(403d) Efficient Production of High Purity Phenolic Glycol Ethers

The manufacture of phenolic glycol ethers (also known as alkylene phenolic glycol ethers), e.g., propylene glycol phenyl ether (PPh) and/or ethylene glycol phenyl ether (EPh), is long known and practiced. These glycol ethers are typically produced in a batch process using excess ethylene oxide in presence of an acid or base catalyst. One common process for making phenolic glycol ethers, e.g., PPh and/or EPh, is a batch process in which propylene oxide (PO) and/or ethylene oxide (EO) is reacted with phenol in the presence of sodium hydroxide (NaOH) which serves as a catalyst. The oxides are added continuously into a mixture of phenol and NaOH catalyst until the amount of residual phenol in the reactor effluent is less than 100 parts per million (ppm). In order to achieve low oxide (less than (<) 15 ppm EO and <400 ppm PO) concentrations in the reactor effluent, a long residence time (e.g., greater than 10 hours) is necessary to complete the oxide conversion and this, in turn, imparts a low capacity (i.e., a poor production rate) to the process. Moreover, the long residence time and the oxide to phenol molar ratio of slightly (e.g., 5% excess oxide) greater than 1 employed to minimize unreacted phenol is such that a significant amount of higher homolog products, e.g., dipropylene glycol phenyl ether, and other impurities are produced. This, in turn, requires significant distillation effort to purify the EPh and PPh products, even if the reactor effluent is neutralized with an acid, e.g., phosphoric acid, to remove the NaOH catalyst in order to avoid further reaction and decomposition. In addition, filtration of the resulting salt, i.e., sodium phosphate, requires an intensive operation.

In those instances in which a significant amount of higher homolog is desired, e.g., diethylene or triethylene glycol phenyl ether, conventional practice is to recycle mono-product to react further with the oxides to produce the desired higher homolog products (in particular the di-product). However, this lowers the productivity of the process as a larger reactor volume is needed to accommodate the longer reaction time, or it requires a larger capital investment so as to allow recycling of mono-products. Moreover, while a simple phenol drying unit may be sufficient for mono-product production, usually a more intense operation, e.g., two or more phenol drying units coupled in series, is necessary to remove water from phenol recycle in order to obtain the desired glycol by-product purities.

In this work, an alternative process for the production of EPh and PPh as a continuous process will be presented that eliminates the need for catalyst neutralization, salt filtration, and long residence times for reaction completion while at the same time improving the selectivity, and hence quality, of the products