1. Field of the Invention
This invention relates to an efficient method for neutralizing an alkoxylation catalyst. More particularly, this invention relates to a new use for partially spent ion exchange resins and an environmentally attractive method of neutralizing alkoxylation catalysts and removing potassium ions from polyol and alkoxylated alkyl phenol products. Example 2 demonstrates a reduction in potassium to less than 1 ppm.
This method is not only efficient and inexpensive, but also reduces problems inherent in disposal of a partially depleted acidic resin catalyst and reduces the impact on the environment of disposing of filter cakes which remain after using currently available methods to neutralize soluble base catalysts used in alkoxylation reactions.
2. Description of Related Art
One of the most critical fields of study in industrial chemical processes is that of devising methods to remove impurities from products and effluent streams at low cost and, also, to avoid having to dispose of chemical compositions such as catalysts which are still partially active. Plants producing or using basic materials such as ammonia, organic amines, alkali salts or caustic have waste streams that often need to be neutralized. The manufacture of polyols and alkyl phenol alkoxylates presents such a problem.
Polyols and alkyl phenol alkoxylates ar usually manufactured by the base catalyzed addition of propylene oxide or ethylene oxide to various initiators. The catalyst used is potassium hydroxide or another soluble base. The amount of potassium in the final product is critical in order to maintain control of downstream reactions. With one procedure, the catalyst is removed by neutralizing the base with a small excess of H.sub.2 SO.sub.4, absorbing the formed salt, (usually K.sub.2 SO.sub.4) with magnesium silicate, then filtering the product after heating to reduce the viscosity. The filter cake is then disposed of in a land fill.
In the past ion exchange resins have been used to produce polyols and, in fact, worked well. The disadvantage involved the fact that the solution used to regenerated the resin is considered a hazardous waste and is expensive to get rid of properly.
The use of ion exchange resins for removal of magnesium and noncarbonate minerals from water is known in the field of water treatment or water softening. The cost and frequency of regeneration are principal disadvantages. The ion-exchange material generally used in softening water are styrene-divinyl benzene copolymers. Kirk-Othmer Encyclopedia of Chemical Technology, 8, 70 and 24, 425 (1982).
Another aspect of the background for this invention is that the current transition to unleaded fuels in the U.S. has caused a demand for the addition of oxygenates into gasoline which has lead to the development of methyl-tert-butylether as a gasoline additive. The demand for MTBE has caused it to be the fastest growing chemical of the 80's and the demand will grow rapidly in the 90's. Chemical Business, January 1992, p.24. MTBE and other chemicals such as ethyl-tert-butylether (ETBE) and tert-amyl methylether (TAME) are made by the addition of alcohol to an olefin catalyzed by a sulfonic acid ion exchange resin.
The consumption of MTBE is currently about 180,000 barrels per day and could be as high as 670,000 barrels per day by the year 2000. Ibid, p. 25. Another reference indicates the demand would reach 1.2 million barrels per day by the year 2000. (Chemical Week, Nov. 20, 1991, p. 36.)
Due to the demand for high productivity the ion exchange catalyst is used until reduced activity makes it more reasonable to exchange it for a fresh catalyst. This corresponds to a point of about 70-90%, and generally about 85%, of its original activity. This means there are enormous amounts of used catalyst that must be disposed of. Disposal of this partially spent catalyst gives rise to environmental concerns and often requires some sort of permit. It would be extremely efficient from a commercial and environmental viewpoint to accomplish a desirable goal using this partially spent catalyst, reduce the remaining activity of the resin so that disposal of it is not as objectionable and eliminate the production of a filter cake which requires disposal.
It would be a distinct advance in the art if an inexpensive means were available for neutralizing an alkoxylation catalyst and reducing impermissible levels of potassium in polyol and alkoxylated alkyl phenol products. It would be advantageous if this could be accomplished with a substance which to this point has had to be discarded while activity remains due to purity requirements of the primary product, i.e. MTBE, ETBE or TAME. To remove potassium from polyols and alkoxylated alkyl phenols with a partially spent catalyst, that normally entails disposal problems, and eliminate the neutralization of potassium hydroxide and the resulting filter cake would be quite efficient in every respect.