New technology for removing pulp lignin

The paper industry has always been regarded as a big polluter. Paper mills handle 100 million tons of pulp every year, which causes many poisons to be discharged into rivers, lakes and seas. A new issue of the United States "Science News" reported that chemists have developed a new process that can make papermaking a pollution-free operation.

Wood pulp contains cellulose and lignin. Cellulose is a raw material for papermaking, and lignin is a polymer like glue. It is a byproduct that is useless for papermaking. In general, paper mills use chlorine dioxide or chlorine to remove lignin by oxidation. However, this reaction process decomposed lignin to produce chloride contaminants. Therefore, if the paper mill can produce no chloride, pollution problems can be solved.

Wien Stoke and others from the Forestry Products Laboratory of the U.S. Department of Agriculture invented a new method for removing lignin from pulp. The researchers found that several types of polyoxometalates are reusable inorganic catalysts containing oxygen and metals that remove both lignin from the pulp without decomposing cellulose. The first step in the process is to use a polyoxometal cation to oxidize lignin and dissolve it in water. This process will produce an acidic solution of cellulose, but other polyoxometal cations will make the solution neutral, ie the pH is neutral. The second step is to add oxygen to the reaction mixture. The polyoxygen metal cation that was initially added will act as a catalyst, further decomposing the soluble lignin until the reaction product is only water and carbon dioxide. At the same time, the initially added polyoxometalate is returned to its original state and can be used again.

Collins of Carnegie Mellon University said that this new process uses "smart chemistry" but it is not very efficient at the moment and it uses a lot of polyoxygen metal cations. He believes that the polyoxygen metal cations used in the processes of Wayne Stockton and others contain heavy metals. In the event of a leak, it will pollute the paper mills. However, Wayne Stoke said that research on polyoxometalates shows that the potential for heavy metal contamination is minimal. Storromberg, head of technology for ANDRITZ-ASTRROM, which manufactures equipment for the pulp and paper industry, is also very optimistic. He said that the cost of using this new process is the same as that of traditional delignification processes. , but the new process has high benefits. Stromberg predicts that the process based on polyoxometalates will be put into commercial production in about 5 years.