Historically, different industries have used the forest for different purposes during different periods. The early mining industry used wood as pit props to support the mine galleries but even more for the fire-setting used to blast for the ore. The steel industry in those days was also a big consumer of wood as charcoal. Next to cast its eyes on the forests was the forest products industry, first for sawmills and later for pulp and paper production. Having been King of the Hill for almost a century utilizing wood as its raw material, the forest products industry might soon face the chemical industry as a raw material competitor.
Although we have focused on beech and poplar, any kind of hardwood can be used for production of phenols, says Jürgen Puls
Organosolv - a promising biorefinery process
"We are running a project coordinated by Dechema, Society for Chemical Engineering and Biotechnology, and funded by FNR, Agency for Renewable Resources, in Germany, says Jürgen Puls, vTI Institute of Wood Technology and Wood Biology in Hamburg. This joint project aims to develop a full-scale process in which wood can be used for production of chemicals.
In Germany, beech and poplar are available at reasonable prices while the competition for softwood is stiff. Hardwood species as well as lignocellulosic residues from annual plants are ideal substrates for a lignocellulose biorefinery. The delignification of these raw materials is easier to achieve than lignin removal from softwood.
"At the beginning, this was a six-month project but as the results were promising, a two-year project was launched," Puls adds. "We did a literature study on the organosolv process based on ethanol and chose it as the basic process for component separation. It allows for an effective utilization of all wood components; cellulose, hemicellulose, lignin and extractives."
Organosolv pulping processes have been developed to avoid disadvantages in existing processes, especially with regard to the need for extremely large production units due to complicated chemical recovery systems. However, for the time being the Organocell process in Kelheim in Germany, which started its operations in 1992 based on spruce and with a capacity of 430 tonnes/day, is the only commercial plant.
Figure 1 - The organosolv process separates the different wood components into platform chemicals and products for different uses
From 100 G to 400,000 tonnes
Based on a factorial design, the optimal parameters, - ethanol:water ratio, temperature, time, liquor:wood ratio and addition of catalysts - were identified regarding accessibility of the cellulose fraction for cellulolytic enzymes as well as for lignin recovery and hemicellulose fermentability. Optimization of pulping parameters was achieved in the 100-g scale and verified in the 1-kg scale. Plans are now underway to build a pilot plant with a capacity of 1.25 tonnes/week of wood chips. When the process is developed and fine tuned on that scale, it is hoped that the 400,000-tonne/yr full-scale biorefinery will become a reality.
"As far as we have seen, organosolv pulping is one of the promising options for component separation including a material use for lignin," Puls continues.
High saccharification rates of beechwood polysaccharides can be obtained by high pulping temperatures or by addition of acids at lower temperatures. Co-pulping of wood and bark has been systematically investigated. Presence of bark has no negative effect on the sacharification rate and lignin utilization.
All components can be used
In the process the main components of hardwood; extractives, cellulose, hemi-cellulose and lignin, are separated as shown in Fig. 1. The extractives can be used in pharmacological products. Through enzymatic hydrolyses the main components cellulose and hemi-cellulose are turned into platform chemicals. In this process the lignin precipitates and is separated. It can be used in products like glue and certain plastics but the best value is to break it down (by a pyrolysis process) to phenol monomers, which have very big market opportunities, as they can be used as a raw material for many kinds of plastic.
"The chemical industry has a totally different view on wood as raw material compared to the pulp industry," says Puls. "The pulp industry wants to treat the fibres as gently as possible in order not to jeopardise paper properties like strength and opacity. The chemical industry, on the other hand, is looking for the monomers to be used as building blocs for polymer products like plastic."
"A very important part of the project has been the financial control and calculations to make sure that the end result will be economically viable. That has meant a cost pressure on raw material and process and I am happy to say that the calculations show that the proposed process will be profitable. I am therefore very optimistic about the future potential for the organosolv process as an import biorefinery process," Puls concludes.