Pulping temperature

Low consistency pulping (3—6% soflds) is common in newsprint and many tissue mills. Medium (6—12%) and high consistency pulping (12—18% sohds) is common in mills deinking office papers. Pulping temperature is typically 40—55°C, the pH is usually 9.0—10.5, and process time ranges from 4 to 60 minutes. 

Preconditioning is used commercially by chip-potato processors to compensate the unpredictable nature of reconditioning of process varieties and to achieve market flexibility (Brook et al., 1995). During this phase, the storage environment is maintained at conditions similar to the wound healing phase (12-16°C) with the pulp temperature actively controlled in order to eliminate pools of reducing sugars in process potatoes. The duration of this phase is dependent... 

FIGURE 10.9 Products obtained on oxidation of coniferyl alcohol with polysulfide solution at pulping temperature. (Brunow, G. and Miksche, G.E., Acta Chem Scand, B29, 349-352, 1975 Berthold, E. and Gellerstedt, G., Holzforschung, 52, 490-498, 1998.)... 

Flash dryers for pulp are in operation with capacities of up to 500 BDMT/d (bone-dry metric tons). One such plant dries pulp from approximately 60%-12% water in a two-stage dryer. The lower moisture bound is critical, as overheating below it can cause thermal cross-linking that makes reconstitution of the original fiber difficult. Pulp temperature is maintained below 70°C in both stages, with air inlet... 

The collecting capabilities of oxidized paraffin soaps are worse than those of oleic acids when the pulp temperature is less than 40 °C. According to the flotation tests, the collecting capabilities of oxidized paraffin soaps become better than those of oleic acids when the pulp temperature approaches 70 °C. Therefore, the solubilities of oxidized paraffin soaps are improved by adopting emulsifier or other additives when reagents are used at the normal temperature level. 

The kinetics of the flotation process are an important factor and some of the relative reaction rates may be quite different, allowing some opportunity for differentiation by this means, and placing emphasis on the importance of process residence times. Other factors of importance in control of the process are the pulp density, pulp temperature, aeration rates and bubble size. 

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). 

Cotton linters or wood pulp are nitrated using mixed acid followed by treatment with hot acidified water, pulping, neutralization, and washing. The finished product is blended for uniformity to a required nitrogen content. The controlling factors in the nitration process are the rates of diffusion of the acid into the fibers and of water out of the fibers, the composition of mixed acid, and the temperature (see Cellulose esters, inorganic esters). 

Pulp-like olefin fibers are produced by a high pressure spurting process developed by Hercules Inc. and Solvay, Inc. Polypropylene or polyethylene is dissolved in volatile solvents at high temperature and pressure. After the solution is released, the solvent is volatilised, and the polymer expands into a highly fluffed, pulp-like product. Additives are included to modify the surface characteristics of the pulp. Uses include felted fabrics, substitution in whole or in part for wood pulp in papermaking, and replacement of asbestos in reinforcing appHcations (56). 

Two Other chemical processes that rely on hydrothermal processing chemistry are wet oxidation and supercritical water oxidation (SCWO). The former process was developed in the late 1940s and early 1950s (3). The primary, initial appHcation was spent pulp (qv) mill Hquor. Shordy after its inception, the process was utilized for the treatment of industrial and municipal sludge. Wet oxidation is a term that is used to describe all hydrothermal oxidation processes carried out at temperatures below the critical temperature of water (374°C), whereas SCWO reactions take place above this temperature. 

Grinder Variables. The quaUty of pulp depends on wood species, moisture content, and grinder variables such as peripheral stone speed, grit size and number per unit area, and pattern on the stone surface. Process variables that affect pulp quaUty include grinding pressure pit consistency, ie, consistency in the space immediately below the grinder (2—6%) and temperature (40—80°C). The combination of moisture and raised temperature tends to soften the lignin. 

---