Background technology
In pure terephthalic acid (PTA) production process, what adopt at present mostly is the liquid phase high-temperature oxidation, this technology is raw material with the p-Xylol, acetic acid is solvent, wherein acetic acid incomplete combustion generation ritalin is one of main side reaction, and this is the big and higher major cause of PTA production cost of acetic acid consumption amount.PTA manufacturer generally is recycled to ritalin in the oxidation reactor at present, to suppress the generation of ritalin, reduce the consumption of acetic acid, but this can not fundamentally solve the recycling problem of by-product methyl acetate.And methyl acetate hydrolysis is generated acetic acid and methyl alcohol, not only can solve the ritalin by-product recovery and utilize problem, and can provide important chemical material for Chemical Manufacture, acetic acid can be used as the raw material continuation recycle that PTA produces, and methyl alcohol also is important chemical material.The hydrolysis process of methyl acetate of domestic and foreign current mainly adopts exchange resin catalyzed hydrolysis process of fixed bed cation and reactive distillation catalytic hydrolysis process at present.
In recent years, Dichlorodiphenyl Acetate methyl esters catalytic hydrolysis has carried out a large amount of research both at home and abroad.CN1171174A has reported the method for ritalin reactive distillation hydrolysis system acetic acid and methyl alcohol, this reaction and rectification device comprises rectifying section, conversion zone and stripping section, under high water to ester ratio and high reflux ratio, the discharging of tower still, the methyl acetate hydrolysis rate reaches more than 99.5%, but the tower bottoms water content that this method for hydrolysis obtains is higher.The methyl acetate catalysis hydrolysis process of CN1927792A report comprises catalytic rectifying tower, hydrolyzed solution knockout tower, extractive distillation column, methanol rectifying tower, and wherein dilute acetic acid is delivered to the acetic acid concentration tower and carried dense.Because this technology catalytic distillation column overhead adopts total reflux operation, the discharging of tower still is only arranged, contain methyl alcohol, water, ritalin and acetic acid quaternary mixed solution in the tower bottoms, wherein methyl alcohol and ritalin, water and ritalin all form azeotrope, cause the later separation difficulty.
Summary of the invention
The objective of the invention is deficiencies such as, later separation difficulty higher at the existing tower bottoms water content of existing hydrolysis process of methyl acetate, and provide a kind of fixed-bed reactor and extraction-catalytic rectifying tower coupled pure terephthalic acid produce in catalytic hydrolysis process for by-product methyl acetate.
Technical scheme of the present invention is: catalytic hydrolysis process for by-product methyl acetate during a kind of pure terephthalic acid produces, and concrete steps are as follows:
1) by-product methyl acetate in pure terephthalic acid's production process and hydromassage you enter the fixed-bed reactor FBR that contains strong acid cation exchange resin catalyst than the mixed mixture A in 1:1~6 and carry out catalytic hydrolysis reaction;
2) the hydrolyzed solution B in the fixed-bed reactor introduces in the extraction-catalytic rectifying tower, and wherein extraction-catalytic rectifying tower T1 is followed successively by extraction-rectifying section 1, conversion zone 2, stripping section 3 from top to bottom; The water C that unhydrolysed ritalin and extraction-rectifying section 1 top add among the hydrolyzed solution B is in these tower conversion zone 2 reactions, cat head distillates ritalin and a spot of water E, be recycled in the fixed-bed reactor and react, the discharging of tower still is the mixed solution D of water, acetic acid and methyl alcohol;
3) extraction-catalytic rectifying tower T1 tower still discharging mixed solution D introducing methanol distillation column T2 separates, and cat head distillates methyl alcohol F, and the discharging of tower still is the mixed solution G of acetic acid and water.
Wherein temperature of reaction is 50~65 ℃ in the step 1) fixed-bed reactor, air speed be 0.5~1.5 cubic metre/(cubic meter reaction volume hour).Wherein loading catalyst is a storng-acid cation exchange resin in the fixed-bed reactor bed, 1~2 year work-ing life of catalyzer.
In the step 1; owing to contain some metal ion in the ritalin raw material from last workshop section; at first enter fixed-bed reactor; Zeo-karb in the fixed-bed reactor is on the one hand as hydrolyst; in addition can also be as the ion-exchanger of metal ion; thereby can protect the catalyzer in the conversion zone in extraction-catalytic rectifying tower, make the catalyst life of conversion zone filling in extraction-catalytic rectifying tower extend to 2~3 years greatly.The replacing of catalyzer is changed with respect to catalyzer in the extraction-catalytic rectifying tower and is wanted a lot of easily in the fixed-bed reactor, so this technology can reduce operation easier.
Hydrolyzed solution B in the said fixing bed bioreactor is 1/5~1/2 introducing from extraction-catalytic rectifying tower T1 stripping section top.
Among above-mentioned extraction-catalytic rectifying tower T1, the theoretical plate number of extraction-rectifying section 1 is 1~15, and conversion zone 2 theoretical plate numbers are 15~45, and stripping section 3 theoretical plate numbers are 10~20.
Above-mentioned steps 2) raw materials components mole ratio of ritalin is 2~8:1 in the water of extraction-rectifying section 1 top adding and the step 1); Reflux ratio is 1~5:1, the charging air speed be 0.05~0.5 cubic metre/(cubic meter reaction volume hour).Water as reactant simultaneously also as ritalin and the isolating extraction agent of methanol azeotrope.
Above-mentioned steps 3) among the methanol distillation column T2, reflux ratio is 0.5~5:1, theoretical plate number 15~50.
1 couple of the present invention describes in further detail below in conjunction with accompanying drawing.
Filling storng-acid cation exchange resin in the fixed-bed reactor FBR, extraction-catalytic rectifying tower T1 is divided into three parts: top extraction-rectifying section 1, middle part conversion zone 2, bottom stripping section 3, wherein extraction-rectifying section and stripping section load conventional fillers or column plate, and conversion zone filling storng-acid cation exchange resin is tied up bag or other catalytic distillation elements.Filling conventional fillers or column plate in the methanol distillation column.
Material A ritalin and water at first enter fixed-bed reactor FBR and carry out catalytic hydrolysis reaction.
Hydrolyzed solution in the fixed-bed reactor is that material B enters extraction-catalytic rectifying tower T1 stripping section top, material C (water) adds from extraction-rectifying section top, water as reactant simultaneously also as ritalin and the isolating extraction agent of methanol azeotrope, cat head extraction ritalin and a spot of water, partial reflux, partial material E (cat head extraction ritalin and a spot of water) is circulated among the fixed-bed reactor FBR; The mixed solution of tower still extraction acetic acid, first alcohol and water.
Material D (mixed solution of acetic acid, first alcohol and water) enters methanol distillation column T2 to be separated, and overhead product methyl alcohol is discharged as material F, and the mixed solution of tower still product acetic acid and water is discharged as material G.
Beneficial effect:
(1) owing to adopts fixed bed and extraction-catalytic distillation coupling and catalyzing hydrolysis process, more existing catalytic rectifying tower, hydrolyzed solution knockout tower, extractive distillation column, methanol rectifying tower four-column process flow technology, flow process shortening, equipment minimizing.And operation is easier, can cut down the consumption of energy greatly simultaneously.
(2) in the methyl acetate hydrolysis process, the charging water to ester ratio is the important factor that influences the methyl acetate hydrolysis rate, and ritalin separates with methanol azeotrope and often makes water as extraction agent, the total reflux operation that catalytic rectifying tower adopts in the off the beaten track ritalin reactive distillation of the present invention hydrolysis process is provided with extraction-rectifying section.In extraction-catalytic rectifying tower, water is added by extraction-rectifying section top, water at extraction-rectifying section as ritalin and the isolating extraction agent of methanol azeotrope, as the reactant reaction that is hydrolyzed, promptly a tower plays two towers, is extractive distillation column at conversion zone, it is again catalytic rectifying tower, obviously can obtain obvious energy-saving effect, thereby can realize that the cat head discharging is ritalin and a spot of water, the discharging of tower still is the mixed solution of acetic acid, first alcohol and water.Methanol Recovery Tata still extraction aqueous acetic acid, directly be sent to PTA produce in existing acetic acid recycle section carry out acetic acid and reclaim.
(3) the present invention reduces the extracting rectifying tower in the existing methyl acetate catalysis rectification hydrolysis technique, thereby reduces facility investment and energy consumption.
(4) under operation conditions optimization, the ritalin total conversion rate generally reaches 50%-95%, is up to more than 99%, and the mass concentration of methyl alcohol is for generally reaching 80%-99.5%, and is the highest by 99.9%, satisfy PTA produce in to the specification of quality of fuel methanol.
Embodiment
The invention will be further described below by specific embodiment, and each example operation condition is pressed in the table 1 and implemented.
Embodiment 1
Water and ritalin 6:1 in molar ratio enter fixed-bed reactor, 57 ℃ of temperature of reaction, air speed be 0.6 cubic metre/(cubic meter reaction volume hour), catalyzer is an Amberlyst35 type storng-acid cation exchange resin.T1 tower water and ritalin be 3:1 in molar ratio, T1 extraction-rectification section theoretical plate number 4, T1 conversion zone theoretical plate number 20, T1 stripping section theoretical plate number 15, reflux ratio 4.2,0.1 cubic metre of T1 tower air speed/(cubic meter reaction volume hour), T2 theoretical plate number 18, reflux ratio 4.5.
Embodiment 2
Water and ritalin 3:1 in molar ratio enter fixed-bed reactor, 52 ℃ of temperature of reaction, air speed be 0.9 cubic metre/(cubic meter reaction volume hour), catalyzer is 001 * 7 type storng-acid cation exchange resin.T1 tower water and ritalin be 5:1 in molar ratio, T1 extraction-rectification section theoretical plate number 13, T1 conversion zone theoretical plate number 31, T1 stripping section theoretical plate number 11, reflux ratio 1.4,0.3 cubic metre of T1 tower air speed/(cubic meter reaction volume hour), T2 theoretical plate number 34, reflux ratio 2.9.
Embodiment 3
Water and ritalin 1:1 in molar ratio enter fixed-bed reactor, 63 ℃ of temperature of reaction, air speed be 1.4 cubic metres/(cubic meter reaction volume hour), catalyzer is a D001 type storng-acid cation exchange resin.T1 tower water and ritalin be 7:1 in molar ratio, T1 extraction-rectification section theoretical plate number 8, T1 conversion zone theoretical plate number 43, T1 stripping section theoretical plate number 17, reflux ratio 3.0,0.4 cubic metre of T1 tower air speed/(cubic meter reaction volume hour), T2 theoretical plate number 45, reflux ratio 1.3.
Table 1
Detailed |
Example 1 |
Example 2 |
Example 3 |
FBR water ester mol ratio |
6.0 |
3.0 |
1.0 |
Temperature of reaction |
57℃ |
52℃ |
63℃ |
T1 tower water ester mol ratio |
3.0 |
5.0 |
7.0 |
The FBR air speed |
0.6 |
0.9 |
1.4 |
The T1 air speed |
0.1 |
0.3 |
0.4 |
The T1 reflux ratio |
4.2 |
1.4 |
3.0 |
T1 extraction-rectification section theoretical plate number |
4 |
13 |
8 |
T1 conversion zone theoretical plate number |
20 |
31 |
43 |
T1 stripping section theoretical plate number |
15 |
11 |
17 |
Catalyzer |
Amberlyst35 type Zeo-karb |
001 * 7 type Zeo-karb |
D001 type Zeo-karb |
The T2 reflux ratio |
4.5 |
2.9 |
1.3 |
The T2 theoretical plate number |
18 |
34 |
45 |
Methanol quality concentration/% |
93.5 |
98.5 |
99.9 |
Methyl acetate hydrolysis rate/% |
83.6 |
94.8 |
99.9 |