Adducts urea dewaxing

Urea dewaxing, in which urea forms adducts with straight-chain paraffins that separated by filtration from the dewaxed oil. 

Urea dewaxing a continuous dewaxing process for producing low-pour-point oils, and using urea which forms a solid complex (adduct) with the straight-chain wax paraffins in the stock the complex is readily separated by filtration. 

Urea has the remarkable property of forming crystalline complexes or adducts with straight-chain organic compounds. These crystalline complexes consist of a hoUow channel, formed by the crystallized urea molecules, in which the hydrocarbon is completely occluded. Such compounds are known as clathrates. The type of hydrocarbon occluded, on the basis of its chain length, is determined by the temperature at which the clathrate is formed. This property of urea clathrates is widely used in the petroleum-refining industry for the production of jet aviation fuels (see Aviation and other gas-TURBINE fuels) and for dewaxing of lubricant oils (see also Petroleum, refinery processes). The clathrates are broken down by simply dissolving urea in water or in alcohol. 

It should be noted that thiourea, the sulfur analog of urea, also forms clath-rates, but the larger size of the sulfur atom results in larger channels in the adducts which admit compact22 molecules such as branched and cyclic hydrocarbons19 and selectivity is no longer a feature. As a result, no commercial applications of thiourea to dewaxing have been developed. 

In the Edeleanu process, waxy feed is mixed (Figure 9.15) in one of several reactors with urea and with recycled and fresh methylene chloride whose vaporization controls the exothermic reaction with urea. Prior to filtration, the adduct passes through a series of baffles to encourage complete reaction. After washing, the adduct is filtered from the oil, which proceeds to a stripper (to remove the methylene chloride) and then to product storage. The separate adduct stream from the filter is decomposed by steam at 75°C, then sent to a separator and subsequently stripped of solvent to yield the n-parafflns. The dewaxed oils disengage from the aqueous phase in a separator. 

Source Urea-Adduct Process Gains Ground in Lube-Oil Dewaxing, Chemical Engineering 114—118 (November, 1956). With permission. 

Fig. 7-4. Flow sheet of an adductive crystallization process to dewax crude oil by the aid of aqueous urea solution and methylene chloride, process of Deutsche Erdol AG.

Anon., Urea-adduct Process Gains Ground in Lube-oil Dewaxing, Chem. Eng., November, 1956, p. 114. 

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