Methods of pulp fiber treatment

Abstract

In some embodiments, a method may include treating pulp in pulp and paper mills. The methods may include providing a peracetate oxidant solution and generating a reactive oxygen species. The peracetate solution may include peracetate anions and a peracid. In some embodiments, the peracetate solution may include a pH from about pH 10 to about pH 12. In some embodiments, the peracetate solution has a molar ratio of peracetate anions to peracid ranging from about 60:1 to about 6000:1. In some embodiments, the peracetate solution has a molar ratio of peracetate to hydrogen peroxide of greater than about 16:1. The peracetate oxidant solution may provide enhanced treatment methods of bleaching, brightening, and delignifying pulp fibers involving the use of peracetate oxidant solutions.

Description

PRIORITY CLAIM[0001]This application claims priority to U.S. Provisional Patent Application No. 62 / 263,900 entitled “METHODS OF MICROBIAL CONTROL” filed on Dec. 7, 2015, all of which is incorporated by reference herein.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present disclosure generally relates to pulp fiber treatment using peracetate oxidant solutions. The disclosure more particularly relates to methods of bleaching, brightening, and delignifying pulp fibers involving the use of peracetate oxidant solutions.[0004]2. Description of the Relevant Art[0005]A variety of methods have been developed for delignification of wood pulp fibers after the initial pulping to achieve brighter unbleached grades and bleachable grades (e.g., kappa number 10-15). Common delignification methods include reductive methods (e.g., extended or enhanced sulfide digestion), oxidative methods (e.g., oxygen delignification, alkaline hydrogen peroxide extraction and combinations), and...

AI Technical Summary

Benefits of technology

The patent text describes a method for delignifying, brightening, and bleaching fibers using a peracetate oxidant solution. The text explains that the ROS generated by the peracetate formulation, particularly singlet oxygen, are the primary chemical species responsible for the delwigntification process. This is in contrast to the use of peracetic acid in combination with hydrogen peroxide, which has lower performance efficiency and higher cost for delignification. Additionally, the patent text discusses a method for reducing the microbial load in a slurry containing microbes using the peracetate oxidant solution.

Problems solved by technology

Reactive oxygen radical species such as superoxide and peroxyl radicals are known to form during higher pressure and temperature oxygen delignification processes and can cause damage to cellulose fibers.

It is generally known in the art that cellulose fibers are susceptible to damage by radical species, which reduces fiber yield and fiber strength.

However, excessive alkali concentrations or exposure times will also cause damage to cellulose fiber.

Relying on a dye mediated photooxidation process is not practical for pulp delignification due to optically opaque pulp mixtures and the rapid breakdown of photosensitive dyes by singlet oxygen and other ROS.

Furthermore, there are few economically viable options for delignification of wood and non-wood pulps on smaller scales than those feasible for traditional pulp and kraft pulp mills.

Oxygen delignification has very high capital costs and significant operating and maintenance costs.

A small fraction of the sodium peracetate can be present as peracetic acid, however, peracetic acid is consumed by reactions with sodium peracetate and does not reach significant concentrations in solution.

Exposure to sodium peracetate solution is limited to inhalation of an aerosol or mist and exposure to liquid concentrates.

The use of elevated concentrations of chlorine dioxide in water treatment is particularly hazardous.

Pulp bleaching operations using chlorine dioxide at several hundred to several thousand mg / L concentrations and elevated temperatures pose severe exposure hazards over large areas if not properly contained.

Gases are more difficult to contain than liquid solutions with low vapor pressures.

Water used in chlorine and chlorine dioxide bleaching stages is not compatible with recovery boilers and other process equipment outside of the bleaching circuit due to the highly corrosive chloride and chlorate content.

Chlorides would accumulate in closed loop processes in a pulp mill used upstream of the bleaching circuit causing corrosion damage to conventional process equipment.

Corrosivity of radical compounds used in the delignification, brightening and bleaching stages is another issue, especially when these compounds come in contact with various process materials such as steel, copper and brass alloys.

Compounds that are gases in their native form are the most volatile and present the greatest corrosion and occupational exposure hazards, including chlorine, chlorine dioxide and ozone.

Importantly, when biofilms and their detritus detach from surfaces in the wet end papermaking process, they can cause holes and other defects in finished paper products.

Some bacteria are pathogenic, for example, Legionella pneumophila, which poses health risks.

Some algae, such as cyanobacteria, produce algal toxins that pose potential health hazards.

Commonly used oxidizing biocides are effective in the treatment of water with relatively low levels of contaminants, however significant issues arise when higher concentrations of organic materials and salinity are present.

Microbial resistance to chlorine and bromine-based oxidizing biocides is a growing issue in municipal and industrial water systems.

Oxidizing biocides based on free chlorine and bromine in water react readily with organic materials to form halogenated disinfection byproducts, which are persistent in the environment and often exhibiting high toxicity.

Peroxyacetic acid (PAA), which is a stabilized mixture of PAA, hydrogen peroxide, acetic acid and water, is an effective biocide, but not as efficient as chlorine dioxide in that higher doses are necessary to achieve similar performance.

PAA performance declines as pH becomes more alkaline and promotes non-beneficial decomposition reactions between PAA, hydrogen peroxide and metal contaminants.

Corrosivity of oxidizing biocides is another issue, especially when the biocides come in contact with various process materials such as steel, copper and brass alloys.

Biocide materials that are gases in their native form are the most volatile and present the greatest corrosion and occupational exposure hazards, including chlorine, chlorine dioxide and ozone.

The direct reaction of peracetate with pulp is minimal, which contrasts with the use of peracetic acid in combination with hydrogen peroxide as the primary oxidants, which have much lower performance efficiency (and therefore, higher cost) for delignification, brightening and bleaching.

Applying the peracetate oxidant in high doses in a single step process is effective, but this approach can be costlier compared to multiple, lower doses of oxidant.

The capital cost for the peracetate oxidant technology is almost negligible compared to traditional processes including oxygen delignification and chlorine dioxide bleaching lines.

Minimal capital cost may offset the total cost of ownership to use the peracetate oxidant technology in facilities having little to no existing infrastructure for brightening or bleaching of fiber.

A small fraction of the sodium peracetate can be present as peracetic acid, however, peracetic acid is consumed by reactions with sodium peracetate and does not reach significant concentrations in solution.

Exposure to sodium peracetate solution is limited to inhalation of an aerosol or mist and exposure to liquid concentrates.

The use of elevated concentrations of chlorine dioxide in water treatment is particularly hazardous.

Pulp bleaching operations using chlorine dioxide at several hundred to several thousand mg / L concentrations and elevated temperatures pose severe exposure hazards over large areas if not properly contained.

Gases are more difficult to contain than liquid solutions with low vapor pressures.

Images