CN103880581A - Crystallization method for p-xylene - Google Patents
Crystallization method for p-xylene Download PDFInfo
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- CN103880581A CN103880581A CN201210553056.0A CN201210553056A CN103880581A CN 103880581 A CN103880581 A CN 103880581A CN 201210553056 A CN201210553056 A CN 201210553056A CN 103880581 A CN103880581 A CN 103880581A
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Abstract
The invention relates to a crystallization method for p-xylene, and mainly solves the problems that energy consumption is large, precooler fouling is server and a crystal is difficult to wash in the prior art. According to the crystallization method, a mixed xylene raw material enters a raw material intermediate tank; an overflow mother liquid in a magma tank flows out from the upper part and enters a kettle-type crystallizer for crystallization, concentrated magma flows out from the lower part and is separated by a solid-liquid separator for obtaining a filtered mother liquid and p-xylene crystal, and the filtered mother liquid enters the kettle-type crystallizer for crystallization; the p-xylene crystal is heated and melt in a fusion tank; magma in the kettle-type crystallizer is divided into two portions and flows out, magma I is subjected to heat exchange by a casing pipe type crystallizer and returns to the kettle-type crystallizer, and magma II is concentrated by a thickening device for obtaining a pre-separated mother liquid and concentrated magma; and the concentrated magma is separated by the solid-liquid separator for obtaining p-xylene crystal and a crystallization filtered mother liquid, and p-xylene crystal returns to the magma tank. The technical scheme relatively well solves the problems and is applicable to industrial production of p-xylene.
Description
Technical field
The present invention relates to a kind of crystallization method of p-Xylol.
Background technology
P-Xylol is the important source material of polyester industrial, mainly for the production of pure terephthalic acid (PTA) or pure terephthalic acid's dimethyl ester (DMT), and then removing to produce polyester (PET) by PTA and DMT, separating mixed dimethyl is the main production method of p-Xylol.Xylol is mainly made up of p-Xylol, m-xylene, o-Xylol and ethylbenzene, and the boiling point between each component differs very little, larger but fusing point differs, and can adopt crystallization process separating paraxylene.
Patent US5498822 discloses a kind of crystallization method of separating paraxylene, and the method is first carried out pre-cooled to xylol raw material by pre-cooler, is then separated and is obtained highly purified p-Xylol product by single-stage crystallisation process.In actual crystallization production process, the temperature of refrigerant temperature and xylol raw material differs greatly, p-Xylol in raw material is easily at the heat-transfer surface crystallization of pre-cooler, thereby reduce the heat transfer effect of pre-cooler, when serious, can stop up pre-cooler, follow-up crystallisation process cannot normally be carried out, thereby need often pre-cooler to be cleaned.For kettle type crystallization device, stirring rake is difficult to accomplish to scrape wall and stirs, still wall will inevitably can form crystal dirt layer, thereby greatly affect heat transfer efficiency, though can reduce the crystal scale formation on still wall by the method that improves mixing speed, mixing speed is too fast, can make size of microcrystal greatly reduce, affect follow-up filtration washing operation, thereby, also need regularly kettle type crystallization device to be cleaned.The cleaning of carrying out frequently pre-cooler and crystallizer will increase the running cost of crystallization production process, is also unfavorable for the continuous and steady operation of production process.In single-stage crystallisation process, for obtaining the higher rate of recovery, Tc is conventionally lower, gained p-Xylol crystalline temp is also lower, therefore, and in the time using pure p-Xylol liquid product to wash, pure p-Xylol easily in washing process recrystallization separate out, and then obstruction filtration channel, make washing process be difficult to carry out, be difficult to obtain good washing effect.
Summary of the invention
Technical problem to be solved by this invention is that the energy consumption existing in the crystallization method of existing production p-Xylol is large, pre-cooler fouling is serious, crystal washs difficult problem, and a kind of crystallization method of new p-Xylol is provided.The method has advantages of that energy consumption is low, pre-cooler fouling light, crystal convenient for washing.
For solving the problems of the technologies described above, the present invention adopts technical scheme as follows: a kind of crystallization method of p-Xylol,
A) in the incoming stock tundish of xylol raw material, a part of raw material I turns back in raw material tundish after cooling through mother liquor heat exchanger and pre-cooler, and a part of raw material II enters in magma tank, and its Raw I is 1～100:1 with the ratio of the weight of raw material II;
B) the overflow mother liquor in magma tank flows out from top to enter and kettle type crystallization device, carries out crystallization, concentrated magma separates and obtains filtrated stock and p-Xylol crystal through solid-liquid separator from flow out bottom, filtrated stock enters and in kettle type crystallization device, carries out crystallization, wherein, overflow mother liquor is 0.1～10:1 with the ratio of the weight of filtrated stock;
C) p-Xylol crystal fusing after heating in melting tank, the p-Xylol of 5～30% weight returns to solid-liquid separator as washings, and the p-Xylol of 70～95% weight is as product introduction products pot;
D) magma in kettle type crystallization device is divided into two portions outflow, magma I turns back in kettle type crystallization device after extension type crystallizer heat exchange, magma II obtains pre-separation mother liquor and concentrated magma after thickener is concentrated, and wherein magma I is 1～100:1 with the ratio of the weight of magma II;
E) concentrated magma separates and obtains p-Xylol crystal and crystallization filtrated stock through solid-liquid separator, and p-Xylol crystal turns back in magma tank;
F) pre-separation mother liquor is divided into two strands after mixing with crystallization filtrated stock, first gang of crystalline mother solution I that accounts for 5～95% weight returns in crystallizer, second gang of crystalline mother solution II that accounts for 5～95% weight carries out xylol raw material I after cooling entering mother liquor tank through mother liquor heat exchanger, wherein, pre-separation mother liquor is 0.1～10:1 with the ratio of the weight of crystallization filtrated stock.
In technique scheme, preferred technical scheme, magma tank is adiabatic operation; Kettle type crystallization device is adiabatic operation; First gang of crystalline mother solution I that accounts for 5～95% weight turns back in double-pipe crystallizer; Overflow mother liquor and filtrated stock enter in double-pipe crystallizer; Preferred technical scheme, solid-liquid separator is whizzer, filter or crystal washing tower; Preferred technical scheme, thickener is gravity settling tank, solid-liquid cyclone.
In technique scheme, before xylol raw material enters crystallizer, utilize crystalline mother solution to carry out xylol raw material cooling, reclaimed the cold of crystalline mother solution, reduced the energy consumption of precooling process.Xylol raw material after precooling does not directly enter in crystallizer, but turn back in raw material tundish, from raw material tundish, drawing separately one raw material enters and in crystallizer, carries out crystallization again, its benefit is: the flow that enters the xylol raw material of pre-cooler can be very large, not limited by the feed rate of follow-up crystallizer, thereby can improve the flow velocity of raw material in pre-cooler, with the heat transfer effect of strengthening pre-cooler, can prevent that p-Xylol crystallization in precooling process from forming brilliant dirt simultaneously.The benefit that magma tank is set is: utilize the raw material that temperature is higher to heat up to crystal, both reclaimed the cold of crystal, and melted again parts of fine small-crystalline, the magma after intensification is convenient to solid-liquid separation, and the crystalline temp obtaining is higher, can prevent the recrystallization phenomenon of washings in washing process; Melt portions fine crystals can improve the crystal mean particle size in magma tank, is convenient to follow-up solid-liquid separation, and the p-Xylol after fusing can enter in follow-up crystallizer and carry out crystallization, can not cause product loss; Magma solid content in magma tank is lower, can not meet the charging requirement of follow-up whizzer, therefore the partial mother liquid in magma tank is shifted out by overflow, thereby magma is concentrated.Magma in kettle type crystallization device does not freeze by kettle type crystallization device, enter in double-pipe crystallizer and freeze but draw a part of magma, its benefit is: the adiabatic operation of kettle type crystallization device, without chuck refrigeration, can prevent that p-Xylol from forming brilliant scar at kettle type crystallization wall face; Magma freezes in double-pipe crystallizer, and the p-Xylol crystal of crystallization can be scraped by scraper in time, thereby guarantees the heat exchange efficiency of double-pipe crystallizer; Crystal in double-pipe crystallizer can continued growth in kettle type crystallization device, and oarse-grained crystal is conducive to follow-up solid-liquid separation process; The internal circulating load of magma can arrange very large, thereby the magma flow velocity in raising double-pipe crystallizer is with the heat transfer effect of reinforcement sleeves crystallizer.For guaranteeing that magma has good mobility in double-pipe crystallizer, the solid content in general control magma, below 35%, thereby turns back in crystallizer the solid content to regulate magma in crystallizer by a part of crystalline mother solution.For follow-up centrifugal separation equipment, for guaranteeing to reach optimum operation operating mode, the solid content in general requirement charging magma is 50～60%, therefore uses thickening apparatus to carry out pre-separation to magma, makes magma after concentrated meet the charging requirement of whizzer.Overflow mother liquor and filtrated stock directly do not enter kettle type crystallization device, but first after double-pipe crystallizer is cooling, turn back in kettle type crystallization device again, can reduce the magma internal circulating load that enters double-pipe crystallizer, reduce fragmentation and the wearing and tearing of crystal in course of conveying.
Use the crystallization method of production p-Xylol of the present invention to carry out the crystallization production of p-Xylol, the energy consumption for cooling of raw material precooling process has saved 31.8%, the cleaning interval of pre-cooler and double-pipe crystallizer can extend to 240 days by 90 days maximums, efficiently solve pre-cooler and the serious problem of double-pipe crystallizer fouling, in magma tank, utilize raw material to heat up to crystal, follow-up solid-liquid separation and crystal washing effect are improved, the purity of p-Xylol product reaches 99.9%, has obtained good technique effect.
Brief description of the drawings
Fig. 1 is the schematic flow sheet of the crystallization method of p-Xylol of the present invention.
Fig. 2 is the another kind of schematic flow sheet of the crystallization method of p-Xylol of the present invention.
Fig. 3 is the another kind of schematic flow sheet of the crystallization method of p-Xylol of the present invention.
Fig. 4 is the schematic flow sheet of the crystallization method of existing p-Xylol.
As described in Figure 1, in the incoming stock tundish 1 of xylol raw material a, a part of raw material b turns back in raw material tundish 1 after pre-cooled through mother liquor heat exchanger 2 and pre-cooler 3, and a part of raw material c enters in magma tank 4 crystal is heated up.Overflow mother liquor d in magma tank 4 flows out from top to enter and kettle type crystallization device 8, carries out crystallization, and concentrated magma e separates and obtains filtrated stock f and p-Xylol crystal g through solid-liquid separator 5, and filtrated stock f enters and in kettle type crystallization device 8, carries out crystallization.P-Xylol crystal g is fusing after heating in melting tank 6, and a part is washed the crystal in solid-liquid separator 5 as washings h, and a part enters products pot 7 as product i.Magma in kettle type crystallization device 8 divides two portions to flow out, and magma j turns back in kettle type crystallization device 8 after extension type crystallizer 9 heat exchange, and magma k obtains pre-separation mother liquor l and concentrated magma m after thickener 10 thickenings.Concentrated magma m separates and obtains p-Xylol crystal n and crystallization filtrated stock o through solid-liquid separator 11.P-Xylol crystal k turns back in magma tank 4, pre-separation mother liquor l is divided into two strands after mixing with crystallization filtrated stock o, first gang of crystallization filtrated stock p returns in kettle type crystallization device 8, and second gang of crystallization filtrated stock q carries out after cooling entering in mother liquor tank 12 to xylol raw material b by mother liquor heat exchanger 2.
As described in Figure 2, in the incoming stock tundish 1 of xylol raw material a, a part of raw material b turns back in raw material tundish 1 after pre-cooled through mother liquor heat exchanger 2 and pre-cooler 3, and a part of raw material c enters in magma tank 4 crystal is heated up.Overflow mother liquor d in magma tank 4 flows out from top to enter and kettle type crystallization device 8, carries out crystallization, and concentrated magma e separates and obtains filtrated stock f and p-Xylol crystal g through solid-liquid separator 5, and filtrated stock f enters and in kettle type crystallization device 8, carries out crystallization.P-Xylol crystal g is fusing after heating in melting tank 6, and a part is washed the crystal in solid-liquid separator 5 as washings h, and a part enters products pot 7 as product i.Magma in kettle type crystallization device 8 divides two portions to flow out, and magma j turns back in kettle type crystallization device 8 after extension type crystallizer 9 heat exchange, and magma k obtains pre-separation mother liquor l and concentrated magma m after thickener 10 thickenings.Concentrated magma m separates and obtains p-Xylol crystal n and crystallization filtrated stock o through solid-liquid separator 11.P-Xylol crystal k turns back in magma tank 4, pre-separation mother liquor l is divided into two strands after mixing with crystallization filtrated stock o, first gang of crystallization filtrated stock p returns in double-pipe crystallizer 9, and second gang of crystallization filtrated stock q carries out after cooling entering in mother liquor tank 12 to xylol raw material b by mother liquor heat exchanger 2.
As described in Figure 3, in the incoming stock tundish 1 of xylol raw material a, a part of raw material b turns back in raw material tundish 1 after pre-cooled through mother liquor heat exchanger 2 and pre-cooler 3, and a part of raw material c enters in magma tank 4 crystal is heated up.Overflow mother liquor d in magma tank 4 flows out from top to enter and double-pipe crystallizer 9, carries out crystallization, and concentrated magma e separates and obtains filtrated stock f and p-Xylol crystal g through solid-liquid separator 5, and filtrated stock f enters and in double-pipe crystallizer 9, carries out crystallization.P-Xylol crystal g is fusing after heating in melting tank 6, and a part is washed the crystal in solid-liquid separator 5 as washings h, and a part enters products pot 7 as product i.Magma in kettle type crystallization device 8 divides two portions to flow out, and magma j turns back in kettle type crystallization device 8 after extension type crystallizer 9 heat exchange, and magma k obtains pre-separation mother liquor l and concentrated magma m after thickener 10 thickenings.Concentrated magma m separates and obtains p-Xylol crystal n and crystallization filtrated stock o through solid-liquid separator 11.P-Xylol crystal k turns back in magma tank 4, pre-separation mother liquor l is divided into two strands after mixing with crystallization filtrated stock o, first gang of crystallization filtrated stock p returns in double-pipe crystallizer 9, and second gang of crystallization filtrated stock q carries out after cooling entering in mother liquor tank 12 to xylol raw material b by mother liquor heat exchanger 2.
As described in Figure 4, after pre-cooler 2 is pre-cooled, carry out crystallization from the xylol raw material a of head tank 1 in crystallizer 3, the magma b in crystallizer 3 obtains p-Xylol crystal c and crystallization filtrated stock d after solid-liquid separator 4 solid-liquid separation.P-Xylol crystal c melts in melting tank 5, and one is washed the crystal in solid-liquid separator 4 as washings e, and a part enters products pot 6 as product f.Crystallization filtrated stock d is divided into two strands, and first gang of crystallization filtrated stock g returns in crystallizer 3, and second gang of crystallization filtrated stock h enters mother liquor tank 7.
Below by embodiment, the present invention is further elaborated.
Embodiment
[embodiment 1]
The crystallization method of separating paraxylene of the present invention.
As described in Figure 1, in the incoming stock tundish 1 of xylol raw material a, temperature is 30 DEG C, flow is 1075kg/h, and p-Xylol content is 80wt%, and a part of raw material b turns back in raw material tundish 1 after pre-cooled through mother liquor heat exchanger 2 and pre-cooler 3, its flow is 5375 kg/h, part raw material c enters in magma tank 4 crystal is heated up, and its flow is 1075kg/h, and temperature is 15 DEG C.The service temperature of magma tank 4 is 3.5 DEG C, overflow mother liquor d flows out from top to enter and kettle type crystallization device 8, carries out crystallization, concentrated magma e separates and obtains filtrated stock f and p-Xylol crystal g through solid-liquid separator 5, filtrated stock f enters and in kettle type crystallization device 8, carries out crystallization, Tc is-17 DEG C, wherein, overflow mother liquor d is 0.6:1 with the ratio of the weight of filtrated stock f.P-Xylol crystal g is fusing after heating in melting tank 6, and temperature of fusion is 20 DEG C, and the p-Xylol of 20% weight washs the crystal in solid-liquid separator 5 as washings h, and the p-Xylol of 20% weight enters products pot 7 as product i.Magma in kettle type crystallization device 8 divides two portions to flow out, and magma j turns back in kettle type crystallization device 8 after extension type crystallizer 9 heat exchange, and its flow is 48m
3/ h, magma k obtains pre-separation mother liquor l and concentrated magma m after thickener 10 thickenings, and its flow is 2.7m
3/ h.Concentrated magma m separates and obtains p-Xylol crystal n and crystallization filtrated stock o through solid-liquid separator 11.P-Xylol crystal k turns back in magma tank 4, pre-separation mother liquor l is divided into two strands after mixing with crystallization filtrated stock o, first gang of crystallization filtrated stock p that accounts for 76% weight returns in kettle type crystallization device 8, second gang of crystallization filtrated stock q that accounts for 24% weight carries out after cooling entering in mother liquor tank 12 to xylol raw material b by mother liquor heat exchanger 2, wherein, pre-separation mother liquor l is 1.5:1 with the ratio of the weight of crystallization filtrated stock o.
[embodiment 2]
The crystallization method of production p-Xylol of the present invention.
According to the operational condition of embodiment 1, adopt the crystallization method of production p-Xylol as described in Figure 2, wherein, the flow of xylol raw material b is 10750kg/h.
[embodiment 3]
The crystallization method of production p-Xylol of the present invention.
According to the operational condition of embodiment 1, adopt the crystallization method of production p-Xylol as described in Figure 3, wherein, the flow of xylol raw material b is 16125kg/h.
[comparative example 1]
The crystallization method of existing production p-Xylol.
According to the operational condition of embodiment 1, adopt the crystallization method of production p-Xylol as described in Figure 4, the results are shown in Table 1 for it.
Table 1
| Comparative run | Embodiment 1 | Embodiment 2 | Embodiment 3 | Comparative example 1 |
| The p-Xylol rate of recovery (%) | 83 | 83 | 83 | 83 |
| P-Xylol purity (%) | 99.9 | 99.9 | 99.9 | 99.7 |
| The precooling energy consumption for cooling (%) that mother liquor heat exchange is saved | 31.8 | 31.8 | 31.8 | 0 |
| The pre-cooler cleaning interval (my god) | 120 | 180 | 240 | 90 |
| The kettle type crystallization device cleaning interval | Nothing | Nothing | Nothing | 90 |
| The double-pipe crystallizer cleaning interval | 120 | 180 | 240 | Nothing |
Can find out by comparative example, the method for separating paraxylene crystallization of the present invention has reduced the energy consumption of sepn process effectively, and the mother liquor cold of recovery accounts for 1/3 left and right of precooling institute energy requirement; Utilize the large flow circulation of raw material in pre-cooler effectively to prevent the scale formation in pre-cooler, extended the cleaning interval of pre-cooler; Utilize the large flow circulation of magma in double-pipe crystallizer effectively to prevent the scale formation in double-pipe crystallizer, extended the cleaning interval of double-pipe crystallizer; Meanwhile, because kettle type crystallization device is adiabatic operation, therefore without carrying out routine cleaning; Utilize raw material to heat up to crystal, improved solid-liquid separation and crystal washing effect, product purity is also improved.
Claims (7)
1. a crystallization method for p-Xylol, comprises the following steps:
A) in the incoming stock tundish of xylol raw material, a part of raw material I turns back in raw material tundish after cooling through mother liquor heat exchanger and pre-cooler, and a part of raw material II enters in magma tank, and its Raw I is 1～100:1 with the ratio of the weight of raw material II;
B) the overflow mother liquor in magma tank flows out from top to enter and kettle type crystallization device, carries out crystallization, concentrated magma separates and obtains filtrated stock and p-Xylol crystal through solid-liquid separator from flow out bottom, filtrated stock enters and in kettle type crystallization device, carries out crystallization, wherein, overflow mother liquor is 0.1～10:1 with the ratio of the weight of filtrated stock;
C) p-Xylol crystal fusing after heating in melting tank, the p-Xylol of 5～30% weight returns to solid-liquid separator as washings, and the p-Xylol of 70～95% weight is as product introduction products pot;
D) magma in kettle type crystallization device is divided into two portions outflow, magma I turns back in kettle type crystallization device after extension type crystallizer heat exchange, magma II obtains pre-separation mother liquor and concentrated magma after thickener is concentrated, and wherein magma I is 1～100:1 with the ratio of the weight of magma II;
E) concentrated magma separates and obtains p-Xylol crystal and crystallization filtrated stock through solid-liquid separator, and p-Xylol crystal turns back in magma tank;
F) pre-separation mother liquor is divided into two strands after mixing with crystallization filtrated stock, first gang of crystalline mother solution I that accounts for 5～95% weight returns in crystallizer, second gang of crystalline mother solution II that accounts for 5～95% weight carries out xylol raw material I after cooling entering mother liquor tank through mother liquor heat exchanger, wherein, pre-separation mother liquor is 0.1～10:1 with the ratio of the weight of crystallization filtrated stock.
2. the crystallization method of p-Xylol according to claim 1, is characterized in that magma tank is adiabatic operation.
3. the crystallization method of p-Xylol according to claim 1, is characterized in that kettle type crystallization device is adiabatic operation.
4. the crystallization method of p-Xylol according to claim 1, is characterized in that first gang of crystalline mother solution I that accounts for 5～95% weight turns back in double-pipe crystallizer.
5. the crystallization method of p-Xylol according to claim 1, is characterized in that overflow mother liquor and filtrated stock enter in double-pipe crystallizer.
6. the crystallization method of p-Xylol according to claim 1, is characterized in that solid-liquid separator is whizzer, filter or crystal washing tower.
7. the crystallization method of p-Xylol according to claim 1, is characterized in that thickener is gravity settling tank, solid-liquid cyclone.
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