Preparation system and preparation method of pentaerythritol ester

Abstract

The invention relates to the field of fine chemical engineering, in particular to a pentaerythritol ester preparation system and a preparation method thereof.The pentaerythritol ester preparation system comprises an esterification reaction kettle, a temporary storage tank, a preheater, an esterification reaction tower, a heat exchanger, a molecular distiller and a post-treatment kettle; a downcomer communicated with the uppermost layer of catalytic reaction unit is arranged above the uppermost layer of catalytic reaction unit, every two adjacent layers of catalytic reaction units are communicated through the downcomer, a flash tank is arranged below the bottommost layer of catalytic reaction unit, and the gas outlet end of the flash tank is communicated with the multiple layers of catalytic reaction units through a gas rising pipe; a feed port II communicated with the fatty acid feed end is formed in one side of the bottom of the esterification reaction tower. A two-step esterification method is adopted, fatty acid entering from the bottom is changed into fatty acid steam through the flash tank, the fatty acid steam is in countercurrent contact with liquid in the downcomer in the multiple layers of catalytic reaction units and fully reacts, and pentaerythritol ester which is completely esterified and has a low acid value and a low hydroxyl value is obtained.

Description

Technical Field

[0001] The invention relates to the field of fine chemicals, in particular to a preparation system and a preparation method of pentaerythritol ester. Background Art

[0002] Pentaerythritol ester, a neopentyl polyol ester, has different applications based on different fatty acids. It is mainly used in aviation engine oil, lubricating oil, air compressor oil, and refrigeration oil base oil. In addition, due to its special molecular structure and the absence of hydrogen atoms on the β-carbon atom, pentaerythritol ester has excellent high and low temperature performance, viscosity-temperature performance, thermal oxidation stability, good lubrication performance and a high viscosity index. It is also self-biodegradable and non-biotoxic. It is a green lubricant and is widely used as a base oil in synthetic ester-type flame-resistant hydraulic oils. Its market share in the lubricant market is gradually increasing.

[0003] The direct esterification reaction of pentaerythritol ester is the most studied production process at present, but pentaerythritol is a multi-hindered structure with a high degree of branching, which makes it have a serious steric hindrance effect with fatty acids during the esterification process, and the esterification reaction is a reversible reaction, which makes it difficult to react completely to obtain esters with high acid value and high hydroxyl value. If pentaerythritol ester is not completely esterified, the residual fatty acids make the product easy to corrode and oxidize, and the residual hydroxyl groups will increase the emulsification properties of the lubricant. Therefore, complete esterification is a key point to ensure the purity of the base oil and the quality of the oil.

[0004] Among the technologies that have been disclosed so far, most of them are to put alcohol, fatty acid and catalyst into a reactor at one time, and obtain the product through high-temperature reflux reaction. The high reaction temperature and long reaction time cause the product to have dark color and poor thermal stability, and the hydroxyl value and acid value are both large, which seriously affects the performance and service life of the oil product and may also cause corrosion of metal parts.

[0005] Therefore, the present invention provides a novel preparation system and method of pentaerythritol ester. Summary of the invention

[0006] The invention aims to provide a preparation system and a preparation method of pentaerythritol ester. Through the design of an esterification reaction kettle, a temporary storage tank, a preheater, an esterification reaction tower, a heat exchanger, a molecular distiller, a post-treatment kettle and a flash tank, continuous production of materials can be achieved. Through the structure of several layers of catalytic reaction units in the esterification reaction tower, fatty acids entering from a fatty acid feeding end are used for raw material supplementation, which are converted into fatty acid vapor through a flash tank and countercurrently contacted and fully reacted with liquid in a downcomer in several layers of catalytic reaction units, so that pentaerythritol can be completely esterified, thereby obtaining pentaerythritol ester with low acid value and low hydroxyl value.

[0007] In order to solve the above technical problems, the present invention provides a preparation system of pentaerythritol ester, comprising an esterification reaction kettle, a temporary storage tank, a preheater, an esterification reaction tower, a heat exchanger, a molecular distiller and a post-treatment kettle, wherein the bottom outlet of the esterification reaction kettle is connected to the top inlet of the temporary storage tank through a pipeline 1, the bottom outlet of the temporary storage tank is connected to the upper feed inlet 1 of the esterification reaction tower through a pipeline 2, the preheater is installed on the pipeline 2, and the esterification reaction tower is provided with a plurality of layers of catalytic reaction units, and the upper part of the catalytic reaction unit on the uppermost layer is provided with a A downcomer, and the catalytic reaction units of two adjacent layers are connected through the downcomer, a flash tank is provided below the catalytic reaction unit of the bottom layer, and the gas outlet end of the flash tank is connected with the catalytic reaction units of several layers through a riser, the flash tank is arranged at the bottom of the esterification reaction tower, a discharge port is provided at the lower side of the esterification reaction tower, and the discharge port is located on the upper side of the flash tank, a feed port 2 connected with the liquid inlet end of the flash tank is provided on the bottom side of the esterification reaction tower, and the heat exchanger is arranged on one side of the esterification reaction tower;

[0008] One side of the heat exchanger is respectively provided with an inlet 1 and an outlet 2, and the other side is respectively provided with an outlet 1, an inlet 2 and an inlet 3, the inlet 1 is connected with the discharge port through a pipeline 3, the outlet 1 is communicated with the inlet 1 and is connected with the inlet of the molecular distiller through a pipeline 4, the inlet 2 is connected with the bottom outlet 1 of the molecular distiller through a pipeline 5, the inlet 3 is connected with the fatty acid feed end through a pipeline 6, the outlet 2 is communicated with the inlet 2 and the inlet 3 and is connected with the feed port 2 through a pipeline 7, a bottom outlet 2 is provided on the upper side of the bottom outlet 1, the bottom outlet 2 is connected with the feed port of the post-treatment kettle through a pipeline 8, and the outlet pipeline 9 of the post-treatment kettle is connected with a pentaerythritol ester storage tank.

[0009] Preferably, an air outlet is provided at the top of the esterification reaction tower, and the air outlet is connected to a primary condenser and a secondary condenser in sequence through pipeline ten, a pipeline eleven is connected in parallel to the pipeline between the primary condenser and the secondary condenser, and the other end of the pipeline eleven is arranged in parallel on the pipeline five.

[0010] Preferably, several layers of the catalytic reaction units are arranged on the inner side of the riser, the outer wall of the riser is fixed to the inner wall of the esterification reaction tower, the catalytic reaction units of each layer include a bottom plate and a catalytic frame and a packing frame arranged on the bottom plate from the outside to the inside, the downcomer of the top layer is installed in the esterification reaction tower through a tower tray and is located above the bottom plate of the layer, and the lower end of the downcomer of each layer is located on the outer side of the catalytic frame of the layer and is fixed to the bottom plate;

[0011] A gas path 1 is provided between the lower outer wall of the downcomer and the riser, a plurality of liquid inlets 1 communicating with the outer wall of the catalytic frame are provided on the lower inner wall of the downcomer, a catalyst is placed in the catalytic frame and two circumferentially arranged gas distribution plates are provided therein, a plurality of gas inlets are provided on the two gas distribution plates, and a gas path 2 is formed between the two gas distribution plates, the gas path 2 is communicated with the gas path 1, a liquid inlet 2 communicating with the stuffing frame is provided on the inner wall of the catalytic frame, a stuffing is placed in the stuffing frame and a liquid outlet is provided at the bottom center of the stuffing frame, and the liquid outlet is communicated with the catalytic reaction unit of the next layer through the downcomer.

[0012] Preferably, the downcomer includes a main pipe, a plurality of transition pipes and branch pipes which are sequentially connected from top to bottom and communicate with each other internally. The transition pipe is located above the filler and the catalyst and has a plurality of air holes on its upper and lower surfaces. The branch pipe is fixed to the outer wall of the filler frame and has a plurality of liquid inlets therebetween.

[0013] Preferably, the filler is a structural filler, which is made of corrugated stainless steel and has a plurality of small holes formed thereon.

[0014] In addition, the present invention also provides a method for preparing pentaerythritol ester, which is prepared by using the above-mentioned pentaerythritol ester preparation system, and the preparation method comprises the following steps:

[0015] S1. Add fatty acid, pentaerythritol and solid catalyst into an esterification reaction kettle, replace with nitrogen three times, control the reaction temperature to 160-220° C., start vacuuming after 1 hour of reaction, and continue the reaction of the reaction system under vacuum reflux for 2-3 hours to obtain the first esterification reaction product, and continuously introduce nitrogen during the reaction;

[0016] S2, after cooling the esterification reaction kettle to 70-120° C., the first esterification reaction product is circulated through a filter press to filter out the solid catalyst, and then transferred to a temporary storage tank through a pipeline 1, the temperature is maintained at 70-120° C., and nitrogen is continuously introduced to achieve nitrogen sealing;

[0017] S3, the material in the temporary storage tank is heated to 180-220° C. through the preheater on the pipeline 2, pumped into the esterification reaction tower, enters the esterification reaction tower from the upper feed port 1 of the esterification reaction tower, enters several layers of catalytic reaction units through the downcomer, and at the same time, the fatty acid is heated to 150-220° C. through the pipeline 5 through the heat exchanger, and enters the flash tank at the bottom of the esterification reaction tower from the feed port 2 through the pipeline 6. After passing through the flash tank, the fatty acid becomes fatty acid vapor and enters several layers of catalytic reaction units upward through the riser, and is mixed with the liquid phase material entering from the feed port 1 for reaction;

[0018] Among them, in the catalytic reaction units of several layers, the fatty acid vapor enters the catalytic reaction unit of each layer through the ascending pipe, and after fully reacting with the descending liquid phase feed in the catalytic reaction unit of the corresponding layer, the unreacted fatty acid vapor enters the catalytic reaction unit of the upper layer through the ascending pipe, and the liquid phase material after the reaction enters the catalytic reaction unit of the next layer through the downcomer of the lower layer, and this is repeated, and the liquid phase material coming out of the catalytic reaction unit of the bottom layer is discharged from the discharge port to obtain a crude pentaerythritol ester product;

[0019] S4, the crude pentaerythritol ester product is sent to the heat exchanger through pipeline 3, and after heat exchange in the heat exchanger, it is sent to the molecular distiller through pipeline 4 to remove fatty acids in the product, and the acid value is controlled to be lower than 0.2 mg KOH / g. After the molecular distillation is completed, it is sent to the post-treatment kettle through pipeline 7 for alkali washing to remove residual fatty acids, and the acid value is controlled to be lower than 0.05 mg KOH / g. After the alkali washing is completed, a decolorizing agent is added for decolorization, and finally it is circulated and filtered through a filter press to remove the decolorizing agent and soap to obtain a pure pentaerythritol ester.

[0020] Preferably, the fatty acid in S1 is one or more of pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, and capric acid, or the fatty acid is one or more of glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid, or the fatty acid is a mixture of a monobasic acid and a dibasic acid.

[0021] Preferably, the solid catalyst in S1 is one or more of stannous oxalate, stannous chloride, stannous oxide, and a solid acid catalyst, or one or more of stannous oxalate, stannous chloride, stannous oxide, and a solid acid catalyst is loaded by an activated carbon support.

[0022] Preferably, the molar ratio of fatty acid to pentaerythritol in S1 is 2-3:1, and the solid catalyst accounts for 0.05-0.2% of the total mass of fatty acid and pentaerythritol, and is put into the esterification reaction kettle together.

[0023] Preferably, the reflux reaction is carried out in S1 under vacuum conditions of -0.08 to -0.095 MPa; the reaction conditions of the esterification reaction tower in S3 are controlled to be 180 to 220°C, the pressure is below 3000 Pa, and the number of catalytic reaction units is set to 5 to 10 layers.

[0024] The beneficial effects of the present invention are:

[0025] 1. The preparation system of pentaerythritol ester of the present invention can realize continuous production of materials through the design of esterification reaction kettle, temporary storage tank, preheater, esterification reaction tower, heat exchanger, molecular distiller, post-treatment kettle and flash tank. And through the structure of several layers of catalytic reaction units in the esterification reaction tower, fatty acid entering from the fatty acid feed end is used for raw material supplement, which is converted into fatty acid vapor through the flash tank and countercurrently contacts and fully reacts with the liquid in the downcomer in several layers of catalytic reaction units, so that pentaerythritol can be completely esterified, thereby obtaining pentaerythritol ester with low acid value and low hydroxyl value.

[0026] 2. The present invention connects a primary condenser and a secondary condenser through the gas outlet of the esterification reaction tower, a pipeline 11 is connected in parallel to the pipeline between the primary condenser and the secondary condenser, and the other end of the pipeline 11 is arranged in parallel on the pipeline 5. Through this design, the fatty acid gas discharged from the top of the esterification reaction tower can be condensed and recovered through the primary condenser, and then heated through the inlet 2 of the heat exchanger and enters the flash tank through the pipeline 7 as a supplement of fatty acids, thereby improving the utilization rate of resources.

[0027] 3. The present invention adopts the design of several layers of catalytic reaction units and downcomers, so that the liquid in the esterification reaction tower enters the downcomer through the tower plate, enters the catalytic reaction unit of the uppermost layer from the downcomer, and specifically enters the catalyst frame through the first liquid inlet, fully reacts with the gas coming out of the second gas path under the action of the catalyst, and then enters the packing frame through the second liquid inlet, enters the downcomer of the next layer from the liquid outlet after buffer filtration of the packing, and starts a new layer of catalytic reaction, until it comes out from the liquid outlet of the catalytic reaction unit of the lowermost layer, and the completely esterified pentaerythritol ester with low acid value and low hydroxyl value is discharged through the discharge port.

[0028] 4. The downcomer of the present invention includes a main pipe, a plurality of transition pipes and branch pipes which are sequentially connected from top to bottom and internally communicated. The design of the transition pipe can play a buffering role on the descending liquid. In combination with the design that a plurality of air holes are opened on the upper and lower surfaces of the transition pipe, not only can the incompletely reacted gas enter the downcomer from the air holes opened on the lower surface to react with the descending liquid, but also can make the incompletely reacted gas escape from the air holes on the upper surface and merge with the gas in the second gas path, and enter the catalytic reaction unit on the upper layer together to participate in the reaction, thereby increasing the number of contacts between the gas and the liquid and improving the reaction efficiency.

[0029] 5. The present invention changes the existing process and adopts a two-step esterification method to prepare pentaerythritol ester. In particular, in the second step esterification reaction, the first esterification reaction product and fatty acid are respectively fed reversely into the esterification reaction tower. Through the structural design of the downcomer, the gas riser and several layers of catalytic reaction units in the esterification reaction tower, the reaction time is effectively shortened while ensuring the complete esterification reaction, avoiding the generation of by-products in the oil product caused by long-term high temperature, so that the pentaerythritol ester has good color and stability. In addition, a solid catalyst with high activity is used in both steps of the reaction process to avoid the introduction of other impurities and ensure the purity of the pentaerythritol ester. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 It is a structural schematic diagram of a preparation system of pentaerythritol ester of the present invention;

[0032] Figure 2 It is a partial structural schematic diagram of a catalytic reaction unit of the preparation system of pentaerythritol ester of the present invention;

[0033] In the figure: 1-esterification reactor, 2-temporary storage tank, 3-preheater, 4-esterification reaction tower, 5-heat exchanger, 6-molecular distiller, 7-post-treatment reactor, 8-pipeline one, 9-pipeline two, 10-catalytic reaction unit, 11-flash tank, 12-pipeline three, 13-pipeline four, 14-pipeline five, 15-pipeline six, 16-pipeline seven, 17-pipeline eight, 18-pipeline nine, 19-pentaerythritol ester storage tank, 20-pipeline ten, 21-primary condenser, 22-secondary condenser, 23-pipeline ten 1, 100-downcomer, 200-ascending pipe, 300-gas circuit one, 400-liquid inlet one, 500-gas circuit two, 600-liquid inlet two, 700-liquid outlet, 101-bottom plate, 102-catalytic frame, 103-filling frame, 104-gas distribution plate, 1001-main pipe, 1002-transition pipe, 1003-branch pipe, 41-feed port one, 42-discharge port, 43-feed port two, 44-gas outlet, 61-upper inlet, 62-bottom outlet one, 63-bottom outlet two. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In a specific embodiment of the present invention, Figure 1-2 As shown, a preparation system of pentaerythritol ester includes an esterification reaction kettle 1, a temporary storage tank 2, a preheater 3, an esterification reaction tower 4, a heat exchanger 5, a molecular distiller 6 and a post-treatment kettle 7. The bottom outlet of the esterification reaction kettle 1 is connected to the top inlet of the temporary storage tank 2 through a pipeline 18, and the bottom outlet of the temporary storage tank 2 is connected to the upper feed port 141 of the esterification reaction tower 4 through a pipeline 29. The preheater 3 is installed on the pipeline 29. A plurality of layers of catalytic reaction units 10 are arranged in the esterification reaction tower 4. A downcomer 100 connected to the upper catalytic reaction unit 10 is arranged above the uppermost layer. The catalytic reaction units 10 of two adjacent layers are connected through a downcomer 100. A flash tank 11 is provided below the catalytic reaction unit 10 of the bottom layer. The gas outlet end of the flash tank 11 is connected with the catalytic reaction units 10 of several layers through a gas riser 200. The flash tank 11 is arranged at the bottom of the esterification reaction tower 4. A discharge port 42 is provided at the lower side of the esterification reaction tower 4. The discharge port is located at the upper side of the flash tank 11. A feed port 2 43 connected with the liquid inlet end of the flash tank 11 is provided at the bottom side of the esterification reaction tower 4. The heat exchanger 5 is arranged at one side of the esterification reaction tower 4.

[0036] One side of the heat exchanger 5 is respectively provided with an inlet 1 and an outlet 2, and the other side is respectively provided with an outlet 1, an inlet 2 and an inlet 3. The inlet 1 is connected to the discharge port 42 through a pipeline 3 12, the outlet 1 is connected to the inlet 1 and is connected to the upper inlet 61 of the molecular distiller 6 through a pipeline 4 13, the inlet 2 is connected to the bottom outlet 1 62 of the molecular distiller 6 through a pipeline 5 14, the inlet 3 is connected to the fatty acid feed end through a pipeline 6 15, the outlet 2 is connected to the inlet 2 and the inlet 3 and is connected to the feed port 2 43 through a pipeline 7 16, a bottom outlet 2 63 is provided on the upper side of the bottom outlet 1 62, the bottom outlet 2 63 is connected to the feed port of the post-processing kettle 7 through a pipeline 8 17, and the discharge port of the post-processing kettle 7 is connected to the pentaerythritol ester storage tank 19 through a pipeline 9 18.

[0037] The pentaerythritol ester preparation system of the present invention can realize continuous production of materials through the design of an esterification reaction kettle, a temporary storage tank, a preheater, an esterification reaction tower, a heat exchanger, a molecular distiller, a post-treatment kettle and a flash tank. The fatty acid entering the fatty acid feeding end is used to supplement the raw material through the structure of the multiple layers of catalytic reaction units in the esterification reaction tower. The fatty acid vapor is converted into fatty acid vapor through the flash tank and fully reacts with the liquid in the downcomer in the multiple layers of catalytic reaction units, so that the pentaerythritol can be completely esterified, thereby obtaining the pentaerythritol ester with low acid value and low hydroxyl value.

[0038] In this embodiment, the volume of the temporary storage tank 2 is larger than that of the esterification reactor 1, which is convenient for continuous production. Specifically, during continuous production, the material is transferred from the esterification reactor 1 to the temporary storage tank 2. At this time, the inside of the esterification reactor 1 is empty, and the next batch of materials can be continuously added to the esterification reactor 1 to continue the reaction. Then, the reacted material is transferred to the temporary storage tank 2. After the capacity in the temporary storage tank 2 meets the requirements, it is transferred from the bottom outlet of the temporary storage tank 2 to the upper feed port 41 of the esterification reaction tower 4 through the pipeline 9. Of course, the catalyst can be filtered out by circulation during the transportation process, and the filtered catalyst can be recovered and reused.

[0039] Specifically, an air outlet 44 is provided at the top of the esterification reaction tower 4, and the air outlet 44 is connected to the primary condenser 21 and the secondary condenser 22 in sequence through the pipeline 10 20. A pipeline 11 23 is connected in parallel to the pipeline between the primary condenser 21 and the secondary condenser 22, and the other end of the pipeline 11 23 is arranged in parallel on the pipeline 5 14. Through this design, the fatty acid gas discharged from the top of the esterification reaction tower 4 can be condensed and recovered through the primary condenser 21, and then heated by the heat exchanger 5 to enter the flash tank 11 as a supplement of fatty acids, thereby improving the utilization rate of resources; and even if there is excess unreacted fatty acid vapor after the esterification is complete, it can be recovered through the primary condenser and the secondary condenser, leaving a batch for use.

[0040] like Figure 2 As shown, several layers of catalytic reaction units 10 are arranged on the inner side of the riser 200, and the outer wall of the riser 200 is fixed to the inner wall of the esterification reaction tower 4. The catalytic reaction units 10 of each layer include a bottom plate 101 and a catalytic frame 102 and a packing frame 103 arranged on the bottom plate 101 from the outside to the inside. The downcomer 100 of the uppermost layer is installed in the esterification reaction tower 4 through a tower tray and is located above the bottom plate 101 of this layer. The lower end of the downcomer 100 of each layer is located on the outer side of the catalytic frame 102 of this layer and is fixed to the bottom plate 101.

[0041] A gas path 300 is provided between the lower end outer wall of the downcomer 100 and the riser 200, a plurality of liquid inlets 400 communicating with the outer wall of the catalyst frame 102 are provided on the lower end inner wall of the downcomer 100, a catalyst is placed in the catalyst frame 102 and two annularly arranged gas distribution plates 104 are provided therein, a plurality of gas inlets are provided on the two gas distribution plates 104, and a gas path 2 500 is formed between the two gas distribution plates 104, the gas path 2 500 is communicated with the gas path 300, a liquid inlet 2 600 communicating with the packing frame 103 is provided on the inner side wall of the catalyst frame 102, a packing is placed in the packing frame 103 and the bottom of the packing frame 103 A liquid outlet 700 is provided in the center, and the liquid outlet 700 is connected to the catalytic reaction unit 10 of the next layer through the downcomer 100; in this embodiment, the lower end of the riser 200 is fixed to the upper end of the flash tank 11 and connected to its gas outlet end, the upper end of the riser 200 is fixed below the tower plate, and a plurality of gas outlet holes are provided on the tower plate. Specifically, the fresh fatty acid entering is converted into fatty acid vapor by the flash tank 11, and enters the riser 200 from the gas outlet end, and then the gas enters the gas path 2 500 upward from the gas path 1 300 of the catalytic reaction unit of each layer, and then comes out from the hole on the gas distribution plate 104 to countercurrently contact and react with the liquid coming down from the downcomer 100;

[0042] The liquid entering the esterification reaction tower 4 enters the downcomer 100 through the tower plate, then enters the catalyst frame 102 through the liquid inlet 1 400, fully reacts with the gas coming out of the gas path 2 500 under the action of the catalyst, and then enters the packing frame 103 through the liquid inlet 2 600, enters the downcomer 100 of the next layer from the liquid outlet 700 after buffer filtration of the packing, and starts a new layer of catalytic reaction until it comes out from the liquid outlet 700 of the catalytic reaction unit at the bottom layer, and is discharged from the esterification reaction tower 4 through the discharge port 42 to obtain a completely esterified pentaerythritol ester with low acid value and low hydroxyl value.

[0043] Specifically, the downcomer 100 in this embodiment includes a main pipe 1001, a plurality of transition pipes 1002 and a branch pipe 1003 which are sequentially connected from top to bottom and communicate with each other internally. The transition pipe 1002 is located above the filler and the catalyst. The upper and lower surfaces of the transition pipe 1002 are provided with a plurality of air holes (not shown in the figure). The branch pipe 1003 is fixed to the outer side wall of the filler frame 102 and a plurality of liquid inlets 400 are provided therebetween. Specifically, the plurality of transition pipes 1002 may be distributed in a ring shape.

[0044] Here, the transition pipe can be arranged obliquely, which can play a buffering role for the descending liquid. In addition, the design here combines the upper and lower surfaces of the transition pipe with a plurality of air holes, which can not only allow the incompletely reacted gas to enter the downcomer from the air holes opened on the lower surface to react with the descending liquid, but also allow the incompletely reacted gas to escape from the air holes on the upper surface and merge with the gas in gas path two, and enter the upper catalytic reaction unit together to participate in the reaction, thereby increasing the number of contacts between the gas and the liquid and improving the reaction efficiency.

[0045] Specifically, the filler is a structural filler, which is made of corrugated stainless steel and has a plurality of small holes thereon, so as to increase the filtering effect.

[0046] In addition, the present invention also provides a method for preparing pentaerythritol ester, which is prepared by using a pentaerythritol ester preparation system, and the preparation method comprises the following steps:

[0047] S1. Add fatty acid, pentaerythritol and solid catalyst into an esterification reaction kettle. Specifically, the molar ratio of fatty acid to pentaerythritol is 2 to 3:1, and the solid catalyst accounts for 0.05 to 0.2% of the total mass of fatty acid and pentaerythritol. Add them together into the esterification reaction kettle. After nitrogen replacement three times, the reaction temperature is controlled to be 160 to 220° C. After reacting for 1 hour, vacuuming is started, and the reaction system is allowed to continue to react for 2 to 3 hours under vacuum reflux. The reflux reaction is carried out under vacuum conditions of -0.08 to -0.095 MPa. After the reflux reaction is completed, the acid value is controlled to be less than 2 mgKOH / g to obtain a first esterification reaction product. Nitrogen is continuously introduced during the reaction. The introduction of nitrogen here can not only completely isolate the material from the air and protect the material from oxidation, but also continuously remove the water produced by the reaction to promote the esterification reaction to proceed in a positive direction.

[0048] Here, the fatty acid is one or more of valeric acid, caproic acid, heptanoic acid, octanoic acid, nonanoic acid, and capric acid, or the fatty acid is one or more of glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid, or the fatty acid is a mixture of a monobasic acid and a dibasic acid;

[0049] The solid catalyst is one or more of stannous oxalate, stannous chloride, stannous oxide, and a solid acid catalyst, or one or more of stannous oxalate, stannous chloride, stannous oxide, and a solid acid catalyst is loaded by an activated carbon support agent;

[0050] S2. After cooling the esterification reaction kettle to 70-120° C., the first esterification reaction product is filtered out of the solid catalyst through a filter press, and then transferred to a temporary storage tank through a pipeline 1, the temperature is maintained at 70-120° C., and nitrogen is continuously introduced to achieve nitrogen sealing to prevent the material from being oxidized and discolored by air;

[0051] S3, the material in the temporary storage tank is heated to 180-220° C. through the preheater on the pipeline 2, pumped into the esterification reaction tower, enters the esterification reaction tower from the upper feed port 1 of the esterification reaction tower, enters several layers of catalytic reaction units through the downcomer, and at the same time, the fatty acid is heated to 150-220° C. through the pipeline 5 through the heat exchanger, and enters the flash tank at the bottom of the esterification reaction tower from the feed port 2 through the pipeline 6. After passing through the flash tank, the fatty acid becomes fatty acid vapor and enters several layers of catalytic reaction units upward through the riser, and is mixed with the liquid phase material entering from the feed port 1 for reaction;

[0052] Among them, in several layers of catalytic reaction units, fatty acid vapor enters the catalytic reaction units of each layer through the riser upward, and after fully reacting with the descending liquid phase feed in the catalytic reaction units of the corresponding layer, the unreacted fatty acid vapor enters the catalytic reaction units of the upper layer through the riser, and the liquid phase material after the reaction enters the catalytic reaction units of the next layer through the downcomer of the lower layer, and this is repeated. The liquid phase material coming out of the catalytic reaction unit of the bottom layer is discharged from the discharge port to obtain a crude ester product of pentaerythritol ester with low acid value and low hydroxyl value that is completely esterified; in this embodiment, the reaction conditions of the esterification reaction tower are controlled to be 180-220°C, the pressure is below 3000Pa, and the number of catalytic reaction units is set to 5-10 layers.

[0053] S4, sending the crude pentaerythritol ester product to the heat exchanger through pipeline 3, and after heat exchange in the heat exchanger, sending it to the molecular distiller through pipeline 4 to remove fatty acids in the product, and controlling the acid value to be lower than 0.2 mg KOH / g, and after the molecular distillation, sending it to the post-treatment kettle through pipeline 7 for alkali washing to remove residual fatty acids, and controlling the acid value to be lower than 0.05 mg KOH / g, and adding a decolorizing agent for decolorization after the alkali washing, and finally filtering through a filter press to remove the decolorizing agent and soap to obtain a pure pentaerythritol ester; the decolorizing agent here can be activated clay, activated carbon, etc.

[0054] In the present invention, there is no special restriction on the refining process of pentaerythritol ester, and the pentaerythritol ester can be purified by refining using the oil refining technology well known to those skilled in the art.

[0055] The present invention divides the esterification synthesis process into two steps. In the first step, fatty acid, pentaerythritol and catalyst are added into an esterification reaction kettle at a suitable ratio (the molar ratio of fatty acid to pentaerythritol is 2-3:1, and the solid catalyst accounts for 0.05-0.2% of the total mass of fatty acid and pentaerythritol), and the reaction temperature is controlled at 160-220° C. to carry out a preliminary reaction for 1 hour, and then vacuuming is started, and a reflux reaction is carried out for 2-3 hours under a vacuum condition of -0.08--0.095 MPa to obtain a first esterification reaction product;

[0056] In the second step, the first esterification reaction product and the fatty acid are respectively fed in reverse into the esterification reaction tower, and react layer by layer in the esterification reaction tower until the reaction at the bottom layer is complete, and the second reaction product, i.e., crude pentaerythritol ester, is obtained by discharging the product from the liquid outlet of the bottom layer through the discharge port. In the second step, the design of the downcomer, the riser and several layers of catalytic reaction units in the esterification reaction tower can promote the complete esterification of pentaerythritol, thereby obtaining pentaerythritol ester with low acid value and low hydroxyl value.

[0057] The present invention changes the existing process and adopts a two-step esterification method to prepare pentaerythritol ester. In particular, in the second step esterification reaction, the first esterification reaction product and the fatty acid are respectively fed into the esterification reaction tower in reverse. Through the structural design of the downcomer, the gas riser and the several layers of catalytic reaction units in the esterification reaction tower, the reaction time is efficiently shortened while ensuring the complete esterification reaction, avoiding the generation of byproducts in the oil product caused by long-term high temperature, so that the pentaerythritol ester has good color and stability, and a solid catalyst with high activity is used in both steps of the reaction process to avoid the introduction of other impurities and ensure the purity of the pentaerythritol ester. In order to further understand the present invention, the present invention is described in detail below in conjunction with specific embodiments.

[0058] Example 1

[0059] First, isooctanoic acid and isononanoic acid in a mass ratio of 3:1 are mixed, and then put into an esterification reaction kettle with pentaerythritol in a molar ratio of 2.5:1, and a solid catalyst stannous oxalate with a mass fraction of 0.1% is added. After nitrogen replacement three times, the temperature is raised to control the reaction temperature to 160°C, and nitrogen protection is always introduced during the reaction. After reacting for 1 hour, vacuum is started and the temperature is raised to 200°C, and the vacuum is maintained at -0.08 to -0.095MPa. The reaction system is allowed to continue to react under vacuum reflux for 2.5 hours to obtain the first esterification reaction product, and the acid value is detected to be 1.1mgKOH / g;

[0060] After cooling the esterification reaction kettle to 70-80°C, the first esterification reaction product is filtered out of the solid catalyst through a filter press, and then transferred to a temporary storage tank, and the temperature is maintained at 70-120°C. Subsequently, the first esterification reaction product is heated to about 210°C through a preheater, and then pumped into the esterification reaction tower from the upper feed port 1, and at the same time, the mixed fatty acid of isooctanoic acid and isononanoic acid is pumped into the flash tank at the bottom of the esterification reaction tower, and the tower body temperature is controlled at about 210°C. The two undergo an esterification reaction in the esterification reaction tower to obtain a second esterification reaction product, and the hydroxyl value is measured to be 0.8 mgKOH / g;

[0061] The second esterification reaction product is then pumped into a molecular distiller, and after molecular distillation and deacidification, the acid value is measured to be 0.16 mgKOH / g. Finally, in a post-treatment kettle, the temperature is controlled at 70-80° C., 1000 ppm of sodium carbonate powder is added and stirred for 40 minutes, and then 0.5% of activated carbon is added and stirred for 40 minutes, and the pure products of isooctanoic acid and isononanoic acid pentaerythritol ester are obtained by cyclic filtration.

[0062] Example 2

[0063] First, valeric acid, caproic acid and adipic acid in a molar ratio of 1:1:0.5 are mixed, and then added to an esterification reactor in sequence with pentaerythritol in a molar ratio of 2.8:1, and solid catalyst stannous oxide with a mass fraction of 0.15% is added. After nitrogen replacement three times, the temperature is raised to control the reaction temperature to 160°C, and nitrogen protection is always introduced during the reaction. After reacting for 1 hour, vacuuming is started, and the vacuum is maintained at -0.08 to -0.095MPa. The reaction system is allowed to continue to react for 3 hours under vacuum reflux to obtain the first reaction product, and the acid value is detected to be 1.2mgKOH / g;

[0064] After cooling the esterification reaction kettle to 70-80°C, the first esterification product is filtered out of the solid catalyst through a filter press, and then transferred to a temporary storage tank 2, and the temperature is maintained at 70-120°C. Subsequently, the first esterification product is heated to about 200°C through a preheater, and then pumped into the esterification reaction tower from the upper feed port 1. At the same time, the mixed fatty acid of valeric acid, caproic acid, and adipic acid is pumped into the flash tank at the bottom of the esterification reaction tower, and the tower body temperature is controlled at about 200°C. The two undergo an esterification reaction in the esterification reaction tower to obtain a second esterification product, and the hydroxyl value is measured to be 0.6 mgKOH / g;

[0065] The second esterification reaction product is then pumped into molecular distillation. After molecular distillation and deacidification, the acid value is measured to be 0.15 mgKOH / g. Finally, in a post-treatment kettle, the temperature is controlled at 70-80° C., 1000 ppm of 32% sodium hydroxide liquid is added and stirred for 40 minutes, and then 0.5% of white clay is added and stirred for 40 minutes. During the whole process, a vacuum negative pressure state is maintained, and the mixed fatty acid pentaerythritol ester pure product is obtained by cyclic filtration.

[0066] The experimental data of the two groups of embodiments show that the present invention can prepare a completely esterified pentaerythritol ester with low acid value and low hydroxyl value, and the pentaerythritol ester has good color and stability, and exhibits excellent performance in various physical and chemical index tests of base oil.

[0067] The above disclosures are merely two preferred embodiments of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A system for preparing pentaerythritol ester, characterized in that: The invention comprises an esterification reaction kettle (1), a temporary storage tank (2), a preheater (3), an esterification reaction tower (4), a heat exchanger (5), a molecular distiller (6) and a post-treatment kettle (7), wherein the bottom outlet of the esterification reaction kettle (1) is connected to the top inlet of the temporary storage tank (2) through a pipeline (8), the bottom outlet of the temporary storage tank (2) is connected to the upper feed port (41) of the esterification reaction tower (4) through a pipeline (9), the preheater (3) is installed on the pipeline (9), and the esterification reaction tower (4) is provided with a plurality of layers of catalytic reaction units (10), the top of the catalytic reaction unit (10) is provided with a downcomer (100) connected thereto, and the catalytic units (10) of the two adjacent layers are connected to each other. The reaction units (10) are connected to each other through a downcomer (100); a flash tank (11) is provided below the catalytic reaction unit (10) at the bottom layer; the gas outlet end of the flash tank (11) is connected to the catalytic reaction units (10) at several layers through a gas riser (200); the flash tank (11) is arranged at the bottom of the esterification reaction tower (4); a discharge port (42) is provided at the lower side of the esterification reaction tower (4); the discharge port is located at the upper side of the flash tank (11); a second feed port (43) connected to the liquid inlet end of the flash tank (11) is provided at the bottom side of the esterification reaction tower (4); and the heat exchanger (5) is arranged at one side of the esterification reaction tower (4); The heat exchanger (5) is provided with an inlet 1 and an outlet 2 on one side, and an outlet 1, an inlet 2 and an inlet 3 on the other side. The inlet 1 is connected to the discharge port (42) through a pipeline 3 (12). The outlet 1 is connected to the inlet 1 and connected to the upper inlet (61) of the molecular distiller (6) through a pipeline 4 (13). The inlet 2 is connected to the bottom outlet 1 (62) of the molecular distiller (6) through a pipeline 5 (14). The inlet 3 is connected to the fatty acid feed end through a pipeline 6 (15). The outlet 2 is connected to the inlet 2 and the inlet 3 and connected to the feed port 2 (43) through a pipeline 7 (16). A bottom outlet 2 (63) is provided on the upper side of the bottom outlet 1 (62). The bottom outlet 2 (63) is connected to the feed port of the post-treatment kettle (7) through a pipeline 8 (17). The discharge port of the post-treatment kettle (7) is connected to a pentaerythritol ester storage tank (19) through a pipeline 9 (18).

2. A system for preparing pentaerythritol ester according to claim 1, characterized in that: The top of the esterification reaction tower (4) is provided with an air outlet (44), and the air outlet (44) is connected to a primary condenser (21) and a secondary condenser (22) in sequence through a pipeline (20), and a pipeline (23) is connected in parallel to the pipeline between the primary condenser (21) and the secondary condenser (22), and the other end of the pipeline (23) is arranged in parallel to the pipeline (14).

3. The system for preparing pentaerythritol ester according to claim 1, characterized in that: Several layers of the catalytic reaction units (10) are arranged on the inner side of the riser (200), the outer wall of the riser (200) is fixed to the inner wall of the esterification reaction tower (4), each layer of the catalytic reaction units (10) comprises a bottom plate (101) and a catalytic frame (102) and a packing frame (103) arranged on the bottom plate (101) from the outside to the inside, the downcomer (100) of the uppermost layer is installed in the esterification reaction tower (4) through a tower tray and is located above the bottom plate (101) of the layer, the lower end of the downcomer (100) of each layer is located outside the catalytic frame (102) of the layer and is fixed to the bottom plate (101), A gas path (300) is provided between the lower outer wall of the downcomer (100) and the riser (200); a plurality of liquid inlets (400) are provided on the lower inner wall of the downcomer (100) and communicate with the outer wall of the catalyst frame (102); a catalyst is placed in the catalyst frame (102) and two annularly arranged gas distribution plates (104) are provided therein; a plurality of gas inlets are provided on the two gas distribution plates (104); and the two gas distribution plates (104) are provided with a plurality of gas inlets. 4), the second gas path (500) is connected to the first gas path (300), the inner wall of the catalyst frame (102) is provided with a second liquid inlet (600) connected to the filling frame (103), a filling material is placed in the filling frame (103) and a liquid outlet (700) is provided at the bottom center of the filling frame (103), and the liquid outlet (700) is connected to the catalytic reaction unit (10) of the next layer through the downcomer (100).

4. A system for preparing pentaerythritol ester according to claim 3, characterized in that: The downcomer (100) comprises a main pipe (1001), a plurality of transition pipes (1002) and a branch pipe (1003) which are sequentially connected from top to bottom and communicate with each other internally. The transition pipe (1002) is located above the filler and the catalyst. The upper and lower surfaces of the transition pipe (1002) are provided with a plurality of air holes. The branch pipe (1003) is fixed to the outer wall of the filler frame (102) and a plurality of liquid inlets (400) are provided between them.

5. The system for preparing pentaerythritol ester according to claim 3, characterized in that: The filler is a structural filler, which is made of corrugated stainless steel and has a plurality of small holes.

6. A method for preparing pentaerythritol ester, using the pentaerythritol ester preparation system as claimed in any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: S1. Add fatty acid, pentaerythritol and solid catalyst into an esterification reaction kettle, replace with nitrogen three times, control the reaction temperature to 160-220° C., start vacuuming after 1 hour of reaction, and continue the reaction of the reaction system under vacuum reflux for 2-3 hours to obtain the first esterification reaction product, and continuously introduce nitrogen during the reaction; S2, after cooling the esterification reaction kettle to 70-120° C., the first esterification reaction product is circulated through a filter press to filter out the solid catalyst, and then transferred to a temporary storage tank through a pipeline 1, the temperature is maintained at 70-120° C., and nitrogen is continuously introduced to achieve nitrogen sealing; S3, the material in the temporary storage tank is heated to 180-220° C. through the preheater on the pipeline 2, pumped into the esterification reaction tower, enters the esterification reaction tower from the upper feed port 1 of the esterification reaction tower, enters several layers of catalytic reaction units through the downcomer, and at the same time, the fatty acid is heated to 150-220° C. through the pipeline 5 through the heat exchanger, and enters the flash tank at the bottom of the esterification reaction tower from the feed port 2 through the pipeline 6. After passing through the flash tank, the fatty acid becomes fatty acid vapor and enters several layers of catalytic reaction units upward through the riser, and is mixed with the liquid phase material entering from the feed port 1 for reaction; Among them, in the catalytic reaction units of several layers, the fatty acid vapor enters the catalytic reaction unit of each layer through the ascending pipe, and after fully reacting with the descending liquid phase feed in the catalytic reaction unit of the corresponding layer, the unreacted fatty acid vapor enters the catalytic reaction unit of the upper layer through the ascending pipe, and the liquid phase material after the reaction enters the catalytic reaction unit of the next layer through the downcomer of the lower layer, and this is repeated, and the liquid phase material coming out of the catalytic reaction unit of the bottom layer is discharged from the discharge port to obtain a crude pentaerythritol ester product; S4, the crude pentaerythritol ester product is sent to the heat exchanger through pipeline 3, and after heat exchange in the heat exchanger, it is sent to the molecular distiller through pipeline 4 to remove fatty acids in the product, and the acid value is controlled to be lower than 0.2 mg KOH / g. After the molecular distillation is completed, it is sent to the post-treatment kettle through pipeline 7 for alkali washing to remove residual fatty acids, and the acid value is controlled to be lower than 0.05 mg KOH / g. After the alkali washing is completed, a decolorizing agent is added for decolorization, and finally it is circulated and filtered through a filter press to remove the decolorizing agent and soap to obtain a pure pentaerythritol ester.

7. The method for preparing pentaerythritol ester according to claim 6, characterized in that: The fatty acid in S1 is one or more of pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, and capric acid, or the fatty acid is one or more of glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid, or the fatty acid is a mixture of monobasic acid and dibasic acid.

8. The method for preparing pentaerythritol ester according to claim 6, characterized in that: The solid catalyst in S1 is one or more of stannous oxalate, stannous chloride, stannous oxide, and solid acid catalysts, or one or more of stannous oxalate, stannous chloride, stannous oxide, and solid acid catalysts are loaded by an activated carbon support.

9. The method for preparing pentaerythritol ester according to claim 6, characterized in that: The molar ratio of fatty acid to pentaerythritol in S1 is 2-3:1, and the solid catalyst accounts for 0.05-0.2% of the total mass of fatty acid and pentaerythritol, and is put into the esterification reaction kettle together.

10. The method for preparing pentaerythritol ester according to claim 6, characterized in that: The reflux reaction is carried out in the S1 under vacuum conditions of -0.08 to -0.095 MPa; the reaction conditions of the esterification reaction tower in the S3 are controlled to be 180 to 220° C., the pressure is below 3000 Pa, and the number of catalytic reaction units is set to 5 to 10 layers.

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