In search of an environmentally friendly pulping process for wood residues

29. October 2020

Lignocellulose (LC) from wood or annual plants is the most frequently occurring renewable raw material on earth.

LC-containing raw materials are used in the production of paper and materials as well as in obtaining material components for fuels, synthetics and basic components for the chemical industry. In addition, considerable amounts of LC are energetically exploited, although legal requirements demand to prioritize material utilisation. LC-containing residues and waste accrue, for example, in the timber and forestry industry and in agriculture. Today’s preferred source materials for the manufacture of biofuels and high-grade platform chemicals are agricultural residues from annual plants, such as grain straw. Specific biorefinery concepts and process routines have already been developed for such organic raw materials and introduced to the market. Timber residues, such as wood of inferior quality, landscape conservation wood or used wood, are being exploited to a lesser extent in the production of paper and materials. However, the larger part of wood residues is not recycled materially. The main reason for this is insufficient efficiency, the environmental compatibility and profitability of available wood-pulping and hydrolysis processes. 
Available processes for wood pulping and the prehydrolysis of wood are mainly based on chemical processes with concentrated acids, alkaline solutions or organic solvents as well as high temperatures and pressures, and some of them are no longer economical today. As alternatives, research efforts focus on steam explosion (SE), CO2 explosion and treatment with hydrogen peroxide. Although the most extensive investigations have been carried out on the SE process so far, no industrial application on wood has yet been implemented. Solution for the technical and scientific issues primarily require basic experimental investigations into model raw materials.
The objective of the recently launched project is the “Material Flow Analysis and Modelling of the Steam Explosion Process for Pulping Lignocellulose as Basis for Biorefinery Applications”. This is based on the complete recording of all solid, liquid and gaseous material flows as well as investigations into the influence of various raw material and process parameters on the quantitative and qualitative composition of the pulping products. The latter is carried out by taking into account product properties that have hardly been studied so far but are decisive for biorefinery applications, with the degree of separation of lignin and cellulose components and cellulose crystallinity in particular. Appropriate qualitative and quantitative analytical methods are being developed. Furthermore, an intensification of quasi-continuous SE pulping by new approaches in process control and equipment modifications is envisaged. 
After accomplishing the project, the then elaborated model can – at low testing and optimisation efforts – be adapted to end-product-oriented SE control for specific source materials and product requirements. This facilitates the fast and cost-saving integration of SE pulping processes into various processes for the holistic material recycling of wood and wood residues for the production of basic chemicals and fuels. Corresponding applications are expected to be realised within the scope of application-oriented follow-up projects or industrial research projects with industrial partners.

The project is co-funded by the Federal Ministry of Economics and Energy within the framework of pre-competitive research for small and medium-sized enterprises via the INNO-KOM innovation support program. The project sponsor is the EuroNorm GmbH.

The contact person for the “STEAMEX” project is:
Marco Mäbert (IHD)