POLYESTER POLYCONDENSATION WITH LITHIUM TITANYL OXALATE CATALYST

Abstract

This invention relates to a method for manufacturing polyesters, in particular, to using a lithium titanyl oxalate as the catalyst for such reaction to provide fast reactions with excellent color properties for the resulting polyester. The present invention provides an improved method of producing polyester by the polycondensation of polyester forming reactants wherein the improvement comprises utilizing, as the polycondensation catalyst, lithium titanyl oxalate. The improved process produces a polyester of improved color versus other titanyl oxalate catalysts and a novel polyester without the presence of antimony.

Description

BACKGROUND OF THE INVENTION

[0002] This invention relates to a method for manufacturing polyesters, in particular, to using a lithium titanyl oxalate as the catalyst for such reaction to provide fast reactions with excellent color properties for the resulting polyester.

[0003] Description of the Prior Art

[0004] Polycondensation reactions used conventionally in the manufacture of polyesters require an extremely long period of time without a catalyst. Therefore, various types of catalysts are used in order to shorten the reaction time. For example, antimony trioxide and manganese acetate are generally used.

[0005] Titanyl oxalate compounds have been suggested as catalysts for polycondensation reactions to produce polyesters. However, titanyl oxalate compounds when used as polycondensation catalysts in the manufacture of polyesters have caused color problems in the resulting polyester.

[0006] Polyesters are obtained by esterification, ester interchange or polycondensation of dibasic acids such as terephthalic acid and isophthalic acid or esters thereof, functional derivatives of acid chlorides and glycols such as ethylene glycol and tetramethylene glycol or oxides thereof and functional derivatives of carbonic acid derivatives. In this case, a single polyester is obtained when one dibasic acid component and glycol component is used. Mixed copolyesters can be obtained when at least two or more types of dibasic acid component and glycol component are mixed, esterified or subjected to ester interchange and then subjected to polycondensation. When a singlepolyester or two or more initial polycondensates of a mixed copolyester are subjected to polycondensation, an ordered polyester is obtained. In this invention, the term polyester is a general designation for these three types.

[0007] Prior literature has disclosed titanyl oxalate compounds for use as polycondensation catalysts for polyesters. The titanyl oxalate compounds disclosed include potassium titanyl oxalate, ammonium titanyl oxalate, lithium titanyl oxalate, sodium titanyl oxalate, calcium titanyl oxalate, strontium titanyl oxalate, barium titanyl oxalate, zinc titanyl oxalate and lead titanyl titanate. However, based upon the examples in such literature references, only potassium and ammonium titanyl oxalate have actually been used to catalyze the polyester forming reaction. See for example Japanese Patent Publication 42-13030, published on 25, July, 1967. European Patent application EP 0699700 A2 published on Mar. 6, 1996 assigned to Hoechst and entitled “Process for production ofThermostable, Color-neutral, Antimony-Free Polyester and Products Manufactured From It” discloses the use as polycondensation catalyst, however only potassium titanyl oxalate and titanium isopropylate were used for such a catalyst, and, while improved color and antimony free polyester are disclosed, cobalt or optical brighteners were also employed. Lithium titanyl oxalate was not employed and the present invention's discovery of substantial color improvement with lithium titanyl oxalate versus potassium titanyl oxalate. Other patents have disclosed potassium titanyl oxalate as a polycondensation catalyst for making polyester such as U.S. Pat. No. 4,245,086, inventor Keiichi Uno et al., Japanese Patent JP 06128464, Inventor Ishida, M. et al. U.S. Pat. No. 3,957,886, entitled “Process of Producing Polyester Resin, Inventors Hideo, M. et al, at column 3, line 59 to column 4, line 10, contains a disclosure of titanyl oxalate catalysts for polyesters including a listing of many types of titanyl oxalate catalyst. However, only potassium titanyl oxalate and ammonium titanyl oxalate were used in the examples and lithium titanyl oxalate was not even listed among their preferred titanyl oxalate catalysts.

SUMMARY OF THE INVENTION

[0008] The present invention provides an improved method of producing polyester by the polycondensation of polyester forming reactants wherein the improvement comprises utilizing, as the polycondensation catalyst, lithium titanyl oxalate. The improved process produces a polyester of improved color versus other titanyl oxalate catalysts and a novel polyester without the presence of antimony. In addition lithium titanyl oxalate can be used as a polycondensation catalyst in combination with other catalysts to achieve a combination of the attributes of each catalyst in the mixture. Such mixtures include lithium titanyl oxalate with antimony oxide and/or potassium titanyl oxalate K2TiO(C2O4)2. Such mixtures include lithium titanyl oxalate with antimony oxide and/or potassium titanyl oxalate K2TiO(C2O4)2.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The production of polyester by polycondensation of polyester forming reactants is well known to those skilled in the polyester art. A catalyst is usually employed such as antimony oxide. Titanyl oxalate catalysts such as potassium titanyl oxalate and ammonium titanyl oxalate have also been suggested as catalysts for the polycondensation reaction to produce polyester. The present invention is based upon the discovery that one titanyl oxalate (lithium titanyl oxalate) is surprisingly superior in catalyst performance for polycondensation reactions by producing polyesters of superior color (white) in comparison to other titanyl oxalate catalysts. The need for an antimony containing catalyst can thereby be eliminated, and an antimony free polyester can thereby be produced with lithium titanyl oxalate as the catalyst. Such advantages provided by using lithium titanyl oxalate are retained when lithium titanyl oxalate is used in combination with other polycondensation catalysts for producing polyester as long as lithium titanyl oxalate comprises at least 5 parts per million based on the weight of titanium in the reaction mixture. Included within the meaning of the term “lithium titanyl oxalate” as used herein are dilithium titanyl oxalate [LiTiO(C2O4)2] and mono lithium titanyl oxalate wherein one of the lithiums of di lithium titanyl oxalate is replaced with another alkaline metal such as potassium (e.g., LiKTiO(C2O4)2) and such compounds with or without water of hydration. -Lithium titanyl oxalate catalysts can be combined with antimony catalyst to achieve the benefits of both catalysts when elimination of antimony is not a requirement for the resulting catalyzed product.

[0010] In addition to catalyzing polycondensation reactions, titanyl oxalates of the formula M2TiO(C2O4)2(H2O)n wherein each M is independently selected from potassium, lithium, sodium and cesium are useful for catalyzing esterification and transesterification reactions when used in catalytically effective amounts with reactants known to participate in esterification or transesterification reactions. An advantage to lithium titanyl oxalate catalyst in esterification and transesterification reaction is that it has excellent air stability versus Ti(OR)4. The titanyl oxalate may be anhydrous (n=0) on contain some water of hydration, i.e. n representing the amount of water of hydration. A catalytically effective amount is suitable. Preferred is at least 5 parts of titanyl oxalate based on the weight of titanium per million parts of esterification or transesterification reaction mixture being.

[0011] Reactants for forming polyesters via a polycondensation reaction are well known to those skilled in the art and disclosed in patents such as U.S. Pat. No. 5,198,530, inventor Kyber, M., et al., U.S. Pat. No. 4,238,593, inventor B. Duh, U.S. Pat. No. 4,356,299, inventor Cholod et al, and U.S. Pat. No. 3,907,754, inventor Tershasy et al, which disclosures are incorporated herein by reference. The art is also described in “Comprehensive Polymer Science, Ed. G. C. Eastmond, et al, Pergamon Press, Oxford 1989, vol. 5, pp. 275-315, and by RE. Wilfong, J. Polym. Science, 54 (1961), pp. 385-410. A particularly important commercial specie of polyester so produced is polyester terephthalate (PET).

[0012] A catalytically effective amount of lithium titanyl oxalate is added to the polyester forming reactants. Preferred is from 30 parts to 400 parts per million of catalyst based on the weight of polyester formiing reactants and based on the weight of titanium in the catalyst.

[0013] The superior performance oflithium titanyl oxalate versus other titanyl oxalate catalyst for catalyzing the polycondensation reaction to form polyester is established by the following examples.

Preparation of Polyethyleneterephthalate (EET) Using DMT and Ethylene Glycol

[0014] 305 g of dimethylterephthalate (DMT, 1.572 moles) and 221 g of ethylene glycol (3.565 moles) in the presence of 0.120 g Li2TiO(C2O4)2(H2O)4(3.68×10−4 moles) are loaded into a 1.8 liter cylindrical reactor equipped with a bladed stirrer and a motor. The system is heated to 195° C. at atmospheric pressure under nitrogen and maintained at this temperature for 90 minutes, continuously distilling off methanol as it is produced. The pressure is then reduced to 0.1 mbar for 20 minutes. The reaction temperature is then raised to 275-280° C. and maintained under these conditions for 2.5 hours. The polyester obtained is cooled by immersion in water. This rapid cooling resulted in the formation of a PET plug which could be easily removed from the broken glass reactor. The recovered PET plug was then granulated to simplify analysis.

Preparation of PET Using Terephthalic Acid and Ethylene Glycol

[0015] 150 g of ethylene glycol (2.417 moles), 350 g of terephthalic acid (2.108 moles), and 0.120 g of Li2TiO(C2O4)2(H2O)4 (3.68×10−4 moles) are mixed into a reaction paste at 40° C. The paste is then added to an equal amount of agitated molten oligomer at 250° C. in a vessel equipped with a column to collect distillates. The temperature is then raised to 265° C. and maintained until no additional water is collected. The pressure is then reduced incrementally to 0.1 mbar for 20 minutes. The reaction temperature is then raised to 275-280° C. and maintained under these conditions for 2.5 hours. The polyester obtained is cooled by immersion in water.

[0016] This rapid cooling resulted in the formation of a PET plug which could be easily removed from the broken glass reactor. The recovered PET plug was then granulated to simplify analysis.

General Procedure for the Evaluation of Polycondensation Catalysts

[0017] Evaluation of catalysts was performed in an upright tubular glass reactor equipped with a stainless steel stirrer designed to produce a thin film on the walls of the reactor during polycondensation. Volatiles produced under reaction conditions were collected in a series of cold traps, from which they can be identified and quantified. The reactor and traps were attached to a manifold which permitted the contents of the apparatus to be placed under vacuum or inert atmosphere. Polyethyleneterephthalate (PET) was produced which is probably the most commercially important polyester produced today.

[0018] Bis(hydroxyethyl)terephthalate (BHET) and catalyst(s) were added to a reactor and, after evacuation to remove residual air and moisture, the reactor contents were then blanketed with nitrogen. The reactor and contents was then heated to 260° C. by immersion into an oil bath. Temperature was monitored by a thermocouple on the outside wall of the reactor. At 260° C., the reactor stirrer is activated to mix the melted BHET and the catalyst, and stirring at constant speed is maintained throughout the evaluation. The temperature and pressure inside the reactor were then adjusted incrementally to a final value of 280° C. and 0.05 mbar; reactor contents were stirred for 2.5 hours under these conditions. After this time, the apparatus was placed under a nitrogen atmosphere, and the reactor was quickly immersed in a liquid nitrogen bath. This rapid cooling resulted in the formation of a PET plug which could be easily removed from the broken glass reactor. The recovered PET plug was then granulated to simplify analysis. Analyses for the PET samples produced is summarized in Table 1.

EXAMPLES

Example A. (Benchmark—antimony catalyst)

[0019] 42.72 grams of BHET and 0.0153 grams of Sb2O3 were reacted at a catalyst concentration of 299 ppm Sb according to procedure above.

Example 1

[0020] 43.50 grams of BHET and 0.0212 grams of Li2TiO(C2O4)2(H2O)4 were reacted at a catalyst concentration of 79 ppm Ti according to the procedure above.

Example 2

[0021] 39.87 grams of BHET and 0.0096 grams ofLi2TiO(C2O4)2(H2O)4 were reacted at a catalyst concentration of 39 ppm Ti according to the procedure above.

Example B

[0022] 42.98 grams of BHET and 0.0058 grams of K2TiO(C2O4)2(H2O)2 were reacted at a catalyst concentration of 19 ppm Ti according to the procedure above.

Example C

[0023] 38.45 grams of BHET and 0.01 08 grams of K2TiO(C2O4)2(H2O)2 were reacted at a catalyst concentration of 39 ppm Ti according to the procedure above.

Example D

[0024] 2 0 42.98 grams of BHET and 0.0057 grams of K2TiO(C2O4)2(H2O)2 with 0.0035 grams of Co(O2CCH3)2 were reacted at a catalyst concentration of 19 ppm Ti and 19 ppm Co according to the procedure above.

Example E

[0025] 39.78 grams of BHET and 0.0078 grams of Cs2Tio(C2O4)2(H2O), were reacted at a catalyst concentration of 19 ppm Ti according to the procedure above.

Example F

[0026] 43.05 grams of BHET and 0.0057 grams of Na2Tio(C2O4)2(H2O). were reacted at a catalyst concentration of 19 ppm Ti according to the procedure above.

[0027] Table 1. Data for PET produced during catalyst evaluation. IV is the intrinsic viscosity, Mw is the weight average molecular weight, Mn is the number average molecular weight, and color Was assigned by visual inspection.

[0028] The procedure of the above examples was repeated with the type and amount of catalyst as shown in Table 2. The resulting PET product was analyzed and the analytical results are given in Table 2. Clearly superior PET product was obtained with the catalyst and the catalyst mixtures of the present invention. The ratio of the catalyst mixtures in Table 2 given in the column headed “Mix ratio” are weight ratios.

Esterification and Transesterification Evaluation

[0029] Several metal oxalates [M2To(C2O4)2(H2O)] were evaluated as esterification catalysts using the reaction of 2-ethylhexanol (20% excess) with phthalic anhydride at 220° C., The rate of reaction was measured by following the acid number of the composition versus time. The results are summarized in Table 3 for titanates where M═Li, Na, K, or Cs. The catalysts were employed using 25 mg M/l 00 g of phthalic anhydride. The results for the same reaction using butyl stannoic acid as the catalyst are also shown in the table (catalyst concentration 51.2 mg Sn/lOOg anhydride).

[0030] The results indicate that the Li, K, Na and Cs titanates catalyze the esterification reaction and would therefore catalyze a transesterification reaction.

TABLE 1
Ex. #	Catalysts Evaluate	IV (dl/g)	Mw (g/mol)	Mn (g/mol)	Mw/Mn	Color
A	Sb2O3, 299 ppm Sb	0.743	102100	50100	2.04	white
1	Li2TiO(C2O4)2(H2O)4	0.879	105000	49200	2.13	yellow
	@, 79 ppm Ti
2	Li2TiO(C2O4)2(H2O)4,	0.678	85500	42900	1.99	white
	@ 39 ppm Ti
B	K2TiO(C2O4)2(H2O)2,	0.703	95500	47300	2.02	slight yellow
	@ 19 ppm Ti
C	K2TiO(C2O4)2(H2O)2,		99100	47400	2.09	yellow
	@ 39 ppm Ti
D	K2TiO(C2O4)2(H2O)2/Co(OAc)2	0.678	101300	49700	2.04	purple/blue
	@ 19 ppm Ti/19 ppm Co
E	Cs2TiO(C2O4)2(H2O)n,		110400	54700	2.02	grey/green
	@ 19 ppm Ti
F	Na2TiO(C2O4)2(H2O)n,		74700	38500	1.94	grey/yellow
	@ 19 ppm Ti

[0031]

TABLE 2
		Mix ratio				Mw	Mn	Cab IV	M⊖CHO
Ex #	Catalyst	(w/w)	g BHET	ppm Sb	ppm Ti	(PS Units g/mol)	(dL/g)	(ppm)	Color
G	Cat. Sb		42.6	68		61800	31650	0.595	106	white
H	Cat. Sb		42.9	140		74100	35550	0.673	108	near white
I	Cat. Sb		42.6	222		81650	41250	0.738	132	light grey
J	Cat. Sb		42.7	307		88000	43650	0.778	52	grey
3	Cat. Li		42.6		18.2	69850	34250	0.641	62	white
4	Cat. Li		42.6		37.9	79850	37800	0.717	48	near white
5	Cat. Li		42.6		53.0	89850	42350	0.792	130	faint yellow
K	Cat. K		42.6		16.4	70000	33750	0.642	91	near white
L	Cat. K		42.6		34.8	84550	39800	0.752	123	faint yellow
6	Cat. Sb + Li	1/1	42.6	59	11.8	82100	39950	0.741	143	white
7	Cat. Sb + Li	1/1	42.7	103	20.5	94100	44300	0.823	76	near white
8	Cat. Sb + Li	1/1	42.7	153	30.3	100000	46350	0.867	155	faint grey
9	Cat. Sb + Li	1.96/1	42.6	155	15.3	91800	44100	0.808	145	white
10	Cat. Sb + Li	2.96/1	42.6	149	9.7	86650	43050	0.773	147	white
11	Cat. Sb + Li	3.95/1	42.7	151	7.4	85050	42150	0.762	97	white
M	Cat. Sb + K	1/1	42.7	115	19.4	84000	42000	0.754	317	near white
	Cat. Sb + K
N	Cat. Sb + K	1.96/1	42.7	155	13.5	85200	44000	0.763	243	v.faint grey
O	Cat. Sb + K	2.86/1	42.7	149	8.8	83650	40950	0.752	197	white
P	Cat. Sb + K	4.21/1	42.7	156	6.2	79850	40250	0.725	277	white
Cat. Sb = Sb2O3, 299 ppm Sb
Cat. Li = Li2TiO(C2O4)2(H2O)4
Cat. K = K2TiO(C2O4)2(H2O)2

[0032]

TABLE 3
Catalyst Performance In DOP Esterification
Phthalic Anhydride + 2-EHA at 220° C., 20% Excess of Alcohol
25 mg M (Ti or Zr) or 51.2 mg Snl/100 g anhydride
Acid Numbers
	16% Ti		.2H2O
Catalyst:	Li2TiO(Ox)2	Na2TiO(OX)2	K2TiO(Ox)2	Cs2TiO(Ox)2	Butyl Stannoic Acid
Source:	10044-175A	10044-171	10044-122	10044-181
	318.80
Time (hrs)
0.0	243	243	243	243	243
1.0	26.6	30.9	16.7	20.5	34.0
2.0	6.2	11.3	2.2	2.1	10.2
3.0	0.3	1.9	0.5	0.6	0.3
3.5	0.12	0.73	0.08	0.28
4.0	0.06	0.27	0.06	0.02	0.06
5.0		0.11			0.05
6.0

Claims

1. In a process of producing a polyester by the catalyzed polycondensation of polyester forming reactants in the presence of a polycondensation catalyst, the improvement which comprises utilizing lithium titanyl oxalate as the catalyst.

2. The improved process of claim 1 wherein the amount of lithium titanyl oxalate present is from 5 parts per million to 400 parts per million based on the weight of titanium per part of polyester forming reactant.

3. The process of claim 1 wherein the lithium titanyl oxalate is di lithium titanyl oxalate

4. The process of claim 1 wherein the lithium titanyl oxalate is mono lithium titanyl oxalate.

5. The process of claim 3 wherein the mono lithium titanyl oxalate is of the formula LiKTiO(C2O4)2.

6. The process of claim 3 wherein the lithium titanyl oxalate contains water of hydration.

7. The process of claim 4 wherein the lithium titanyl oxalate contains water of hydration.

8. The process of claim 5 wherein the lithium titanyl oxalate contains water of hydration.

9. An antimony free polyester produced by the process of claim 1.

10. The process of claim 1 further comprising utilizing an antimony containing catalyst in combination with the lithium titanyl oxalate catalyst.

11. The process of claim 10 wherein said lithium titanyl oxalate catalyst comprises at least 5 parts per million based on the weight of titanium in the reaction mixture.

12. In a catalyzed esterification or transesterification reaction, the improvement which comprises utilizing as the catalyst a titanyl oxalate of the formula M2TiO(C2O4)2(H2O)n wherein each M is independently selected from potassium, lithium, sodium and cesium and n is zero or represents the amount of water of hydration

13. The improved reaction of claim 12 wherein the amount of lithium titanyl oxalate present is from 5 parts per million to 400 parts per million based on the weight of titanium per part of polyester forming reactant.

14. The reaction of claim 12 wherein the lithium titanyl oxalate is di lithium titanyl oxalate.

15. The reaction of claim 12 wherein the lithium titanyl oxalate is mono lithium titanyl oxalate.

16. The reaction of claim 14 wherein the mono lithium titanyl oxalate is of the formula LiKTiO(C2O4)2.

17. The reaction of claim 14 wherein the lithium titanyl oxalate contains water of hydration.

18. The reaction of claim 15 wherein the lithium titanyl oxalate contains water of hydration.

19. The reaction of claim 16 wherein the lithium titanyl oxalate contains water of hydration.

20. An antimony free polyester produced by the reaction of claim 12.

21. The reaction of claim 12 further comprising utilizing an antimony containing catalyst in combination with the lithium titanyl oxalate catalyst.

22. The reaction of claim 20 wherein said lithium titanyl oxalate catalyst comprises at least 5 parts per million based on the weight of titanium in the reaction mixture.