Tuesday, June 16, 2009

Paper Bleaching Process


The pulp and paper sector is an important and growing in the United States. But this impressive economic impact is reduced by environmental damage caused by the bleaching process of this industry.
The main reason for the bleaching of pulp lignin content to get a dough lightly. Lignin is degraded during the process of chromophoric groups, which represent 90% of the dark color associated with the unbleached pulp.

Conventional bleaching process of pulp consists of a sequence of steps of alkaline, acid, hydrogen peroxide and sodium, oxygen, dithionite salts, sodium and water BISULFITE process, with a variety chlorination treatment. Chlorination treatment using chlorine gas, hypochlorite salts and chlorine dioxide (ClO2).

The environmental effects of bleaching
Unfortunately, bleaching caused serious impacts on our land.
Release of waste water bleach is the most serious problem for the pulp and paper. Examples of pollutants dioxins and chlorine compounds.

Dioxin
The green represents the levels of chlorine atoms.
The gray area represents the atoms Arbon
Red indicates the areas of atomic oxygen.
Dioxin causes serious damage to our health by setting up in our bodies in large quantities.
Case Study
The Seveso incident focused world attention on the risks associated with the chemical industry. A chemical factory in Seveso, Italy, 200 people employed in the production of 2,4,5-trichlorophenol Swiss Givaudan Corporation, a subsidiary of Hoffmann-LaRoche. On 10 July 1976, a building of pressure in the reactor caused a breach of safety valve, and a cloud of 2,4,5-trichorolphenol and other chemicals were released into the atmosphere.
One of the chemicals released is 2,3,6,7-tetrachlorobenzo-4-dioxin, also known as dioxin recently. It is a byproduct from the manufacture of 2,4,5-trichlorophenol, which is an important intermediate in the manufacture of 2,4,5-trichlorophenoxyethanoic acid (2,4,5-T), a herbicide used for cleaning and hexachlorophene, a bacteria that is used to treat acne, sterilization of wounds of the skin and cleaning.
Dioxin is stable to heat, acids and bases, is practically insoluble in water but soluble in some organic solvents. It is 10 000 times more toxic than cyanide ion. When a person is exposed to dioxin over a long period, residues of dioxins accumulate in the liver and fat cells. Symptoms include liver cirrhosis, damage to the heart, kidneys, spleen, central nervous system, lungs and pancreas, memory and concentration problems and depression. The skin disease, chloracne is caused by the organism in its attempt to get rid of this poison through the skin. Dioxin has a teratogenic effect of genes, leading to birth defects.
Among the children in Seveso, 134 were confirmed chloracne and 250 of the 730 pregnant women chose abortion. The entire city is evacuated. Hoffmann-LaRoche agreed to pay for damages and the establishment of a fund to pay damages to those affected. During a period of several years, many layers of topsoil contaminated with dioxin have been removed and buried 10m under plastic and Clement.
Many countries now use of the herbicide 2,4,5-T, because it contains dioxin and replaced by more expensive, but less dangerous herbicide. The accident in Seveso transferred from the European Community (EC) to a set of guidelines to prevent similar accidents. This law, known as the Seveso Directive requirements for inspection of hazardous industrial activities in the Member States of the EC.
Preventive measures
1. H2O2 quickly replacing chlorine as a bleaching agent to the brightness of the pulp. But in the absence of a stabilizer, a large part of the peroxide is wasted due to the degradation catalyzed by heavy metals in both pulp and equipment. Therefore, many products are manufactured for transition metals that act as catalysts.
2. Another alternative is the use of ozone O3, bleaching by ozone through a high-voltage transmission network of electric field. There are no harmful by-products formed by this process.
3. We, as consumers, can also contribute to safeguarding the environment through the use of unbleached or totally chlorine-free paper.


No comments: