Crystallization method for preparing purified aromatic dicarboxylic acids

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to the improved method for isolating crystalline terephthalic acid comprising less 150 mas. p. p. per million (ppm) of p-toluic acid with respect to weight of terephthalic acid. Method involves the following steps: (1) preparing a solution containing from 10 to 35 wt.-% of dissolved terephthalic acid wherein from 150 to 1100 ppm of p-toluic acid is dissolved with respect to mass of terephthalic acid at temperature from 260°C to 320°C and under pressure providing maintaining the solution in liquid phase; (2) charge of solution from step (1) to crystallization zone comprising multitude amount of associated crystallizers wherein the solution is subjected for cooling at evaporation at the controlled rate by the moderate pressure and temperature reducing resulting to crystallization of terephthalic acid and wherein the solution pressure at the end of crystallization zone is equal to atmosphere pressure or lower; (3) condensation of solvent evaporated from crystallizers and recovering the condensed solution to the crystallization zone to place of descending flow from crystallizer wherein solvent is removed by evaporation, and (4) isolation of solid crystalline terephthalic acid comprising less 150 ppm of p-toluic acid with respect to the terephthalic acid mass by separation of the phase liquid-solid substance under atmosphere pressure. The advantage of method is preparing the end product in improved crystalline form and carrying out the process under atmosphere pressure or pressure near to atmosphere pressure.

EFFECT: improved method of crystallization.

3 cl, 1 dwg, 1 tbl, 2 ex

 

Terephthalic acid (TPA) is one of the main elements of the structure upon receipt of a linear polyester resins used in the production of polyester films, packaging materials and bottles. TN used in the manufacture of such polyester resins must meet certain minimum criteria of purity. Purified is terephthalic acid, in which there are no significant concentrations of 4-carboxybenzene (4-KBA) and p-Truelove acid, which in large quantities are present in untreated commercially available types of terephthalic acid. As KBA, and Truelove acid are products of partial oxidation, educated when receiving TPA catalytic oxidation of p-xylene. Purified form is also characterized by the absence of coloring impurities, which give the characteristic yellow hue of the crude material. Coloring admixtures are aromatic compounds having a structure of benilov, forenoon and/or anthraquinones. 4-KBA and p-tolarova acid is particularly interfere with the polymerization process, as they act as agents breaking a chain, in the process, the condensation reaction between terephthalic acid and ethylene glycol in obtaining poly(ethyleneterephthalate) (PET).

To obtain purified terephthalic acid (TCI) of neo is isenau TFA 4-KBA and coloring impurities hydronaut, 4-KBA to p-Truelove acid and coloring impurities to compounds which are colorless solids. Usually the crude terephthalic acid is dissolved in a solvent such as water, is subjected to the hydrogenation of impurities in the liquid phase in the presence of immobilized or fixed catalyst layer. 4-KBA turns into p-Truelove acid with high yield.

The process of hydrogenation takes place at elevated temperatures between 250°280°using the partial pressure of hydrogen of from 0.5 to 20 bar absolute bar (0.05 to 2.0 MPa). The concentration of TFA in aqueous TFA solution fed to the hydrogenation reactor, is usually from 15 to 30 wt.%. The hydrogenation product stream is typically passed through a number of facilities for crystallization, in which purified terephthalic acid (OTC) crystallizes from the solution in crystalline form, which can be easily filtered and dried.

Multi-stage method of equilibrium crystallization is disclosed in U.S. patent 3452088, which describes the controlled evaporation or distillation of the solvent by regulating the back pressure on the number of stages to control the speed at which crystallizes the flow of products of hydrogenation. In the US 3542088 revealed that it is necessary to avoid rapid cooling of the stream after hydrogenation to temperatures nige° With as sharp or sudden cooling causes joint precipitation of other impurities, especially p-Truelove acid, which contaminate the purified TPA product. It's a warning in a more General form is repeated in U.S. patent 3931305, which States that "the phenomenon of deposition of impurities is anomalous because, although still more than enough solvent-water to prevent saturation or Supernature p-Truelove acid, p-tolarova acid nevertheless falls out of solution". In U.S. patent 3452088 believe that the phenomenon of pollution in some way dependent on the rate of crystallization and the final temperature of crystallization and extraction of product and not only on the concentration of the p-Truelove acid in solution". In U.S. patent 3931305 concluded that the primary factor determining the concentration of p-Truelove acid in the final product TFK is the lowest temperature at which the distilled product after hydrogenation. This is a function of the speed at which it is cooled to the temperature. Determined that to obtain the concentration of the p-Truelove acid less than 150 h/million in the final TPA desired final temperature of the filter from 121 to 149°if the raw material has a concentration of from 500 ppm to 6000 h/million

In U.S. patent 3931305 described, which system is which TPA is crystallized in several consecutive interconnected molds, in a temperature-dependent deposition of TPA becomes critical when the temperature is below 160-182°C. Thus, in the patent '305 recommended that a large part of the TFK crystallized before achieved minimum contamination of the p-Truelove acid. More specifically, in patent '305 described crystallization 75-95% of the initial dissolved TPA in almost equal portions in the first two zones of crystallization at a temperature of from 160 to 182°With subsequent crystallization of the remaining 5-25% of the original TPA dissolved in decreasing differential portions.

Another limitation allocation TFA, containing no p-Truelove acid, due to the low processing temperatures at which the solid TPA can be separated from the mother liquor of crystallization. Proceeding from the prior art presented above, this temperature is above the normal boiling point of the aqueous solvent. Therefore, any process of separating solids TPA from the mother liquor of crystallization should be carried out at pressures above atmospheric. Such restrictions require the use of equipment for separation, which has a more robust design than the equipment for operation at atmospheric or close to atmospheric pressure. Therefore, from the point of view of the major capital costs, it is desirable to use equipment for separation at atmospheric or close to atmospheric pressure.

Brief description of the invention

This invention relates to a method for allocation of purified TPA from the hydrogenation product obtained in the hydrogenation process of the solution of the crude TPA, which are applied sequentially interconnected molds. The present invention presents a method of separation of crystalline terephthalic acid containing less than 150 mass parts per million (ppm/mass) p-Truelove acid relative to the weight of terephthalic acid, which involves the following stages:

(1) preparation of a solution containing from 10 to 35 wt.% dissolved terephthalic acid, which dissolved from 150 to 1100 ppm/wt. p-Truelove acid, relative to the mass present terephthalic acid and having a temperature of from 260 to 320°C, at a pressure sufficient to maintain the solution in liquid phase;

(2) loading the solution from stage (1) in the crystallization zone comprising many interconnected molds, in which the solution is subjected to cooling by evaporation to a controlled velocity by gradually lowering the pressure and temperature, leading to crystallization of terephthalic acid, and the pressure of the solution at the end of the crystallization zone is equal to atmospheric pressure or below;

(3) condensation of the solvent evaporated from the mold, and otvrashenie condensed solvent in the crystallization zone, namely, in the mold, following the mold in which it is received; and

(4) isolation of crystalline terephthalic acid containing less than 150 ppm/mass p-Truelove acid relative to the weight of terephthalic acid, by separating the liquid - solids at ambient pressure.

In accordance with this invention the solvent evaporated from the at least one mold member of the crystallization zone, condense and recycle one or more subsequent stage of crystallization. The advantages obtained by the use of the new method include allocation of terephthalic acid in the superior crystalline form with a smaller number of "small particles", small crystals or particles of TPA, which can cause problems during processing and transportation of TPA. Another advantage is the selection of the product under atmospheric or close to atmospheric pressure.

To obtain the same selection of TPA on stage, as described in U.S. patent 3931305, in the method in accordance with this invention the temperature should be set as closely as possible to each other to minimize the abrupt cooling of the stream after hydrogenation, when the main part of the TFK crystallizes from solution. At the temperatures specified in U.S. patent 3931305, pain is the first part of the TFK will crystallize out of solution when the set temperature, if the system works as described in this invention. For the specified time and the speed of production volume of molds required for the process described here, much less than the amount required to known methods, as the initial concentration of TPA in solution is much higher, thus giving the same content of suspended solids in the stream of the final product. Smaller volume, which is required for molds, allows significant cost savings. Crystallization of TPA at higher temperatures leads to fewer p-Truelove acid, which crystallizes in conjunction with TPA. It also features a method in accordance with this invention from the ways and frequency of the critical temperatures, are described in U.S. patent 3931305.

Recycling the condensed solvent directly back into the mould from which it evaporated, known as full irrigation, does not meet the requirements of the present invention, since such a flow irrigation acts as an additional flow of raw materials, diluting the flow of raw materials PTA. Such an increased flow of raw materials will require increased capacity to save the specified time, which is undesirable.

Brief description of drawings

In the present drawing shows a process diagram, which is Aya shows how the selection of crystalline terephthalic acid, embodying the principles of this invention. Although this invention allows for various options, the drawing shows further detail of a preferred variant of the present invention. However, this description should be considered only explanatory and does not limit the invention described certain options.

Detailed description of the invention

The crude aromatic carboxylic acid, such as TFA, can be obtained by various known methods of oxidation. For example, p-Xylen may be subjected to reaction with oxygen or oxygen-containing gas in the presence of an oxidation catalyst and solvent based aliphatic carboxylic acid in the first reactor. Catalytic oxidation of p-xylene in the first reactor is at the first temperature to obtain an intermediate product. The intermediate product is loaded into the second reactor, in which the product from the first reactor reacts with oxygen, which is loaded into the second reactor at a second volumetric flow rate equal to 3% of the volumetric flow rate in the first reactor. The intermediate product digeridoo (autoclave) in the second reactor to obtain the pure product. Alternative TPA can be obtained in the reactor recirculating flow, in which p-xylene interacts with KIS what oredom in the presence of solvent and catalyst oxidation. Under this alternative method, a gas containing at least 50% oxygen, is fed into the reactor recirculating flow. The temperature in the reactor is maintained at a level of from 100 to 200°and a pressure of from 6.9 to 13.8 bar diameter - bark (from 100 to 200 pounds per inch2- f/d2). The contents kept in the reactor for 30 to 90 minutes. Another way to obtain the crude TPA involves the oxidation mixture comprising 30:1 solvent:p-xylene in the reaction zone with a continuous flow displacement formed by multiple reactors with flow displacement, many tank reactors with continuous mixing or combination thereof. The temperature at the inlet to the reaction zone with a stream of displacement is less than the temperature of the exit.

Solid crude terephthalic acid (NTC) is obtained, for example, by oxidation of p-xylene is recovered from the oxidation process in the usual method of separation of solid and liquid substances. NTK usually contains impurities such as 4-KBA, fluorenone and p-tolarova acid. For example, the combined total concentration of 4-KBA and p-Truelove acid in solid NTC is usually from 150 to 1100 ppm/wt., more often from 150 to 900 h/million/wt. and even more often from 150 to 500 ppm/wt.

Cleaning the STC includes the hydrogenation of STC to convert KBA in p-Truelove acid and coloring particles, or predestine the s coloring particles, in colorless compounds. Get the NTK solution with a concentration of from 10 to 35 wt.% solid NTC, preferably from 25 to 35 wt.% NTC, in a solvent such as acetic acid or preferably water. The NTK solution obtained by heating the solvent or suspension of the STC to a temperature sufficient to dissolve the NTC to the desired concentration, for example, a temperature of from 260 to 320°C. Solutions, requiring temperatures in the range of from 260 to 320°using as solvent water, require the solution was stored at high pressure, for example pressure from 46,9 to 113 bar absolute bar (from 680 to 1640 pounds per inch2absolute - f/d2a).

The NTK solution is subjected to hydrogenation in the liquid phase by the interaction of the slurry with hydrogen in the presence of a hydrogenation catalyst, for example a noble metal of group VIII catalytic media, while hydronauts certain impurities to other compounds. In the crude TFA fluorenone and 4-KBA become fluorine and p-Truelove acid, respectively. Assuming that there is a practically complete conversion of 4-KBA in p-Truelove acid, and assuming that the NTK solution fed to the reactor hydrogenation, has a total combined concentration of 4-KBA and p-Truelove acid from 150 to 1100 ppm/wt., concentration only p-Truelove acid in the stream PR is the product of the hydrogenation reactor 110 is from 150 to 1100 ppm wt. in relation to the weight of TFA present. Also, if the combined total concentration of 4-KBA in p-Truelove acid in the solution fed to the hydrogenation reactor, is from 150 to 900 ppm/wt. or from 150 to 500 ppm/wt. and Pets almost complete conversion of 4-KBA, the concentration of the p-Truelove acid in the product stream from the hydrogenation reactor is from 150 to 900 ppm/wt. or from 150 to 500 ppm/wt. respectively.

The flow temperature of the hydrogenation product typically ranges from 260 to 320°C. a Stream of the hydrogenation product is loaded into the crystallization zone comprising a set or sequence of connected crystallizers, which together reduce the temperature of the stream after hydrogenation to a lower, typically from 75 to 150°more often from 90 to 110°C. Reduction in temperature is accompanied by precipitation from a solution of TFA in the form of a white crystalline solid. Crystal TPA at the last stage of crystallization is separated from the solvent by a conventional device for separating solid and liquid substances, such as a centrifuge or a rotary vacuum filter. The crystallization zone may contain two to eight, preferably three to six, most preferably from four to five, mold, or stages of crystallization. The number of stages Cree is tallization, used in the process can affect the quality of the final product. Correct setting of the temperature in successive interconnected molds increases the purity of the final product relative to the p-Truelove acid.

Many degrees of crystallization includes the first and last stage of crystallization. The temperature at the first stage of crystallization is usually from 200 to 260°and the temperature at the last stage of crystallization is usually from 80 to 100°C. operating temperature on the speed of crystallization may gradually decrease from the first to the last stage of crystallization.

The last stage of crystallization gives a suspension of the product, which contains in terms of the solid is less than 25 ppm 4-KBA and less than 150 ppm/wt. p-Truelove acid. In accordance with this invention an aromatic dicarboxylic acid, such as TFA, crystallized at the first stage of crystallization by cooling the hydrogenated stream is cooled by evaporation with controlled velocity (or instantaneous evaporation) at lower pressure compared to the pressure of the flow) inside the first mold or the degree of crystallization. The solvent is removed from the mould in the form of steam, condense, and some or all of the condensed solvent is returned to the crystallization zone instead of downstream of the mold, from which the evaporated solvent. Additional aromatic dicarboxylic acid is crystallized in the second stage crystallization at a second temperature which is less than the first, viparita solvent. The solvent is condensed from the vapor of solvent received during the previous mold, and/or fresh solvent may be added at the second stage of crystallization.

Each of the many stages of crystallization has a mass flow rate of material entering the mould in and out of the mold. The mass flow rate of material entering the first stage of crystallization, may be from 0.7 to 1.3 times the mass flow rate of material leaving the last stage of crystallization. Preferably the mass flow rate of material entering the first stage of crystallization, almost equal to the mass flow rate of material leaving the last stage of crystallization.

Each stage of crystallization in the method in accordance with this invention has many similar operating devices, comprising the following main elements:

1) crystallization Luggage or container (mold), equipped with a device for mixing, such as one or more blades;

2) supply line into the mould;

line removal of the product from the mold;

4) line removal of distillate and vapor of the solvent from the mold, suitable to the capacitor, in which a certain amount or all of the solvent in the vapor condenses; and

5) supply line solvent at a point downstream or part of the crystallization zone for loading liquid condensed in the condenser.

Crystallization chamber is a tank of constant volume with good stirring, containing suspension or TPA crystals. The solvent is usually water, saturated with TPA at the operating temperature of the mold. Can also be used other solvents, such as acetic acid. Operating temperature in each crystallization chamber in combination with the temperature with the concentration of the loaded stream determines the number of TPA crystallizes at each step. For crystallization of a greater portion of TFA, the temperature should be lowered to the point at which the solubility of TPA in a solvent, for example water, is reduced, which allows you to crystallize more TFA. Independent control of the pressure determines the operating temperature of crystallization chambers. Pressure is controlled by regulating the shutter in crystallization chambers, for example, but not limited to, a valve in the line distillate.

The result is e low pressure (relative pressure flow, loaded into the crystallization chamber), the solvent is vaporized and removed from the crystallization chamber in the form of steam, thus concentrating the solution. Part of settling TPA crystallizes on the crystals existing in the vessel, and part of the TFK crystallizes in the form of some new crystals. The amount of TPA, which was transformed from the liquid phase to the solid phase, is a function of operating temperature (controlled decrease in pressure) of the mold from the equilibrium concentration of TPA at this temperature.

Usually the raw material into the first mold serves below the surface contained in suspension in the direction of the bottom of the tank, in which the hydrostatic pressure is higher. Increased pressure at this point in the crystallization chamber and the ambient fluid to prevent excessive evaporation. In crystallization chambers are devices for mixing, such as blades. If the product from the hydrogenation reactor is served in the first crystallization chamber in an area of sufficient mixing can be minimized local oversaturation, which promotes the formation of small or fine crystals.

Product flow continuously out of each crystallization chamber. The product stream is preferably removed from the zone of good mixing crystallization chamber t is thus, to the content of the product stream was present in high quantities in each crystallization chamber. The flow of product loaded at the cascade or the subsequent stage of crystallization, operating at a lower temperature, preferably in an area with good stirring, following crystallization chamber. As each subsequent crystallization camera operates at a lower temperature, crystallizes part of the TFK remaining in the solution, which can be determined using equilibrium concentrations of TPA at the operating temperature of the second crystallization chamber 124.

As noted above, the distillate or solvent vapor is removed from the first and subsequent stages of crystallization and transferred to the condenser for cooling and condensing steam. Either some or all of the distillate can be condensed at this stage. In addition, the cooling steam to a temperature of almost below the boiling point can also be carried out in the condenser. All or part of the condensed solvent is recycled to the crystallization zone at a point downstream from the mould, from which the solvent is removed in the form of steam. Preferably the condensed solvent is recycled to the crystallization zone loading of condensed solvent in-line removal of the product from crystallizatio is a, from which the solvent has been removed in the form of steam. Any condensed solvent is not returned or recycled to the crystallization zone, can be used anywhere in the TPA treatment system, for example, to obtain a solution NTC loaded into the hydrogenation reactor. The final crystallization camera operates as a holding tank for the suspension, keeping the suspension before phase separation of liquid and solid connections. The second and subsequent crystallizers operate the same way as the first mold.

The condensed solvent from the upper stage of crystallization can be recycled to the degree of crystallization, which is immediately after or recycled to the degree of crystallization than the next stage of crystallization. As a condensed and fresh solvent may be submitted in one of the subsequent steps of the mould.

The flow of product from one or all stages of crystallization may be diluted with a diluent, such as water, at a temperature of equal to or almost equal to the operating temperature degree of crystallization, which removes the product flow. The addition of the diluent into the flow of the product helps to reduce the overall concentration of TFA and any impurities present in the product flow. If the product flow is C of each of the mold, the solvent is not added, the total concentration of TFA in each thread product continues to grow. In crystallization processes, in which the diluent is not recycled, the product stream from the hydrogenation reactor has a degree of dilution, which allows to obtain an output with a predetermined concentration of solid TPA, continuing after the final stage of crystallization. That is, knowing the amount of liquid added and the remote, and knowing the volume of the crystallizing TPA may be determined concentration of solid TPA. Adding diluent (possibly water) to flow from each stage of crystallization of the dilution required for the initial flow of raw materials, much lower.

Liquid diluent to be added in the product flow can occur from many sources. First, the condensate from the degree of crystallization, which removes the product may be condensed and partially or completely recycled back into the flow of product from this stage. Secondly, it can be used fresh solvent, for example water, in quantities greater than, less than or equal to the amount of liquid removed as distillate. Thirdly, if you use more than one stage of crystallization, the condensate from the degree that is different from the immediately preceding stage can be recycled to the target degree of crystallization. Usually Conde the sat is heated to a temperature equal to the operating temperature prior to the step of crystallization.

In each case, either some or all of the condensed solvent recycle stream of product coming on-stage crystallization, or additional solvent serves on the degree of crystallization may also be a combination of them. If you have more than two stages of crystallization, the percentage of solvent supplied to each stage of crystallization may vary. For example, at some stage of crystallization can be fed the amount of solvent equal to the number of evaporated during the previous step, and at some stage crystallization solvent is not given.

Additional injection of diluent may be some areas of the transfer lines between the molds. Typically, these lines include a valve for controlling the flow rate of the product from one stage of crystallization to the other. While on stage crystallization is expressed as the amount of degree of crystallization, divided by the volume flow rate of suspension of the product from the degree of crystallization. Alternate adding in-line transfer/loading line dilution liquid can be added directly into the crystallization chamber. In this case, the dilution liquid is preferably dobavlaut the liquid surface, more preferably, the basis of the crystallization chamber, in the area of good mixing.

If the entire distillate from each crystallization chamber is recycled into the flow of the product from this crystallization chamber, the concentration of TFA, applied to the degrees of crystallization, will be equal to each other regardless of whether TPA in the liquid or solid phase. Thus, the concentration of the original flow of liquid TPA is approximately equivalent to the concentration of solids in the final product, provided that a small part of TPA remains in solution and does not crystallize.

Compared to the sequential crystallization of TPA, which is not applied to the recycling of condensed solvent in descending stream, the stream from the hydrogenation reactor in the first crystallization chamber can be more concentrated and may have reduced the flow rate. Reduced flow velocities with the same degree of crystallization to the other gives the decrease in the rate of flow of the product. To save a predetermined time at a lower flow rate volume crystallization of the chamber should be reduced. When almost constant flow rate, for example, on the steps of crystallization with upward flow, at high temperature, and the downstream flow, etc is a low temperature, should be almost equal size and the same time.

In General, the strategy choice of the temperature profile for the many stages of crystallization is to select a temperature at which crystallization of the lower part of the PTA at each grade level, compared with the previous stage. It was found that this technique allows not only to crystallize a smaller amount of TPA on each downward step, but also to minimize contamination of the product by-products. Ideally, this mechanism gives the biggest advantage when using an infinite number of degrees of crystallization, in conditions close to periodic. The practical limitation of operations does not allow it. In this invention, the highest concentration of TFA in the original thread improves this mechanism, as higher concentrations allow a greater amount of TPA to crystallize at higher temperatures (in the initial stages).

Line removal of product from the final catalyst leads to the conventional apparatus for separating liquid - solid substances for the selection of crystalline TPA product containing less than 150 ppm/wt. p-Truelove acid. As the temperature at the last stage of crystallization may be below the boiling point of the solvent, can be applied vacuum filter (instead of n is pornoho filter). Wet crystalline TPA can be washed before discharge into the dryer. The filtered mother liquor and the liquid used for washing, collect for recirculatory on stage hydrogenation. Part of the filtered liquid may be evacuated to reduce the number of impurities in the system.

According to the drawing solvent, such as water, and the solid crude terephthalic acid (NTC) load capacity for dissolving the STC 160. In the tank for dissolving 160 solid NTC diluted with a solvent, such as water, to a concentration of from 10 to 35 wt.% solid NTC, more often 25-35 wt.% solid NTC. Dilute NTC is brought to a temperature, for example, from 260°320°S, which is sufficient to dissolve all solid NTC. At elevated temperature and pressure solid NTC becomes a solution. The solution NTC served with hydrogen in the hydrogenation reactor 110, in which the impurities present hydronauts in the liquid phase. The hydrogenation reactor comprises one or more layers of conventional hydrogenation catalyst such as a noble metal of group VIII on the substrate for the catalyst. The hydrogenation product is removed from the hydrogenation reactor 110 and served through the valve 130 in the first crystallization chamber 122 at a point below the surface of the suspension containing vessel 122, almost at the bottom of the tank 122, where hydrostatics the second pressure is higher. In the first crystallization chamber 122 and other crystallization chambers has a device for mixing, such as the blade 170.

The product stream is continuously removed from the crystallization chamber 122 through the pipe 140. The product stream is removed from the zone with good stirring crystallization chamber 122 so that the content of the product stream has an average total concentration in the crystallization chamber 122. The product stream is fed through valve 134 to the second, consecutive, crystallization chamber 124, which operates at a pressure and temperature lower than the temperature and pressure in the mold 122. The flow of product is loaded into an area with good stirring crystallization chamber 124. Since the next crystallization chamber 124 operates at a lower temperature, part of the TFK remaining in solution crystallizes, this part is determined by using the equilibrium concentration of TPA at the operating temperature of the second crystallization chamber 124.

Vaporous solvent is continuously removed from the first stage of crystallization 122 through a pipe 142 and load in the heat-exchange condenser 150 for cooling, where all or part of the solvent is condensed. Subsequent cooling of the vapor to a temperature substantially below the boiling point can also be conducted in the heat exchanger. Part or the, return of the condensed solvent is loaded into the product stream 140 through the valve 136. Any condensed solvent is not recycled in the flow of product may be removed through a pipe 144. The second mold 124 works the same as the first catalyst 110, and includes a crystallization chamber 124, with the blade 172. The product is removed from the crystallization chamber 124 through a pipe 146. Vaporous solvent is removed from the second crystallization chamber 124 and served in the capacitor 152, in which the vaporous solvent is condensed, and the condensed solvent is recycled through valve 138 and/or removed through the pipe 148. Fresh, additional solvent, for example water, add in the following system of crystallization shown in the drawing, through lines 143 and/or 147.

The product of crystallization is removed from the mold 124 through the pipe 146 and transferred through valve 137 in the separation zone liquid - solid 180. The temperature at the last stage of crystallization may be less than usually the boiling point of the solvent, which allows to separate the liquid and solid material through the vacuum filter. When the separation of liquid - solid 180 remove the mother liquor from the crystal pellet in the first zone. The crystal cake is then washed in the second zone.

Examples

A new way of crystallization in accordance with this invention is further illustrated SL is blowing examples.

Comparative example

The data presented in the table for this comparative example, were taken from the example 8 of U.S. patent 3931305. Subsequent evaporative cooling is performed on each of the six stages of the mould without recirculatory solvent evaporated at every stage of the mold. In the table the selection of the sample refers to the place in a sequential system of crystallization in which measure the temperature and take the sample to measure the mass percentage of solid TPA, degree refers to the degree of crystallization in the sequence of the 6-speed crystallization. Stage 1 - Stage 2 shows that the sample was taken from the flow of product between the first and second mold. Temperature means the temperature in the °and solid TFA refers to the total wt.%. in relation to the total weight of TPA loaded on the degree of crystallization 1, solid TFA.

In example 8 of U.S. patent 3931305 flow on the first stage of crystallization, contains 18 wt.% dissolved TPA. Upon evaporation of the solvent (evaporative cooling) and the absence of recirculatory TPA becomes more concentrated when passing through the stage of crystallization. After the last stage of mold, the total concentration of TPA (the sum of the concentrations of liquids and solids) is approximately equal solid is emesto, remaining in the product flow. That is, almost all of TPA, which was loaded on the first step in liquid form, turned into a solid, and the solid substance contains almost no other components. In the presence of solubility curve of TFA and water can be modeled determining the amount of solids remaining in the product flow. The simulation can be conducted with the knowledge of the temperature at each step of crystallization and the amount of crystallized TPA. The simulation shows the amount of solids remaining in the product flow from the end of the mold, equal 31,40%.

Table
Comparative exampleExample 1Example 2
The selection of the sampleTemperatureSolid TPATemperatureSolid TPATemperatureSolid TPA
Step 1 Raw material276,670276,670276,670
Stage 1 Stage 2251,6742,08251,6771,76265,2042,0
Stage 2 Stage 3204,4493,28204,4495,98218,2593.32 per
Stage 3 Stage 4165,5698,69165,5699,02175,0798,62
Stage 4 Stage 5135,0099,63135,0099,68139,4499,63
Step 5 Step 6121,1199,79121,1199,80123,3399,79
Step 6 Product100,0099.91 per100,0099.91 per100,0099.91 per

Example 1

The column showing the temperature and solid TFA for example 1 in the table show the number of solid TPA obtained under the same operating temperatures for each of the mold, but at 100% condensate recycle system in the download location to the next mold. The same retention time of solids in each crystallizer reach by increasing the concentration of solid substances up to 30% in the original thread in the first crystallizer and reduced size of the upper mold. The same speed reaches a lower total flow rate at the first stage crystallization this example, 71,76% TFA crystallizes in the first stage unlike 42.08% in the comparative example. At the second stage crystallizes 95,98% unlike 93,28% in the comparative example. Example 1 shows that a greater amount of TPA can be crystallized at a given temperature when using 100% recirculatory solvent.

Example 2

The column showing the temperature and solid TFA for example 2 in the table shows the data for the process that produces the output for the same amount of crystallized TFA (degree of crystallization), and that in the comparative example. In the same way as in example 1, 100% of the condensed solvent recycle. The results show that 42,08% TFA can be crystallized at the first stage, even if the temperature in the first stage above, 264,1°unlike 251,7°in the comparative example. At higher temperatures the mixture is far from the solubility curve p-Truelove acid. Therefore, at high temperatures is a joint crystallization of p-Truelove acid. It is expected that the crystals obtained when 264,1°will be cleaner than the crystals obtained when 251,67°C. Example 2 shows that the purity can be increased without reducing the quality of the product.

1. The method of selection of crystalline terephthalic acid containing less than 150 parts by weight per million (ppm/wt.) p-Truelove acid relative to the weight of terephthalic acid, which involves the following stages:

< num="67"> (1) preparation of a solution containing from 10 to 35 wt.% dissolved terephthalic acid, which dissolved from 150 to 1100 ppm/wt. p-Truelove acid, relative to the mass present terephthalic acid and having a temperature of from 260 to 320°C, at a pressure sufficient to maintain the solution in liquid phase;

(2) loading the solution from stage (1) in the crystallization zone comprising many interconnected molds, in which the solution is subjected to cooling by evaporation with a controlled speed through a gradual reduction of pressure and temperature, leading to crystallization of terephthalic acid, and the pressure of the solution at the end of the crystallization zone is equal to atmospheric pressure or below;

(3) condensation of the solvent evaporated from the mold, and returning the condensed solvent in the crystallization zone at a location downstream of the mould, from which the solvent is evaporated; and

(4) isolation of crystalline terephthalic acid containing less than 150 ppm/wt. p-Truelove acid relative to the weight of terephthalic acid, separation of liquid - solids at atmospheric pressure.

2. The method according to claim 1, wherein the solution from step (1) contains from 25 to 35 wt.% dissolved terephthalic acid, in which process is prohibited from 150 to 900 ppm/wt. p-Truelove acid, relative to the mass present terephthalic acid, and many interconnected mold includes from two to eight molds.

3. The method according to claim 2, in which the temperature in the first crystallizer is from 200 to 260°and the temperature in the last crystallizer is from 80 to 100°and With many interconnected mold includes from three to six molds.



 

Same patents:

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to the improved method for chemical reutilization of depleted polyethylene terephthalate, especially to non-classified crumbs of utilized polyethylene terephthalate articles resulting to preparing terephthalic acid and ethylene glycol. Method involves hydrolysis of utility waste polyethylene terephthalate with aim for its depolymerization and involves the following steps: (a) separation of polyethylene terephthalate component in the parent raw by its transfer to fragile form by using crystallization, grinding and the following screening processes; (b) continuous two-step hydrolysis of polyethylene terephthalate carried out at the first step by injection of steam into polymer melt followed by carrying out the hydrolysis reaction of products from the first step with ammonium hydroxide and by the following (c) precipitation of terephthalic acid from aqueous solution of hydrolysis products from the second step with inorganic acid and separation of terephthalic acid by filtration method and by the following (d) extraction of ethylene glycol by rectifying from solution of the second step hydrolysis products after separation of terephthalic acid. This technologically simple and effective method provides possibility for treatment of very contaminated the parent raw and providing high purity of end products.

EFFECT: improved treatment method.

5 cl, 1 ex

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to a continuous method for preparing highly pure terephthalic acid. Method involves oxidation of p-xylene with oxygen-containing gas in acetic acid medium in the presence of catalyst comprising heavy metal salts, such as cobalt and manganese and halide compounds under increased pressure and temperature up to the definite degree of conversion of para-xylene to terephthalic acid at the first step and the following two-step additional oxidation of prepared reaction mixture and isolation of the end product. Mixing time of reagents is <25 s, oxidation at the first step is carried out at temperature 180-200°C up to conversion degree of p-xylene 95%, not above, oxidation at the second step is carried out at temperature 175-185°C and before feeding to the third step of oxidation the reaction mass is heated to 200-260°C, kept for 8-12 min and oxidized at temperature 180-200°C in the presence of catalyst comprising Ni and/or Zr salts additionally. As halide compounds method involves using XBr or XBr + XCl wherein X is H, Na, Li followed by isolation of solid products of oxidation after the third step and successive treatment with pure acetic acid and water in the mass ratio terephthalic acid : solvent = 1:3. Invention provides intensification of process and to enhance quality of terephthalic acid.

EFFECT: improved method for preparing.

1 tbl, 1 dwg, 14 ex

The invention relates to an improved method of reducing the content of 4-carboxybenzene in the production of terephthalic or 3-carboxymethylthio in the production of isophthalic acid, comprising: (a) dissolving crude terephthalic acid or crude isophthalic acid in a solvent at a temperature of from 50 to 250With obtaining a solution; (b) crystallization of the purified acid from this solution by reducing the temperature and/or pressure; (C) the Department specified crystallized terephthalic acid or isophthalic acid from the solution; (d) adding an oxidant to the reactor oxidation carboxyanhydride for oxidation specified filtered solution of stage (C), leading to the transformation of 4-carboxybenzene or 3-carboxymethylthio in terephthalic acid or isophthalic acid; (e) evaporating the solvent from this solution from step (d); (f) cooling the concentrated solution from step (e) for crystallization additional quantities of purified terephthalic acid or isophthalic acid and filtering the specified slurry and recycling the most part, the mother liquor from step (f) in the devices is

The invention relates to an improved process for the preparation of terephthalic and isophthalic acids

The invention relates to the purification of terephthalic acid which is a raw material for producing polyester resin

The invention relates to a method for producing aromatic carboxylic acids by exothermic liquid-phase oxidation reaction of the corresponding alkylaromatic parent compound in the liquid-phase reaction mixture consisting of water, low molecular weight monocarboxylic acid as a solvent, the oxidation catalyst on the basis of heavy metal and a source of molecular oxygen in the reaction conditions leading to the gaseous exhaust stream of high pressure water-containing gaseous by-products and gaseous low molecular weight monocarboxylic acid, followed by distillation of the aromatic carboxylic acid and separation of the exhaust flow high pressure, while the exhaust flow high-pressure direct high-performance distillation column to remove at least 95 wt.% low molecular weight monocarboxylic acid from the waste stream, with the formation of the second exhaust flow high-pressure containing water and gaseous by-products formed in the oxidation process, and then the second exhaust stream of high pressure is directed to the means for the release of energy from the second exhaust flow

The invention relates to a method for and apparatus for producing purified terephthalic acid from its liquid dispersion containing impurities in the form of unreacted starting materials, solvents, products of side reactions and/or other undesirable materials

The invention relates to an improved process for the preparation of terephthalic acid

The invention relates to a method for the production of terephthalic acid and installation for its implementation

FIELD: crystal growing.

SUBSTANCE: invention relates to adipic acid crystals and treatment thereof to achieve minimum crystal caking. Crystals are prepared by crystallization of adipic acid from aqueous medium or between treating it with aqueous solution. Crystals are then subjected to ripening stage, that is crystals are held at temperature between 10 and 80°C until content of exchangeable water in crystals falls below 100 ppm, while using an appropriate means to maintain ambient absolute humidity at a level of 20 g/m3. Renewal of ambient medium is accomplished by flushing crystal mass with dry air flow having required absolute humidity. Means to maintain or to lower absolute humidity contains moisture-absorption device placed in a chamber. Content of exchangeable water in crystals is measured for 300 g of adipic acid crystals, which are enclosed in tightly sealed container preliminarily flushed with dry air and containing 2 g of moisture absorbing substance. In chamber, temperature between 5 and 25°C is maintained for 24 h. Content of water will be the same as amount of water absorbed by absorbing substance per 1 g crystals. Total content of water exceeds content of exchangeable water by at least 20 ppm.

EFFECT: minimized caking of crystals and improved flowability.

13 cl, 5 ex

The invention relates to an improved method of reducing the content of 4-carboxybenzene in the production of terephthalic or 3-carboxymethylthio in the production of isophthalic acid, comprising: (a) dissolving crude terephthalic acid or crude isophthalic acid in a solvent at a temperature of from 50 to 250With obtaining a solution; (b) crystallization of the purified acid from this solution by reducing the temperature and/or pressure; (C) the Department specified crystallized terephthalic acid or isophthalic acid from the solution; (d) adding an oxidant to the reactor oxidation carboxyanhydride for oxidation specified filtered solution of stage (C), leading to the transformation of 4-carboxybenzene or 3-carboxymethylthio in terephthalic acid or isophthalic acid; (e) evaporating the solvent from this solution from step (d); (f) cooling the concentrated solution from step (e) for crystallization additional quantities of purified terephthalic acid or isophthalic acid and filtering the specified slurry and recycling the most part, the mother liquor from step (f) in the devices is

The invention relates to an improved method of processing the reaction mixture obtained by direct oxidation of cyclohexane to adipic acid, in liquid phase, in a solvent and in the presence of dissolved in the reaction medium, catalyst, including decantation two liquid phases: upper non-polar phase containing mainly unreacted cyclohexane, and the lower polar phase containing mainly solvent, adipic acid and the resulting acid, the catalyst and other reaction products and unreacted hydrocarbons, distillation of the lower polar phase or, if necessary, the entire reaction mixture with obtaining, on the one hand, distillate, containing, at least a part of the most volatile compounds such as unreacted cyclohexane, the solvent, the intermediate reaction products and water, and, on the other hand, residue from distillation, containing adipic acid and the resulting carboxylic acid, the catalyst, and the method includes a step of adding to the residue after distillation of the organic solvent in which adipic acid has a solubility less than or equal to 15 wt

The invention relates to an improved method of isolation and purification of adipic acid, used for the production of polyamide-6,6 or polyurethanes, which consists in treating the reaction mixture obtained by direct oxidation of cyclohexane to adipic acid by molecular oxygen in an organic solvent and in the presence of a catalyst, removing by-products from the reaction mixture and the adipic acid by crystallization, and before adipic acid from the reaction environment carry out consistently the following operations: the decantation of the two phases of the reaction medium with the formation of the upper organic the cyclohexane phase, containing mainly cyclohexane, and the lower phase, containing mainly the solvent, the resulting dicarboxylic acid, the catalyst and other reaction products and unreacted cyclohexane; distillation bottom phase to separate, on the one hand, distillate containing at least a part of the most volatile compounds, such as organic solvent, water and unreacted cyclohexane, cyclohexanone, cyclohexanol, complex cyclohexylamine esters and possibly lactones, and, with the pin acid from residue from distillation by means of crystallization and thus obtained crude adipic acid is subjected in aqueous solution purification by hydrogenation and/or oxidation with subsequent crystallization and recrystallization of the purified adipic acid in water

The invention relates to an improved process for the preparation of terephthalic and isophthalic acids

The invention relates to an improved method for producing isophthalic acid used in copolymerization ways of producing fibers, films, plastic bottles and structures made of polyester resin, which consists in the oxidation of metaxalone in the reaction solvent to obtain a liquid dispersion

The invention relates to chemical technology of obtaining low molecular weight aliphatic acids, which are valuable raw materials for the chemical, petrochemical and forestry industry

The invention relates to a method of purification by crystallization or recrystallization in water adipic acid, which is one of the main substances used to obtain polyamide 6-6, which contains traces of catalyst, with a minimum purity specified adipic acid is at least 95%, and the specified crystallization or recrystallization is carried out in the presence of a strong proton acid and/or in the presence of carbon monoxide

The invention relates to a method of purification of adipic acid, which is used to obtain polyamide

The invention relates to a technology for technical formate sodium from aqueous solution technical Chlorella, which is a waste product of chloroform

FIELD: crystal growing.

SUBSTANCE: invention relates to adipic acid crystals and treatment thereof to achieve minimum crystal caking. Crystals are prepared by crystallization of adipic acid from aqueous medium or between treating it with aqueous solution. Crystals are then subjected to ripening stage, that is crystals are held at temperature between 10 and 80°C until content of exchangeable water in crystals falls below 100 ppm, while using an appropriate means to maintain ambient absolute humidity at a level of 20 g/m3. Renewal of ambient medium is accomplished by flushing crystal mass with dry air flow having required absolute humidity. Means to maintain or to lower absolute humidity contains moisture-absorption device placed in a chamber. Content of exchangeable water in crystals is measured for 300 g of adipic acid crystals, which are enclosed in tightly sealed container preliminarily flushed with dry air and containing 2 g of moisture absorbing substance. In chamber, temperature between 5 and 25°C is maintained for 24 h. Content of water will be the same as amount of water absorbed by absorbing substance per 1 g crystals. Total content of water exceeds content of exchangeable water by at least 20 ppm.

EFFECT: minimized caking of crystals and improved flowability.

13 cl, 5 ex

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