosic biomass into biofuels can be categorized into two distinct approaches, namely thermochemical and biochemical approaches. These two approaches utilize biomass components differently. In one thermochemical approach, called fast pyrolysis, biomass is subjected to heat in the absence of oxygen which make the biomass components rapidly decompose to form simpler compounds. Upon rapid cooling, these compounds condense to form a liquid mixture; called bio-crude oil (BCO) The physicochemical properties of the compounds in BCO have a large variability, since they are derived from different biomass components. The “light” compounds are derived from cellulose and hemicelluloses, and the ‘heavy’ compounds are derived from lignin. For converting BCO to produce hydrocarbon fuels, the lignin-derived compounds are preferred, since the compounds derived from cellulose and, particularly hemicellulose, tend to be highly oxygenated with low boiling points and convert to light gaseous compounds during upgrading process. In biochemical approach, at the present states of technologies, only the carbohydrate portion, i.e. cellulose and hemicelluloses that can be converted into sugars. The presence of lignin in biomass is seen as a “nuisance’ of the process, which often ends up as a ‘waste’ product.

In ordered to utilize lignocellulosic biomass optimally, a ‘hybrid’ process, which is a combination of biochemical and thermochemical (fast pyrolysis) approaches is proposed. In the process, biomass is first pretreated by hydrolysis prior to the primary processes. The severity level of hydrolysis determines the separation levels of biomass components to be further processed either via fermentation or fast pyrolysis.

In this presentation, to be reported are the results of thermochemical study of lignocellulosic biomass after hydrolysis pretreatments. Analytical pyrolysis combined with gas chromatography and mass spectrometry (Py-GCMS) is used to study the chemical composition of volatile products from previously hydrolyzed biomass. The feedstock used in this study which includes starch, switchgrass and wheat straws are to be compared to waste lignocellulosic biomass such as paper mill sludge, spent mushroom substrate and reed grass. Effects of the variability of biomass feedstock and the severity level of hydrolysis pretreatment on the chemical composition and yield distribution of the fast pyrolysis products will be evaluated. The chemical composition study of pyrolyzed biomass would then aid in the understanding of the chemistry behind the different compounds to further enhance the process of upgrading bio-crude oil. By this, ground work is laid for advanced studies which include the use of catalyst to optimize the thermochemical conversion portion of lignocellulosic biomass in an advanced hybrid biorefineries.