Silicones: Unique Chemicals for Petroleum Processing

Summary Silicones are specialty chemicals that are often critical in certain production operations. Their primary use in petroleum applications is as foam control agents. The physical and chemical properties of silicones are described, and foam and antifoam theory is discussed. State-of-the-art silicone use in selected key petroleum applications is outlined. The unique properties of silicones that should be considered by petroleum engineers in solving problems in other types of applications are emphasized. Introduction It is ironic that a material not present on earth naturally can be a critical material in the production of one of the earth's most desirous natural resources-crude oil. But such is the case with silicones and their use as foam control agents in certain petroleum processes. Silicones are not present in nature. They must be made by a complex process that starts with sand or quartz and ends with highly refined chemicals with unique physical and chemical properties. Ref. 1 provides a comprehensive review of silicone chemistry and technology. Silicones were not available commercially until 1943. Since that time, silicones have experienced a phenomenal growth in volume, types of products, and number of applications. While important in many industries, silicones or the manner in which they can best be used very often are not fully understood by the application engineer. This paper describes the nature of silicones and the physical and chemical properties that make them unique. The relationship of these properties to present and potential applications in the petroleum industry is discussed. Specific emphasis is placed on their use as foam control agents in petroleum processes. Nature of Silicones To better understand silicones, it is useful to examine in greater detail the most common of the silicone products, polydimethylsiloxanes. Structurally, a polydimethylsiloxane (PDMS) consists of a polymeric inorganic backbone of alternating silicon and oxygen atoms with methyl groups attached to silicon, represented by The value of n, or the degree of polymerization, can range from 0 to 2,500 and can be controlled to give fluids with viscosities from 0.65 to 10(6) cp (0.65 × 10(-3) to 10(3) Pa.s) at 77 degrees F (25 degrees C). Unlike hydrocarbons, which become waxes or solids beyond chain lengths of C 14, silicones, particularly PDMS, are colorless liquids or flowable gums even at very long chain lengths. Except at very short chain lengths, silicones can be regarded as nonvolatile polymers with very low vapor pressure, even at high temperatures. PDMS materials are nonpolar and nonionic, are very insoluble in water, and are hydrophobic to the extent that an important use is as a water repellent. They arc soluble in common organic solvents such as diesel fuel, kerosene, and toluene. JPT P. 1197^