CN1356262A

CN1356262A - Process for recovering food-class CO2 from tail gas generated in preparing Na2S2O4.2H2O powder

Info

Publication number: CN1356262A
Application number: CN01129769A
Authority: CN
Inventors: 钟存仁
Original assignee: ZHONGCHENG CHEMICAL CO Ltd GUANGDONG
Current assignee: Guangdong Zhongcheng Chemicals Inc.
Priority date: 2001-10-16
Filing date: 2001-10-16
Publication date: 2002-07-03
Anticipated expiration: 2021-10-16
Also published as: CN1125775C

Abstract

A process for recovering food class CO2 from the tail gas generated by preparing Na2S2O4.2H2O powder includes activated carbon adsorption, recovering solvent, alkali washing, water washing, washing with acidic solution of potassium permagnate, secondary adsorption by activated carbon, desulfurizing by hydralysis and catalyst, adsorption by molecular sieve, drying and rectifying. Its advantages include high safety, high purity and high output rate.

Description

Recovery of food grade CO from tail gas from sodium hydrosulfite production2Method (2)

The invention relates to the recovery of food grade CO from tail gas in the production of sodium hydrosulfite₂The method of (1).

The company adopts a sodium formate method to produce sodium hydrosulfite. The scientific name of Sodium hydrosulfite is Sodium hydrosulfite, the English name is Sodiumdithionite or Sodium hydrosulfite (SD for short), and the CA registration number is 7775-14-6. It is a well-known reducing agent in industry and is mainly used for textile printing and dyeing and papermaking bleaching.

Sodium formate method for producing sodium hydrosulfite uses excessive sodium formate (excessive 10%) and liquid SO₂In a reaction kettle using 80% (V) methanol water solution as solvent, the sodium hydrosulfite is intermittently synthesized by batch reaction at the temperature of 80 +/-2 ℃ and under the normal pressure, and simultaneously, stoichiometric CO is generated₂The gas is discharged as tail gas in the synthesis process, the principle of the sodium hydrosulfite synthesis reaction is shown in a reaction equation ①, a production process flow block diagram is shown in an attached figure 1, the patent technology only relates to the tail gas discharged in the synthesis process, and the tail gas is purified and recoveredFood grade liquid CO₂Without the technology of sodium hydrosulfite production.

--------①

The SD manufacturers produced by the sodium formate method worldwide have Clariant company in the United states; BASF, RVC (Clariant), Idrosol, Inc., Germany, Europe; mitsubishi gas corporation, Hansol corporation of Korea, Tamil Nadu corporation and Gulshan chemical Bhiooaid corporation of India, have a production scale of about 1 to 3.5 ten thousand tons/year, and also have a production scale of 1 to 3 ten thousand tons/year in domestic Wuxi Volkswagen, Wujiang Jiuzhou, Hunan Zhonghua, Hefei chemical plant, Nicoti Jinhe, and the like. The company has a scale of 16 ten thousand tons/year and has two production lines of 8 ten thousand tons/year. On such a large production scale that CO is present₂The gas emission amount is greatly purified and recovered, and great economic benefitscan be achieved.

Retrieve food grade CO from American glassmaking furnace exhaust gas₂Japanese food grade CO recovery from glutamic acid fermentation waste gas₂Recovery of food grade CO from urea production, both in Japan and domestically₂And also high concentrations of CO emitted from the combustion₂CO recovery from waste gas by Pressure Swing Adsorption (PSA)₂The report of the method for purifying and recovering food-grade CO from the synthetic tail gas generated in the sodium formate method for producing sodium hydrosulfite is not seen so far₂The report of (1).

The CO discharged from the synthesis pot is generated due to impurities in the synthesis raw materials and the generation of complex side reactions₂The tail gas has complex components, contains a large amount of toxic and harmful substances and greatly exceeds the national emission standard. In order to protect the environment and increase the economic benefit of enterprises, the company recovers the synthesis tail gas. The main components of the synthesis tail gas are shown in the attached table 1.

The invention aims to change waste into valuable, reduce environmental pollution and initiate the recovery of food-grade CO from tail gas generated in the production of sodium hydrosulfite₂A method.

The purpose of the invention is realized as follows:

synthetic tailThe gas purification and recovery process comprises solvent recovery (activated carbon), alkali and water washing, and potassium permanganate (KmnO)₄) The process flow block diagram of the purification and recovery process comprises the procedures of washing of an acid solution, secondary purification of activated carbon, combined fine desulfurization treatment of a hydrolysis catalyst, drying of a molecular sieve, medium-pressure rectification purification and the like, and is shown in an attached figure 2.

The active carbon solvent recovery procedure is to recover methanol, methyl formate and the like in the synthetic tail gas, has obvious removal effect on organic matters, adopts two-tower adsorption to alternately operate, switches once in 2-5 hours, and regenerates and desorbs at 120 ℃ by steam. The adsorption operation condition is normal temperature, the air speed is 500-^-1. After solvent recovery, the average removal rate of methanol in the tail gas is 75%, the average removal rate of EO is 90%, the average removal rate of methyl mercaptan is 60%, and the average removal rate of methyl formate is 80%.

The alkali and water washing process is to wash and remove acid gas such as SO₂And other soluble substances which are soluble in water and have a low vapor pressure, such as methanol, methyl formate, and the like. First, dilute Na for 5 percent is collected₂CO₃The tail gas is leached by the aqueous solution and then leached by clean tap water, the tail gas is washed in a countercurrent way, the operation conditions are normal temperature and normal pressure, and the gas space velocity is 500-^-1. SO after tail gas is washed₂The removal rate of (2) was 95 to 99%, the average removal rate of methyl formate was 50%, the average removal rate of methyl mercaptan was 20%, the average removal rate of methanol was 85%, and the average removal rate of EO was 70%.

The tail gas of the potassium permanganate acidic solution washing is KMnO₄Removing easily oxidized impurities such as methyl mercaptan and SO in tail gas by strong oxidizing property of acid solution₂Etc., KMnO₄The solution concentration is 5-10g/L, diluted H is used₂SO₄Adjusting the pH value to 1-2, carrying out countercurrent leaching on the tail gas from top to bottom at normal temperature and normal pressure, wherein the space velocity of the tail gas is 800-^-1From KMnO₄The removal rate of methyl mercaptan in tail gas after the acid solution washing is 100 percent, the average removal rate of methyl formate is 75 percent, and SO is added₂The removal rate is more than 99 percent.

The secondary purification of active carbon is to utilize the adsorption capacity of active carbon to remove small amount of organic matter from tail gasThe adsorption and desorption are alternately carried out, the desorption is purged by steam at the temperature of 120-^-1After the tail gas is secondarily purified by the activated carbon, the average removal rate of the methanol is 45%, the removal rate of the methyl formate is 100%, and the average removal rate of the COS is 65%.

The combined fine removal treatment of hydrolysis catalyst is to remove the trace carbonyl sulfide (COS<2X 10)^-6Catalytic hydrolysis to H in the presence of hydrolysis catalyst₂S is removed again, the technology adopts the combination of T504 hydrolysis catalyst and EF-2 (provided by Hubei chemistry) of fine iron oxide desulfurizer, the COS in the tail gas can be completely removed, the operating condition temperature is 50-100 ℃, the pressure is 1.8-2.5Mpa, and the gas space velocity is about 300-^-1The reaction equation is shown in ②, and COS in the synthetic tail gas after hydrolysis and fine desulfurization is less than 0.05 multiplied by 10^-6mol/mol。

The water in the synthetic tail gas is removed by adsorption and drying of a molecular sieve, the company adopts an adsorption bed mixed with a 3A molecular sieve and a 13X molecularsieve to remove water and can adsorb partial trace organic impurities and trace sulfides, the adsorption bed of the molecular sieve is alternately switched by adsorption and desorption, the adsorption operation conditions are normal temperature, the pressure is 1.8-2.5Mpa, and the gas space velocity is 800-^-1And hot air blowing at 150 ℃ is adopted during regeneration until water desorption is complete. The methanol removal rate is 100 percent and the water removal rate is more than 90 percent after the methanol is adsorbed by a molecular sieve.

The purification tower is used for removing specific CO in tail gas by rectification under the condition of 40-50 ℃ and 1.8-2.5Mpa of medium pressure₂Light fractions, e.g. O₂、N₂、CH₄Etc. in the tail gas entering the purifying tower₂0.2-0.5% of N₂The content is 1-2%, the removal rate after purification is more than 99%, and simultaneously, the trace methane and ethylene in the tail gas can be removed by 30-50%. At this time, CO in the released gas₂The yield is 50-70%.

The SD synthetic tail gas, CO, is treated by the whole process of the procedures₂The yield is 50-70%.

The content of CO2 in the purified synthesis tail gas is more than 99.95 percent, and the quality of the synthesis tail gas is completely in accordance with the standard after inspectionFood grade CO 1999 Korea Cola₂New quality standard of additive. The results of the test are shown in the attached Table 2. (inspection Unit: institute of Chinese patent chemical industry, quality inspection station of Chinese patent chemical industry)

The average removal rates of impurities in the above steps are summarized in Table 3. The method for detecting impurities in each purification process comprises the following steps: 1. methane, ethylene, methanol, methyl formate, ethylene oxide, methyl mercaptan, etc

The detection method comprises gas chromatography FID detector, GDX-103 chromatographic column, and column temperature of 90%

DEG C, the detector temperature is 120 ℃; 2. SO2, CO2

The test method is gas chromatography FPD detector, Parapak Ps column, column temperature 75 deg.C,

the temperature of the detector is 120 ℃; 3. o2, N2

The detection method comprises gas chromatography, TCD detector, 13X molecular sieve column, and column temperature of 60 deg.C.

Bridge current 120 mA; 4. moisture content

The inspection method is a mirror dew point method;

example 1:

at 15m³Adding 3m of circulating mother liquor (mainly methanol solvent) into a synthesis kettle³Starting to stir, 2530Kg of methanol aqueous solution containing sodium formate and Na are slowly added within 60-80 minutes₂S₂O₅2610Kg of methanol aqueous solution, then SO2 with concentration of 380g/L is dropped into the solution within 180 minutes of 120-₂Methanol solution 4.5m³The reaction temperature is controlled to be 80 +/-2 ℃, the pressure is controlled to be 0.2Mpa, the reaction is carried out for 4 hours (4.7 tons of sodium hydrosulfite can be produced, and CO is produced₂Gas 1.1 ton). The reaction adopts low-temperature water condensation reflux liquid to condense the tail gas containing CO₂92% (V) and methanol 860X 10^-6mol/mol, methyl formate 6500X 10^-6mol/mol，SO2 8520×10^-6mol/mol, etc., and the tail gas is treated and purified by the method of the invention to obtain 99.95 percent of liquid CO₂Product, yield 70%.

Practice proves that the method is mature, safe and reliable, high in yield, high in purification purity and remarkable in economic benefit, and is a pioneering invention for changing waste into valuable.

Claims

1. Recovery of food grade CO from tail gas in sodium hydrosulfite production₂The method is characterized by comprising the steps of adsorbing and recovering a solvent by using active carbon, washing with alkali and water, washing with a potassium permanganate acidic solution, adsorbing and purifying the active carbon for the second time, carrying out fine desulfurization by combining a hydrolysis catalyst, adsorbing, drying and dehydrating by using a molecular sieve, and rectifying and purifying the light component gas in a purification tower.

2. The recovered food-grade CO of claim 1₂The method is characterized in that the solvent is recovered by the adsorption of the activated carbon by adopting two towers for adsorption and desorption, the two towers are alternately operated for 2 to 5 hours, the steam is regenerated and desorbed at 120 ℃, and the air speed of the normal temperature gas is 500-1000 hours^-1Adsorption is carried out under the conditions.

3. The recovered food-grade CO of claim 1₂The method is characterized in that the alkali and water washing and sprinkling are carried out at normal temperature and normal pressure and at a gas space velocity of 500-^-1Under the condition of using 5% diluted Na₂CO₃The tail gas is leached by the water solution in a countercurrent way, and then the tail gas is leached by the clean tap water in a countercurrent way.

4. The recovered food-grade CO of claim 1₂The method is characterized in that the concentration of the potassium permanganate acid solution is 5-10g/L, the pH value is adjusted to 1-2 by dilute sulphuric acid, the tail gas is leached in a counter-current way from top to bottom at normal temperature and normal pressure, and the space velocity of the tail gas is 800-^-1。

5. The recovered food-grade CO of claim 1₂The method is characterized in that the secondary adsorption and purification of the active carbon are alternately carried out by adsorption and desorption, the desorption is purged by steam at the temperature of 120-^-1Under the condition of the reaction.

6. According to claim1 said recovered food grade CO₂The method is characterized in that the hydrolysis catalyst combination fine desulfurization adopts the combination of T504 hydrolysis catalyst and iron oxide fine desulfurizer EF-2 at the temperature of 50-100 ℃, the pressure of 1.8-2.5Mpa and the gas airspeed of 300-800h^-1Under the condition of the reaction.

7. The recovered food-grade CO of claim 1₂The method is characterized in that the adsorption, drying and dehydration of the molecular sieve is realized by adopting an adsorption bed mixed with a 3A molecular sieve and a 13X molecular sieve to remove water, the adsorption bed of the molecular sieve is alternately switched for adsorption and desorption, the pressure at normal temperature is 1.8-2.5Mpa, and the gas space velocity is 800-^-1Adsorbing under the condition, and blowing by hot air at 150 ℃ during regeneration until water desorbs air.

8. The recovered food-grade CO of claim 1₂The method is characterized in that the rectification and purification of the light component removal gas in a purification tower are carried out at the temperature of 40-50 ℃ and the medium pressure of 1.8-2.5 Mpa.