CN103880586B - The multistage crystallization method of p-Xylol - Google Patents
The multistage crystallization method of p-Xylol Download PDFInfo
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Abstract
The present invention relates to a kind of multistage 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, part 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; Magma in magma tank obtains pre-separation mother liquor and concentrated magma after thickener thickening, pre-separation mother liquor enters in first degree crystalline device and carries out crystallization, concentrated magma is separated through solid-liquid separator and obtains filtrated stock and paraxylene crystals, and filtrated stock enters in first degree crystalline device and carries out crystallization; Magma in first degree crystalline device is separated through solid-liquid separator and obtains paraxylene crystals and first degree crystalline filtrated stock, and paraxylene crystals is fusing after heating in melting tank; Magma in secondary crystallizer is separated through solid-liquid separator and obtains paraxylene crystals and secondary 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 crystallization production.
Description
Technical field
The present invention relates to a kind of multistage 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.Carry out the running cost that pre-cooler cleaning will increase crystallization production process frequently, be also unfavorable for the continuous and steady operation of later crystallization 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 multistage 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 multistage crystallization method of p-Xylol, comprises following step:
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) pre-separation mother liquor and concentrated magma is obtained after the magma thickening in magma tank, pre-separation mother liquor enters in first degree crystalline device and carries out crystallization, concentrated magma is separated through solid-liquid separator and obtains filtrated stock and paraxylene crystals, filtrated stock enters in first degree crystalline device and carries out crystallization, wherein, pre-separation 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 first degree crystalline device is separated through solid-liquid separator, obtain paraxylene crystals and first degree crystalline filtrated stock, paraxylene crystals is 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;
E) first degree crystalline filtrated stock is divided into two strands, and first gang of first degree crystalline filtrated stock I accounting for 5 ~ 95% weight returns in first degree crystalline device, and second gang of first degree crystalline filtrated stock II accounting for 5 ~ 95% weight enters in secondary crystallizer and carry out crystallization;
F) magma in secondary crystallizer is separated through solid-liquid separator, obtains paraxylene crystals and secondary crystallization filtrated stock, and paraxylene crystals turns back in magma tank;
G) secondary crystallization filtrated stock is divided into two strands, first gang of secondary crystallization filtrated stock I accounting for 5 ~ 95% weight returns in secondary crystallizer, and second gang of secondary crystallization filtrated stock II accounting for 5 ~ 95% weight enters mother liquor tank after mother liquor heat exchanger cools xylol raw material I.
In technique scheme, magma tank is adiabatic operation; First degree crystalline device and secondary crystallizer are vertically scrape wall crystallizer, are taper bottom it; First gang of first degree crystalline filtrated stock I accounting for 5 ~ 95% weight turns back to the vertical tapered section scraping wall crystallizer; First gang of secondary crystallization filtrated stock I accounting for 5 ~ 95% weight turns back to the vertical tapered section scraping wall crystallizer; Solid-liquid separator is whizzer, filter or crystal washing tower.
In technique scheme, before xylol raw material enters crystallizer, utilize crystallization filtrated stock to cool xylol raw material, reclaimed the cold of crystallization filtrated stock, decrease 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 utilizes thickener to concentrate the magma in magma tank, to meet the feed needs of follow-up whizzer.Vertically scrape the knot wall phenomenon that wall crystallizer effectively can prevent crystal, and conical lower portion can carry out partial concentration to magma, makes the solid content in magma can meet the feed needs of follow-up whizzer, ensure that whizzer runs under optimum condition.For preventing the magma feed opening being blocked after concentrating, partial crystallization filtrated stock turns back to crystallizer from the tapered section of crystallizer and is used for washing away feed opening, and regulates the magma solid content in crystallizer, to guarantee that crystallisation process carries out continuously.Use the benefit of multistage crystallization process to be: first step crystallisation process carries out at relatively high temperatures, because crystalline temp is higher, therefore crystal washing better, and gained crystal can directly as product; Isolate most of para-xylene product by first step crystallisation process, thus decrease the energy consumption for cooling of follow-up cryogenic crystallization process.
The crystallization using the multistage 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 7%, cleaning interval of pre-cooler maximumly can extend to 240 days by 90 days, efficiently solve the problem that the fouling of precool heat exchanger device is serious, 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 multistage crystallization method of production p-Xylol of the present invention.
Fig. 2 is the schematic flow sheet of the crystallization method of existing production p-Xylol.
In Fig. 1,1 is raw material tundish, and 2 is interchanger, 3 is pre-cooler, and 4 is magma tank, and 5 is thickener, 6 is solid-liquid separator, and 7 is melting tank, and 8 is products pot, 9 is first degree crystalline device, and 10 is solid-liquid separator, and 11 is melting tank, 12 is products pot, 13 is secondary crystallizer, and 14 is solid-liquid separator, and 15 is mother liquor tank.
In Fig. 2,1 is head tank, and 2 is pre-cooler, and 3 is crystallizer, and 4 is solid-liquid separator, and 5 is melting tank, and 6 is products pot, and 7 is mother liquor tank.
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 mother liquor heat exchanger 2 and pre-cooler 3 cool, and a part of raw material c enters in magma tank 4.Magma d in magma tank 4 obtains overflow mother liquor e and concentrated magma f after thickener 5 thickening, overflow mother liquor e flows out to enter first degree crystalline device 9 from thickener 5 top and carries out crystallization, concentrated magma f is separated through solid-liquid separator 6 and obtains filtrated stock g and paraxylene crystals h, and filtrated stock g enters in first degree crystalline device 9 and carries out crystallization.Paraxylene crystals h is fusing after heating in melting tank 7, and a part is washed the crystal in solid-liquid separator 6 as washings i, and a part enters products pot 8 as product j.Magma k in first degree crystalline device 9 is separated through solid-liquid separator 10 and obtains crystallization filtrated stock l and paraxylene crystals m.Paraxylene crystals m is fusing after heating in melting tank 11, and a part is washed the crystal in solid-liquid separator 10 as washings n, and a part enters products pot 12 as product o.Crystallization filtrated stock l is divided into two strands, and first gang of crystallization filtrated stock p returns in crystallizer 9, and second gang of crystallization filtrated stock q enters in secondary crystallizer 13 and carry out crystallization.Magma r in secondary crystallizer 13 is separated through solid-liquid separator 14 and obtains paraxylene crystals s and crystallization filtrated stock t.Paraxylene crystals s turns back in magma groove 4, crystallization filtrated stock t is divided into two strands, first gang of crystallization filtrated stock u returns in crystallizer 13, enters in mother liquor tank 15 after second gang of crystallization filtrated stock v is cooled by mother liquor heat exchanger 2 couples of xylol raw material b.
As described in Figure 2, 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 multistage 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 95wt%, 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 5375 kg/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 11 DEG C, magma d obtains overflow mother liquor e and concentrated magma f after thickener 5 thickening, overflow mother liquor e flows out to enter first degree crystalline device 9 from thickener 5 top and carries out crystallization, concentrated magma f is separated through solid-liquid separator 6 and obtains filtrated stock g and paraxylene crystals h, filtrated stock g enters in first degree crystalline device 9 and carries out crystallization, Tc is 4 DEG C, and wherein, overflow mother liquor e is 4:1 with the ratio of the weight of filtrated stock g.Paraxylene crystals h is fusing after heating in melting tank 7, and temperature of fusion is 20 DEG C, and the p-Xylol of 20% weight washs the crystal in solid-liquid separator 6 as washings i, and the p-Xylol of 80% weight enters products pot 8 as product j.Magma k in first degree crystalline device 9 is separated through solid-liquid separator 10 and obtains crystallization filtrated stock l and paraxylene crystals m.Paraxylene crystals m is fusing after heating in melting tank 11, and temperature of fusion is 20 DEG C, and the p-Xylol of 20% weight washs the crystal in solid-liquid separator 10 as washings n, and the p-Xylol of 80% weight enters products pot 12 as product o.Crystallization filtrated stock l is divided into two strands, and first gang of crystallization filtrated stock p accounting for 60% weight returns in crystallizer 9, and second gang of crystallization filtrated stock q accounting for 40% weight enters in secondary crystallizer 13 and carry out crystallization, and Tc is-13 DEG C.Magma r in secondary crystallizer 13 is separated through solid-liquid separator 14 and obtains paraxylene crystals s and crystallization filtrated stock t.Paraxylene crystals s turns back in magma groove 4, crystallization filtrated stock t is divided into two strands, first gang of crystallization filtrated stock u accounting for 44% weight returns in crystallizer 13, enters in mother liquor tank 15 after second gang of crystallization filtrated stock v accounting for 56% weight is cooled by mother liquor heat exchanger 2 couples of xylol raw material b.
[embodiment 2]
The multistage crystallization method of production p-Xylol of the present invention.
According to the operational condition of embodiment 1, adopt the multistage crystallization method of production p-Xylol as described in Figure 1, wherein, the flow of xylol raw material b is 10750kg/h.
[embodiment 3]
The multistage crystallization method of production p-Xylol of the present invention.
According to the operational condition of embodiment 1, adopt the multistage crystallization method of production p-Xylol as described in Figure 1, 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 2, 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 (%) | 95 | 95 | 95 | 95 |
| P-xylene purity (%) | 99.9 | 99.9 | 99.9 | 99.7 |
| The precooling energy consumption for cooling (%) that mother liquor heat exchange is saved | 7 | 7 | 7 | 0 |
| The pre-cooler cleaning interval (my god) | 120 | 180 | 240 | 90 |
Can be found out by comparative example, the multistage crystallization method of production p-Xylol of the present invention significantly reduces the energy consumption of sepn process, and the mother liquor cold of recovery has saved the refrigerating duty of precooling process; 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 raw material to heat up to crystal, improve solid-liquid separation and crystal washing effect, product purity have also been obtained raising.
Claims (4)
1. a multistage crystallization method for p-Xylol, comprises following step:
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) pre-separation mother liquor and concentrated magma is obtained after the magma thickening in magma tank, pre-separation mother liquor enters in first degree crystalline device and carries out crystallization, concentrated magma is separated through solid-liquid separator and obtains filtrated stock and paraxylene crystals, filtrated stock enters in first degree crystalline device and carries out crystallization, wherein, pre-separation 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 first degree crystalline device is separated through solid-liquid separator, obtain paraxylene crystals and first degree crystalline filtrated stock, paraxylene crystals is 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;
E) first degree crystalline filtrated stock is divided into two strands, and first gang of first degree crystalline filtrated stock I accounting for 5 ~ 95% weight returns in first degree crystalline device, and second gang of first degree crystalline filtrated stock II accounting for 5 ~ 95% weight enters in secondary crystallizer and carry out crystallization;
F) magma in secondary crystallizer is separated through solid-liquid separator, obtains paraxylene crystals and secondary crystallization filtrated stock, and paraxylene crystals turns back in magma tank;
G) secondary crystallization filtrated stock is divided into two strands, first gang of secondary crystallization filtrated stock I accounting for 5 ~ 95% weight returns in secondary crystallizer, and second gang of secondary crystallization filtrated stock II accounting for 5 ~ 95% weight enters mother liquor tank after mother liquor heat exchanger cools xylol raw material I;
Wherein, magma tank is adiabatic operation; First degree crystalline device and secondary crystallizer are vertically scrape wall crystallizer, are taper bottom it.
2. the multistage crystallization method of p-Xylol according to claim 1, is characterized in that first gang of first degree crystalline filtrated stock I accounting for 5 ~ 95% weight turns back to the vertical tapered section scraping wall crystallizer.
3. the multistage crystallization method of p-Xylol according to claim 1, is characterized in that first gang of secondary crystallization filtrated stock I accounting for 5 ~ 95% weight turns back to the vertical tapered section scraping wall crystallizer.
4. the multistage crystallization method of p-Xylol according to claim 1, is characterized in that solid-liquid separator is whizzer, filter or crystal washing tower.
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| CN202245149U (en) * | 2011-09-02 | 2012-05-30 | 中国石油化工股份有限公司 | Helical conveyor for crystal slurry |
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| CN101941883A (en) * | 2009-07-06 | 2011-01-12 | 中国石油化工股份有限公司上海石油化工研究院 | Method for preparing p-xylene by separating and crystallizing mixed xylenes |
| CN102372591A (en) * | 2010-08-23 | 2012-03-14 | 中国石油化工股份有限公司 | Crystallization method for p-xylene production |
| CN102372590A (en) * | 2010-08-23 | 2012-03-14 | 中国石油化工股份有限公司 | Crystallization method for preparing para-xylene from xylol |
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