Ultraäänivaihtoehto rikinpoistolle

Oil refineries are facing increasing supplied of sulfurous crude oil, so-called sour crude, whilst at the same time environmental regulations pressure for lower sulfur content of gasoline. Simultaneously, the costs of conventional hydrodesulfurization (HDS) are rising because of the hydrogen needed. Ultrasonic cavitation treatment is an effective alternative method to remove sulfur from crude oil.

Meet Sulfur Standards in Oil with Sonication

Fossil fuels contain sulfur compounds. These result from the degradation of biological matter containing sulfur during the natural formation of fossil fuels.

Vehicles, such as cars, aircraft and marine vessels or power plants cause sulfur dioxide (SO2) emissions as a result of the petroleum fuel combustion. The same sulfur – even in very low concentrations – causes damages to noble metal catalysts in the downstream catalytic reforming in petroleum refineries. Latest environmental regulations require a very deep desulfurization to meet the ultra-low sulfur diesel (ULSD) specifications.
 

Installation with 192 kW of high-power sonicators for desulfurization of crude oils

Background – Hydrodesulfurization (HDS)

Hydrodesulfurization (HDS) is the standard catalytic process for the removal of sulfur from petroleum products. In this process, the sulfurous fractions of the crude oil are mixed with hydrogen and a catalyst to react to hydrogen sulfide. Typically, the catalyst consists of an alumina base impregnated with cobalt and molybdenum. As the oil supplies get more sour, higher pressures and alternative catalysts are required for the desulfurization. Recalcitrant aromatic sulfur compounds (e.g. 4,6-dimethyldibenzothiophene) cannot be removed using hydrodesulfurization, due to their low reactivity.

Ultrasonically Assisted Desulfurization

An alternative to hydrodesulfurization is the ultrasonically assisted desulfurization. The exposure of liquids to ultrasonic waves of high intensity causes acoustic cavitation. This is the formation and subsequent violent collapse of small vacuum (cavitation) bubbles. Locally, extreme conditions arise from the violent collapse of each bubble:

• Temperature: up to 5000 Kelvin
• Pressure: up to 2000 Atmospheres
• Liquid Jets: up to 1000km/hr.

Such conditions promote a better surface chemistry of catalysts by enhanced micro-mixing. In particular the high local temperatures change the chemical reaction kinetics of the desulfurization process. This effect allows for alternative – Halvempaa – catalysts or alternative desulfurization chemistry to be used. Deshpande et al. (2004) investigates an oxidative system composed of sodium carbonate and hydrogen peroxide in a biphasic system of diesel and acetonitrile. Ultrasonication was applied to the biphasic system. The study achieved a reduction of the DMDBT content by more than 90% in the diesel samples.

High-Performance Sonicator for Desulfurization of Crude

Hielscher is the leading supplier of high capacity sonicators, worldwide. As Hielscher designs and manufactures high-performance ultrasonic processors of up to 16kW power per single device, there is no limit in plant size or processing capacity. Clusters of several 16kW systems are being used the processing of larger volume flows. Industrial fuel processing does not need much ultrasonic energy. The actual energy requirement can be determined using a bench-top sonicator such as the UIP1000hdT. All results from such bench-top trials can be scaled up completely linear, which facilitates to implement the ultrasonic desulfurization process on industrial production scale.

If required, ATEX certified ultrasonicators (e.g. UIP1000-Exd) are available for the sonication in hazardous environments.

Costs of Ultrasonication

Ultrasonication is an effective processing technology. Ultrasonic processing costs result mainly from the investment
for ultrasonic devices, utility costs and maintenance. The outstanding energy efficiency (see chart) of Hielscher ultrasonic devices helps to reduce the utility costs.

Kirjallisuus

Deshpande, A., Bassi, A., Prakash, A. (2004): Ultrasound-Assisted, Base-Catalyzed Oxidation of 4,6-Di­methyl­di­ben­zothio­phene in a Bi­phasic Diesel-Aceto­nitrile System; in: Energy Fuels, 19 (1), 28 -34, 2005.

Mei H., Mei B.W., Yen T.F. (2003): A new method for obtaining ultra-low sulfur diesel fuel via ultrasound assisted oxidative desulfurization; in: Fuel, Volume 82, Number 4, March 2003, pp. 405-414(10), 2003.