US3646196A - Process for controlling pulp chip deterioration with kraft green liquor - Google Patents

Abstract

THIS INVENTION RELATES TO A TREATMENT USED TO CONTROL THE DETERIORATION OF PULP CHIPS DURING OUTDOOR STOCK PILING FOR LONG PERIODS OF TIME. THE TREATMENT INVOLVES A SPRAYING OR DIPPING OF THE PULP CHIPS WITH A KRAFT GREEN LIQUOR WHICH IS A MIXTURE OF SODIUM SULFIDE AND SODIUM CARBONATE IN WATER. THE TREATMENT GREATLY REDUCES THE LOSS OF WOOD SUBSTANCE OVER LONG PERIODS OF OUTDOOR STORAGE. THE LOSS OF WOOD SUBSTANCE IN WOOD CHIPS WITH THE TREATMENT IS APPROXIMATELY ONE-THIRD OR LESS THAN THAT WITHOUT THE TREATMENT.

Description

United States Patent Office 3,646,196 PROCESS FOR CONTROLLING PULP CHIP DETERIORATION WITH KRAFT GREEN LIQUOR Edward L. Springer and Wallace E. Eslyn, Madison, Wis., assiguors to the United States of America as represented by the Secretary of Agriculture No Drawing. Filed Apr. 29, 1970, Ser. N0. 33,074 Int. Cl. A01n 11/00, 11/06 US. Cl. 424-162 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to a treatment used to control the deterioration of pulp chips during outdoor stock piling for long periods of time. The treatment involves a spraying or dipping of the pulp chips with a kraft green liquor which is a mixture of sodium sulfide and sodium carbonate in water. The treatment greatly reduces the loss of wood substance over long periods of outdoor storage. The loss of wood substance in wood chips with the treatment is approximately one-third or less than that without the treatment.

A nonexclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to the stock piling of pulp chips with particular reference to a treatment for reducing the deterioration of wood substance during storage.

(2) Description of prior art In general, outside storage of pulp chips, introduced in the early l950s, resulted from the need to stock pile chips produced from residues of saw mills and veneer plants. When the economic advantages of handling wood as a bulk material became apparent, many mills introduced chipping of logs and stock piling of the chips as an alternative to log storage.

With the increased use of this method of handling wood, it became apparent that there were disadvantages as well as advantages in using this method. One of the primary disadvantages is the loss in wood substance during long periods of chip storage because of fungal action. The average loss is about 1 percent per month in wood substance although large variations in this figure have been noted. Pulp yields from these chips are not greatly affected although exceptions are found usually after long storage. Kraft pulping is usually not affected but tall oil yields tend to be low. In sulphite pulping, chip storage generally results in lower pulp brightness with increased bleaching costs.

The most obvious difference between log and chip storage is that chip piles tend to heat up. Temperatures of 140 to 150 F. are not uncommon. A wide range of temperatures can be found in various parts of the pile with the result that thermophilic, thermotolerant, and mesophilic microorganisms can exist in the pile simultaneously. Heat production is caused by enzymatic respiration of the wood cells, microbial oxidation, and chemical oxidation. Temperatures rise rapidly in the pile reaching a maximum in about 2 weeks, remain high for several months depending on the size of the pile, and then decline gradually to ambient temperature.

3,646,196 Patented Feb. 29, 1972 A chemical treatment used to prevent chip deterioration must meet the following criteria. First, it must be effective for a considerable length of time and the cost must be reasonable in relation to the losses incurred from chip deterioration. Second, it must be compatible with the pulping process, must not cause pollution, and must not be toxic to personnel. The chemical treatment must reduce the heat buildup in the stock piled pulp chips and prevent the growth of micro-organisms if loss in wood substance is to be reduced.

SUMMARY In general, the principal improvement of this invention resides in a chemical treatment to control degradation of pulp chips. A chemical treatment comprising an aqueous mixture of sodium sulfide and sodium carbonate, hereafter called kraft green liquor, was found to substan tially reduce loss of wood substance in pulp chip storage. The kraft green liquor solution is made by simply dissolving the sodium sulfide and sodium carbonate in water by any means available. The treatment of the pulp chips can be accomplished by spraying, dipping, or by any other means available to get the solution on to the chips. The treatment level is determined by the uptake of the treating solution and the percentage of sodium sulfide and sodium carbonate in the solution.

Accordingly, an object of this invention is to provide a treatment to control degradation of chips during outdoor storage. Another o'bject of this invention is the provision of a treatment that will inhibit both the growth of micro-organisms and the production of heat in the stock pile of pulp chips. A further object of this invention is the provision of a chemical treatment which is economical, simple, and quick as compared to mechanical treatments for controlling degradation of pulp chips.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In further illustration of this invention the following examples are given:

Example I The influence of the kraft green liquor on the release of initial heat of fresh wood chips was studied by placing the chips in an insulated box and observing the temperature profiles at the center of the samples. The boxes, constructed of polystyrene foam, have an internal volume of 3.9 cubic feet with a wall thickness of 8 /2 inches. The inside dimensions of the insulated box are 22 /2 by 13 /2 by 22 inches. Each box is fitted with air inlet and outlet manifolds and was fed water-saturated air at ambient temperature at a measured rate, Thermocouples placed in the center of the chip pass and on the outside Wall were used to measure the temperatures. Because temperature profiles of untreated chips can not be satisfactorily duplicated, presumably because of changes in the wood with time, untreated control samples were run with every treated sample.

The kraft green liquor solution used contained 7.7 percent sodium carbonate and 1.9 percent sodium sulfide. The treatment level, determined by uptake of the treating solution, was 2.1 pounds of sodium carbonate and 0.51 pound of sodium sulfide per pounds of ovendried wood.

Fresh aspen chips of 53 percent moisture content by weight were treated by submerging them for 10 minutes in the test solution and draining for 2 hours before placing them in the insulated boxes. For each box with treated samples, there was a box of control samples treated with water instead of the test kraft green liquor solution.

When the chips were submerged in the green liquor solution, an exothermic reaction occurred that raised the 3 temperature of the chips somewhat higher than ambient. The reaction is believed to be caused by hydrolysis of esterlinkages and neutralization of the carboxy groups by the base.

The treated and untreated control chips were kept in their insulated boxes 27 days. The air rate to each box was 1.4 cubic feet per day. When placed in the test box, the temperature in the center of the treated chip mass was 80 F. During the test period this temperature gradually decreased to 78 F. Ambient temperature during this time averaged 74 F. with a variation of less than 2 F. The temperature at the center of the water-soaked sample, or the untreated, was initially at 66 F., rose to 84 F. in 8 days, to 85 in 13 days, and then gradually decreased to 80 F. Thus, little or no heat was evolved by the green liquor treated samples, whereas considerable heat was evolved by the untreated control samples. Although treatment with green liquor caused an immediate exothermic reaction on contact with the chips, it apparently also stopped the natural heat evolving process.

After 27 days in an insulated box, the control chips were covered with fungal growth and had a musty, sour odor. The treated chips showed only traces of microbial growth, were of a somewhat yellowish color, and had no sour odor.

Example 2 The effectiveness of the kraft green liquor treatment in preventing loss of wood substance caused by wood rotting fungi was also investigated. A laboratory method was used to compare weight loss in treated and untreated chips after exposure to fungal attack. Red pine chips, frozen for storage shortly after chipping in the green condition, were used. The chips were screened, knotty or resinous pieces removed, and the remainder well mixed. The chips were then allowed to air dry at room temperature for 3 days. Then they were conditioned at 80 F. and 70 percent relative humidity for 1 Week. At the end of this period, samples of chips were precisely weighed to about grams.

The sample chips were then rewetted by being subjected to a vacuum of about 29 inches of mercury for 20 minutes followed by flooding with distilled water. After draining to remove the excess water, the samples were treated with various concentrations of green liquor. Treatment with the green liquor consisted of dipping the chips for 1 minute in the test solution. The chips were removed from the solution and allowed to drain for 1 hour. They were then placed in incubation tubes, 12-inch long glass cylinders, plugged at the top with cotton, and at the bottom with rubber stopper containing a hole for drainage.

The cylinders filled with chips were then steamed for 30 minutes at 212 F. When cool, half the samples were inoculated with a peniophora fungus and the other half with a mixture of a peniophora and a chrysosporium fungus. Both inoculation organisms are species of the above generic groups and are isolates of southern pine chips. Both are found capable of substantially degrading Wood.

Inoculation Was performed by asceptically scrapping the mycelium from the surface of a test tube culture. The mycelium and 75 milliliters of sterile distilled water were blended in a Waring blender for 20 seconds. When using the mixture of organisms, to maintain comparable levels of inoculation, half of the mycelium from each of the two test tubes were used and blended together as above. The blended mixture was then asceptically poured over the chips and allowed to drain through the stopper at the bottom of the cylinder.

The cylinders were then placed in an incubator and maintained at a temperature of 82 F. for 7 weeks. Then the chips were removed from each of the cylinders, dried, conditioned, and weighed as at the test start, and the weight losses calculated. The results of the various concentrations of kraft grain liquor treatment are indicated in the following table:

WEIGHT LOSS OF TREATED CHIPS Concentration of solution, percent Weight Sodium Sodium Iuocu- Initial Final 2 loss, carbonate sulfide lant 1 weight, g. Weight, g. percent 1 20. 09 18. 63 7. 8 2 20. 05 18. 17 9. 1 1 20. 10 17. 13. 0 2 20. 01 17. 61 12. 0 l .20. 00 19. 2. 8 2 20. 05 19. 87 9 1 20. 05 20.08 2 2 20. 02- 19. 71 l. 6 l 20. 07 19. 83 l. 2 2- 20.06 20. 25 l.0 1 20. 05 20. 00 2 2 20. 01 20. 05 2 1 l=SpecieS of Peniophora; 2=Species of Pencophora and Chrysosporium.

2 Weight corrected for treating chemical.

3 Not treated.

Example 3 Untreated fresh aspen chips soaked in a solution containing 0.77 percent sodium sulfide and 3.1 percent sodium carbonate were placed in tower simulators (see- Springer, E. L., and Zoch, L. L., A Simulator of an Outside Chip Pile, 1'16-117, Tappi 53(1), 1970). The chemical pickup of the wood chips was 0.36 pound of sodium sulfide and 1.38 pounds of sodium carbonate per pounds of chip. The tower simulators are 4 feet in diameter and 16 feet high cylinders insulated with 6 inches of fiberglass insulation. Each simulator was fed with two tower volumes per day of water saturated air. Four bags of approximately 40 pounds each of chips were placed in each tower. The moisture content of the chips in each bag was determined. The chips in the bags were treated the same as the loose chips in the tower. The bags were placed 5 feet below the top of the chip bed in each tower.

The towers were unloaded after 6 months and each bag was reweighed and the moisture content determined. During the test period the outside surfaces of chip towers were maintained at ambient temperature. The average ovendry wood substance loss of the untreated chips was 5 percent. The wood substance loss of the green liquor treated chips was 1.6 percent. The treatment thus greatly reduced the loss of wood substance. Approximately twothirds of the wood loss without treatment was preserved by the treatment.

Having thus disclosd our invention, We claim:

1. The process of limiting the effect of wood destroying fungi on wood chips by dipping or spraying the chips with a fungicidally effective amount of an aqueous mixture comprising .77 to 2.38 percent sodium sulfide and 3.10 to 9.62 percent sodium carbonate.

References Cited GregoryUses and Applications of Chemicals and Related Materials, 1939, Rheinhold Pub. Co., pp. 530-1, 558-9.

Hajny--Outside Storage of Pulpwood Chips, Tappi, Journal of the Technical Assoc. of the Pulp and Paper Industry, vol. 49, No. 10, 1966, pp. 97a-105a.

Springer et al.Control of Pulp Chip Deterioration with Craft Green Liquor, USDA Forest Service Paper #FPLllO, May 1969, pp. 1-5.

ALBERT T. MEYERS, Primary Examiner L. SCHENKMAN, Assistant Examiner US. Cl. X.R. 424-127