Deep Oxidative Desulfurization of FCC Diesel Fuel

Petroleum Science and Technology, 30:2471–2477, 2012 Copyright © Taylor & Francis Group, LLC ISSN: 1091-6466 print/1532-2459 online DOI: 10.1080/10916466.2010.525978

Deep Oxidative Desulfurization of FCC Diesel Fuel with Ultrasound M.-Z. SUN,1 B. ZHANG,1 Y.-H. WU,1 J. ZHU,1 AND D.-Z. ZHAO2 1

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School of Petrochemical Engineering, Shenyang University of Technology, Liaoyang, Liaoning, China 2 School of Petrochemical Engineering, Liaoning University of Petroleum & Chemical Technology, Fushun Liaoning, China Abstract A completely new diesel oil oxidative desulfurization technology was developed for the process of oxidation of FCC diesel by introducing ultrasonic technology to provide additional energy. Hydrogen peroxide and N-dimethylformamide were used as oxidant and extractant, respectively. The effects of several reaction conditions on desulfurization were investigated. The results show that at the presence of ultrasound, ideal desulfurization rate can be reached up to 92.8%. Keywords desulfurization, extraction, FCC diesel, oxidation, ultrasound

1. Introduction SOx are one kind of the main pollutants of car tail gas during the burning of sulfide diesel oil. The requirement for use of low-sulfide fuel is urgent due to the international regulation and environmental protection. As a new diesel oil deep desulfurization technology, oxidative desulfurization (ODS) has received more and more attention (Attar and Corcoran, 1978; Otsuki et al., 2000). There are many oxidants that are capable of oxidizing sulfide, such as air, O3 , NO2 , H2 O2 , ClO2 , and peroxy acid (Tam et al., 1990; Feng et al., 1997; Lu et al., 2001; Cui et al., 2002). Among them, H2 O2 is more popularly favorable owing to its cleanliness production in these years. Recently, ultrasonic technology has been rapidly developed and used in various fields. Ultrasound consists of a list of density longitudinal wave that can easily spread around by liquid medium. When a certain powerful ultrasound spreads in medium, it can produce a list of effects, such as mechanics, thermotics, optics, electricity, and chemistry (Feng and Li, 1992). Ultrasound chemistry is mainly about providing energy and accelerating chemical reaction for chemical reaction by the usage of ultrasound. Here, ultrasound was applied to the deep oxidation of FCC diesel to optimize the reaction (Li et al., 2005). The effects of ultrasound on the oxidation reaction were mainly addressed. It is expected to intensify the reaction process. Address correspondence to M.-Z. Sun, School of Petrochemical Engineering, Shenyang University of Technology, 30 Guanghua Street, Liaoyang, Liaoning 111003, China. E-mail: [email protected]

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2. Experimental 2.1.

Materials, Reagents, and Instruments

The materials, reagents, and instruments used were the following: Materials: FCC diesel oil with a total sulfur content of 1,948 g/g (for its fundamental nature, see Table 1). Reagents: 30% H2 O2 (analytical reagent), 88% formic acid (analytical reagent), 96% N, N-dimethylformamide (DMF; analytical regent). Instruments: Microcoulometric analyzer (WK-2B, Jiangsu Electroanalytical Instrument Factory, China), ultrasound.


2.2.

Experimental Process

The experimental process can be divided into two stages. The first stage is the diesel oil catalytic oxidation. According to certain volume proportion, oxidants and diesel oil reacted in an ultrasonic reactor. The second stage is the diesel oil extraction: according to certain volume proportion, reagent and extractant were blended, oscillated, and extracted at room temperature. Then, the extractant was collected for regeneration. The content of remaining sulfur in the as-obtained purified diesel was analyzed through microcoulometer.

3. Results and Discussion 3.1.

The Effect of Oxidation System Quantity on Sulfur Removal Rate

Sulfide in diesel oil needs a proper oxidation system to be oxidized into polar substance, such as sulfoxide or sulfone, owing to the sulfur amount varying remarkably with oil type. The effect of oxidation system quantity on reaction would also ulteriorly affect the desulfurization result as discussed in the following. The reaction conditions were the following: time 8 min; temperature 30ıC; H2 O2 : formic acid (volume ratio) D 2:1; DMF as extractant; extractant:oil (volume ratio) D 1:2; extraction twice. It can be seen from Figure 1, that under ultrasound effect, sulfur removal rate increased with the increase of oxidation system in the range of the volume ratio of oxidation system over oil smaller than 1:10. When the ratio surpassed 1:10, the sulfur removal rate reduced slightly. The adding amount of oxidation system should be subjected Table 1 The contrast of product quality before and after ultrasonic oxidation

Characteristic

Original diesel

Ultrasonic oxidation desulfurization diesel

Total sulfur, g/g Density, 20ı C g/mL Water soluble acid alkali Copper corrosion, 50ıC 3 hr

1,948 0.868 None Ineligible

140.26 0.853 None Eligible

Deep Oxidative Desulfurization of FCC Diesel Fuel

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Figure 1. The effect of oxidation system quantity on sulfur removal rate. (color figure available online)

to the content of sulfide in diesel oil. When the quantity of oxidation system exceeds the proper adding quantity, it would take side effects and reduce the oil production yield. Simultaneously, excessive oxidants will also increase the production cost. So the proper volume ratio of oxidation system over oil was determined at 1:10 under ultrasound effect. 3.2.

The Effect of Ratio of Oxidant over Catalyst on Sulfur Removal Rate

In an oxidation system, oxidant and catalyst should be matched in proper proportion. Otherwise, unnecessary waste will bring about and take side effect on the whole reaction. So we investigated the effect of the ratio of oxidant over catalyst on desulfurization rate. The reaction condition was oxidation system:oil (volume proportion) D 1:10; other conditions are the same as previously listed. It can be seen from Figure 2 that when the volume ratio of H2 O2 :formic acid is 1:1, the desulfurization rate is the highest. At first, with the adding of oxidant, desulfurization

Figure 2. The effect of ratio of oxidant and catalyst on sulfur removal result. (color figure available online)

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rate increases greatly. According to some reports of related documents, this can be ascribed to the increasing of the probability of oxidant’s contacting with organic sulfur with the increment of usage of hydrogen peroxide. However, desulfurization rate will decline when the adding amount of oxidant reaches some value. Although the amount of hydrogen peroxide increases at this time, surplus H2 O2 volatilizes and decomposes easily if there is not enough formic acid to react with it, so desulfurization rate will not be high. The proper volume ratio of oxidant/H2O2 over catalyst/formic acid is 1:1.


3.3.

The Effect of Reaction Time on Sulfur Removal Rate

If the oxidation time is too long, oxidant H2 O2 would be easily decomposed, leading to the reduction of desulfurization rate. On the contrary, the reaction would be incomplete. The reaction condition was H2 O2 :formic acid (volume ratio) D 1:1; other conditions are the same as previously listed. As it can be seen from Figure 3, under the aid of ultrasound, the desulfurization rate is 63.8% and 81.8% when treated for 3 and 10 min, respectively. When the reaction time was further increased to 10 min, the desulfurization rate and oil yield decreased quickly. Considering the economic reality, the source of energy costs too much, so the most proper reaction time of oxidation desulfurization under the effect of ultrasound is 10 min. 3.4.

The Effect of Reaction Temperature on Sulfur Removal Rate

The temperature is another key factor affecting reaction, which could affect not only the reaction speed but also the oxidation degree. The reaction condition was a time of 10 min; other conditions are the same as previously listed.

Figure 3. The effect of reaction time on sulfur removal rate. (color figure available online)


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Figure 4. The effect of reaction temperature on sulfur removal rate. (color figure available online)

As shown in Figure 4, sulfur removal rate increases greatly with the increase in oxidation temperature. When the reaction temperature was elevated above 50ı C, the sulfur removal rate decreased slowly. In addition, from experimental results, the reaction conducted at a much higher temperature may reduce the oil yield. Therefore, it can be ascertained that the best proper reaction temperature under power ultrasound effect is 50ı C. 3.5.

The Effect of Extractant Quantity on Sulfur Removal Result

The effect of extractant quantity on extract result was investigated by changing the volume proportion of extractant over oil, as shown in Figure 5. The reaction condition was a temperature of 50ı C; other conditions are the same as previously listed. With the dosage of extractant increasing, desulfurization increases monotonously. However, when the volume proportion of extractant over oil exceeds 1, the increasing trend begins to slow down, and the loss of oil yield collecting rate changes much.

Figure 5. The effect of extractant quantity on sulfur removal result. (color figure available online)

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While considering economic reasons of great usage in industry, under the condition of ultrasound, the optimum extractant quantity should be extractant over oil (volume), which is equal to 1.

3.6.

The Effect of Extraction Times on Sulfur Removal Result


The reaction condition was extractant:oil (volume ratio) D 1:1; other conditions are the same as previously listed. It can be seen in Figure 6 that the more the extraction time is used, the higher the desulfurization rate reached is. However, the extraction times should not be infinite due to the large increasing in the amount of solvent usage and the loss of product. The increase of desulfurization rate does not enhance much after extracting twice. So, the optimum extraction time was set to two.

3.7.

The Effect of Ultrasonic Oxidation to Product

In the process of oxidation desulfurization under power ultrasound, whether the component or quality of diesel changes, it is important to the usage of diesel. The diesel and extractant was mixed in the ratio of 1:1. After sufficient extraction, they were separated. The product quality before and after ultrasonic oxidation is listed in Table 1. The sulfur content and density of diesel decrease after ultrasonic oxidation. The reason is that the large molecular thiophene compound in diesel was removed. The quality has reached the international criterion of cleanliness diesel for vehicles. The processes of oxidation and extraction for desulfurization do not have a side effect on the composition and property of diesel.

Figure 6. The effect of extraction times on sulfur removal rate. (color figure available online)


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4. Conclusion The deep oxidative desulfurization of diesel fuel was performed through processes of oxidation reaction and solvent extraction process in the aid of ultrasound. Under the optimum ultrasound oxidation reactions and solvent extraction condition, oxidation system over diesel of 1:10, oxidant/H2O2 and catalyst/formic acid of 1:1, oxidation of 10 min at 50ıC, and extractant:oil ratio of 1:1, the ideal desulfurization rate can be reached up to 92.8%.


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