Paper and pulp

The pulp and paper industry produces paper, cellulose and its derivates from wood. 

In conventional pulp bleaching, chlorine, hypochlorite, and chlorine dioxide are used with or without intermediate alkaline extraction steps. The first step in conventional lignin-dissolving bleaching is the chlorination. Qilorine water is normally used for this chlorination. It converts the residual lignin to products, that are soluble in water and/or alkali. Chlorine and hypochlorite react primarily with the benzene or phenol rings of lignin, in which substitution and oxidation reactions take place. In a separate extraction step, the unwanted soluble substances are removed with water and/or diluted sodium hydroxide solution. 

The effluents from the bleaching process contain chlorinated organic compounds and cannot be disposed of by combustion with the spent cooking liquor. It pollutes the waste water stream with its oxygen demand and its toxic and genotoxic effects, it may even contain polychlorinated dibenzo-ftirans and dibenzo-p-dioxins in small concentrations. The stability of the chloro-organic compounds inaeases its biological and environmental persistence and this increases the tendency to bioconcentration in 

Chlorine is an very effective, selective and inexpensive bleaching agent, but the brightening of the pulp is not sufficient. Therefore, as a third step, the brightening was effected by chlorine dioxide, which is extremely effective and selective in brightening, but is also expensive. 

The production of the chlorine dioxide is carried out at the pulp mill by the reduction of sodium chlorate in dilute aqoeous solutions 

Although chlorine dioxide is toxic and, when present in sufficiently high concentration, explosive, a variety of processes are available for safe on-site 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Hydrosulfite may be purchased as a proprietary formulation containing buffering and stabilizing agents, usually as a dry powder, but sometimes as a solution. The powder is pyrophoric and should be kept dry to avoid the possibiHty of fires. Alternatively, solutions of sodium hydrosulfite may be generated on-site by using a purchased solution of sodium borohydride and sodium hydroxide to reduce sulfur dioxide. 

Recent estimates (19) of U.S. bleaching chemical costs are as foUows  

Traditionally, the pulp and paper industries used chanicals at various stages. In order to reduce the environmental impact of the chanicals, they were replaced by enzymes. Jaworski (2001) documented that enzymes used in the pulp and paper industries reduces the use of chlorine by 10% to 15% and water by 18%. In addition, the use of enzymes improves paper brightness and strength. 

The major amount of corrosion in the pulp and paper industry is in the paper-making process, which uses large amounts of process water. The amount of corrosion inhibitors consumed in the pulp and paper industry from 1996 to 1998 increased an average of 2%/year. About 198 million was spent on corrosion inhibitors in 1998. 

During the past 35 years, the pulp and paper industry had moved from open-water systems to closed-loop systems, thereby increasing the severity of the environment. These white liquors are acidic and very corrosive, and severe crevice corrosion problems may occur whenever the process flow is halted. 

The paper industry in the United States is a mature industry but is expected to maintain steady growth in the upcoming years. 

The demand for paper products is closely related to the economic growth and disposal income. Most paper is consumed by packaging, printing, publishing, and business communications, which are directly tied to business expansions. Similarly, consumption of cardboard and paper shipping containers is tied to the demand for industrial production. 

Competitive materials and technologies such as plastics for packaging and electronic publications/communications are encroaching on traditional markets for paper products. These are not realistically expected to replace paper but will curtail the growth in view of the expected paperless society in the future. 

The working conditions in paper-making favour the growth of many species of micro-organisms in pulp, coating mixes, sizes and other materials used in the industry. Mildew stains on pulp, slime formation in the pulp circulation system and the decomposition of coating mixes are examples of this. 

Appropriate active ingredients for non-persistent slimicides one finds above all among the compounds with activated halogen groups (III.7 and III.15). Other active ingredients belong to the carbamates (III.9 and III.3.4.10.1) and the heterocyclic N,S compounds (III. 13). It is also proposed to use glutaraldehyde (III.2.3) or 3,5-dimethyl-tetrahydro-2-thiono-thiadiazine (III.3.3.16). 

Oxidizing agents (III. 19) are recommended, too, for slime prevention as far as the oxidizing properties of these agents can be tolerated. Using chlorine, hypochlorites or chlorine dioxide problems may arise by the enrichment of corrosion causing chloride ions in the system. 

Moist pulp, papers with an antimicrobial finish, hygienic papers (e.g. paper towels) and mould resistant packaging material (e.g. soap wrappers) are produced with the addition of non-volatile microbicides which are virtually insoluble in water, so that good retention is guaranteed. Water soluble microbicides can be applied together with size solutions and coating mixes. Proposals are 2-phenyl-phenol and Dichlorophen (III.5.4.1 and III.5.7.3) and carbamates (III.9). 

For the in-tank protection of coating mixes, filler suspensions and size solutions preservatives which are used for aqueous coatings or glues and adhesives are suggested. 

In the production of ammonia-based sulfite pulp, the amount of ammonia used per ton of pulp varies from mill to mill. The industry average is about 125 pounds (56.7 kilograms) of ammonia per ton of sulfite pulp. This industry also uses ammonia for stack gas scrubbing and wastewater treatment57. 

In this section, some details will be given of two other key industries where the uses of peroxygens are very much linked to environmental factors pulp and paper bleaching and metal extraction, recovery and finishing. 

Also summarised in this section are the uses of peroxygens in hydrometallurgy, metal recovery/recycling and metal surface treatment, since this is another sizeable application area where environmental gains can be obtained. 

Stock The pulp stream within the manufacturing process 

CTMP ChemoThermoMechanical Pulp APMP Alkaline Peroxide Mechanical Pulp 

Any subscripted numbers refer to % of chlorine equivalent used 

Each of the compounds listed in Table 16.4,1 can be identified by its pyrolysis products and may be used for the characterization of a material (chemical or mechanical pulps), or for the determination of the nature of specks or deposits in pulp or paper, etc. Of particular interest may be the use of pyrolysis for the identification of specific types of inks on paper [87]. 

One example of the use of pyrolysis for the analysis of pulp is the determination of the amount of sulfur. This can be done by measuring the amount of H2S, COS, SO2, CH3SH, CH3SCH3, and CS2 in the pyrolysates. The study [88] has been done on H, Na and Ca forms of thermomechanical pulp (TMP) and on H, Na and Ca forms of kraft pulp 

Another application of Py-GC in paper analysis has been the determination of wet strength polyamide-epichlorhydrin (PAE) resins [89]. 

Pyrolysis of paper cross-linked with (PAE) resins generate compounds that are easily distinguished from those of cellulose. Table 16.4.2 shows several compounds in the pyrolysate of PAE. 

A linear dependence was found between the level of some of these components (such as cyclopentanone) and the level of PAE in paper. 

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Through the use of lab tests implemented by the pulp and paper companies in the United States and Canada it was determined that all but one manual technique were both unrepeatable and inaccurate. During some years ago the operators of black liquor recovery boilers have been able to take advantage of the latest teehnology to inspect the wall thickness of the near drum generator tubes. The technology utilises immersion ultrasound and automated computer... 

Pulp and paper Pulp and paper industry Pulp and paper mills Pulp bleaching... 

Separation of Fatty Acids. Tall oil is a by-product of the pulp and paper manufacturiag process and contains a spectmm of fatty acids, such as palmitic, stearic, oleic, and linoleic acids, and rosia acids, such as abietic acid. The conventional refining process to recover these fatty acids iavolves iatensive distillation under vacuum. This process does not yield high purity fatty acids, and moreover, a significant degradation of fatty acids occurs because of the high process temperatures. These fatty and rosia acids can be separated usiag a UOP Sorbex process (93—99) (Tables 8 and 9). 

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