A continuous crystallization method of pentaerythritol crystals

Abstract

The application discloses a continuous crystallization method of pentaerythritol crystal, which comprises the following steps: adding pentaerythritol aqueous solution into a nucleation kettle, a first growth kettle, a second growth kettle and a ripening kettle respectively as an initial bottom liquid, adding pentaerythritol seed crystals, continuously adding the pentaerythritol aqueous solution into the nucleation kettle, continuously feeding the crystal slurry suspension of the nucleation kettle into the first growth kettle, continuously feeding the crystal slurry suspension of the first growth kettle into the second growth kettle, continuously feeding the crystal slurry suspension of the second growth kettle into the ripening kettle, continuously feeding the crystal slurry suspension in the ripening kettle to a solid-liquid separation section, obtaining pentaerythritol crystal after solid-liquid separation, and obtaining pentaerythritol crystal product after drying. 3 The application has high production efficiency, small batch difference, small energy loss and is suitable for large-scale industrial production. The pentaerythritol product obtained by the method has a D50 of 350-400 mu m, a D90 of 580-630 mu m, a rest angle of 30 degrees and a bulk density of 0.75 g / cm

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of crystallization technology in chemical engineering industry, and particularly relates to a continuous crystallization method of pentaerythritol crystals. BACKGROUND

[0002] Pentaerythritol (PE) is an organic chemical product prepared by the reaction of formaldehyde and acetaldehyde under the action of an alkaline catalyst, and its chemical name is 2,2-bishydroxymethyl-1,3-propanediol. It is mainly used to produce lubricants, alkyd resins, polyurethanes, surfactants, emulsifiers, medicines, pesticides, explosives and the like, and has a wide application in the fields of resins, coatings, chemical industry, pharmaceuticals and national defense.

[0003] According to the different catalysts used, the production method of pentaerythritol can be divided into two production methods of "calcium method" and "sodium method". The "calcium method" uses calcium hydroxide as a catalyst, and the quality of the produced pentaerythritol product is better, and the raw material cost is low, but the process flow is longer, and the settling and filtration process must be added to remove calcium ions in the post-treatment, and the residual "calcium ash" in the product has a catalytic effect on the decomposition of pentaerythritol at high temperature, and calcium ions can also catalyze the self-polymerization of formaldehyde, which is not conducive to improving the yield of pentaerythritol. The "sodium method" uses sodium hydroxide as a condensation catalyst, compared with the "calcium method", the production cost of the "sodium method" is slightly higher, but the by-product sodium formate is easily dissolved in water, the post-treatment steps are less, the process flow is shorter, and the remaining "sodium ash" will not cause the decomposition of pentaerythritol. At present, the pentaerythritol production manufacturers in China mainly adopt the "sodium method" production process.

[0004] As a tetraol, pentaerythritol is easily esterified to form acids and esters, so it is mainly used as a raw material for alkyd resin coatings, mainly used as architectural coatings and automobile primer and the like. In industry, pentaerythritol tetranitrate (also known as PETN, too) can be obtained by esterification of pentaerythritol with concentrated nitric acid at 5-15℃, which is a high-performance primary explosive, and its explosive power is greater than that of TNT, and it is mainly used as a booster explosive or mixed with TNT. Too has the effect of dilating blood vessels, and is a long-acting vasodilator, which can be used to treat angina pectoris.

[0005] Currently, the research on pentaerythritol at home and abroad mainly focuses on the synthesis process, but the research on the process of strengthening the crystallization process to obtain products with uniform particle size and good flowability has not been paid attention to, especially under the premise of ensuring product quality, how to improve production efficiency, and there is no relevant research. Chinese invention patent CN101265166B discloses a production method of mono-pentaerythritol, di-pentaerythritol and tri-pentaerythritol. In the production, inert gas is used for pressurized pre-condensation in the pre-condensation reactor, and then the reaction solution is transferred to the main condensation reactor pressurized by inert gas for reaction. The reaction process is complex, and the yield of pentaerythritol produced is also low. Batch crystallization not only has large differences between batches, but also has great limitations in the utilization of equipment and optimization of production capacity.

[0006] Therefore, there is an urgent need in the prior art for a multi-stage continuous crystallization process that fits the kinetics of pentaerythritol crystal growth, to reduce energy consumption, improve production efficiency and avoid batch-to-batch differences, suitable for large-scale industrial production, and to improve the crystal habit and particle size of pentaerythritol crystals, improve the flowability and bulk density of the product. SUMMARY

[0007] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a continuous crystallization method for pentaerythritol crystals, to reduce energy consumption, improve production efficiency and avoid batch-to-batch differences, suitable for large-scale industrial production, and to improve the crystal habit and particle size of pentaerythritol crystals, improve the flowability and bulk density of the product.

[0008] The purpose of the present application is achieved by the following technical solution: a continuous crystallization method for pentaerythritol crystals, comprising the following steps:

[0009] (1) Prepare a 35-45wt% pentaerythritol aqueous solution at 100℃;

[0010] (2) Preparation of initial bottom liquid: under stirring at 100-105℃ and 100-300rpm, add 20% of the volume of the inner cavity of the nucleation kettle, the first-stage growth kettle, the second-stage growth kettle and the maturation kettle with pentaerythritol aqueous solution as the initial bottom liquid, add 1-10wt% of pentaerythritol in the pentaerythritol aqueous solution, 80-150μm pentaerythritol seed crystals, and incubate for 30-90min. After the temperature of the nucleation kettle, the first-stage growth kettle, the second-stage growth kettle and the maturation kettle is reduced to the set temperature of each kettle, continuously feed and discharge;

[0011] (3) Nucleation kettle crystallization: under stirring at 100-300rpm, control the temperature to 92-98℃, continuously add pentaerythritol aqueous solution into the nucleation kettle, ensure that the temperature rises by ≤5℃, nucleation occurs, and the crystal growth time is 70-110min, and the crystal particle size is maintained at 80-180μm;

[0012] (4) Primary growth kettle crystallization: under stirring at a speed of 100-300 rpm, the temperature is controlled to 75-85°C, the pentaerythritol crystal slurry suspension from the nucleation kettle is continuously added into the primary growth kettle, during the crystal growth, the temperature recovery is ensured to be ≤3°C, the crystal growth time is 250-300 min, and the crystal size is maintained to be 200-360 μm;

[0013] (5) Secondary growth kettle crystallization: under stirring at a speed of 100-300 rpm, the temperature is controlled to 55-65°C, the pentaerythritol crystal slurry suspension from the primary growth kettle is continuously added into the secondary growth kettle, the crystal is grown for the second time, the temperature recovery is ensured to be ≤3°C, the crystal growth time is 250-300 min, and the crystal size is maintained to be 280-450 μm;

[0014] (6) Maturation kettle crystallization: under stirring at a speed of 100-300 rpm, the temperature of the crystallization kettle is controlled to 35-45°C, the pentaerythritol crystal slurry suspension from the secondary growth kettle is continuously added into the maturation kettle, and maturation is carried out, the temperature recovery is ensured to be ≤2°C, the crystal growth time is 200-230 min, and the crystal size is maintained to be 320-480 μm;

[0015] (7) Solid-liquid separation: the crystal slurry suspension continuously discharged from the maturation kettle is separated by a solid-liquid separator to obtain pentaerythritol crystals, and the pentaerythritol crystal product is obtained after drying.

[0016] The present application adopts four-stage crystallization kettles, i.e. a nucleation kettle, a primary growth kettle, a secondary growth kettle and a maturation kettle, to ensure the effective implementation of the continuous crystallization process. During production, the crystal slurry is continuously discharged from the nucleation kettle, enters the primary growth kettle for growth, the crystal slurry of the primary growth kettle is continuously discharged into the secondary growth kettle for further growth, the crystal slurry is continuously discharged from the secondary growth kettle, enters the maturation kettle for maturation, the crystal slurry after maturation is subjected to solid-liquid separation, the solid after separation is discharged from the system, and the mother liquor is returned to the nucleation kettle after extraction for continuous circulation. In the present application, the stirring is realized under the action of stirring paddles.

[0017] The present application does not make specific limitation on the specific transmission process between the crystallization kettles, and the continuous feeding and discharging process can be realized by pump transmission or by overflow mode. The overflow mode is realized by the height difference between the crystallization kettles, and the slope of the overflow pipe, the position of the overflow pipe outlet and the diameter of the overflow pipe need to be considered in the specific transmission process, which can be selected according to actual needs by those skilled in the art.

[0018] Preferably, in the step (1), the pentaerythritol crystal seeds are directly added to the initial bottom liquid, or are added to the initial bottom liquid in the form of an aqueous solution containing the pentaerythritol crystal seeds.

[0019] Preferably, in the step (2), the temperature is controlled to 93-98℃, the crystal growth time is 90-100min, and the crystal size is maintained at 80-160μm under stirring at a speed of 100-260rpm.

[0020] Preferably, in the step (3), the temperature is controlled to 84-85℃, the crystal growth time is 260-280min, and the crystal size is maintained at 200-360μm under stirring at a speed of 100-260rpm.

[0021] Preferably, in the step (4), the temperature is controlled to 63-65℃, the first-stage crystal slurry is continuously added into the second-stage growth kettle, the crystal is grown for the second time, the temperature is guaranteed to rise by no more than 3℃, the crystal growth time is 260-280min, and the crystal size is maintained at 300-450μm under stirring at a speed of 100-260rpm.

[0022] Preferably, in the step (5), the temperature is controlled to 43-45℃, the crystal growth time is 200-230min, and the crystal size is maintained at 360-480μm under stirring at a speed of 100-260rpm.

[0023] Preferably, in the step (6), the temperature is controlled to 43-45℃, the crystal growth time is 200-230min, and the crystal size is maintained at 360-480μm under stirring at a speed of 100-260rpm.

[0024] Preferably, in the step (7), the drying is vacuum drying, the temperature of the vacuum drying is 40-80℃, the vacuum degree is 60-80kPa, and the vacuum drying time is 30-120min.

[0025] The present application has the following advantages: 1. Compared with the existing batch crystallization process, the present application adopts a continuous crystallization mode, which is simple to operate, saves labor, improves the production efficiency of pentaerythritol, reduces batch differences, reduces energy loss, improves the flowability and bulk density of the product, and enables continuous crystallization operation, fast crystal growth rate, and suitability for large-scale industrial production. 2. The D50 of the pentaerythritol obtained by the method of the present application is 350-400μm, the D90 is 580-630μm, the rest angle is 30°, and the bulk density is 0.75g / cm 3 . BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a flowchart of the continuous crystallization method of the pentaerythritol crystal in Example 1.

[0027] Figure 2 is an optical microscope image of the pentaerythritol product obtained in Example 1;

[0028] Figure 3 This is an optical microscope image of the pentaerythritol product obtained in Comparative Example 1. DETAILED DESCRIPTION

[0029] The present invention is described in detail below with reference to the accompanying drawings.

[0030] Example 1

[0031] like Figure 1 As shown, a continuous crystallization method of pentaerythritol crystals comprises the following steps:

[0032] The raw materials are pumped from the raw material tank into the nucleation kettle, the slurry from the nucleation kettle is pumped into the first-stage growth kettle, the slurry from the first-stage growth kettle is pumped into the second-stage growth kettle, the slurry from the second-stage growth kettle is pumped into the maturation kettle, and the slurry in the maturation kettle is transported to the solid-liquid separation section by a pump. The specific operations are as follows:

[0033] (1) preparing a 35 wt% pentaerythritol aqueous solution at 100° C.;

[0034] (2) Preparation of the initial base solution: Under stirring at 100° C. and 100 rpm, a pentaerythritol aqueous solution of 20% of the inner cavity volume of the reactor was added to the nucleation reactor, the primary growth reactor, the secondary growth reactor, and the aging reactor, as the initial base solution. Pentaerythritol seed crystals of 120-150 μm and 10 wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution were added, and the crystals were grown for 90 minutes. After the temperatures of the nucleation reactor, the primary growth reactor, the secondary growth reactor, and the aging reactor were lowered to the set temperatures of the respective reactors, the feed and discharge were continuously carried out under the action of pumps;

[0035] (3) Nucleation reactor crystallization: Under stirring at 100 rpm, control the temperature to 98°C, and continuously add pentaerythritol aqueous solution into the nucleation reactor to ensure that the temperature rise is ≤5°C. The crystal growth time is 90 min and the crystal size is maintained at 100-150 μm;

[0036] (4) Crystallization in the primary growth reactor: Under stirring at 100 rpm, the temperature was controlled to 85°C, and the pentaerythritol slurry suspension in the nucleation reactor was continuously added to the primary growth reactor, ensuring that the temperature rise was ≤3°C. The crystal growth time was 260 min, and the crystal size was maintained at 200-240 μm.

[0037] (5) Secondary growth kettle crystallization: under stirring at 100 rpm, the temperature is controlled to 65°C, the pentaerythritol crystal slurry suspension from the primary growth kettle is continuously added into the secondary growth kettle, the temperature rise is ensured to be ≤3°C, the crystal growth time is 260 min, and the crystal size is maintained at 300-350 μm;

[0038] (6) Maturation kettle crystallization: under stirring at 100 rpm, the temperature of the crystallization kettle is controlled to 45°C, the pentaerythritol crystal slurry suspension from the secondary growth kettle is continuously added into the maturation kettle, the temperature rise is ensured to be ≤2°C, the crystal growth time is 200 min, and the crystal size is maintained at 360-420 μm;

[0039] (7) Solid-liquid separation: the crystal slurry suspension continuously discharged from the maturation kettle is separated by a solid-liquid separator to obtain pentaerythritol crystals, and the pentaerythritol crystal product is obtained after drying.

[0040] Figure 2 The scanning electron microscope (SEM) image of the pentaerythritol crystal product obtained under the above operating conditions shows that the product has uniform particle size and good morphology, and has obvious crystal characteristics. Figure 2 The D50 of the obtained product is 400 μm, the D90 is 630 μm, the angle of repose is 30°, and the bulk density is 0.75 g / cm 3 .

[0041] Example 2

[0042] (1) A pentaerythritol aqueous solution with a concentration of 40 wt% is prepared at 103°C;

[0043] (2) Preparation of initial bottom liquid: under stirring at 200 rpm, 20% of the volume of the inner cavity of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the maturation kettle are added with the pentaerythritol aqueous solution as the initial bottom liquid, 1 wt% of pentaerythritol in the pentaerythritol aqueous solution, and 80-100 μm pentaerythritol seed crystals, and the crystals are incubated for 70 min. After the temperature of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the maturation kettle is reduced to the set temperature of each kettle, continuous feeding and discharging are carried out under the action of the pump;

[0044] (3) Nucleation kettle crystallization: under stirring at 200 rpm, the temperature is controlled to 92°C, the pentaerythritol aqueous solution is continuously added into the nucleation kettle, the temperature rise is ensured to be ≤5°C, the crystal growth time is 70 min, and the crystal size is maintained at 80-120 μm;

[0045] (4) Primary growth kettle crystallization: under stirring at 200 rpm, the temperature is controlled to 75°C, the pentaerythritol crystal slurry suspension from the nucleation kettle is continuously added into the primary growth kettle, the temperature rise is ensured to be ≤3°C, the crystal growth time is 250 min, and the crystal size is maintained at 200-240 μm;

[0046] (5) Secondary growth kettle crystallization: under stirring at 200 rpm, the temperature is controlled to 55°C, the pentaerythritol crystal slurry suspension of the primary growth kettle is continuously added into the secondary growth kettle, the temperature is guaranteed to rise by ≤3°C, the crystal growth time is 250 min, and the crystal size is maintained at 280-320 μm;

[0047] (6) Maturation kettle crystallization: under stirring at 200 rpm, the temperature is controlled to 35°C, the pentaerythritol crystal slurry suspension of the secondary growth kettle is continuously added into the maturation kettle, the temperature is guaranteed to rise by ≤2°C, the crystal growth time is 220 min, and the crystal size is maintained at 320-380 μm;

[0048] (7) Solid-liquid separation: the crystal slurry suspension continuously discharged from the maturation kettle is separated by a solid-liquid separator to obtain pentaerythritol crystals, and after drying, the pentaerythritol crystal product is obtained.

[0049] The D50 of the obtained pentaerythritol crystal product is 350 μm, the D90 is 580 μm, the rest angle is 32°, and the bulk density is 0.73 g / cm 3 .

[0050] Example 3

[0051] (1) A pentaerythritol aqueous solution with a concentration of 45 wt% is prepared at 105°C;

[0052] (2) Preparation of initial bottom liquid: under stirring at 300 rpm, 20% of the volume of the inner cavity of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the maturation kettle are added with the pentaerythritol aqueous solution as the initial bottom liquid, 6 wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution, and 100-140 μm pentaerythritol crystal seeds are added, the crystals are incubated for 60 min, and after the temperature of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the maturation kettle is reduced to the set temperature of each kettle, continuous feeding and discharging are carried out under the action of the pump;

[0053] (3) Nucleation kettle crystallization: under stirring at 300 rpm, the temperature is controlled to 96°C, the pentaerythritol aqueous solution is continuously added into the nucleation kettle, the temperature is guaranteed to rise by ≤5°C, the crystal growth time is 100 min, and the crystal size is maintained at 90-150 μm;

[0054] (4) Primary growth kettle crystallization: under stirring at 300 rpm, the temperature is controlled to 82°C, the pentaerythritol crystal slurry suspension of the nucleation kettle is continuously added into the primary growth kettle, the temperature is guaranteed to rise by ≤3°C, the crystal growth time is 270 min, and the crystal size is maintained at 240-340 μm;

[0055] (5) Secondary growth kettle crystallization: under stirring at 300 rpm, control the temperature to 59°C, continuously add the pentaerythritol crystal slurry suspension of the primary growth kettle into the secondary growth kettle, ensure the temperature recovery ≤3°C, the crystal growth time is 270 min, and keep the crystal size at 330-400 μm;

[0056] (6) Maturation kettle crystallization: under stirring at 300 rpm, control the temperature to 40°C, continuously add the pentaerythritol crystal slurry suspension of the secondary growth kettle into the maturation kettle, ensure the temperature recovery ≤2°C, the crystal growth time is 210 min, and keep the crystal size at 340-420 μm;

[0057] (7) Solid-liquid separation: the crystal slurry suspension continuously discharged from the maturation kettle is separated by a solid-liquid separator to obtain pentaerythritol crystals, and after drying, the pentaerythritol crystal product is obtained.

[0058] The D50 of the obtained pentaerythritol crystal product is 360 μm, the D90 is 600 μm, the rest angle is 34°, and the bulk density is 0.72 g / cm 3 .

[0059] Example 4

[0060] (1) Prepare a pentaerythritol aqueous solution with a concentration of 38 wt% at 102°C;

[0061] (2) Preparation of initial bottom liquid: under stirring at 260 rpm at 102°C, add 20% of the volume of the kettle cavity of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the maturation kettle with the pentaerythritol aqueous solution as the initial bottom liquid, add 3 wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution, and 80-130 μm pentaerythritol crystal seeds, and incubate for 50 min, and after the temperature of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the maturation kettle is reduced to the set temperature of each kettle, continuously feed and discharge under the action of the pump;

[0062] (3) Nucleation kettle crystallization: under stirring at 260 rpm, control the temperature to 93°C, continuously add the pentaerythritol aqueous solution into the nucleation kettle, ensure the temperature recovery ≤5°C, the crystal growth time is 100 min, and keep the crystal size at 100-160 μm;

[0063] (4) Primary growth kettle crystallization: under stirring at 260 rpm, control the temperature to 84°C, continuously add the pentaerythritol crystal slurry suspension of the nucleation kettle into the primary growth kettle, ensure the temperature recovery ≤3°C, the crystal growth time is 280 min, and keep the crystal size at 280-360 μm;

[0064] (5) Secondary growth kettle crystallization: under stirring at 260 rpm, the temperature is controlled to 63°C, the pentaerythritol crystal slurry suspension of the primary growth kettle is continuously added into the secondary growth kettle, the temperature rise is ensured to be ≤3°C, the crystal growth time is 280 min, and the crystal size is maintained at 360-450 μm;

[0065] (6) Maturation kettle crystallization: under stirring at 260 rpm, the temperature is controlled to 43°C, the pentaerythritol crystal slurry suspension of the secondary growth kettle is continuously added into the maturation kettle, the temperature rise is ensured to be ≤2°C, the crystal growth time is 200 min, and the crystal size is maintained at 360-480 μm;

[0066] (7) Solid-liquid separation: the crystal slurry suspension continuously discharged from the maturation kettle is separated by a solid-liquid separator to obtain pentaerythritol crystals, and the pentaerythritol crystal product is obtained after drying.

[0067] The D50 of the obtained pentaerythritol crystal product is 390 μm, the D90 is 620 μm, the rest angle is 33°, and the bulk density is 0.73 g / cm 3 .

[0068] Example 5

[0069] (1) A pentaerythritol aqueous solution with a concentration of 43 wt% is prepared at 104°C;

[0070] (2) Preparation of initial bottom liquid: under stirring at 104°C and 180 rpm, 20% of the volume of the inner cavity of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the maturation kettle are added with the pentaerythritol aqueous solution as the initial bottom liquid, 7 wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution, and 100-150 μm pentaerythritol crystal seeds are added, the crystal is incubated for 60 min, and after the temperature of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the maturation kettle is reduced to the set temperature of each kettle, continuous feeding and discharging are carried out under the action of the pump;

[0071] (3) Nucleation kettle crystallization: under stirring at 180 rpm, the temperature is controlled to 93°C, the pentaerythritol aqueous solution is continuously added into the nucleation kettle, the temperature rise is ensured to be ≤5°C, the crystal growth time is 110 min, and the crystal size is maintained at 100-180 μm;

[0072] (4) Primary growth kettle crystallization: under stirring at 180 rpm, the temperature is controlled to 84°C, the pentaerythritol crystal slurry suspension of the nucleation kettle is continuously added into the primary growth kettle, the temperature rise is ensured to be ≤3°C, the crystal growth time is 300 min, and the crystal size is maintained at 290-340 μm;

[0073] (5) Secondary growth kettle crystallization: under stirring at 180 rpm, the temperature is controlled to 63°C, the pentaerythritol crystal slurry suspension from the primary growth kettle is continuously added into the secondary growth kettle, the temperature recovery is ensured to be ≤3°C, the crystal growth time is 300 min, and the crystal size is maintained at 360-420 μm;

[0074] (6) Maturation kettle crystallization: under stirring at 180 rpm, the temperature is controlled to 43°C, the pentaerythritol crystal slurry suspension from the secondary growth kettle is continuously added into the maturation kettle, the temperature recovery is ensured to be ≤2°C, the crystal growth time is 230 min, and the crystal size is maintained at 340-460 μm;

[0075] (7) Solid-liquid separation: the crystal slurry suspension continuously discharged from the maturation kettle is separated by a solid-liquid separator to obtain pentaerythritol crystals, and the pentaerythritol crystal product is obtained after drying.

[0076] The D50 of the obtained pentaerythritol crystal product is 370 μm, the D90 is 590 μm, the rest angle is 31°, and the bulk density is 0.73 g / cm 3 .

[0077] Comparative Example 1

[0078] Comparative Example 1 is different from Example 1 only in the preparation stage of the initial bottom liquid in step (2), and the others are the same as Example 1.

[0079] Preparation of the initial bottom liquid in Comparative Example 1: under stirring at 100 rpm at 100°C, 8% of the volume of the inner cavity of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the maturation kettle are added with an aqueous pentaerythritol solution as the initial bottom liquid, 10% of the mass of pentaerythritol in the aqueous pentaerythritol solution, and 120-150 μm pentaerythritol crystal seeds, and then the nucleation kettle, the primary growth kettle, the secondary growth kettle and the maturation kettle are continuously fed and discharged under the action of the pump, respectively.

[0080] Figure 3 The scanning electron microscope (SEM) image of the pentaerythritol product obtained under the operating conditions of Comparative Example 1 can be seen that the particle size distribution is poor, the agglomeration phenomenon is serious, and there is no obvious crystal characteristics.

[0081] The D50 of the obtained pentaerythritol product is 200 μm, the D90 is 330 μm, the rest angle is 42°, and the bulk density is 0.62 g / cm 3 . By comparison, it can be seen that when other conditions are unchanged, too little initial bottom liquid will make stirring unable to play a role, heat and mass transfer will be limited, and obvious secondary nucleation will occur, thereby causing the product particle size to decrease significantly and increasing the difficulty of filtration and drying.

[0082] Comparative Example 2

[0083] Comparative Example 2 differs from Example 1 only in that the nucleation kettle crystallization step (3) is different.

[0084] Comparative Example 2 nucleation kettle crystallization: the temperature of the crystallization kettle is controlled at 90°C with stirring at 100 rpm, the aqueous pentaerythritol solution is continuously added into the nucleation kettle, the temperature rise is ≤9°C, and the crystal growth time is 80-100 min.

[0085] The D50 of the obtained pentaerythritol product is 160 μm, the D90 is 320 μm, the angle of repose is 44°, and the bulk density is 0.63 g / cm 3 By comparison, it can be seen that when the temperature rise of the nucleation kettle is too high, the supersaturation of the next stage of the growth kettle is too high, obvious secondary nucleation occurs, which leads to a significant decrease in the particle size of the product, and increases the difficulty of filtration and drying.

[0086] Comparative Example 3

[0087] Comparative Example 3 differs from Example 1 only in that the primary growth kettle crystallization step is different, and the rest of the preparation method is the same as Example 1.

[0088] Comparative Example 3 primary growth kettle crystallization: the temperature is controlled at 55°C with stirring at 200 rpm, the pentaerythritol crystal slurry suspension from the nucleation kettle is continuously added into the primary growth kettle, the temperature rise is ensured to be ≤3°C, and the crystal growth time is 240-260 min.

[0089] The D50 of the obtained pentaerythritol product is 180 μm, the D90 is 280 μm, the angle of repose is 42°, and the bulk density is 0.65 g / cm 3 By comparison, it can be seen that when the temperature of the primary growth kettle is reduced to 55°C and other conditions remain unchanged, the average particle size of the crystal will decrease significantly, which is not conducive to subsequent separation and drying.

[0090] Comparative Example 4

[0091] Comparative Example 4 differs from Example 1 only in that it does not include the maturation kettle crystallization step, and the rest of the preparation method is the same as Example 1.

[0092] The D50 of the obtained pentaerythritol product is 150 μm, the D90 is 300 μm, the angle of repose is 46°, and the bulk density is 0.60 g / cm 3 By comparison, it can be seen that when the maturation kettle crystallization step is cancelled, the particle size of the crystal decreases relatively, the production efficiency decreases, and the amount of waste liquid and waste solid increases.

[0093] Finally, it should be noted that the above is only to illustrate the technical solutions of the present application, and is not a limitation on the scope of protection of the present application, and simple modifications or equivalent replacements of the technical solutions of the present application by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

Claims

1. A continuous crystallization method for pentaerythritol crystals, characterized in that The steps include: (1) preparing a 35-45 wt% pentaerythritol aqueous solution at 100° C.; (2) Preparation of the initial base solution: adding a pentaerythritol aqueous solution of 20% of the inner cavity volume of the nucleation kettle, the primary growth kettle, the secondary growth kettle, and the aging kettle respectively at 100-105° C. and 100-300 rpm with stirring, as the initial base solution, adding 1-10 wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution and 80-150 μm pentaerythritol seed crystals, and growing the crystals for 30-90 minutes. After the temperature of the nucleation kettle, the primary growth kettle, the secondary growth kettle, and the aging kettle drops to the set temperature of each kettle, continuous feeding and discharging are carried out respectively; (3) Nucleation kettle crystallization: Under stirring at a speed of 100-300 rpm, control the temperature to 92-98°C, and continuously add pentaerythritol aqueous solution into the nucleation kettle to ensure that the temperature rises ≤ 5°C, crystal nucleation occurs, the crystal growth time is 70-110 minutes, and the crystal size is maintained at 80-180 μm; (4) Crystallization in the primary growth reactor: Under stirring at a speed of 100-300 rpm, the temperature is controlled to 75-85°C, and the pentaerythritol slurry suspension in the nucleation reactor is continuously added to the primary growth reactor. During the crystal growth process, the temperature rise is ensured to be ≤3°C, the crystal growth time is 250-300 min, and the crystal size is maintained at 200-360 μm; (5) Crystallization in a secondary growth kettle: Under stirring at a speed of 100-300 rpm, control the temperature to 55-65°C, and continuously add the pentaerythritol slurry suspension from the primary growth kettle into the secondary growth kettle to allow the crystals to grow secondary. Ensure that the temperature rise is ≤3°C, the crystal growth time is 250-300 min, and the crystal size is maintained at 280-450 μm. (6) Crystallization in a aging kettle: Under stirring at a speed of 100-300 rpm, the temperature of the crystallization kettle is controlled to 35-45°C, and the pentaerythritol slurry suspension from the secondary growth kettle is continuously added to the aging kettle for aging, ensuring that the temperature rise is ≤ 2°C, the crystal growth time is 200-230 minutes, and the crystal size is maintained at 320-480 μm; (7) Solid-liquid separation: The crystal slurry suspension continuously discharged from the aging kettle is separated by a solid-liquid separator to obtain pentaerythritol crystals, which are then dried to obtain pentaerythritol crystal products.

2. The method for continuous crystallization of pentaerythritol crystals according to claim 1, wherein: In the step (2), the pentaerythritol seed crystals are directly added to the initial base liquid, or added to the initial base liquid in the form of an aqueous solution containing the pentaerythritol seed crystals.

3. The method for continuous crystallization of pentaerythritol crystals according to claim 1, wherein: In the step (2), the pentaerythritol aqueous solution is added to the nucleation kettle, the primary growth kettle, the secondary growth kettle and the aging kettle respectively under stirring at 100-102° C. and 100-260 rpm, and pentaerythritol seed crystals of 80-150 μm and 3-10 wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution are added, and the crystals are grown for 50-90 minutes.

4. The method for continuous crystallization of pentaerythritol crystals according to claim 1, wherein: In the step (3), the temperature is controlled to 93-98° C. under stirring at a speed of 100-260 rpm, the crystal growth time is 90-100 min, and the crystal size is maintained at 80-160 μm.

5. The method for continuous crystallization of pentaerythritol crystals according to claim 1, wherein: In the step (4), the temperature is controlled to 84-85° C. under stirring at a speed of 100-260 rpm, the crystal growth time is 260-280 min, and the crystal size is maintained at 200-360 μm.

6. The method for continuous crystallization of pentaerythritol crystals according to claim 1, wherein: In the step (5), the temperature is controlled to 63-65°C under stirring at a speed of 100-260 rpm, and the pentaerythritol slurry suspension in the first growth kettle is continuously added to the second growth kettle for secondary growth of the crystals, ensuring that the temperature rise is ≤3°C, the crystal growth time is 260-280 minutes, and the crystal size is maintained at 300-450 μm.

7. The method for continuous crystallization of pentaerythritol crystals according to claim 1, wherein: In the step (6), the temperature of the crystallization kettle is controlled to 43-45° C. under stirring at a speed of 100-260 rpm, the crystal growth time is 200-230 min, and the crystal size is maintained at 360-480 μm.

8. The method for continuous crystallization of pentaerythritol crystals according to claim 1, wherein: In the step (7), the drying is vacuum drying, the vacuum drying temperature is 40-80°C, the vacuum degree is 60-80kPa, and the vacuum drying time is 30-120min.

Images