Interreg

Limiting CO2 emissions and protecting the climate presents Germany and the Netherlands with major challenges. A fundamental element that can contribute to the achievement of the climate goals is the use of biomass to generate sustainable energy or as a raw material for new, high-quality products. Biomass plays a special role on both sides of the border, especially in the Euroregio with its agricultural character and numerous biogas plants. The first stand-alone pyrolysis plant in Europe was operational at the end of 2014 in Hengelo. Pyrolysis is a technique for extracting oil from biomass. This involves the thermal decomposition of chemical compounds at high temperatures with the extraction of oxygen, with the result that oil is produced out of biomass. In principle, this is the same process which oil went through for hundreds of years deep in the earth, only artificially. The thus extracted pyrolysis oil can be used as a fuel or as a raw material for biobased materials.

Goal
The INTERREG VA Groen Goud project brings together a German-Dutch consortium of two universities and several small and medium-sized enterprises (SMEs) from both countries to jointly research innovations for the production of pyrolysis oil and the production of high-quality chemicals from low-grade biomass residues. Not only different biomass flows, such as fermentation residues from biogas plants and residues from forestry and agriculture were tested as a starting product, but also different pyrolysis processes and the subsequent pyrolysis oil fractionation. The goal of the project was twofold:
1. The development of pyrolysis as an application for low-quality biomass flows.
2. The use of pyrolysis oil for energy purposes and the processing of the oil into high-quality chemicals.

Approach and workpackages
In order to achieve these goals, five workpackages (WPs) were implemented. In these workpackages, the project partners worked closely together, with the project partner with the greatest expertise in the relevant field taking the lead. In terms of content, the workpackages followed on from each other. In WP 1 an inventory of biogenic residues was made under the direction of FH-Münster. Based on this, a selection was made of ten residual mass flows, which were then tested in the pyrolysis and fractionation process under the leadership of BTG in WP 2. In addition, another selection process was used which resulted in three residues which were tested on a large scale in the mini pyrolysis plant and in the pilot plant of BTG. These experiments showed that the fermentation residues from a NawaRo plant (a biogas plant operating on renewable raw materials) were best suitable for the pyrolysis process. The processing went the most smoothly and the oil production was the most effective. This pyrolysis oil can be used as fuel. However, it was phase-separated, so that further fractionation was technically not possible. In the case of maize digestate, an alternative biomass flow that was added later, the oil could be further fractionated in order to achieve a better result. The processing of the pyrolysis oil was the aim of WP 3: Under the leadership of the Saxion Hogeschool, research was carried out into whether and how the various fractions could be used for high-quality purposes. The focus was on improving the sour water fraction and the pyrolytic sugar fraction. The use of an innovative freeze crystallization process, in which the water is frozen and can be removed as ice from the liquid, has proved successful for both fractions. This process makes it possible to efficiently turn the sour water fraction and the pyrolytic sugar fraction into a suitable fuel and purified water (ice). Due to the watery characteristics of these pyrolysis fractions, microbiological treatment techniques were also tested, as many microorganisms grow very well in watery environments. A long-term test in which the sour watery fraction was fermented into biogas showed that the bacteria are still able to produce biogas after six months. It has been shown that the bacteria can survive in a thinned sour, watery fraction, although it may contain toxic materials for microorganisms. This means that in the future it will be possible to design a new fermenter in which the sour watery fraction continuously will be turned into sustainable biogas and relatively clean wastewater. Besides methane production, pyrolytic sugars and the sour water fraction have also proven to be valuable electron donors for various microbiological processes, for example in sewage treatment plants. It has been demonstrated that sulphate can be converted into sulphide and selenate into selenium. The replacement of currently used electron donors such as glycerol or ethanol can lead to effective cost savings.
In addition, promising experiments were carried out at project partner Foreco, an innovative company in the wood industry, in collaboration with BTG, to use pyrolytic lignin as a raw material for certain resins or composites or as a wood preservative. Twenty-one mixtures (formulations) were produced and are currently being tested in a pilot plant (impregnation). Until these products are ready for the market, further development steps are needed, which will be carried out at the end of the subsidy phase. A patent application is currently under consideration.
Parallel to this, in workpackage 4 and also led by Saxion, the upgrading of the anorganic fraction was investigated. If for pyrolysis low-quality biomass flows, such as dried digestate are used, the amount of anorganic fraction increases to 40-50 %. With this high percentage, it seems wise to also convert the anorganic fraction into a useful product in addition to the pyrolysis oil. The anorganic fraction consists mainly ashes. This is currently considered as hazardous waste by the law because it contains heavy metals. Although the calcium and magnesium in the ash are useful to stabilize the pH value of the soil, heavy metals currently make it impossible to use the ash directly as a fertilizer. However, filtration experiments have shown that it is possible to remove the heavy metals from the ash. This offers the prospect of converting the ash, which until now has been considered as waste, into a product for soil improvement.
Workpackage 5 examined the environmental impact of the production and use of pyrolysis oil as part of a Life Cycle Analysis (LCA) led by BTG. In particular, the use of digestate from a NawaRo plant as an alternative raw material in relation to the use of forest residues was investigated. Although the environmental impacts of using forest residues have been shown to be lower, this does not mean that they are always the better alternative. After all, the digestate is a lower quality waste. In addition, the use of pyrolysis fractions to treat wood preservation was investigated. In this application, the pyrolytic sugars obtained by separating the pyrolytic oil fractions may replace creosote. The creosote produced from coal tar is currently used to prevent wood degradation. The use of pyrolytic sugar to protect wood results in significantly better values than creosote in terms of human health damage and the increase of raw material scarcity, which are two crucial parameters for the evaluation of the environmental impact.
The cost-benefit analysis, which was carried out at the same time, showed that the entire value chain from the pyrolysis of the maize silage to the fractionation of the oil and the use of the sugar fraction as a wood preservative is economically achievable.

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