A method for synthesizing chlorobutane using HCl as a byproduct of methyl allyl chloride.

Abstract

This invention relates to the field of organic synthesis and industrial by-product resource utilization technology, specifically to a method for synthesizing n-butane chloride using HCl, a by-product of methyl allyl chloride. This invention directly utilizes HCl, a by-product of the methyl allyl chloride production process, eliminating the need for purchased chlorination reagents and reducing the raw material cost of n-butane chloride by more than 40%, while simultaneously solving the pollution problem caused by HCl emissions. The composite catalyst (ionic liquid-zinc chloride / γ-Al₂O₃) works synergistically, achieving a n-butanol conversion rate ≥98% and a n-butane chloride selectivity ≥99%, avoiding heavy metal pollution from traditional catalysts. After two-stage distillation, the purity of n-butane chloride is ≥99.8%, meeting the requirements of high-end applications such as butyllithium synthesis. The process is continuous and stable: the fixed-bed continuous reaction mode ensures that the catalyst retains ≥92% activity after 15 cycles, suitable for industrial scale-up. Unreacted n-butanol is recycled, reducing wastewater discharge by 80% and eliminating waste gas emissions, meeting green chemical requirements.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis and resource utilization of industrial by-products, specifically to a method for synthesizing chlorobutane (1-chlorobutane) by using hydrogen chloride (HCl), a by-product generated during the chlorination of isobutylene to produce methyl allyl chloride, as a raw material and reacting it with n-butanol in a catalytic reaction. Background Technology

[0002] Butane chloride (CAS: 109-69-3) is an important fine chemical intermediate, widely used in the synthesis of butyllithium, the preparation of phenylbutazone (a pharmaceutical product), the synthesis of cyproconazole (an pesticide), and as a solvent for polyether production. There is an urgent market demand for high-purity products with a purity ≥99.5%. Current synthetic processes for butane chloride mainly involve the reaction of n-butanol with chlorinating agents (concentrated hydrochloric acid, thionyl chloride, phosphorus trichloride, etc.). The route using hydrochloric acid as the chlorinating agent has become mainstream due to its low cost, but it suffers from the following problems: The raw material hydrochloric acid needs to be purchased externally, which increases production costs, and the concentration fluctuations affect the stability of the reaction; Traditional processes use metal catalysts such as ZnCl2, which easily generate wastewater containing heavy metals, posing a significant environmental challenge. The reaction conversion rate is limited (the conversion rate of n-butanol is usually ≤90%), and impurities such as dibutyl ether are produced as byproducts, making it difficult to improve the purity of the product. It is not effectively combined with industrial by-product HCl, resulting in low resource utilization.

[0003] On the other hand, in the industrial process of producing methyl allyl chloride from isobutylene by reacting it with chlorine, approximately 0.6 tons of HCl gas are produced as a byproduct for every ton of methyl allyl chloride produced. Direct discharge of this byproduct HCl would cause equipment corrosion and environmental pollution. Currently, it is mostly absorbed by water to produce dilute hydrochloric acid for sale, but this method has low added value, high transportation costs, and results in resource waste.

[0004] While existing technologies have reported the synthesis of chlorobutane from HCl and n-butanol (e.g., CN104326863A using DMSO as a catalyst), they have not been adapted to address the unique characteristics of HCl as a byproduct of methyl allyl chloride (containing trace amounts of chlorine, isobutylene, and other impurities). Furthermore, these technologies suffer from drawbacks such as high catalyst consumption and the need for pressurized reactions. Therefore, developing a high-efficiency, environmentally friendly, and low-cost process for synthesizing chlorobutane from HCl produced by methyl allyl chloride, thereby achieving the dual goals of byproduct resource utilization and product value enhancement, has significant industrial application value. Summary of the Invention

[0005] This invention provides a method for synthesizing chlorobutane using HCl, a byproduct of methyl allyl chloride, which solves the problems of low utilization rate of byproduct HCl, high production cost of chlorobutane, and heavy environmental pressure in existing processes, and realizes a green cycle of "byproduct recovery - product synthesis".

[0006] This invention is achieved through the following technical solution: The technical solution of this invention includes three core processes: purification of by-product HCl, catalytic synthesis of chlorobutane, and product separation and purification, as detailed below: Step 1: Purification treatment of by-product HCl The byproduct HCl gas (containing 90-95% HCl, trace amounts of chlorine, isobutylene, and methyl allyl chloride) generated during the synthesis of methyl allyl chloride from isobutylene and chlorine is passed into a purification tower for two-stage treatment. First stage: Wash with a 5-10% sodium sulfite aqueous solution to remove trace amounts of chlorine gas (reaction: Cl2+Na2SO3+H2O=2HCl+Na2SO4), washing temperature 20-30℃, gas-liquid volume ratio 10-20:1; Second stage: The activated carbon adsorption column (particle size 2~5mm, adsorption temperature 30~40℃, space velocity 500~1000h⁻¹) removes organic impurities such as isobutylene and methyl allyl chloride to obtain purified HCl gas with a purity ≥99.5%.

[0007] Step 2: Catalytic synthesis of n-chlorobutane Purified HCl gas, n-butanol (industrial grade, purity ≥99%), and composite catalyst are introduced into a fixed-bed reactor in a specific ratio to carry out a continuous chlorination reaction. The reaction raw material ratio is: HCl to n-butanol in a molar ratio of 1.2~2.0:1; Composite catalyst: Using γ-Al₂O₃ as a support, loaded with 5-10% by mass of imidazole ionic liquid (1-butyl-3-methylimidazolium chloride) and 2-5% by mass of zinc chloride, the preparation method is as follows: (1) The γ-Al2O3 support was calcined at 500~600℃ for 4~6h and then cooled to room temperature; (2) Dissolve imidazole ionic liquid and zinc chloride in ethanol at a mass ratio of 3~5:1 to prepare an impregnation solution with a concentration of 10~15wt%. In this step, 10~15wt% does not refer to a single component. The catalyst contains 5~10% imidazole ionic liquid and 2~5% zinc chloride. 10~15wt% is the common mass fraction of the above components. (3) The calcined γ-Al2O3 was immersed in the impregnation solution and impregnated at room temperature for 12-16 h, and then dried under reduced pressure at 60-80℃ for 8-10 h to obtain the composite catalyst. Reaction conditions: reaction temperature 90~120℃, reaction pressure 0.3~0.8MPa, n-butanol mass hourly space velocity 0.5~2.0h⁻¹, HCl gas volume hourly space velocity 1000~3000h⁻¹; Reaction equation: CH3CH2CH2CH2OH + HCl → CH3CH2CH2CH2Cl + H2O.

[0008] Step 3: Product separation and purification (1) The reaction products (containing chlorobutane, water, unreacted n-butanol and trace amounts of HCl) from the outlet of the fixed-bed reactor are fed into a water separator and allowed to stand at 40~50℃ to separate into layers. The organic phase (chlorobutane and n-butanol) overflows from the upper layer, while the aqueous phase (containing trace amounts of HCl) is sent to a neutralization tank for treatment. (2) The organic phase enters the distillation column (theoretical plate number 25~35), the reflux ratio is controlled at 2~4, the top temperature of the column is 77~78℃ to collect the chlorobutane fraction, and the bottom temperature of the column is 117~118℃ to recover unreacted n-butanol (recovery rate ≥95%), which is then recycled to the synthesis reactor. (3) Pass the top fraction into a precision distillation column (theoretical number of plates 40~50), with a reflux ratio of 3~5 and a top temperature of 77.2~77.5℃ to collect high-purity chlorobutane product.

[0009] Because water and n-butanol are partially miscible, and although n-butane chloride is the main organic phase, the presence of trace amounts of HCl in the system will exacerbate phase interface interference, leading to a decrease in separation efficiency. In addition, n-butane chloride and unreacted n-butanol are the core components of the organic phase, and their boiling points are similar. Furthermore, the contradiction between "high purity" and "low energy consumption" must be considered. This invention achieves high purity of n-butane chloride by strictly controlling the temperature of the water separator (40~50℃ to suppress emulsification), optimizing the parameters of the distillation column (theoretical plate number, reflux ratio), and rationally designing the water phase treatment unit.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: Achieving by-product resource utilization: Directly utilizing HCl, a by-product of the production process of methyl allyl chloride, eliminates the need to purchase chlorination reagents, reduces the cost of raw materials for chlorobutane by more than 40%, and solves the pollution problem caused by the emission of by-product HCl. High catalytic efficiency: The composite catalyst (ionic liquid-zinc chloride / γ-Al2O3) works synergistically, achieving a n-butanol conversion rate of ≥98% and a chlorobutane selectivity of ≥99%, avoiding heavy metal pollution from traditional catalysts; High product purity: After two-stage distillation, the purity of chlorobutane is ≥99.8%, meeting the needs of high-end applications such as butyllithium synthesis; Continuous and stable process: Fixed-bed continuous reaction mode, the catalyst activity retention rate is ≥92% after 15 cycles, suitable for industrial scale-up; Unreacted n-butanol is recycled, wastewater discharge is reduced by 80%, and there is no waste gas emission, which meets the requirements of green chemical industry. Attached Figure Description

[0011] The invention will now be further described with reference to the accompanying drawings.

[0012] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0013] The invention will now be further described with reference to the accompanying drawings. Example

[0014] Step 1: Purification treatment of by-product HCl The byproduct HCl gas (containing 90-95% HCl, trace amounts of chlorine, isobutylene, and methyl allyl chloride) generated during the synthesis of methyl allyl chloride from isobutylene and chlorine is passed into a purification tower for two-stage treatment. First stage: Wash with a 5-10% sodium sulfite aqueous solution to remove trace amounts of chlorine gas (reaction: Cl2+Na2SO3+H2O=2HCl+Na2SO4), washing temperature 20-30℃, gas-liquid volume ratio 10-20:1; Second stage: The activated carbon adsorption column (particle size 2~5mm, adsorption temperature 30~40℃, space velocity 500~1000h⁻¹) removes organic impurities such as isobutylene and methyl allyl chloride to obtain purified HCl gas with a purity ≥99.5%.

[0015] Step 2: Catalytic synthesis of n-chlorobutane The purified HCl gas, n-butanol (industrial grade, purity ≥99%), and composite catalyst are introduced into a fixed-bed reactor in a certain proportion to carry out a continuous chlorination reaction: the molar ratio of HCl to n-butanol is 1.2~2.0:1. Composite catalyst: Using γ-Al₂O₃ as a support, loaded with 5-10% by mass of imidazole ionic liquid (1-butyl-3-methylimidazolium chloride) and 2-5% by mass of zinc chloride, the preparation method is as follows: (1) The γ-Al2O3 support was calcined at 500~600℃ for 4~6h and then cooled to room temperature; (2) Dissolve imidazole ionic liquid and zinc chloride in ethanol at a mass ratio of 3~5:1 to prepare an impregnation solution with a concentration of 10~15wt%. In this step, 10~15wt% does not refer to a single component. The catalyst contains 5~10% imidazole ionic liquid and 2~5% zinc chloride. 10~15wt% is the common mass fraction of the above components.

[0016] (3) The calcined γ-Al2O3 was immersed in the impregnation solution and impregnated at room temperature for 12-16 h, and then dried under reduced pressure at 60-80℃ for 8-10 h to obtain the composite catalyst. Reaction conditions: reaction temperature 90~120℃, reaction pressure 0.3~0.8MPa, n-butanol mass hourly space velocity 0.5~2.0h⁻¹, HCl gas volume hourly space velocity 1000~3000h⁻¹; Reaction equation: CH3CH2CH2CH2OH + HCl → CH3CH2CH2CH2Cl + H2O.

[0017] Step 3: Product separation and purification (1) The reaction products (containing chlorobutane, water, unreacted n-butanol and trace amounts of HCl) from the outlet of the fixed-bed reactor are fed into a water separator and allowed to stand at 40~50℃ to separate into layers. The organic phase (chlorobutane and n-butanol) overflows from the upper layer, while the aqueous phase (containing trace amounts of HCl) is sent to a neutralization tank for treatment. (2) The organic phase enters the distillation column (theoretical plate number 25~35), the reflux ratio is controlled at 2~4, the top temperature of the column is 77~78℃ to collect the chlorobutane fraction, and the bottom temperature of the column is 117~118℃ to recover unreacted n-butanol (recovery rate ≥95%), which is then recycled to the synthesis reactor. (3) Pass the top fraction into a precision distillation column (theoretical number of plates 40~50), with a reflux ratio of 3~5 and a top temperature of 77.2~77.5℃ to collect high-purity chlorobutane product.

[0018] Example 2 1. Purification of by-product HCl The byproduct HCl gas (93% HCl, 0.8% Cl2, 0.2% organic impurities) generated from the methyl allyl chloride production unit was passed into a purification tower. The first stage involved washing with an 8wt% sodium sulfite aqueous solution (gas-liquid ratio 15:1, temperature 25°C). The second stage involved adsorption using an activated carbon column (space velocity 800 h⁻¹, temperature 35°C) to obtain purified gas with HCl purity of 99.7%. In this embodiment, the byproduct HCl gas generated during the methyl allyl chloride production process typically consists of 90-95% HCl, trace amounts of Cl2 (0.5-1.0%), and organic impurities (isobutylene and methyl allyl chloride, totaling 0.1-0.5%). Through two-stage treatment, the total impurity content was reduced to below 0.3%, and the final purity was determined by gas chromatography, yielding HCl with a purity of 99.7%.

[0019] 2. Preparation of composite catalysts (1) Take γ-Al2O3 support (particle size 2~3mm) and calcine it at 550℃ for 5h, then cool it to room temperature; (2) Dissolve 1-butyl-3-methylimidazolium chloride and zinc chloride in ethanol at a mass ratio of 4:1 to prepare a 12wt% impregnation solution; (3) The calcined γ-Al2O3 was immersed in the impregnation solution and impregnated at room temperature for 14 h, and then dried under reduced pressure at 70 °C for 9 h to obtain a composite catalyst with a loading of 8% ionic liquid + 3% zinc chloride.

[0020] 3. Catalytic synthesis reaction A fixed-bed reactor (25 mm inner diameter, 800 mm length) was loaded with 100 g of the above catalyst. Purified HCl gas and n-butanol (molar ratio 1.5:1) were introduced. The reaction temperature was controlled at 105 °C, the pressure at 0.5 MPa, the mass hourly space velocity (HHSV) of n-butanol at 1.2 h⁻¹, and the volume hourly space velocity (VHSV) of HCl at 2000 h⁻¹. The reaction was run continuously for 24 h. Sampling analysis showed that the conversion rate of n-butanol was 98.5%, and the selectivity of chlorobutane was 99.2%.

[0021] 4. Separation and purification After the reaction products are separated by a water separator, the organic phase enters the first distillation column (30 trays, reflux ratio 3). Crude n-chlorobutane is collected at the top of the column at 77.3℃, and n-butanol is recovered from the bottom of the column (recovery rate 96.2%). The crude product is then distilled in a precision distillation column (45 trays, reflux ratio 4) to obtain n-chlorobutane product with a purity of 99.85% and a yield of 97.8%.

[0022] In this embodiment, the product was identified as chlorobutane by infrared spectroscopy. The purity of the product was determined by gas chromatography using the area normalization method, and the purity was verified by chloride ion content determination (titration method).

[0023] 5. Catalyst Cyclic Stability Experiment Under the same process conditions, the system was continuously cycled 15 times, with each cycle lasting 8 hours. The results are as follows: Loop count n-Butanol conversion rate (%) Chlorinated n-butane selectivity (%) Product purity (%) 1 98.5 99.2 99.85 5 98.1 99.1 99.83 10 97.5 99.0 99.80 15 96.8 98.9 99.78 The results show that the catalyst maintains excellent performance after 15 cycles, meeting the requirements of continuous industrial production.

[0024] Example 3 Comparative experimental data project Method of the present invention Prior art (CN104326863A) <![CDATA[Prior art (catalyzed by ZnCl2)]]> HCl source Methyl allyl chloride byproduct (after purification) Purchased concentrated hydrochloric acid (30wt%) Purchased concentrated hydrochloric acid (30wt%) n-Butanol conversion rate (%) 98.5 92.3 89.7 Chlorinated n-butane selectivity (%) 99.2 97.5 96.1 Product purity (%) 99.8 99.5 98.3 Catalyst cycle number ≥15 ≤8 ≤5 Raw material cost (RMB / ton) 6800 11500 11200 .

Claims

1. A method for synthesizing chlorobutane using HCl as a byproduct of methyl allyl chloride, characterized in that: Includes the following steps: (1) Purification of by-product HCl: The by-product HCl gas in the production process of methyl allyl chloride is washed with sodium sulfite aqueous solution and adsorbed by activated carbon in sequence to obtain purified HCl gas with a purity of ≥99.5%. (2) Catalytic synthesis: Purified HCl gas and n-butanol undergo chlorination reaction in a fixed-bed reactor under the action of a composite catalyst. The reaction temperature is 90~120℃, the pressure is 0.3~0.8MPa, and the molar ratio of HCl to n-butanol is 1.2~2.0:

1. (3) Separation and purification: The reaction product is separated into layers by a water separator and then subjected to two-stage distillation to obtain chlorobutane product.

2. The method according to claim 1, characterized in that, In step (1), the by-product HCl gas from the production process of methyl allyl chloride is sequentially treated by two stages: washing with sodium sulfite aqueous solution and adsorption with activated carbon. The steps are as follows: First stage: Wash with a sodium sulfite aqueous solution of 5-10% by mass to remove trace amounts of chlorine gas. The washing temperature is 20-30℃ and the gas-liquid volume ratio is 10-20:

1. Second stage: Organic impurities are removed by an activated carbon adsorption column to obtain purified HCl gas with a purity of ≥99.5%.

3. The method according to claim 2, characterized in that, Second stage: adsorption through an activated carbon column with a particle size of 2-5 mm, an adsorption temperature of 30-40℃, and a space velocity of 500-1000 h⁻¹.

4. The method according to claim 1, characterized in that, In step (2), the composite catalyst uses γ-Al2O3 as a support and is loaded with 5-10% by mass of 1-butyl-3-methylimidazolium chloride and 2-5% by mass of zinc chloride. The mass ratio of imidazolium ionic liquid to zinc chloride is 3-5:

1.

5. The method according to claim 4, characterized in that, In step (2), the composite catalyst is prepared as follows: (1) The γ-Al2O3 support was calcined at 500~600℃ for 4~6h and then cooled to room temperature; (2) Dissolve imidazole ionic liquid and zinc chloride in ethanol to prepare an impregnation solution with a concentration of 10-15 wt%. (3) The calcined γ-Al2O3 is immersed in the impregnation solution obtained in step (2), impregnated at room temperature for 12~16h, and dried under reduced pressure at 60~80℃ for 8~10h to obtain the composite catalyst.

6. The method according to claim 1, characterized in that, In step (2), the mass hourly space velocity of n-butanol is 0.5~2.0 h⁻¹, and the volume hourly space velocity of HCl is 1000~3000 h⁻¹.

7. The method according to claim 1, characterized in that, The product separation and purification steps in step (3) are as follows: (1) The reaction product from the outlet of the fixed bed reactor is fed into a water separator and allowed to stand at 40~50℃ to separate into layers. The organic phases of chlorobutane and n-butanol overflow from the upper layer, while the aqueous phase is sent to a neutralization tank for treatment. (2) The organic phase enters the distillation column, the reflux ratio is controlled at 2~4, the temperature at the top of the column is 77~78℃ to collect the chlorobutane fraction, and the temperature at the bottom of the column is 117~118℃ to recover the unreacted n-butanol, which is then recycled to the synthesis reactor. (3) Pass the top fraction into a precision distillation column with a reflux ratio of 3 to 5 and a top temperature of 77.2 to 77.5°C to collect high-purity chlorobutane product.

8. The method according to claim 7, characterized in that, The first distillation column has 25-35 theoretical plates and a reflux ratio of 2-4; the precision distillation column has 40-50 theoretical plates and a reflux ratio of 3-5.

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