Kraft Pulping Liquor Chemistry
Kraft pulping is a process which uses chemicals to convert wood chips into individual fibers to make paper or other cellulose-based products. There are a number of chemical processes for pulping wood, but the kraft process is by far the most prevalent. One reason for this is that the chemicals in the cooking liquor can be recovered, recycled, and used again. This module will cover the chemistry of kraft cooking, the testing of the cooking liquor, and the process for reclaiming the active cooking chemicals.
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Learning Objectives
• Identify the major compounds, which make up wood
• Describe white liquor and its chemical makeup
• Identify the major steps in the kraft liquor cycle
• Describe how wood is “cooked” to become pulp
• Describe how to determine AA, EA, TTA, and sulfidity
• Describe the hazards associated with cooking liquors
• Describe the impact of high chlorides in the liquor cycle
• Describe how chlorides can be removed from liquor
Specs
| Course Level | Intermediate |
| Languages | English, Portuguese, Polish, Russian |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
What is the “”liquor cycle”” in the kraft pulping process?
The term “”liquor cycle”” refers to a sequence of processes which reclaim and recover the primary chemical components from spent cooking liquor for reuse.
What is the chemical compound use in the kraft pulping process which increase yield and fiber strength?
The compound which is added to enhance cooking liquor is sodium sulfide (Na2S).
What the “”color”” name for the liquor which is put into digester to cook chips?
Liquor charged to the digester for cooking is called “”white liquor””.
What is a common laboratory test which yields alkalinity and sulfidity values for a liquor sample.
The commonly used triation for testing alkalinity is called the “”ABC test””.
What is the term for chemical compounds which are not involved in the primary liquor reactions, but can have a large effect on operations.
These non-primary compounds are called “”non process elements””.
Sample Video Transcript
Before discussing the chemistry of pulping, it is important to know something about the composition of wood. Wood is made up of a wide variety of complex, organic compounds. The three main compounds are cellulose, hemicelluloses, and lignin. Cellulose makes up 40% to 45% of the dry weight of wood, and it consists of long, straight, strong chains of glucose molecules. Hemicelluloses are shorter branched chains of glucose and other sugars which are not as strong as cellulose. The amount of hemicelluloses in dry wood is typically between 20% and 30%. Cellulose and hemicelluloses function as supporting materials in the cell walls in wood fibers. Lignin refers to a group of organic compounds which are present in the outer layers of the cell walls and serve as the glue which holds the fibers together.
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