Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Treatment with particular chemical
Reexamination Certificate
2003-02-28
2003-11-18
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Treatment with particular chemical
C162S017000, C162S076000, C162S077000, C162S090000
Reexamination Certificate
active
06649023
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for digesting woodchips used in papermaking. The process employs a digester additive, which is a mixture of (a) a polyglycoside, and (b) a polyoxyalkylene glycol. The digester additives are compatible and stable at elevated temperatures in the highly alkaline white liquor used in the digestion of woodchips into pulp. The invention also relates to the digester additive compositions.
BACKGROUND OF THE INVENTION
In the Kraft process for making paper, woodchips are cooked (digested) in a digester at an elevated temperature in white liquor. The white liquor is essentially a caustic solution containing polysulfides. The woodchips swell in the presence of the caustic and the polysulfides penetrate into the capillaries of the wood. This process dissolves the lignin in the woodchips that binds the wood fibers of the wood together. Ideally, all of the woodchips are cooked uniformly during the digestion process. However, in practice, not all of the fibers in woodchips will be separated. Any unseparated particles will be classified as “rejects”. If a large quantity of rejects are screened out during this pulping process, “low yield” (defined as dry weight of pulp produced per unit dry weight of wood consumed) will result.
Over the years, anthraquinone (AQ) was and is still successfully used in the pulping industries as a digester additive. AQ enhances the pulping rate, and most importantly, reduces the amount of “rejects” and leads to increases in yield. However, AQ can be expensive to use and it is relatively insoluble in white liquor, even at an elevated temperature. This insolubility in white liquor creates processing problems, such as pipe and screen plugging, and scaling in the digester. It is also known that the use of AQ detrimentally affects the tall oil by-product recovered during the pulping process.
In order to obviate the problems associated with using AQ, surfactants are added to the white liquor to reduce or eliminate the plugging and scaling problems normally encountered with AQ. In addition, certain surfactants and surfactant mixtures are known to provide wetting properties that allow quick and more uniform penetration of the cooking liquor into the capillaries of woodchips, thus reducing the “rejects” as well as reducing the cooking time. U.S. Pat. Nos. 4,906,331 and 5,127,993 disclose the use of polyoxyalkylene glycols' (POGs') that can reduce-reject and increase yield. However, these POGs (such as PLURONIC® F108 & L-62 polyols) are not compatible in the alkaline white liquors.
U.S. Pat. Nos. 5,298,120 and 5,501,769 disclose a digester additive that is a diester of the same POGs reacted with oleic acid. The patents indicate that the diester results in improved dispersibility in the white liquor. With heat in alkaline white liquor, the diester will saponify (hydrolyze) back to the original POGs for them to work. Since it takes time for the saponification to occur, these diesters by then is already dispersed in the white liquor resulting in a relatively more uniform cooking of the woodchips in the digester.
U.S. Pat. No. 5,250,152 discloses a blend of ethoxylated alcohols and dialkylphenols as digester additives that can increase yields and reduce rejects. U.S. Pat. Nos. 6,036,817 and 5,728,265 disclose a number of surfactants, including sulfosuccinates, polyglycosides, and poly(methyl-alkylsilicone) as chip penetrating aids.
JP Patents 06033386 & 07527528 disclose the use of AQ and surfactants (including ethoxylate secondary alcohols and alkyphenols blends). WO 9529288 claims AQ treated with rosin with a polyvalent metal and water-soluble surfactant. DE 3905311 discloses AQ with substituted polyglycol ether like alkylphenol or naphthol of a 2-ring aromatic hydroxy compound with 4-20 moles of EO. These inventions emphasize a lower AQ level usage complemented by surfactants in an attempt to reduce the problem of AQ scaling and plugging during pulping.
Ethoxylated alkylpenols, dialkyl phenols, both primary and secondary alcohols, are also documented in many disclosures. However, they are neither soluble nor dispersible in the highly alkaline white liquor rendering them marginally effective. At elevated temperature above 150° C., the solubility of these surfactants worsens. This issue is addressed in U.S. Pat. Nos. 5,298,120 and 5,501,769 that disclose attempts to disperse the POG uniformly throughout the white liquor by transforming the POGs' into its diester equivalent before use.
SUMMARY OF THE INVENTION
The invention relates to a process for digesting woodchips used in papermaking. The process employs digester additives, which are mixtures of (a) a polyglycoside, and (b) a polyoxyalkylene glycol. The mixtures are compatible and stable at elevated temperatures in the highly alkaline white liquor used in the digestion of woodchips into pulp. The invention also relates to the digester additive compositions.
The digester additives are effective in reducing both the Kappa number and percentage of rejects during the cooking of woodchip to pulp. However, unlike most surfactant-based digester additives used commercially, the new digester additives are miscible with and effective with highly alkaline white (cooking) liquors having high solids, especially at temperature >160° C. The use of the digester additives results in the uniform cooking of the woodchips in the digester, improve good yields of woodpulp and a decrease in % of rejects, and a lack of deposits on the digesting equipment that is commonly associated with the use of anthraquinone. The combination of (a) and (b) exhibits unexpected and synergistic benefits.
BEST MODE AND OTHER MODES OF PRACTICING THE INVENTION
The polyglycosides used in the surfactant mixtures include glycosides and glycoside derivatives such as alkyl glycosides, alkoxylated alkyl glycosides, polyglycosides, polyalkylglycosides, alkoxylated polyalkylglycosides, alkylpolysaccharides, and the like. A glycoside is a composition comprised predominantly of an acetal or ketal of a saccharide with an alcohol. Typical saccharides from which the glycoside is derived include glucose, fructose, mannose, galactose, talose, gulose, allose, altrose, idose, arabinose, xylose, lyxose and ribose. The preferred glycosides are glucosides due to the ready availability of glucose as a starting material. The synthesis of polylglycosides is disclosed in U.S. Pat. Nos. 3,598,865; 3,721,633; 3,772,269; 3,640,998; and 3,839,318, which are hereby incorporated by reference.
Akyl and alkoxy polyglycosides, preferably alkyl polyglycosides for use in the present invention have the formula:
R
1
O—(glycosyl)
x
where R
1
is selected from the group consisting of alkyl, alkylphenyl, hydroxyalkyl, hydroxyalkylphenyl, and mixtures thereof in which the alkyl groups-contain from about 6 to about 30, preferably from about 8 to about 16, carbon atoms; and x is 1 to 5, preferably from 1 to 4. The glycosyl is preferably a monsaccharide (glucose). To prepare these compounds, the alcohol or alkylpolyethoxy alcohol is formed first and then reacted with glucose, or a source of glucose, to form the glucoside (attachment at the 1-position). The additional glycosyl units can then be attached between their 1-position and the preceding glycosyl units 2-, 3-, 4- and/or 6-position, preferably predominately the 2-position.
Alkylpolysaccharides are disclosed in U.S. Pat. No. 4,565,647. These compositions have a hydrophobic group containing from about 6 to about 30 atoms, preferably from about 10 to about 16 carbon atoms and a polysaccharide, e.g., a polyglycoside, hydrophilic group containing from about 11/2 to about 10, preferably from about 11/2 to about 3, most preferably from about 1.6 to about 2.7 saccharide units. Any reducing saccharide containing 5 or 6 carbon atoms can be used, e.g., glucose, galactose and galactosyl moieties can be substituted for the glucosyl moieties.
Typical hydrophobic groups include alkyl groups, either saturated or unsaturated, branched or unbranched containing from about 6 to about 30, preferably
Khan Abdul Q.
Wai George K.
Ashland Inc.
Griffin Steven P.
Halpern M.
Hedden David L.
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