GB825475A - Process for the production of alkanolamines - Google Patents

Abstract

Di- or tri-alkanolamines or a mixture comprising di- and tri-alkanolamines are prepared by passing a gas containing an alkylene oxide gaseous under the reaction conditions through a monoalkanolamine, dialkanolamine or a mixture of mono- and di-alkanolamines liquid under the reaction conditions and continuously venting from the reaction zone at least part of the gas. The gas mixture may contain an inert gas such as nitrogen. It is preferably passed through the alkanolamine starting material at a rate such that part of the alkylene oxide, preferably 1-5% by weight, remains unreacted. In a preferred embodiment the gas consists substantially of alkylene oxide free from inert gas. It is desirable to pass an inert gas, e.g. nitrogen, through the alkanolamine starting material to remove substances such as oxygen which would react with the alkylene oxide, and also through the product to remove unreacted alkylene oxide, or the latter may be removed by reducing the pressure. At atmospheric pressure, temperatures of 80-120 DEG C. are suggested for alkanolamines having less than 4 carbon atoms in each alkane radical. Pressures of 0.5 to 20 atmospheres are mentioned. Unreacted alkylene oxide vented from the reaction zone is normally absorbed, e.g. in alkanolamines, perhaps in aqueous solution or in acidified water. It is preferred that the carbon chains in the alkanolamine starting material contain 4 or less carbon atoms each and in the alkylene oxide 3 or less. The chains may be straight or branched. The progress of the reaction may be followed by the increase in volume of the liquid reaction mixture or by equivalent weight determinations. Examples describe the reaction of ethylene oxide with mono- and with di-ethanolamine to form triethanolamine and of propylene oxide with di-isopropanolamine to give a mixture of di- and tri-isopropanolamine which is then mixed with mono-isopropanolamine.