CN103880581B - The crystallization method of p-Xylol - Google Patents
The crystallization method of p-Xylol Download PDFInfo
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- CN103880581B CN103880581B CN201210553056.0A CN201210553056A CN103880581B CN 103880581 B CN103880581 B CN 103880581B CN 201210553056 A CN201210553056 A CN 201210553056A CN 103880581 B CN103880581 B CN 103880581B
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Abstract
The present invention relates to a kind of crystallization method of p-Xylol, mainly solve the problem that the energy consumption existed in prior art is large, pre-cooler fouling is serious, crystal washing is difficult, the present invention is by adopting in the incoming stock tundish of xylol raw material; Overflow mother liquor in magma tank flows out to enter kettle type crystallization device from top and carries out crystallization, and be separated through solid-liquid separator after concentrated magma flows out from bottom and obtain filtrated stock and paraxylene crystals, filtrated stock enters in kettle type crystallization device and carries out crystallization; Paraxylene crystals is fusing after heating in melting tank; Magma in kettle type crystallization device is divided into two portions to flow out, and magma I turns back in kettle type crystallization device after extension type crystallizer heat exchange, and magma II obtains pre-separation mother liquor and concentrated magma after thickener is concentrated; Concentrated magma is separated through solid-liquid separator and obtains paraxylene crystals and crystallization filtrated stock, and paraxylene crystals turns back to the technical scheme in magma tank, solves this problem preferably, can be used in p-Xylol industrial production.
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 gone to produce polyester (PET) by PTA and DMT, separating mixed dimethyl is the main production process of p-Xylol.Xylol is primarily of p-Xylol, m-xylene, o-Xylol and ethylbenzene composition, and the boiling point difference between each component is very little, but fusing point difference is comparatively large, 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 by pre-cooler to xylol raw material, is then separated by single-stage crystallisation process and obtains highly purified para-xylene product.In the crystallization production process of reality, the temperature difference of refrigerant temperature and xylol raw material is very large, p-Xylol in raw material is easily at the heat-transfer surface crystallization of pre-cooler, thus reduce the heat transfer effect of pre-cooler, pre-cooler can be blocked time serious, later crystallization process normally cannot be carried out, thus need often to clean pre-cooler.For kettle type crystallization device, stirring rake is difficult to accomplish that scraping wall stirs, still wall inevitably will form crystal dirt layer, thus greatly affect heat transfer efficiency, though the method by improving mixing speed reduces the crystal scale formation on still wall, but mixing speed is too fast, size of microcrystal can be made greatly to reduce, affect follow-up filtration washing operation, thus, also need regularly to clean kettle type crystallization device.The cleaning carrying out pre-cooler and crystallizer frequently 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 usually lower, gained paraxylene crystals temperature is also lower, therefore, when using pure p-Xylol liquid product to wash, the easily recrystallization precipitation in washing process of pure p-Xylol, and then blocking 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 existed in the crystallization method of existing production p-Xylol is large, pre-cooler fouling is serious, the problem of crystal washing difficulty, provides a kind of crystallization method of new p-Xylol.The method has that energy consumption is low, pre-cooler fouling is light, the advantage of 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 mother liquor heat exchanger and pre-cooler cool, 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 to enter kettle type crystallization device from top and carries out crystallization, be separated through solid-liquid separator after concentrated magma flows out from bottom and obtain filtrated stock and paraxylene crystals, filtrated stock enters in kettle type crystallization device and carries out crystallization, wherein, overflow mother liquor is 0.1 ~ 10:1 with the ratio of the weight of filtrated stock;
C) paraxylene crystals fusing after heating in melting tank, the p-Xylol of 5 ~ 30% weight returns 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 to flow out, 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 is separated through solid-liquid separator and obtains paraxylene crystals and crystallization filtrated stock, and paraxylene crystals 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 accounting for 5 ~ 95% weight returns in crystallizer, second gang of crystalline mother solution II accounting for 5 ~ 95% weight enters mother liquor tank after mother liquor heat exchanger cools xylol raw material I, 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 accounting 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 cool xylol raw material, reclaimed the cold of crystalline mother solution, decreased 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, draw separately one raw material again enter in crystallizer and carry out crystallization, its benefit is: the flow entering the xylol raw material of pre-cooler can be very large, feed rate not by later crystallization device limits, thus the flow velocity of raw material in pre-cooler can be improved, to strengthen the heat transfer effect of pre-cooler, can prevent p-Xylol crystallization in precooling process from forming brilliant dirt simultaneously.The benefit arranging magma tank is: the raw material utilizing temperature higher heats up to crystal, both reclaimed the cold of crystal, and melted again part fine crystals, the magma after intensification is convenient to solid-liquid separation, and the crystalline temp obtained is higher, the recrystallization phenomenon of washings in washing process can be prevented; 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 later crystallization device and carry out crystallization, can not cause product loss; Magma solid content in magma tank is lower, can not meet the feed needs of follow-up whizzer, therefore the partial mother liquid in magma tank is shifted out by overflow, thus concentrates magma.Magma in kettle type crystallization device is not freezed by kettle type crystallization device, but draw a part of magma and enter in double-pipe crystallizer and freeze, its benefit is: the adiabatic operation of kettle type crystallization device, without the need to chuck refrigeration, can prevent p-Xylol from forming brilliant scar in kettle type crystallization wall face; Magma freezes in double-pipe crystallizer, and the paraxylene crystals of crystallization can be scraped by scraper in time, thus 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, thus the magma flow velocity improved in double-pipe crystallizer is with the heat transfer effect of reinforcement sleeves crystallizer.For guaranteeing that magma has good mobility in double-pipe crystallizer, a part of crystalline mother solution, below 35%, thus turns back in crystallizer to regulate the solid content of magma in crystallizer by the solid content in general control magma.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 the magma after concentrating meet the feed needs of whizzer.Overflow mother liquor and filtrated stock directly do not enter kettle type crystallization device, but first turn back in kettle type crystallization device again after double-pipe crystallizer cooling, then can reduce the magma internal circulating load entering double-pipe crystallizer, reduce the fragmentation of crystal in course of conveying and wearing and tearing.
The crystallization using the crystallization method of production p-Xylol of the present invention to carry out p-Xylol is produced, the energy consumption for cooling of raw material precooling process has saved 31.8%, cleaning interval of pre-cooler and double-pipe crystallizer maximumly can extend to 240 days by 90 days, efficiently solve pre-cooler and the serious problem of double-pipe crystallizer fouling, in magma tank, utilize raw material to heat up to crystal, improve follow-up solid-liquid separation and crystal washing effect, the purity of para-xylene product reaches 99.9%, achieves good technique effect.
Accompanying drawing explanation
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 through mother liquor heat exchanger 2 and pre-cooler 3 pre-cooled after turn back in raw material tundish 1, a part of raw material c enters in magma tank 4 and heats up to crystal.Overflow mother liquor d in magma tank 4 flows out to enter kettle type crystallization device 8 from top and carries out crystallization, and concentrated magma e is separated through solid-liquid separator 5 and obtains filtrated stock f and paraxylene crystals g, and filtrated stock f enters in kettle type crystallization device 8 and carries out crystallization.Paraxylene crystals 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 thickening.Concentrated magma m is separated through solid-liquid separator 11 and obtains paraxylene crystals n and crystallization filtrated stock o.Paraxylene crystals 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, enters in mother liquor tank 12 after second gang of crystallization filtrated stock q is cooled by mother liquor heat exchanger 2 couples of xylol raw material b.
As described in Figure 2, in the incoming stock tundish 1 of xylol raw material a, a part of raw material b through mother liquor heat exchanger 2 and pre-cooler 3 pre-cooled after turn back in raw material tundish 1, a part of raw material c enters in magma tank 4 and heats up to crystal.Overflow mother liquor d in magma tank 4 flows out to enter kettle type crystallization device 8 from top and carries out crystallization, and concentrated magma e is separated through solid-liquid separator 5 and obtains filtrated stock f and paraxylene crystals g, and filtrated stock f enters in kettle type crystallization device 8 and carries out crystallization.Paraxylene crystals 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 thickening.Concentrated magma m is separated through solid-liquid separator 11 and obtains paraxylene crystals n and crystallization filtrated stock o.Paraxylene crystals 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, enters in mother liquor tank 12 after second gang of crystallization filtrated stock q is cooled by mother liquor heat exchanger 2 couples of xylol raw material b.
As described in Figure 3, in the incoming stock tundish 1 of xylol raw material a, a part of raw material b through mother liquor heat exchanger 2 and pre-cooler 3 pre-cooled after turn back in raw material tundish 1, a part of raw material c enters in magma tank 4 and heats up to crystal.Overflow mother liquor d in magma tank 4 flows out to enter double-pipe crystallizer 9 from top and carries out crystallization, and concentrated magma e is separated through solid-liquid separator 5 and obtains filtrated stock f and paraxylene crystals g, and filtrated stock f enters in double-pipe crystallizer 9 and carries out crystallization.Paraxylene crystals 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 thickening.Concentrated magma m is separated through solid-liquid separator 11 and obtains paraxylene crystals n and crystallization filtrated stock o.Paraxylene crystals 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, enters in mother liquor tank 12 after second gang of crystallization filtrated stock q is cooled by mother liquor heat exchanger 2 couples of xylol raw material b.
As described in Figure 4, from the xylol raw material a of head tank 1 after pre-cooler 2 is pre-cooled, in crystallizer 3, carry out crystallization, the magma b in crystallizer 3 obtains paraxylene crystals c and crystallization filtrated stock d after solid-liquid separator 4 solid-liquid separation.Paraxylene crystals 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%, a part of raw material b through mother liquor heat exchanger 2 and pre-cooler 3 pre-cooled after turn back in raw material tundish 1, its flow is 5375kg/h, part raw material c enters in magma tank 4 and heats up to crystal, 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 to enter kettle type crystallization device 8 from top and carries out crystallization, concentrated magma e is separated through solid-liquid separator 5 and obtains filtrated stock f and paraxylene crystals g, filtrated stock f enters in kettle type crystallization device 8 and 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.Paraxylene crystals 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 obtain pre-separation mother liquor l and concentrated magma m after thickener 10 thickening, and its flow is 2.7m
3/ h.Concentrated magma m is separated through solid-liquid separator 11 and obtains paraxylene crystals n and crystallization filtrated stock o.Paraxylene crystals 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 accounting for 76% weight returns in kettle type crystallization device 8, enter in mother liquor tank 12 after second gang of crystallization filtrated stock q accounting for 24% weight is cooled by mother liquor heat exchanger 2 couples of xylol raw material b, 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-xylene 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 be found out by comparative example, the method for separating paraxylene crystallization of the present invention significantly reduces the energy consumption of sepn process, and the mother liquor cold of recovery accounts for about 1/3 of precooling institute energy requirement; Utilize the large discharge of raw material in pre-cooler to circulate the scale formation that effectively prevent in pre-cooler, extend the cleaning interval of pre-cooler; Utilize the large discharge of magma in double-pipe crystallizer to circulate the scale formation that effectively prevent in double-pipe crystallizer, extend the cleaning interval of double-pipe crystallizer; Meanwhile, because kettle type crystallization device is adiabatic operation, therefore without the need to carrying out routine cleaning; Utilize raw material to heat up to crystal, improve solid-liquid separation and crystal washing effect, product purity have also been obtained raising.
Claims (6)
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 mother liquor heat exchanger and pre-cooler cool, 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 to enter kettle type crystallization device from top and carries out crystallization, be separated through solid-liquid separator after concentrated magma flows out from bottom and obtain filtrated stock and paraxylene crystals, filtrated stock enters in kettle type crystallization device and carries out crystallization, wherein, overflow mother liquor is 0.1 ~ 10:1 with the ratio of the weight of filtrated stock;
C) paraxylene crystals fusing after heating in melting tank, the p-Xylol of 5 ~ 30% weight returns 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 to flow out, 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 is separated through solid-liquid separator and obtains paraxylene crystals and crystallization filtrated stock, and paraxylene crystals 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 accounting for 5 ~ 95% weight returns in crystallizer, second gang of crystalline mother solution II accounting for 5 ~ 95% weight enters mother liquor tank after mother liquor heat exchanger cools xylol raw material I, wherein, pre-separation mother liquor is 0.1 ~ 10:1 with the ratio of the weight of crystallization filtrated stock;
Wherein, magma tank is adiabatic operation.
2. the crystallization method of p-Xylol according to claim 1, is characterized in that kettle type crystallization device is adiabatic operation.
3. the crystallization method of p-Xylol according to claim 1, is characterized in that first gang of crystalline mother solution I accounting for 5 ~ 95% weight turns back in double-pipe crystallizer.
4. 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.
5. the crystallization method of p-Xylol according to claim 1, is characterized in that solid-liquid separator is whizzer, filter or crystal washing tower.
6. 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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