JPH0657603B2 - Chlorine dioxide production method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing chlorine dioxide from an alkali metal chlorate, a mineral acid and a reducing agent. The process described above is carried out in a vessel operating below atmospheric pressure, whereby water is taken off by evaporation with chlorine dioxide and the alkali metal salt of the mineral acid is crystallized in the reaction vessel. Is taken out from there. According to the invention, the reducing agent utilized is a methanol condensate, which has been purified by separation and adsorption.

[Prior Art and Problems to be Solved by the Invention] Chlorine dioxide used as an aqueous solution is commercially available mainly for bleaching pulp, water purification, oil bleaching, removal of phenols from industrial waste, etc. Pretty important. Therefore, it is desired to provide a method capable of efficiently producing chlorine dioxide.

The main chemical reactions involved in such a manufacturing method are roughly described by the formula ClO ₃ ⁻ + Cl ⁻ + 2H ⁺ → ClO ₂ + 1 / 2Cl ₂ + H ₂ O [1].

The chlorate ion is supplied by an alkali metal chlorate, preferably sodium chlorate, the chloride ion is supplied by an alkali metal chloride, preferably sodium chloride, or hydrogen chloride, and the hydrogen ion is a mineral acid, usually Is supplied by sulfuric acid and / or hydrochloric acid. A method for producing chlorine dioxide is described in, for example, US Pat.
3,702 and 3,864,456.

In the existing manufacturing method of chlorine dioxide (ClO ₂ ),
Often, a by-product chlorine gas (Cl ₂ ) is also generated. It is due to the use of chloride ion as a reducing agent according to equation [1]. This chlorine by-product has previously been used as a bleach in aqueous solutions in paper mills.
Today, chlorine dioxide bleaching is becoming more prevalent 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. Sulfur dioxide is used as the reducing agent in U.S. Pat. No. 3,933,988 and methanol is used as the reducing agent in U.S. Pat. For example, in the method according to US Pat. No. 4,465,658, the utilization rate of methanol is very low. Although the consumption of methanol is 190 to 200 kg per ton of chlorine dioxide produced, the theoretical consumption is calculated by the formula 6NaClO ₃ + CH ₃ OH + 4H ₂ SO ₄ → 6ClO ₂ + CO ₂ + 5H ₂ O + 2Na ₃ H (SO ₄ ) According to ₂ [2], it is only 79 Kg / ton.

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

However, the direct reaction between the chlorate ion and methanol is very slow, and the true reducing agent in this case is the formula
Chlorine ion that reacts according to [1]. The chlorine produced then reacts with methanol according to the formula CH ₃ OH + 3Cl ₂ + H ₂ O → 6Cl ⁻ + CO ₂ + 6H ⁺ [3] to regenerate chloride ions.

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

A more effective method using methanol as the reducing agent is described in US Pat. No. 4,770,868. According to this patent, the loss of methanol depends largely on the way the methanol is added to the reactor. According to that US patent, the yield is improved by introducing a reducing agent into the crystallization zone of the reactor.

[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, wherein a methanol-rich condensate is used as a methanol source. This provides a method by which the efficiency of the method is further improved.

In the production of sulfated cellulose, chips are boiled in a pulping solution called white liquor. After boiling, the waste pulping solution (black liquor) is separated from the pulp. The black liquor is allowed to evaporate, and the residue is sent to a recovery furnace to recover valuable species. A methanol-rich condensate is obtained when the black liquor is evaporated. Typical compositions of such methanol-rich condensates are 40-90% methanol 5-20% ethanol 0.2-5% mercaptans and other organic compounds such as terpenes and mercaptans. The methanol-rich condensate had a very unpleasant odor and was an industrial waste in the pulp industry, which was usually incinerated so as not to harm the effluent. Various methods have been developed for purifying the condensate to recover methanol, an important feedstock in the chemical industry. For example, Canadian Patent No. 1,088,957 discloses a method for purification in various steps, especially involving chemical purification.

It is now possible to purify the methanol-rich condensate (hereinafter referred to as raw methanol) by a very simple purification method so that it can be used as a reducing agent in the chlorine dioxide production method. Surprisingly became clear. As is well known, chlorine dioxide generators are usually sensitive to organic impurities, which can cause explosive decomposition reactions. It is therefore surprising that a simple purification step could convert crude methanol to a quality that gives good operating conditions in a chlorine dioxide reactor, especially to obtain an acceptable industrial feedstock. It was surprising in view of known techniques, such as Canadian Patent No. 1,088,957, which require a number of complicated steps with energy-consuming distillation and a number of expensive chemical species.

Thus, the availability of crude methanol from the pulp industry in a simple manner as a source of methanol to replace industrial grade methanol, which is considerably more expensive than crude methanol, reduces the cost of producing chlorine dioxide. It

Methanol rich rich condensates from other pulp boiling processes, such as crude methanol from a sulfite pulp boiling process as well as crude methanol from an organic solvent process, can also be purified according to the present invention. However, today the sulphate pulp process predominates and at the same time the crude methanol obtained from this process is the most dirty.

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 layers of non-polar organic compound are easily separated. The appropriate amount of water added is 0.07 to 4.0 times, preferably 0.2 to 2.0 times (volume basis) the amount of crude methanol. The water addition may be carried out batchwise with mixing in a stirred tank, or the two streams may be continuously mixed in a pipe equipped with a static mixer or leading to a separate mixing tank. May be. After mixing, crude methanol /
The aqueous dispersion is sent to a container for phase separation. This vessel may be designed as a settler, column or other suitable device, including coalescence filters, packed nets.
droplet separatio for net structures
It may be equipped with specific equipment for n). The non-polar layer is separated and the remaining methanol-water phase is contacted with the adsorbent. The amount of adsorbent for the methanol-water phase is
It varies depending on the degree of fouling of the crude methanol and the capacity of the adsorbent. The above amount of adsorbent is most easily determined in lab tests. Usually, the adsorbent has the ability to hold an amount of solvent equivalent to 50-5000 times its own weight before it needs to be regenerated.

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

The contact with the adsorbent is carried out by various methods. The adsorption may be carried out, for example, in a fixed or fluidized bed of zeolite particles. Another possibility is to use a column packed with an adsorbent, or to use a suspension of the adsorbent and crude methanol in a stirring tank. The adsorbent may be regenerated by known methods by elution, desorption and / or heat treatment or may be incinerated for energy generation and decomposition.

Methanol purified by this method is a registered trademark of SVP
(Single container method) It can be used in a methanol reactor without any disadvantage and in good yield.

When chlorine dioxide is produced from sodium chlorate in an SVP reactor using methanol purified according to the present invention, the reaction is 50-100 ° C, preferably 50-7 ° C.
At a temperature of 5 ° C and below atmospheric pressure, suitably 60-4
It is operated and operated properly under a pressure of 00 mmHg. Under these conditions, a sufficient amount of the reaction medium boils or the water evaporates so that the chlorine dioxide formed is diluted to a safe concentration. The acidity in the reactor is maintained between 2-11N by adding sulfuric acid or other mineral acids. In the reactor, the sodium salt of mineral acid is crystallized continuously and it is separated off in a suitable manner. In order to avoid product losses at the start and during process changes, small amounts of chloride ions are added, preferably in the form of sodium chloride, so that their concentration in the reactor is in the range of 0.001 to 0.8 mol /. Is appropriate.

[Examples] The present invention will be described by the following examples. here,
"Parts" and "percents" mean "parts by weight" and "percentages by weight" unless otherwise specified.

Example 1 [Using crude methanol as a reducing agent] The SVP chlorine dioxide reactor was maintained at 72 ° C. and 150 mmHg, and C
It was operated at a production rate of 10 ₂ of 90 g / h. 550 g / N
A solution of aClO ₃ and 7 g of NaCl was added continuously at 35 g / h. Methanol in the form of a 50% solution
The flow was 30 g / h and 50% sulfuric acid was added at a rate sufficient to maintain the acidity at 6.0N. After operating for about 1.5 h, foaming and overboiling in the reactor (overbo
The reactor had to be closed due to serious operational disturbances such as explosion accompanied by lightning such as iling) and flash. At the same time, so-called whiteout (a phenomenon that occurs when the production of chlorine dioxide is reduced or stopped) occurred intermittently.

The methanol used was analyzed and found to contain 0.85% dry matter and 1.9% sulfur. Furthermore, when diluted with water, the formation of a foreign phase was observed. This meant the presence of more apolar organic compounds, perhaps terpenes.

Example 2 [Use crude methanol purified from the method described in Canadian Patent 1,088,957 (from the sulfate process) as the reducing agent] Canadian patent except that the crude methanol was not sodiumated and distilled. Example 2 in No. 1,088,957
And purified according to 4.

The following operation was performed according to Example 2 in Canadian Patent No. 1,088,957.

120 g of 30% H ₂ SO _{4 in} 0.5 crude methanol was added and the solution was stirred. About 45g of precipitated sulfate
I separated it. The heavier non-polar phase was separated by draining with a separatory funnel. The polar phase contained about 63% by weight methanol.

The following procedure was followed according to Example 4 in Canadian Patent No. 1,088,957.

30 g Na ₂ SO ₄ and H ₂ SO in 0.5 crude methanol
120 g of residual acid, including ₄ 38 g, was added and the solution was stirred. About 70 g of the precipitate was filtered off. The heavier non-polar phase was separated by draining with a separatory funnel. The polar phase contained about 70% by weight methanol.

The crude methanol purified in this way was then used for the production of chlorine dioxide in the SVP methanol reactor. The same process conditions as in Example 1 were adopted. When methanol purified according to Examples 2 and 4 of Canadian Patent No. 1,088,957 is used, in both cases explosions and driving disturbances in the form of lightning, such as flashes, appear, with a conspicuous yield. Fell.

Example 3 [Used Crude Methanol (from Sulfate Process) According to the Invention] 120 g of distilled water was added to 0.5 of crude methanol. The solution was stirred in a separatory funnel and the heavier non-polar phase was drained. Then, 10 g of zeolite (Zeolite A) was added to the polar phase and stirred. After the contact time of about 10 minutes,
The zeolite mass was separated to obtain a methanol solution containing 70% by weight of methanol. This purified crude methanol was used for the production of chlorine dioxide in the SVP methanol reactor under the same experimental conditions as in Example 1. The reaction proceeds without any driving disturbance such as explosion or foaming,
The yield was 95% or more, which was sufficient.

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

From these figures it is clear that only the amount of terpenes is significantly reduced. The amount of other impurities remained somewhat unchanged or unchanged. Therefore, it was very surprising that the crude methanol purified according to the method of the present invention worked in a sensitive chlorine dioxide production process.

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-52-156804 (JP, A) JP-A-52-2066 (JP, A) JP-A-52-2876 (JP, A) Published by Japan Pulp and Paper Institute "Pulp treatment and bleaching" (Sho 43-1-27) P. 229-230 "5.3.5 Solvay method"

Claims (4)

[Claims] 1. In a reaction vessel, alkali metal chlorate, sulfuric acid and methanol as a reducing agent are maintained at a temperature of about 50 ° C. to about 100 ° C. and water is evaporated in such a proportion as to generate chlorine dioxide. By reacting in a reaction medium at a pressure below atmospheric pressure sufficient to cause a mixture of chlorine dioxide and water vapor to be removed from the evaporation zone in the reaction vessel and an alkali metal sulfate salt in the reaction vessel. In the method for producing chlorine dioxide which is deposited in the crystallization zone of the above, the reducing agent used is that the non-polar phase is separated by diluting the crude methanol with water, and the remaining methanol-
The method for producing chlorine dioxide as described above, which is crude methanol purified by bringing an aqueous phase into contact with an adsorbent. 2. A process according to claim 1, characterized in that the adsorbent used is zeolite. 3. A process according to claim 1, characterized in that the adsorbent used is activated carbon. 4. The method according to claim 1, characterized in that the adsorbent used is a polymeric adsorbent.