SU1114331A3 - Process for producing chlorine dioxide - Google Patents

Abstract

1. METHOD OF OBTAINING CHLORINE DIOXIDE by reducing the chlorate ions with chloride ions in an aqueous medium containing sodium chlorate, methanol, and sulfuric acid at boiling point and reduced pressure, removing sodium hydrosulfate. characterized in that, in order to reduce energy consumption and reduce the consumption of sulfuric acid, sodium hydrosulfate is treated with an aqueous solution of methanol with weight ratios of water, methanol and sodium hydrosulfate (in terms of hydrotriosodium sulfate) equal to

Description

The invention relates to a highly efficient method for producing chlorine dioxide used, in part, in the pulp and paper industry. A method for producing chlorine dioxide using sodium chlorate sulfuric acid and methanol is known. The mechanism for the formation of chlorine dioxide is that chlorine, which is formed in parallel with chlorine dioxide, reacts with methanol to form chloride ions, which then reduce the chlorate ions to chlorine and chlorine dioxide, namely: + 2H, SO + .- 2Cf02 + 2NaHS04 + CHO + ZHjO The reaction medium, in which chlorine dioxide is formed and which contains sodium chlorate, methanol and sulfuric acid, is held at its boiling temperature, usually in the range from 50 ° C to 85 ° C under pressure atmospheric. Evaporated water serves to dilute chlorine dioxide to remove from the reaction zone. The reaction medium has a high overall acidity normality exceeding 9 N. A byproduct precipitating from the reaction medium together with the onset of saturation is sodium acid sulfate, which may be sodium bisulfate NaHSO or sodium acid sulfate double sulfate NaaH (SOi) 2. Nearly iOO% chlorine dioxide is obtained, which is removed from the reaction zone by virtually chlorine-free lj. However, the removal of sodium hydrosulfate from the reaction zone leads to a decrease in the concentration of sulfuric acid, the concentration of which requires high energy consumption. The purpose of the invention is to reduce energy consumption and reduce the consumption of sulfuric acid. This goal is achieved in that according to the method for producing chlorine dioxide by reducing the chloro-ions with chloride ions in an aqueous medium containing sodium chlorate, methanol and sulfuric acid at a temperature of boiling and reduced pressure, removing sodium hydrosulfate, the sodium hydrosulfate is treated with an aqueous methanol piacTBopoM and weighing and weighing. x water, methanol and sodium hydrosulfate (in terms of hydrosodium-sodium sulfate) equal to (0.4-1.4): (O, 1-2.0): 1.0, the precipitate of the sodium sulfate formed is separated from the liquid phase, and the liquid phase etsirkuliruyut in the aquatic environment. In addition, after the separation of sodium sulfate, the liquid phase is divided into two parts, one of which, a third of the stream, is recycled to the aqueous medium, and methanol is extracted from the other and sent to sodium hydrosulfate. The prototype method includes an initial stage of stripping the light ends, which is necessary to remove dissolved gases and sodium chlorate residues that otherwise inhibit the reaction. This operation is unnecessary in this method, since the starting product is sodium hydrosulfate in the solid phase, which is formed in the reaction zone during the production of chlorine dioxide. The proposed method differs from the prototype method in that the starting products are in different phase states, besides the volumes of water and methanol that need to be added to the effluent water stream to form solid neutral sodium sulfate, in the known method significantly exceed the volumes used in the proposed. As a result of the use of large volumes of water and methanol, considerable evaporation is necessary, firstly, to isolate the methanol used, secondly, to concentrate the aqueous solution of sulfuric acid to a concentration sufficient for reuse in the generator. In the proposed method, methanol is used as an alcohol (the use of other water-soluble alcohols and ketones is also appropriate). The weight ratio of water to acid sodium sulfate is from about 0.4: 1 to 1.4: 1, preferably from 0.6: 1 to about 0.8: 1. The ratios of water to sodium hydrosulfate given above are critical values because with values less than 0.4: 1, only slight conversion of hydrosulfate A to neutral sulfate is observed, while with values weighing more than 1.4 : 1, large quantities of neutral sulphate are dissolved in the aqueous phase. When the weight ratios are within the critical range, the resulting aqueous phase contains sulfuric acid in a concentration sufficient to recycle it in the process of generating chlorine dioxide without concentration. The sodium hydrosulfate precipitated from the reaction medium has various forms, one of which may be NaiH (SOi}) -, which depends on the general normality of the acid in the reaction medium. To calculate the weight of water and methanol used to carry out the sodium acid sulfate acid exchange reaction, the weight of sodium acid sulfate must be measured as an equivalent weight of Na HCSOij.) In the case when sodium hydrosulfate is present in a different form, the NaAH (ZOL) l, such as sodium bisulfate or a mixture of sodium bisulfate and the double salt of hydro and middle sodium sulfate, the weight of sodium hydrosulfate is converted to an equivalent weight of Na 11 (504) 2. when sodium hydrogen sulfate is defined as), the weight for the exchange reaction is the actual weight of sodium hydrosulfate. The weight ratio of methanol to sodium hydrosulfate (calculated for (50z) 2 is less sensitive than the weight ratio of water, and can vary from 0.1 to 2: 1. Preferred weight ratios of methanol to sodium hydrosulfate from 0.3: 1 to 0, 8: 1 with the preferred ratios of water to sodium hydrogen sulfate mentioned above. Due to the miscibility of methanol with water, the presence of methanol reduces the volume of water in which sodium sulfate is capable of dissolving and thereby slowing the dissolution of neutral sodium sulfate in the aqueous phase. With increasing weight from When methanol is consumed, the amount of neutral sodium sulfate, dissolved in the aqueous phase, drops until the weight ratio of methanol reaches a value at which a further increase in methanol will not lead to an increase in the yield of neutral sodium sulfate in the solid phase (maximum yield 80-85 wt. %). Therefore, increasing the weight ratio of methanol 314 to sodium acid sulfate above about 2: 1 is not rational. A part of the aqueous phase resulting from the exchange reaction can be recycled directly to the reaction medium, producing chlorine dioxide, providing at least a part, preferably the entire amount of methanol required. This recycle stream also supplies some of the sulfuric acid required for the chlorine dioxide production process. Methanol recycled to the reaction medium in this way does not need to be removed from the recycled portion of the aqueous phase, since it is removed from the remaining portion of the aqueous phase to produce a sulfuric acid solution that can be concentrated to normal acid enough to be recycled to the dioxide generation process. chlorine. The use of steam to replenish the aqueous phase is limited by the need to desorb methanol. Typically, water and methanol are added to sodium hydrosulfate in the solid phase as a solution containing the required amounts of water and methanol. Since methanol reduces the solubility of neutral sodium sulfate in the aqueous phase, it is added after the initial addition of water. The exchange reaction takes place over a wide range of temperatures, usually from 10 to. The reaction proceeds efficiently at room temperature (from 20 to 25 ° C), however, it is preferable to have a temperature range from 20 to. The exchange reaction can be carried out in a batch process, preferably continuous, since the process is associated with continuous chlorine production. The exchange reaction is carried out in a reaction vessel or in a decantation washing column. The mixture of water-methanol mixture with sodium hydrosulfate for the exchange reaction is accompanied by stirring in the reaction vessel. Although stirring increases the mass transfer involved in the exchange reaction, strong crushing is not necessary. suitable and should be used only for gentle mixing, despite the longer period of time required for this. The time required for completion of the exchange reaction is from 10 minutes at high stirring speeds to 60 minutes at decantation. The drawing shows the implementation of the proposed method. According to FIG. 1, a chlorine diode generator 1 produces a gas mixture of chlorine dioxide and steam into pipe 2, from which chlorine dioxide is absorbed by water, forming an aqueous solution for use in bleaching wood pulp or for other purposes. Generator 1 produces chlorine dioxide from the sodium chlorate solution loaded into generator 1 via conduit 3, sulfuric acid is loaded into generator 1 via conduit 4 and methanol via conduit 5. The aqueous reaction medium with an overall normality of the acid is greater than about 9 and is maintained at its boiling point is lower than the temperature at which significant decomposition of chlorine dioxide occurs, usually from 30 to 85 ° C at a pressure below atmospheric, determined by the boiling point. The pressure range is from 20 to 400 mm Hg. Acidic sodium sulfate is continuously precipitated from the reaction medium at the same time as the start of the reaction medium. The volume of the reaction medium in generator 1 is maintained mainly constant by introducing into the generator 1 an aqueous phase in a volume corresponding to the volume of water evaporating from the reaction medium, forming a gaseous product stream, and the volume of water removed with sludge containing sodium hydrosulfate in the solid phase. Sodium hydrosulphate precipitated from the reaction medium in generator 1 is directed through line 6 to reactor 7. Sodium hydrosulphate, usually the double salt of hydro- and middle-sodium sulfate, is removed from generator 1 in the form of sludge with the reaction medium and before entering the reactor 7 is separated from it by pre-filtration. In the reactor 7, the acidic sodium sulfate comes in contact with the water supplied through the pipeline 8 and the methanol supplied through the pipeline 9. The weight ratio of water to sodium hydrosulfate (calculated for (S04) 2) in the reactor is from 0.4: 1 to 1.4: 1, preferably from 0.6: 1 to 0.8: 1. The weight ratio of methanol to sodium hydrogen sulfate (calculated for Na 111 (504) 2) is from 0.01 to 2: 1, preferably from 0.3: 1 to 0.8: 1. The temperature of the medium in contact with the reactor 7 with sodium hydrosulfate in the solid phase is preferably from 20 to. As a result of the exchange reaction, solid anhydrous neutral sodium sulfate is obtained with the formation of sulfuric acid. Neutral sodium sulfate and the aqueous phase are separated from each other, for example, by filtration. Neutral sodium sulfate is removed through conduit 10 and used for the production of sodium and sulfur in pulp mills associated with a chlorine dioxide generator 1. The aqueous phase containing sulfuric acid, methanol and some dissolved sodium sulfate is removed through conduit 11 and then divided into two streams, one of which, containing about 1/3 of the volume of the aqueous phase, is recycled through conduit 12 to conduit 5, the feed generator chlorine dioxide with methanol, in order to partially or preferably completely provide the generator with 1 methanol. Any deficiency in such demand is replenished through conduit 13 connected to the methanol feed conduit 5. Sulfuric acid, which is part of the aqueous phase in conduit 12, partially satisfies the need of the reaction medium in generator 1 for sulfuric acid. The rest, usually 2/3 of the volume of the aqueous phase, is routed through conduit 14 to the methanol distillation column 15, in which methanol is removed from the aqueous phase. Methanol vapors are directed through conduit 16 to condenser 17, where they are converted to liquid methanol, which is further transported through conduit 18 to conduit 9, a reactor 7 fed with methanol, in which the exchange reaction takes place. The missing amount of methanol is fed to the reactor 7 through line 19. A solution of sulfuric acid with a reduced methanol content is recycled through line 20 to the stream feeding the chlorine dioxide generator with sulfuric acid through line 4. 711 Additional supply of sulfuric acid is carried out through line 21 through line 4, feeding sulfuric acid. Thus, the proposed method produces chlorine dioxide mostly free of chlorine, with high efficiency, without the need to introduce catalytic additives into the reaction medium. At the same time, sodium sulfate is obtained as a by-product in a neutral form, preferably in an anhydrous neutral form, so that sulfuric acid is not carried away from the reaction system with the by-product. Example 1. Preparation of sodium hydrogen sulfate in a known manner. The chlorine dioxide generator is put into operation to discharge chlorine dioxide from sodium chlorate, sulfuric acid and methanol. The reaction medium is maintained at boiling point at a pressure below atmospheric. The double salt of the acidic and middle sodium sulfate is precipitated from the reaction medium. The parameters characterizing the process are as follows. The conditions of the process temperature, ° C 74 135 pressure, mm Hg. Reagent concentration and feed rate, ml / min 33; 3.4 MeOH,% 9; 3.6 HjSO, M 6.74; 10.5 NaClO; j, M Concentration of reagents in the generator liquid HjSO, M NaClO, M 31 8 (SO) Crystals in the solid phase Chlorine dioxide production rate, gl / min efficacy per chlorate,% gas analysis,% Example 2. The exchange reaction of the double solygidro and middle sodium sulfate, carried out in various conditions. A series of experiments was carried out in such a way that the solid double salt of hydro- and medium-sodium sulfate was in contact with water and / or methanol at a moderate temperature of 20 ° C while slowly mixing the sludge for 15 minutes. optimal process conditions; g each time, the weight of sodium sulfate released and the proportion of sulfur " Q acid remaining in sodium sulfate are determined. Taking into account the process efficiency, the residual concentration of sulfuric acid, less than about 1%, corresponds to almost 100% conversion of sodium hydrosulfate to neutral sodium sulfate. A. The lower critical limit of the weight ratio of water to acidic sodium sulfate. The results of the experiments, carried out in order to show the critical nature of the lower limit of the water weight ratio:), equal to 0.4: 1, are presented in Table 1. Table 1

The value of output loses its meaning due to high products.

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15.2 acid content in these

As can be seen from Table 1, in order to achieve complete conversion of the exchange into neutral sulfate, it is necessary that the lower limit of the weight ratio of water to acid sodium sulfate be at least 0.4: 1.

As can be seen from Table 2, an increase in the weight ratio of water to acid sodium sulfate should not be carried out above a value of 1.4: 1, since a further increase leads to the disappearance of the precipitate from the reaction.

The results table. 3 shows a sharp increase in the yield of neutral sodium sulfate, even with a low weight ratio of methanol to acid sodium sulfate, as 0.1: 1.

G. Critical nature of the upper limit of the weight ratio

B. The upper critical limit of the weight ratio of water to acidic sodium sulphate.

The results of experiments conducted in order to show the critical nature of the upper limit of the weight ratio of water: Na HCSO (j) / equal to 1.4: 1 are presented in Table 2.

table 2

B. Sensitivity of the reaction to the presence of methanol during the reaction.

The results of the experiments, 30 to show the sensitivity of the exchange reaction to the presence of methanol, are presented in Table. 3

Table 3

methanol to sodium hydrosulfate.

The results of experiments carried out in order to show the critical nature of the upper limit of the weight ratio of methanol to acidic sodium sulfate are given in table. four

As can be seen from Table 4, an increase in the molar ratio of methanol to sodium hydrosulfate above 2: 1 does not lead to a further increase in yield.

D. Results obtained in the preferred ranges.

As can be seen from Table 5, in those cases when the weight ratio H20: .Na, H (80 X is in the preferred range from 0.6 to 0.8: 1 and: 45: (SO) 2 is in the preferred range from O, J to 0.8: 1, the yield of the product exceeds 75%, while simultaneously reducing the results of experiments carried out using

H20: Na H (S04) 2 and CHjOH: Na H (S04) 2, the values of which are between the critical limit values, are shown in Table 5 in order to show the optimal results.

Table 5

com level of acid, less than 0.6%.

The proposed method produces chlorine dioxide free of chlorine, and neutral sodium sulfate is formed as a by-product. The method reduces energy consumption and reduces the consumption of sulfuric acid.

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Claims (2)

1. METHOD FOR PRODUCING CHLORINE DIOXIDE by reduction of chlorate ions by chloride ions in an aqueous medium containing sodium chlorate, methanol and sulfuric acid at a boiling point and reduced pressure to remove the resulting sodium hydrogen sulfate, characterized in that, in order to reduce energy consumption and reduce sulfuric consumption acids, sodium bisulfate is treated with an aqueous solution of methanol at a weight ratio of water, methanol and sodium bisulfate (in terms of hydrotrin sodium sulfate) equal to (0.4-1.4):: (0.1-2.0): 1.0, sediment form Osya sodium sulfate from the liquid phase and the liquid phase is recycled to the aqueous medium. 2. The method of pop. 1, characterized in that after the separation of sodium sulfate, the liquid phase is divided into two parts, one of which, a third of the stream, is recycled to the aqueous medium, and methanol is extracted from the other and sent to sodium hydrosulfate. SU „„ 1114331>