CN103772131A - Multi-stage crystallization method for producing p-xylene - Google Patents
Multi-stage crystallization method for producing p-xylene Download PDFInfo
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- CN103772131A CN103772131A CN201210412573.6A CN201210412573A CN103772131A CN 103772131 A CN103772131 A CN 103772131A CN 201210412573 A CN201210412573 A CN 201210412573A CN 103772131 A CN103772131 A CN 103772131A
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Abstract
The invention relates to a multi-stage crystallization method for producing p-xylene. The problems of high energy consumption, serious scaling of a precooler and difficulty in crystal washing in the prior art are mainly solved. According to the technical scheme, the method comprises the following steps: feeding mixed xylene raw materials into a raw material intermediate tank; causing overflow mother liquor in a crystal slurry tank to flow out of the upper part and enter a primary crystallizer for crystallization, causing concentrated crystal slurry to flow out of the lower part, performing separation to obtain filtered mother liquor and p-xylene crystals by using a solid-liquid separator, causing the filtered mother liquor to enter the primary crystallizer for crystallization, performing separation on the crystal slurry in the primary crystallizer to obtain p-xylene crystals and primary crystallized-filtered mother liquor by using the solid-liquid separator, and heating and melting the p-xylene crystals in a melting tank; dividing the primary crystallized-filtered mother liquor into two jets, performing separation on crystal slurry in a secondary crystallizer to obtain p-xylene crystals and secondary crystallized-filtered mother liquor, and returning the p-xylene crystals into the crystal slurry tank. According to the method, the problems are well solved; the method can be used for p-xylene crystallization production.
Description
Technical field
The present invention relates to a kind of multistage crystallization method of producing 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.Carry out frequently pre-cooler and clean the running cost that will increase crystallization production process, be also unfavorable for the continuous and steady operation of follow-up crystallisation 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, a kind of multistage crystallization method of new production p-Xylol is provided, and the method has that energy consumption is low, pre-cooler fouling is light, crystal washing is easy to advantage.
For solving the problems of the technologies described above, the present invention adopts technical scheme as follows: a kind of multistage crystallization method of producing 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 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 one-level crystallizer, carries out crystallization, concentrated magma is from flow out bottom, separate through solid-liquid separator, obtain filtrated stock and p-Xylol crystal, filtrated stock enters and in one-level crystallizer, carries out crystallization, wherein, overflow mother liquor is 0.1～10:1 with the ratio of the weight of filtrated stock;
C) magma in one-level crystallizer separates through solid-liquid separator, obtain p-Xylol crystal and one-level crystallization filtrated stock, described p-Xylol crystal is fusing after heating in melting tank, wherein, the described p-Xylol of 5～30% weight returns to solid-liquid separator as washings, and the described p-Xylol of 70～95% weight is as product introduction products pot;
D) one-level crystallization filtrated stock is divided into two strands, and first gang of one-level crystallization filtrated stock I that accounts for 5～95% weight returns in one-level crystallizer, and second gang of one-level crystallization filtrated stock II that accounts for 5～95% weight enters and in secondary crystallization device, carry out crystallization;
E) magma in secondary crystallization device separates and obtains p-Xylol crystal and secondary crystallization filtrated stock through solid-liquid separator, and p-Xylol crystal turns back in magma tank;
F) secondary crystallization filtrated stock is divided into two strands, first gang of secondary crystallization filtrated stock I that accounts for 5～95% weight returns in secondary crystallization device, and second gang of secondary crystallization filtrated stock II that accounts for 5～95% weight carries out xylol raw material I after cooling entering mother liquor tank through mother liquor heat exchanger.
In technique scheme, preferred technical scheme, magma tank is adiabatic operation; One-level crystallizer and secondary crystallization device are the vertical wall crystallizer of scraping, and its bottom is taper; First gang of one-level crystallization filtrated stock I that accounts for 5～95% weight turns back to the vertical tapered section of scraping wall crystallizer; First gang of secondary crystallization filtrated stock I that accounts for 5～95% weight turns back to the vertical tapered section of 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 carry out xylol raw material cooling, reclaimed the cold of crystallization filtrated stock, 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.
Vertical knot wall phenomenon of scraping wall crystallizer and can effectively prevent crystal, and conical lower portion can carry out partial concentration to magma, makes solid content in magma can meet the charging requirement of follow-up whizzer, guarantees that whizzer moves under optimum condition.For preventing the magma feed opening being blocked after concentrated, partial crystallization filtrated stock turns back to and crystallizer, is used for washing away feed opening from the tapered section of crystallizer, 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 under comparatively high temps, because crystalline temp is higher, therefore better, gained crystal can be directly as product in crystal washing; Isolate most of p-Xylol product by first step crystallisation process, thereby reduced the energy consumption for cooling of follow-up cryogenic crystallization process.Use the multistage 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 7%, the cleaning interval of pre-cooler can extend to 240 days by 90 days maximums, efficiently solve the serious problem of precool heat exchanger device fouling, in magma tank, utilize raw material to heat up to crystal, improved follow-up solid-liquid separation and crystal washing effect, the purity of p-Xylol product has reached 99.9%, has obtained 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, and 3 is pre-cooler, and 4 is magma tank, 5 is solid-liquid separator, and 6 is melting tank, and 7 is products pot, and 8 is one-level crystallizer, and 9 is solid-liquid separator, 10 is melting tank, and 11 is products pot, and 12 is secondary crystallization device, and 13 is solid-liquid separator, and 14 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 are cooling, and a part of raw material c enters in magma tank 4.Overflow mother liquor d in magma tank 4 flows out from top to enter and one-level crystallizer 8, carries out crystallization, and concentrated magma e separates and obtains filtrated stock f and p-Xylol crystal g through solid-liquid separator 5 from flow out bottom, and filtrated stock f enters and in one-level crystallizer 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 j in one-level crystallizer 8 separates and obtains crystallization filtrated stock k and p-Xylol crystal l through solid-liquid separator 9, p-Xylol crystal l is fusing after heating in melting tank 10, a part is washed the crystal in solid-liquid separator 9 as washings m, and a part enters products pot 11 as product n.One-level crystallization filtrated stock k is divided into two strands, and first gang of one-level crystallization filtrated stock o returns in one-level crystallizer 8, and second gang of one-level crystallization filtrated stock p enters and in secondary crystallization device 12, carry out crystallization.Magma q in secondary crystallization device 12 separates and obtains p-Xylol crystal r and secondary crystallization filtrated stock s through solid-liquid separator 13, and p-Xylol crystal r turns back in magma tank 4.Secondary crystallization filtrated stock s is divided into two strands, and first gang of secondary crystallization filtrated stock t returns in secondary crystallization device 12, and second gang of secondary crystallization filtrated stock u carries out xylol raw material b after cooling entering mother liquor tank 14 through mother liquor heat exchanger 2.
As described in Figure 2, 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 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 ℃, flow is 1075kg/h, and p-Xylol content is 95wt%, 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 ℃.The service temperature of magma tank 4 is 11 ℃, overflow mother liquor d flows out from top to enter and one-level crystallizer 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 one-level crystallizer 8, carries out crystallization, Tc is 4 ℃, wherein, overflow mother liquor d is 4:1 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 ℃, and the p-Xylol of 20% weight washs the crystal in solid-liquid separator 5 as washings h, and the p-Xylol of 80% weight enters products pot 7 as product i.Magma j in one-level crystallizer 8 separates and obtains crystallization filtrated stock k and p-Xylol crystal l through solid-liquid separator 9, p-Xylol crystal l is fusing after heating in melting tank 10, temperature of fusion is 20 ℃, the p-Xylol of 20% weight washs the crystal in solid-liquid separator 9 as washings m, and the p-Xylol of 80% weight enters products pot 11 as product n.One-level crystallization filtrated stock k is divided into two strands, and first gang of one-level crystallization filtrated stock o that accounts for 60% weight returns in one-level crystallizer 8, and second gang of one-level crystallization filtrated stock p that accounts for 40% weight enters in secondary crystallization device 12 and carry out crystallization, and Tc is-13 ℃.Magma q in secondary crystallization device 12 separates and obtains p-Xylol crystal r and secondary crystallization filtrated stock s through solid-liquid separator 13, and p-Xylol crystal r turns back in magma tank 4.Secondary crystallization filtrated stock s is divided into two strands, first gang of secondary crystallization filtrated stock t that accounts for 44% weight returns in secondary crystallization device 12, and second gang of secondary crystallization filtrated stock u that accounts for 56% weight carries out xylol raw material b after cooling entering mother liquor tank 14 through mother liquor heat exchanger 2.
[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-Xylol 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 find out by comparative example, the multistage crystallization method of production p-Xylol of the present invention has reduced the energy consumption of sepn process effectively, and the mother liquor cold of recovery has been saved the refrigerating duty of precooling process; 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 raw material to heat up to crystal, improved solid-liquid separation and crystal washing effect, product purity is also improved.
Claims (6)
1. a multistage crystallization method of producing 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 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 one-level crystallizer, carries out crystallization, concentrated magma is from flow out bottom, separate through solid-liquid separator, obtain filtrated stock and p-Xylol crystal, filtrated stock enters and in one-level crystallizer, carries out crystallization, wherein, overflow mother liquor is 0.1～10:1 with the ratio of the weight of filtrated stock;
C) magma in one-level crystallizer separates through solid-liquid separator, obtain p-Xylol crystal and one-level crystallization filtrated stock, described p-Xylol crystal is fusing after heating in melting tank, wherein, the described p-Xylol of 5～30% weight returns to solid-liquid separator as washings, and the described p-Xylol of 70～95% weight is as product introduction products pot;
D) one-level crystallization filtrated stock is divided into two strands, and first gang of one-level crystallization filtrated stock I that accounts for 5～95% weight returns in one-level crystallizer, and second gang of one-level crystallization filtrated stock II that accounts for 5～95% weight enters and in secondary crystallization device, carry out crystallization;
E) magma in secondary crystallization device separates and obtains p-Xylol crystal and secondary crystallization filtrated stock through solid-liquid separator, and p-Xylol crystal turns back in magma tank;
F) secondary crystallization filtrated stock is divided into two strands, first gang of secondary crystallization filtrated stock I that accounts for 5～95% weight returns in secondary crystallization device, and second gang of secondary crystallization filtrated stock II that accounts for 5～95% weight carries out xylol raw material I after cooling entering mother liquor tank through mother liquor heat exchanger.
2. the multistage crystallization method of production p-Xylol according to claim 1, is characterized in that magma tank is adiabatic operation.
3. the multistage crystallization method of production p-Xylol according to claim 1, is characterized in that one-level crystallizer and secondary crystallization device are the vertical wall crystallizer of scraping, and its bottom is taper.
4. the multistage crystallization method of production p-Xylol according to claim 3, is characterized in that in step d), and first gang of one-level crystallization filtrated stock I that accounts for 5～95% weight turns back to the vertical tapered section of scraping wall crystallizer.
5. the multistage crystallization method of production p-Xylol according to claim 3, is characterized in that in step f), and first gang of secondary crystallization filtrated stock I that accounts for 5～95% weight turns back to the vertical tapered section of scraping wall crystallizer.
6. the multistage crystallization method of production p-Xylol according to claim 1, is characterized in that solid-liquid separator is whizzer, filter or crystal washing tower.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105294384A (en) * | 2015-10-29 | 2016-02-03 | 中石化南京工程有限公司 | Device for separating p-xylene crystal |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| 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 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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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 |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105294384A (en) * | 2015-10-29 | 2016-02-03 | 中石化南京工程有限公司 | Device for separating p-xylene crystal |
| CN105294384B (en) * | 2015-10-29 | 2017-05-10 | 中石化南京工程有限公司 | Device for separating p-xylene crystal |
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