The application is based on dividing an application of following Chinese patent application:
Embodiment
Describe now the present invention in detail.
According to the present invention, during the preparation terephthalic acid, solid-liquid separates and washing step carries out continuously with individual equipment under certain pressure, this equipment can carry out obtaining the solid-liquid separating step of terephthalic acid cake from reaction mixture, also can wash the step of terephthalic acid cake, as, with equipment such as screening separating centrifuge, rotary vacuum filter, flat rubber belting formula strainers.Then, after the washing terephthalic acid cake, filter cake washes in the low atmosphere of pressure ratio washing step pressure, thereby just can utilize terephthalic acid cake and/or the interior of liquid that be attached on the filter cake can evaporate the liquid that is attached on the filter cake.
The method for preparing terephthalic acid according to the present invention comprises two reactions steps, i.e. oxidation step (A) and reduction reaction step (E), and each step links to each other with solid-liquid separating step and washing step.Carry out with single equipment commonly used with at least one solid-liquid separating step that links to each other and washing step in step (A) and the step (E), terephthalic acid cake prepared in these steps is washed to remove liquid attached to it.
Preferably, the solid-liquid separating step that links to each other with oxidation step or reduction reaction step and washing step carry out with single equipment commonly used, and terephthalic acid cake prepared in these steps is washed to remove the liquid that is attached on the filter cake.In this manual, step (A)~(D) refers to crude terephthalic acid (CTA) preparation process sometimes, and step (E)~(H) refers to purified terephthalic (PTA) preparation process sometimes.
[step (A)]
In step (A), to contain acetic acid in main solvent, under the condition that catalyzer exists, p-Xylol is by the oxidation of molecular oxygen institute.
Terephthalic acid is aromatic dicarboxylic acid, and according to the present invention, terephthalic acid can make with common processes.Typically, terephthalic acid can react under the condition that catalyzer exists by p-Xylol and molecular oxygen and make, and described catalyzer contains heavy metal, such as cobalt, iron and manganese, preferably contains salt and the bromine of these heavy metals.
Used reaction medium preferably mainly contains acetic acid.Be 2~6 times of p-Xylol consumption such as the consumption of acetic acid solvent.Except acetic acid, acetic acid solvent also can contain other component, such as water.The consumption of other component should not affect reaction, for example, account for gross weight 10% or lower.
Typically, the temperature that oxidizing reaction is carried out is 130~250 degrees centigrade, and preferred 150~230 degrees centigrade, pressure is 0.2~12Mpa, preferred 0.3~7Mpa, further preferred 1~3Mpa, most preferably 1~1.5Mpa.
The reactor that is used for oxidizing reaction has no particular limits, and the form of typical reactor is the complete tempering tank of belt stirrer.Reaction is preferably carried out continuously.Reaction times (mean residence time) is 30~300min.Oxidizing reaction can be carried out in a step.But in order to increase the transformation efficiency of p-Xylol, also can increase additional reactor to carry out oxidizing reaction in additional reactor in subordinate phase, temperature of reaction is slightly lower than the temperature in the main reactor, preferred 140~190 degrees centigrade.The form of the additional reactor in the subordinate phase except form is the reactor of complete mixing grooved, can be plug flow reactor.
Oxidizing reaction can be converted into terephthalic acid with the p-Xylol of 95wt% or more (preferred 99wt% or more), thereby makes slurries, and wherein, the xln that contains terephthalic acid is separated.The impurity of trace also may produce, and impurity typically has 4-carboxyl benzaldehyde (being also sometimes referred to as " 4-CBA ").Usually, in the prepared mixture of oxidizing reaction, the content of 4-CBA is 500~500ppm of terephthalic acid.
[step (B)]
Step (B) is the solid-liquid separating step, wherein, is separated into crude terephthalic acid filter cake and reaction mother liquor by the prepared slurries that contain terephthalic acid crystals of step (A).
Step (B) and subsequent step (C) preferably carry out with single general-purpose equipment.
And used crude terephthalic acid refers to and does not also carry out reduction reaction to remove the filter cake of 4-CBA here.Typical crude terephthalic acid contains the above 4-CBA of 500ppm that accounts for terephthalic acid.
Except the acetic acid as solvent, the reaction mother liquor by the solid-liquid resulting separation also contains water, heavy metal catalyst, byproduct of reaction, such as paratolunitrile, 4-CBA and methyl acetate.
Separate if the screening centrifuge decanter is used to solid-liquid, it operates under the centrifugal force of 500~2000G usually.
Solid-liquid separator operates being not less than under the atmospheric pressure usually, preferably is not less than 0.2Mpa, further preferably is not less than 0.3Mpa; And be not higher than 22Mpa, preferably be not higher than 12Mpa, further preferably be not higher than 7Mpa, particularly preferably be not higher than 1.5Mpa, most preferably be not higher than 1.2Mpa.And for more energy-efficient, solid-liquid separates preferably in the situation of the pressure of the oxidation reaction process that has kept at least a portion step (A) and carries out.
When step (A) finished, if the pressure that requires to increase in the solid-liquid separator makes it carry out step (B) under the pressure that is higher than step (A), the pressure of separator can increase with for example pump when transmitting slurries.
[step (C)]
In step (C), the crude terephthalic acid filter cake that is obtained by step (B) is not less than under the atmospheric condition at pressure, cleans with washings.As described below, step (C) and step before (B) are preferably carried out in single general-purpose equipment.
Washings has no particular limits, and can be aqueous solvent, also can be oil-based solvent.But preferably contain with as the acetic acid of the major constituent of oxidation solvent identical contain acetic acid solution.The acetic acid component preferably is not less than 90%, except acetic acid, and the acetate esters that vaporization heat is relatively low, all available such as methyl acetate, ethyl acetate, propyl acetate or butylacetate.
Pressure in the washing step is not less than normal atmosphere usually, preferably is not less than 0.2Mpa, further preferably is not less than 0.3Mpa; And be not higher than 22Mpa, preferably be not higher than 12Mpa, further preferably be not higher than 7Mpa, particularly preferably be not higher than 1.5Mpa, most preferably be not higher than 1.2Mpa.
[single general-purpose equipment]
In order to reduce according to the used number of devices of method of the present invention, step (B) and step (C) are preferably carried out in single general-purpose equipment.And by using single general-purpose equipment, solid-liquid separating step (B) can carry out under identical pressure with washing step (C).
Step (B) and the used single general-purpose equipment of step (C) can be flat rubber belting formula strainer, rotary vacuum filter or screening centrifuge decanter (screening separating centrifuge).Wherein, the screening centrifuge decanter is only.The integration apparatus that the screening centrifuge decanter is separated and washed for carrying out simultaneously solid-liquid.When reacted crude terephthalic acid filter cake passed washing position with strainer, washings was sprayed on the filter cake, with this washing leaching cake.After passing through strainer, washings can be separated from filter cake and be recovered.
The screening centrifuge decanter can be disclosed the sort of of WO98/18750 or WO93/24440.It is separated into solid and liquid with slurries under the effect of centrifugal force.Solid is placed in the washing position that is sent on the spiral plate with strainer.
Material and the shape of strainer have no particular limits.Such as, it can be porcelain filter, wire screen or metal diagrid.Select suitable a kind of after having considered erosion resistance and having stopped up tendency.If use the metal diagrid, that will select then that a part of filter cake can pass the sort ofly stops up avoiding.When screening drew off the centrifuge decanter, all mother liquors that are attached on the filter cake all had been removed at filter cake, and therefore, the contained impurity of such filter cake seldom.
In the screening centrifuge decanter, mother liquor and washings can reclaim respectively, but may have the part washings sneaks in the mother liquor.The ability of the washing leaching cake that screening centrifuge decanter tool is very high also under high pressure is suitable for industrial application.
If use the screening centrifuge decanter, the pressure in the pressure in the solid-liquid separating step (B) and the washing step (C) is basic identical.
[step (D)]
In the step (D), remain on the filter cake that is made by step (C)/or interior liquid be removed by evaporation.
Moisture eliminator used among the present invention has no particular limits,, as long as it can carry out any of drying operation described below, but be typically the possess discharge valve pressure drying device of (it is sometimes referred to as " valve ").Discharge valve has no particular limits, as long as it can be transported to low-tension side from the high-tension side with powder.It can be successive type or batch-type.For example, it can be disclosed the sort of of WO91/09661.Except single valve, also available such as a plurality of valves that United States Patent (USP) 5589079 is disclosed, disclosed valve or the valving of WO00/71226 or United States Patent (USP) 4127935 is also available.
In the discharge valve upstream, usually be equipped with filter cake reserved slit (filter cake chamber).The filter cake of washing and separation is retained in the filter cake reserved slit in step (C).Then by opening valve, filter cake is extracted in the powder storage tanks.The opening degree of valve is preferred controlled, so that total energy keeps a certain amount of filter cake in the filter cake reserved slit.
The working pressure of filter cake reserved slit and step (C) is basic identical.Pressure in the pressure ratio filter cake reserved slit in the powder storage tanks is low.By low pressure atmosphere is arrived in the press cake release (flushing) that adds in the filter cake reserved slit, be attached to the boiling point lowering of the liquid on the filter cake.Because the reduction of boiling point, sensible heat namely is stored in the interior energy in terephthalic acid cake and/or attached thereon the liquid, is used to evaporate the liquid that is attached on the filter cake.Before filter cake was about to draw off from the filter cake reserved slit, the temperature of filter cake (TB) preferably was higher than the liquid boiling point (Bp) under atmospheric pressure that is attached on the filter cake.
In the discharge valve upstream, the pressure in the moisture eliminator usually remains on and is not less than normal atmosphere, preferably is not less than 0.2Mpa, further preferably is not less than 0.3Mpa; And be not higher than 22Mpa, preferably be not higher than 12Mpa, further preferably be not higher than 7Mpa, particularly preferably be not higher than 1.5Mpa, most preferably be not higher than 1.2Mpa.
If the screening centrifuge decanter is used for carrying out step (B) and step (C), then the pressure in step (B) and the step (C) remains on and is not less than normal atmosphere.When terephthalic acid cake was transported in the filter cake reserved slit, terephthalic acid cake should keep their pressure in the screening centrifuge decanter in step (D).Therefore, the pressure in step (B) and step (C) and the pressure in the filter cake reserved slit of step (D) (being the pressure of valve upstream) all should be not less than normal atmosphere, preferably are not less than 0.2Mpa, further preferably are not less than 0.3Mpa; And be not higher than 22Mpa, preferably be not higher than 12Mpa, further preferably be not higher than 7Mpa, particularly preferably be not higher than 1.5Mpa, most preferably be not higher than 1.2Mpa.If the pressure gap between the pressure in barometric point and the above steps is too small, then in when flushing, it is not enough that the release of interior energy is tending towards, and therefore is difficult to the liquid on the filter cake of being attached to of evaporation q.s.If pressure is too large, then must increase the withstand voltage properties of various device and parts, this can improve the expense of whole plant.
Before being about to discharging, the temperature of filter cake need remain on 50~350 degrees centigrade, and preferred 100~300 degrees centigrade, further preferred 130~250 degrees centigrade.Be attached to liquid boiling point Bp and preferred 5~200 degrees centigrade of the difference (being that TB deducts Bp) between the temperature T B of filter cake before being about to discharging under atmospheric pressure on the filter cake, further preferred 10~150 degrees centigrade, particularly preferably 15~100 degrees centigrade.
The internal pressure of powder storage tanks preferably keeps 1 normal atmosphere, but in the flushing process, the gas that produces when being attached to the liquid evaporation on the filter cake can increase to the pressure of powder storage tanks a little higher than normal atmosphere, and this gas can be discharged from.In the case, the pressure of powder storage tanks can be brought down below normal atmosphere.
The steam that part steps (D) produces can be recovered and recycle in the step of preparation terephthalic acid.The steam that step (D) produces comprises that mainly filter cake when washing with washings, remains in the steam of the washings on the filter cake.If use in the step (C) acetic acid as washings, its steam then, namely acetic acid vapor can be by easily as the solvent of the oxidizing reaction of step (A).This steam is the reactor of supplying step (A) directly, and perhaps before supplied reactor, it can be condensed to reclaim its heat energy in heat exchanger.
And at least a portion is clamped into the step that the crystal that contains terephthalic acid in the steam that step (D) produces could be recovered and resupply the preparation terephthalic acid.When in step (D), utilize to be stored in filter cake and/or to be attached to interior in the liquid on the filter cake in the time of washing the crude terephthalic acid filter cake and be attached to liquid on the filter cake with evaporation, the pressure of system can sharply descend in a short period of time.This crystal that may cause containing terephthalic acid is clamped in the steam of the liquid evaporation generation that is attached on the filter cake.In order to improve the productive rate of terephthalic acid, the terephthalic acid crystals that this steam is carried secretly preferably is recovered.The crystal that reclaims can resupply CTA or PTA preparation process.But because the resulting crystal of step (D) has experienced oxidizing reaction, if only by reclaiming terephthalic acid crystals, the preferred supplying step of this crystal (E) such as bag filter.More preferably, the terephthalic acid crystals that is clamped in the steam that step (D) produces contacts to make slurries with the solution that mainly contains acetic acid, the direct or indirect supplying step of the slurries that obtain thus (A) and/or step (B).
[step (E)]
In step (E), the crude terephthalic acid that is made by step (D) is dissolved in the main moisture solvent, contacts at least a portion impurity of removing in the crude terephthalic acid filter cake with hydrogen by CTA under the condition that catalyzer exists.
When carrying out reduction reaction, solubleness is lower at normal temperatures owing to crude terephthalic acid, must be to its heating so that its be dissolved in the main moisture solvent.Reduction reaction is carried out under 230~330 degrees centigrade usually, preferred 250~310 degrees centigrade.Reduction reaction also must carry out keeping solvent to be in liquid state under the pressure that is higher than the solvent vapour pressure.Reduction reaction is carried out between 3~12Mpa usually, preferred 5~10Mpa.
In step (E), the 4-CBA that is included in the crude terephthalic acid is reduced into paratolunitrile.
[step (F)]
In step (F), the pressure and temperature of the reaction soln that is obtained by step (E) is lowered so that terephthalic acid crystallization in main moisture solvent.
Crystallization can be carried out continuously or intermittently carry out.Typically, crystallization is carried out continuously, and pressure reduces by 2~6 times, preferred 3~5 times in the mode that progressively reduces simultaneously.In crystallisation process, because the flash distillation of solvent, the temperature of system reduces.Because the solubleness of paratolunitrile in water that the 4-CBA reduction obtains is higher than terephthalic acid, the terephthalic acid preferential precipitation.If but Pressure Drop is to normal atmosphere, temperature will be down to about 100 degrees centigrade, cause thus paratolunitrile and terephthalic acid cocrystallization.Therefore, final crystallization pressure preferably is not less than 0.2Mpa, further preferably is not less than 0.3Mpa, especially preferably is not less than 0.5Mpa.Its upper limit preferably is not higher than 3Mpa, further preferably is not higher than 1Mpa, especially preferably is not higher than 0.7Mpa.The steam that produces in the crystallisation process can reclaim and be recycling in the step of preparation terephthalic acid.
[step (G)]
Step (G) is the solid-liquid separating step, and wherein, the slurries that contain terephthalic acid crystals that made by step (F) are separated into purified terephthalic filter cake and main moisture reaction mother liquor.
Here used " purified terephthalic " refers to the terephthalic acid that 4-CBA was wherein carried out reduction reaction.Contained 4-CBA is not higher than the 30ppm of terephthalic acid in the common purified terephthalic.
The solid-liquid separating step carries out with the mode identical with step (B), identical pressure basically.But in step (G), the upper limit of pressure range particularly preferably is not higher than 1Mpa, most preferably is not higher than 0.7Mpa.
Except the water as solvent, the reaction mother liquor of solid-liquid resulting separation also contains the paratolunitrile that the acetic acid, heavy metal catalyst, byproduct of reaction 4-CBA, the 4-CBA that sneak in a small amount of formerly oxidizing reaction obtain through reduction, etc.
[step (H)]
In step (H), the purified terephthalic filter cake that is obtained by step (G) washs with washings, except washings main moisture, this step is identical with step (C).
[single general-purpose equipment]
Step (G) and step (H) are preferably carried out in single general-purpose equipment, and it can be used the sort of in the step (C).
A kind of as in these equipment, the screening centrifuge decanter is the integration apparatus that a kind of solid-liquid lock out operation and washing operation all can carry out.When the purified terephthalic filter cake that obtains when reaction passed with the washing position of strainer, washings was sprayed on the filter cake, with this washing leaching cake.After passing through strainer, washings can be separated from filter cake and be recovered.But the part washings may be sneaked in the mother liquor.
Washings has no particular limits, and can be that aqueous solvent also can be oil-based solvent.But preferably as mother liquor, contain water as the liquid of its major constituent.Because the mother liquor that is attached on the filter cake can wash to remove with washings, when filter cake was discharged out from the screening centrifuge decanter, the foreign matter content of filter cake had reduced.But the part washings can be attached on the filter cake.
[step (I)]
In step (I), all are attached on the purified terephthalic/or interior liquid all be removed by evaporation, except purified terephthalic replaces crude terephthalic acid is dried, step (I) is identical with step (D).
[practical place of the present invention]
The invention is characterized in: the crystal that can reclaim respectively mother liquor, filtrate and have a small amount of liquid attached to it by simple operationss such as separation, washing and extractions.Because crystal can be with a small amount of liquids recovery attached to it, the volume that this just may omit independent moisture eliminator or reduce moisture eliminator, so can save energy.Mother liquor can be reclaimed without separating with filtrate.But since mother liquor in foreign matter content than slightly high in the filtrate, they preferably are separated from each other and respectively recycle in different steps.
The separable recyclability of mother liquor and filtrate has been brought for whole technical process and is highly profitable and actual advantage.Advantage is following listed.
At least a portion washings (washings of filtration) that is used for washing crude terephthalic acid filter cake can reclaim and be recycling in the step of preparation terephthalic acid after processing with it or with it.Because the foreign matter content in the filtrate is lower than in the isolated mother liquor, it can be used as the direct feed of solvent of oxidizing reaction to step (A).Filtrate can be used as also that absorption agent absorbs and reclaims the terephthalic acid crystals that is clipped in the solvent vapour that step (D) produces.
Reclaim the crystal that contains terephthalic acid from least part of filtrate for washing crude terephthalic acid filter cake, and also be possible with the step that the crystal that reclaims resupplies the preparation terephthalic acid.Crystal can solid-liquid separates or impel terephthaldehyde's acid crystal to reclaim through reducing temperature or pressure by filtrate is directly carried out.The common method that any solid-liquid separates all can be in order to reach this purpose, such as centrifugal separation, filtration method or the precipitator method.The crystal that reclaims can resupply any oxidation step or hydrogen reduction step.But because these reactions are finished basically, therefore preferably supply with oxidation step, particularly step (A) and/or step (B).
And, reclaim at least a portion contains the acetic acid of separating by slurries being carried out solid-liquid separate from the crude terephthalic acid slurries mother liquor, and in the step of preparation terephthalic acid, carry out recycle with the mother liquor of recovery or with the mother liquor after its processing.For example, the oxidation solvent that such mother liquor can be used as step (A) is recycled, because it contains a lot of useful components, comprises catalyst for oxidation reaction and reaction medium.
From at least a portion mainly contains the mother liquor of the acetic acid of separating by slurries being carried out solid-liquid separate from the crude terephthalic acid slurries, reclaim the crystal that contains terephthalic acid, and the crystal that reclaims to be resupplied in the step of preparation terephthalic acid also be possible.Crystal can be directly will separate the solid-liquid lock out operation that the mother liquor that obtains adds through solid-liquid, and perhaps isolated mother liquor reclaims with the solid-liquid lock out operation that adds again after impelling crystallization through cooling or step-down at mother liquor and obtains.The additional solid-liquid lock out operation that carries out after impelling crystallization can carry out with any separation method commonly used, such as centrifugal separation, filtration method or the precipitator method.The crystal that reclaims can resupply any oxidation step or hydrogen reduction step, but preferred supplying step (A), because contain acetic acid solvent in the crystal.
The temperature and pressure and the temperature and pressure in the solid-liquid sepn process that separate the mother liquor that obtains through solid-liquid are substantially the same.The mother liquor that separates is preferably supplied with oxidation step when keeping temperature and pressure.By with high temperature mother liquor supplied reactor, can reduce that oxidation reaction product is heated to predetermined required energy or the sensible heat of temperature of reaction.This helps the recovery of energy in the oxidation reaction process.If but all recycles of separation mother liquor, then contained impurity tends to accumulate in system in the mother liquor, thereby reduces the quality of the terephthalic acid of solid-liquid separation gained.Therefore, the separation mother liquor (preferred 10~30%) of part must be cleaned to prevent the accumulation of impurity.Mother liquor after the purification contains acetic acid solvent and is used for the catalyzer of oxidizing reaction, and the derivative and next organic impurity of the impurity from the p-Xylol raw material, such as M-nitro benzoic acid.Keep high temperature such as fruit mother liquor, the mother liquor after the purification also may contain the terephthalic acid that is contained in the separation mother liquor.Mother liquor after the purification is condensed to evaporate has high boiling component as the residual solvent of residue.Residue contains as the cobalt compound of catalyst component and manganic compound and organic impurity.Catalyst component can reclaim in follow-up catalyst recovery and circulation step and circulate.In order to reclaim the terephthalic acid that is dissolved in the high temperature mother liquor, by evaporating solvent, mother liquor is rinsed and condensation.When mother liquor came condensation by flushing and cools off, terephthalic acid can precipitate.Throw out can separate to reclaim by solid-liquid.Reclaim thus the solid ingredient that obtains and preferably supply with oxidation step.Behind the mother liquor that separates by solid-liquid through purifying, from residual separation solution, can selectively separate and reclaim active substance such as acetic acid, water and catalyzer, and the separation that obtains thus and recover materials can recycles in the step of preparation terephthalic acid.
And, be recovered and directly or after processing be recycling in the step for preparing terephthalic acid by the purified terephthalic slurries being carried out resulting, the main moisture separation mother liquor at least a portion of solid-liquid separation.Separate mother liquor and can carry out solid-liquid separation, distillation or purify with film, and the reduction reaction solvent cycle that can be used as step (E) is utilized.
And, from least a portion of the mother liquor that mainly contains the water of separating from purified terephthalic, can reclaim the crystal that contains terephthalic acid.The crystal that reclaims can resupply the step of preparation terephthalic acid.Crystal preferably by condensation and/or refrigerated separation mother liquor with the precipitation terephthalic acid crystals, then mother liquor is carried out solid-liquid separation and reclaims and obtain.Solid-liquid separation can adopt any method commonly used, such as centrifugal separation, filtration method and the precipitator method.Reclaim thus the crystal (secondary crystal) that obtains and to resupply oxidation step or hydrogen reduction step.But because their intermediate content is higher, therefore preferably supply with one of them of oxidation step, especially step (A), resulting mother liquor (secondary mother liquid) also can be direct or indirect here is recycled as the solvent of the reduction reaction of step (E).
And at least a portion that is used to wash the washings (filtrate) of refining terephthalic acid cake can reclaim and directly or after treatment be recycling in the step of preparation terephthalic acid.Because the foreign matter content of the washings that obtains that reclaims is lower, it can be used as the reduction reaction solvent of step (E) easily.The filtrate that obtains that reclaims can be distilled or purify with film.It also can be used as the terephthalic acid crystals that absorption agent is used for absorbing and reclaiming the solvent vapour that sandwiches step (I) generation.
If be used for the washings of the refining terephthalic acid cake of washing contain just like, the terephthalic acid by strainer, the crystal that contains terephthalic acid can reclaim from least part of washings by solid-liquid separation, and resupplies the step of preparation terephthalic acid.Crystal can carry out solid-liquid separation after temperature or pressure make its crystallization and obtains by the direct solid-liquid separation of washings or through reducing.Solid-liquid separation can adopt any common method, such as centrifugal separation, filtration method and the precipitator method.The crystal that reclaims can resupply the preparation process of CTA or PTA, but since their reaction be done, therefore preferred supplying step (F) and/or separating step (G).
At least a portion of the steam that step (I) produces can reclaim and be recycling in the step of preparation terephthalic acid.The steam that step (I) produces is mainly the washings steam that is attached on the filter cake in the washing process of step (H).Therefore, if in the step (H), water is as washings, and water vapour produces in step (I).Such water vapour can be used as the reduction reaction solvent of step (E) easily.Such steam is the reactor of supplying step (E) directly, and perhaps before supplied reactor, it can be condensed to reclaim its heat energy in heat exchanger.
At least a portion that sandwiches the crystal that contains terephthalic acid in the steam that step (I) produces can be recovered and be recycling in the step of preparation terephthalic acid.When the purified terephthalic filter cake is rinsed to utilize the interior energy that is stored in filter cake and/or is attached to the liquid on the filter cake in step (I), when boiling off the liquid that is attached on the filter cake, pressure in the system sharply descends in a short period of time, and this crystal that may cause containing terephthalic acid sandwiches in the steam that is attached to the liquid on the filter cake.In order to improve the productive rate of terephthalic acid, the terephthalic acid crystals that this steam is carried secretly preferably reclaims.The crystal that reclaims can resupply the preparation process of CTA or PTA.But because resulting crystal has passed through reduction reaction and washing, it can be used as the finished product.Terephthalic acid crystals is preferably with the form of slurries, by slurries are contacted to reclaim with main moisture solution.The slurries that obtain thus can supplying step (E)~(G).
[preferred implementation]
With reference now to Fig. 1, preferred implementation according to preparation method of the present invention is described.
Among Fig. 1, numeral 1 is the used oxidation reactor of step (A); 2 is crystallizer tank; 3 for carrying out the separator/washer of step (B) and step (C); 4 is the powder storage tanks.Between separator/washer 3 and powder storage tanks, have filter cake reserved slit and discharge valve (all not shown).Separator/washer 3 prepared crude terephthalic acid filter cakes wash into powder storage tanks 4 from the filter cake reserved slit, and the liquid that here is attached on the filter cake is evaporated.Numeral 5 is the used reduction reactor of step (E); 6 is the used crystallizer tank of step (F); 7 for carrying out the separator/washer of step (G) and step (H); 8 is moisture eliminator.Between separator/washer 7 and moisture eliminator 8, have filter cake reserved slit and discharge valve (all not shown).Separator/washer 7 prepared purified terephthalic are rinsed moisture eliminator 8 and are attached to all liquid on the filter cake with evaporation.Moisture eliminator 8 also plays the powder storage tanks simultaneously.Because the liquid that is attached on the filter cake mainly is water, simply it can not be evaporated fully by flushing, so filter cake carries out drying in moisture eliminator 8.
Numeral 11 represents solvent recovering system (such as distillation column).The mother liquor that it stays after with oxidizing reaction becomes single component with the mixture separation that contains acetic acid that obtains from other position of flow process.Mother liquor contains the acetic acid as solvent, water and high boiling component such as impurity and the catalyst for oxidation reaction that oxidizing reaction produces.Acetic acid can be supplied with oxidation reactor 1 by pipeline 110.Water can be conveyed into by pipeline 112, and, goes out of use or recycle when purifying or after purifying as process water.Remain in the impurity of bottom land, then after having reclaimed useful component such as catalyzer, go out of use.
Can after washing, be transported to oxidation reactor by pipeline 131 for separating of the washings in device/washer 3 (mainly containing acetic acid).If need and will separate with washings through the terephthalic acid of strainer, then washings is transported in the solid-liquid separator 31 by pipeline 132.The on stream recycle of the terephthalic acid that separates and acetic acid.
When terephthalic acid cake was washed into the powder storage tanks, the liquid that is attached on the filter cake evaporated and gasifies with sandwiching part terephthalic acid in gas.The gas that contains terephthalic acid crystals is responded into liquid and is transported to solid-liquid separator 41 to be isolated into terephthalic acid and mainly to contain the solution of acetic acid.On the other hand, in solid withdrawer 42, the terephthalic acid crystals that sandwiches in gas contacts to obtain slurries with acetic acid, and gas is condensed.Slurries and phlegma are supplied to oxidation reactor by pipeline 101.
Be transported to solid-liquid separator from separator/washer 7 mother liquors that separate, that be used for reduction reaction by pipeline 121.In solid-liquid separator 21, terephthalic acid and the reaction intermediate that is precipitated out by condensation and/or refrigerated separation mother liquor such as paratolunitrile is separated and reclaim.Main moisture residue reaction mother liquor goes out of use, perhaps purifies by evaporation or with film, and as the process water recycle.Contained active substance in the water can be reclaimed by ion-exchange or absorption such as catalyst for oxidation reaction or paratolunitrile.
The used filtrate (solution is mainly moisture) of separator/washer 7 is transported to solid-liquid separator 51 by pipeline 151 after washing.In solid-liquid separator 51, contain the solid ingredient of the terephthalic acid that sees through from strainer and washings by separated from one another.The isolated terephthalic acid of institute and water can be recycling in the flow process respectively.In this case, solid ingredient preferably is returned in the crystallizer tank 6, and isolated washings preferably is returned in the reduction reactor 5 simultaneously.The washings itself that contains terephthalic acid also can be recovered during the course and need not pass through solid-liquid separator 51.
When terephthalic acid cake was rinsed into moisture eliminator 8, the liquid that is attached on the filter cake evaporated and gasifies with sandwiching part terephthalic acid in gas.The gas that contains terephthalic acid is condensed into liquid state and is transported to solid-liquid separator 61, and is separated into terephthalic acid and main moisture liquid attached to it.On the other hand, in solid recovery system 62, the terephthalic acid crystals that sandwiches in gas contacts to obtain slurries with water, simultaneously the gas cold liquid that congeals into.Slurries and phlegma can be transported to any one of reduction reactor 5, crystallizer tank 6 or separator/washer 7.
Solid- liquid separator 21,31,41,51,61 any one clearer may be equipped with all.By solid separated from one another and liquid, or independent solid or independent liquid all can resupply by pipeline 101,102,103,105,106,107,171,175,176 and/or 177 any one step of preparation terephthalic acid.Solid may be in the same place by remix with liquid, and, when walking around solid-liquid separation step, solidliquid mixture also can pass through any one step of pipeline 101,102,103,105,106,107,171,175, the standby terephthalic acid of 176 and/or 177 direct the supply systems.Its part also can go out of use.Final product is by pipeline 109 dischargings.
[embodiment]
Describe now embodiments of the invention, must be understood that by people, the present invention be not limited to for embodiment.
P-Xylol, 5 times of weight are fed in the acetic acid of p-Xylol and as Cobaltous diacetate, manganese acetate and the hydrogen bromide of catalyzer and can produce in the liquid-phase oxidation reactor in workshop of terephthalic acid with 39 tons speed per hour, and be 197 degrees centigrade in temperature, pressure is oxidizing reaction 90 minutes (average retention time) under the condition of 1.45Mpa.Catalyzer uses with such amount: the total content of cobalt metal is the 280ppm of weight of solvent, and the total content of manganese is the 280ppm of weight of solvent, and the total content of bromine is the 700ppm of weight of solvent.
Gas as for carry out oxidizing reaction with molecular oxygen can use air.Airborne oxygen content is 21%.Pressurized air is supplied to reactor, and the volume content of oxygen is 5% from the gas (back refers to waste gas sometimes) of reactor discharging.Then, through continuous being transported in the additional oxidation reactor of low temperature of the slurries of oxidation, and the air (oxygen content: 21%) also be supplied to as oxidizing reaction gas, with at 190 degrees centigrade, 1.3Mpa condition under carry out the additional oxidizing reaction 35 minutes (average retention time) of low temperature, thereby the volume content of oxygen is 6% in the waste gas.
The slurries that made by the additional oxidizing reaction of low temperature under atmospheric pressure carry out solid-liquid separation continuously in three grades of intermediate treatment grooves, the crude terephthalic acid particle is dry in moisture eliminator as thermal source with steam.
Dry terephthaldehyde's granulates is converted into water-soluble serous, then adds hydrogen purification in the reduction reaction atmosphere of 280 degrees centigrade and 8Mpa.Then, it is carried out continuous crystallisation.In last crystallizer tank, pressure is reduced to 0.62Mpa, and temperature is reduced to 160 degrees centigrade.
[embodiment 1]
The slurries that contain purified terephthalic that aforesaid way obtains are admitted in the integrated screening centrifuge decanter of separator/washer in (screening separating centrifuge), and then filter cake is by flush valve (discharge valve).Used flush valve is disclosed the sort of of WO91/09661.Be 0.64Mpa at the pressure that is configured in the filter cake reserved slit of valve upstream, the powder storage tanks that is configured in the valve downstream then is exposed under the normal atmosphere.Valve is opened a second at every turn, discharging 23kg filter cake.Slurries supply with in the screening centrifuge decanter with 4.5 tons speed per hour and washings (water) with per hour 2.0 tons of supplies.
The mother liquor that whizzer is separated contains the impurity of 900ppm, then contains the impurity of 240ppm in order to the washings that washs isolated filter cake.The filter cake of discharging contains the impurity of 115ppm.Their content liquid (being attached to the weight of filter cake after the weight of the liquid on the filter cake/drying) is 4.3%.
[comparative example 1]
Except not using the washings, test is carried out under the condition identical with embodiment 1.The filter cake of discharging contains the impurity of 160ppm.
[comparative example 2]
Suppose the inseparable recovery of mother liquor and washings, contained impurity is 590ppm in the recovery liquid.
[comparative example 3]
Suppose and do not use flush valve, if interiorly can be not useable for evaporating the liquid that is attached on the filter cake, then according to thermal equilibrium, infer that the content of liquid is 8.8%.
[result]
When embodiment 1 compares with comparative example 1, can find out that the screening centrifuge decanter plays a very important role in the washing of filter cake.When comparative example 1 compares with comparative example 2, can find out by independently reclaiming washings, can utilize easily the low washings of foreign matter content.When embodiment 1 compares with comparative example 3, can find out by using interior energy, can save a lot of energy.These advantages are by obtaining during use screening centrifuge decanter in conjunction with interior.
[embodiment 2]
The terephthalic acid slurries that make by the low-temperature oxidation reaction are introduced directly into screening centrifuge decanter (screening separating centrifuge) when walking around crystallizer tank.Pressure in the screening centrifuge decanter remains on about 0.93Mpa.Slurries are with per hour 20 tons speed supply, and washings (acetic acid) is with per hour 18 tons speed supply.
In the screening centrifuge decanter, by solid-liquid separation, slurries are separated into filter cake and mother liquor.Filter cake washs with washings (acetic acid).The filter cake that washs is transported to the filter cake reserved slit, and the pressure of filter cake reserved slit remains on about 0.93Mpa.In the bottom of filter cake reserved slit, the flush valve disclosed such as WO91/09661 be equipped with, by opening flush valve, the filter cake that is stored in the filter cake reserved slit is sent to the powder storage tanks that is exposed under the normal atmosphere.When filter cake when the filter cake reserved slit is sent to the powder storage tanks, be stored in the liquid that is attached on the filter cake and the interior heat energy that can be released and be attached to the liquid on the filter cake as evaporation in the filter cake.After the flushing, the content liquid of filter cake (being attached to the dry weight of the weight/filter cake of the liquid on the filter cake) is 0.2%.
Therefore, in the preparation process of CTA, under high pressure, by separating and washing terephthalic acid slurries, can eliminate necessary crystallizer tank and moisture eliminator in CTA preparation process up to now.This can simplify whole plant.
[embodiment 3]
In embodiment 2, the reaction mother liquor of screening in the centrifuge decanter is separated and reclaim under the pressure of 185 degrees centigrade temperature and 0.93Mpa.By purifying the reaction mother liquor of 20wt%, the reaction mother liquor of remainder can be recycling in the oxidation reactor.
That is exactly not to be depleted as the required energy of oxidizing reaction by under high pressure separating and wash the terephthalic acid slurries, can effectively use the energy that is stored in the reaction mother liquor.
[embodiment 4]
In embodiment 2, when filter cake in when flushing, the solution major part that mainly contains acetic acid that is attached on the filter cake is evaporated with 2 tons speed per hour.The filter cake of drying part is sandwiched in the acetic acid vapor after the evaporation.Then acetic acid vapor is introduced in the solid recovery system from its bottom by pipeline, and liquid acetic acid is sprayed into from the top of solid recovery system, so that the acetic acid that sprays contacts with the terephthalic acid that sandwiches in acetic acid steam, obtains thus slurries.Resulting slurries are directly supplied with oxidation step.
Acetic acid vapor by the solid recovery system contains a small amount of methyl acetate by-product.Therefore, by reclaiming acetic acid in the steam and methyl acetate and they being supplied with oxidation step, can reduce the loss of acetic acid solvent.