CN101596371A - Apparatus and method for purifying formic acid solution by batch azeotropic distillation - Google Patents

Abstract

The present invention relates to a kind of apparatus and method of intermittent azeotropic rectifying method purifying formic acid solution.Device comprises: rectifying column body of the tower, heat-insulation layer, tower still, heating jacket, condenser, phase-splitter and product storage tank; Body of the tower is installed heat-insulation layer outward, and the body of the tower lower end connects the tower still, and the upper end connects condenser and phase-splitter respectively, and phase-splitter connects condenser and product storage tank respectively.At first adopting cyclohexane to make entrainer, is that 10% the dilute formic acid aqueous solution tentatively is concentrated to 30% with mass concentration; Re-use chlorobenzene and make entrainer, the azeotropic mixture of earlier continuous extraction chlorobenzene of cat head and water treats that the mixing of tower top temperature extraction chlorobenzene-formic acid-water in the time of 95 ℃-102 ℃ is formed, and the mass fraction of formic acid can reach 60%-70% after the phase-splitting; Use compression rectification at last, controlled pressure is at 4atm, and the tower still can reach the concentration formic acid and high solution about 80-85%.The present invention has that technological process is reasonable, apparatus structure is simple, efficient is high, cost is low and the characteristics of suitable industrialization continued operation.

Description

Apparatus and method for purifying formic acid solution by batch azeotropic distillation

technical field

The invention relates to a device and method for purifying formic acid solution by intermittent azeotropic distillation, in particular to purifying 10% dilute formic acid solution into 80-85% higher concentration formic acid by adopting heterogeneous azeotropic distillation.

technical background

Formic acid, commonly known as formic acid, is the simplest fatty acid and an important organic chemical raw material. It is widely used in pesticides, leather, textiles, printing and dyeing, medicine and rubber industries. It can also be used to prepare various solvents, plasticizers, and rubber solidification. Agents, animal feed additives and new process synthetic insulin, etc. In the production of medicines and spices and the acid treatment of textiles and leather, a large amount of low-concentration formic acid solution will be produced, which has no practical application value. Recovering low-concentration formic acid and enriching it (w%>85%) can not only reduce environmental pollution, but also create considerable economic value. Formic acid can be miscible with water in any proportion and form an azeotropic mixture (w _water %=22%), and a high-concentration formic acid solution cannot be obtained by ordinary rectification.

In the past, methods for purifying formic acid have been reported in the literature. Add new entrainer in water-containing formic acid as British patent report in 1948, the weak point of this type of method is: entrainer propyl formate, isobutyl formate etc. generally need to be prepared from anhydrous formic acid, simultaneously these The entrainer is easy to be hydrolyzed. During the distillation process, it is hydrolyzed by heat to generate formic acid and propanol or butanol, so that the separation cannot continue. As reported in Chinese patent CN1063483 in 1992, the additive thionyl dichloride was used to make it react with formic acid aqueous solution for dehydration, and then vacuum distillation, but because the process is more complicated, it will cause certain pollution to the environment and will bring Because of the high cost, it is rarely used. Another example is the boric anhydride purification method reported in Chinese literature in 2006, using boric anhydride (boron trioxide) to react with water in dilute formic acid to form boric acid, which can be distilled to obtain high-concentration formic acid, and the remaining boric acid can be reused through drying and dehydration. However, boric acid is dried and dehydrated into boric anhydride, which can only be carried out at a temperature above 300° C., which is difficult to implement industrially, and boric anhydride is expensive, and the production cost is too high. Another example is that U.S. Patent US-A4877490 and US-A4909907 etc. have introduced the method that extraction and rectification obtains high concentration formic acid solution with ethyl benzoate, diethylene glycol methyl ester or benzoic acid acetic anhydride etc. as extraction agent, but because extraction agent price Expensive, and these extractants are all high-boiling substances, making it very difficult to recover and reuse, and the extraction effect is not ideal, so these methods are not easy to realize industrially.

Contents of the invention

The object of the present invention is to provide a kind of apparatus and method of batch azeotropic rectification method purification formic acid solution, adopt heterogeneous phase azeotropic rectification method that 10% formic acid dilute solution is purified to be the higher concentration formic acid of 80-85%. The invention has the characteristics of reasonable technological process, simple device structure, high efficiency, low cost and suitable for industrial continuous operation.

A device for purifying formic acid solution by a batch azeotropic distillation method provided by the invention comprises: a rectification tower body, an insulating layer, a tower kettle, a heating mantle, a condenser, a phase separator and a product storage tank; The lower end of the tower body is connected to the tower kettle, the upper end is respectively connected to the condenser and the phase separator, and the phase separator is respectively connected to the condenser and the product storage tank.

The condenser includes a product vapor riser pipe, a parallel condensation chamber body, a condensation pipe, a thermometer, a condensate water outlet, a condensate water inlet, a reflux ratio regulator, a phase separator in the condensation chamber and a sampling port.

A thermometer is installed at the upper end of the product steam ascending pipe, a reflux ratio regulator and a phase separator in the condensing chamber are installed under the condensed water outlet and condensed water inlet of the condensed pipe in the condensing chamber, and a sampling port is set at the lower end of the condensing chamber.

The method that a kind of batch azeotropic rectification method purification formic acid solution provided by the invention comprises the steps:

1) primary purification

The operating pressure of the rectification tower is normal pressure, the number of theoretical plates is 15-30, the entrainer cyclohexane and 10% formic acid dilute solution are added into the tower kettle together, the mass ratio is 4-9, and the reflux ratio is 0.8- 2. The temperature at the top of the tower is controlled at 68-69°C, and the temperature at the bottom of the tower is controlled at 71-72°C. According to the triangular phase diagram of formic acid-water-cyclohexane, what evaporates first is the azeotropic composition of cyclohexane and water. When the quality of the water produced is about 70% of the raw material, stop the operation, and the tower kettle will A formic acid solution with a mass concentration of 30% can be obtained.

2) Secondary purification

Chlorobenzene and formic acid solution with a mass concentration of 30% are added to the bottom of the rectification tower together, the operating pressure of the rectification tower is normal pressure, the number of theoretical plates is 15-30, and the mass ratio of chlorobenzene and formic acid solution is 3-5, The reflux ratio is 1.5-3, the temperature at the top of the tower is controlled at 94-99°C, and the temperature at the bottom of the tower is controlled at 96-101°C. According to the triangular phase diagram of formic acid-water-chlorobenzene, the azeotropic composition of chlorobenzene and water is produced first at the top of the tower. The concentration also increased gradually. Extract the distillates with a temperature range of 94-98°C at the top of the tower, and after phase separation in a phase separator, a formic acid solution with a mass concentration of 60-70% can be obtained.

3) Pressurized distillation

Add the formic acid solution that the mass concentration is 60-70% to the bottom of the rectification tower, the operating pressure is 4atm (the azeotropic composition under this pressure is shown in Table 3), the reflux ratio is 5-10, and the initial control tower top temperature is 143-144 °C, the temperature of the tower bottom is 152-153 °C, as the water evaporates from the top of the tower, the temperature also rises, when the temperature of the top of the tower reaches 152-154 °C, the operation is stopped, and the available mass concentration of the tower bottom is 80-85% of formic acid solution.

The beneficial effects of the present invention are mainly reflected in:

1) 10% dilute formic acid solution can be purified to 80-85% higher concentration formic acid.

2) According to the formic acid-water-vapour-liquid equilibrium relationship, the present invention proposes an operation method in which an entrainer is required in the tower kettle, and adopts cyclohexane and chlorobenzene as the entrainer respectively. The entrainer is low in price, rich in resources, and easy to recycle.

3) The azeotropic rectification process adopted in the present invention utilizes entrainer and formic acid and water to form ternary azeotrope to produce the method for high-concentration formic acid from tower top in the secondary purification process, which is different from general azeotropic refiner distilled and it works.

4) The technological process adopted by the present invention is reasonable, and the device structure is simple, which is very suitable for industrial operation.

Description of drawings

Figure 1 is a schematic diagram of the device of the present invention.

Figure 2 is a schematic diagram of the structure of the condenser used in the experiment.

Detailed ways

The present invention adopts intermittent azeotropic distillation equipment, as shown in the figure, and Fig. 1 is a schematic diagram of the device of the present invention. Among them, 1 is the body of the rectification tower, 2 is the insulation layer, 3 is the tower kettle, 4 is the heating jacket, 5 is the condenser, 6 is the phase separator, and 7 is the product storage tank. Figure 2 is a schematic diagram of the structure of the condenser used in the experiment. Among them, 8 is a thermometer, 9 is a condensed water outlet, 10 is a condensed water inlet, 11 is a reflux ratio regulator, 12 is a phase separator in a condensation chamber, and 13 is a sampling port.

An insulation layer 2 is installed outside the tower body 1, the lower end of the rectification tower body 1 is connected to the tower kettle 3, and the upper end is respectively connected to the condenser 5 and the phase separator 6, and the phase separator 6 is respectively connected to the condenser 5 and the product storage tank 7.

The condenser includes: product steam riser pipe and parallel condensation chamber body, condensation pipe, thermometer 8, condensate water outlet 9, condensate water inlet 10, reflux ratio regulator 11, condensation chamber phase separator 12 and sampling port 13.

A thermometer 8 is installed at the upper end of the product steam riser pipe, a reflux ratio regulator 11 and a phase separator 12 in the condensation chamber are arranged below the condensed water outlet 9 and the condensed water inlet 10 in the condensing chamber, and a sampling port 13 is arranged at the lower end of the condensing chamber.

The parameters of the batch distillation tower used in the experiment are: the height of the effective packing section is 0.8m, the diameter of the tower column is 30mm, and a 3mm×3mm high-efficiency stainless steel θ ring packing is installed inside; the tower kettle is a 250ml three-necked bottle, and the tower body, thermometer and glass plug; the reflux ratio is controlled by a relay and an electromagnet, and samples are taken at the top of the tower; the tower kettle is heated by an electric heating mantle, and the heating power is 200W; The number is 20.

The condenser is a phase-separation condenser. After the steam rising from the top of the tower is condensed by the condenser, it is separated in the phase separator by density difference, and the organic phase is refluxed into the tower at the top, and water is extracted. Since cyclohexane and water, chlorobenzene and water and formic acid can form heterogeneous azeotropes, their azeotropic compositions are shown in Table 1 and Table 2 respectively.

Table 1 Azeotropic composition of formic acid-water-cyclohexane system

Table 2 Azeotropic composition of formic acid-water-chlorobenzene system

Table 3 Azeotropic composition of formic acid-water at 4atm

The method for purifying formic acid solution by intermittent azeotropic distillation includes the following steps: firstly, cyclohexane is used as entrainer, and the dilute formic acid aqueous solution with a mass concentration of 10% is initially concentrated to 30%; then chlorobenzene is used as entrainer, and the tower At the top, the azeotrope of chlorobenzene and water is continuously extracted, and the mixed composition of chlorobenzene-formic acid-water is extracted when the temperature at the top of the tower is 95°C-102°C. After phase separation, the mass fraction of formic acid can reach 60%-70% %; Finally, pressurized rectification is used to control the pressure at 4atm, and the tower kettle can reach a high-concentration formic acid solution of about 80-85%. Specific steps:

1) primary purification

Open the feed inlet, add 20ml mass concentration of 10% formic acid solution and 160ml cyclohexane, check whether the joints are well sealed, after cooling water is passed into the tower top condenser, turn on the heating power supply to reboiler Heating, when the liquid in the reboiler starts to boil, the tower body insulation circuit starts to be connected. Maintain total reflux, keep the temperature at the top of the tower stable at 69°C, adjust the reflux ratio to 1, collect the extracted products in a phase separator for layering, return the organic phase to the rectification tower, and extract the water phase until the extracted product When the volume of the aqueous phase reaches 15ml, stop the operation. After taking out the product from the tower kettle, the phase separation, the concentration of formic acid is 38.4%

2) Secondary purification

Open feed inlet, add 21ml mass concentration and be 30% formic acid solution and 79ml chlorobenzene, keep tower top temperature after total reflux to be 92 ℃, adjust reflux ratio to be 1.5, take out the azeotropic composition of chlorobenzene and water. When the temperature at the top of the tower rose to 94.5°C, the fractions were collected again until the temperature rose to 98.5°C. After phase separation of the extracted ternary mixture, the mass concentration of formic acid was 60.1%, and the yield was 68%.

3) Pressurized distillation

Add 100ml of formic acid solution with a mass concentration of 60% in the rectifying tower, the pressure is 4atm, keep the tower top temperature at 144.2°C after total reflux, and adjust the reflux ratio to 6. When the temperature at the top of the tower rises to 150° C., the operation is stopped. The mass concentration of formic acid in the tower still product is 82%, and the yield of formic acid is 96.7%.

Claims (5)

1, a kind of device of intermittent azeotropic rectifying method purifying formic acid solution is characterized in that comprising: rectifying column body of the tower, heat-insulation layer, tower still, heating jacket, condenser, phase-splitter and product storage tank; Body of the tower is installed heat-insulation layer outward, and the body of the tower lower end connects the tower still, and the upper end connects condenser and phase-splitter respectively, and phase-splitter connects condenser and product storage tank respectively.

Described condenser comprises product vapor uptake and parallel condensation chamber body, condenser pipe, thermometer, condensation-water drain, condensed water import, reflux ratio adjuster, condensation chamber phase-splitter and thief hatch.

Below the product vapor uptake installation thermometer suitable for reading, the condensation-water drain of condensation chamber interior condenser tube and condensed water import reflux ratio adjuster and condensation chamber phase-splitter are arranged, thief hatch is established in the condensation chamber lower end.

2, a kind of method of utilizing the device purifying formic acid solution of the described intermittent azeotropic rectifying method purification of claim 1 is characterized in that the step that comprises:

1) elementary purification: the operating pressure of rectifying column is a normal pressure, entrainer cyclohexane and 10% formic acid weak solution together add in the tower still, its mass ratio is 4-9, tower top temperature is controlled at 68-69 ℃, and tower still temperature is controlled at 71-72 ℃, according to the triangular phase diagram of formic acid-water-cyclohexane, what steam at first is the azeotropic composition of cyclohexane and water, when the quality of the water of extraction be raw material 70% the time, shut-down operation, it is 30% formic acid solution that the tower still can obtain mass concentration;

2) secondary purification: with chlorobenzene and mass concentration is that 30% formic acid solution joins rectifier bottoms together, the rectifying column operating pressure is a normal pressure, the mass ratio of chlorobenzene and formic acid solution is 3-5, tower top temperature is controlled at 94-99 ℃, tower still temperature is controlled at 96-101 ℃, triangular phase diagram according to formic acid-water-chlorobenzene, cat head extraction at first be that the azeotropic of chlorobenzene and water is formed, continuous extraction along with water and chlorobenzene, tower top temperature rises gradually, and the concentration of formic acid in cat head also raises gradually, and extraction tower top temperature scope is at 94-98 ℃ cut, in phase-splitter, after the phase-splitting, can obtain the formic acid solution that mass concentration is 60-70%;

3) compression rectification: with mass concentration is the formic acid solution adding rectifier bottoms of 60-70%, originally controlling tower top temperature is 143-144 ℃, tower still temperature is 152-153 ℃, along with moisture steams from cat head, temperature also rises thereupon, shut-down operation when tower top temperature arrives 152-154 ℃, the tower still can get the formic acid solution that mass concentration is 80-85%.

3, according to the method for the described purifying formic acid solution of claim 2, it is characterized in that number of theoretical plate is 15-30 in the step 1), reflux ratio is 0.8-2.

4, according to the method for the described purifying formic acid solution of claim 2, it is characterized in that step 2) in number of theoretical plate be 15-30, reflux ratio is 1.5-3.

5, according to the method for the described purifying formic acid solution of claim 2, it is characterized in that operating pressure is 4atm in the step 3), reflux ratio is 5-10.

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