Dehydration of n-propanol and methanol to produce etherified fuel additives

Abstract

An ether is an organic compound that consists of an oxygen atom bonded to two alkyl or aryl groups. In this work, we investigate the bimolecular dehydration of two alcohols, n-propanol and methanol with catalysts that are used in transesterification. Experiments were carried out to evaluate the feasibility of promoting etherification reaction using methanol and n-propanol as model alcohols. When methanol and n-propanol are reacted together, three types of ethers can be produced; i.e., dimethyl ether, methyl-propyl ether (also referred to as methoxypropane), and di-propyl ether. The latter two ethers are of more fuel interest due to their ability to stay in liquid phase at room temperature; however, the ability of catalysts to selectively produce liquid ethers is not established. Initial studies were conducted to discern the effect of sulfuric acid, amberlyst-36 and titanium isopropoxide, catalysts that are known to be effective for transesterification, at four levels of temperature on the substrate conversion, ether yield and selectivity using n-propanol. Subsequent studies with n-propanol and methanol additionally looked at the impact of select catalyst concentrations and reaction conditions. Studies indicate that liquid mixtures of 1-methoxypropane and di-propyl ethers could be formed by reacting n-propanol and methanol in the presence of sulfuric acid or Amberlyst 36. Higher concentrations of sulfuric acid (5% w/w) coupled with higher temperatures (>140 °C) favored substrate conversion and ether yields. However, it was revealed that the selectivity toward specific ethers, i.e., coupling of the two larger alcohols to produce di-propyl ether vs larger one with the smaller one to produce methoxypropane could be controlled by appropriate selection of the catalyst. We anticipate the results being a starting point for a simple technique to produce specific ethers using a mixture of alcohols that could be applied for applications such as transesterification byproduct utilization.