FIELD OF THE INVENTION

[0001] This invention pertains to the preparation of bis(2-ethylhexyl) terephthalate (DOTP) and methyl 2-ethylhexyl terephthalate (MOTP) from dimethyl terephthalate (DMT). More specifically, this invention pertains to a process for the preparation of DOTP and MOTP by the trans-e sterification of dimethyl terephthalate with 2-ethylhexanol (2-EHOH) at elevated temperature to control the ratio of MOTP to DOTP in a product mixture.

BACKGROUND OF THE INVENTION

[0002] Bis(2-ethylhexyl) terephthalate, also known as dioctyl terephthalate or DOTP, is used as a plasticizer in a variety of polymeric materials such as polyvinyl chloride. DOTP is an alternative plasticizer to diisononyl phthalate (DINP). However, DOTP’s performance is not always sufficient in many flexible polymers such as polyvinyl chloride (PVC) to replace DINP. A desirable replacement plasticizer will exceed the performance of DOTP while having a better cost position. A novel alternative to DINP is a blend of bis(2-ethylhexyl) terephthalate (DOTP) and methyl 2-ethylhexyl terephthalate (MOTP). The MOTP and DOTP plasticizer blend possesses a better performance profile than DOTP alone and is a viable alternative to DINP.

[0003] DOTP can be prepared by the titanate-catalyzed transesterification of dimethyl terephthalate (DMT) with 2-EHOH. Direct esterifications of TPA with 2-EHOH under conditions similar to those used for the transesterification of DMT have produced slow reaction rates and sporadic problems with foaming. US-2002028963-A1 discloses an esterification process wherein water is removed by azeotropic distillation together with an alcohol. JP-60004151 -A (JP-03004052-B) discloses the reaction of TPA and 2-EHOH under elevated pressures and temperatures. JP 2001031794-A discloses the preparation of terephthalic acid esters by reacting at least one of C9-C18 monohydric alcohol and 2-ethylhexanol with terephthalic acid. Finally, US-5,532,495 discloses a multi-step esterification process that includes removing water and a portion of the alcohol reactant from the reaction mixture.

[0004] A need exists for an efficient method to make MOTP and DOTP plasticizer blends that can be used as plasticizers in materials such as polyvinyl chloride.

BRIEF SUMMARY OF THE INVENTION [0005] We have developed a process for the preparation of bis(2-ethylhexyl) terephthalate (DOTP) and methyl 2-ethylhexyl terephthalate (MOTP) by the esterification of TPA with 2-EHOH and methanol at elevated temperature and optionally elevated pressure.

[0006] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP) blend comprising: a. reacting dimethyl terephthalate and 2-ethylhexanol in the presence of a catalyst while distilling methanol from said reaction; b. monitoring the reaction of step a) to detect a desired DOTP/MOTP product distribution; and c. recovering a DOTP/MOTP blend from said reaction.

[0007] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP) blend comprising: a. adding dimethyl terephthalate, 2-ethylhexanol, a catalyst and an inert gas to a reactor to form a reaction mixture; b. heating said reaction mixture of step a) to a desired temperature while monitoring said mixture to detect a desired DOTP and MOTP product distribution; and c. recovering a DOTP and MOTP blend from said reaction mixture. [0008] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP) blend comprising: a. adding dimethyl terephthalate, 2-ethylhexanol, titanium(IV) isopropoxide and nitrogen to a reactor to form a reaction mixture; b. heating said reaction mixture of step a) to a desired temperature, refluxing the reaction mixture and distilling methanol from said reaction mixture; c. monitoring the reaction mixture of step b) to detect a desired DOTP/MOTP product distribution; d. cooling said reaction mixture of step c); e. adding an aqueous hydroxide solution to said reaction mixture of step d), to form a first aqueous component and a first organic component, said first organic component containing DOTP, MOTP and 2-ethylhexanol; f. separating said first aqueous component of step e) from said first organic component of step e); g. adding water to said first organic component of step f) to form a second aqueous component and a second organic component containing DOTP, MOTP and 2-ethylhexanol; h. separating said second aqueous component from said second organic component of step g); i. removing 2-ethylhexanol from said second organic component from step h) to form a mixture containing DOTP and MOTP; and j. filtering and drying said solution of step i) to recover a DOTP/MOTP blend.

[0009] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP) blend comprising: a. reacting dimethyl terephthalate and 2-ethylhexanol in the presence of a catalyst while distilling methanol from said reaction; b. monitoring the reaction of step a) to a detect a desired amount of methanol; and c. recovering a DOTP/MOTP blend from said reaction.

[0010] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP) blend comprising: a. adding dimethyl terephthalate, 2-ethylhexanol, a catalyst and nitrogen to a reactor to form a reaction mixture; b. heating said reaction mixture of step a) while distilling methanol from said reaction mixture; c. monitoring the reaction mixture of step b) to detect a desired amount of methanol; and d. recovering a DOTP and MOTP blend from said reaction mixture. [0011] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP)blend comprising: a. adding dimethyl terephthalate, 2-ethylhexanol, a catalyst and nitrogen to a reactor to form a reaction mixture; b. heating said reaction mixture of step a) to a desired temperature, and distilling methanol from said reaction mixture: c. monitoring the reaction mixture of step b) to detect a desired amount of methanol; d. cooling said reaction mixture of step c); e. adding an aqueous hydroxide solution to said reaction mixture of step d), to form a first aqueous component and a first organic component, said first organic component containing DOTP, MOTP and 2-ethylhexanol; f. separating said first aqueous component of step e) from said first organic component of step e); g. adding water to said first organic component of step f) to form a second aqueous component and a second organic component containing DOTP, MOTP and 2-ethylhexanol; h. separating said second aqueous component from said second organic component of step g); i. removing 2-ethylhexanol from said second organic component from step h) to form a mixture containing DOTP and MOTP; and j. filtering and drying said solution of step i) to recover a DOTP/MOTP blend.

[0012] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP) blend comprising: a. reacting DOTP and methanol in the presence of a catalyst while distilling methanol from said reaction; b. monitoring the reaction of step a) to a detect a desired DOTP/MOTP product distribution; and c. recovering a DOTP/MOTP blend from said reaction.

[0013] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP) blend comprising: a. adding DOTP, methanol, a catalyst and nitrogen to a reactor to form a reaction mixture having a liquid phase and a gaseous phase; b. heating said reaction mixture of step a), and distilling a gaseous mixture of methanol and 2-ethylhexanol from said reaction mixture gaseous phase of step a), and adding liquid methanol to said reaction mixture liquids phase of step a); c. monitoring the reaction mixture of step b) to a detect a desired DOTP and MOTP product distribution; and d. recovering a DOTP and MOTP blend from said reaction mixture. [0014] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP) blend comprising: a. adding DOTP, methanol, a catalyst and nitrogen to a reactor to form a reaction mixture having a liquid phase and a gaseous phase; b. heating said reaction mixture of step a), and distilling a gaseous mixture of gaseous methanol and 2-ethylhexanol from said reaction mixture gaseous phase of step a), and adding liquid methanol to said reaction mixture liquids phase of step a); c. monitoring the reaction mixture of step b) to a detect a desired DOTP/MOTP product distribution; d. cooling said reaction mixture of step c); e. adding an aqueous hydroxide solution to said reaction mixture of step d), to form a first aqueous component and a first organic component, said first organic component containing DOTP, MOTP and 2-ethylhexanol; f. separating said first aqueous component of step e), from said first organic component of step e); g. adding water to said first organic component of step f) to form a second aqueous component and a second organic component containing DOTP, MOTP and 2-ethylhexanol; h. separating said second aqueous component from said second organic component of step g); i. removing 2-ethylhexanol from said second organic component from step h) to form a mixture containing DOTP and MOTP; and j. filtering and drying said solution of step i) to recover a DOTP/MOTP blend.

[0015] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP) blend comprising: a. reacting terephthalic acid and 2-ethylhexanol in the presence of a catalyst to form a first reaction product; b. reacting methanol with the first reaction product of step a) while monitoring the reaction of methanol and the first reaction product to a detect a desired DOTP/MOTP product distribution; and c. recovering a DOTP/MOTP blend from said reaction. [0016] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP) blend comprising: a. heating a first reaction mixture of terephthalic acid and 2- ethylhexanol in the presence of a catalyst to form a first reaction product; b. adding methanol to the first reaction product of step a), to form a second reaction mixture; c. heating and monitoring the reaction mixture of step b) to a detect a desired DOTP and MOTP product distribution; and d. recovering a DOTP and MOTP blend from said reaction mixture. [0017] In one embodiment the invention is a method of making a methyl 2- ethylhexyl terephthalate (MOTP) and bis(2-ethylhexyl) terephthalate (DOTP) blend comprising: a. heating a first reaction mixture of terephthalic acid and 2- ethylhexanol in the presence of a catalyst to form a first reaction product; b. adding methanol to the first reaction product of step a), to form a second reaction mixture; c. heating and monitoring the reaction mixture of step b) to a detect a desired DOTP and MOTP product distribution; d. cooling said reaction mixture of step c); e. adding an aqueous hydroxide solution to said reaction mixture of step d), to form a first aqueous component and a first organic component, said first organic component containing DOTP, MOTP and 2-ethylhexanol; f. separating said first aqueous component of step e) from said first organic component of step e); g. adding water to said first organic component of step f) to form a second aqueous component and a second organic component containing DOTP, MOTP and 2-ethylhexanol; h. separating said second aqueous component from said second organic component of step g); i. removing 2-ethylhexanol from said second organic component from step h) to form a mixture containing DOTP and MOTP; and j. filtering and drying said solution of step i) to recover a DOTP/MOTP blend.

DETAILED DESCRIPTION

Definitions

[0018] In this specification and in the claims that follow, reference will be made to a number of terms, which shall be defined to have the following meanings.

[0019] Values may be expressed as “about” or “approximately” a given number. Similarly, ranges may be expressed herein as from “about” one particular value and/or to “about” or another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect.

[0020] As used herein, the terms “a,” “an,” and “the” mean one or more. [0021] As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination, B and C in combination; or A, B, and C in combination.

[0022] As used herein, the terms “comprising,” “comprises,” and “comprise” are open-ended transition terms used to transition from a subject recited before the term to one or more elements recited after the term, where the element or elements listed after the transition term are not necessarily the only elements that make up the subject. [0023] As used herein, the terms “having,” “has,” and “have” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above.

[0024] As used herein, the terms “including,” “includes,” and “include” have the same open-ended meaning as “comprising,” “comprises,” and “comprise” provided above.

[0025] “Chosen from” as used herein can be used with “or” or “and.” For example, Y is chosen from A, B, and C means Y can be individually A, B, or C. Alternatively, Y is chosen from A, B, or C means Y can be individually A, B, or C, or a combination of A and B, A and C, B and C, or A, B, and C.

Invention

[0026] In an embodiment of this invention a batch or continuous reactor can be used in the conversion of dimethyl terephthalate to a bis(2-ethylhexyl) terephthalate and methyl 2-ethylhexyl terephthalate blend.

[0027] The simplest reactor for the method requires a vapor dividing head and access ports for charging material. The reactor is charged with dimethyl terephthalate, 2-ethylhexanol, and catalyst. The volatile by-product of the reaction is methanol and is removed by way of vapor dividing head to a pot temperature, then allowed to reflux. When the desired amount of methyloctyl terephthalate is reached, material is then treated with sodium hydroxide solution, decanted, then washed with water. This step will remove a majority of the remaining DMT. The excess 2-ethylhexanol is then stripped, and steam- stripped to remove residual amounts. After steam stripping the material is dried at reduced pressure, then filtered.

[0028] Another embodiment of this invention is a method of producing a MOTP and DOTP blend by monitoring the amount of methanol removed from the reaction mixture.

[0029] Another embodiment of this invention is a method of producing a MOTP and DOTP blend by transesterification of DOTP using methanol to achieve the MOTP and DOTP product blend desired.

[0030] Another embodiment of this invention is a method of producing a MOTP and DOTP blend by the mixed esterification reaction of terephthalic acid (TPA) and methanol/2-ethylhexanol. Because of the significant difference in the boiling points of methanol and 2-ethylhexanol, this reaction can be run under ambient or above ambient pressures.

[0031] In another embodiment of the invention the stoichiometric amount of 2-ethylhexanol can range from less than 2:1 (0 mol% excess) to 3:1 (50 mol% excess). The preferred amount is a 5 mol% excess of 2-ethylhexanol with the unreacted alcohol being recycled to the process. The amount of methyloctyl terephthalate produced is controlled by the pot temperature. At the preferred charge of 5 mol% excess of 2-ethylhexanol, a pot temperature of 160-176 °C produces 26.5-19.7% methyloctyl terephthalate. This range is consistent with the amount of methyloctyl terephthalate produced in the reaction mixture with excess 2-ethylhexanol remaining in the mixture. With the final material producing 23.04% at a pot temperature of 174 °C, 22.20% at a pot temperature of 176 °C, and 24.55% at a pot temperature of 170 °C. The target amount of methyloctyl terephthalate produced can be controlled by reactor temperature in batch or continuous process. The reactor temperature is also dependent upon the amount of 2-ethylhexanol that is charged to the reactor.

[0032] Suitable catalysts include strong protic acids such as tosylic, sulfuric, p-toluenesulfonic, phosphoric, and methanesulfonic acids, Lewis acids such as compounds of tin, titanium, yttrium, zirconium, scandium and zinc, and alkali and alkaline earth metal salts and oxides such as BaO, SrO, CaO, MgO and LiCI. The preferred catalyst is tetraisopropyl titanate (TIPT).

EXAMPLES

[0033] This invention can be further illustrated by the following examples thereof, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

[0034] Each example used the same equipment with the exception of reactor size. The material charges will be described for each example.

Abbreviations

[0035] mL is milliliter; wt % is weight percent; eq is equivalent(s); hrs or h is hour(s); mm is millimeter; m is meter; GC is gas chromatography; °C is degree Celsius; min is minute; tR is retention time; g is gram; mmol is millimole; mol is mole; kg is kilogram; L is liter; w/v is weight/volume; pL is microliter; Tg is glass transition temperature; MW is molecular weight.

Example 1

[0036] Equipment: Round bottom flask, stir bar, stir plate, 10” Penn State packed column, vapor dividing head, magnet for lifter, condenser, fraction cutter, receiver, and thermometers.

The molar ratio of each run is labeled.

240.9g 2-Ethylhexanol (mw-130.23; 1.85 moles)

194.2g DMT (mw-194.19; 1 mole)

0.23g TIPT (500ppm) Table 1 :

Example 2 260.5g 2-Ethylhexanol (mw-130.23; 2 moles)

194.2g DMT (mw-194.19; 1 mole)

0.23g TIPT (500ppm)

Table 2:

Example 3

Table 3 shows the same molar ratios as in example 2, but gradually increasing temperatures.

Table 3: Example 4

[0037] Equipment: 1-L round bottom flask, stir bar, 10” Penn State packed column, vapor dividing head, condenser, fraction cutter, receiver, and thermocouples [0038] Charges:

273.5g 2-Ethylhexanol (mw-130.23; 2.1 moles)

194.2g DMT (mw-194.19; 1 mole)

0.09g TIPT (200ppm)

[0039] Heat reaction stopping at 170C and gc for % mono in an effort to produce 20% monomethyl material.

[0040] After reaction was complete, the material was hazy at room temperature. Charged to a 1 -L drop bottom flask, heat to 90 °C (at 30 °C pot was clear) and washed once with 2.5 wt% NaOH (200g) and once with Dl Water (200g). The organic layer was then stripped to 150 °C at 7 mmHg, then steam stripped at 150 °C at 50 mmHg. After steam stripping, the material was dried. 321 3g material was produced.

Table 4:

Example 5

820.5g 2-Ethylhexanol (mw-130.23; 6.3 moles)

582.6g DMT (mw-194.19; 3 mole)

0.27g TIPT (200ppm)

[0041] Heat reaction stopping at 170 °C and gc for % monomethyl in an effort to produce 20% mono material.

[0042] After reaction was complete, the material was hazy at room temperature. Charged to a 5-L drop bottom flask, heated to 90 °C (at 30 °C pot was clear) and washed once with 2.5% NaOH (400g) and once with Dl Water (400g), pH still acidic (5). Washed with 2.5 wt% NaOH (400g) and once with Dl Water (400g) (pH 8). Decants went well, lot of solids in first caustic wash. The organic layer was then stripped to 150 °C at 7 mmHg, then nitrogen sparged at 150 °C at 50 mmHg. 1019.3g of material was produced.

Table 5:

Example 6

[0043] Example 6 is repeat of example 5.

820.5g 2-Ethylhexanol (mw-130.23; 6.3 moles) 582.6g DMT (mw-194.19; 3 mole)

0.27g TIPT (200ppm)

[0044] Heat reaction stopping at 170 °C and gc for % monomethyl in an effort to produce 20% mono material.

[0045] After reaction was complete, the material was hazy at room temperature. Charged to a 5-L drop bottom flask, heated to 70 °C (at 30 °C pot was clear) and washed twice with 2.5 wt% NaOH (400g) and once with Dl Water (400g), pH 9. The organic layer was then stripped to 150 °C at 7 mmHg, then nitrogen sparged at 150 °C at 50 mmHg. 1001.1 g of material was produced. Table 6:

Example 7

[0046] Charges:

286.5g 2-Ethylhexanol (mw-130.23; 2.2 moles) 194.2g DMT (mw-194.19; 1 mole)

0.1 Og TIPT (200ppm)

Table 7:

Example 8

390.7g 2-Ethylhexanol (mw-130.23; 3 moles) 194.2g DMT (mw-194.19; 1 mole) 0.29g TIPT (500ppm)

Table 8:

Example 9

[0047] Equipment: 1-L round bottom flask, stir bar, feed pump, feed tank, condenser, receiver, simple distillation head, and thermocouples [0048] Charges:

585.9g DOTP(mw-390.6; 1.5 moles)

60g MeOH

0.6g TIPT (lOOOppm)

[0049] A pot was set up for sub-surface MeOH addition and a simple distillation head. MeOH was charged to the pot prior to heating. GC samples were taken as temperature was increased.

Table 9:

Example 10

[0050] Equipment: 1-L round bottom flask, stir bar, 10” Penn State packed column, decanter, feed pump, feed tank, condenser, receiver, and thermocouples.

[0051] Charges: 221.4g 2-ethylhexanol (mw 130.23; 1.7 moles)

166.1 g TPA (mw 166.13; 1 mole)

0.387g TIPT (lOOOppm)

28.4g 2-ethlyhexanol charged to decanter [0052] A pot was set up for subsurface MeOH addition. The pot was heated to react 2-ethylhexanol with TPA and begin the MeOH subsurface feed after reaction was complete.

Table 10:

[0053] In the specification, there have been disclosed certain embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.