Online Viscosity Measurement and Control Method for Preventing Coking of Liquid in MMA Esterification Process

Abstract

The invention discloses an online viscosity measurement and control method for preventing coking of feed liquid in an MMA esterification process, comprising the following steps: 1. laying a polymerization inhibitor pipeline on each reactor; 2. installing a remote control switch valve on the polymerization inhibitor pipeline; 3. sequentially spraying the polymerization inhibitor into each reactor at intervals T through the polymerization inhibitor pipeline via the remote control switch valve; 4. installing an online viscometer (9) in a No. 4 esterification evaporator, installing an emergency discharge valve (10) on a connecting pipeline between the No. 4 esterification evaporator and a waste acid regeneration treatment device (12), and electrically connecting the online viscometer to the emergency discharge valve and the remote control switch valve of the No. 4 esterification evaporator; 5. monitoring the viscosity of the feed liquid in the No. 4 esterification evaporator with the online viscometer, and controlling the viscosity of the feed liquid via the remote control switch valve or the emergency discharge valve. The invention can solve the problem of inaccurate manual judgment of the viscosity of the feed liquid in the No. 4 esterification evaporator in the prior art.

Description

Technical Field

[0001] The present invention relates to an MMA (Methyl methacrylate) esterification production process, in particular to an online viscosity measurement and control method for preventing liquid material from coking in an MMA esterification process. Background Art

[0002] Methyl methacrylate (MMA) is the main raw material for the production of organic glass sheets, PMMA molding compounds, and high-end coatings. It is widely used in military industry, optical fiber, bathroom fixtures, high-end adhesives, high-end paints, PVC modifier ACR, aquariums, outdoor billboards, display light guide materials, and other fields.

[0003] There are many production processes for methyl methacrylate (MMA), including the acetone cyanohydrin process (ACH process), the isobutylene oxidation process, and the ethylene process. The acetone cyanohydrin process is the earliest industrialized method for producing MMA. Due to its mature technology and its ability to utilize hydrocyanic acid, a byproduct of acrylonitrile, the acetone cyanohydrin process currently accounts for approximately 80% of total MMA production worldwide. This process effectively utilizes hydrocyanic acid, a byproduct of acrylonitrile production, and offers a high yield of MMA, which are key technical advantages.

[0004] During the acylation reaction stage of the acetone cyanohydrin (ACH) process, ACH and sulfuric acid are added to the reaction in a certain ratio to form an amide salt intermediate, which is then sent to the esterification process to continue the reaction to produce methyl methacrylate (MMA). The esterification process mainly sets up an esterification reactor and five esterification evaporators connected in series (referred to as 1# to 5# esterification evaporators in sequence). Because MMA is very easy to polymerize, the nozzles and overflow pipes on the top of each esterification reactor and esterification evaporator are very prone to blockage. In particular, in the feed liquid of the last esterification evaporator (5#), improper operation will cause polymerization and coking, forming a sticky coke cake floating on the feed liquid, causing the entire esterification process to stop production, empty the feed and clean up. The inspection and maintenance cycle can be as long as more than ten days, seriously affecting the long-term operation of the device.

[0005] Currently, the conventional method for preventing coking of the feed solution in the MMA esterification process involves observing the feed solution viscosity using sight glasses on the last two (4# and 5#) esterification evaporators and the sight glass in the overflow pipe. This allows for manual assessment of the feed solution viscosity and blockage, and determines whether to urgently discharge a portion of the feed solution in the second (4#) esterification evaporator to a spent acid regeneration (SAR) unit to prevent further polymerization with the feed solution in the final (5#) esterification evaporator, which could cause viscosity, coking, and blockage of pipes and equipment. However, accurate manual judgment is difficult and requires a high level of professional expertise. In actual processes, coking of the feed solution in the 5# esterification evaporator still frequently occurs, leading to production stoppages. Therefore, there is a need to provide an online viscosity measurement and control method for preventing feed solution coking in the MMA esterification process that can address the existing problem of inaccurate manual judgment of the feed solution viscosity in the 4# esterification evaporator. Summary of the Invention

[0006] The object of the present invention is to provide an online viscosity measurement and control method for preventing coking of the feed liquid in the MMA esterification process, which can solve the problem of inaccurate manual judgment of the viscosity of the feed liquid in the 4# esterification evaporator in the prior art.

[0007] The present invention is achieved in that:

[0008] An online viscosity measurement and control method for preventing coking of feed liquid in an MMA esterification process comprises the following steps:

[0009] Step 1: Install polymerization inhibitor pipelines on the esterification reaction kettle, 1# esterification evaporation kettle, 2# esterification evaporation kettle, 3# esterification evaporation kettle, 4# esterification evaporation kettle and 5# esterification evaporation kettle;

[0010] Step 2: Install a remote control on / off valve on each polymerization inhibitor pipeline;

[0011] Step 3: Periodically spray the polymerization inhibitor into the esterification reaction kettle, 1# esterification evaporation kettle, 2# esterification evaporation kettle, 3# esterification evaporation kettle, 4# esterification evaporation kettle and 5# esterification evaporation kettle at intervals T through the remote control switch valve through the polymerization inhibitor pipeline;

[0012] Step 4: Install an online viscometer in the 4# esterification evaporator, and install an emergency discharge valve on the connecting pipeline between the 4# esterification evaporator and the waste acid regeneration treatment device. The online viscometer is electrically connected to the emergency discharge valve and the remote control switch valve KSV on the inhibitor pipeline corresponding to the 4# esterification evaporator;

[0013] Step 5: The viscosity of the liquid in the 4# esterification evaporator is monitored in real time by an online viscometer, and the viscosity of the liquid in the 4# esterification evaporator is controlled within a normal range by starting the remote control switch valve or emergency discharge valve corresponding to the 4# esterification evaporator.

[0014] The interval time T is 10 minutes.

[0015] In the step 5, when the viscosity of the liquid in the 4# esterification evaporator is within the range of 0 to 1 cP, the MMA esterification process proceeds normally;

[0016] When the viscosity of the liquid in the 4# esterification evaporator is within the range of 1 to 10 cP, the online viscometer opens the remote control switch valve on the polymerization inhibitor pipeline corresponding to the 4# esterification evaporator, sprays the polymerization inhibitor into the 4# esterification evaporator, and forcibly reduces the viscosity of the liquid in the 4# esterification evaporator until the viscosity of the liquid reaches the normal value, and then closes the remote control switch valve;

[0017] When the viscosity of the liquid in the 4# esterification evaporator exceeds 10 cP, the online viscometer closes the remote control switch valve corresponding to the 4# esterification evaporator, and the online viscometer opens the emergency discharge valve to discharge the liquid in the 4# esterification evaporator into the waste acid regeneration treatment device through the emergency discharge valve through the pipeline.

[0018] If the online viscometer opens the remote control switch valve corresponding to the 4# esterification evaporator, the remote control switch valve is in the closed state, that is, one of the other five remote control switch valves is in the open state, then the remote control switch valve corresponding to the 4# esterification evaporator is opened and the polymerization inhibitor is sprayed into the 4# esterification evaporator, while the other five remote control switch valves continue to periodically spray the polymerization inhibitor according to the interval T; if the remote control switch valve is in the open state, the remote control switch valve is kept open, and the other five remote control switch valves continue to periodically spray the polymerization inhibitor according to the interval T.

[0019] The flow rate of the liquid discharged through the emergency discharge valve is much greater than the flow rate of the liquid overflowing from the 3# esterification evaporator into the 4# esterification evaporator, thereby emptying the liquid in the 4# esterification evaporator.

[0020] During the process of discharging the liquid in the 4# esterification evaporator, the five remote control switch valves except the remote control switch valve corresponding to the 4# esterification evaporator still perform periodic injection of the polymerization inhibitor according to the interval T.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. Since an online viscometer is provided in the 4# esterification evaporator, the viscosity of the feed liquid in the 4# esterification evaporator can be monitored in real time. The viscosity of the feed liquid in the 4# esterification evaporator can be adjusted by spraying a polymerization inhibitor or discharging the feed liquid, thereby preventing the viscous feed liquid from overflowing into the 5# esterification evaporator, causing polymerization and coking, or even production stoppage, thereby ensuring the normal production operation of the MMA esterification process.

[0023] 2. Since the present invention is provided with an inhibitor switch and an emergency discharge valve controlled by an online viscometer, the viscosity of the feed liquid in the entire process flow can be effectively controlled by spraying the inhibitor into each reactor. At the same time, when the online viscometer detects that the viscosity of the feed liquid in the 4# esterification evaporator exceeds 1 cP, the inhibitor switch can be activated to spray the inhibitor into the 4# esterification evaporator to forcibly reduce the viscosity of the feed liquid. When the online viscometer detects that the viscosity of the feed liquid in the 4# esterification evaporator exceeds 10 cP, the emergency discharge valve is activated to discharge part of the feed liquid to the waste acid regeneration treatment device, effectively avoiding the risk of polymerization and coking due to excessive viscosity of the feed liquid in the 4# esterification evaporator. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a process flow chart of an online viscosity measurement and control method for preventing coking of feed liquid in the MMA esterification process.

[0025] In the figure, 1 esterification reactor, 2 crude MMA deacidification tower, 3 esterification reactor transfer pump, 4 1# esterification evaporator, 5 1# esterification evaporator transfer pump, 6 2# esterification evaporator, 7 3# esterification evaporator, 8 4# esterification evaporator, 9 online viscometer, 10 emergency discharge valve, 11 5# esterification evaporator, 12 waste acid regeneration treatment device. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] Please see the attached Figure 1An online viscosity measurement and control method for preventing coking of a feed solution in an MMA esterification process is disclosed. The online viscosity measurement and control method is applied to the MMA esterification process. The equipment in the MMA esterification process mainly includes an esterification reactor 1, a crude MMA deacidification tower 2, an esterification reactor transfer pump 3, a first esterification evaporator 4, a first esterification evaporator transfer pump 5, a second esterification evaporator 6, a third esterification evaporator 7, a fourth esterification evaporator 8, a fifth esterification evaporator 11, and a spent acid regeneration (SAR) treatment device 12. The existing process flow of the MMA esterification process is as follows: MAAS from the amidation process and water and methanol from various processes enter the esterification reactor 1 for reaction. The product after the reaction in the esterification reactor 1 passes through the crude MMA deacidification tower 2, and is condensed from the top of the tower to obtain a crude MMA product, which is then sent to a refining process for purification. Part of the material in the esterification reactor 1 is pumped by the esterification reactor delivery pump 3 into the 1# esterification evaporation kettle 4 for reaction, and then delivered to the 2# esterification evaporation kettle 6 by the 1# esterification evaporation kettle delivery pump 5 for reaction. The material in the 2# esterification evaporation kettle 6 overflows into the 3# esterification evaporation kettle 7, the 4# esterification evaporation kettle 8 and the 5# esterification evaporation kettle 11 in sequence, and finally the waste acid regeneration treatment device 12 in the 5# esterification evaporation kettle 11. The unreacted materials and MMA vapor in the 2# esterification evaporation kettle 6, the 3# esterification evaporation kettle 7, the 4# esterification evaporation kettle 8 and the 5# esterification evaporation kettle 11 are all collected into the 1# esterification evaporation kettle 4, and the steam generated in the 1# esterification evaporation kettle 4 is then sent to the esterification reactor 1 for reaction and recovery.

[0028] The online viscosity measurement and control method comprises the following steps:

[0029] Step 1: Inhibitor pipelines are arranged on the esterification reaction kettle 1, the 1# esterification evaporator 4, the 2# esterification evaporator 6, the 3# esterification evaporator 7, the 4# esterification evaporator 8 and the 5# esterification evaporator 11, so that the polymerization inhibitor is sprayed into the esterification reaction kettle 1, the 1# esterification evaporator 4, the 2# esterification evaporator 6, the 3# esterification evaporator 7, the 4# esterification evaporator 8 and the 5# esterification evaporator 11 respectively through the polymerization inhibitor pipeline.

[0030] Step 2: A remote control switch valve KSV is installed on each inhibitor pipeline. The remote control switch valves KSV on the esterification reactor 1, 1# esterification evaporator 4, 2# esterification evaporator 6, 3# esterification evaporator 7, 4# esterification evaporator 8 and 5# esterification evaporator 11 are respectively recorded as KSV1 to KSV6.

[0031] Each polymerization inhibitor pipeline is externally connected to a polymerization inhibitor pumping mechanism. By opening and closing the remote control switch valve KSV, the polymerization inhibitor is sprayed into the esterification reactor 1, 1# esterification evaporator 4, 2# esterification evaporator 6, 3# esterification evaporator 7, 4# esterification evaporator 8 and 5# esterification evaporator 11 through the polymerization inhibitor pipeline via the remote control switch valve. The opening and closing and the opening degree of each remote control switch valve KSV can be controlled independently or in a linked manner, thereby ensuring that the viscosity of the material liquid in each reactor in the process flow meets the process requirements.

[0032] Step 3: Periodically spray the polymerization inhibitor into the esterification reactor 1, 1# esterification evaporator 4, 2# esterification evaporator 6, 3# esterification evaporator 7, 4# esterification evaporator 8 and 5# esterification evaporator 11 through the remote control switch valve KSV through the polymerization inhibitor pipeline at intervals T.

[0033] The main components of the polymerization inhibitor are a mixed solution made of hydroquinone, phenothiazine (diphenylamine sulfide), 2,4-dimethyl-6-tert-butylphenol, N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine, methanol, etc. It is often used in the MMA esterification process to reduce the viscosity of the feed liquid and prevent the feed liquid from coking. The injection amount of the polymerization inhibitor can be adjusted according to actual production needs.

[0034] Preferably, the interval time T is 10 minutes, that is, 10 minutes after the polymerization inhibitor is sprayed into the esterification reactor 1 through the remote control switch valve KSV through the polymerization inhibitor pipeline, the polymerization inhibitor is sprayed into the 1# esterification evaporator 4 through the remote control switch valve KSV through the polymerization inhibitor pipeline. After another 10 minutes, the polymerization inhibitor is sprayed into the 2# esterification evaporator 6 through the remote control switch valve KSV through the polymerization inhibitor pipeline, and so on, until the polymerization inhibitor is sprayed into the 5# esterification evaporator 11, completing one cycle, and then the next cycle is carried out. The polymerization inhibitor is sprayed into each reactor in turn, which can effectively prevent the polymerization of the liquid feed.

[0035] Step 4: An online viscometer 9 is installed in the 4# esterification evaporator 8, and an emergency discharge valve 10 is installed on the connecting pipeline between the 4# esterification evaporator 8 and the waste acid regeneration treatment device 12. The online viscometer 9 is electrically connected to the emergency discharge valve 10 and the remote control switch valve KSV on the inhibitor pipeline corresponding to the 4# esterification evaporator 8.

[0036] Preferably, the remote control switch valve KSV and the emergency discharge valve 10 can both adopt vacuum pressure switches of the prior art, and the online viscometer 9 can adopt the HYJY-NDJ viscometer of the prior art.

[0037] Step 5: The online viscometer 9 monitors the viscosity of the liquid in the 4# esterification evaporation kettle 8 in real time, and controls the viscosity of the liquid in the 4# esterification evaporation kettle 8 within a normal range by starting the remote control switch valve KSV or the emergency discharge valve 10.

[0038] When the viscosity of the liquid in the 4# esterification evaporator 8 is within the range of 0 to 1 cP (including 1 cP), the MMA esterification process proceeds normally.

[0039] When the viscosity of the liquid in the 4# esterification evaporator 8 is within the range of 1 to 10 cP (1 cP excluded and 10 cP included), the online viscometer 9 sends a VISA signal to the remote control switch valve KSV on the inhibitor pipeline corresponding to the 4# esterification evaporator 8, causing the remote control switch valve KSV to open and spray the inhibitor into the 4# esterification evaporator 8, forcibly reducing the viscosity of the liquid in the 4# esterification evaporator 8 until the viscosity reaches a normal value, i.e., 0 to 1 cP.

[0040] Preferably, the online viscometer 9 uses two independent control circuits for the on-off control of the remote control valve KSV on the inhibitor pipeline corresponding to the 4# esterification evaporator 8 and the periodic on-off control of the six remote control valves KSV, so that the forced injection of the inhibitor into the 4# esterification evaporator 8 does not affect the periodic injection of the inhibitor into other reactors, thereby ensuring the normal production of the MMA esterification process.

[0041] If the online viscometer 9 sends a VISA signal to the remote control switch valve KSV on the polymerization inhibitor pipeline corresponding to the 4# esterification evaporator 8 and opens the remote control switch valve KSV, the remote control switch valve KSV is in the closed state, that is, one of the other five remote control switch valves KSV is in the open state, then the remote control switch valve KSV corresponding to the 4# esterification evaporator 8 is opened and the polymerization inhibitor is sprayed into the 4# esterification evaporator 8, while the other five remote control switch valves KSV continue to periodically spray the polymerization inhibitor according to the interval T, that is, every 10 minutes, the polymerization inhibitor is periodically sprayed into the esterification reactor 1, the 1# esterification evaporator 4, the 2# esterification evaporator 6, the 3# esterification evaporator 7 and the 5# esterification evaporator 11, completing one cycle and then proceeding to the next cycle; if the remote control switch valve KSV is in the open state, the remote control switch valve KSV remains open, and the other five remote control switch valves KSV continue to periodically spray the polymerization inhibitor according to the interval T.

[0042] When the viscosity of the liquid in the 4# esterification evaporator 8 exceeds 10 cP, the viscosity of the liquid in the 4# esterification evaporator 8 has reached an asphalt-like viscous liquid. If the liquid overflows into the 5# esterification evaporator 11, there is a risk of coking. The online viscometer 9 sends a VISA signal to the remote control switch valve KSV on the inhibitor pipeline corresponding to the 4# esterification evaporator 8 to close the remote control switch valve KSV. The online viscometer 9 sends a VISA signal to the emergency discharge valve 10 to open the emergency discharge valve 10, and the liquid in the 4# esterification evaporator 8 is discharged into the waste acid regeneration treatment device 12 through the emergency discharge valve 10 via the pipeline. This prevents the polymerized high-viscosity liquid from overflowing into the 5# esterification evaporator 11, which may cause polymerization coking or even a production stoppage accident.

[0043] The flow rate of the liquid discharged through the emergency discharge valve 10 is much greater than the flow rate of the liquid overflowing from the 3# esterification evaporator 7 into the 4# esterification evaporator 8, thereby quickly emptying the liquid in the 4# esterification evaporator 8 and preventing the high-viscosity liquid from overflowing into the 5# esterification evaporator 11.

[0044] During the discharge process of the liquid in the 4# esterification evaporator 8, the five remote control switch valves KSV other than the remote control switch valve KSV corresponding to the 4# esterification evaporator 8 continue to periodically spray the polymerization inhibitor according to the interval T, that is, every 10 minutes, the polymerization inhibitor is periodically sprayed into the esterification reaction kettle 1, the 1# esterification evaporator 4, the 2# esterification evaporator 6, the 3# esterification evaporator 7 and the 5# esterification evaporator 11 in sequence to complete one cycle, and then the next cycle is carried out.

[0045] Example 1:

[0046] In the MMA esterification process of a certain production plant, polymerization inhibitor pipelines are arranged on the esterification reactor 1, 1# esterification evaporator 4, 2# esterification evaporator 6, 3# esterification evaporator 7, 4# esterification evaporator 8 and 5# esterification evaporator 11, so that the polymerization inhibitor is sprayed into the esterification reactor 1, 1# esterification evaporator 4, 2# esterification evaporator 6, 3# esterification evaporator 7, 4# esterification evaporator 8 and 5# esterification evaporator 11 respectively through the polymerization inhibitor pipelines.

[0047] A remote control switch valve KSV is installed on each polymerization inhibitor pipeline, and the polymerization inhibitor is sprayed into the esterification reactor 1, 1# esterification evaporator 4, 2# esterification evaporator 6, 3# esterification evaporator 7, 4# esterification evaporator 8 and 5# esterification evaporator 11 in sequence through the remote control switch valve KSV through the polymerization inhibitor pipeline at an interval of 10 minutes.

[0048] An online viscometer 9 is provided in the 4# esterification evaporation kettle 8, and an emergency discharge valve 10 is provided on the connecting pipeline between the 4# esterification evaporation kettle 8 and the waste acid regeneration treatment device 12. The online viscometer 9 is electrically connected to the emergency discharge valve 10 and the remote control switch valve KSV on the inhibitor pipeline corresponding to the 4# esterification evaporation kettle 8.

[0049] Online viscometer 9 monitors the viscosity of the liquid in esterification evaporator 4# in real time. During the MMA esterification production process, online viscometer 9 detects that the viscosity of the liquid in esterification evaporator 4# reaches 3 cP. Online viscometer 9 sends a VISA signal to the remote control valve KSV on the inhibitor line corresponding to esterification evaporator 4#, causing it to open and continuously inject inhibitor into esterification evaporator 4#, forcibly reducing the viscosity of the liquid in esterification evaporator 4# until the viscosity drops to 0.8 cP. Online viscometer 9 then sends a VISA signal to the remote control valve KSV on the inhibitor line corresponding to esterification evaporator 4#, causing it to close. During this process, the other five remote control valves KSV continue to periodically inject inhibitor into esterification reactor 1, esterification evaporator 1# 4, esterification evaporator 2# 6, esterification evaporator 3# 7, and esterification evaporator 5# 11 at 10-minute intervals.

[0050] After the viscosity of the liquid in the 4# esterification evaporator 8 reaches the normal value, the MMA esterification process resumes normal production, and the polymerization inhibitor is periodically sprayed into the esterification reactor 1, 1# esterification evaporator 4, 2# esterification evaporator 6, 3# esterification evaporator 7, 4# esterification evaporator 8 and 5# esterification evaporator 11 through six remote control switch valves KSV at time intervals of 10 minutes.

[0051] Example 2:

[0052] In the MMA esterification process of a certain production plant, polymerization inhibitor pipelines are arranged on the esterification reactor 1, 1# esterification evaporator 4, 2# esterification evaporator 6, 3# esterification evaporator 7, 4# esterification evaporator 8 and 5# esterification evaporator 11, so that the polymerization inhibitor is sprayed into the esterification reactor 1, 1# esterification evaporator 4, 2# esterification evaporator 6, 3# esterification evaporator 7, 4# esterification evaporator 8 and 5# esterification evaporator 11 respectively through the polymerization inhibitor pipelines.

[0053] A remote control switch valve KSV is installed on each polymerization inhibitor pipeline, and the polymerization inhibitor is sprayed into the esterification reactor 1, 1# esterification evaporator 4, 2# esterification evaporator 6, 3# esterification evaporator 7, 4# esterification evaporator 8 and 5# esterification evaporator 11 in sequence through the remote control switch valve KSV through the polymerization inhibitor pipeline at an interval of 10 minutes.

[0054] An online viscometer 9 is provided in the 4# esterification evaporation kettle 8, and an emergency discharge valve 10 is provided on the connecting pipeline between the 4# esterification evaporation kettle 8 and the waste acid regeneration treatment device 12. The online viscometer 9 is electrically connected to the emergency discharge valve 10 and the remote control switch valve KSV on the inhibitor pipeline corresponding to the 4# esterification evaporation kettle 8.

[0055] The online viscometer 9 monitors the viscosity of the liquid in the 4# esterification evaporator 8 in real time. During the MMA esterification production process, the online viscometer 9 detects that the viscosity of the liquid in the 4# esterification evaporator 8 reaches 5 cP. The online viscometer 9 then sends a VISA signal to the remote control valve KSV on the inhibitor line corresponding to the 4# esterification evaporator 8, causing it to open and continue spraying the inhibitor into the 4# esterification evaporator 8. During the inhibitor injection process, the online viscometer 9 detects that the viscosity of the liquid in the 4# esterification evaporator 8 continues to rise and reaches 20 cP. The online viscometer 9 then sends a VISA signal to the emergency discharge valve 10, causing it to open. The online viscometer 9 then sends a VISA signal to the remote control valve KSV on the inhibitor line corresponding to the 4# esterification evaporator 8, causing it to close and discharge the liquid in the 4# esterification evaporator 8 through the emergency discharge valve 10 and the pipeline into the spent acid regeneration treatment device 12.

[0056] During the process of discharging the feed liquid from the 4# esterification evaporator 8, the other five remote control switch valves KSV continue to periodically spray the polymerization inhibitor into the esterification reactor 1, the 1# esterification evaporator 4, the 2# esterification evaporator 6, the 3# esterification evaporator 7 and the 5# esterification evaporator 11 at time intervals of 10 minutes.

[0057] After the discharge of the liquid in the 4# esterification evaporator 8 is completed, the MMA esterification process resumes normal production, and the polymerization inhibitor is periodically sprayed into the esterification reactor 1, 1# esterification evaporator 4, 2# esterification evaporator 6, 3# esterification evaporator 7, 4# esterification evaporator 8 and 5# esterification evaporator 11 through six remote control switch valves KSV at time intervals of 10 minutes.

[0058] The above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An online viscosity measurement and control method for preventing coking of feed liquid in an MMA esterification process, characterized by: The following steps are involved: Step 1: Installing polymerization inhibitor pipelines on the esterification reaction kettle (1), the 1# esterification evaporation kettle (4), the 2# esterification evaporation kettle (6), the 3# esterification evaporation kettle (7), the 4# esterification evaporation kettle (8) and the 5# esterification evaporation kettle (11); Step 2: Install a remote control on / off valve on each polymerization inhibitor pipeline; Step 3: Periodically spraying the polymerization inhibitor into the esterification reaction kettle (1), the 1# esterification evaporation kettle (4), the 2# esterification evaporation kettle (6), the 3# esterification evaporation kettle (7), the 4# esterification evaporation kettle (8) and the 5# esterification evaporation kettle (11) at intervals T through the remote control switch valve through the polymerization inhibitor pipeline; Step 4: An online viscometer (9) is installed in the 4# esterification evaporation kettle (8), and an emergency discharge valve (10) is installed on the connecting pipeline between the 4# esterification evaporation kettle (8) and the waste acid regeneration treatment device (12). The online viscometer (9) is electrically connected to the emergency discharge valve (10) and the remote control switch valve on the inhibitor pipeline corresponding to the 4# esterification evaporation kettle (8); Step 5: The viscosity of the liquid in the 4# esterification evaporation kettle (8) is monitored in real time by an online viscometer (9), and the viscosity of the liquid in the 4# esterification evaporation kettle (8) is controlled within a normal range by activating the remote control switch valve or the emergency discharge valve (10) corresponding to the 4# esterification evaporation kettle (8); In the step 5, when the viscosity of the liquid in the 4# esterification evaporator (8) is within the range of 0 to 1 cP, the MMA esterification process proceeds normally; When the viscosity of the liquid in the 4# esterification evaporator (8) is within the range of 1 to 10 cP, the online viscometer (9) opens the remote control switch valve on the polymerization inhibitor pipeline corresponding to the 4# esterification evaporator (8), sprays the polymerization inhibitor into the 4# esterification evaporator (8), and forcibly reduces the viscosity of the liquid in the 4# esterification evaporator (8), and then closes the remote control switch valve after the viscosity of the liquid reaches a normal value; When the viscosity of the liquid in the 4# esterification evaporation kettle (8) exceeds 10 cP, the online viscometer (9) closes the remote control switch valve corresponding to the 4# esterification evaporation kettle (8), and the online viscometer (9) opens the emergency discharge valve (10), and the liquid in the 4# esterification evaporation kettle (8) is discharged into the waste acid regeneration treatment device (12) through the pipeline through the emergency discharge valve (10).

2. The method for measuring and controlling online viscosity of the MMA esterification process to prevent coking of the feed liquid according to claim 1, wherein: The interval time T is 10 minutes.

3. The online viscosity measurement and control method for preventing coking of the feed liquid in the MMA esterification process according to claim 1, characterized in that: If the online viscometer (9) opens the remote control switch valve corresponding to the 4# esterification evaporator (8), the remote control switch valve is in a closed state, that is, one of the other five remote control switch valves is in an open state, then the remote control switch valve corresponding to the 4# esterification evaporator (8) is opened and the polymerization inhibitor is sprayed into the 4# esterification evaporator (8), while the other five remote control switch valves continue to periodically spray the polymerization inhibitor according to the interval time T; if the remote control switch valve is in an open state, the remote control switch valve is kept open, and the other five remote control switch valves continue to periodically spray the polymerization inhibitor according to the interval time T.

4. The online viscosity measurement and control method for preventing coking of the feed liquid in the MMA esterification process according to claim 1, characterized in that: The flow rate of the liquid discharged through the emergency discharge valve (10) is much greater than the flow rate of the liquid overflowing from the 3# esterification evaporator (7) into the 4# esterification evaporator (8), thereby emptying the liquid in the 4# esterification evaporator (8).

5. The online viscosity measurement and control method for preventing coking of liquid feed in the MMA esterification process according to claim 1 or 4, characterized in that: During the discharge of the liquid in the 4# esterification evaporator (8), the five remote control switch valves other than the remote control switch valve corresponding to the 4# esterification evaporator (8) still perform periodic injection of the polymerization inhibitor according to the interval time T.

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