Continuous crystallization method of pentaerythritol crystal

Abstract

The invention discloses a continuous crystallization method of pentaerythritol crystals, which comprises the following steps: respectively adding a pentaerythritol aqueous solution as an initial base solution into a nucleation kettle, a first-stage growth kettle, a second-stage growth kettle and a curing kettle, adding pentaerythritol seed crystals, continuously adding the pentaerythritol aqueous solution into the nucleation kettle, and continuously crystallizing to obtain the pentaerythritol crystals. The crystal slurry suspension of the nucleation kettle continuously enters a first-stage growth kettle, the crystal slurry suspension of the first-stage growth kettle continuously enters a second-stage growth kettle, the crystal slurry suspension of the second-stage growth kettle continuously enters a curing kettle, the crystal slurry suspension in the curing kettle is continuously conveyed to a solid-liquid separation section, and pentaerythritol crystals are obtained after solid-liquid separation; and drying to obtain a pentaerythritol crystal product. The method is high in production efficiency, small in batch-to-batch difference, small in energy consumption loss and suitable for large-scale industrial production. According to the pentaerythritol product obtained by the method disclosed by the invention, the D50 is 350-400 microns, the D90 is 580-630 microns, the angle of repose is 30 degrees, and the bulk density is 0.75 g / cm < 3 >.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical engineering industrial crystallization, and in particular relates to a continuous crystallization method of pentaerythritol crystals. Background Art

[0002] Pentaerythritol (PE) is an organic chemical product made by the reaction of formaldehyde and acetaldehyde in the presence of an alkaline catalyst. Its chemical name is 2,2-bis(hydroxymethyl)-1,3-propanediol. It is mainly used to produce lubricants, alkyd resins, polyurethanes, surfactants, emulsifiers, medicines, pesticides, and explosives. It is widely used in resins, coatings, chemicals, pharmaceuticals, and national defense.

[0003] According to the different catalysts used, the production methods of pentaerythritol can be divided into two production methods: "calcium method" and "sodium method". "Calcium method" uses calcium hydroxide as a catalyst, and the pentaerythritol produced is of good quality and low raw material cost, but the process flow is long, and the post-treatment must add sedimentation and filtration steps to remove calcium ions, and the "calcium ash" remaining in the product has a catalytic effect on the decomposition of pentaerythritol at high temperature. Calcium ions can also catalyze formaldehyde self-polymerization, which is not conducive to improving the yield of pentaerythritol. "Sodium method" uses sodium hydroxide as a condensation catalyst. Compared with the "calcium method", the production cost of "sodium method" is slightly higher, but its by-product sodium formate is easily soluble in water, the post-treatment steps are few, the process flow is short, and the remaining "sodium ash" will not decompose pentaerythritol. At present, pentaerythritol manufacturers in my country mainly use the "sodium method" production process.

[0004] As a tetrahydric alcohol, pentaerythritol is easily esterified to form acid and ester, so it is mostly used as a raw material for alkyd resin coatings, mainly used as architectural coatings and automotive primers. In industry, pentaerythritol is esterified with concentrated nitric acid at 5-15°C to obtain pentaerythritol tetranitrate (also known as PETN, Tyen), which is a high-performance high explosive with greater explosive power than TNT. It is mostly used as a booster or mixed with TNT. Tyen also has the effect of vasodilation, is a long-acting vasodilator, and can treat angina pectoris.

[0005] At present, the research work about pentaerythritol at home and abroad is mainly concentrated in the synthesis process, but the research work on the product with uniform particle size and good fluidity obtained by strengthening the crystallization process has not been taken seriously, especially under the premise of ensuring product quality, how to improve production efficiency, there is no relevant research. Chinese invention patent CN101265166B discloses a production method of monopentaerythritol, dipentaerythritol and tripentaerythritol, which needs to be pressurized precondensed with inert gas in the precondensation reactor during production, and then the reaction solution is transferred to the main condensation reactor pressurized with inert gas to react, the reaction process is complicated, and the yield of producing pentaerythritol is also low. Intermittent crystallization not only has large differences between batches, but also has great limitations for the utilization of equipment and the optimization of production capacity.

[0006] Therefore, there is an urgent need in the prior art for a multi-stage continuous crystallization treatment method that is consistent with the growth kinetics of pentaerythritol crystals, so as to reduce energy consumption, improve production efficiency and avoid batch differences, be suitable for large-scale industrial production, and improve the crystal habit and particle size of pentaerythritol crystals, and improve the fluidity and bulk density of the product. Summary of the invention

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

[0008] The object of the present invention is achieved through the following technical scheme: A continuous crystallization method of pentaerythritol crystals, comprising the following steps: (1) preparing a 35-45 wt% pentaerythritol aqueous solution at 100° C.; (2) Preparation of initial bottom solution: adding 20% ​​of the volume of the inner cavity of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the aging kettle as the initial bottom solution under stirring at 100-105° C. and 100-300 rpm, adding 1-10wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution and 80-150 μm pentaerythritol seeds, and growing the crystals for 30-90 min. 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 performed respectively; (3) Nucleation reactor crystallization: under stirring at a speed of 100-300 rpm, control the temperature to 92-98° C., continuously add pentaerythritol aqueous solution into the nucleation reactor, ensure that the temperature rises by ≤5° C., crystal nucleation occurs, the crystal growth time is 70-110 min, 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, the temperature is controlled to 55-65° C., and the pentaerythritol slurry suspension in the primary growth kettle is continuously added to the secondary growth kettle for secondary growth of crystals, ensuring 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 in 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 min, 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 a pentaerythritol crystal product.

[0009] The present invention adopts four-stage crystallization kettles, namely a nucleation kettle, a primary growth kettle, a secondary growth kettle and a maturation kettle, to ensure that the continuous crystallization process is effectively implemented. During production, the slurry is continuously discharged from the nucleation kettle and enters the primary growth kettle for growth. The slurry of the primary growth kettle continuously enters the secondary growth kettle for further growth. The slurry is continuously discharged from the secondary growth kettle and enters the maturation kettle for maturation. The maturated slurry is subjected to solid-liquid separation. The separated solid is discharged from the system, and the mother liquor is returned to the nucleation kettle for continuous circulation after extraction. In the present invention, stirring is achieved under the action of a stirring paddle.

[0010] The present invention does not specifically limit the specific transmission process between the crystallization kettles, and the continuous feeding and discharging process can be realized by pump transmission or by overflow. The overflow method is to realize the transmission process through the height difference between the crystallization kettles. In the specific transmission process, the slope of the overflow pipe, the overflow pipe outlet position and the overflow pipe diameter need to be considered, and those skilled in the art can make a selection according to actual needs.

[0011] Preferably, in step (1), the pentaerythritol seed crystals are directly added to the initial base solution, or are added to the initial base solution in the form of an aqueous solution containing the pentaerythritol seed crystals.

[0012] Preferably, 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 min.

[0013] Preferably, 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.

[0014] Preferably, 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.

[0015] Preferably, 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 primary growth kettle is continuously added to the secondary growth kettle, and the crystals are grown for a second time, ensuring that the temperature rise is ≤3°C, the crystal growth time is 260-280 min, and the crystal size is maintained at 300-450 μm.

[0016] Preferably, in 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.

[0017] Preferably, in step (7), the drying is vacuum drying, the vacuum drying temperature is 40-80° C., the vacuum degree is 60-80 kPa, and the vacuum drying time is 30-120 min.

[0018] The beneficial effects of the present invention are as follows: 1. Compared with the existing intermittent crystallization process, the present invention adopts a continuous crystallization method, which is simple to operate, saves labor, improves the production efficiency of pentaerythritol products, reduces batch differences, reduces energy consumption losses, improves the fluidity and bulk density of products, and enables continuous crystallization operations, fast crystal growth rate, and is suitable for large-scale industrial production. 2. The D50 of pentaerythritol obtained by the method of the present invention is 350-400μm, D90 is 580-630μm, the angle of repose is 30°, and the bulk density is 0.75g / cm 3 . BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart of the continuous crystallization method of pentaerythritol crystals in Example 1; Figure 2 is an optical microscope image of the pentaerythritol product obtained in Example 1; Figure 3 This is an optical microscope image of the pentaerythritol product obtained in Comparative Example 1. DETAILED DESCRIPTION

[0020] The present invention is described in detail below with reference to the accompanying drawings.

[0021] Example 1

[0022] like Figure 1 As shown, a continuous crystallization method of pentaerythritol crystals comprises the following steps: The raw materials are pumped from the raw material tank into the nucleation kettle, the slurry in the nucleation kettle is pumped into the primary growth kettle, the slurry in the primary growth kettle is pumped into the secondary growth kettle, the slurry in the secondary 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 operation is as follows: (1) preparing a 35 wt% pentaerythritol aqueous solution at 100° C.; (2) Preparation of initial bottom solution: adding 20% ​​of the volume of the inner cavity of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the aging kettle as the initial bottom solution under stirring at 100° C. and 100 rpm, adding 10 wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution and 120-150 μm pentaerythritol seed crystals, and growing the crystals for 90 min. 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, the materials are continuously fed and discharged by the action of pumps; (3) Nucleation reactor crystallization: Under stirring at 100 rpm, control the temperature to 98°C, continuously add pentaerythritol aqueous solution into the nucleation reactor, 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; (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 to ensure that the temperature rise was ≤ 3° C. The crystal growth time was 260 min, and the crystal size was maintained at 200-240 μm; (5) Crystallization in the secondary growth kettle: Under stirring at 100 rpm, the temperature was controlled to 65° C., and the pentaerythritol slurry suspension in the primary growth kettle was continuously added to the secondary growth kettle to ensure that the temperature rise was ≤ 3° C. The crystal growth time was 260 min, and the crystal size was maintained at 300-350 μm; (6) Crystallization in a aging kettle: Under stirring at a speed of 100 rpm, the temperature of the crystallization kettle was controlled to 45° C. The pentaerythritol slurry suspension in the secondary growth kettle was continuously added to the aging kettle to ensure that the temperature rise was ≤ 2° C. The crystal growth time was 200 min, and the crystal size was maintained at 360-420 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 a pentaerythritol crystal product.

[0023] Figure 2 The SEM image of the pentaerythritol crystal product obtained under the above operating conditions is shown in FIG. Figure 2 It can be seen that the product has uniform particle size, good morphology and obvious crystal characteristics. The D50 of the obtained product is 400μm, D90 is 630μm, the angle of repose is 30°, and the bulk density is 0.75g / cm 3 .

[0024] Example 2

[0025] (1) preparing a 40 wt% pentaerythritol aqueous solution at 103° C.; (2) Preparation of initial bottom solution: adding 20% ​​of the volume of the inner cavity of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the aging kettle as the initial bottom solution under stirring at 103° C. and 200 rpm, adding 1wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution and 80-100 μm pentaerythritol seeds, and growing the crystals for 70 min. 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, the materials are continuously fed and discharged by the action of pumps; (3) Nucleation reactor crystallization: Under stirring at 200 rpm, control the temperature to 92°C, continuously add pentaerythritol aqueous solution into the nucleation reactor, ensure that the temperature rise is ≤5°C, the crystal growth time is 70 min, and the crystal size is maintained at 80-120 μm; (4) Crystallization in the primary growth reactor: Under stirring at 200 rpm, the temperature was controlled to 75° C., and the pentaerythritol slurry suspension in the nucleation reactor was continuously added to the primary growth reactor to ensure that the temperature rise was ≤ 3° C. The crystal growth time was 250 min, and the crystal size was maintained at 200-240 μm; (5) Crystallization in the secondary growth kettle: Under stirring at 200 rpm, the temperature was controlled to 55° C., and the pentaerythritol slurry suspension in the primary growth kettle was continuously added to the crystallization in the secondary growth kettle, ensuring that the temperature rise was ≤3° C. The crystal growth time was 250 min, and the crystal size was maintained at 280-320 μm; (6) Crystallization in a aging kettle: Under stirring at a speed of 200 rpm, the temperature is controlled to 35° C., and the pentaerythritol slurry suspension in the secondary growth kettle is continuously added to the aging kettle to ensure that the temperature rise is ≤ 2° C. The crystal growth time is 220 min, and the crystal size is maintained at 320-380 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 a pentaerythritol crystal product.

[0026] The D50 of the obtained pentaerythritol crystal product is 350 μm, the D90 is 580 μm, the angle of repose is 32°, and the bulk density is 0.73 g / cm 3 .

[0027] Example 3

[0028] (1) preparing a 45 wt% pentaerythritol aqueous solution at 105° C.; (2) Preparation of initial bottom solution: adding a pentaerythritol aqueous solution of 20% of the inner cavity volume of the reactor to the nucleation reactor, the primary growth reactor, the secondary growth reactor and the aging reactor respectively under stirring at 105° C. and 300 rpm as the initial bottom solution, adding pentaerythritol seed crystals of 100-140 μm and 6 wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution, and growing the crystals for 60 min. After the temperature of the nucleation reactor, the primary growth reactor, the secondary growth reactor and the aging reactor is reduced to the set temperature of each reactor, the materials are continuously fed and discharged by the action of pumps respectively; (3) Nucleation reactor crystallization: Under stirring at 300 rpm, control the temperature to 96°C, continuously add pentaerythritol aqueous solution into the nucleation reactor, ensure that the temperature rise is ≤5°C, the crystal growth time is 100 min, and the crystal size is maintained at 90-150 μm; (4) Crystallization in the primary growth reactor: Under stirring at 300 rpm, the temperature was controlled to 82° C., and the pentaerythritol slurry suspension in the nucleation reactor was continuously added to the primary growth reactor to ensure that the temperature rise was ≤ 3° C. The crystal growth time was 270 min, and the crystal size was maintained at 240-340 μm; (5) Crystallization in the secondary growth kettle: Under stirring at 300 rpm, the temperature was controlled to 59° C., and the pentaerythritol slurry suspension in the primary growth kettle was continuously added to the secondary growth kettle to ensure that the temperature rise was ≤ 3° C. The crystal growth time was 270 min, and the crystal size was maintained at 330-400 μm; (6) Crystallization in a aging kettle: under stirring at 300 rpm, the temperature was controlled to 40° C., and the pentaerythritol slurry suspension in the secondary growth kettle was continuously added to the aging kettle to ensure that the temperature rise was ≤ 2° C. The crystal growth time was 210 min, and the crystal size was maintained at 340-420 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 a pentaerythritol crystal product.

[0029] The D50 of the obtained pentaerythritol crystal product is 360 μm, the D90 is 600 μm, the angle of repose is 34°, and the bulk density is 0.72 g / cm 3 .

[0030] Example 4

[0031] (1) preparing a 38 wt% pentaerythritol aqueous solution at 102° C.; (2) Preparation of initial bottom solution: adding a pentaerythritol aqueous solution of 20% of the inner cavity volume of the reactor to the nucleation reactor, the primary growth reactor, the secondary growth reactor and the aging reactor respectively under stirring at 102° C. and 260 rpm as the initial bottom solution, adding pentaerythritol seed crystals of 80-130 μm and 3 wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution, and growing the crystals for 50 min. After the temperature of the nucleation reactor, the primary growth reactor, the secondary growth reactor and the aging reactor is reduced to the set temperature of each reactor, the materials are continuously fed and discharged by the action of pumps respectively; (3) Nucleation reactor crystallization: Under stirring at 260 rpm, control the temperature to 93°C, continuously add pentaerythritol aqueous solution into the nucleation reactor, ensure that the temperature rise is ≤5°C, the crystal growth time is 100 min, and the crystal size is maintained at 100-160 μm; (4) Crystallization in the primary growth reactor: Under stirring at 260 rpm, the temperature was controlled to 84° C., and the pentaerythritol slurry suspension in the nucleation reactor was continuously added to the primary growth reactor to ensure that the temperature rise was ≤ 3° C. The crystal growth time was 280 min, and the crystal size was maintained at 280-360 μm; (5) Crystallization in the secondary growth kettle: Under stirring at 260 rpm, the temperature was controlled to 63° C., and the pentaerythritol slurry suspension in the primary growth kettle was continuously added to the secondary growth kettle to ensure that the temperature rise was ≤ 3° C. The crystal growth time was 280 min, and the crystal size was maintained at 360-450 μm; (6) Crystallization in a aging kettle: Under stirring at 260 rpm, the temperature was controlled to 43° C., and the pentaerythritol slurry suspension in the secondary growth kettle was continuously added to the aging kettle to ensure that the temperature rise was ≤ 2° C. The crystal growth time was 200 min, and the crystal size was maintained at 360-480 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 a pentaerythritol crystal product.

[0032] The obtained pentaerythritol crystal product has a D50 of 390 μm, a D90 of 620 μm, a repose angle of 33°, and a bulk density of 0.73 g / cm3 .

[0033] Example 5

[0034] (1) preparing a 43 wt% pentaerythritol aqueous solution at 104° C.; (2) Preparation of initial bottom solution: adding a pentaerythritol aqueous solution of 20% of the inner cavity volume of the reactor to the nucleation reactor, the primary growth reactor, the secondary growth reactor and the aging reactor respectively under stirring at 104° C. and 180 rpm as the initial bottom solution, adding pentaerythritol seed crystals of 100-150 μm and 7 wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution, and growing the crystals for 60 min. After the temperature of the nucleation reactor, the primary growth reactor, the secondary growth reactor and the aging reactor is reduced to the set temperature of each reactor, the materials are continuously fed and discharged by the action of pumps respectively; (3) Nucleation reactor crystallization: Under stirring at 180 rpm, control the temperature to 93°C, continuously add pentaerythritol aqueous solution into the nucleation reactor, ensure that the temperature rise is ≤5°C, the crystal growth time is 110 min, and the crystal size is maintained at 100-180 μm; (4) Crystallization in the primary growth reactor: Under stirring at 180 rpm, the temperature was controlled to 84° C., and the pentaerythritol slurry suspension in the nucleation reactor was continuously added to the primary growth reactor to ensure that the temperature rise was ≤ 3° C. The crystal growth time was 300 min, and the crystal size was maintained at 290-340 μm; (5) Crystallization in the secondary growth kettle: Under stirring at 180 rpm, the temperature was controlled to 63° C., and the pentaerythritol slurry suspension in the primary growth kettle was continuously added to the secondary growth kettle to ensure that the temperature rise was ≤ 3° C. The crystal growth time was 300 min, and the crystal size was maintained at 360-420 μm; (6) Crystallization in the aging kettle: Under stirring at 180 rpm, the temperature is controlled to 43° C., and the pentaerythritol slurry suspension in the secondary growth kettle is continuously added to the aging kettle to ensure that the temperature rise is ≤ 2° C. The crystal growth time is 230 min, and the crystal size is maintained at 340-460 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 a pentaerythritol crystal product.

[0035] The obtained pentaerythritol crystal product has a D50 of 370 μm, a D90 of 590 μm, a repose angle of 31°, and a bulk density of 0.73 g / cm 3 .

[0036] Comparative Example 1

[0037] The difference between Comparative Example 1 and Example 1 is only the preparation stage of the initial base solution in step (2), and the rest is the same as Example 1.

[0038] Comparative Example 1 Preparation of the initial base liquid: Under stirring at 100°C and 100 rpm, an aqueous pentaerythritol solution of 8% of the inner cavity volume of the kettle was added to the nucleation kettle, the primary growth kettle, the secondary growth kettle and the aging kettle respectively as the initial base liquid, and pentaerythritol seeds of 120-150 μm and 10% of the mass of pentaerythritol in the pentaerythritol aqueous solution were added. Subsequently, the nucleation kettle, the primary growth kettle, the secondary growth kettle and the aging kettle were continuously fed and discharged under the action of pumps.

[0039] Figure 3 This is a scanning electron microscope (SEM) image of the pentaerythritol product obtained under the operating conditions of Comparative Example 1. It can be seen that the particle size distribution is poor, the agglomeration phenomenon is relatively serious, and there is no obvious crystal feature.

[0040] The obtained pentaerythritol product has a D50 of 200 μm, a D90 of 330 μm, a repose angle of 42°, and a bulk density of 0.62 g / cm 3 By comparison, it can be seen that when other conditions remain unchanged and too little initial bottom liquid is reserved, stirring will not work, heat and mass transfer will be limited, and obvious secondary nucleation will occur, which will lead to a significant reduction in product particle size and increase the difficulty of filtration and drying.

[0041] Comparative Example 2

[0042] The difference between Comparative Example 2 and Example 1 is only the nucleation reactor crystallization in step (3), and the rest is the same as Example 1.

[0043] Comparative Example 2 Nucleation kettle crystallization: Under stirring at a speed of 100 rpm, the temperature of the crystallization kettle was controlled to be 90°C, and the pentaerythritol aqueous solution was continuously added into the nucleation kettle, the temperature rose by ≤9°C, and the crystal growth time was 80-100 min.

[0044] The obtained pentaerythritol product has a D50 of 160 μm, a D90 of 320 μm, an angle of repose of 44°, and a bulk density of 0.63 g / cm 3 By comparison, it can be seen that when other conditions remain unchanged, if the temperature of the nucleation reactor rises too high, the supersaturation of the next growth reactor will be too high, and obvious secondary nucleation will occur, which will lead to a significant reduction in the product particle size and increase the difficulty of filtering and drying.

[0045] Comparative Example 3

[0046] The difference between Comparative Example 3 and Example 1 is only the crystallization step in the primary growth reactor, and the rest of the preparation method is the same as that of Example 1.

[0047] Comparative Example 3: Crystallization in the primary growth kettle: Under stirring at 200 rpm, the temperature was controlled to 55°C, and the pentaerythritol slurry suspension in the nucleation kettle was continuously added into the primary growth kettle to ensure that the temperature rise was ≤3°C, and the crystal growth time was 240-260min.

[0048] The obtained pentaerythritol product has a D50 of 180 μm, a D90 of 280 μm, a repose angle of 42°, and a bulk density of 0.65 g / cm 3 By comparison, it can be seen that when the temperature of the first-stage growth reactor is reduced to 55°C and other conditions remain unchanged, the average particle size of the crystal will be significantly reduced, which is not conducive to subsequent separation and drying.

[0049] Comparative Example 4

[0050] The difference between Comparative Example 4 and Example 1 is that the aging kettle crystallization step is not included, and the rest of the preparation method is the same as that of Example 1.

[0051] The obtained pentaerythritol product has a D50 of 150 μm, a D90 of 300 μm, an angle of repose of 46°, and a bulk density of 0.60 g / cm 3 By comparison, it can be seen that when the ripening kettle crystallization step is eliminated, the crystal size is relatively reduced, the production efficiency is reduced, and the waste liquid and waste solid generated increase.

[0052] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

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 initial bottom solution: adding 20% ​​of the volume of the inner cavity of the nucleation kettle, the primary growth kettle, the secondary growth kettle and the aging kettle as the initial bottom solution under stirring at 100-105° C. and 100-300 rpm, adding 1-10wt% of the mass of pentaerythritol in the pentaerythritol aqueous solution and 80-150 μm pentaerythritol seeds, and growing the crystals for 30-90 min. 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 performed respectively; (3) Nucleation reactor crystallization: under stirring at a speed of 100-300 rpm, control the temperature to 92-98° C., continuously add pentaerythritol aqueous solution into the nucleation reactor, ensure that the temperature rises by ≤5° C., crystal nucleation occurs, the crystal growth time is 70-110 min, 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, the temperature is controlled to 55-65° C., and the pentaerythritol slurry suspension in the primary growth kettle is continuously added to the secondary growth kettle for secondary growth of crystals, ensuring 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 in 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 min, 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 a pentaerythritol crystal product.

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

3. The continuous crystallization method of pentaerythritol crystals according to claim 1, characterized in that: 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 continuous crystallization method of pentaerythritol crystals according to claim 1, characterized in that: 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 continuous crystallization method of pentaerythritol crystals according to claim 1, characterized in that: 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, characterized in that: 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 primary growth kettle is continuously added to the secondary growth kettle for secondary growth of crystals, ensuring that the temperature rise is ≤3° C. The crystal growth time is 260-280 min, and the crystal size is maintained at 300-450 μm.

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

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