IABORATORY STUDIES ON DISPERSANTS FOR HIGH-VISCOUS OILS
Haruo Shiraishi, Toshiyuki Iwamoto and Akihiro Mochizuki
Taiho Industry Co.ltd.
JAPAN
ABSTRACT
Dispersants are believed to be ineffective in dispersing oils with viscosity of more than 2,000cSt. Present dispersants produced in Japan are actually ineffective for these oils. Therefore, laboratory tests have been carried out with mixtures of solvents and surfactants, which are likely to be amenable to oils with viscosity of 10,000 cSt. The other test was also conducted to investigate the relationship between the droplet-size of dispersed oil and the adherence of the droplets to other objects. The procedures for the tests were based on a dispersant effectiveness test standard stipulated in the Japanese Law Relating to the Prevention of Marine Pollution and Maritime Disaster. Under the test standard, effective dispersion rate of a, dispersant should be more than 60 96 after a settling time of 30 seconds and more than 20 96 after a settling time of 10 minutes. In addition, artificial sea water is used, temperature and oil/dispersant ratio are fixed, mixing energy for dispersion is consistent, and a premixed dispersant application method is used, for experiments,
The result of the tests shows that certain combinations of some surfactants with some solvents are able to disperse oil with viscosity of 10,000cSt, and when oil drop[et-size is less than 30/μ m in diam. the adherence of the droplet is significantly reduced.
1 Introduction
There has been an oil clean-up technique in which dispersants are applied to oil in the water, and thereby an oil-in-water emulsion is developed.
Currently, chemical dispersants used in many countries are classified into three categories: conventional dispersants, concentrated dispersants and self-mixing dispersants. Both conventional and concentrated dispersants require agitation for promoting dispersion of an oil slick after sprayed. Self-mixing dispersants are ones, which do not require agitation when there occurs a wind of more than No.3 on the Beaufort Scale.
Although these dispersants are quite effective in dispersion against oils which are relatively fresh shortly after spill and of low viscosity, the effectiveness is extremely reduced if the dispersant is used against high-viscosity oil or heavily weathered oil which has lost its low boiling point fraction owing to evaporation and with which as much as 60-800/* water is absorbed.
For instance, it is reported that during the spill of Exxon Valdez the opportunity using dispersants was lost owing to weathering of the spilled oil before EPA in the U.S.A granted approval of the use of dispersants.
Meanwhile, it is said that heavy fuel oils with high viscosity have often been involved in accidental spillage in Japanese jurisdiction. Present dispersants are not amenable to these high-viscosity oils.
This paper focussed on the development of dispersants which can disperse high-viscosity oils and weathered crude oils, by, conducting dispersibility tests using mixtures of solvents and surfactants which have been screened. Furthermore, it reports the dispersibility limitations of conventional dispersants carrying out some tests against high-viscosity oils.
2 Effectiveness of conventional dispersants on high-viscosity oils
Effectiveness tests were carried out on heavy fuel oil(bunkerC) with various viscosity using
