Ultrasonic Marine Fuel Desulphurization
- I carburanti per uso marittimo sono interessati da nuove normative, che richiedono un contenuto di zolfo pari o inferiore allo 0,5%m/m.
- Ultrasound-assisted oxidative desulfurization (UAOD) is an established method that accelerates the oxidation reaction and is an economical and safe process.
- UAOD processes can be run at ambient temperature and atmospheric pressure and allow for a selective removal of sulfur compounds from hydrocarbon fuels.
- Hielscher high-performance ultrasonic systems are easy to install and safe to operate on-board or on-shore.
Low Sulphur Marine Fuels
L'Organizzazione Marittima Internazionale (IMO) ha implementato nuove norme che impongono alle navi di tutto il mondo di utilizzare carburanti marini con un contenuto di zolfo dello 0,5%m/m a partire da gennaio 2020. Queste nuove normative richiedono profondi cambiamenti nel trattamento dei combustibili marini: per soddisfare le nuove norme sui combustibili a basso tenore di zolfo, è necessario un processo di desolforazione efficiente.
Ultrasonically-assisted oxidative desulphurization (UAOD) of liquid hydrocarbon fuels such as gasoline, naphtha, diesel, marine fuel, etc. is a highly efficient and viable method to remove sulphur from large volumes streams of heavy fuels.
Flowchart of 2-stage ultrasonic oxidative desulphurization
Oxidative Desulphurization
Oxidative Desulphurization (ODS) is an environmental-friendly and economical alternative to hydrodesulphurization (HDS) since oxidized sulfur compounds can be significantly easier separated from the heavy fuel oils. After the oxidative desuphurization step, the extracted sulphur compounds are separated by physical methods e.g. using non-miscible polar solvent and subsequent gravity, adsorption or centrifugal separation. Alternatively, thermal decomposition can be used to remove the oxidized sulfur.
For the oxidative desulphurization reaction, an oxidant (e.g., hydrogen H2O2, sodium chlorite NaClO2, nitrous oxide N2O, sodium periodate NaIO4), a catalyst (e.g., acids) as well as a phase-transfer reagent are required. The phase-transfer reagent helps to promote the heterogeneous reaction between the aqueous and oil phases, which is the rate-limiting step of the ODS reaction.
- highly efficient – fino al 98% di desolforazione
- economical: low investment, low operational costs
- no catalyst poisoning
- easy, linear scale-up
- safe to operate
- onshore & offshore (onboard) installation
- ROI veloce
Ultrasonically-Assisted Oxidative Desulphurization
Whilst hydrodesulphurization (HDS) requires higher investment costs, high reaction temperature of up to 400ºC, and high pressure of up to 100atm in the reactors, the ultrasound-assisted oxidative desulfurization process (UAOD) is much more convenient, efficient and greener. The UAOD greatly enhances reactivity of the catalytic sulphur removal and offers at the same time lower operating cost, higher safety and environmental protection. Industrial ultrasonic flow reactor systems increase the desulfurization rate due to a highly effective dispersion and thereby improved reaction kinetics. Since the ultrasonic processing provides nano-scale dispersions, the mass transfer between the different phases in the heterogeneous reaction is drastically increased.
Ultrasonic (acoustic) cavitazione increases the reaction rate and mass transfer by the extreme conditions, which are reached within the cavitational hot-spots. During the cavitation bubble implosion, very high temperatures of approx. 5,000K, very fast cooling rates, pressures of approx. 2,000atm and accordingly extreme temperature and pressure differentials are locally reached. The implosion of the cavitation bubble also results in liquid jets of up to 280m/s velocity, which creates very high shear forces. These extraordinary mechanical forces accelerate the oxidation reaction time and increase the sulfur conversion efficiency within seconds.
More Complete Sulphur Removal
Whilst mercaptans, thioethers, sulfides and disulfides can be removed by the conventional hydrodesulphurization (HDS) process, for the removal of thiophenes, benzothiophens (BT), dibenzothiophenes (DBT) and 4,6-dimethyldibenzothiophenes (4,6-DMDBT) a more sophisticated method is required. Ultrasonic oxidative desulphurization is highly effective when it comes to the removal of even hardly removable sulfur refractory compounds (e.g., 4,6-dimethyldibenzothiophene and other alkyl-substituted thiophene derivatives). Ebrahimi et al. (2018) report a efficienza di desolforazione fino al 98,25% utilizzando un sonoreattore Hielscher optimized for sulphur removal. Furthermore, the ultrasonically oxidized sulfur compounds can be separated via a basic water wash.
Effect of multi-step UAOD process at optimum parameters
Ultrasonic Desulphurization Feasibility Test with UP400S
Shayegan et al. 2013 combined ultrasonication (UP400S) with hydrogen peroxide as oxidant, FeSO as catalyst, acetic acid as pH adjuster and methanol as extraction solvent in order to reduce the sulfur amount of gas oil.
The reaction rate constants during oxidative desulphurization can be greatly increased by adding metal ions as catalyst and using sonication. The ultrasound energy can reduce the activation energy of the reaction. The ultrasonication treatment breaks the boundary layer between solid catalysts and reagents and provides a homogeneous mix of catalysts and reagent – improving thereby the reaction kinetics.
The sulphur extraction process is a crucial step during desulphurization with the goal to recover the total volume of desulphurized gas oil. Using a liquid-liquid extraction using methanol as the solvent is a simple extraction process, but to ensure a high efficiency an efficient mixing of the immiscible phases is essential. Only when a maximum interface and subsequently maximum mass transfer take place between the phases, a high extraction rate is achieved. Ultrasonication and the generation of acoustic cavitation provides the intense mixing of the reactant phases and lowers the activation energy of the reaction.
High Performance Ultrasonic Units for Marine Fuel Desulphurization
Hielscher Ultrasonics is the market leader of high power ultrasonic systems for demanding applications such as UAOD on industrial scale. High amplitudes of up to 200µm, 24/7 operation under full load and heavy duty, robustness and user-friendliness are key-features of Hielscher ultrasonicators. Ultrasonic systems of different power classes and various accessories such as sonotrodes and flow reactor geometries allow for the most suitable adaption of the ultrasonic system to your specific fuel, processing capacity and environment.
The table below gives you an indication of the approximate processing capacity of our ultrasonicators:
| Volume di batch | Portata | Dispositivi raccomandati |
|---|---|---|
| 10 - 2000mL | 20 - 400mL/min | UP400St |
| 0,1 - 20L | 0,2 - 4L/min | UIP2000hdT |
| 10 - 100L | 2 - 10L/min | UIP4000hdt |
| n.a. | 10 - 100L/min | UIP16000 |
| n.a. | più grande | cluster di UIP16000 |
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High-power ultrasonic processors from lab to pilot and industrial scale.
Literature / References
- Ebrahimi, S.L.; Khosravi-Nikou, M.R.; Hashemabadi, S.H. (2018): Sonoreactor optimization for ultrasound assisted oxidative desulfurization of liquid hydrocarbon. Petroleum Science and Technology Vol. 36, Issue 13, 2018.
- Prajapati, A.K.; Singh, S.K.; Gupta, S.P.; Mishra, A. (2018): Desulphurization of Crude Oil by Ultrasound Integrated Oxidative Technology. IJSRD – International Journal for Scientific Research & Development Vol. 6, Issue 02, 2018.
- Shayegan, Z.; Razzaghi, M.; Niaei, A.; Salari, D.; Tabar, M.T.S.; Akbari, A.N. (2013): Sulfur removal of gas oil using ultrasound-assisted catalytic oxidative process and study of its optimum conditions. Korean J. Chem. Eng., 30(9), 2013. 1751-1759.
- Štimac, A.; Ivančević, B.; Jambrošić, K. (2001): Characterization of Ultrasonic Homogenizers for Shipbuilding Industry.
Research Results on Ultrasonically-Assisted Oxidative Desulphurization (UAOD)
Prajapati et al. (2018): Desulphurization of Crude Oil by Ultrasound Integrated Oxidative Technology. IJSRD – International Journal for Scientific Research & Development Vol. 6, Issue 02, 2018.
Prajapati et al. (2018) describe the benefits of a Hielscher ultrasonic reactor for the ultrasound-assisted oxidative desulfurization (UAOD). UAOD has become an viable alternative technology to the traditional hydrotreating, which is impaired by significant investment and operational costs due to high-pressure, high-temperature hydrodesulphurization equipment, boilers, hydrogen plants, and sulphur recovery units. Ultrasound-assisted oxidative desulfurization permits carrying out the process for deep removal of sulphur under much milder conditions, faster, safer and much more economically.
Ultrasound-assisted oxidative desulfurization (UAOD) process was applied to diesel oil and petroleum product feedstock containing model sulphur compounds (benzothiophene, dibenzothiophene and dimethyldibenzothiophene). The influence of oxidant amount, volume of solvent for the extraction step, time and temperature of ultrasound treatment (UIP1000hdT20 kHz, 750 W, operante al 40%). Utilizzando le condizioni ottimizzate per UAOD, è stata ottenuta una rimozione dello zolfo fino al 99% per i composti modello nei prodotti petroliferi in entrata, utilizzando una proporzione molare di H2O2:acido acetico:zolfo di 64:300:1, dopo 9 minuti di trattamento a ultrasuoni a 90ºC, seguito da estrazione con metanolo (rapporto solvente-olio ottimizzato di 0,36). Utilizzando la stessa quantità di reagente e 9 minuti di ultrasuoni, la rimozione dello zolfo è stata superiore al 75% per i campioni di gasolio.
The Importance of High Ultrasonic Amplitudes
Ultrasonic intensification of commercial-scale oxidative desulfurization of crude oil requires the use of an industrial-size flow-through ultrasonic processor able to maintain high vibration amplitudes of about 80 – 100 microns. The amplitudes directly relate to the intensity of ultrasonic cavitations-generated shear forces and must be maintained at a sufficiently high level for the mixing to be efficient.
The experiments performed by Prajapati et al. show that ultrasonication enhances the desulfurization reaction. L'efficienza di desolforazione è stata di circa il 93,2%. when high-performance ultrasound is applied.
Shayegan et al. (2013): Sulfur removal of gas oil using ultrasound-assisted catalytic oxidative process and study of its optimum conditions. Korean Journal of Chemical Engineering 30(9), September 2013. 1751-1759.
Ultrasound-assisted oxidative desulfurization process (UAOD) was applied to reduce sulfur compounds of gas oil containing various types of sulfur content. The environmental regulation requires a very deep desulfurization to eliminate the sulfur compounds. UAOD is a promising technology with lower operating cost and higher safety and environmental protection. For the first time the typical phase transfer agent (tetraoctyl-ammonium-bromide) was replaced with isobutanol because using isobutanol is much more economical than TOAB, imposing no contamination. The reaction was carried out at optimal point with various temperatures, in single-, two- and three step-procedures, investigating the effect of gradual increase of H2O2 e TOAB al posto dell'isobutanolo. La concentrazione totale di zolfo nella fase oleosa è stata analizzata con il metodo ASTM-D3120. La massima rimozione di circa il 90% per il gasolio contenente 9.500 mg/kg di zolfo è stata ottenuta in tre fasi durante 17 minuti di processo a 62±2°C quando 180,3 mmol di H2O2 was used and extraction carried out by methanol.
Akbari et al. (2014): Investigation of process variables and intensification effects of ultrasound applied in oxidative desulfurization of model diesel over MoO3/Al2O3 catalyst. Ultrasonics Sonochemistry 21(2), March 2014. 692–705.
A new heterogeneous sonocatalytic system consisting of a MoO3/Al2O3 catalyst and H2O2 combinato con gli ultrasuoni è stato studiato per migliorare e accelerare l'ossidazione dei composti di zolfo modello del diesel, con un conseguente significativo aumento dell'efficienza del processo. L'influenza degli ultrasuoni sulle proprietà, l'attività e la stabilità del catalizzatore è stata studiata in dettaglio mediante tecniche GC-FID, PSD, SEM e BET. Una conversione superiore al 98% di DBT in diesel modello contenente 1000 μg/g di zolfo è stata ottenuta con la nuova desolforazione assistita da ultrasuoni a H2O2rapporto molare zolfo/3, temperatura di 318 K e dosaggio del catalizzatore di 30 g/L dopo 30 minuti di reazione, contrariamente alla conversione del 55% ottenuta durante il processo silenzioso. Questo miglioramento è stato notevolmente influenzato dai parametri operativi e dalle proprietà del catalizzatore. Gli effetti delle principali variabili di processo sono stati studiati utilizzando la metodologia della superficie di risposta nel processo silenzioso rispetto all'ultrasuonizzazione. Gli ultrasuoni hanno fornito una buona dispersione del catalizzatore e dell'ossidante attraverso la rottura del legame idrogeno e la deagglomerazione nella fase oleosa. La deposizione di impurità sulla superficie del catalizzatore ha causato una rapida disattivazione negli esperimenti silenziosi, con un'ossidazione del DBT pari solo al 5% dopo 6 cicli di reazione silenziosa con catalizzatore riciclato. Oltre il 95% del DBT è stato ossidato dopo 6 cicli assistiti da ultrasuoni, dimostrando un grande miglioramento della stabilità grazie alla pulizia della superficie durante gli ultrasuoni. Dopo 3 ore di sonicazione è stata osservata anche una notevole riduzione delle dimensioni delle particelle, che potrebbe garantire una maggiore dispersione del catalizzatore nel carburante modello.
Afzalinia et al. (2016): Ultrasound-assisted oxidative desulfurization process of liquid fuel by phosphotungstic acid encapsulated in a interpenetrating amine-functionalized Zn(II)- based MOF as catalyst. Ultrasonics Sonochemistry 2016
In this work, ultrasound-assisted oxidative desulfurization (UAOD) of liquid fuels performed with a novel heterogeneous highly dispersed Keggin-type phosphotungstic acid (H3PW12O40PTA) incapsulato in un MOF amino-funzionalizzato (TMU-17 -NH2). Il composito preparato presenta un'elevata attività catalitica e riutilizzabilità nella desolforazione ossidativa di combustibili modello. La desolforazione ossidativa assistita da ultrasuoni (UAOD) è un nuovo metodo per eseguire la reazione di ossidazione dei composti contenenti zolfo in modo rapido, economico, ecologico e sicuro, a condizioni miti. Le onde ultrasonore possono essere applicate come strumento efficace per ridurre il tempo di reazione e migliorare le prestazioni del sistema di desolforazione ossidativa. Il PTA@TMU-17-NH2 ha potuto eseguire completamente la desolforazione dell'olio modello con 20 mg di catalizzatore, rapporto molare O/S di 1:1 in presenza di MeCN come solvente di estrazione. I risultati ottenuti indicano che la conversione di DBT in DBTO2 raggiunge il 98% dopo 15 minuti a temperatura ambiente. In questo lavoro, abbiamo preparato per la prima volta il TMU-17-NH2 e il composito PTA/TMU-17-NH2 mediante irradiazione a ultrasuoni e lo abbiamo impiegato nel processo UAOD. Il catalizzatore preparato presenta un'eccellente riutilizzabilità senza lisciviazione del PTA e perdita di attività.