PULP MAKING PROCESS.pptx

Industrial Chemical Process

1. PULP MAKING PROCESS by Johra Said Ali

2. Introduction The making of paper products from wood includes two main technological fields; Pulp technology- deals with the liberation of fibres fixed in the wood or plant matrix Paper technology- this is the knowledge of how to unify the fibres to form the paper web Main raw materials for making pulp is wood although any cellulosic material can be used to make pulp i.e. flax, cotton linters, and bagasse.

3. Introduction Contd. The fibre from nearly any plant or tree can be used for paper. However, the strength and quality of fibre, and other factors that can complicate the pulping process, varies among tree species. In general, the softwoods (coniferous; e.g., pines, firs, and spruces) yield long and strong fibres that impart strength to paper and are used for boxes and packaging. Hardwoods (deciduous), on the other hand, generally have shorter fibres and therefore produce a weaker paper, but one that is smoother, more opaque, and better suited for printing. Both softwoods and hardwoods are used for papermaking and are sometimes mixed to provide both strength and printability to the finished product.

4. Components of Wood Cellulose , the fibers of primary interest in papermaking, comprises about 50 percent of wood by oven dry weight. Lignin, which holds the wood fibers together, is a complex organic chemical. It is largely burned for the generation of energy used in pulp and paper mills. Hemicellulose is similar to cellulose in composition and function. It plays an important role in fiber -to- fiber bonding in papermaking. Several extractives (e.g. oleoresins and waxes) are contained in wood but do not contribute to its strength properties. These too are removed during the pulping process.

5. Structure of wood

6. Pulping Process The main aim of the pulping process is to liberate the fibre from the wood matrix. There are two main processes involved: Mechanical pulping Chemical pulping Other methods include solvent, oxygen, catalytic, and enzymatic processing, but are economically unfeasible.

7. Mechanical Pulping Softwoods are mainly used in this process because of their long fibres. S ince both lignin and cellulose fibres remain intact, the yield of paper per unit volume of wood is greater than that produced by chemical pulping (about 90-95%). Paper produced by mechanical pulping have the below characteristics They produce weak paper The paper discolours and becomes brittle with age Short useful life span The paper is mostly used in manufacturing newsprint, printing papers, towelling, tissue, and coated specialty papers that do not require high-strength. Secondary uses include wallpaper and paperboard.

8. Types of Mechanical Pulping S tone groundwood process, debarked short logs (roundwood) are fed whole against wet stone grinders by hydraulic rams.. The abrasion of the grinding wheel against the wood physically separates the wood fibers . Refiner mechanical pulping (RMP) uses chips instead of logs. The chips are passed through a refiner that has fixed rotating disks operating under a stream of water. Thermo-mechanical process (TMP); the wood chips are steamed for several minutes under pressure and subsequently refined in one or two stages in rapid rotating disks. Chemical Thermomechanical pulping ; it involves treating softwood chips with mild sulfite solutions to modify the lignin and partially delignify the wood prior to grinding in a refiner.

9. Refiner mechanical pulping

10. Chemical Pulping Chemical pulping involves treating wood chips with chemicals to remove the lignin and hemicelluloses, thus separating and cleaning the fibres. Delignification gives the fibres greater flexibility, resulting in a substantially stronger paper (due to greater contact between the fibres in the finished sheet) than can be manufactured from high-lignin fibres produced by mechanical pulping. Paper strength and durability is gained at the expense of fibre yield (may yield only half the fibre that can be recovered by the use of mechanical pulping techniques). Two major chemical pulping processes; Kraft (sulphate) pulping Sulphite pulping

11. Chemical Pulping SULPHATE PULPING (KRAFT) SULPHITE PULPING Cooking Liquor: NaoH , Na2S and Na2CO3 (Recoverable) Cooking Liquor:Aques solution of SO2 and Alkali or Alkaline earthe metals Used for all fibrous materials Used for Hardwoods Digester conditions:2-5 hrs, 10 atms , 170-180 0C 6- 10 hrs, 4-6 atms , 120-150 0C Brown colored pulp (less lignin removed) Dull white pulp (more lignin removed) Less aggressive process pH 12-14 Very aggressive process pH 2-4 Requires thorough bleaching Requires less bleaching Does not destroy hemicellulose Destroys hemicellulose Acidic extractives removed Acidic extractives remain in fibre Manufactures strong brown bags, paperboards and boxes etc Manufactures book paper, tissue papers etc

12. Chemical recovery in Kraft Pulping process

13. Bleaching Process Main aim of bleaching is to increase the paper brightness. Bleached papers are : whiter, brighter, softer and more absorbent. Bleaching sequence depends on: Cost of bleaching chemicals Type and condition of pulp Desired brightness of paper to be produced Response to environmental guidelines and regulations Chemical Pulp Bleaching The main source of colour is from lignin and resins. The process takes place in stages: Chlorination Alkaline Extraction Hypochlorite stage Chlorine dioxide and Oxygen gas stage

14. Mechanical pulp Bleaching Mechanical pulping produces pulp that contains a high percentage of lignin that must be neutralized from yellowing the paper.  If mechanical pulp was bleached with the same methods used for chemical pulps the yield would drop drastically countering the main advantage of mechanical pulping. Therefore , the bleaching system for mechanical pulp must eliminate colored material without degrading the pulp. The bleaching process can either be stage wise or one process is sufficient. The steps involve: Peroxide Reducing Bleaches Continuous Bleaching

15. Chemically produced pulps before and after bleaching