Process Holds Promise For Recycling Pressure Treated Wood

Todd F. Shupe  |  7/29/2005 1:34:17 AM

News Release Distributed 07/27/05

A process for recycling treated wood products could save on disposal costs and liability concerns by keeping treated wood out of high-cost landfills, according to developers at the LSU AgCenter.

The process uses liquefaction to extract chemicals from the wood and leave a liquefied wood product that is chemical free. Experts say it’s environmentally friendly and appears to offer economic benefits.

"Disposal of decommissioned preservative-treated wood has increasingly become a major concern because the popular disposal options – incineration or land filling – are becoming more costly and impractical," said Dr. Todd Shupe, a researcher in the LSU AgCenter’s School of Renewable Natural Resources.

"Recycling – both of treated wood and of the preservatives – must be considered as a viable alternative," he said. "Open burning of treated wood generally is not allowed by law and not recommended by the treating industry"

Finding new uses for treated products is important to Louisiana because nearly half of the state’s southern yellow pine lumber production is treated with either creosote, penta or chromated copper arsenate (CCA). Most material was treated with CCA before the industry voluntarily phased CCA out for consumer uses. Now, the three chemicals are largely used for industrial applications ranging from utility poles to highway and bridge guardrails.

"Wood treaters in the United States can no longer treat wood with chromated copper arsenate for residential uses, such as lumber," Shupe said.

CCA is a chemical wood preservative containing chromium, copper and arsenic. CCA, which has been used to treat lumber since the 1940s, is used to protect wood from rotting caused by insects and microbial agents.

The U.S Environmental Protection Agency has classified CCA as a restricted-use product for use only by certified pesticide applicators and has worked with manufacturers to voluntarily phase out CCA use for wood products around the home and in children's play areas. After the end of 2003, no wood treater or manufacturer may treat wood with CCA for residential uses, and pressure-treated wood containing CCA is no longer produced for use in most residential settings, including decks and play sets.

Nevertheless, CCA-treated wood products are still widely used in industrial applications such as utility poles, railroad crossties and guardrails, Shupe said.

The products eventually will come out of service and have to be dealt with, said Doug Arnold, president of Arnold Forest Products in Shreveport. "We need to do something with it when it’s out of use."

Arnold’s company produces CCA-treated products such as guard rail posts for state agencies. He said the industry needs a less-expensive method for disposing of treated wood products, and he sees the LSU AgCenter-developed liquefaction process as a reasonable alternative.

"The drive behind it is to use what we’ve put on the market in the past and recycle it," Arnold said. "The technology is here. We just need to take advantage of it."

In the process developed by Shupe and his colleagues, wood is ground and liquefied with an organic solvent. "The process uses relatively low temperature, short reaction time and small amounts of organic reagents," Shupe said.

Shupe said the process is economically viable and environmentally friendly. "This approach has the best opportunity for success," he said. "There’s zero discharge, and it produces multiple products."

The end products from the process include the chemicals originally used to treat the wood as well as nontoxic, liquefied wood that can be used for resins, molded wood products, foams and plastics.

Using liquefaction to turn wood into liquid was developed in the 1970s in Japan. There, the liquid wood is used for manufacturing a variety of resins and molded products, said Chung Hse, who has been working with Shupe on the project.

In the LSU AgCenter process, the wood is put in solution with an organic solvent, said Hse, a principal wood scientist at the U.S. Department of Agriculture Forest Service Southern Research Station in Pineville and an adjunct professor in the LSU AgCenter.

The liquefied wood can be diluted with a solvent and then mixed with other chemicals so the CCA can be removed from the solution. After the metals are taken out, the process yields liquified wood for other applications.

Hse said the work is done in a pressurized cooker at about 150 degrees centigrade.

Shupe said the process efficiently and effectively takes the metals out of the liquid wood at a rate higher than 99 percent for all three elements.

"Nobody has shown an ability to remove those three elements at that high a rate," Shupe said. "We can do it quickly and efficiently."

The next step in the research is the development of a pilot plant to see if the process can be done economically, as well, Shupe said.

The wood that comes out of the reaction is "finer than finely ground – it’s very, very viscous, syrupy," Shupe said. "It’s actually liquefied."

"The process is now technologically viable," Shupe said. "Once the technology proves economically viable, there will be a domestic market."

He noted competitive products include steel, which is non-renewable and requires significant energy consumption for production.

"Research along these lines is helpful in facilitating the long-term future of the wood preservative industry," Shupe said. "The industry uses a renewable resource and provides jobs.

"Even if CCA-treated wood products are no longer produced, there’s still a lot of CCA material being decommissioned, and it needs to be disposed of," Shupe said. "The material that’s obsolete, damaged, whatever – it will sustain a recycling industry for many years."

The liquefaction technology can easily be used to create products from non-treated wood, as well, Shupe said, adding that one of the products that can be made from preservative-free liquefied wood is phenol.

With oil prices more than $50 a barrel, liquefied wood could provide a cost-effective alternative for oil-based phenol, he said. 

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