CN1660765A

CN1660765A - New technique of esterifying reaction for producing ethyl acetate

Info

Publication number: CN1660765A
Application number: CN 200410089418
Authority: CN
Inventors: 齐峻; 顾培忠; 曾义红; 陈大胜
Original assignee: WUJING CHEMICAL CO Ltd SHANGHAI
Current assignee: WUJING CHEMICAL CO Ltd SHANGHAI
Priority date: 2004-12-13
Filing date: 2004-12-13
Publication date: 2005-08-31

Abstract

An esterifying process for preparing ethyl acetate includes such steps as proportionally mixing acetic acid with alcohol, adding sulfuric acid as catalyst, steam heating while esterifying reaction in reactor, rectifying the azeotrope of ester, water, alcohol and acid in esterifying tower and separating. It features that its esterifying reaction is divided into two steps performed respectively in preesterifying apparatus and reactor for high speed and conversion rate.

Description

Esterification process for producing ethyl acetate

The technical field is as follows:

the invention relates to a process for producing ethyl acetate, in particular to a novel esterification reaction process for producing ethyl acetate.

Secondly, background art:

according to the standard free energy rule; delta F is less than 0, and the reaction process can be carried out spontaneously. If Δ F>0, it cannot be performed.

Esterification reaction:

25℃	CH₃COOH	C₂H₅OH	CH₃COOC₂H₅	H₂O
25℃	CH₃COOH	C₂H₅OH	CH₃COOC₂H₅	H₂O	free energy F (Kc/mol)	-93.16	-41.79	-79.27	-56.69

Then, Δ F is-93.16-41.79- (-79.27-56.69) ═ 1.01Kc/mol, so that the esterification reaction of acetic acid and ethanol can theoretically proceed spontaneously at room temperature. However, since Δ F ═ RTlnK and lnK ═ Δ F/RT, the absolute value of Δ F is small although smaller than zero, so that K is small, and since K ═ K is small₁/k₂So that the reaction rate constant k of the reaction is positive₁And reaction rate constant k of reverse reaction₂The ratio is small, so that the reaction speed r ═ dH/dt ═ k1C of the esterification reaction_HC_OH-k₂C_EC_wThe reaction rate of (2) is greatly affected by the product, which is why the esterification reaction is difficult to proceed without a catalyst. Therefore, it is an essential means to increase the reaction rate of the system by adding a catalyst, rapidly renewing the reaction interface, and increasing the concentration of acetic acid and ethanol in the reaction material as much as possible, in order to smoothly progress the reaction.

Since the reaction must be carried out in the presence of a catalyst, sulfuric acid is currently the catalyst of choice by most manufacturers. The corrosiveness of the sulfuric acid is strong, and the corrosiveness of the sulfuric acid in a dilute solution is enhanced as the concentration of the sulfuric acid in a reaction system is increased. Because of this property of sulfuric acid, the amount of catalyst added must be strictly controlled in order to control corrosion of the equipment. Generally, a method of feeding materials periodically is adopted, and because the catalyst cannot be continuously supplemented and the reaction can hardly be carried out without sulfuric acid, the method brings difficulty to the selection of an ethyl acetate reaction system.

Thirdly, the invention content:

the invention aims to overcome the defects of low esterification reaction speed and low reaction conversion rate in the prior art, improve the reaction speed of a system, improve the conversion rate of the esterification reaction, further increase the yield of an esterification product and reduce the unit consumption of raw materials.

The invention is realized by the following steps: a process for preparing ethyl acetate by esterifying reaction includes proportionally mixing acetic acid with alcohol, adding sulfuric acid as catalyst, and heating in steamThe liquid is subjected to esterification reaction, the reacted solution generates an ester, water, alcohol and acid azeotropic system, and the ester, water, alcohol and acid azeotropic system enters an esterification tower for rectification and separation, and a product is obtained at the tower top. The method is characterized in that: the esterification reaction process is carried out in a pre-ester reactor and a reaction kettle step by step. The esterification reaction is firstly carried out in a pre-ester reactor by connecting a tubular reactor, namely the pre-ester reactor in series in front of a reaction kettleThe first step of reaction is carried out, and the gas-liquid mixture after the reaction enters the reaction kettle to carry out the second step of reaction, so as to quickly achieve the reaction equilibrium separation. Because of the high concentration of reactants in the pre-ester reactor, after sufficient contact with the more stable catalyst, the simulated plug flow rapidly proceeds to near first order reactions (C)_E≈0，C_W0), i.e. a better conversion is obtained in a shorter time (but still an equilibrium conversion is not reached). The gas-liquid two-phase reactor with basically controllable outlet enters the bottom of the reaction kettle, the gas plays a certain stirring role in the kettle, so that the materials in the secondary reaction can be fully mixed, separated and removed, the reaction rate is improved, and the balance conversion rate is finally achieved.

The invention has the beneficial effects that: the improved method of the invention unexpectedly improves the reaction rate of an esterification reaction system, improves the conversion rate of products, reduces the load of a concentration tower and a refining tower in the subsequent process, reduces the generation of low-ester byproducts, improves the productivity of the esterification tower, reduces the energy consumption and increases the economic benefit.

Fourthly, explanation of the attached drawings:

the attached figure is a flow chart of the structure of esterification reaction equipment for producing ethyl acetate.

In the figure: 1. a pre-ester device; 2. a reaction kettle; 3. an esterification tower; 4. a condenser; 5. a cooler; 6. a separator.

The fifth embodiment is as follows:

the traditional ethyl acetate reaction system is basically a four-tower process, a reactor of the traditional ethyl acetate reaction system is a vertical tank with a heater, in order to ensure the reaction and the concentration of products at the top of the tower, the content of ethanol in a tower kettle is generally required to be very low, namely the conversion rate of the ethanol must be as high as possible, under the condition of a certain reaction temperature, the residence time of the reaction must be ensured to improve the conversion rate of the ethanol, and the volume design of the reactor is relatively large. As can be seen from the reaction kinetic equation, after the fresh mixture is added into the reaction system,the concentration is immediately diluted, so that the reaction rate of the whole reaction system is low and the effective yield of the apparatus is lowered. To improve the capacity of the device, it is critical to improve the reaction conditions so that the reaction conditions are more consistent with the reaction rules. From the kinetic equation of the ethyl acetate reaction, it can be concluded that in the high concentration region of the raw material, due to k₂*C_E*C_H20The product value is small, k₁*C_H*C_OHProduct due to C_H、C_OHThe concentration of (b) is high and increased, so that the reaction rate (r) is large, and thus the reaction rate of the whole reaction system is increased.

Based on the theory, the esterification reaction system is modified, so that the esterification reaction is changed from the original one-step synthesis method to the two-step synthesis method. A reactor is connected in series in front of a reaction kettle in the original flow, so that a reaction system is divided into two parts. Introducing acetic acid and ethanol raw materials mixed according to a certain proportion into a first reactor, wherein the proportion (weight percentage) of the raw materials is as follows: 30-70% of acetic acid, 28-50% of ethanol and 2-20% of water, and keeping the temperature of the reactor at 92 +/-5 ℃. And (3) feeding the gas-liquid mixture after the pre-reaction into a reaction kettle, keeping the temperature in the kettle to be 106 +/-5 ℃, continuously vaporizing the reaction product, and feeding the reaction product into an esterification tower for rectification and separation to obtain a crude product. The first reactor simulates a plug flow reactor and is of a tubular structure, and the second reactor changes the conventional coil heating mode into a U-shaped heater.

Example (b):

the mixed raw materials of 50 percent of acetic acid, 45 percent of ethanol and 5 percent of water are continuously fed into a pre-ester device, the temperature of the pre-ester device is controlled at 92 ℃, the mixed solution carries out the first-stage reaction, the gas-liquid mixture after the reaction continuously enters a reaction kettle from the bottom of the reaction kettle to carry out the second-stage reaction, the reaction product is vaporized and enters an esterification tower to be rectified and separated, and a crude ester product is obtained at the tower top.

The continuous operation of the industrial device proves that: because the reaction is sufficient, the reaction conversion rate is improved, the yield of the device is obviously improved, and the operation indexes and results are as follows:

		esterification tower by one-step reaction method				Esterification tower by two-step reaction method
		esterification tower by one-step reaction method				Esterification tower by two-step reaction method			Diameter of tower		φ800				φ1900
Exercise and control device Making Finger-shaped Sign board	Temperature at the top of column (. degree.C.)	74±1				72±1			Diameter of tower		φ800				φ1900
	Temperature at the top of column (. degree.C.)	74±1				72±1			Temperature in column (. degree. C.)	79±1				74±1
	Column pressure difference (mmH)₂O)	1500				300			Temperature in column (. degree. C.)	79±1				74±1
	Column pressure difference (mmH)₂O)	1500				300			Knot Fruit	Tower unit yield (t/d)	6				68.5
Yield per unit area of the column (t/d.m²)	11.9				24.17					Tower unit yield (t/d)	6				68.5
Yield per unit area of the column (t/d.m²)	11.9				24.17			Tower top component (w/w)％		Esters	Alcohol(s)	Water (W)	Acid(s)	Esters	Alcohol(s)	Water (W)	Acid(s)
92.07	1.65	6.275	0.005	95.276	1.00	3.72	0.004			Esters	Alcohol(s)	Water (W)	Acid(s)	Esters	Alcohol(s)	Water (W)	Acid(s)

Claims

1. A new esterification process for producing ethyl acetate, which comprises the steps of putting mixed raw materials according to a certain proportion into a reactor, carrying out esterification reaction by sulfuric acid catalysis and steam heating, vaporizing the reacted solution to form an ester, alcohol, water and acid azeotropic system, feeding the azeotropic system into an esterification tower for rectification and separation, and obtaining a product at the top of the tower, and is characterized in that: the ethyl acetate esterification reaction process is carried out in two steps, wherein raw materials are connected in series with a reactor before passing through a reaction kettle, so that the esterification reaction is carried out in two steps in two devices of the reactor and the reaction kettle.

2. The esterification process for producing ethyl acetate according to claim 1, wherein: the reactor connected in series in front of the reaction kettle is a tubular reactor, also called a pre-ester reactor, and simulates a plug flow reactor, so that the mixed raw materials are subjected to a first-step reaction in the pre-ester reactor.

3. The esterification process for producing ethyl acetate according to claim 1, wherein: the heater in the reactor is a U-shaped heater, the U-shaped heateris a U-shaped heating tube bundle which is divided into four groups, the U-shaped heater is arranged at the middle upper part and the middle lower part of the reaction kettle in a two-group and two-group mode, and the U-shaped heater is staggered in the vertical direction and arranged in a shape like a Chinese character '#' in a overlook mode.

4. The esterification process for producing ethyl acetate according to claim 1, wherein the raw materials are added to the reactor in the following ratio (by weight): 30-70% of acetic acid, 28-50% of ethanol and 2-20% of water.