By Kenneth Norris, Contributing Editor, Pulp & Paper International
The breakthrough could substantially benefit regions such as China and India, which together account for approximately 80% of the total global non-wood paper production. By significantly boosting the process economics when using straw as a feedstock, papermaking could improve in areas that suffer from limited wood resources. In the US, the use of VSEP technology could increase the domestic supply of non-wood sourcing material, reducing transportation costs for feedstock, and open new opportunities for various other agricultural cellulosic materials in paper production.
"Long term, the use of non-wood paper could become a significant portion of the overall paper production market," says Greg Johnson, president of New Logic Research. "This source of cellulose would satisfy a market demand for non-wood paper or recycled paper as part of many company's pledge to sustainable practices."
Profitable material
With an eye toward economics and sustainability in papermaking, Dr. McKean has been developing a process that uses wheat straw to make paper. An expert in bioscience and paper manufacturing, his research focuses on black liquor as a byproduct of the pulping process. In partnership with New Logic Research, Dr. McKean has been studying the performance of VSEP nanofiltration in concentrating low molecular weight lignin recovered from black liquor.
Working with wheat farmers in eastern Washington State, Dr. McKean considered how the existing VSEP technology could be expanded to convert waste straw into a profitable material. By implementing straw within a commercial papermaking process, the fiber can be purchased from farmers that would have previously discarded this otherwise usable material, typically by burning the crop residual to clear the land and return nutrients to the ground.
"By using this source of cellulose that would normally be wasted, an offset to tree cellulose consumption can be accomplished by reducing the need for wood pulp," says Johnson. "Another part of the overall benefit of this process is that the cellulosic material can be extracted and used instead of being burned away in the fields. This allows 100% beneficial use of the wheat plant materials."
Using straw to make paper may have stronger economic benefits than wood, especially in regions where wood resources are limited or cost-prohibitive. Historically, paper has been made from a variety of crops as source materials, including straw, hemp and linen. These crop fibers are harvestable within a year timeframe, as opposed to wood that can take years or decades to harvest. And while wood pulp does yield a brighter whiteness in the final product, alternative fibers can be superior in terms of cost, technical performance and environmental impact.
Valuable byproducts
Black liquor derived from wheat straw processing can be filtered using the same methods as with wood pulp production. The VSEP technology is able to process either type of wastewater to separate lignin from the black liquor and produce a clear caustic filtrate that can be reused. Lignin recovery is a high value process and there are multiple uses for lignin in the pulp and paper industry, including using it as a biomass product for energy production, either by combustion or through gasification to a liquid fuel.
In a lab-scale model, Dr. McKean and his research team have demonstrated using straw in the papermaking process. Straw hay is added to a pulp digester and after conversion to a slurry, a roll of straw pulp paper emerges. The black liquor residue is sent through the VSEP nanofiltration system, extracting the lignin in a concentrate, leaving a clear filtrate containing wood sugars and minerals.
The theory is to use centralized pulp plants located near wheat crops. Farmers would be able to extract value by way of pulp, lignin and glycols from wheat straw. Once the value-added products are extracted, these minerals can be returned to the land as would be normally done through burning. The process allows the farmer to be financially rewarded for their wheat crop and gain the additional benefits for the farmland.
"Dr. McKean's extensive research has show definitively that VSEP is highly effective in recovering valuable byproducts from the papermaking process," says Johnson. "The only thing more gratifying than seeing his pilot plant running smoothly is meeting with the farmers who will directly benefit from the new process."
New Logic and others are in the early stages of discussions to install a larger pilot plant near a wheat farming area. The larger plant would be a continuous demonstration facility for potential investors and clients. Dr. McKean is also continuing his research, looking at ways to fine tune the wheat straw process for commercial application.
As a side benefit to recovery of lignin by way of VSEP, the raw material can be used as a chemical industry base stock for fertilizer, adding to its value as a commodity and introducing a secondary revenue stream.
