JP2002266273A - Method for dehydrating lime mud - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for dehydrating lime mud in low foaming tendency stably affording reduction in the water content of lime mud cake even under fluctuation of process conditions. SOLUTION: This method for dehydrating lime mud involves addition of (A) a polyoxyethylene polyoxypropylene alkyl ether of general formula (1): R1 O[CH2 CH(CH3 )O]m [CH2 CH2 O]n H (wherein, R1 is a 10-22C alkyl; m is an integer of 2-10; and n is larger than m, being an integer of 5-20) and (B) a 2nd polyoxyethylene polyoxypropylene alkyl ether of general formula (2): R2 O[CH2 CH(CH3 )O]p [CH2 CH2 O]q H (wherein, R2 is a 10-22C alkyl; p is an integer of 15-30; and q is an integer of 2-10) as the active ingredients.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for dewatering lime mud in a causticizing step of kraft pulp production. More specifically, the present invention relates to a lime mud dewatering method for reducing the water content of a lime mud cake obtained by dehydrating a lime mud mainly composed of calcium carbonate generated in a causticizing step.

[0002]

2. Description of the Related Art In a causticizing process in the production of kraft pulp, a smelt obtained by burning a recovered black liquor in a boiler is dissolved, and quicklime is poured into a green liquor as a supernatant, and a lime is added to the green liquor. In this step, sodium carbonate is converted into sodium hydroxide, and the generated calcium carbonate is removed to prepare a white liquor used as a cooking liquor for wood chips. Green liquor is usually
It is a strong alkaline aqueous solution containing sodium carbonate and sodium sulfide as main components.
Quicklime reacts with water to form calcium hydroxide, which undergoes an exchange reaction with sodium carbonate in the green liquor to produce water-insoluble calcium carbonate. As a result, the green liquor contains a slurry (hereinafter referred to as "lime mud") containing water-soluble sodium hydroxide, sodium sulfide and water-insoluble calcium carbonate.

[0003] Lime mud is separated into solid and liquid by a filter, and the filtrate is sent to a pulp digestion process as a white liquor containing sodium hydroxide and sodium sulfide, and the lime mud cake separated on the filter surface is peeled off and removed from the kiln. The lime is burnt and regenerated into quicklime, and is used again in the causticizing process. Filters used for solid-liquid separation include an Oliver filter, a Young filter and a precoat filter, and the separated lime mud cake usually has a water content of 30% by weight to 40% by weight. However, when the filter is clogged, the moisture content of the lime mud cake increases, which not only hinders the dewatering process, but also requires a large amount of fuel when firing in the kiln. Therefore, the operation of the apparatus is stopped to clean the filter cloth surface. However, if the frequency of cleaning is high, the operation is hindered.

[0004] In order to improve the dewatering properties of lime mud, the application of various dehydration accelerators has been proposed. For example, a method using a cationic polymer (JP-A-57-4834)
No. 0), a method using a combination of polyoxyethylene alkylphenyl ether and polyoxyethylene polyoxypropylene alkyl ether (JP-A-62-121700).
JP-A-7-48), a method using a combination of a polyoxyethylene alkyl phenyl ether and a nonionic surfactant such as a polyoxyethylene polyoxypropylene condensate.
793), a method using a 3 to 4 mole addition product of a linear alcohol having 10 to 14 carbon atoms with ethylene oxide (Japanese Patent Laid-Open No. 2000-344518), and the like.

[0005] However, in the method using a cationic polymer, lime mud is aggregated, but the dehydration effect is not increased, and conversely, water is entrapped in the aggregate to sometimes reduce the dehydration rate. Further, a method using a combination of polyoxyethylene alkylphenyl ether and polyoxyethylene polyoxypropylene alkyl ether, a method using a nonionic surfactant such as polyoxyethylene alkyl phenyl ether and polyoxyethylene polyoxypropylene condensate, In the method using 3 to 4 moles of ethylene oxide of a linear alcohol having 10 to 14 moles, many bubbles enter the lime mud, dehydration is hindered, the water content of the cake does not decrease, and the effect of adding a dehydration accelerator is obtained. Was not able to be done. Furthermore, due to fluctuations in the causticizing step, stable dehydration may not be achieved even when the above-mentioned dehydration accelerator is added.

On the other hand, considering the natural environment,
"Act on the Estimation of Emissions of Specific Chemical Substances into the Environment and the Improvement of Management" (Heisei 11)
(Promulgated on July 13, 2008), “Poly (oxyethylene) octyl phenyl ether”, “Poly (oxyethylene) alkyl ether (C12-15)”, etc. are registered as “Pollutant Release and Transfer” (hereinafter “PRTR”). Was required). Nonionic surfactants such as specific polyoxyethylene alkylphenyl ethers, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene polyoxypropylene condensates, etc .;
This is the case with molar adducts, and there has been an increasing movement in the industry to refrain from using these compounds. Therefore, a dehydration accelerator which does not fall under the PRTR and has less influence on the natural environment has been demanded.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing kraft pulp which has low foamability in a causticizing process.
An object of the present invention is to provide a lime mud dewatering method capable of stably reducing the water content of a lime mud cake even when process conditions vary.

[0008]

Means for Solving the Problems The invention according to claim 1 for solving the above technical problem is a method for dehydrating lime mud, wherein (A) the general formula (1) [wherein R ₁ has 10 to 10 carbon atoms. 2
2, an alkyl group, m is an integer of 2 to 10, and n is an integer of 5 to 20 larger than m. A polyoxyethylene polyoxypropylene alkyl ether represented by the formula:
Formula (2) wherein R ₂ is an alkyl group having 10 to 22 carbon atoms, p is an integer of 15 to 30, and q is an integer of 2 to 10. Is added as an active ingredient.

[0009]

Embedded image

Embedded image The invention according to claim 2 is the method for dewatering lime mud according to claim 1, wherein the A component: B component is 90:10 to 50:
50 (weight ratio).

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is characterized in that polyoxyethylene polyoxypropylene alkyl ether obtained by adding propylene oxide and ethylene oxide to a higher alcohol is used in combination of two types having different addition numbers of propylene oxide and ethylene oxide. And

One component (A component) is a polyoxyethylene polyoxypropylene alkyl ether represented by the general formula (1), and the other component (B component) is a polyoxyethylene polyoxyethylene represented by the general formula (2). It is a polyoxypropylene alkyl ether. In the general formulas (1) and (2), R ₁ and R ₂ are higher alcohol residues, each independently being an alkyl group having 10 to 22 carbon atoms, preferably 12 to 18 carbon atoms.

The higher alcohol may be straight-chain or branched, and includes natural alcohols such as coconut oil-reduced alcohol, and synthetic alcohols such as oxo method and Ziegler method. Examples of higher alcohols include lauryl alcohol, dovanol 23 (trademark, synthetic alcohol by the oxo method having 12 to 13 carbon atoms: Mitsubishi Chemical Corporation), stearyl alcohol, isostearyl alcohol, and oleyl alcohol. More than species are used.

The polyoxyethylene polyoxypropylene alkyl ether of the component A is obtained by adding propylene oxide to the higher alcohol in an amount of 2 to 10 mol, preferably 3 to 6 mol.
And ethylene oxide in an amount of 5 to 20 mol, preferably 8 to
The number of addition moles of ethylene oxide [n in general formula (1)] is larger than the number of addition moles of propylene oxide [m in general formula (1)]. If the number of moles of ethylene oxide added is smaller than the number of moles of propylene oxide added, it is difficult to dissolve or emulsify in water, and the dehydration promoting effect is reduced.

The component A is a component having a higher number of added ethylene oxides than propylene oxide and a high water solubility.
It is particularly effective for obtaining the effect of improving dehydration.

The polyoxyethylene polyoxypropylene alkyl ether of the component B is obtained by adding propylene oxide to the above higher alcohol in an amount of 15 to 30 mol, preferably 20 to 30 mol.
25 and 2 to 10 moles, preferably 3 to 8 of ethylene oxide.

The component B is a component having a smaller number of added ethylene oxides than propylene oxide and a low water solubility, and is particularly effective for obtaining the effect of suppressing the generation of bubbles.

The number of additions of ethylene oxide and propylene oxide in the components A and B is limited due to the effect of suppressing the dehydration and foaming of lime mud. Inferior to those within the above range.

The addition of ethylene oxide and the addition of propylene oxide to the higher alcohol may be random or block, and the addition of ethyleneoxy or propylene oxide may be performed for both components A and B. . Preferably propylene oxide is added first,
Next, it is a block adduct to which ethyleneoxy has been added.

The method of adding propylene oxide and ethylene oxide to the higher alcohol is not particularly limited, and it is produced by a general method. For example, a higher alcohol is put in a pressure vessel, and an alkali metal is used as a catalyst. A hydroxide, for example, sodium hydroxide is added and dissolved at about 0.3% by weight (relative to higher alcohol), and a predetermined amount of propylene oxide is stirred while stirring at a temperature of about 150 to 160 ° C. and a pressure of about 3 kg / cm ^2. After blowing and reacting a predetermined amount, ethylene oxide is blown, reacted, cooled, neutralized with a mineral acid such as sulfuric acid, and then filtered.

The carbon number of the higher alcohol in the present invention,
Both the number of moles of ethylene oxide and the number of moles of propylene oxide are statistical average values, and actually include components larger and smaller than these figures.

The combination ratio of the component A and the component B differs depending on the respective compounds of the component A and the component B. Preferably, the component A and the component B are 9: 1 to 5: 5 (weight ratio). Preferably, component A: component B = 8: 2 to 6: 4 (weight ratio). If the combination ratio is out of this range, the effects of the present invention may not be sufficiently obtained.

The place where the lime mud dehydration accelerator of the present invention is added is not particularly limited, and is appropriately selected according to the water content of the lime mud cake and the operating conditions of the vacuum dehydrator. Is added to the vat of a vacuum dehydrator, the vat of a washing machine, the storage tank of lime mud, and the piping line connected to these.

The amount of addition may be determined as appropriate according to the operating conditions of the causticizing process and the solid content of the lime mud. As a rule, the total of the effective components A and B is 1%.
0-100 ppm (active ingredient-mg / lime mud solids-kg), preferably 20-50 ppm (active ingredient-
mg / lime mud solids-kg). Usually, the addition amount is adjusted in view of the water content of the lime mud cake.

The two kinds of polyoxyethylene polyoxypropylene alkyl ethers of the present invention can be added to the process directly by using a chemical pump, by adding them as an aqueous solution, or by adding an appropriate organic solvent, for example, It is dissolved and added to methanol, ethanol, propyl alcohol, isopropyl alcohol, ethylene glycol, diethylene glycol, propylene glycol, ethylene glycol dimethyl ether, alcohols such as methylcellosolve, butylcellosolve, dioxane, ethylene carbonate and the like. The addition is performed continuously or intermittently.

In the addition, the polyoxyethylene polyoxypropylene alkyl ether of the component A and the component B may be added separately, or both may be mixed and added. However, in practice, both are mixed at a predetermined ratio to form a solution, which is added using a chemical pump.

The location of addition is not particularly limited, and is appropriately selected depending on the water content of the cake of the lime mud and the operating condition of the vacuum dehydrator. In general, a vacuum for dehydrating the lime mud is generally used. It is appropriately added to a dewatering machine vat, a washing machine vat, a lime mud storage tank, or a piping line connected to these.

In application, a dehydration accelerator conventionally used, for example, a cationic polymer, polyoxyethylene alkylphenyl ether, polyoxyethylene polyoxypropylene condensate, or the like, as long as the effects of the present invention are not impaired. It does not matter even if an ethylene oxide adduct of a linear alcohol is used in combination.

[0028]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

[Dehydration Test-1] Solid-liquid separation of lime mud (solid content: about 25% by weight) was performed using an Oliver filter, and the water content of the lime mud cake was about 30.
From the causticizing process of Kraft Pulp Mill A operating between about 40 wt% to about 40 wt%, the cake moisture content is about 4%.
Lime mud (solid concentration 2
5%) and subjected to the test.

500 g of lime mud is placed in a 1 L beaker, and stirred with a stirrer having propeller blades.
Warmed to 70 ° C. An aqueous solution of the dehydration accelerator having the composition described in Table 1 was added to the solution, and 300 ppm was obtained using a microsyringe.
(Active ingredient of dehydration accelerator-mg / lime mud solid content-
kg) and stirred at 120 rpm for 1 minute. Caliber 9
No.2 filter paper was spread on a perforated plate of a Buchner funnel having a diameter of about 6 cm.
And suction filtered. After performing suction for 30 seconds, the suction was stopped, the weight (W1) of the filtered lime mud cake was measured, and the cake was dried in a dryer at 105 ° C. for 6 hours. After cooling, the weight (W2) of the lime mud cake was measured, and the water content (%) of the lime mud cake was determined by the following equation. The test results are shown in Table 1.

Water content (%) of lime mud cake =
{(W1-W2) / W1} × 100 [Expansion test] 300 mL of heated lime mud is placed in a 500-mL stoppered test tube, a predetermined amount of a dehydration accelerator is added with a microsyringe, and slowly up and down five times. And then allowed to stand, and the height of foam from the liquid surface due to foaming after 30 seconds was measured. When the foaming property is high, the decrease in dehydration property is reduced. The test results are shown in Table 1.

[0032]

[Table 1] By adding 300 ppm (based on lime mud slurry solids) of the two polyoxyethylene polyoxypropylene alkyl ethers of the present invention, the conventional polyoxyethylene alkyl phenyl ether, polyoxyethylene polyoxypropylene condensate, linear alcohol The water content of the lime mud cake was reduced as compared with the case where the ethylene oxide adduct was used, the generation of bubbles was reduced, and uniform dehydration was performed.

As is evident from the above test results, the dehydration method using two kinds of polyoxyethylene polyoxypropylene alkyl ethers of the present invention uses the conventional dehydration method using a lauryl alcohol adduct of 3 to 4 mol of ethylene oxide. Compared to the method and the dehydration method using polyoxyethylene alkylphenol ether and ethylene oxide propylene oxide polymer in combination, a remarkable dehydration effect is obtained and there is no lime mud foaming, so the dehydration is performed uniformly and the moisture content is lower Lime mud cake was obtained.

[Dewatering Test-2] At the pulp and paper maker B, the operating conditions of the causticizing process (the lime mud solid content is about 25% by weight) fluctuate, and the water content of the lime mud cake using the Oliver filter is about The problem was as high as 35 to 40% by weight. Lime mud cake moisture content about 40
When the weight% was reached, the Oliver filter was stopped and the filter cloth surface was cleaned. The clogging cleaning of the Oliver filter has an effect on the operation because the cleaning is performed in a timely manner in accordance with the clogging condition of the filter in addition to the periodic cleaning once every 8 hours. Also, when the water content of the lime mud cake was high, the amount of fuel oil used in the firing kiln also increased. Thus, the operation was carried out by adding 300 to 500 ppm (based on lime mud solids) of lauryl alcohol with 3 moles of ethylene oxide adduct to the vat of the Oliver filter for the purpose of accelerating the dehydration, but the operation was not sufficiently improved. The causticizing process of this plant and the operating conditions of the kiln are as follows.

The number of washings of the Oliver filter: 1-2
Times / 8 hours ・ Oliver filter operation vacuum degree: 430-510mm
Hg • Oliver filter drum rotation speed: 0.8 to 2.4
rpm-Lime mud slurry temperature: 50-60 ° C-Cyclone outlet exhaust gas temperature after firing kiln: 150-
170 ° C. ・ Amount of calcined kiln heavy oil used: 1,300 (L / h) Therefore, the two kinds of polyoxyethylene polyoxypropylene alkyl ethers of the present invention were added to a vat of an Oliver filter as active ingredients in an amount of 300 ppm (based on lime mud solids). ) Was added continuously for 8 hours, whether or not lime mud slurry in the vat was foamed, the average value of the water content (% by weight) of the lime mud cake every 2 hours, the number of Oliver filter washings (times / 8 hours), 8 Evaluation was made based on the average value of the cyclone exhaust gas temperature (° C.) after the calcination kiln and the average amount of the calcination kiln heavy oil used (L / h). When the water content of the lime mud cake decreases, the cyclone exhaust gas temperature (° C.) after the firing kiln increases, and the amount of heavy oil used in the firing kiln (L /
h) becomes smaller. The results are shown in Table 2.

[0036]

[Table 2] By combining the two polyoxyethylene polyoxypropylene alkyl ethers of the present invention, the lime mud cake moisture content is reduced by about 5-8% by weight,
The amount of heavy oil used in the firing kiln led to a reduction of about 6 to 13% by weight, which reduced costs and achieved only one cleaning of the Oliver filter at the time of operation, greatly improving work efficiency and reducing costs. Benefits can be obtained.

[0037]

According to the present invention, the water content of the lime mud cake is reduced by dehydrating the lime mud by combining the two polyoxyethylene polyoxypropylene alkyl ethers of the present invention, and the amount of heavy oil used in the kiln is reduced. , And cost reduction is achieved, and a great merit can be obtained.

Claims (2)

[Claims] (A) General formula (1) wherein R ₁ is an alkyl group having 10 to 22 carbon atoms, m is an integer of 2 to 10, and n is an integer of 5 to 20 larger than m. A polyoxyethylene polyoxypropylene alkyl ether represented by the general formula (2) [wherein R ₂ has 10 to ₂ carbon atoms;
2 is an alkyl group, p is an integer of 15 to 30, q is 2 to 10
Is an integer. ] A method for dehydrating lime mud, comprising adding a polyoxyethylene polyoxypropylene alkyl ether represented by the formula (1) as an active ingredient. Embedded image Embedded image 2. Component A: Component B: 90:10 to 50: 5
The lime mud dewatering method according to claim 1, wherein the lime mud is added at 0 (weight ratio).