Crystallization of Crude Oils

Petroleum or crude oils are complex mixtures of hydrocarbons and other chemicals, like paraffins, naphthenes, asphaltenes and resins. Responsible for the problems that occur during production and transportation of crude oils in pipeline systems are typically the high molecular weight paraffins and asphaltenes. At high temperatures, the paraffin molecules are dissolved in the crude oil. If, during the transportation through pipe lines, the temperature of oil decreases below its wax appearance temperature (cloud point) followed by the pour point at a lower temperature, the solubility of wax decreases and wax molecules start to precipitate out of the crude oil. It will be shown that the crystallization process, when cooling crude oils, can be observed by means of rheological measurements combined with microscopy.

Introduction

Petroleum or crude oils are complex mixtures of hydrocarbons and other chemicals, like paraffins, naphthenes, asphaltenes and resins. Responsible for the problems that occur during production and transportation of crude oils in pipeline systems are typically the high molecular weight paraffins and asphaltenes. At high temperatures, the paraffin molecules are dissolved in the crude oil. If, during the transportation through pipe lines, the temperature of oil decreases below its wax appearance temperature (cloud point) followed by the pour point at a lower temperature, the solubility of wax decreases and wax molecules start to precipitate out of the crude oil. In order to prevent or to minimize the wax crystallization, paraffin control products (paraffin inhibitors) are mixed to the crude oil.

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