1. Field of the invention
The present invention relates to a process for producing a polyhydric alcohol which is useful as a raw material for polyester resins, alkyd resins, polyurethane resins, polycarbonate resins, plasticizers, surfactants, lubricating oils, basis for cosmetics, reactive monomers and the like.
2. Description of the Related Arts
There is known, as a process for producing a polyhydric alcohol, a two-stage reaction process in which an aliphatic aldehyde and formaldehyde are subjected to an aldol condensation reaction, and subsequently to a crossed Cannizzaro reaction each in the presence of a base catalyst, said aliphatic aldehyde being represented by the formula (i) ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 are each a hydrogen atom or a straight-chain or branched aliphatic hydrocarbon group having 1 to 22 carbon atoms with the proviso that at least one of them is a hydrogen atom.
The above-mentioned process is described in Japanese Patent Application Laid-Open No. 139141/1988 corresponding to U.S. Pat. No. 4,814,509, Japanese Patent Application Laid-Open No. 162538/1983 corresponding to U.S. Pat. No. 4,514,578 end the like, but each process described therein is based on the premise that the objective polyhydric alcohol is produced in combination with a formic acid salt.
Examples of the base catalyst to be used in the above-mentioned process include a hydroxide of an alkali metal or an alkaline earth metal and a carbonate of any of the aforesaid metals, which are exemplified by sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate and lithium carbonate; and an amine compound, especially a tertially amine such as trimethylamine, triethylamine, diethylmethylamine, dimethylethylamine, diisopropylamine and tributylamine.
As a process for producing neopentyl glycol (hereinafter abbreviated to "NPG") which is one of polyhydric alcohols, there is described a process in which hydroxypivaldehyde (hereinafter abbreviated to "HPA") is synthesized at first by an aldol condensation reaction in the first reaction stage and then the resultant HPA is hydrogenated into NPG in Japanese Patent Application Publication No. 53421/1982 corresponding to EP 44412, Japanese Patent Application Laid-Open No. 299239/1989 corresponding to U.S. Pat. No. 4933493, and Japanese Patent Application Laid-Open No. 182442/1992 corresponding to U.S. Pat. No. 5,395,989, and the like patent.
A process for producing trimethylol propane (hereinafter abbreviated to "TMP") which comprises effecting hydrogenation after the aldol condensation reaction in the same manner as above is described in Japanese Patent Application Laid-Open No. 92705/1978 corresponding to U.S. Pat. No. 412,290, Japanese Patent Application Laid-Open No. 287738/1988 corresponding to U.S. Pat. No. 5,149,861 and the like.
The production of a polyhydric alcohol in the presence of a base catalyst is accompanied with the by-production of a formic acid salt in an equimolar amount to the polyhydric alcohol as the main objective product. The formic acid salt as the by-product is utilized, for example, for the production of a hydrosulfite, etc., but is limited in its demand. Thus it follows that most of the by-produced formic acid salt is inevitably subjected to waste disposal, which incurs great expense, since it is accompanied by environmental pollution.
On the other hand, the process for producing NPG which comprises an aldol condensation reaction and successive hydrogenation requires a high pressure of about 50 to 150 kg/cm.sup.2 in the hydrogenation reaction, thereby complicating the production equipment.
Moreover in the case of producing TMP by a process similar to the above, the objective TMP is obtained only at a low yield and less production rate per unit time; besides there has never been found an example demonstrating an industrial production of TMP by the foregoing process.