RU2053015C1 - Catalyst for oxidation of sulfide sulfur of white liquor - Google Patents

Abstract

FIELD: wood-pulp and paper industry. SUBSTANCE: catalyst for oxidation of sulfide sulfur of white liquor has transition metal oxide, pyrite cinder and carrier in form of low-density polyethylene. Transition metal oxide is used in form of antimony oxide (3) and manganese oxide (4) with the following amount of components, mas.%: pyrite cinder 15-17; antimony oxide (3) 17-20; manganese oxide 5-7; the balance, low-density polyethylene. EFFECT: higher efficiency. 2 tbl

Description

 The invention relates to the production of heterogeneous catalysts for the liquid-phase oxidation of a sulfide medium of sulfate white liquor to polysulfide in the process of obtaining a polysulfide cooking liquor and can be used in the pulp and paper industry in the technology of producing cellulose by the polysulfide method.

 Catalysts for the oxidation of sulfide sulfur of white liquor to polysulfide are known, which are activated carbon, modified with metals, metal oxides and sulfides, and treated with hydrophobic reagents (1, 2, 3).

These catalysts exhibit a relatively high catalytic activity and selectivity in the oxidation of only sulfate white liquor purified from suspended particles. In the presence of suspended in an amount of 10 mg / DM ^{3 the} catalyst reduces its activity by 20-25 after 25-50 hours of continuous operation.

Catalysts analogues possess low mechanical strength and low resistance to the action of the white liquor and products of oxidation of sodium sulfide at 60-90 ° ^C.

 The regeneration of the catalysts by means of water circulation and weak hydrochloric acid for 2-5 hours ensures the restoration of the catalytic activity by an average of 90. The total duration of the catalysts is from 90 days to 1 year.

 When introducing the technology for producing a polysulfide cooking liquor, a relatively complex technological installation is required, which should contain powerful pumps for polishing white liquor from suspended impurities. The presence of the reagent compartment of the acid preparation unit is also required. All this increases capital and operating costs.

 Closest to the proposed catalyst is a catalyst made on the basis of pyrite cinder and variable metal oxide of oxide using PVD as a carrier (4).

 The prototype catalyst has a relatively high catalytic activity in the oxidation of sulfide sulfur of white liquor, but with insufficient selectivity in relation to the output of polysulfides.

To eliminate the above disadvantages, a heterogeneous catalyst for the oxidation of sulfide sulfur of white liquor is proposed, containing transition metal oxide, pyrite cinder and a high pressure polyethylene carrier, characterized in that it contains antimony (III) oxide and manganese (IV) oxide as a transition metal in the following ratio components, wt. Pyrite cinder 15-17 Antimony (III) oxide 17-20 Manganese (IV) oxide 5-7
High pressure polyethylene
The proposed catalyst has a high catalytic activity, selectivity and stability without polishing white liquor.

When oxidizing white liquor with a sulfide content of 29-31 with a degree of conversion of sulfide sulfur of 65-80, the concentration of polysulfide sulfur was 8.5-8.7 g / dm ³ . If the initial sulfide content of white liquor is 33-35, the concentration of polysulfide sulfur in the cooking polysulfide solution will be 9.5-10.5 g / dm ³ in units. sulfur, with the degree of conversion of sulfide sulfur 75-85 Efficiency and selectivity of the proposed catalyst are maintained at the same level throughout all tests.

The proposed component composition of the catalyst is an effective means of changing the catalytic properties and selectivity of the catalyst, since it determines the necessary metal-oxygen bond strength, and, therefore, the necessary catalytic efficiency and selectivity, which remains constant during the oxidation of white liquor containing suspended impurities up to 80 mg / dm ³ . The preservation of the catalytic activity of the catalyst can be explained by the fact that the catalyst during the oxidation process is coated with a protective layer of oxygen, which increases the hydrophobicity of the outer surface of the catalyst.

 In addition, pores at the atomic level are contained on the external geometric surface of the catalyst, which are much smaller than the size of suspended impurities present in white liquor.

PRI me R 1. The catalyst composition, wt. pyrite cinder 15; antimony (III) oxide 17; manganese (IV) oxide 7; high pressure polyethylene the rest is obtained at an industrial unit for the production of carbon black concentrate from polyethylene. Granular high-pressure polyethylene in the amount of 36.4 kg; pyrite cinder 9.0 kg; antimony oxide 10.2 kg; 4.2 kg of the manganese oxide is charged into the drum, where the entire catalyst mass at 120-130 ^{° C} was stirred well for 20 minutes and then fed to the screw die, which allows to obtain a catalyst in the form of granules of 3-7 mm in diameter. Similarly, catalyst samples are prepared containing pyrite cinder, antimony oxide, manganese oxide and high-pressure polyethylene in various weight ratios. The direct fusion of finely dispersed particles of metal oxides into a thermoplastic polymer ensures their strong retention on a polymer carrier and stable operation of the catalyst. Mechanical wear of the catalyst does not lead to a decrease in activity and selectivity during operation as a result of surface renewal and the appearance of new active particles located in the polymer mass.

 PRI me R 2. The catalyst in the form of granules 3-5 mm, in the amount of 350 g of the composition, wt. pyrite cinder 15; antimony (III) oxide 17; manganese (IV) oxide 7; high pressure polyethylene the rest was loaded in a continuous layer of a certain height into a catalytic reactor for the oxidation of white sulfate liquor with atmospheric oxygen. The reactor consists of two glass tubes with a working part height of 700 mm each, interconnected by a transition of 80-100 mm long and a diameter of 8-10 mm, which serves to redistribute the phases. Both parts of the reactor are equipped with a jacket designed to create an operating temperature inside the reactor.

Oxidation of white liquor composition: total alkalinity 105.0-112.0 g / DM ³ units Na ₂ O; NaOH 76.0-75.0 g / dm ³ units Na ₂ O; active alkalinity 95.0-102.3 g / dm ³ units. Na ₂ O; sulfide content 30-32% thiosulfate sulfur 0.8-1.3 g / dm ³ units sulfur; polysulfide sulfur 0.4-0.5 g / dm ³ units sulfur; suspended impurities 70-80 mg / dm ^3, was carried out in a continuous manner at 80-85 ^{° C} and for air flow to the flow of white liquor 10. The feed liquor in a reactor and air was carried out in cocurrent from the top at a rate of 0.6 and 6.0 cm / c, respectively, with a nozzle providing good phase mixing before feeding them to the catalyst. The contact time of the alkali catalyst was 30 minutes. The experiments were carried out without polishing the liquor.

 The efficiency of the catalyst was evaluated by the following indicators: oxidation state of sulfide sulfur; the concentration of polysulfides in oxidized liquor; selectivity of the oxidation process.

 The content of sulfide and polysulfide sulfur in the initial and oxidized liquors was determined by potentiometric method.

 Experiments with samples of catalysts with different ratios of these components were carried out under the same conditions. The results are presented in table. 1.

 The synergistic effect of the catalytic activity, selectivity and stability of the proposed catalyst is achieved with the specified ratio of the components. A further increase or decrease in the content of each catalytically active component decreases the catalytic activity and / or selectivity of the catalyst.

 PRI me R 3. To assess the stability of the proposed catalyst relative to the prototype catalyst, comparative experiments were carried out under the conditions described in example 2. In this case, the oxidation state of sodium sulfide, the content of polysulfide sulfur and the selectivity of the process were determined. The experimental results are given in table. 2.

 An analysis of the results shows that the proposed catalyst under the same conditions has high catalytic activity and selectivity for the yield of polysulfides. If the selectivity of the process for polysulfides on the prototype catalyst is 30-35, then on the proposed catalyst 72-74 which is very significant.

Over the course of 300 hours of operation, the degree of oxidation and selectivity on the proposed catalyst remained practically unchanged; the polysulfide concentration remained at the level of 8.9–9.2 g / dm ³ .

The experiments were carried out without prior polishing of the liquor with suspended particles up to 80.0 mg / dm ³ .

 As a result of all studies, it was found that the proposed catalyst in comparison with the prototype has a higher catalytic activity and selectivity.

 Using the proposed catalyst will solve the problem of producing polysulfide cellulose for various purposes without catalyst regeneration (washing with water and acid) and polishing sulfate white liquor from suspended solids. All this will significantly reduce capital and operating costs in the production of pulp in this way. In addition, the widespread industrial introduction of the polysulfide method of producing cellulose instead of the sulfate method, which until now has been restrained by the lack of an effective catalyst, will solve a number of common pulp and paper problems: increasing pulp yield by 1-3 will provide significant savings in wood raw materials; will reduce atmospheric emissions by 50-70 for mercaptans and 90-100 for hydrogen sulfide.

Claims (1)

White alkali sulfide sulfur oxidation catalyst containing transition metal oxide, pyrite cinder and high pressure polyethylene support, characterized in that the catalyst contains antimony (III) oxide and manganese (IV) oxide in the following ratio of components, wt. %:
Pyrite cinder - 15 - 17
Antimony (III) oxide - 17 - 20
Manganese (IV) oxide - 5 - 7
High Pressure Polyethylene - Else

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