Optimized process for preparing acrylic acid by oxidizing propylene through two-step method

Abstract

The invention relates to the technical field of preparation of acrylic acid by propylene oxide through a two-step method, and discloses an optimized and innovative process for preparing acrylic acid through a two-step propylene oxide method, which comprises the following steps: firstly, controlling the temperature of a reactor by controlling circulating heat-conducting fused salt in the process, performing multi-point temperature measurement and APC technology prediction control, and introducing SIS system linkage; the temperature control is quicker and more accurate, the temperature of each point of the reactor is prevented from being too high, the catalyst is protected, and the quality of the product acrylic acid is better. Due to the fact that explosive gas is easily formed after propylene, air and inert materials are mixed, in order to enable production to be safer and more stable, a novel APC predictive control technology and a DCS monitoring control scheme are adopted in the process, SIS system linkage control is combined, the proportion of the mixed gas is located in a safe area, production is safer and more reliable, and meanwhile the product conversion rate is the highest. According to the optimization process for preparing the acrylic acid by oxidizing the propylene through the two-step method, the production is safer and more reliable, the energy is saved, the efficiency is high, the product quality is higher, the propylene conversion rate and the acrylic acid yield are higher, the expected value of the conversion rate reaches 97%, and the total yield value reaches 88% or above.

Description

Technical Field

[0001] The present invention relates to the technical field of acrylic acid preparation, and specifically to an optimized process for preparing acrylic acid by the two-step oxidation of propylene. Background Art

[0002] Acrylic acid is an organic compound and the simplest unsaturated fatty acid. Due to the presence of unsaturated bonds in its structure, its chemical properties are relatively active. It is prone to polymerization in air, can undergo reduction reactions with hydrogen, esterification reactions with alcohols, and addition reactions with hydrogen halides. Acrylic acid is mainly used in the preparation of acrylate esters, superabsorbent polymers, etc., and is widely used in fields such as coatings, textiles, sanitary products, and water retention agents. There are many production processes for acrylic acid, including the preparation of acrylic acid from acetylene, ethylene, ketene, and vinyl cyanide. However, these processes all have their own disadvantages. Some have been discontinued, some are too old, or the production volume is not large. The process of preparing acrylic acid by the oxidation of propylene has the best technical economy.

[0003] Currently, the disadvantages of the two-step oxidation of propylene to prepare acrylic acid are low conversion rate and yield, lack of automation, poor production safety, high operation difficulty, and high precision requirements for process parameter control. We have optimized this process to achieve a conversion rate of up to 97% and a total yield of over 88%. The production control is more accurate, the degree of automation is higher, and the production is also safer. Summary of the Invention

[0004] The purpose of the present invention is to provide an optimized process for preparing acrylic acid by the two-step oxidation of propylene, so as to solve the defects of low existing conversion rate and yield, poor production safety, high operation difficulty, and high precision requirements for process parameter control as mentioned in the above background art.

[0005] To achieve the above purpose, the present invention provides the following process optimizations:

[0006] Optimization 1: Use circulating molten salt to control the reactor temperature, and adopt multi-point control at different depths with thermocouple temperature sensors. At the same time, adopt multi-point temperature measurement and APC technology for predictive control and introduce the SIS interlock control system, making the production safer and more reliable, and also making the temperature control more accurate and timely, protecting the catalyst. And since the reactor temperature directly affects the quality of the product acrylic acid, this highly efficient and sensitive temperature control system results in higher product quality.

[0007] Optimization 2: Since the mixture of propylene, air and inert gas is extremely likely to form an explosive gas mixture with an explosion critical value, and according to the reaction principle, the closer to the critical value, the higher the reaction conversion rate. Therefore, to ensure production safety while maximizing the reaction conversion rate and product yield, we adopt APC predictive control technology and DCS control monitoring system, and introduce SIS interlock control. This advanced production system makes the production safer, with higher conversion rate and yield, energy-saving, efficient and more automated.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0009] (1) By using APC technology with predictive control function, high-precision DCS monitoring system and SIS interlock system to control the proportion of reaction gases, the formation of explosive proportion gases is avoided, making the production process safer.

[0010] (2) For the optimized two-step oxidation process of propylene to prepare acrylic acid, through APC predictive control technology, DCS system and SIS control, the raw material conversion rate and product yield are maximized on the premise of safe production.

[0011] (3) Through molten salt heat exchange and temperature control, combined with APC predictive control technology, SIS interlock system and multi-point temperature measurement, the temperature control of the reactor is easier and more accurate, and the catalyst is not easily damaged by high temperature. Since the reaction temperature directly affects the product quality, accurate temperature control makes the quality of the product acrylic acid higher.

[0012] (4) By adopting advanced control monitoring system and interlock control system, the production operation is easier, more automated, and the production parameter control is more accurate. Specific Embodiments

[0013] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0014] Example 1: When propylene is mixed with an inert material in air, an explosive gas mixture is easily formed, and there is a critical ratio relationship between them, that is, the explosion curve relationship. Operating outside the explosion curve is safe, while operating inside the explosion curve will cause an explosion. However, the closer the operation is to the explosion curve, the more dangerous it is, and the higher the conversion rate. The farther away from the explosion curve, the safer the operation, but the lower the conversion rate. Therefore, according to the production characteristics of this device, a DCS operation station is specifically set up to monitor the explosion curve of the acrylic acid reaction unit, and combined with an APC technology operation station to predict and control the reaction gas ratio in advance, making the production safer and more reliable. According to the explosion curve, when the device is started up, quickly cross the explosion hazard area and enter the safe area, select the best operating point, maximize the conversion rate, steadily increase the production load, and enable the device to reach the production capacity as soon as possible. During the production process, strictly monitor and constantly monitor this mixing process. Once the mixing ratio deviates, the feed is automatically cut off through the SIS system interlock and nitrogen is introduced to ensure the safety of the device.

[0015] Example 2: The temperature control of the acrylic acid oxidation reactor is achieved by controlling the circulating heat-conducting molten salt. The high or low temperature of the oxidation reactor directly affects the quality of the product (acrylic acid). Therefore, the reactor temperature control system adopts a control method of using the average temperature and temperature difference to control the molten salt flow rate to ensure that the oxidation reaction temperature is controlled within a stable operating range. In order to accurately reflect the catalyst temperature of each bed layer in a timely manner, multiple groups of multi-point thermocouple temperature sensors (with different insertion depths for each point) are set on the oxidation reactor, and according to different insertion depths, distributed in a spiral shape, one point is selected from each group as a typical temperature detection point. At the same time, in order to prevent the catalyst from being burned out, we adopt APC operation station predictive control to prevent the temperature from being too high in advance and introduce it into the SIS to participate in the safety interlock of the oxidation reactor.

[0016] It should be noted that:

[0017] (1) DCS is the abbreviation of the distributed control system, also known as the "distributed control system" or "distributed computer control system". It is a new generation of instrument control system based on microprocessors, adopting the design principle of decentralized control functions, centralized display and operation, and taking into account both decentralized autonomy and comprehensive coordination. This system enables instrument monitoring to be digitized, with high precision and greater reliability, capable of real-time control of production and faster and more timely responses.

[0018] (2) SIS represents the safety instrument control system, also known as the safety interlock system. It is mainly the interlock control part in the factory control system, which adjusts or shuts down the system according to the detection results of the instruments in the system, and has the advantages of fast response speed and high safety, making the production more automated and safer.

[0019] (3) APC represents advanced control technology. The biggest difference from the classic PID controller is that it no longer controls only a single variable, but rather controls multiple variables of the controlled object as a whole. It has a prediction function and can analyze the operating conditions of multiple loops currently, so as to predict the future of each loop in the controller. According to the prediction results, the loop is adjusted, which can reasonably limit the change amount and change rate of the control variable, ensure the stability of the control system and the robustness to uncertain factors, and thus can optimize the control effect to the greatest extent possible.

[0020] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art of this industry should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

[0021] Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. It relates to the optimization and innovation of the process for preparing acrylic acid from propylene oxide by a two-step method, characterized in that, Interlock with advanced APC technology, DCS system and SIS system, control the temperature by circulating molten salt, prevent high-temperature damage to the catalyst, adjust the proportion of reaction mixed gas, optimize the production process, and achieve safe production and high reactant conversion rate and high-quality product yield.

2. For the process optimization and innovation described in Claim 1, control the temperature of the oxidation reactor by circulating heat-conducting molten salt, adopt APC technology, and introduce an SIS interlock system to ensure temperature stability and prevent catalyst damage due to high temperature. Since this temperature directly affects the quality of the product acrylic acid, molten salt heat exchange is used, multiple-point temperature measurement is adopted, combined with APC technology and SIS interlock control, which protects the catalyst and also makes the quality and yield of the product acrylic acid higher.

3. For the process optimization and innovation described in Claim 1, since explosive gases are easily formed after the mixing of propylene, air and inert materials, there is an explosion critical point, but at the same time, the closer to the explosion critical point, the higher the conversion rate. In order to ensure production safety and achieve a high conversion rate at the same time, we have adopted a DCS monitoring system for real-time monitoring, used APC technology to achieve early prediction control, and combined with SIS interlock control of the mixed gas ratio, making the production safer and more reliable, the production gas entering the safe zone of proportion, maximizing the conversion rate, more safe and efficient, and making the production more automated.