Patent Application
20080027208
The solutions of the invention may exhibit haziness yet constitute solutions in which no precipitation occurs. Precipitates are deemed formed when by the eye one can observe the presence of the catalyst metal particulates settled at the bottom of the vessel.
A series of Lithium-Aluminum mixes was prepared in solutions of polyethylene glycol with an average molecular weight (Mn) of 200 (PEG 200) and ethylene glycol (EG). The lithium source used was lithium hydroxide monohydrate and the aluminum source was aluminum isopropoxide.
Mixes were prepared on a stirring hot plate, with temperature controlled by a thermocouple placed in an EG blank in the center of the plate. Temperature target was 125° C. Agitation was accomplished by a magnetic spin bar. Stirring rate was set to 400 rpm. The mixes were prepared in 125 ml bottles with septum caps. A small hypodermic needle was used as a nitrogen inlet, to allow nitrogen to sweep over the mixes while heating. Two more small hypodermic needles were then used as a nitrogen outlet. The flow rate was not quantitatively measured, but a qualitative assessment was made (i.e. when a slight ripple was noticed in the mix, the flow was deemed to be sufficient).
After the EG blank reached 125° C. (which took about 45 minutes), the mixes were allowed to continue stirring and heating for another 3.5 hours. At the end of this time period, they were removed from the hot plate and the nitrogen sweep was removed.
One set of samples was allowed to sit at room temperature. They were observed daily to see when/if they would go out of solution (over a 14 day period). Another set of samples was prepared the same way, but upon completion they were placed in an oven at 65° C. Observations were again made over a 14 day period.
While the first set of samples was prepared only at a 1 to 1 mole ratio of lithium to aluminum (with a 3000 ppm aluminum target), the second set contains mixes at 1 to 1, 3 to 1, and 5 to 1 mole ratios, with the same 3000 ppm aluminum target. Table 1 lists the chemicals used to prepare the mixes, and how long each mix remained in solution.
The 1 to 1 mole ratio solution prepared in 100% PEG 200 remained in solution during the entire 14-day observation period. Up to 25% EG can be added to the PEG 200 solution and still maintain 14-day solubility of the 1:1 mole ratio catalyst at 65° C. However, the 3:1 and 5:1 catalyst mole ratios prepared in a 25% EG/75% PEG 200 mixture did not remain in solution for even one day at 65° C.
The experiments described in this Example 2 demonstrate that highly stable 1:1 Li/Al solutions can be prepared in diethylene glycol (“DEG”) and that these solutions give equivalent catalytic activity and polymer properties to mixes made in EG.
All catalyst mixes were prepared in a 250 ml glass bottle containing a magnetic stir bar and septa lined cap. A ¼ in. hole was punched through the septa to serve as both a nitrogen inlet and vent during heating. Desired levels of lithium, aluminum, and glycol were added to each catalyst bottle. In every case, the lithium was added first as lithium hydroxide monohydrate followed by aluminum as aluminum isopropoxide. The glycol was then added as either diethylene glycol or an ethylene glycol/diethylene glycol mixture. Solutions were heated on a hotplate equipped with five heating sections. The middle heating section contained an EG blank equipped with a stainless steel thermocouple to monitor its temperature. The four remaining sections, located at each corner, were used for all Li/Al catalyst mixes. Their solution temperatures were estimates based on the EG blank. Solutions were prepared at 60, 90, and 120° C. under an N2 sweep (1.2 SCFH) with a stirring speed of 300 rpm. Heating times varied from a minimum of 3 hours to a maximum of 24 hours. Each solution was visually judged to determine its solubility and color. After heating was complete, the solutions were allowed to cool to room temperature. Solutions were inspected periodically over a 22 day period to determine their stability to precipitation. In some instances, the solutions were placed in an oven pre-set at 65° C. to assess their stability. The results are reported in Table 4.
The results reported in Table 4 show that 1:1 Li to Al mole ratio catalyst solutions made with DEG at reaction temperatures of 90° C. and 125° C. and allowed to cool to ambient conditions or kept at 65° C. are clear and stable against precipitation over a period of at least one (1) week, and in many cases over 22 days. 1:1 Li to Al mole ratio catalyst solutions containing mixtures of EG with DEG are more likely to precipitate, and in 100% EG, they readily precipitate out of solution when cooled to ambient conditions. A 3:1 Li to Al mole ratio catalyst in DEG is also stable. The stability of the 5:1 mole ratio samples was not determined because it was previously determined that a 5:1 mole ratio of Li:Al catalysts are stable for long periods of time in 100% ethylene glycol as the solvent. When EG is added as an additional solvent, the catalyst tends to become more soluble as the molar ratio of Li:Al increases, and becomes less soluble as the molar ratio of Li:Al approaches 1:1. This phenomena is more apparent as the amount of EG in the solvent mix increases. Thus, when mixing EG or other solvents with DEG, the molar ratio of the M:Al should be adjusted to ensure that the solution continues to remain stable.
The data in Table 5 illustrate the maximum solubility of a 1:1 Li/Al catalyst solution in DEG. The weight percentages reported Table 5 are based on the charged amount of Al. However, we have determined by testing the final product using ICP-OES that the Li and Al concentration was higher than charged, presumably due to losses of isopropanol, water and DEG during the preparation. For the 1.69 wt % (charged) Al solution, the measured amount of Al was 2.5 wt % and the measured amount of Li was 0.54 wt %. The maximum solubility of Al in DEG at a 1:1 Li/Al mole ratio is approximately 2.5 wt %. Highly concentrated solutions are preferred because they minimize the amount of DEG incorporated into the polymer from the catalyst mix. Mixes were prepared at 125° C. on a hotplate with nitrogen sweep. The flow rate of the nitrogen sweep was not quantified, but was visually determined as enough flow to cause a ripple in the liquid (as described in Example 1). Catalyst solutions were held at 65° C. and room temperature. Observations were made on a daily basis.
Lithium/Aluminum catalyst solutions prepared with 0, 50, and 100 wt % DEG were evaluated during melt phase polymerization of PET to determine their catalytic activity. The Al concentration in these solutions was targeted to 3000 ppm, except for Example 4-7 which was a 2.5 wt % Al solution. PET polymerizations were conducted on a Camile automated polymer stand using the conditions shown in Table 6. In all cases, the Li/Al molar ratio was targeted to 1:1 and the catalyst was added to TPA-based oligomer prior to heating. Finished polymers were coarsely ground to approximately 3 mm and characterized by the following test methods:
tetrachloroethane solution
The results given in Table 7 demonstrate that polymers made with 1:1 mole ratio Li to Al catalyst in DEG and EG/DEG mixtures, have similar polymerization rates, polymer color, and polymer haze, compared to those in which the catalyst was contained solely in EG.
In the following experiment, a concentrated Li/Al mix in DEG (2.5 wt % Al and 0.54 wt % Li) which was clear and contained no precipitate was diluted in EG to give the stated Al concentrations as follows:
In each of Samples 5-1, 5-2, and 5-3, the solutions were initially clear and colorless when first mixed together. However, the solutions precipitated overnight to form milky white precipitates. The results indicate that aluminum solutions tend to precipitate in the presence of EG at Al concentrations of 3000 or more. However, as shown in Table—4_, a 1:1 and 3:1 molar ratio of Li/Al at Al concentrations of 3000 in 100% DEG remained stable over two weeks.
This example illustrates the benefit of a high nitrogen flow rate during the catalyst solution preparation. Catalyst mixes were prepared by charging 4.65 grams of lithium hydroxide monohydrate, 22.71 grams of aluminum isopropoxide and 150 grams of DEG to a reaction flask. The flask was equipped with an inlet for a nitrogen sweep, a heating mantle, a thermocouple to measure the reaction temperature, a magnetic stir bar and distillation head connected to a water-jacketed condenser to remove the volatile reaction by-products. The heat-up rate was 1.7° C./min (i.e. heating from ambient temperature to 125° C. took about 1 hour). The reaction was heated with stirring and using a nitrogen flow rate as indicated in the Table 9.
In Experiment A, the solubility was complete within one hour of heating at 125° C. with a high nitrogen sweep of 1.25 SCFH. Experiment B illustrates that lithium hydroxide can be pre-dissolved before addition of aluminum isopropoxide and slightly faster solubility is obtained. Experiments C and D illustrate that the rate of dissolution is slowed down when a low nitrogen sweep is used relative to the high nitrogen sweep.
