PROFILE: CARBOLEA
Professor Michael Hayes, project co-ordinator at the University of Limerick discusses how alternative sources of energy are needed to satisfy current and future transport and energy needs.
The Chemical and Environmental Sciences Department of the University of Limerick’s involvement in the Second Generation Biorefining (SGB) of lignocellulosic biomass (part of the Carbolea Research Group) have been greatly advanced by DIBANET, a €3.7m research programme funded under the EU Seventh Framework Programme.
This project, co-ordinated by Carbolea, was a response to the Energy 2008 Call – ‘Significant enhancement of the co-operation between key researchers and industries from the EU and Latin America in the field of biofuels’. DIBANET stands for the ‘Development of Integrated Biomass Approaches NETwork’ and the project was entitled ‘The Production of Sustainable Diesel Miscible Biofuels from the Residues and Wastes of Europe and Latin America’.
DIBANET aimed for an integrated approach to provide maximum returns from the feedstock materials as outlined in Fig. 1. The targeted products, from the acid hydrolysis, at elevated temperatures and pressures, of lignocellulosic materials were levulinic acid (LevA) and formic acid from the C6 sugars and furfural from the C5 sugars (in hemicelluloses). It became obvious that the non-carbohydrate components in biomass were influencing the yields of LevA obtained. As a result, a patented lignocellulose pretreatment process (Haverty et al., 2012 – Authothermal, single stage, performic acid pretreatment of Miscanthus x giganteus for the rapid fractionation of its biomass components into a lignin/hemicellulose-rich liquor and a cellulosic digestible pulp’. Bioresource Technology 109, 173-177) was developed which allows a pure, highly crystalline cellulose to be separated as a solid residue from the lignocellulosic digest, leaving the hemicellulose and lignin in solution and suitable for recovery/upgrading.
Research focus
The research involvements of the Carbolea Group address many aspects of SGB processes and products. A major emphasis is focusing on the production of LevA and on the mechanisms involved in the transformation processes. We have, for example, developed:
- Rapid analytical methods (using near infrared spectroscopy) that determine accurately the different sugars and lignin, even in wet unground biomass. These infrared models allow the value of biomass for biorefining purposes to be determined much more rapidly and at a lower cost than standard methods. A spinoff company ‘Celignis Limited’ has been established to commercialise the service. It will also provide standard wet-chemical methods for characterising biomass;
- A (patented) pretreatment process (referred to above) for obtaining a cellulose rich pulp and a hemicellulose and lignin-rich liquor from lignocellulosic biomass; and
- The production of levulinic acid and co-products in high yields from biomass (both virgin and pretreated).
The major focus in the DIBANET submission was on the production of ethyl-levulinate as a diesel supplement. However, as the DIBANET project developed it became evident gammavalerolactone (GVL), butan-2-ol, pentan-2-ol, and nonane from LevA would provide better value as fuels.
Methyltetrahydrofuran, a petroleum additive and a fuel in its own right, can be sourced in the furfural, though we consider that the value of furfural as a platform chemical far exceeds its potential value as a fuel. LevA also has enhanced value as a platform chemical for the production of numerous ‘green’ products, including biodegradable plastics.
Pretreatment
The cellulose, freed in the pretreatment process from the hemicellulose/lignin entrainment, is enzymatically hydrolysable to glucose which can then be fermented to ethanol. We have tested our cellulosic pulp and found that it provides greater rates of sugar release, under enzymatic hydrolysis, than other pretreated biomass. The lignin and hemicelluloses are recoverable from the liquor from the pretreatment process, and we are working on obtaining value added products from the lignin.
The economics of SGB, based on the production of LevA from the cellulose recovered from lignocellulosic biomass, are encouraging. Miscanthus x giganteus, when harvested in Ireland at the end of its growing season can be expected to have an average yield of 16 tonnes per hectare. The LevA acid can be recoverable in close to quantitative yields from the cellulose. When all costs related to the growing, transport, and biorefining of the Miscanthus are taken into account we estimate that an equal volume/mass of LevA can be produced at a cost competitive at this time for a barrel of Brent crude oil. From about 23% of the arable land in Ireland, enough LevA can be produced to replace the imports of oil at this time.
Our recent research in Carbolea has significantly improved the biorefining process catalysed by sulphuric acid. However, it will be important to develop more environmentally benign procedures, other than the use of H2SO4, for the production of LevA. Our work has shown that solid acid catalysts and ionic liquids have little promise. However, uses of some H+-exchange resins show promise, especially when applied to cellulose recovered from our pretreatment process.
Indeed, our in-depth studies of the mechanisms of conversions of C6 sugars to LevA has confirmed the importance of isomerisation of glucose (from cellulose) to fructose and of its rapid progress to the key intermediate hydroxymethylfurfural (HMF) in the path to LevA. We have seen that significantly less browning condensation reactions take place in the conversion of fructose to HMF to LevA. We see value in acid catalysed ethanolysis which produces good yields of ethyl-levulinate (EL), even from biomass, but especially from the cellulose liberated in the pre-treatment process. The LevA and ethanol are readily recoverable from the EL.
We have a significant focus on finding added value for the lignin from the biomass pretreatment process. Valuable lignols are recoverable from hydropyrolysis, but there is much research needed to recover the abundant chemicals that are contained in the lignins.
The environmental initiatives that require biofuel additives to transport fuels are the catalysts that have led to the development of a sustainable industry based on non-food crops and food crop residues. It is unlikely that we will have the capacity to replace fossil fuels for transport, but alternative sources of energy will satisfy transport and energy needs. However, the great challenge will be to replace petrochemicals that sustain the manufacturing industry. It is clear that there must be a major effort in the synthesis of platform chemicals from biomass feedstocks. We are committed to this area, and we will welcome collaboration, particularly in future Horizon 2020 projects.
Professor Michael Hayes
Project Co-ordinator
+353 (0)61 202568
