JPS63117909A - Production of calcium thiocyanate - Google Patents

Abstract

PURPOSE:To easily and inexpensively obtain the title calcium thiocyanate by adding excess calcium hydroxide to the waste liq. from ammonia-process wet desulfurization for coke-oven gas, etc., and carrying out deammoniation reaction under specified conditions. CONSTITUTION:A waste liq. contg. ammonium thiocyanate and ammonium thiosulfate and generated in the ammonia-process wet desulfurization for coke- oven gas, etc., is used as the starting material. Calcium hydroxide or calcium oxide in the amt. sufficient to substitute all the ammonium salts in the waste liq. for the calcium salts is added to the waste liq., and then deammoniation reaction is carried out under the conditions where the formed calcium thiosulfate is decomposed. The calcium sulfite, sulfur, and calcium sulfate formed in the deammoniated liq. and substantially insoluble in the liq. are separated and removed as cake. The liq. freed of the cake is concentrated and then cooled to obtain calcium thiocyanate.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing calcium thiocyanate from waste liquid of ammonia wet desulfurization such as coke oven gas, and more specifically, a method for producing calcium thiocyanate as a setting and hardening accelerator in the field of concrete. , relates to a process for producing calcium thiocyanate for use as a replacement for calcium chloride, which may be banned for future use in antifreeze agents or accelerated AE water reducers. In addition,
In the following explanation, these uses will be collectively referred to as accelerators.

[Conventional technology and problems] Calcium chloride has been the most widely used accelerator, but in recent years, regulations have been implemented on the total amount of chloride from the viewpoint of safety and durability of concrete, and reinforced concrete Calcium is virtually unavailable. The superiority of thiocyanine P1 salt as an effective non-chloride accelerator to replace calcium chloride has been known in the past, for example, in German Patent No. 15.
78716 (1933). Among thiocyanates, alkali metal salts such as sodium salts may trigger alkaline aggregate reactions in concrete, but calcium salts form stable double salts with cement compounds, so this risk is avoided. It is known to be the most preferable.

Incidentally, calcium thiocyanate has conventionally been produced by reacting ammonium thiocyanate with calcium hydroxide. However, since ammonium thiocyanate, which is a starting material, is extremely expensive, naturally the produced calcium thiocyanate is also more expensive than calcium chloride.

On the other hand, in the ammonia process wet desulfurization waste liquid of coke oven gas, hydrogen sulfide and hydrogen cyanide in coke oven gas are absorbed by an ammonia aqueous solution using picric acid or 1,4-naphthoquinone-2-sulfonic acid as a redox catalyst. It is what was done. Well-known wet desulfurization methods include the 7max method and the Takahax method, depending on the catalyst used. The waste liquid is usually a colored aqueous solution containing ammonium thiocyanate at 800 to 2000 m01/TrL3, ammonium thiosulfate at 200 to 100100 O/m3, and ammonium sulfate at 50 to 200 mol/m3. Among these three components, ammonium sulfate is
Although it can be easily separated from other components based on mutual solubility, since the mutual solubility of ammonium thiocyanate and ammonium thiosulfate is close and large, it is difficult to separate them based on the solubility difference. For this reason, in processing such waste liquid, sulfur compounds are converted into sulfur dioxide gas by combustion decomposition and recovered as a final product of sulfuric acid or gypsum, or recovered as ammonium sulfate by wet oxidation. However, in this waste liquid treatment, ammonium thiocyanate, which is useful as a raw material for chemical products, is completely wasted.

For this reason, the present inventors have found conditions that do not decompose calcium thiosulfate using the waste liquid of the ammonia method wet desulfurization as a starting material, and have already applied for a method for producing a mixed aqueous solution of calcium thiocyanate and calcium thiosulfate. Such a mixed aqueous solution can be used as a promoter for industrial 1iWi
Although the value is not small, the concentration of calcium thiosulfate is 1
When it is 0% or more, crystal precipitation is observed at low temperatures, so it is necessary to lower the mixed aqueous solution 1111 degrees when used.

Also, Dio la! There is a problem in that calcium is easily decomposed in the air and it is impossible to powderize the mixed aqueous solution.

The present invention can easily and inexpensively produce calcium thiocyanate by adding calcium hydroxide or calcium oxide to the waste liquid and carrying out a deammonia reaction under conditions that decompose calcium thiosulfate, contrary to the invention of the previous application. This is an attempt to provide a possible method.

Means for Solving Problem 1] The present invention uses a waste liquid containing ammonium thiocyanate and ammonium thiosulfate produced in ammonia wet desulfurization of coke oven gas as a starting material, and converts all of the ammonium salts in the waste liquid into calcium. A step of adding a sufficient amount of calcium hydroxide or calcium oxide to replace the salt and performing a deammonification reaction under conditions that decompose the calcium thiosulfate produced, and This method is characterized by comprising a step of separating and removing calcium sulfite, sulfur and calcium sulfate substantially insoluble in the reaction solution as a cake.

The present invention will be explained in detail below.

First, a waste liquid containing ammonium thiocyanate and ammonium thiosulfate produced in the ammonia method wet desulfurization of coke oven gas, etc., is used as a starting material.
Adding enough calcium hydroxide or calcium oxide to replace all of the nium salts with calcium salts, that is, 1/2 or more of the moles of each ammonia, and The deammonization reaction is carried out under conditions that decompose the produced calcium thiosulfate. In this step, the conditions for decomposing the produced calcium thiosulfate are: (1) setting the concentration of ammonium thiosulfate in the waste liquid to a concentration of 14.5% by weight or more, preferably more than 15% by weight; (2) setting the reaction temperature to 80% by weight or more; The temperature may be set at a temperature above .degree. C., preferably below the boiling point, and more preferably (2) aeration may be carried out during and/or after the above deammonization reaction. If these conditions are not met, ammonium thiosulfate will not be sufficiently converted to calcium sulfite and sulfur in the deammonification reaction, resulting in calcium thiocyanate [
J. Contains polysulfides and colloidal sulfur, and as time passes, precipitates are gradually formed and the appearance is significantly impaired. In particular, the concentration of ammonium thiosulfate in the waste liquid was
At a low concentration of 4.5% by weight without vortex, although the produced calcium thiosulfate itself is an unstable compound,
Most of it dissociates into calcium ions and thiosulfate ions, increasing the stability and, in turn, reducing the degradability of calcium thiosulfate.

Next, after performing the deammonization reaction, excess calcium hydroxide or calcium oxide, the generated calcium sulfite, sulfur, and calcium sulfate are separated and removed as a cake by a filtration operation, and the filtrate is a brown transparent calcium thiocyanate with no ammonia odor. Obtain an aqueous solution. Thereafter, solid calcium thiocyanate is produced by further concentrating to 65% or more and cooling in a low humidity environment.

[Works] When calcium hydroxide or calcium oxide is simply added to the waste liquid containing ammonium thiocyanate and ammonium thiosulfate produced in the ammonia-method wet desulfurization of coke oven gas, etc., and a deammonium removal reaction is performed, calcium thiosulfate is produced during the reaction. is not sufficiently converted into calcium sulfite and sulfur, and the obtained calcium thiocyanate contains polysulfide and colloidal sulfur, and as time passes, a precipitate is gradually formed and the appearance is significantly impaired. Therefore, in the present invention, the produced calcium thiocyanate is removed by carrying out the deammoniation reaction under the conditions that the concentration of ammonium thiosulfate in the waste liquid is 14.5% or higher and the reaction temperature is 80°C or higher. Can be converted to substantially insoluble calcium sulfite and sulfur. Therefore, the calcium sulfite, sulfur, and calcium sulfate produced by the subsequent filtration process can be separated and removed as a cake, and a transparent brown calcium thiocyanate aqueous solution without ammonia odor can be obtained as a filtrate.

In addition, if airage is performed during and/or after the completion of the above deammonification reaction, the deammonification reaction can be accelerated.
This promotes the decomposition of calcium thiosulfate, improves the conversion efficiency into calcium sulfite and sulfur, and further agglomerates colloidal sulfur, making it possible to efficiently produce high-quality calcium thiocyanate. In this case, bubbling with nitrogen gas instead of aeration (air bubbling) has no effect at all in promoting the decomposition of calcium thiosulfate, and the decomposition of calcium thiosulfate can only be promoted by aeration. This is because all of the calcium thiosulfate, which was confirmed by the inventors' experiments, is not directly decomposed and converted into calcium sulfite and sulfur, but some of it passes through polysulfides, which undergo oxidation. This is supported by the fact that it is ultimately converted into calcium sulfite and sulfur.

Furthermore, since ammonia is generated by the deammonium reaction of the present invention, if the calcium thiocyanate production equipment is installed near the ammonia method wet desulfurization equipment such as coke oven gas, the ammonia can be used as an alkali source of the wet desulfurization equipment. It can be reused as

[Embodiments of the invention] Examples of the present invention will be described in detail below.

Example 1 First, ammonium thiocyanate 2 was added to a 1β reaction flask.
500 g of concentrated liquid of ammonia process wet desulfurization waste liquid of coke oven gas containing 3.6% ammonium thiosulfate, 21.4% ammonium thiosulfate, and 0.6% ammonium sulfate, and 250 g of cake washing liquid.
Add 12 g of calcium hydroxide with a purity of 95%.
0 g was added, the temperature was raised, and while aeration was carried out under the boiling point with an air amount of 5β7 m1n, the deammonia reaction was carried out until the amount of ammonium water used as a drain became 350 tnll. Next, after aeration was continued for 1.5 cycles, filtration was performed using Nutsche. Calcium thiocyanate was found to be 33.1% and calcium thiol was 0.1%.
294 g of filtrate containing 8% was obtained, after washing 152 g
A wet cake was obtained.

Example 2 250 g of the filtrate obtained in Example 1 was concentrated to 125 g using a rotary evaporator and cooled in a VAT to obtain a solid calcium thiocyanate.

Example 3 First, 1 part of ammonium thiocyanate was added to 5 reaction flasks.
Unconcentrated liquid of ammonia process wet desulfurization waste liquid of coke oven gas containing 1.7%, ammonium thiosulfate 11.8%, ammonium sulfate 0.3%, and ammonia 1.5% 5000
(After adding j, the condensed water is concentrated under the boiling point until it becomes 1400-16.1% ammonium thiocyanate, 16.3% ammonium thiosulfate, and 0.4% ammonium 4iiiIIIl (all values are calculated values) A concentrated liquid containing
Add 70g of calcium hydroxide and 690g of 95% pure calcium hydroxide, and while performing aeration with an air flow rate of 5β/min, the ammonium water drain becomes 1500 #! i! The temperature is raised until
The deammoniation reaction was carried out below the boiling point. Then 30
After aeration was performed for 1 hour at an air flow rate of β/min, 1733 g of filtrate containing 30.3% of calcium thiocyanate and 283% of calcium thiosulfate was obtained by filtration using a NUDGE, and after washing, 11,779 wet cakes were obtained. was gotten.

[Effects of the Invention IA] As detailed above, according to the present invention, it is possible to promote concrete production from ammonia process wet desulfurization waste liquid such as coke oven gas, which in the past could only be recovered as low value-added products such as sulfuric acid and gypsum. This method has remarkable effects such as being able to easily and inexpensively produce high value-added calcium thiocyanate useful as a reagent, and furthermore allowing the ammonia produced by the deammonia reaction to be reused as an alkali source in the wet ammonia method 1152IiIII.

Applicant's agent: Patent attorney Takehiko Suzue =13-

Claims (5)

[Claims] (1) Using a waste liquid containing ammonium thiocyanate and ammonium thiosulfate produced in the ammonia wet desulfurization of coke oven gas as a starting material, a sufficient amount of water to replace all of the ammonium salts in the waste liquid with calcium salts. A step of adding calcium oxide or calcium oxide and performing a deammonification reaction under conditions that decompose the calcium thiosulfate produced, and a step of adding sulfurous acid, which is substantially insoluble in the reaction solution, generated in the reaction solution after the deammonization reaction. 1. A method for producing calcium thiocyanate, comprising a step of separating and removing calcium, sulfur and calcium sulfate as a cake. (2) The conditions for decomposing the produced calcium thiosulfate are such that the content of ammonium thiosulfate in the waste liquid is 14.
The method for producing calcium thiocyanate according to claim 1, characterized in that the content is set at 5% by weight or more. (3) The method for producing calcium thiocyanate according to claim 1, wherein the condition for decomposing the produced calcium thiosulfate is that the reaction is carried out at a temperature of 80° C. or higher. (4) The method for producing calcium thiocyanate according to claim 1, characterized in that ammonia produced by the deammonia reaction is reused as an alkali source in wet ammonia desulfurization. (5) The method for producing calcium thiocyanate according to claim 1, characterized in that aeration is carried out during and/or after the completion of the deammoniation reaction.