Revolutionizing the production of biofuels, residual biomass proves to be a game changer

Decarbonization of economy, including transition to bio-based economy is one of the key topics within the climate agenda. This transitions requires unprecedent changes in the economy patterns and this should be done in sustainable manner. The enhancement of resource efficiency through the use of lignocellulosic residues of agricultural, forestry or industrial origin, may help further on to meet the European Green Deal's decarbonization targets. This thesis focuses on the analysis of environmental and economic feasibility of emerging multi-product lignocellulosic value chains that use residual biomass, and, in particular, those applying the lignin solvolysis technology developed by the Dutch start-up Vertoro.

In the 2010s, there was a boom in the construction of commercial biorefineries using lignocellulosic residues and utilizing bio-chemical conversion route. One of the advantages of such a biorefinery is that it produces sulfur-free lignin, thus allowing to target different fuel and chemical applications. However, those biorefineries were primarily focusing on the valorization of carbohydrates while neglecting the ligneous part that was traditionally burnt on-site for energy supply. Thus, it was important first to answer the question whether those biorefineries would benefit from sourcing lignin to applications other than on-site energy supply. The developed models showed that from 40 to 60% of lignin can be extracted while serving all biorefinery energy needs. However, the economic feasibility of using extracted lignin for BTX, that was considered as the best chemical candidates for lignin valorization, would be still constraint by the lignin feedstock cost.

Lignin value's warming impact

The second important pillar of sustainability assessment is environmental analysis that uses the life cycle assessment method, or LCA. Although LCA was put by the International Organization for Standardization into a standardized framework, it has never been uniformized in detail. As a result, the lack of standardized procedure, especially when it concerns assigning environmental burdens within a multi-product system, that is known as an allocation procedure, may impose significant uncertainty in LCA results. Therefore, it was important to analyze how the allocation procedure can impact the environmental profile of lignocellulosic value chains.

One of the main observations related to this analysis concerns an extensive use of processing residues within a biorefinery. The analyses showed that the methodological assumption about the value of lignin can significantly impact global warming potential results of co-products. Additionally, this assumption imposes the uncertainty on whether cellulosic ethanol can be qualified as an advanced biofuel under the European Renewable Energy Directive.

Role of infrastructure

Another important research finding concerns the role of infrastructure in a biorefinery value creation process. Although the impact of infrastructure on the cost and environmental footprint can be significant, logically, it should not dominate the main conversion processes. This impact was analyzed with regard to a biorefinery with dilute acid pretreatment co-producing cellulosic ethanol and crude lignin oil via solvolysis of residual lignin. The analysis showed that the contribution of infrastructure exceeded reasonable economic and environmental limits for such processes as biomass pretreatment and lignin drying. In fact, these technological hotspots are interconnected via significant amount of water that first is added to biomass to acquire pumpable properties and then need to be separated from target products. This requires significant energy input and additionally, extensive wastewater treatment. Therefore, it was concluded that decreasing the amount of solids already in the pretreatment section, could improve the environmental and economic feasibility of a biorefinery.

Environmental and economic advantages

The potential improvements were further tested within the so-called ‘lignin-first’ biorefinery concept using novel biomass solvolysis pretreatment technology. Generally, that biorefinery revealed environmental and economic advantages over contemporary biorefinery while further improvements can be achieved via thorough evaluation of biorefinery energy integration option and feedstock logistics scenarios.

Title of PhD thesis: Sustainability assessment of emerging multi-product lignocellulosic value chains using residual biomass: lessons learned and perspectives of development. Supervisors: Prof. David Smeulders, Prof. Yvonne van der Meer and University Researcher Michael Boot.