EP2406425B1

EP2406425B1 - Method and chemical composition to improve efficiency of mechanical pulp

Info

Publication number: EP2406425B1
Application number: EP10706889.2A
Authority: EP
Inventors: Prasad Duggirala; Sergey M. Shevchenko
Original assignee: Nalco Co LLC
Current assignee: ChampionX LLC
Priority date: 2009-03-09
Filing date: 2010-03-04
Publication date: 2019-10-02
Anticipated expiration: 2030-03-04
Also published as: CA2753944C; BRPI1009542A2; US20100224333A1; EP2406425A1; JP5669762B2; RU2011135609A; CA2753944A1; KR101718557B1; CN102348848A; KR20110128915A; WO2010104725A1; JP2012519785A; BRPI1009542B1; RU2530386C2

Description

Background of the Invention

This invention relates to improving fiber quality and process efficiency in mechanical pulping. More specifically, the invention relates to using specialty chemical compositions such as combinations of a reductive chemical and a chelant in an alkaline medium to improve the process efficiency and brightness of a paper product produced from a pulp material manufactured in such a process. The invention has particular relevance for decreasing freeness, providing energy and chemical savings, and enhancing brightness of paper products.
Mechanical pulping is a common method to produce pulp. One advantage mechanical pulping has over other pulping methods is that the pulping process does not result in a significant loss of mass. Mechanical pulping operations unfortunately are very energy-intensive and they tend to produce pulps with low strength. Chemical treatment, such as alkalization, is sometimes used to increase strength and save energy, at the expense of brightness. Several technologies are currently practiced in mechanical pulping to manufacture products such as stone ground wood (SGW), pressurized ground wood (PGW), refiner mechanical pulp (RMP), pressurized RMP (PRMP), thermo-RMP (TRMP), and thermo-mechanical pulp (TMP).
One currently known method of reducing the energy required in mechanical pulping is through alkalization that leads to reducing the freeness of the pulp. The common prior art method of reducing the freeness of pulp is to add alkali to wood chips during the mechanical pulping process. Unfortunately, adding alkali to wood chips also causes a drop in the brightness of the resulting paper. To compensate for this brightness drop, additional bleach must be added during the bleaching stage of the papermaking process thereby reducing or eliminating any overall cost savings.
As a result, papermakers are forced to make an undesirable tradeoff. They must either choose to reduce energy costs but accept a loss in brightness or they must use additional bleach and sacrifice cost savings. Thus there is a clear need for a technology that provides energy savings without jeopardizing optical properties of paper made from such pulp.

Brief Summary of the Invention

At least one embodiment of the invention is directed towards a composition and a method of its use. The composition improves the papermaking process. The composition comprises a base, a small quantity of a strong reductive chemical comprising NaBH₄, and a chelating agent. The composition is added to the papermaking process before or during the mechanical pulping of wood chips. The composition decreases the energy consumption in pulp manufacturing but does not induce a net decrease in brightness of paper produced from the paper pulp when compared to paper similarly produced from similar paper pulp that did not have the composition added to its wood chips. The composition can be an aqueous solution or slurry capable of being applied at any stage of the mechanical pulping process, before or during the refining, e.g., in a wood chip washing operation, chip soaking, sprayed over the chips, and may be capable of being added directly into a refiner.
At least one embodiment of the invention is directed towards a composition wherein the base is magnesium hydroxide. Also disclosed is a composition wherein the base is magnesium hydroxide and an alkali or alkaline earth metal hydroxide such as sodium hydroxide. One preferred composition can induce the resulting pulp to be more effectively bleached by peroxide or hydrosulfite bleaching including but not limited to treatment with magnesium hydroxide. Treatment of wood chips before or during mechanical pulping with small quantities of magnesium hydroxide, activates the pulp to subsequent bleaching, specifically peroxide bleaching.
The invention is directed towards a composition in which the reductive chemical comprises sodium borohydride. Further disclosed is a composition in which the reductive chemical is sodium borohydride and a chemical selected from the list consisting of: water soluble hydrosulfites (dithionites), sulfites, bisulfites, metabisulfites, formidinesulfinic acid, salts of formidinesulfinic acid, borohydrides, phosphines, phosphonium tertiary salts; more specifically, alkali or alkaline earth metal hydrosulfites, borohydrides, sodium hydrosulfite, and any combination thereof. The chelating agent can be a transitional metal ion chelant selected from the list consisting of: organic hydroxyacids, aminophosphonates, aminophosphates, aminocarboxylates; more specifically, salts of DTPA, salts of EDTA, salts of DTMPA, and any combination thereof.

Detailed Description of the Invention

The following definitions are provided to determine how terms used in this application, and in particular how the claims, are to be construed. The organization of the definitions is for convenience only and is not intended to limit any of the definitions to any particular category.
"CSF" means Canadian Standard Freeness a described by TAPPI methods and standards and measured in millimeters.
"Freeness" means the measure of the rate at which a suspension of pulp may be drained, and is typically measured according to the Canadian Standard Freeness test, as defined by TAPPi methods and standards. Changes in freeness can result from both chemical and physical changes in pulp.
"Mechanical pulping" means a physical change caused by converting pulpwood logs and chips into pulp by the use of mechanical energy.
"Chemimechanical pulping" means a mild chemical change occurring in a wood grinding or chip refining process. Chemimechanical pulping commonly improves paper strength or facilitates paper production.
"Refiner groundwood" means mechanical pulp made with a grinder and put through a rubbing, brushing, crushing, fraying, or cutting treatment in a pulp mill processing machine called a refiner.
"Refiner mechanical pulp" means pulp made by processing untreated wood chips in mechanical atmospheric refiners.
"Refiner" means a machine for mechanical treating fibers in pulp and paper mills when rubbing, brushing, crushing, fraying, or cutting is desired to process or impart certain properties to the finished pulp slurry and the sheet web formed on the paper machine.
"Small Quantity" means a concentration of an additive added to a suspension of paper pulp, which is insufficient to induce any substantial chemical changes in the pulp that are normally associated with chemimechanical pulping.
It has been known that causing a change in freeness, normally caused by alkalization, can reduce the energy needed in the pulping process (see for example US Published Application 2008/0105392 ). In at least one embodiment, very small quantities of chemicals as defined above are added to wood chips that results in low energy costs when the wood chips are mechanically pulped. The low energy costs are the result of a synergistic combination of the chemicals that both reduces pulp freeness and improves brightness of the pulp. Normally, freeness reduction results from the changes in physical pulp properties such as swelling of fibers. Alkaline environments can cause such swelling. However because alkali environments also increase oxidation and cause phenolic group ionization in lignin, which is always present in a high-yield (mechanical) pulp, it causes yellowing of the resulting paper. As a result either the paper has a lower brightness or more bleaching chemicals must be used, thereby increasing costs.
In the Invention, this problem is addressed in two ways. First, magnesium hydroxide is used as a source of alkalinity. The magnesium hydroxide activates the pulp in the following peroxide or hydrosulfite bleaching stages, thereby increasing the degree of brightness that results from bleaching. Second, the reaction in the refiner is adjusted to be reductive not oxidative. This also inhibits any brightness loss that uncontrolled oxidation would otherwise cause. In addition, a chelating agent may be added which further reduces any yellowing because it immobilizes transition metal cations that could otherwise catalyze yellowing reactions. In at least one embodiment, magnesium hydroxide is combined with one or more reducing agents including sodium borohydride and one or more chelating agents prior to the refining or in the refiner. In at least one embodiment, this combination is followed by peroxide bleaching.
In this application the specialty chemicals are used in very small quantities and are believed to operate against the pulp only at a mechanical level and not at a chemimechanical level. Because of the low quantity used, no significant chemical changes occur in the pulp. The low quantity of specialty chemicals, however, is sufficient to cause the freeness reduction in the pulp and thereby reduce the energy consumption during the mechanical pulping process. Because relatively little chemical changes occur in the pulp, this method can freely be used with most if not all currently known techniques used in most operating mills manufacturing mechanical pulp, which include but are not limited to TMP, RMP, and/or groundwood based pulps.
Small quantities of at least one reductive chemical and at least one chelant in an alkaline medium can be used to treat wood chips during manufacturing of mechanical pulp. When these chemicals are so combined, instead of the brightness loss that is typical of alkaline treatments, a brightness gain occurs.
The small quantity of at least one reductive chemical and at least one chelant in an alkaline medium, applied prior to or at the refining stage, can enhance the bleaching process performed later in the papermaking process. In at least one embodiment, the specialty chemicals added prior to or at the refining stage (i.e. magnesium hydroxide in a mixture with reductive chemical(s) including sodium borohydride and, chelant(s)) induce pulp activation towards subsequent bleaching, which then requires less bleaching materials to achieve the same degree of brightness. In at least one embodiment, the bleaching is peroxide or hydrosulfite bleaching.
The at least one of the sources of alkali comprises magnesium hydroxide (MH). In at least one embodiment, the MH is used by itself, and the positive effect on brightness is observed after the peroxide or hydrosulfite bleaching stage.
Also disclosed herein is a combination of the MH with sodium hydrosulfite and a chelant, which does not fall within the claimed invention.At least one of the reductive chemicals may be sodium hydrosulfite (SH). The SH may be combined with magnesium hydroxide and a chelant in a combination which does not fall within the claimed invention. In at least one embodiment, small quantities of a strong reductive chemical such as SH with sodium borohydride (BH) are combined with MHAlso disclosed are small quantities of a strong reductive chemical such as SH with or without BH are combined with sodium hydroxide in a combination which does not fall within the claimed invention.
In at least one embodiment, at least one of the reductive chemicals is very small quantity of BH. Also disclosed, the BH is combined with sodium hydrosulfite and a chelant in a combination which does not fall within the claimed invention. In at least one embodiment the source of alkali is MH. Also disclosed is a small quantity of a strong reductive chemical such as SH with BH combined with MH.
This method makes use of chemicals commonly available in paper mills but uses them in a novel manner. As shown in the following references, while use of BH and hydrosulfite is known in paper manufacture, it has only been used in bleaching processes, under neutral to slightly acidic conditions, and in kraft pulping processes, and not in mechanical pulping processes. (See for example patents and patent applications: US 5,129,987 , EP 141826 , US 2004/0000380 , EP 485074 , WO 88010334 , EP 00027369 , DE 2826821 , JP 48038328 as well as journal articles: " Premix": a novel process for improving bleaching of mechanical pulps for using a mixture of reductive agents, Wasshausen, J. et al. Pulp & Paper Canada, (2006), Volume 107 Issue 3, Pages 44-47 and New hydrosulfite route reduces groundwood bleach costs, Sellers, F. G. Pulp & Paper (1973) Volume 47 Issue 12, pages 80-82.
In addition, sodium borohydride assisted peroxide bleaching is disclosed in Further Understanding of Sodium Borohydride Assisted Peroxide Bleaching of Mechanical Pulps, He, Zh., Appita Journal (2005), Volume 58 issue 1, pages 72-76. The direct use of BH as a bleaching chemical is disclosed in US 2004/000380 WO 1996/020308 , and WO 90011403 and its use as a pre-bleaching/mulit-stage bleaching chemical is disclosed in WO 01059205 . Use of large amounts (1-3%) of BH on kraft pulping was described in Determination of kraft NaBH4 pulping condition of Uldag fir, by Akgul, M., Pakistan Journal of Biological Sciences (2006) Volume 9 page 13. Finally, pre-treatment of wood chips with several chemicals for kraft and sulfite cooking is described in DE 1955641 and DE 2105324 .
The use of magnesium hydroxide in the refiner is described among other places in Chinese Patent Application CN 2008-10014053 20080123 . This description is directed to a process known as refiner bleaching conducted with Mg(OH)₂ and hydrogen peroxide. None of any of these references describes using magnesium hydroxide in mechanical pulping, either by itself or in combination with small amounts of reductive chemicals, or use of these chemicals in mechanical pulping operations in a basic environment.
US 4,324,612 discusses the use of sodium dithionite which is added to a spray shower applied to a stone surface in preparation of bleached stone groundwood spruce pulp, which is then followed by further bleaching of the screened pulp in a peroxide tower. This reference however does not include the use of base for energy savings and does not mention using magnesium.
US 5,129,987 discusses refiner bleaching with alkaline sodium hydrosulfite. This reference however is essentially a high-consistency bleaching process involving high doses of the hydrosulfite typical of bleaching procedures.
WO 9722749 discusses a method of reducing the energy in a pulping process but it involves adjusting the pH and overall different treatment procedure targeting the crystalline structure of cellulose.
US 5,338,402 utilizes similar chemicals to the invention but only in quantities large enough for chemimechanical pulping, targeting different pulp properties, and under different process conditions. For example, it mentions manufacturing CTMP that involves cooking at a temperature equal to or greater than 100 C using a reducing agent more electronegative than the sulfite ion together with sodium sulfite or bisulfite or a mixture of sulfur dioxide and sodium 'hydroxide. The reducing agent may be thiourea dioxide, sodium borohydride, or sodium Dithionite.
Another prior art source describes a multistage pretreatment process involving a reducing agent but is dissimilar to the inventive one step process. The source describes producing bleached pulp from wood chips via a process involving pretreatment of the chips first with at least one reducing agent (e.g., with a mixture of sodium sulfite and sodium borohydride) and then with an alkaline peroxide solution. The pretreatments were followed by refiner defibration. ( Brightening of Douglass-Fir Groundwood, Betz, R. G., Styan G. E., Pulp Paper Magazine Canada (1974) Volume 75 Pages 111-114).
In another prior art, the energy expended in the mechanical refining and beating of groundwood pulps was proposed to be lowered while improving brightness and strength properties by the addition of sodium dithionite directly to the refiner or beater. ( Treatment of Mechanical Wood Pulp with Reductive Bleaching Chemicals in Refiners, Melzer, J.; Auhorn, W., Wochenblatt fur Papierfabrikation (1986), Volume 114, Number 8, pages 257-260. This method however is dissimilar to the inventive process because it lacks alkali, uses much more hydrosulfite and essentially is a hydrosulfite refiner bleaching.
WO 2008058003 A2 provides a composition and method for improving a mechanical pulping process by decreasing freeness and amount of shives, providing energy and chemical savings, and enhancing brightness and mechanical strength of paper product made from a pulp material in the process. The composition includes formulations, such as surfactants, chelants, hydrotopes, reductive and oxidative pulp modifiers, and pH-controlling chemicals. The method includes selectively introducing these formulations to the pulp material in the mechanical pulping process.
WO 2005/106110 describes a method of producing hardwood pulp. The method comprises treating hardwood chips with one or more than one Family 11 xylanase enzyme in the absence of adding an oxidizing enzyme for about 5 minutes to about 120 minutes, to produce a treated chip mixture. The treated chip mixture is then mechanically refined to produce the hardwood pulp.
In at least one embodiment although the specialty chemicals darken the pulp, the resulting paper is not dark. The pulp is darkened due to alkalization. However, because the specialty chemicals activate the pulp, the process of subsequently bleaching the darkened mechanical pulp is enhanced and less bleach is needed. This method is particularly effective with magnesium hydroxide as the source of alkali, and when the bleaching is accomplished by peroxide bleaching. Pulp activation targeted towards post-refiner bleaching can be achieved by application of magnesium hydroxide alone.
Also disclosed herein, prior to the mechanical pulp undergoing peroxide bleaching or hydrosulfite bleaching, magnesium hydroxide and sodium hydrosulfite may be combined with the mechanical pulp in a refiner to produce brighter mechanical pulp, in a combination which does not fall within the claimed invention. A chelant is also added to wood chips prior to the refining operation or in the refiner.
The specialty chemical is magnesium hydroxide, with a chelant. We found that, unlike sodium hydroxide, magnesium hydroxide improves pulp brightness after hydrosulfite and, especially, peroxide bleaching by pulp activation towards these processes, while immediate post-refining brightness may still decrease.
In at least one embodiment, the specialty chemicals are in the form of an aqueous solution or slurry that can be fed directly to the refiner or sprayed over wood chips.
In at least one embodiment, the specialty chemicals are in the form of an aqueous solution or slurry that can be applied on wood chips during soaking or washing operations.
The foregoing may be better understood by reference to the following example, which is presented for purposes of illustration and is not intended to limit the scope of the invention.
Several methods presented below, were used to simulate the environment in which the invention can be practiced. Pulp samples were obtained from Midwestern American mills and from European mills (softwood TMP, TMP 1^st and 2^nd rejects). The doses are based on actives unless stated otherwise. DTPA has always been used in a form of a 38% solution (normally used in the industry) and the doses refer to this solution.

Test A. High temperature shock conditions: borohydride-based compositions with sodium hydroxide

Experimental tests were conducted under wet temperature shock conditions simulating those in a refiner where to mechanical treatment occurs. Samples of TMP were placed in stainless steel digesters and the chemicals added in water so that the end consistency was 3-5% dry pulp in slurry. The samples were kept at 150°C for 10 minutes in a rotating digester setup, cooled down, washed, pH measured and had handsheets made from them. The pH in all the samples went from alkaline to slightly acidic, indicating a finished chemical reaction; therefore no acidification of the slurries was needed.

Test B. Moderate temperature shock conditions: hydrosulfite-containing compositions with sodium hydroxide

Experimental tests were conducted under wet temperature shock conditions simulating those in a refiner where mechanical treatment occurs. Samples of TMP were placed in degassed flasks under septa (soft plastic that protects the content from air but can be penetrated with a needle) and chemicals were added via a syringe in a flow of nitrogen, to a total consistency of 3.6%. The samples were kept at 80°C for 1 hour 15 minutes in a water bath, cooled down, washed, pH measured and handsheets were made upon acidification to pH 5. The pH of the samples after the process was slightly alkaline. In a test where sodium borohydride was applied, it was used in a form of Rohm&Haas' product Borol, which is (39% NaOH, 12% NaBH₄). The target alkalinity (for example, 0.75% NaOH, 0.25% NaBH4 to o.d. pulp) was maintained by varying quantities of introduced sodium hydroxide.

Test C. Hydrosulfite treatment with sodium hydroxide followed by bleaching

The samples were prepared as described in Test B, washed, dewatered and bleached under standard conditions (70°C, 1 h, 1.5% NaOH, 2% H₂O₂). The samples were washed, and handsheets were made upon acidification to pH 5.

Test D. Freeness improvement

A protocol was developed that simulated both mechanical and temperature effects of the thermomechanical process better that just a shock temperature treatment. The pulp was mixed with the chemicals at 10% consistency and then beaten in a PFI-type laboratory pulp refiner (150°C). Then the pulp was diluted to 3% and exposed to heat as described in Test A. Freeness (CSF) of the pulp treated in presence of 0.75-1 % NaOH was about 20 ml lower than in the control; borohydride and DTPA did not affect the result.

Test E. High temperature shock conditions: hydrosulfite-containing compositions with magnesium hydroxide

A brightness test was conducted under wet temperature shock conditions simulating those in the refiner (no mechanical treatment). Samples of TMP were placed in plastic bags and mixed well with magnesium hydroxide and DTPA. The bags were opened, and the samples transferred into stainless steel digesters and degassed with nitrogen, for 7 minutes each. The remaining chemicals were added via a syringe into the volume of the pulp in a nitrogen flow. The 5%-consistency samples were kept at 150°C for 10 min in a rotating digester setup, cooled down, washed, pH measured and either handsheets were made or the pulp was subsequently bleached. The pH in all of the samples went from alkaline to slightly acidic, indicating a finished chemical reaction; therefore no acidification of the slurries was needed.

Test F. Moderate temperature shock conditions: hydrosulfite-containing compositions with magnesium hydroxide

The assessment of the effect of reductive chemicals on brightness was conducted under wet temperature shock conditions simulating those in the refiner (no mechanical treatment). Samples of TMP were placed in degassed flasks under septa and chemicals added via a syringe, to total consistency 5%. Magnesium hydroxide as a dilute slurry and DTPA were added first, mixed well with the pulp, then reductive chemicals added. After mixing, the samples were kept at 80°C for 1 h 15 min in a water bath, cooled down, washed, and pH measured and handsheet made (no pH adjustment) or the pulp subsequently bleached.

Test G. Hydrosulfite treatment with magnesium hydroxide followed by peroxide bleaching

Samples were prepared as described in Test E or F, washed with 2L DI water, dewatered and bleached under standard conditions (70°C, 1 h, 1.5% NaOH, 2% H₂O₂). The samples were washed with 2L DI water and handsheets made upon acidification to pH 5.

Test H. Hydrosulfite treatment with magnesium hydroxide followed by hydrosulfite bleaching

Samples were prepared as described in Test E or F, washed with 1L DI water, dewatered and bleached under standard conditions (70°C, 1 h, 1 Na₂S₂O₄). The samples were washed with 2L DI water, and handsheets were made.
The results of tests A-H are provided in the following tables 1-18 in which the parenthesis next to the table number indicates which data corresponds to which tests.

TABLES

Table 1 (A) (Reference samples)

Sample	Brightness
Control	52.10
0.5% NaOH	49.66
0.5% NaOH + 0.25% NaBH₄	52.96
0.5% NaOH + 0.1% NaBH₄	51.71

Table 2 (A) (Reference samples)

Sample	Brightness
Control	52.82
0.5% NaOH	49.64
0.5% NaOH + 0.1% NaBH₄	51.88
0.5% NaOH + 0.1% NaBH₄ + 0.1% DTPA	52.53
1% (CH₃)₄NOH	50.38
1% (CH₃)₄NOH + 0.1% NaBH₄	51.95
0.5% NaOH + 0.25% [(HOCH₂)₄P]₂SO₄	51.44

The data of Tables 1 and 2 demonstrate that minimal quantities of the specialty chemicals can fully compensate for the brightness loss due to alkalization of the pulp. A chelant noticeably increases the effect of borohydrate.

Table 3 (A) (Reference samples)

Sample	Brightness
Control	52.42
0.75% NaOH	50.02
0.75% NaOH + 0.25% NaBH₄	52.88
0.75% NaOH + 0.1% NaBH₄	52.10
0.75% NaOH + 0.1% NaBH₄ + 0.1% DTPA	53.13
1% NaOH + 0.25% NaBH₄	51.92

Table 4 (A) (Reference samples)

Sample	Brightness
Control	52.30
0.75% NaOH	49.27
0.75% NaOH + 0.23% NaBH₄	52.5
0.75% NaOH + 0.1% NaBH₄	51.62
0.75% NaOH + 0.05% NaBH₄	51.01
0.75% NaOH + 0.05% NaBH₄ + 0.05% DTPA	51.47
0.75% NaOH + 0.025% NaBH₄ + 0.05% DTPA	50.6

The data in Table 3 and 4 demonstrate that the optimal alkalinity that can be applied without a brightness loss is 0.75%.

Table 5 (B) (Reference compositions)

Sample	Brightness
Control	55.82
0.75%NaOH	54.08
0.75% NaOH + 0.2% Na₂S₂O₄	55.02
0.75% NaOH + 0.5% Na₂S₂O₄	55.92
0.75% NaOH + 0.2% Na₂S₂O₄ + 0.05% NaBH₄	55.98
0.75% NaOH + 0.2% Na₂S₂O₄ + 0.05% NaBH₄ + 0.05% DTPA	56.21
0.75% NaOH + 0.2% Na₂S₂O₄ + 0.025% NaBH₄ + 0.05% DTPA	55.66

Table 5 lists the effect on brightness upon the thermal treatment of the pulp after the composition underwent peroxide bleaching.

Tables 6-9 list the effect of the compositions (prototype products, 27% total solids) on paper products.

Table 6 (C) (Reference compositions)

Sample	Brightness
Control	61.17
0.75% NaOH	59.78
0.75% NaOH + 0.3% Na₂S₂O₄ + 0.05% DTPA	62.33
0.75% NaOH + 0.3% Na₂S₂O₄ + 0.025% NaBH₄ + 0.05% DTPA (I)	63.79
0.75% NaOH + 0.3% Na₂S₂O₄ + 0.0125% NaBH₄ + 0.05% DTPA (II)	63.81

Table 7 (C) (Reference compositions)

Sample	Brightness
Control	61.36
0.75% NaOH	58.90
0.75% NaOH + 0.025% NaBH₄ + 0.05% DTPA	63.46
0.75% NaOH + 0.3% Na₂S₂O₄ + 0.025% NaBH₄ + 0.05% DTPA (I)	66.38
0.75% NaOH + 0.3% Na₂S₂O₄ + 0.0125% NaBH₄ + 0.05% DTPA (II)	64.22

Table 8 (C) (Reference compositions)

Sample	Brightness
Control	60.34
0.75%NaOH	58.57
0.75% NaOH + 0.3% Na₂S₂O₄ + 0.025% NaBH₄ + 0.05% DTPA	65.48
0.75% NaOH + 0.3% Na₂S₂O₄ + 0.0125% NaBH₄ + 0.05% DTPA	65.74

Tables 9 and 10 provide the effect of one of preferred compositions, 19% NaOH, 0.316% NaBH₄, 0.48% DTPA, 6.32% Na₂S₂O₄ (26.1-27.2% solids, depends on the impurities in the solid hydrosulfite). The composition was then diluted in paper pulp slurry so that the NaOH was reduced to 0.75% to o.d. pulp. Table 9 (B) (Reference samples)

Sample Brightness

Control 49.71

0.75% NaOH 48.62

Prototype Product (first try) 50.57

Prototype Product (second try) 49.83

Prototype Product (third try) 50.01

Table 10 (B) (Reference samples)

Sample Brightness

Control 49.40

0.75% NaOH 46.68

Prototype Product (first try) 49.45

Prototype Product (second try) 50.15

Prototype Product (third try) 50.06

Table 11 indicates the effect of using magnesium hydroxide as the alkali. Magnesium hydroxide is less expensive than other alkali. Compositions containing magnesium hydroxide requires less energy to undergo the pulping process. When substituting magnesium hydroxide for sodium hydroxide the replacement ratio is 0.75% sodium hydroxide for 0.5% magnesium hydroxide.

Table 11 (F,G)

	Brightness, unbleached	Brightness, bleached
Control	49.09	55.18
0.5% Mg(OH)₂	49.05	60.49
0.5% Mg(OH)₂+0.05%DTPA	49.67	60.86
0.5% Mg(OH)₂+0.05%DTPA +0.25% Na₂S₂O₄	52.28	61.99
0.5% Mg(OH)₂+0.05%DTPA+0.25% Na₂S₂O₄+0.0125%NaBH₄ ^◆	54.44	62.42
0.5% Mg(OH)₂+0.05%DTPA+0.125% Na₂S₂O₄+0.0125%NaBH₄ ^◆	53.56	62.54
0.25% Mg(OH)₂	49.91	61.15
0.05%DTPA	50.45	56.58

^◆samples of the invention

Table 12 (F, G)

	Brightness, bleached
Control	55.41
0.5% Mg(OH)₂+0.05%DTPA +0.25% Na₂S₂O₄	62.11
0.5% Mg(OH)₂+0.05%DTPA +0.125% Na₂S₂O₄	61.07
0.5% Mg(OH)₂+0.05%DTPA +0.125% Na₂S₂O₄+0.0125%NaBH₄ ^◆	61.34
0.125% Mg(OH)₂+0.05%DTPA +0.125% Na₂S₂O₄	61.90
0.125% Mg(OH)₂+0.05%DTPA +0.125% Na₂S₂O₄+0.0125%NaBH₄ ^◆	62.03
0.125%Mg(OP)₂	61.17

^◆ samples of the invention

Table 13 (E,G)

	Brightness, unbleached	Brightness, bleached
Control	49.67	54.17
0.5% Mg(OH)₂	46.92	57.72
0.5% Mg(OH)₂+0.05%DTPA	46.50	59.35
0.5% Mg(OH)₂+0.05%DTPA+0.25% NaS₂O₄	49.68	59.85
0.5% Mg(OH)₂+0.05%DTPA+0.25% NaS₂O₄+0.0125%NaBH₄ ^◆	50.27	60.05
0.25% Mg(OH)₂+0.05%DTPA+0.25% NaS₂O₄+0.0125%NaBH₄ ^◆	52.76	61.48
0.25% Mg(OH)₂	48.03	59.17
0.05%DTPA	49.46	56.21

^◆ samples of the invention

Table 14 (E,G)

	Brightness, unbleached	Brightness, bleached
Control	48.58	54.4
0.5% Mg(OH)₂	46.95	58.95
0.75% NaOH	47.59	48.55
0.5% Mg(OH)₂+0.05%DTPA +0.25% Na₂S₂O₄+0.0125%NaBH₄ ^◆	51.55	60.74
0.25% Mg(OH)₂+0.05%DTPA +0.25% Na₂S₂O₄+0.0125%NaBH₄ ^◆	54.33	61.77
Prototype Product based on NaOH, see above (0.75% NaOH)	50.41	53.17
Prototype Product based on NaOH, see above (0.75% NaOH)	50.59	53.36
Control, bleaching with 0.05% MgSO₄		54.61
Control, bleaching with 0.05% MgSO₄ +0.05 %DTPA*		55.42

^◆ samples of the invention

The data from Tables 11-14 demonstrate why using magnesium hydroxide is preferred. There is no magnesium-related brightness loss under moderate conditions (75°C, no bleaching), while under severe conditions (150°C, no bleaching) better simulating a refining process, magnesium-related brightness loss occurs. However, in both cases there is a significant magnesium-induced brightness improvement after bleaching. Reductive chemicals further significantly improve post-refining brightness: a major effect of hydrosulfite, less from extra borohydride. Magnesium-reductive pulp pre-treatment clearly shows performance in refining applications. This effect is new and, as shown in Tables 14-16 (alternative pulps were used in 15 and 16), it cannot be achieved by just presence of magnesium ions in the pulping slurry. The pre-treatment is required, and this stage is automatically achieved when the proposed chemistry is present at the stage of mechanical pulping.

Table 15 (G) (Reference samples)

Chemistry	Application	Brightness
Control		56.40
0.05% MgSO₄+0.125%DTPA	In liquor	57.47
0.125% MgSO₄	Mixed with pulp before bleaching	57.95
0.25%MgSO₄	Mixed with pulp before bleaching	58.17
0.125% Mg(OH)₂	Mixed with pulp before bleaching	58.60
0.25% Mg(OH)₂	Mixed with pulp before bleaching	58.84
0.125% Mg(OH)₂	Mixed with pulp, kept at 50°C for 30 min before bleaching	60.18
0.25% Mg(OH)₂	Mixed with pulp, kept at 50°C for 30 min before bleaching	60.36
0.125% Mg(OH)₂	Mixed with pulp, kept at 70°C for 60 min before bleaching	60.23
0.25% Mg(OH)₂	Mixed with pulp, kept at 70°C for 60 min before bleaching	60.07

Table 16 (F,G)

	Brightness, bleached
Control	59.50
0.5% Mg(OH)₂+0.05%DTPA +0.25% Na₂S₂O₄	66.93
0.5% Mg(OH)2+0.05%DTPA +0.125% Na₂S₂O₄	66.12
0.125% Mg(OH)₂+0.05%DTPA +0.125% Na₂S₂O₄	66.42
0.125% Mg(OH)₂+0.05%DTPA +0.125% Na₂S₂O₄+0.0125%NaBH₄ ^◆	67.14

^◆ sample of the invention

The positive effect of the specialty chemicals is also observed in the subsequent hydrosulfite bleaching as illustrated in Tables 17 (mild conditions, full compensation) and 18 (severe conditions better simulating the refining process, a significant brightness gain).

Table 17 (F,H)

Sample	Brightness
Control	59.22
0.5% Mg(OH)₂	57.79
0.5% Mg(OH)₂+0.05%DTPA +0.25% Na₂S₂O₄+0.0125%NaBH₄ ^◆	59.68
0.5% Mg(OH)₂+0.05%DTPA +0.125% Na₂S₂O₄	58.43

^◆ sample of the invention

Table 18 (E,H)

Sample	Brightness
Control	51.42
0.5% Mg(OH)₂	51.97
0.5% Mg(OH)₂+0.05%DTPA	52.46
0.5% Mg(OH)₂+0.05%DTPA +0.25% Na₂S₂O₄	56.03
0.5% Mg(OH)₂+0.05%DTPA +0.25% Na₂S₂O₄+0.0125%NaBH₄ ^◆	55.43
0.5% Mg(OH)₂+0.05%DTPA +0.125% Na₂S₂O₄+0.0125%NaBH₄ ^◆	53.67

^◆ sample of the invention

Changes can be made in the composition, operation, and arrangement of the method of the invention described herein without departing from the invention as defined in the claims. While this invention may be embodied in many different
forms, there are described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. Furthermore, the invention encompasses any possible combination of some or all of the various embodiments described herein.
The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term "comprising" means "including, but not limited to".

Claims

A composition that improves a mechanical papermaking process, the composition comprising:
a base comprising magnesium hydroxide, and

a small quantity of a reductive chemical comprising NaBH₄, and a chelating agent

wherein the composition is added to the papermaking process no later than when the mechanical pulping of wood chips occurs.
The composition of claim 1 in which the chelating agent is a transitional metal ion chelant selected from the list consisting of: organic hydroxyacids, aminophosphonates, aminophosphates, aminocarboxylates, salts of DTPA, salts of EDTA, salts of DTMPA, and any combination thereof.
The composition of claim 1 in which composition is an aqueous solution or slurry for use in spraying wood chips, socking wood chips, washing wood chips, or for use in a refiner, or a combination thereof.
The composition of claim 1 in which the reductive chemical further comprises sodium hydrosulfite.
Use of the composition of claim 1 to reduce the freeness of paper in a papermaking process when the composition is added no later than when the mechanical pulping of wood chips occurs.
A method of improving a mechanical pulping process, the method comprising:
adding to pulp material prior to the conclusion of a mechanical pulping process the composition according to claim 1,

wherein the composition decreases the freeness of the resulting paper pulp and increases the brightness of the resulting paper pulp.
The method of claim 6 in which the composition is an aqueous solution or slurry capable of being added in according to one method selected from: being sprayed over wood chips, soaking of wood chips, washing of wood chips, added in a refiner, and any combination thereof.
The method of claim 6 wherein the composition is a synergistic mixture of magnesium hydroxide, sodium hydrosulfite sodium borohydride, sodium hydroxide, and a chelant.
The method of claim 8 further comprising the step of combining magnesium hydroxide with sodium hydrosulfite in a refiner which produces brighter mechanical pulp after subsequent peroxide or hydrosulfite bleaching.
The method of claim 6 in which the base is only magnesium hydroxide in a dosage of 0.05-0.5%.