Using a catalyst to improve the Deilgnifying (Bleaching) Activity of Hydrogen Peroxide Allowing for a Potential Replacement of Chlorine-Based Delignification Processes
Overview the U.S. paper and pulp industry produces about 70 million lb of paper and paperboard each year from its 600 paper mills. Production of paper requires that raw wood be converted into pulp. This process generally requires the lignin portion of the wood to be decomposed, usually by chemical means, allowing isolation of polysaccharide pulp, which is then used to make paper. Such a chemical delignification process (from which about 90% of all pulp is made) generally requires 1 lb of chemicals for every 5 lb of paper produced.
Problem. The manufacture of bleached (white) paper generally requires the use of chlorine-containing chemicals to remove residual lignin from the pulp in the final stages of the delignification process. The use of these chlorine-containing chemicals in the bleaching process creates organochlorine waste products (often called absorbable organic halides or AOXs), including dioxine and furans. These substances tend to bioaccumulate and biomagnify and are suspected of causing various health problems among humans, including cancer.
Solution. Tetraamido-macrocyclic ligand (TAML) activators developed by Terrence Collins of Carnegie Mellon University work as catalysts to increase the oxidizing ability of hydrogen peroxide (H2O2) The use of H2O2, along with these activators has the potential to replace the chlorine-containing compounds that are currently in use in paper delignification and bleaching processes. H2O2 bleaching produces only envi ronmentally benign byproducts, namely water and oxygen, thus eliminating the chlorinated organic byproducts that are associated with chlorine delignification and bleaching processes.
Background
It is estimated that in the United States, the per person consumption of paper pulp is almost 600 Ib each year. Paper pulp can be produced from raw wood through either a chemical or mechanical delignification process.
Wood is composed of about 70% polysaccharides (a combination of cellulose and hemicellu lose, which is used to make paper) and 30% lignin (which acts as a "glue" to hold the polysaccharide fibers together) In making paper, most of the lignin must be removed, because its presence in paper creates a brown discoloration 12 In addition, significant quantities of lignin in paper that is initially white can cause the paper to "yellow" over time. Almost 80% of the world's paper mills rely on a Kraft process to remove lignin from the raw wood starting material. In this process, logs are chipped into smaller pieces and then placed in a bath of sodium hydroxide and sodium sulfide, which results in depolymerization of the lignin (Figure 1). As the lignin breaks down, the wood chips lose their rigidity, and a slurrylike solution of polysaccharides is formed (pulp).