BHT (butylated hydroxytoluene) multistage melt crystallization purification method

Abstract

A multistage melt crystallization purification method for BHT (butylated hydroxytoluene) adopts a two-stage melt crystallization process and comprises the following steps: firstly, melting a crude product BHT, and then separating mother liquor M1 through first-stage crystallization (cooling to 60-65 DEG C at a speed of 0.5-2 DEG C / h); and then, carrying out secondary melting on the primary crystal, carrying out secondary crystallization (cooling to 65-68 DEG C at the speed of 0.1-0.5 DEG C / h) and separating mother liquor M2, carrying out gradient heating (0.1-0.5 DEG C / 20min) to 68-70 DEG C, sweating and discharging sweat M3, and finally, melting to obtain BHT liquid with the purity of more than or equal to 99.9%. And recycling the mother liquor M1 to a synthesis rectification process, and respectively returning the mother liquor M2 and the mother liquor M3 to the primary crystallizer and the secondary crystallizer for cyclic utilization. According to the method, a solvent is not needed, the yield is remarkably improved through mother liquor recycling, high-temperature decomposition is avoided, the product purity is high, the stability is good, the sliced finished product is not prone to discoloring, the technological process is energy-saving and efficient, and the method is suitable for industrial production of medicine and food-grade BHT.

Description

Technical Field

[0001] The invention relates to a BHT multi-stage melt crystallization purification method. Background Art

[0002] BHT is a commonly used antioxidant. Its industrial synthesis often contains unreacted monomers (such as p-cresol), isomers, and oxidation byproducts. For its synthesis method, see Chinese patent CN202010717563.8. Traditional purification methods (such as solvent recrystallization and distillation) have the following drawbacks:

[0003] 1) Risk of solvent residue (not meeting pharmaceutical / food grade standards);

[0004] 2) High-temperature distillation leads to thermal decomposition of BHT;

[0005] 3) The multi-step purification process is complex and energy-intensive.

[0006] Although melt crystallization can avoid the introduction of solvents, it is difficult to achieve high purity and high yield at the same time in a single crystallization step, and residual impurities in the mother liquor can easily lead to crystal encapsulation defects. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a BHT multi-stage melt crystallization purification method, which adopts a two-stage melt crystallization method, uses no solvent, has high product purity, and improves the yield by recycling the mother liquor. The finished product after slicing is not easy to change color, and is more energy-efficient than the traditional distillation process.

[0008] In order to solve the above technical problems, the present invention provides a BHT multi-stage melt crystallization purification method, comprising the following steps:

[0009] (1) heating the crude BHT until it is completely melted;

[0010] (2) Primary crystallization: Cool down to 60-65°C at 0.5-2°C / h to separate the mother liquor M1;

[0011] (3) Secondary crystallization: The crystals obtained from the primary crystallization are heated until completely melted, cooled to 65-68°C at a rate of 0.1-0.5°C / h, the mother liquor M2 is separated, and then the temperature is gradually increased to 68-70°C at a rate of 0.1-0.5°C / 20 min to induce sweating, and the sweat M3 is discharged. Finally, the temperature is increased to 75-80°C to melt and obtain BHT liquid with a purity of ≥99.9%;

[0012] (4) Melting and slicing: The secondary finished product is pumped into the melting slicer through the conveying pump, and then conveyed to the back-end packaging system through the auger conveyor;

[0013] The mother liquor M1 is recycled to the BHT synthesis distillation process, the mother liquor M2 is directly returned to the primary crystallizer, and the sweat liquid M3 is returned to the secondary crystallizer.

[0014] Advantages of the present invention: The present invention adopts a two-stage melt crystallization method, uses no solvent, has high product purity, and improves the yield by recycling the mother liquor. The finished product after slicing is not easy to change color, and is more energy-efficient than the traditional distillation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a process flow diagram of the present invention. DETAILED DESCRIPTION

[0016] Example 1:

[0017] See also Figure 1 A BHT multi-stage melt crystallization purification method comprises the following steps:

[0018] (1) Crude BHT (purity 98.3%) was heated to 75°C until completely melted;

[0019] (2) Primary crystallization: cooling to 61°C at 1°C / h to separate mother liquor M1 (accounting for 20% of the raw material mass);

[0020] (3) Secondary crystallization: The crystals obtained from the primary crystallization were heated to 75°C until completely melted, then cooled to 67°C at a rate of 0.3°C / h, and the mother liquor M2 (accounting for 10% of the raw material mass) was separated. The temperature was then increased to 69°C at a rate of 0.1-0.5°C / 20min to induce sweating, and sweat M3 (accounting for 5% of the raw material mass) was discharged. Finally, the temperature was increased to 75°C to melt and obtain BHT liquid with a purity of 99.93%;

[0021] (4) Melting and slicing: The secondary finished product is pumped into the melting slicer through the conveying pump, and then conveyed to the back-end packaging system through the auger conveyor;

[0022] The mother liquor M1 is recycled to the BHT synthesis distillation process, the mother liquor M2 is directly returned to the primary crystallizer, and the sweat liquid M3 is returned to the secondary crystallizer.

[0023] Example 2:

[0024] See also Figure 1 A BHT multi-stage melt crystallization purification method comprises the following steps:

[0025] (1) Crude BHT (purity 98.1%) was heated to 75°C until completely melted;

[0026] (2) Primary crystallization: cooling to 60°C at 1°C / h to separate the mother liquor M1 (accounting for 19% of the raw material mass);

[0027] (3) Secondary crystallization: The crystals obtained from the primary crystallization were heated to 75°C until completely melted, then cooled to 68°C at a rate of 0.3°C / h, and the mother liquor M2 (accounting for 9% of the raw material mass) was separated. The temperature was then increased to 70°C at a rate of 0.1-0.5°C / 20min for sweating, and sweat M3 (accounting for 4% of the raw material mass) was discharged. Finally, the temperature was increased to 75°C for melting to obtain BHT liquid with a purity of ≥99.91%;

[0028] (4) Melting and slicing: The secondary finished product is pumped into the melting slicer through the conveying pump, and then conveyed to the back-end packaging system through the auger conveyor;

[0029] The mother liquor M1 is recycled to the BHT synthesis distillation process, the mother liquor M2 is directly returned to the primary crystallizer, and the sweat liquid M3 is returned to the secondary crystallizer.

[0030] In the above embodiments, both the primary crystallization and the secondary crystallization adopt the existing plate crystallizer, and the melt slicing also adopts the existing melt slicing machine.

Claims

1. A BHT multi-stage melt crystallization purification method, characterized in that: The following steps are involved: (1) heating the crude BHT until it is completely melted; (2) Primary crystallization: Cool down to 60-65°C at 0.5-2°C / h to separate the mother liquor M1; (3) Secondary crystallization: The crystals obtained from the primary crystallization are heated until completely melted, cooled to 65-68°C at a rate of 0.1-0.5°C / h, the mother liquor M2 is separated, and then the temperature is gradually increased to 68-70°C at a rate of 0.1-0.5°C / 20 min to induce sweating, and the sweat M3 is discharged. Finally, the temperature is increased to 75-80°C to melt and obtain BHT liquid with a purity of ≥99.9%; (4) Melting and slicing: The secondary finished product is pumped into the melting slicer through the conveying pump, and then conveyed to the back-end packaging system through the auger conveyor; The mother liquor M1 is recycled to the BHT synthesis distillation process, the mother liquor M2 is directly returned to the primary crystallizer, and the sweat liquid M3 is returned to the secondary crystallizer.

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