About the Programme

Resources and Mapping

Pretreatment Platform


One of the primary challenges for biomass utilization is the ability to process it continuously and efficiently, ie providing the first stage of the process capability to produce cost-competitive fuels. For HTL, that means proving feedstocks in continuous HTL units. Especially for lignocellulosic feedstock, this forms a challenge due to the biomass predisposition to form two-phase (in the case of coarse particles) or thick (in the case of fines) mixtures. Pumping systems for slurries with high consistency are either expensive or unable to deliver a homogeneous feed at the pressures required in near- or supercritical conditions of water (up to 420 °C and 300 bar). Low solid loading of the feedstock slurries and high energy inputs for biomass comminution has also proven to be major barriers for utilization of lignocellulosic biomasses in continuous HTL facilities.

A number of pretreatment strategies are currently being pursued. One promising approach to solving these issues involves partial solid biomass dissolution in an alkaline medium at medium temperatures. By this approach, almost single phase homogeneous liquid HTL feeds with solid loadings significantly higher than 20 % wt. can be prepared from large biomass particles such as wood chips. The research activities are focused on optimizing the alkaline pretreatment process, integration of the pretreatment stage in the complete process and on evaluating the effect of pretreatment on biocrude product quality. Besides alkaline pretreatment, other pretreatment methods such as lignocellulosics co-processing with recycled biocrude or co-processing with algae are investigated. The latter approach fits into a general focus on feedstock mixing to obtain optimal ratios of components – lignin, cellulose, hemicellulose, proteins and lipids – as well as serving as a conditioning agent for the physical properties of the feedstock slurry.

Conversion technology platform

Green liquids: Hydrothermal Liquefaction (HTL)

HTL of biomass into high value, liquid fuel precursor compounds is a viable, energy efficient and biomass-flexible chemical process; in fact, more so than most other processes for liquid fuel production. However, the variety of biomass is enormous, which poses a technology “understanding” challenge since biomass composition - along with process conditions - is directly related to product yield and quality.

One way of simplifying the biomass diversity is to decompose biomass into its original building blocks, and then considering biomass as various combinations of these. Since any thinkable biomass consists of at most five relevant building blocks (cellulose, hemicellulose, lignin, lipids and protein; starch is not included as it represents food), this negates the need to process each individual biomass at all conceivable conditions in order to evaluate it for HTL.

Research into the conversion step is therefore focused on understanding the conversion of the individual building blocks into value-added chemical compounds, but also how synergies can be obtained through interactions between the building blocks, and how to provide the optimal reaction environment for this. Fundamental understanding of the chemical reactions of the building blocks in a hydrothermal environment allows one not only to predict the yield, composition and quality of the product, but also to the “tailor” the input biomass, e.g. by mixing different biomasses, in a drive to optimize the process.

Research into HTL is conducted across a range of reactor sizes and types, from micro-batch reactors suitable for parametric studies under very well controlled conditions to a pilot scale continuous HTL research facility, capable of processing real feedstocks at approximately 50 kg/h.

Green Gases 1: biogas
Green Gases 2: Biomass Gasification
Green solids – Combustion

Upgrading
 

Even though HTL bio-crude can be processed to quite high quality in terms of oxygen content and heating value, it still falls short of most fuel specifications. In order to reach marketable qualities, upgrading measures need to be taken. Obviously, the less upgrading effort the more cost-effective is the process, so for this part, research is focused on determining the most efficient and least intensive upgrading pathway to reach a predefined quality. Typically, this involves fractionation through vacuum distillation and hydrotreatment, either alone or as part of a refinery feed mixture with fossil crude. Effort is also devoted to understanding miscibility effects with fossil fuels, as well as stability issues. Finished grade fuels can be tested in in-house engine and jet test facilities.

Biorefining and integration