Digester Additive Formulations and Use Thereof for Pulp Production

This application claims the benefit under 35 U.S.C. § 119(e) of prior U.S. Provisional Patent Application No. 63/632,056 filed Apr. 10, 2024, which is incorporated in its entirety by reference herein.

The present invention relates to a digester additive formulation for a pulping process, methods of using a digester additive formulation in the pulping process, and products thereof.

In the pulp making industry, kraft pulping is a common method of producing pulp from raw materials, such as wood chips. The production of pulp using the kraft pulping process involves cooking wood chips in a digester vessel (digester) at high temperatures and with the addition of sodium sulfide and caustic (cooking liquor). The cooking liquor is added to screened wood chips prior to the cooking. Once the wood chips and cooking liquor are added to the digester, the wood chip mixture is subjected to 200-370° F., and a pressure as high as 130 psi. The time it takes for digestion can vary between 4-8 hours. Digestion can occur either in a batch or a continuous process.

The result of the above-mentioned cooking process is the hydrolysis and/or depolymerization of the lignin of the wood chips. Whilst these conditions are somewhat directed at delignification, cellulose is also damaged during the cook. The Kappa number, also known as the Kappa value or K number, is a measure to quantify the lignin content in wood pulp. The lower the Kappa number, the more cellulose quality is impacted. During the cooking process, operators attempt to balance lignin removal and cellulose degradation. Thus, an objective of the process is to maximize pulp yield (as measured by the conversion of wood to pulp), reduce rejects, and maintain the quality of the pulp (as measured with pulp viscosity and pulp strength).

Over many years, various additives have been used in an attempt to improve pulp production. These additives are broadly classified as catalysts and surfactants. Although the exact mechanism of catalysts is not fully elucidated, the catalysts appear to speed up the rate of delignification whilst also protecting the cellulose integrity. Anthraquinone (AQ) is the most commonly known of these catalysts and has been used since at least 1977. However, due to regulatory issues and toxicity concerns, this catalyst has fallen out of favor and is banned in many countries. There have been many research efforts to find better and safer AQ alternatives. None of these, however, have been commercialized.

In contrast to the catalysts, surfactants have a different mode of action. Specifically, surfactants do not increase the rate of delignification or protect the cellulose structure. Rather, surfactants function by reducing the surface activity of the cooking liquor, thereby ensuring wetting and thus better liquor penetration into the wood chips, which invariably results in more efficient cooking and less rejects. This typically results in better conversion of wood chips to pulp. Some examples of surfactants are shown in U.S. Pat. No. 2,999,045 that describes the use of EO/PO block copolymers to improve pulp cooking in the digester whilst U.S. Pat. No. 4,952,277 shows a process of making paper by adding to the medium surface-active molecules, such as ethoxylated nonylphenol alcohol.

Accordingly, a need exists for improving wood pulping processes in general and specifically, a need exists for improved digester additive formulations that facilitate a higher pulp viscosity and an increased pulp yield when used during a pulp making process.

A feature of the present invention is to provide a digester additive formulation for a kraft pulping process.

Another feature of the present invention is to provide a digester additive formulation that improves pulp viscosity and increases pulp yield from a kraft pulping process.

An additional feature of the present invention is to provide a wood pulp mixture for a kraft pulping process, which includes a digester additive formulation that improves pulp viscosity and increases pulp yield.

Another feature of the present invention to provide a method of making pulp by including a digester additive formulation that improves pulp viscosity and increases pulp yield of a kraft pulping process.

Additional features and advantages of the present invention will be set forth in part in the description that follows, and in part will be apparent from the description, or can be learned by practice of the present invention. The objectives and other advantages of the present invention will be realized and attained by means of the formulations, elements, and combinations particularly pointed out in the description and appended claims.

To achieve these and other advantages and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention, in part, relates to a digester additive formulation for a kraft process for producing wood pulp. The digester additive formulation includes phenyl tetracarboxylic acid or a derivative or salt thereof, and a macromolecule polymer. The phenyl tetracarboxylic acid is of the structure shown in Formula I:

and the macromolecule polymer comprises a structure selected from the group of structures of Formulae II-V:

wherein the moiety [P,S] denotes either a phosphate group or a sulfate group, the moiety R can be either hydrogen, a hydrocarbyl group (e.g., containing from 1 to 16 carbon atoms), or an aryl group (e.g., containing from 1 to 16 carbon atoms), and each X can independently be hydrogen or a metal cation (e.g., K+ or Na+); and

wherein each of Rand Rcan independently be hydrogen, a hydrocarbyl group (e.g., containing from 1 to 16 carbon atoms), or an aryl group (e.g., containing from 1 to 16 carbon atoms).

It has been found, according to the present invention, that a synergistic effect occurs from the combination of phenyl tetracarboxylic acid or a derivative or salt thereof, and one of a group of special macromolecule polymers, which forms the digester additive formulation of the present invention. Specifically, when adding the combination of phenyl tetracarboxylic acid or a derivative or salt thereof, and the macromolecule polymer, as a digester additive formulation during a kraft pulping process, pulp viscosity and pulp yield are significantly improved, as compared to a kraft pulping process without the use of the digester additive formulation.

The present invention further relates to a mixture comprising oven dried wood chips for use in a kraft process for making wood pulp, and the digester additive formulation of the present invention, wherein the digester additive formulation is present in the mixture in an amount of from 0.001% by weight to 10% by weight, based on the weight of the oven-dried wood chips, for example, in an amount of from 0.001% by weight to 8% by weight, in an amount of from 0.01% by weight to 8% by weight, in an amount of from 0.05% by weight to 7% by weight, in an amount of from 0.1% by weight to 6% by weight, or in an amount of from 0.2% by weight to 2% by weight, based on the weight of the oven-dried wood chips.

The present invention further relates to a method comprising: mixing together wood chips, white liquor, dilution water, and the digester additive formulation of the present invention to form a wood pulp mixture.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide a further explanation of the present invention, as claimed.

A digester additive formulation is provided for a kraft process of producing wood pulp. The digester additive formulation comprises a phenyl tetracarboxylic acid or a derivative or salt thereof in combination with a macromolecule polymer. When used as a digester additive formulation in a process of producing wood pulp, the phenyl tetracarboxylic acid or a derivative or salt thereof and the macromolecule polymer has a synergistic effect that improves the viscosity of the resulting pulp and the overall pulp yield.

As used herein, “pulp” also referred to herein as “wood pulp”, refers to a fibrous material derived from a raw wood material, such as wood chips, that has undergone a chemical, pressure, and temperature treatment, such as a kraft process.

“Kraft process,” also referred to herein as “kraft pulping” or “kraft pulping process,” is a process of chemically converting raw material, such as wood or wood chips, to pulp. The kraft process uses a “cooking liquor” as a chemical for “cooking” (chemical pulping process) the raw material, also referred to herein as “white liquor”, which can be a combination of sodium hydroxide and sodium sulfide, and optionally sodium carbonate and/or sodium polysulfide. The mixture of wood chips and white liquor are subjected to increased temperature and pressure in a digester vessel.

Unless stated otherwise, a “digester additive formulation” refers to a multi-component additive that is added to a digester vessel (as separate components or pre-combined) during a pulp production process, such as a kraft process. A “digester additive formulation” does not consist of a single compound or molecule but rather refers to a multi-component additive.

“Macromolecule polymer” refers to a large molecule composed of repeating monomers that are covalently bonded together through polymerization reactions, forming long chains or networks.

“Block copolymer” refers to a type of polymer including two or more distinct polymer blocks, or segments, linked together covalently. These segments are typically composed of different monomers.

“Surfactant” refers to an organic compound which can lower the surface tension of a liquid, the interfacial tension between two liquids, or the interfacial tension between a liquid and a solid.

According to various embodiments of the present invention, a digester additive formulation is provided for a kraft process for producing wood pulp. The digester additive formulation can include a phenyl tetracarboxylic acid or a derivative or salt thereof, and a macromolecule polymer.

In certain embodiments, the phenyl tetracarboxylic acid has the structure shown in Formula I:

Phenyl tetracarboxylic acid is also known in the art as 1,2,4,5 benzyl-tetracarboxylic acid. As an option, derivatives, salts, or a combination thereof, of the phenyl tetracarboxylic acid, can be used. For example, a derivate or salt of the phenyl tetracarboxylic acid can be used instead of Formula I in the digester additive formulation, or in addition to Formula I in the digester additive formulation.

The phenyl tetracarboxylic acid or derivative or salt thereof, can be a derivative of phenyl tetracarboxylic acid. The derivative of phenyl tetracarboxylic acid can be, for example, selected from the group consisting of alkyl-substituted phenyl monocarboxylic acids, alkyl-substituted phenyl dicarboxylic acids, alkyl-substituted phenyl tricarboxylic acids, and alkyl-substituted phenyl tetracarboxylic acids. The phenyl tetracarboxylic acid or derivative or salt thereof can be a salt of phenyl tetracarboxylic acid.

The phenyl tetracarboxylic acid or derivative or salt thereof, can be a substituted phenyl tetracarboxylic acid, that is, a structure including a substituted moiety on the phenyl ring. For example, the phenyl tetracarboxylic acid or derivative or salt thereof can be an alkylphenyl-substituted tetracarboxylic acid. The phenyl tetracarboxylic acid or derivative or salt thereof, can be an alkoxyphenyl-substituted tetracarboxylic acid. The phenyl tetracarboxylic acid or derivative or salt thereof, can be methoxylated, ethoxylated, propoxylated, or the like. The phenyl tetracarboxylic acid or derivative or salt thereof, can be a phenyl-substituted tetracarboxylic acid.

The phenyl tetracarboxylic acid or derivative or salt thereof is combined with a macromolecule polymer to form the digester additive formulation of the present invention. The macromolecule polymer is a large molecule composed of repeating structural units of monomers. The macromolecule polymer is characterized by a high molecular weight and long-chain structure.

The macromolecule polymer of the present invention can be a surfactant. A surfactant refers to an organic compound which can lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid.

The macromolecule polymer can comprise any of a number of specific structures. Certain macromolecule polymer structures have shown synergistic effects that improve the viscosity of resulting pulp and the overall pulp yield when used in combination with phenyl tetracarboxylic acid or a derivative or salt thereof, during a pulp production process.

The macromolecule polymer can be of the structure shown in Formula II:

wherein the value of each x in Formula II can independently be, for example, from 12 to 141, and the value of y can be from 20 to 56. The value of the first x in Formula II can be the same or different than the value of the second x in Formula II. The sum of both x's in Formula II can be, for example, from 24 to 282. The value of each x in Formula II can independently be from 15 to 75. The value of y in Formula II can be from 25 to 35. The macromolecule polymer structure of Formula II can be a block copolymer of polyethylene oxide and polypropylene oxide (an EO/PO block copolymer).

The macromolecule polymer can be of the structure shown in Formula III:

wherein the value of each x in Formula III can independently be from 12 to 141 and the value of y in Formula III can be from 20 to 56. The value of each x in Formula III can independently be from 15 to 75. The sums of the values of the two x's in Formula III can be from 24 to 282. The value of the first x in Formula III can be the same or different than the value of the second x in Formula III. The value of y in Formula III can be from 25 to 35. The R group can be any alkyl, aryl, alkenyl, or alkynyl group, or the like. The R group can contain, for example, from 1 to 16 carbon atoms (e.g., from 1 to 12 carbon atoms or from 1 to 8 carbon atoms, or from 1 to 6 carbon atoms). The macromolecule polymer of Formula III can be, for example, a monoester of a fatty acid esterified from an EO/PO block copolymer.

Examples of fatty acids of Formula III can include, but are not limited to, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, palmitoleic acid, oleic acid, gadoleic acid, erucic acid, nervonic acid, linoleic acid, alpha-linolenic acid, gamma-linolenic acid, arachidonic acid, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), elaidic acid, vaccenic acid, conjugated linoleic acid (CLA), ricinoleic acid, and eleostearic acid.

The macromolecule polymer can be of the structure shown in Formula IV:

wherein the moiety [P,S] denotes either a phosphorus or a sulfur, but not both, the moiety R can be hydrogen, a hydrocarbyl group (e.g., containing from 1 to 16 carbon atoms or from 1 to 12 carbon atoms or from 1 to 8 carbon atoms or from 1 to 6 carbon atoms), or an aryl group (e.g., containing from 1 to 16 carbon atoms or from 1 to 12 carbon atoms or from 1 to 8 carbon atoms or from 1 to 6 carbon atoms), and each X can independently be hydrogen or a metal cation (e.g., K+ or Na+). In Formula IV, both X's can be same or different. In Formula IV, each X can be hydrogen. In Formula IV, the value of x can be from 5 to 100, for example, from 6 to 20, and the value of y can be from 8 to 40, for example, from 10 to 20. The macromolecule polymer of Formula IV can be, for example, a linear alkyl ethoxylated phosphate or a linear alkyl ethoxylated sulfate.

The macromolecule polymer can be of the structure shown in Formula V: