Emulsions chemical selection

The selection of chemicals that will provide the refiner or oil producer with a cost-effective emulsion-breaking program that meets or exceeds all performance parameters is usually the function of a chemical service company. The selection process has historically been viewed as a black art that produces as many failures as successes. This assessment of the situation has been realistic. However, with an ever-increasing understanding of emulsions and emulsion-breaking chemicals, the development of new test procedures and devices, and a well-organized method of chemical selection, many of the failures can be eliminated. 

Regardless of the test method used to select chemicals, the true capabilities of the treating chemicals must be determined by commercial application in the treating system of concern. All test work in chemical selection is merely a method of reducing the risk of failure an oil treater is subjected to when changing emulsion-breaking chemicals or testing a new facility. 

Emulsions have a ha2y appearance when compared to the bright color of treated oil. As a crude oil emulsion separates, the color tends to brighten. Brightening of oil can be encouraging, but it can also be deceptive if taken as the sole qualification for chemical selection. While bright color is no guarantee of a successful chemical, lack of it assures that the compound is not worthy of further consideration. 

Specific advancements ia the chemical synthesis of coUoidal materials are noteworthy. Many types of genera ting devices have been used to produce coUoidal Hquid aerosols (qv) and emulsions (qv) (39—43) among them are atomizers and nebulizers of various designs (30,44—50). A unique feature of produciag Hquid or soHd coUoids via aerosol processes (Table 3) is that material with a relatively narrow size distribution can be routinely prepared. These monosized coUoids are often produced by relying on an electrostatic classifier to select desired particle sizes ia the final stage of aerosol production. 

Elastomeric Fibers. Elastomeric fibers are polyurethanes combiaed with other nonelastic fibers to produce fabrics with controlled elasticity (see Fibers, elastomeric). Processing chemicals must be carefully selected to protect all fibers present ia the blend. Prior to scouriag, the fabrics are normally steamed to relax uneven tensions placed on the fibers duriag weaving. Scouriag, which is used to remove lubricants and siting, is normally conducted with aqueous solutions of synthetic detergents and tetrasodium pyrophosphate, with aqueous emulsions of perchloroethylene or with mineral spidts and sodium pyrophosphate. 

A.sahi Chemical EHD Processes. In the late 1960s, Asahi Chemical Industries in Japan developed an alternative electrolyte system for the electroreductive coupling of acrylonitrile. The catholyte in the Asahi divided cell process consisted of an emulsion of acrylonitrile and electrolysis products in a 10% aqueous solution of tetraethyl ammonium sulfate. The concentration of acrylonitrile in the aqueous phase for the original Monsanto process was 15—20 wt %, but the Asahi process uses only about 2 wt %. Asahi claims simpler separation and purification of the adiponitrile from the catholyte. A cation-exchange membrane is employed with dilute sulfuric acid in the anode compartment. The cathode is lead containing 6% antimony, and the anode is the same alloy but also contains 0.7% silver (45). The current efficiency is of 88—89%, with an adiponitrile selectivity of 91%. This process, started by Asahi in 1971, at Nobeoka City, Japan, is also operated by the RhcJ)ne Poulenc subsidiary, Rhodia, in Bra2il under Hcense from Asahi. 

In the production of crude oil, the greatest part of the crude oil occurs as a water-in-oil emulsion. The composition of the continuous phase depends on the water/oil ratio, the natural emulsifier systems contained in the oil, and the origin of the emulsion. The natural emulsifiers contained in crude oils have a complex chemical structure, so that, to overcome their effect, petroleum-emulsion demulsifiers must be selectively developed. As new oil fields are developed, and as the production conditions change at older fields, there is a constant need for demulsifiers that lead to a rapid separation into water and oil, as well as minimal-residual water and salt mixtures. 

S. Yao, A. G. Fane, J. M. Pope 1997, (An investigation of the fluidity of concentration polarisation layers in crossflow membrane filtration of an oil-water emulsion using chemical shift selective flow imaging), Mag. Reson. Imag. 15, 235. 

Formulations of tetraethyl pyrophosphate as an emulsive concentrate proved to be relatively complex, considering the apparent ease of formulation. Because of the unstable nature of the chemical, dust formulations were considered impossible. It was found after extensive research work that a dust which would be stable for 10 days to 2 weeks could be made with a specially selected and processed filler. 

Chemically, the preparation of a "stable" foam or emulsion requires the use of a surfactant to aid in dispersion of the internal phase and prevent the collapse of the foam (or emulsion) into separate bulk phases. The selection of a surfactant is made on the basis of severity of conditions to be encountered, the gas to be entrained (N2, C02, LPG, CH, or air), the continuous phase liquid (water, alcohol, or oil), and half-life of foam stability desired. 

The major problem in demulsifying crude oil emulsions is the extreme sensitivity to demulsifier composition. There have been attempts (2, 3) to correlate demulsifier effectiveness with some of the physical properties governing emulsion stability. However, our understanding in this area is still limited. Consequently, demulsifier selection has been traditionally based on a trial and error method with hundreds of chemicals in the field. 

Chemical nature of adsorbant can be varied so that it is selective for a particular functional group in the analyte Emulsions are not formed between the two phases... 

Experience is a very useful teacher in selecting demulsifiers. The man who is familiar with the history of treating m an area, the demands of the treating plants, and the performance of the chemicals can do a pretty good job ot picking compounds. However, this approach fails when changes occur in emulsion characteristics, new emulsions are encountered, or new chemicals become available. 

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