Kraft pulping procedure

First, we discuss the problem statements and key features of the learning architecture that are specific to complex systems. This is followed by a brief presentation of the search procedures that are used to build a final solution. The section ends with a summary of the application of the learning architecture to the analysis of a Kraft pulp mill. 

This poses a question concerning deacidification. If a deacidification procedure does not remove aluminum from the cellulose carboxyls, will the paper have the stability that one would expect from a paper with an alkaline filler In an attempt to answer this question, a series of hand-sheets was made from a hardwood kraft pulp. This pulp was selected because (a) it had a carboxyl content of 5.75 mmol/100 g pulp, which is similar to that of some old papers (b) it was easy to beat in a laboratory beater and (c) the physical properties of the handsheets were in the "old... 

In a related approach, Ni et al (1990) have developed a procedure for determining lignin in softwood kraft pulp based on the conversion of methoxyl groups in the lignin to methanol when the pulp is chlorinated under a specified... 

Contamination by enzymes is a main drawback of the procedure, especially in the isolation of residual lignin from semi-bleached pulps. The contaminants cannot be completely removed by the purification procedure described above. Consequently, it is important to determine the nitrogen content of the residual lignin. Typical values of nitrogen content are 2.5% and 7.3% before purification and 0.6% and 2.3% after purification for residual lignins isolated from an unbleached and a semi-bleached southern pine kraft pulp, respectively (Jiang et al. 1987). 

Extraction of HemiceUuloses from Various Pulps. The extraction procedure followed was that of Giertz and McPherson (6). Fifteen grams of unaged pulps [four kinds in all bleached kraft pulp (BP), unbleached kraft pulp (UBP), unbleached groundwood pulp (GP), and chlorited UBP] was treated with 290 mL of 10.9 lithium hydroxide solution for 1 h at room temperature and was stirred intermittently (see Table I for the characteristics of the pulps). After the samples were diluted to about 1 L, the insoluble material was filtered off. The extract (filtrate) was neutralized to pH 6 with 2 M phosphoric acid (300 mL) and was allowed to stand overnight. The precipitated lithium phosphate and /3-cellulose were separated by filtration. The filtrate was then concentrated to about 175 mL under reduced pressure at 30-40 °C. Salts present in the system were further precipitated with methanol and separated by filtration. The filtrate was again concentrated to about 60 mL. The filter paper was immersed into this concentrate to saturate the test sheets. 

The kraft, or sulfate process is today the preeminent chemical pulping process. In Canada alone, 80% of all the chemical pulp produced is by this method, and worldwide some 85% of the total is via this route. The current prominence of this pulping procedure warrants a rather more complete discussion of the details than devoted to the other chemical pulping methods. 

This experiment was carried out in accord with an established procedure (5). Unbleached softwood kraft pulp (USKP) from Douglas fir was obtained from Pope and Talbot (Halsey, Oregon) and washed with deionized water until the effluent was neutral and colorless. USKP (8.0 g, oven-dried) was autoclaved at 121 °C for 40 min, cooled down at room temperature and then inoculated with 3 mL of P. cinnabarinus spore suspension (ca. 9 x lO spores/mL). The moisture content of the culture was adjusted to 80% and the culture was incubated statically at 30 °C. After a pre-determined incubation time, mycelia were carefully removed fiom pulp. Hie treated pulp was analyzed for kappa number. 

The isolation of enzymatic residual LCCs from unbleached softwood Kraft pulps is a well-established procedure producing preparations with high yields (estimated as lignin in isolated preparations per lignin in the original pulp) and relatively low enzyme impurities [46 8]. In contrast, significant problems are encountered when similar procedures are applied to the isolation of enzymatic residual LCCs from hardwood Kraft pulps and semi-bleached pulps [47]. Low yields (25-30%) make these preparations nonrepresentative for the whole pulp LCC. A very large amount of protein impurities... 

Figure IL The SEC molar mass distribution curves for arabino-4-O-methyl-glucuronoxylan (from spruce holocellulose), arabinohexenuronoxylan (kraft pulp) and two different 4 0-methylglucuronoxylans (sulfite and dissolving pulp) obtained by the SEC/MALDI-MS procedure. Each xylan was analyzed separately employing the alkaline (pH 13) buffer SEC system and subsequently graphed on the same MALDI-MS calibrated absolute molar mass scale.

A high yield chemical pulp, eg, 52—53% bleached yield from softwoods, can be obtained, but strength properties ate inferior to those obtained from the kraft process. If a protector, eg, potassium iodide, is added, an additional 2—3% yield is obtained, as is an improvement in all strength properties. The gas penetration problem can be minimized if ftbetization is accompHshed before treatment with oxygen. Oxygen treatment of virtually all types of semichemical and mechanical pulps has been explored (55). Caustic, sodium bicarbonate, and sodium carbonate have been used as the source of base (56,57). In all cases, the replacement of the kraft by these other processes has not been justified over the alternative of pollution abatement procedures. 

---