CS200764B1 - Process for preparing pentaerythritol with increased thermal stability - Google Patents

Abstract

The invention provides a method for preparing pentaerythritol with increased thermal stability. The treatment of pentaerythritol is carried out in the liquid phase, preferably in an aqueous solution, by adding at least one substance forming a poorly soluble to insoluble compound with calcium ions, preferably phosphoric, carbonic, sulfuric, oxalic acid and/or one or more of these compounds, in an amount of 0.1 to 10 moles, preferably 0.8 to 1.5 moles, calculated per 1 mole of calcium present.

Description

The invention solves the method of preparation of pentaerythritol and with increased thermal stability.

Pentaerythritol is conveniently prepared by the condensation of formaldehyde and acetaldehyde in aqueous solution, usually in the presence of sodium or calcium hydroxide [e. Berlow, R. H. Barth, J. E. Snow: The Pentaerythritol, Reinhold Publ. Co., New York 1958) J. F. Vallkeri Foxmaldehyde, Am. Chem. Soo. Monograph Series, New York 1953^.

From an aqueous solution, formaldehyde is most often obtained after neutralization and concentration of the solution to a saturated solution of pentaerythritol and its crystallization. Since the pentaerythritol obtained by this method still contains impurities of secondary substances, namely syrups and sodium or calcium formate, pentaerythritol is usually further purified by recrystallization.

For the delivery of pentaerythritol to processors, the content of OH groups, melting point, water content, ash content and the AJPHA test, which expresses the color stability* of the prepared pentaerythritol, are standardized in the System product.

Pentaerythritol, which meets all customer requirements within the framework of standards, may not be suitable for all applications. In some cases of preparation of glossy and transparent varnishes, it happens that, despite meeting the customer's requirements, the prepared varnish is not sufficiently transparent, or is slightly dull or yellowish.

When testing pentaerythritol for heat resistance in the molten state, it results in larger or smaller sample losses, as well as different coloration of the residue.

In the study of various pentaerythritol samples, we found that pentaerythritol samples that meet all the requirements of the standard when exposed to heat at 20 °C for 1 hour are characterized by a heat loss of 1 to 26% by weight. The product remaining after heat stress is usually white to cream. The color changes to cream with increasing heat loss.

This unforeseen heating of pentaerythritol is eliminated by the application of the method according to the present invention, in which pentaerythritol with increased thermal stability is prepared by treating pentaerythritol in the liquid phase, and preferably in an aqueous solution, by adding at least one substance forming with calcium ions a poorly soluble to insoluble compound, preferably phosphoric, carbonic, sulfuric, oxalic acid and/or these compounds, in an amount of 0.1 to 10 moles, preferably 0.8 to 1.5 moles, calculated per 1 mole of calcium present.

The advantage of the above method is that a product with high thermal stability can be obtained economically in practically one technological cycle without any equipment modifications. Such a product is suitable for the preparation of high-quality varnishes and compositions due to its increased thermal stability.

The essence of the invention is the removal of calcium salts, specifically calcium formate, from a solution. As we have discussed calcium salts, especially calcium formate, by its presence catalyzes the decomposition of pentaerythritol. This is particularly suitable for removal from solution by binding in the form of insoluble salts. It is also possible to remove it from solutions by binding to solid carriers, from which, after removal of the pentaerythritol solution, calcium can be removed by washing, and thus the carrier can be regenerated for further use.

The specific embodiment of the purification operation is that the raw pentaerythritol is dissolved in the required amount of water under heat. The dissolution temperature is usually 80 to 105 °C. After preparing a homogeneous solution, a substance forming poorly soluble to insoluble compounds with calcium ions is added to the solution, most preferably phosphoric acid in an amount close to the stoichiometric amount. The amount is calculated according to the calcium content, and it is most preferable to use the amount necessary for the formation of calcium hydrogen phosphate. The amount of phosphoric acid required is preferably calculated according to the amount of calcium lauryl sulfate or calcium formate in the raw pentaerythritol. After determining the calcium content, 2.4 to 2.8 times the mass of phosphoric acid per calcium is added or, after conversion to calcium formate, e.g. an equal amount by weight of 85% phosphoric acid (0.88 to 1.2 parts by weight of 85% acid per part of calcium formate). It is also possible to use salts of phosphoric acid for binding calcium, e.g. sodium phosphate, ammonium phosphate, etc.

It is also possible to use sulfuric acid and its salts, but their effects are lower than those of phosphoric acid, oxalic acid and its salts, or substances that bind calcium and thus cause its removal from the solution.

The method of implementation may vary. For example, after dissolving the raw pentaerythritol, it is possible to add the appropriate calcium-binding substance, e.g. in the form of a slightly soluble to insoluble compound, and after separating the said compound, e.g. by filtration, to bring the solution into contact with activated carbon and other cleaning substances. Alternatively, it is possible to first apply the cleaning substances and then add the calcium-binding substance and jointly separate the suspensions from the solution, or it is possible to pass the solution through columns filled with cleaning and calcium-binding substances, or the procedure can be combined.

The above procedure allows even from the so-called raw pentaerythritol with low thermal stability, where the losses of pentaerythritol are less than 4% by weight at a temperature of 270 °C in 1 hour, to prepare pentaerythritol with high thermal stability, where the losses are lower than 2% by weight.

While in the first case, after thermal stress, the product is brown to black, in the second case, the product after stress matched the color of the product before thermal stress.

Further advantages as well as the method of implementation are apparent from the examples.

Example 1

The thermal stability of pentaerythritol was monitored. The method of determination was as follows.

g of sample was poured into a 100 ml flask, which was placed in a heated oil bath and equipped with a descending condenser. Heating to a temperature of 270 °C was carried out using silicone oil. After 60 minutes of tempering, the flask was removed from the bath and weighed after cooling. The heat losses of pentaerythritol were determined from the difference in weights. The sample

200 704 pentaerythritol with heat losses of 14.1 wt.% (270 °C, 60 minutes) were treated with vigorous stirring. The treatment conditions as well as the thermal stability results are given in Table 1.

Table 1 Effect of pentaerythritol modifications on thermal stability at a temperature of 270 °C and a time of 1 h.

Additions j”$ massJ Heat losses on the shaft mass.J Product color Standard without surcharge 14.1 yellowish brown + 0.2 * H ₃ PO ₄ 11.2 brown without allowance with cover Staliz. 11 .7 yellowish brown + 1.2% acid, Stavelová prekxyStal. 6.7 yellowish brown + 1.2 i» Na ₂ S0^ recrystallized. 8.5 rye 1.0% (ΝΗ ₄ ) ₂ ΗΡ0 ₄ overlayStal. 3.2 pale yellow 1.2% (NHjPjjSO^ recrystallized, 6.5 yellowish brown 1.2 # (NH^JgCgO^ recrystallized. 7.4 yellowish brown 1,2 <f> ΝΗ^Η00 ₃ overlaySt. 6.6 yellowish brown 3% cation exchange resin. 7.0 rye 0.2% HgSO^ recrystallized. 5.0 yellowish brown 0.11% H ₃ P0^ recrystallized. 1.7 white 0.23% transcrystallized. 3.2 pale yellow 0.58 # ^H 3 ^PO 4 recrystallized. 6.3 pale brown 1.2% HjPO^ recrystallized. 6.3 pale brown 0.06% ^H 3 ^PO 4 Recrystallized. 1.0 white 0.023% ^H 3 ^Po í, Precrystall. 1.1 white 0.011% ^H 3 ^PO 4 recrystallized. 4.2 rye

The best results were achieved with additions of phosphoric acid in the amount of 0.023 to 0.11 wt. per pentaerythritol. While the addition of 0.2 wt. % phosphoric acid to solid pentaerythritol resulted in only a slight decrease in thermal conductivity (from 14.1 to 11.2 wt.), the addition of phosphoric acid to an aqueous solution of pentaerythritol reduced the thermal conductivity of pentaerythritol to 1.0 wt. %. Recrystallization was carried out at a temperature of 90 to 100 °C with a charge of 45 g pentaerythritol per 100 g water.

Example 2

Crude pentaerythritol containing 2.9% by weight of calcium formate was recrystallized with a significant amount of phosphoric acid.

The results of the influence of the amount of phosphoric acid on thermal stability are summarized below.

200784 to table 2.

Table 2 Effect of the final amount of phosphoric acid additions to raw pentahexytritol containing 2.9% calcium formate on the heat loss of the final product (27Ο °C, 60 minutes)

Addition Η ₃ Ρ0^ Heat losses on the shaft of mass.J Product color quantity . the mass.J jmol per mole of calcium formateJ 0.00 0.00 21.2 brown 0.89 0.33 14.0 yellowish brown 1.79 0.67 8.5 rye 2.67 1.00 3.0 yellowish 2.91 1.08 1.6 white 3.49 1.30 1.4 white 5.34 2.00 2.7 yellowish

As can be seen from the results, the addition of 2.67 to 5.34 wt. % of the mixture using 1 to 2 moles of phosphoric acid per mole of calcium formate significantly reduced the heat losses of pentahexytritol. An 8 to 30% excess with respect to the molar amount required to form calcium hydrogen phosphate appeared to be optimal.

Example 3

Crude pentaerythritol b containing 0.055 wt% calcium was purified by recrystallization with activated carbon.

of pentahexytritol was dissolved in 100 g of water heated to 90 °C. After dissolution, 1.5 g of powdered activated carbon, type Carborafin, was added to the solution. After 20 minutes of exposure, the activated carbon was filtered off and increasing amounts of phosphoric acid were added to the solution. The results are summarized in Table 3.

200,704

Table 3

Addition H^PO^ Heat loss mass.J Product color H [jnol/mol CaJ 0 0.00 13.0 yellow-necked 0.011 0.16 4.5 rye 0.022 0.32 3.6 rye 0.038 0.56? 2.8 yellowish-white 0.045 0.667 2.4 yellowish-white 0.057 0.832 2.3 yellowish-white 0.068 1.00 1.6 white 0.102 1.50 2.0 white 0.177 2.16 1.9 white 0.215 3.16 2.7 yellowish white 0.43 6.32 2.7 yellowish-white

We combined the above method by first adding phosphoric acid, and after filtering the activated carbon, or after 20 minutes of activated carbon exposure, we added phosphoric acid and performed crystallization after jointly filtering the activated carbon and calcium phosphate.

The product had approximately the same thermal stability in all cases.

Claims (1)

OBJECT OF THE INVENTION A process for the preparation of pontaorythritol with increased thermal stability, characterized in that the treatment of pontaorythritol is carried out in liquid fusion, preferably in aqueous solution, by the addition of at least one substance which forms poorly soluble to insoluble compounds with calcium ions, preferably phosphorous, carbon, Stfevel and / or compounds thereof, in an amount of 0.1 to 10 moles, preferably 0.8 to 1.5 moles, calculated per 1, had a calcium present.