JPH03290303A - Preparation of chlorine dioxide - Google Patents

Abstract

PURPOSE: To reduce producing cost by allowing an alkali metal chlorate to react with sulfuric acid and a specified reducing agent in a reaction medium under a pressure less than the atmospheric pressure.

CONSTITUTION: The reducing agent consisting of a crude methanol is obtained by mixing the crude methanol obtained from a sulfite pulp boiling process or an org. solvent process and water of 0.07-4.0 time in vol., and after separating a non-polar phase at a vessel for phase separation, allowing the soln. to contact with an adsorbent (e.g. zeolite) to purify. Then the alkali metal chlorate (e.g. NaClO₃), the sulfuric acid and the reducing agent are mixed in a proportion generating chlorine dioxide, and the mixture is allowed to react under the pressure of 60-400 mmHg at 50-100°C and the mixture of the chlorine dioxide and stream is taken out from an evaporating zone, and also an alkali metal sulfate is crystallized at a crystallizing zone of the reaction vessel.

COPYRIGHT: (C)1991,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a process for producing chlorine dioxide from an alkali metal chlorate, a mineral acid and a reducing agent.

The above process is carried out in a vessel operating under sub-atmospheric pressure, whereby water is evaporated off together with chlorine dioxide and the alkali metal salts of mineral acid are crystallized in the reaction vessel. and is taken out from there. According to the invention, the reducing agent utilized is methanol condensate,
It is purified by separation and adsorption.

[Prior art and problems to be solved by the invention] Chlorine dioxide, which is used in the form of an aqueous solution, is used commercially mainly in pulp bleaching, water purification, oil bleaching, removal of phenols from industrial waste, etc. It's quite important.

Therefore, it is desired to provide a method that can efficiently produce chlorine dioxide.

The main chemical reactions involved in such manufacturing methods are [11 It is stated by

The chlorate ions are supplied by an alkali metal chloride, preferably sodium chlorate, the chloride ions are supplied by an alkali metal chloride, preferably sodium chloride, or by hydrogen chloride, and the hydrogen ions are supplied by a mineral acid, usually is supplied by sulfuric acid and/or hydrochloric acid. The method for producing chlorine dioxide is described in, for example, US Patent No. 3.
No. 563.702 and No. 3. 1164.456.

In the existing production method of chlorine dioxide (ClO2),
Often a by-product, chlorine gas (Cu2), is also produced. This is due to the use of chloride ions as a reducing agent according to formula [1].

This chlorine byproduct has previously been used as a bleaching agent in aqueous solutions in paper mills. Today, chlorine dioxide bleaching is becoming more widespread for environmental reasons, thereby reducing the need for chlorine as a bleaching agent.

It is also known to use other reducing agents that do not produce chlorine as a by-product. In U.S. Pat. No. 3,933,988 sulfur dioxide is used as a reducing agent;
U.S. Patent No. 4,081,520, No. 4.145.40
No. 1, No. 4,465. [No. 458 and 4.473.
No. 540, methanol is used as the reducing agent. For example, in the process according to US Pat. No. 4,465,858, the utilization of methanol is very low. The consumption of methanol is 190-2 [10 Kg per ton of chlorine dioxide produced, but the theoretical consumption is only 79 NSF/lon according to the formula % [2].

Thus, only about 40% of the charged methanol is effectively used in existing processes.

However, the direct reaction between chlorate ion and methanol is very slow and the true reducing agent in this case is of the formula [
1]. The produced chlorine then reacts with methanol to regenerate chloride ions according to the formula % [3].

Therefore, it is often necessary to continuously add small amounts of chloride ions to stabilize the production.

A more effective method using methanol as the reducing agent is described in US Pat. No. 4.770.8H.

According to this patent, methanol loss is highly dependent on how methanol is added to the reactor. According to the US patent, the reducing agent is added to the crystallization zone of the reactor.
The yield is improved by introducing it into the zation zone).

[Means for Solving the Problems] As is clear from the claims, the present invention is a method for producing chlorine dioxide using methanol as a reducing agent, which method uses a methanol-rich condensate as a methanol source. This provides a method in which the efficiency of the method is further improved.

In the production of sulfate cellulose, chips are boiled in a bulging solution called white liquor. After boiling, the waste valving solution (black liquor) is separated from the pulp. The black liquor is evaporated and the residue is sent to a recovery furnace to recover valuable species. Upon evaporation of the above black liquor, a methanol-rich condensate is obtained. A typical composition of such a methanol-rich condensate is: 40-90% methanol 5-20% ethanol 0.2-5% mercaptans and other organic compounds (
terpenes, higher mercaptans, etc.). The methanol-rich condensate has a very unpleasant odor and is an industrial waste in the valve industry, which is usually incinerated so as not to harm the effluent. Various methods have been developed to purify the condensate to recover methanol, an important raw material in the chemical industry. For example, Canadian Patent No. 1.088.95
No. 7 discloses methods for purification in various steps, especially involving chemical purification.

The methanol-rich condensate (hereinafter crude methanol) can now be purified by a very simple purification method.
It has surprisingly been found that it is possible to purify chlorine dioxide (called hanol) in such a way that it can be used as a reducing agent in the above-mentioned process for producing chlorine dioxide. As is well known, chlorine dioxide generators are usually sensitive to organic impurities, which can cause explosive decomposition reactions. It is therefore surprising that crude methanol could be converted by a simple purification process to a quality that provides good operating conditions in a chlorine dioxide reactor, especially in order to obtain an acceptable industrial feedstock. , requiring a number of complex steps involving energy-consuming distillation as well as a number of expensive chemical species, e.g. Canadian Patent No. 1,08
This was surprising in light of known techniques such as No. 8,957.

Thus, the cost of producing chlorine dioxide is reduced by being able to utilize crude methanol obtained from Valve Industries in a simple manner as a source of methanol to replace industrial grade methanol, which is considerably more expensive than crude methanol. Ru.

Methanol-rich condensates obtained from other bulb boiling processes, such as, for example, crude methanol obtained from sulfite bulb boiling processes as well as crude methanol obtained from organic solvent processes, can also be purified according to the present invention. However, today the sulfate valve process predominates and at the same time the crude methanol obtained from this process is the dirtiest.

The purification method described above consists of two steps: a separation step and an adsorption step. The crude methanol is diluted with water, whereby the non-polar organic compound layer is easily separated. The appropriate amount of water added above is 0.07 to 4.0 of the amount of crude methanol.
times, preferably 0.2 to 2.0 times (volume basis!fI). The above addition of water may be carried out batchwise by mixing in a stirred tank or by continuously mixing the two liquid streams with a static mixer or in a pipe leading to a separate mixing tank. Good too. After mixing,
The crude methanol/water dispersion is sent to a vessel for phase separation.

The vessel may be designed as a settling tank, column or other suitable device, including coalescence filters, packed net structures, etc.
) etc. droplet separation (droplet 5eparatio
n) may also be provided with specific equipment. The non-polar layer is separated and the remaining methanol-water phase is contacted with an adsorbent. The amount of adsorbent for the methanol-water phase is:
It varies depending on the degree of crude methanol fouling and the capacity of the adsorbent. The amount of adsorbent is most easily determined by laboratory testing. Typically, an adsorbent has the ability to hold an amount of solvent equivalent to 50 to 5000 times its own weight before it requires regeneration.

Useful adsorbents include various types of zeolites, activated carbon, and polymeric adsorbents such as polyacrylamide, polystyrene divinylbenzene, and other macroporous polymer particles.

Contact with the adsorbent can be carried out in various ways.

The above adsorption may be carried out, for example, in a fixed or fluidized bed of zeolite particles. Other possibilities include using columns packed with adsorbent or using a suspension of adsorbent and crude methanol in a stirred tank. The adsorbent may be regenerated in known manner by elution, desorption and/or heat treatment, or it may be incinerated for energy generation and decomposition.

Methanol purified by this method is manufactured under the registered trademark SVP
(Half-vessel method) It is possible to use it in a methanol reactor with good yields without any disadvantages.

When producing chlorine dioxide from sodium chlorate in an SvP reactor using methanol purified according to the invention, the reaction is carried out at a temperature of 50 to 100 °C, preferably 50 to 75 °C, and at atmospheric pressure. Suitably operating under lower pressure, suitably between 60 and 400 mmWg. Under these conditions, sufficient reaction medium boils or water evaporates to dilute the chlorine dioxide formed to a safe concentration. The acidity in the reactor is maintained between 2 and IIN by adding sulfuric acid or other mineral acids. In the reactor the sodium salt of the mineral acid is continuously crystallized and separated in a suitable manner. In order to avoid product losses at start-up and during process changes, small amounts of chloride ions, preferably in the form of sodium chloride, are added such that their concentration in the reactor is in the range 0.001 = 0.8 sol/11. It is appropriate to add it as follows.

[Examples] The present invention will be explained by the following examples. In 22, "parts" and "percent" mean "parts by weight" and "percent by weight" unless otherwise specified.

Example 1 [Using crude methanol as reducing agent] SVP chlorine dioxide reactor at 72°C and 150+un1
It was operated at a C102 production rate of 90 g/h.

550 g/l) of NaC, Q'03 and 7 g of NaC, 9
A solution of 358 g/h was added continuously.

Methanol is added in the form of a 50% solution in a flow of 30 g/h and the acidity is brought to 6. Add 50% sulfuric acid at a rate sufficient to keep it on. After about 1.5 hours of driving time,
Foaming and over-boiling in the reactor
ng) and severe operational disturbances, such as explosions accompanied by flash-like lightning, forced the reactor to be shut down. At the same time, so-called whiteouts (a phenomenon that occurs when chlorine dioxide production declines or stops) occurred intermittently.

The methanol used was analyzed and found to contain 0.85% dry matter and 1.9% sulfur. Furthermore, upon dilution with water, the formation of a heterogeneous phase was observed. This implied the presence of more non-polar organic compounds, perhaps terpenes.

Example 2 [Using crude methanol (from the sulfate process) purified by the method described in Canadian Patent No. 1.088.957 as reducing agent] Except that the crude methanol was not alkalized and distilled. was purified according to Examples 2 and 4 in Canadian Patent No. 1.088.957.

Example 2 in Canadian Patent No. 1,088,957
The following operations were performed according to the following.

120 g of 30% H2SO4 was added to 0.5 g of crude methanol and the solution was stirred. Approximately 45 g of precipitated sulfate was filtered off. The heavier non-polar phase was separated by discharging in a separatory funnel. The polar phase contained approximately 63% methanol by weight.

Example 4 in Canadian Patent No. 1,088,957
The following operations were performed according to the following.

To 0.5 J7 crude methanol was added 120 g of residual acid containing 430 g of Na250 and 0438 g of H2S, and the solution was stirred. 70 g of precipitate was filtered off. The heavier non-polar phase was separated by discharging in a separatory funnel. The polar phase contained approximately 70% methanol by weight.

The crude methanol purified in this way was then used for the production of chlorine dioxide in an SVP methanol reactor. The same process conditions as in Example 1 were adopted. Examples 2 and 4 in Canadian Patent No. 1,088,957
When methanol purified according to the method was used, in both cases operational disturbances appeared in the form of explosions and flash-like lightning, with a concomitant significant reduction in yield.

Example 3 Using crude methanol (from the sulfate process) according to the invention 120 g of distilled water was added to 0.5 g of crude methanol.

The solution was stirred in a separatory funnel and the heavier non-polar phase was discharged. Then 10 g of zeolite (zeolite A) was added to the polar phase and stirred. After a contact time of approximately 10 minutes, the zeolite mass was separated and methanol was added to the
A methanol solution containing 1% by weight was obtained. This purified crude methanol was subjected to SVP under the same experimental conditions as in Example 1.
It was used for the production of chlorine dioxide in a methanol reactor.

The reaction proceeded without any operational disturbance such as explosion or foaming, and the yield was sufficient at over 95%.

When crude methanol purified according to the production method of the present invention was analyzed, the following results were obtained.

Impurities Ratio to the original (before purification) amount in crude methanol Terpenes 35% Thioketals 65% Amines No change in value Ketones No change in value Dimethyl sulfide No change in value From these values, only the amount of terpenes decreased significantly It is clear that The amounts of other impurities either decreased somewhat or remained unchanged. It was therefore very surprising that crude methanol purified according to the method of the present invention was functional in a sensitive chlorine dioxide production process.

Claims (1)

[Claims] 1. In a reaction vessel, an alkali metal chlorate, sulfuric acid, and methanol as a reducing agent are maintained at a temperature of about 50°C to about 100°C in such proportions as to generate chlorine dioxide; By reacting in a reaction medium under subatmospheric pressure sufficient to evaporate the water, a mixture of chlorine dioxide and water vapor is removed from the evaporation zone in the reaction vessel and the alkali metal sulfate is removed. A method for producing chlorine dioxide which is deposited in a crystallization zone in a reaction vessel, wherein the reducing agent used is crude methanol purified by separation and adsorption. 2. Process according to claim 1, characterized in that the crude methanol is purified by separating the non-polar phase by diluting with water and contacting the remaining methanol-water phase with an adsorbent. . 3. Process according to claim 2, characterized in that the adsorbent used is a zeolite. 4. characterized in that the adsorbent used is activated carbon;
The method according to claim 2. 5. Process according to claim 2, characterized in that the adsorbent used is a polymeric adsorbent.