A method of reducing waste water from acrolein production processes

Abstract

The application discloses a method for reducing waste water in acrolein production process, mixed gas A output from a reactor is treated by an acrolein separation and purification unit to purify acrolein, the generated waste water and tail gas are both transported to a stripping tower, the tail gas is subjected to stripping treatment on the waste water and realizes self humidification, and the tail gas subjected to the stripping treatment is connected to an input end of the reactor. Part of the tail gas generated by the acrolein separation and purification unit is connected to the input end of the reactor. The circulating tail gas is subjected to gas stripping on waste liquid in the tower kettle of the stripping tower, so that the circulating tail gas is humidified, the addition amount of water vapor in raw materials is reduced, and finally the waste water emission in the acrolein production process is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of propenal production, and particularly relates to a method for reducing wastewater in a propenal production process. BACKGROUND

[0002] Propenal is the simplest unsaturated aldehyde, which is a colorless, volatile, toxic liquid with a strong irritating odor. Its vapor has an irritating effect on the mucous membranes of the eyes and has a tear-inducing function. Propenal is extremely active in chemical properties due to the carbon-carbon double bond and aldehyde group in the molecule, forming a conjugated system. It is mainly used as an intermediate in chemical production, mainly for the preparation of methionine, glutaraldehyde, glycerol and water treatment agents, etc.

[0003] Currently, propenal is mainly synthesized by partial oxidation of propylene. In addition to propylene and fresh air, a certain amount of tail gas is also added for processes that use tail gas recycling. In addition, a certain proportion of water vapor is also added. The main functions of adding water vapor are: first, as a diluent gas; second, water vapor has a large heat capacity, which is beneficial to the thermal stability of the reaction bed; third, the presence of water vapor not only affects the conversion rate of the reaction, but also affects the distribution of the products. Therefore, water plays a very important role in the raw materials for the production of propylene by oxidation of propylene. The raw material gas mixed in a certain proportion is sent into a fixed bed reactor, and propylene is partially oxidized in the reactor, with a conversion rate of more than 98%. In addition to propenal, there are also water, carbon oxides and other organic components.

[0004] A Chinese patent with publication number CN110551008B discloses a method for recycling tail gas in a propenal production process, which comprises the following steps: S1, sending propylene, oxygen, nitrogen and medium-pressure steam into a reactor to generate a reaction stream; S2, sending the reaction stream into a propenal separation unit to separate propenal and crude propenoic acid; S3, burning the tail gas generated in the propenal separation unit to generate a gas stream; and S4, sending part of the gas stream into a process system for recycling, and the remaining part is discharged into the atmosphere. The method for recycling tail gas in a propenal production process can send the carbon dioxide and water generated by burning the tail gas into the production process for recycling, thereby reducing the steam consumption in the process system. At the same time, the safety of the propenal production process can be ensured. The disclosed invention, although the tail gas from the propenal separation unit is connected to the reactor, the recycling rate of the wastewater is limited.

[0005] To this end, we propose a method for reducing wastewater in a propenal production process and its use method to solve the problems mentioned in the background. SUMMARY

[0006] The present application aims to provide a method for reducing wastewater in a propenal production process to solve the problems mentioned in the background.

[0007] To achieve the above object, the present application provides the following technical solution: a method for reducing waste water in the production of acrolein, mixed gas A output from a reactor is treated in an acrolein separation and purification unit to purify acrolein, the generated column bottom waste water and tail gas are both delivered to a stripping column, the tail gas is used to strip the column bottom waste water and realize self humidification, the tail gas after stripping treatment is boosted by a fan and heated by a heater and then connected to the input end of the reactor. The separation and purification unit is composed of an acrylic acid absorption tower, an acrolein absorption tower and an acrolein product tower, the purpose is to use aqueous solution to absorb acrylic acid and acrolein in the mixed gas A respectively, and to obtain acrolein product by rectification of the acrolein aqueous solution in the acrolein product tower.

[0008] Preferably, a plate-type internal part or packing is installed in the stripping column, which is used to make the liquid fully contact with the gas.

[0009] Preferably, fresh air and tail gas are both humidified by the stripping column, boosted by the fan and heated by the heater and then entered into the reactor inlet, the stripping column uses external circulation heating to heat the column bottom waste water, the gas phase outlet temperature of the stripping column is 45-75℃, and the pressure is -5-25kPaG.

[0010] Compared with the prior art, the present application has the beneficial effects that: part of the tail gas generated by the acrolein separation and purification unit is connected to the input port of the reactor, the fresh air and the circulating tail gas are humidified by the stripping column to strip the column bottom waste liquid, so that the fresh air and the circulating tail gas are humidified, the addition amount of water vapor in the raw material is reduced, and finally the discharge of waste water in the production of acrolein is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 It is a flow diagram of example one;

[0012] Figure 2 It is a flow diagram of example two. DETAILED DESCRIPTION

[0013] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0014] Example one

[0015] Referring to Figure 1, provide a method for reducing acrolein production process wastewater, the reactor output of mixed gas A is treated by acrolein separation and purification unit to purify acrolein, the generated column wastewater and tail gas are transported to the stripping tower, the tail gas is stripped to the column wastewater and realizes self humidification, the tail gas after stripping treatment is connected to the input end of the reactor, and the internal plate inner part or filler of the stripping tower is installed. The plate inner part or filler is used for fully contacting liquid and gas.

[0016] Example two

[0017] Reference Figure 2 Different from example one, fresh air and tail gas are humidified by the stripping tower, fan pressure boosting, heater heating and then enter the reactor inlet.

[0018] The temperature and pressure of fresh air from the environment are lower than those of the tail gas. In order to fully absorb acrolein in the acrolein absorption and purification unit, the exhaust temperature of the tail gas is generally controlled below 15 DEG C. In order to make the fresh air and the circulating tail gas carry more water, the temperature thereof needs to be increased. The stripping tower uses external circulation heating to heat the column wastewater. The temperature of the gas phase outlet of the stripping tower is 45-75 DEG C, and the pressure is-5-25 kPaG.

[0019] The steam consumption and wastewater generation of the following three cases are tested respectively

[0020] 1. In the acrolein production, the tail gas is recycled, the wastewater is not stripped, and is directly incinerated or biologically treated. The steam consumption and wastewater generation of a 10,000 tons / year device during production are shown in Table 1.

[0021] Table 1 Steam consumption and wastewater generation

[0022] steam waste water consumption or production (kg / h) 450.0 906.0

[0023] 2. According to the attached Figure 1 flow, the tail gas is recycled in the acrolein production, and the wastewater is stripped with the tail gas. The wastewater that is not stripped is incinerated or biologically treated. The steam consumption and wastewater generation of a 10,000 tons / year device during production are shown in Table 2.

[0024] Table 2 Steam consumption and wastewater generation

[0025] steam waste water consumption or production (kg / h) 196.0 413.0

[0026] 3. According to the attached Figure 2 flow, the tail gas is recycled in the acrolein production, and the wastewater is stripped with the tail gas. The wastewater that is not stripped is incinerated or biologically treated. The steam consumption and wastewater generation of a 10,000 tons / year device during production are shown in Table 3.

[0027] Table 3 Steam consumption and wastewater generation

[0028] steam waste water consumption or production (kg / h) 0.0 609.0

[0029] From the above test results, it can be concluded that the steam stripping treatment of the column bottom wastewater with tail gas or fresh air plus tail gas can greatly reduce the wastewater generation.

[0030] Finally, it should be noted that the above only for the preferred embodiments of the present application, and is not intended to limit the present application, although the foregoing detailed description of the present application has been made with reference to the foregoing embodiments, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement, within the spirit and principles of the present application, any modification, equivalent replacement, improvement, etc., should be included within the scope of the present application.

Claims

1. A method of reducing acrolein production process wastewater, characterized by: The mixed gas A output from the reactor is treated in a propenal separation and purification unit to purify propenal, the produced tower bottom waste water and tail gas are transported to a stripping tower, the tail gas is used to strip the tower bottom waste water and to humidify itself, the stripped tail gas is transported to the input port of the reactor through a fan and a heater.

2. A method of reducing acrolein production process wastewater according to claim 1, characterized in that: A plate internal part or a packing is installed in the stripping tower to make the liquid and gas fully contact.

3. A method of reducing acrolein production process wastewater according to claim 1, characterized in that: Fresh air is humidified in the stripping tower, pressurized by a fan and heated by a heater, and then enters the reactor inlet.

4. A method of reducing acrolein production process wastewater according to claim 3, characterized in that: The stripping tower uses external circulation heating to heat the tower bottom waste water, the temperature of the gas phase outlet of the stripping tower is 45-75 ℃, and the pressure is -5-25 kPaG.

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