Pre Extraction Research by Gracson Andrews & Dr. Weiping Ban
Dr. Van Heiningen’s research group is working on a project called pre-extraction of modified kraft pulping to increase overall pulp yield and decrease the amount of necessary chemicals for the pulping process. Some background information regarding softwoods and hardwoods is important for understanding the pre-extraction process. Softwoods include woods such as pine, fir, cedar, spruce, redwood, and hemlock. Hardwoods include woods such as birch, beech, aspen, ash, and cottonwood. With standard pulping processes, a percent yield of 40%-45% is obtained with softwoods while hardwoods usually obtain a percent yield of around 50%. However, hardwoods have shorter fibers than softwoods and therefore make a more uniform and consistent product. Because of the longer fibers in softwood, the paper made from softwood is usually stronger than that from hardwood. Any method which increases pulp yield and reduces chemical consumption is beneficial to paper companies because it increases profit and decreases waste. Currently, the group has attained a 5% overall increase in pulp yield, and has also attained a 3% decrease in overall chemical consumption.
The pre-extraction modified pulping process has three main steps. First, the hemicellulose is extracted from the raw wood chips. This step is the extraction step, which is what allows an overall increase in yield. The hemicellulose is set aside for later use. Second, the remaining post-extracted wood chips are made into pulp by cooking with chemicals such as NaOH and NaS (white liquor) at high temperatures around 170 degrees C. The third and final step is adsorption, in which the hemicellulose is redeposited into the pulp mixture. By extracting the hemicellulose before cooking the woods chips to make pulp, a higher overall percent yield is obtained.
The group has successfully created lab size batches of pulp using the new pre-extraction method, but further testing is necessary in regards to the products physical properties. Dr. Ban will be testing the physical properties of the paper made using the pre-extraction process. Because the physical tests will be run on sheets of paper, preparation of 100 grams of product is necessary. Hopefully, the group will be successful in producing 10 to 12 10-gram samples and then concentrating and combining these samples to obtain a larger batch size for use in the physical properties tests. The tests that will be performed include tensile strength, tear strength, burst strength, and fold strength compared against a control sample. Beating, which is blending the pulp to obtain shorter fibers and increase bonding surface area, will also be tested. Tests using different refining times will be performed to determine which beating yields the highest strength paper. A bleaching comparison will also be performed to make sure the bleaching process is not affected by the pre-extraction process.
The experimental analysis of the physical properties testing will allow Dr. Van Heiningen’s group to determine whether this method of pre-extraction can be used to obtain equally viable final products while increasing yield and decreasing chemical consumption in industrial applications.
Interview with Gracson 07/03/07
