Digestion, wood pulp

Wood Pulping. The system Mg(OH)2 S02 H20 is also used in acid bisulfite pulping. Compared to a calcium-based system which is not as amenable to regeneration of the pulping bisulfite (87), fewer technical problems are encountered in the digesters, evaporators, or recovery boiler of the Mg-based process. In the presence of excess SO2, bisulfite forms in a 43% MgSO solution, at 25°C and 101.3 kPa (1 atm) SO2 pressure, to increase MgSO solubihty. 

Kraft Process. The dominant chemical wood pulping process is the kraft or sulfate process. The alkaline pulping Hquor or digesting solution contains about a three-to-one ratio of sodium hydroxide, NaOH, and sodium sulfide, Na2S. The name kraft, which means strength in German,... 

Tall oil rosin is a by-product of paper manufacturing. Raw wood chips are digested under heat and pressure with a mixture of sodium hydroxide and sodium sulfide. Soluble sodium salts of lignin, rosin, and fatty acids are formed, which are removed from the wood pulp as a dark solution. The soaps of the rosin and fatty acids float to the top of the mixture, where they are skimmed off and treated with sulfuric acid to free the rosin and fatty acids. This mixture, known as cmde tall oil (CTO), is refined further to remove color and odor bodies fractional distillation separates the tall oil rosin acids from the fatty acids (see Tall oil). 

The principle uses of Na2S04 are in the manufacture of paper, soaps, and detergents. These accounted for 65% of U.S. consumption from 1990 to 1995, representing a significant shift from 1980 when paper production alone consumed 67%. Pulp (qv) and paper consume only 25% (2). The kraft paper process uses a mixture of sodium sulfide and sodium hydroxide to digest wood chips. Both the sulfide and hydroxide are generated, starting with sodium sulfate as the raw material. 

Holz-kalk, m. pyrolignite of lime (crude calcium acetate), -kaiton, m. wood-pulp board, -kassle, /. cassia lignea, coarse cassia bark, -kasten, m. wooden box, case or vat. -kirsche. /. wild cherry. -kistchen, n. wooden box. -kitt, m. wood cement, joiner s putty, -klotz, m. wooden block, wood block, -kocher, m. (Paper) digester (for wood), -kokle,/. charcoal (from wood). 

Cellulose produds There is little scope for the use of austenitic steels in the alkali processes for the digestion of wood pulp, but both molybdenum-free and molybdenum-bearing steels are extensively used for sulphite pulp digestion, choice depending on concentration, temperature and working experience. 

As described in Section 4-1. one important class of chemical reactions involves transfers of protons between chemical species. An equally important class of chemical reactions involves transfers of electrons between chemical species. These are oxidation-reduction reactions. Commonplace examples of oxidation-reduction reactions include the msting of iron, the digestion of food, and the burning of gasoline. Paper manufacture, the subject of our Box, employs oxidation-reduction chemishy to bleach wood pulp. All metals used in the chemical industry and manufacturing are extracted and purified through oxidation-reduction chemistry, and many biochemical pathways involve the transfer of electrons from one substance to another. 

Wood chip digestion, spent pulping liquor Water High BOD, color, may contain... 

The proximate analyses of many types of by-products used in livestock feed (e.g. brewers grains, coffee grounds, olive cake, peanut hulls, wood pulp) together with digestibility and energy values are given by Boer and Bickel... 

Sulfur dioxide, SO2, is of considerable technological importance as a fungicide, a bleach, a refrigerant, and a digesting agent for wood pulp. It is generally prepared by burning sulfur or sulfides smaller amounts may be prepared in the laboratory by acidification of sulfites. The molecule is nonlinear ... 

In the paper industry, digestion of wood pulp with such compounds as sodium sulfate, sodium... 

Chlorine has been used to bleach wood pulp. Many pulp mills employing the Kraft pulping process prepare sodium hydroxide (needed to digest wood chips) on-site via the electrolysis of brine, a concentrated aqueous solution of sodium chloride. 

KRAFT PROCESS - A wood-pulping process in which sodium sulfate is used in the caustic soda pulp-digestion liquor. Also called Kraft pulping or sulfate pulping. 

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