Pulp and Paper Production

Enzymes in Pulp and Paper Production. Enzyme-modified starch has been used for adhesives to strengthen paper base and for surface coating. Developments since the late 1980s of further uses of enzymes in papermaking include pitch control and bleach boosting, (see Paper Pulp). 

However, in heavy industry, meaning metallurgical (steel and aluminum) processes, mining, petroleum refining, pulp and paper production, and the process industries like ehemical and pharmaceutical production, potable water, wastewater, edible products, and manu-... 

The U.S. industry has several advantages over the rest of the world market modem mills, a highly skilled work force, a large domestic market, and an efficient transportation infrastructure. Major export markets for pulp are Japan, Italy, Germany, Mexico, and France. The U.S. Department of Commerce anticipates exports to grow faster than production for domestic markets through 2004. World Trade Organization (WTO) efforts to reduce tariffs include those on pulp and paper products if these are successful, the U.S. industry expects pulp and paper export rates to increase even further. 

U.S. EPA, National Emission Standards for Hazardous Air Pollutants for Source Category Pulp and Paper Production, 40 CFR Part 430, U.S. EPA, Washington, 1993. 

Chlorinated compounds PCP, PCBs, PCDD/Fs Manufacture of pesticide and herbicide (D) Wood preservation sites (P) Pulp and paper production (P) Municipal waste incineration (P,D) Plastics, fire-retardants manufacture (P,D) Chlorinated phenols -3.6 Chlorinated hydrocarbons - 2.4 [43, 44]... 

One of the most debated environmental issues of the past fifteen to twenty years has been the exploitation of the forests for wood for paper making. Approximately 30% of the earth s land surface is forested, and around half of this is harvested commercially for industrial purposes (Chapter 1). Over 80% of this wood for industrial use comes from the forests of North America, Europe and what was formerly the Soviet Union. Wood has been the primary fibre source for pulp and paper production world-wide for many years, and it is necessary to take a global view of its consumption. Wood consumption world-wide has more than doubled since 1950 from 1.5 billion to 3.5 billion m3 (United Nations Food and Agricultural Organisation). Approximately half of this is used for fuelwood and half for industrial use. The principal driving force for this increase in consumption has been the increase in world population which shows a close correlation with wood consumption (Figure 10.1). 

Dioxins are a particular group of chlorinated organic molecules which have been associated with pulp and paper production and are a concern because of their extreme toxicity. There are two groups of molecular types which fall into the general category referred to as dioxins. These are the polychlorinated dibenzodioxins (PCDDs) and the polychlorinated dibenzofurans (PCDFs). The structures of these molecules are shown in Figure 10.4. 

Wood logs are pushed under the revolving grindstone and crushed by mechanical pressure to yield low-grade pulps. Lignin is not removed during this process and therefore imparts a dark color to the pulp and paper product. 

Marketable goods (e.g., pulp and paper products) can be produced from the vegetation. 

The most important industrial alkalis are the weak alkali ammonia (Section 9.3), caustic soda (sodium hydroxide), and lime (calcium oxide).1-6 For many industrial and agricultural purposes, the most economical source of alkali is lime, which is used in steelmaking and other metallurgical operations ( 45% of U.S. production of lime), in control of air pollution from smokestack gases (Chapter 8), in water and sewage treatment (Sections 9.6 and 14.5), in pulp and paper production (Section 10.4), in reduction of soil acidity, in cement and concrete manufacture (indirectly, as discussed later), and in many chemical processes such as paper making (Section 10.4). In short, lime is one of the most important of all chemical commodities. 

Industrial surfactants find uses in almost every industry, from asphalt manufacturing to carpet fibers, from pulp and paper production to leather processing. Examples of the types of chemicals used as surfactants are fatty alcohol sulfates, alkanolamides, alkoxylates, sulfosuccinates, amines, quaternaries, phosphate esters, acid esters, blockcopolymers, betaines, imidazolines, alkyl sulfonates, etc. 

COD and colored compounds in solutions of the pulp and paper production. 

In the past three years there have been major increases in the utilization of waste tires as a fuel. Applications have included power plants, tire manufacturing facilities, cement kilns, and pulp and paper production. These applications have demonstrated the capability to extract energy value from the tires in an environmentally acceptable manner, while at the same time alleviating tire disposal problems in their communities. 

While the results of the paragraph above raise many questions for which no answers are available, they serve to outline some of the challenges that lay ahead on the way to understanding, and hopefully solving, the problem of photoyellowing of pulp and paper products... 

EPA. 1990c. Dibenzo-para-dioxins/dibenzofurans in bleached wood pulp and paper product referral for action. U. S. Environmental Protection Agency. 55 Federal Register 248 53047-53049. 

Over 90% of acrylamide is used to make polyacrylamides (PAMs), and the remaining 10% is used to make N-methylolacrylamide (NMA) and other monomers. Water treatment PAMs consumed 60% of the acrylamide PAMs for pulp and paper production consume 20% of the acrylamide and PAMs for mineral processing consume 10% of the acrylamide283. 

G. F. Wallace, The Application of Atomic Absorption Spectrophotometry to the Analysis of Pulp and Paper Products, Print. Reprogr./Test. Conf. (Pap.)., 1977, p. 169. 

The case study presented here deals with a pulp and paper production process. The plant produces Bleached Eucalyptus Kraft Pulp, using the ECF process (Elemental Chlorine Free). The Kraft pulping process is performed in two different phases, which influence the final pulp quality the cooking process of wood chips (eucalyptus globules) followed by the pulp bleaching. The cooking process is the phase that most contributes to the preservation of the main pulp characteristics, which, in turn, will ensure high quality paper. 

Crude 10% sodium hydroxide containing sodium chloride is purified in a similar manner to the product of the causticization process. The water is evaporated in nickel or nickel-clad steel (to reduce corrosion) multiple-effect evaporators to about 50% sodium hydroxide concentration. At this concentration, sodium chloride is only about 1% soluble (2%, on a dry basis) in the more concentrated caustic so that the bulk of it crystallizes out and is filtered off. This quite pure sodium chloride is recycled to the cells. Lor many purposes, such as for pulp and paper production, this purity of 50% sodium hydroxide is quite acceptable. If higher purities are required, sodium hydroxide may be separated from residual water and salt by chilling to the double hydrate crystals NaOH 2HiO, m.p. about 6°C, or as NaOH 3.5HiO, with a m.p. of about 3°C, or by counter-current extraction [9]. The sodium hydroxide obtained after these steps contains 2-3 ppm sodium chloride, equivalent to the purity of the mercury cell product ( rayon grade ) [10]. Concentrations of 73% and 100% sodium hydroxide (see details, Section 7.5) are also marketed. 

Mercury loss in the decomposer section occurs as finely divided metal droplets in the sodium hydroxide stream as a result of the vigorous interaction between the deionized water and sodium amalgam streams to ensure as complete sodium removal from the mercury as feasible. Mercury concentrations in the range of 0.5-10 p-g/g (0.5-10 ppm) in the sodium hydroxide as it leaves the decomposer represent a mercury loss rate of 1-20 g/tonne of chlorine produced. This ultimate loss occurs indirectly through processes, which use the sodium hydroxide, such as pulp and paper production. Efficient centrifuging and filtration on porous carbon or other caustic resistant media (occasionally both) are procedures capable of reducing the mercury concentrations in 50% sodium hydroxde to about 0.1 pg/g. 

M.D. Afonso and M.N. Pinho, Membrane separation processes in pulp and paper production. Filtration Separation, 28 (1991) 42-44. 

This final section on extractives explains why extractives are important in utilization, and why processing studies on wood ignore them at their peril. They can be important to solid wood processing as well as to pulp and paper production, and the problems to which they give rise are still being examined and sometimes cured. In some instances wood extractives are beneficial The effects of extractives listed below are only indicative and are not arranged in order of importance. 

There are standard tests for pulp and paper products. Generally pulps are evaluated as pulp handsheets. Some of the more important tests for pulps, and those used frequently on papers, are described later. The tests and the principles behind them are illustrated in Figure 13.3. 

EPA. 1993b. U.S. Environmental Protection Agency. NESHAP for source category pulp and paper production. Proposed rule. Federal Register 58 66078. 

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