Patent Application
20080004475
Formaldehyde
A 49% by weight aqueous formaldehyde solution with a methanol content of 2.0% by weight was distilled at a top pressure of 1.2 bar in a bubble-cap column comprising 45 trays. The feed rate at the 30th tray was 4 kg/h. A product containing 69.4% of methanol and 12% of formaldehyde was withdrawn from the top at a rate of about 75 g/h. 4 kg/h of steam were fed to the heating surfaces in the bottom evaporator. A residual methanol concentration in the bottom discharge of 0.4% by weight was established. The formaldehyde distilled in this way is used for the aldolization reaction described below:
Aldol Reaction
The aldol reaction was carried out in a stirred tank cascade consisting of two heatable stirred tanks interconnected by overflow tubes. The stirred tanks were charged continuously with 700 g/h of a fresh 49% aqueous formaldehyde solution freed of methanol as described above, and 750 g/h of isobutyraldehyde and 40 g/h of fresh trimethylamine as catalyst in the form of a 50% aqueous solution. The temperature in both stirred tanks was about 70° C. With the exception of the reduction in methanol content for the purposes of the present reaction, the reaction procedure is the same as that already indicated in Example 8 of WO 98/28253, the content of whose disclosure is expressly incorporated herein by way of reference.
The effluent was passed directly into the upper region of a column equipped with 1.5 m fabric packing (500 m2/m3 specific surface area) in the rectifying section and 4 m sheet metal packing (250 m2/m3), above the sheet metal packing, where it was separated by distillation at a pressure of 1.5 bar and a bottom temperature of 102° C. into a low-boiling top product, essentially comprising isobutyraldehyde, formaldehyde, water and trimethylamine, and a high-boiling bottom product. The top product was continuously condensed and recycled into the reactors described above at the same pressure.
The bottom product was found to have an isobutyraldehyde concentration of about 0.1%. A methanol concentration of about 1% was achieved into the recycled low boiler (50 g/h).
Hydrogenation
a) Hydrogenation catalyst
b) In addition to water, the bottom product obtained above comprised essentially hydroxypivalinaldehyde, formaldehyde, trimethylammonium formate and traces of isobutyraldehyde. This bottom product was then subjected to continuous hydrogenation. This was done by hydrogenating the reaction solution over the hydrogenation catalyst described above at 40 bar and 115° C. in a primary reactor by the loop/trickle method and in a downstream secondary reactor by the loop method. The apparatus used consisted of a heated primary reactor with a length of 10 m (internal diameter: 27 mm). The loop throughput was 25 l/h of liquid and the reactor feed was adjusted to 4 kg/h, corresponding to a hydrogenation discharge of 4 kg/h. The yield of neopentyl glycol after hydrogenation was 97%.
The procedure in this comparative example was exactly the same as that indicated in example 1 except that the formaldehyde used comprised 2.0% by weight of methanol instead of 0.4% and the low-boiling fraction was removed at a pressure of 1 bar. In the bottom product of the distillation a concentration of approximately 0.7% iso-butyraldehyde was analyzed and in the low boilers removed overhead and recycled (100 g/h) a methanol concentration of approximately 10% was analyzed. The yield was reduced to 94% neopentyl glycol based on isobutyraldehyde.
