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Removal of hydrogen sulfide from light oil with solid base
Fuel Processing Technology 86 (2004) 237 – 244 www.elsevier.com/locate/fuproc
Removal of hydrogen sulfide from light oil with solid base Yongfeng Duan, Yuzhi Xiang, Daohong Xia* State Key Laboratory of Heavy Oil Processing, College of Chemistry and Chemical Engineering, University of Petroleum, 257061 Dongying Shandong, China Accepted 1 December 2003
Abstract A novel solid base with activated carbon as supporter and alkali and earth-alkali compounds as active components has been developed for removal of hydrogen sulfide from light oils. The experimental results indicated that the solid base has excellent adsorption capacity for hydrogen sulfide. In addition, an additive added to feedstock that can promote significantly the removal of hydrogen sulfide for the solid base was also developed. The adsorption capacity of the solid base for hydrogen sulfide was evaluated with dynamic testing. D 2004 Elsevier B.V. All rights reserved. Keywords: Hydrogen sulfide; Removal; Solid base; Adsorption; Additive
1. Introduction Sulfur compounds such as mercaptan and hydrogen sulfide exist in various light oils made from petroleum, which cause foul odors and deteriorate the finished products. Due to their acidity, they are corrosive to metals, which is harmful for storage and use of oil products. Therefore, it is necessary to remove them. In the oil refining industry, a water solution of base such as sodium hydroxide or ammonia is employed to fulfil the purpose of removal of acidic compounds. Although its effectiveness and the low cost of fresh caustic are the reasons for its wide use, the water solution of base, especially sodium hydroxide, always causes some problems, such as spending many caustic materials, and discarding lots of hazardous waste. So environ-
* Corresponding author. Tel.: +86-546-839-2280; fax: +86-546-1971. E-mail address: [email protected] (D. Xia). 0378-3820/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2003.12.008
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mental agencies around the world have tightened the regulations aimed at controlling its disposal. Solid bases merge as an ideal alternative to the aqueous bases to overcome the environmental and economic problems. The reported researches concerning solid base are mostly concentrating in mercaptan oxidation; these solid bases are selected from the group consisting of magnesium, nickel, zinc, copper, aluminum, iron oxides and mixtures thereof [1– 4]. However, as far as we know, the report concerning solid base on removal of hydrogen sulfide was hardly reported. In addition, activated carbon has been widely employed as one of the main sorbents for the hydrogen sulfide removal. Its application mainly aimed at hydrogen sulfide removal in various gases [5– 7]. This paper reports the effects of preparation of solid base for removal of hydrogen sulfide at ambient temperature. The objective is to select the optimum factors for preparation of the solid bases having better abilities for removal of hydrogen sulfide in light oil, and investigate the adsorption capacity of solid base for hydrogen sulfide removal with additive, at different liquid hourly space velocity.
2. Experimental 2.1. Preparation of solid base Activated carbon marked by DV-01 produced in China was used as supporter in this study. Physical properties of the activated carbon are listed in Table 1. The activated carbon was calcined at high temperature for 6 h, then impregnated with an aqueous solution of some mixed metallic salt materials at ambient temperature; after that, caustic solution was added and alkali compounds were produced on the carbon. The saturated activated carbon was filtrated in vacuum for a period of time, then dried for another period of time at 120 jC. 2.2. Experimental oil Petroleum ether (boiling point 90– 120 jC) with 800– 1000 Ag/g hydrogen sulfide concentration was used as experimental oil. 2.3. Capability test of solid base for H2S removal One gram of solid base was loaded in a 200-ml flask, and 100-ml experimental oil was added, then the solution was electromagnetically stirred at ambient temperature with
Table 1 Physical properties of activated carbon BET surface area/m2 g 1 Bulk density/g ml 1 Pore volume/ml g 1 Particle size/mesh
945.8 0.707 0.72 6 – 16
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protection of nitrogen; the stirred speed was 350 rpm. The hydrogen sulfide concentration in light oil was analyzed with period by the method of GB/T1792-88. 2.4. The dynamic adsorption of solid base for H2S removal The dynamic test was carried out to evaluate the capacity of solid base for H2S removal. Ten grams of solid base was loaded in a glass column (length 150 mm, diameter 2.5 mm). A petroleum ether feedstock containing 580 Ag/g hydrogen sulfide was processed at a steady liquid hourly space velocity; the test was stopped when outlet concentration of hydrogen sulfide reached 100 Ag/g. The experiments were carried out at ambient temperature. 2.5. Calculation of adsorption quantity The adsorption quantity of hydrogen sulfide by solid base is as follows: Xg ¼ ðC0 Ct ÞqV 103 =M Xg: adsorption quantity of hydrogen sulfide, mg/g; C0: concentration of hydrogen sulfide in pre-adsorption oil, Ag/g; Ct: concentration of hydrogen sulfide in oil at t hour, Ag/g; q, V: density, vol. of oil, g/ml, ml; M: quality of the solid base used, g.
3. Results and discussion 3.1. The effect of different chemical components of solid base on the removal of H2S With different alkaline materials, six kinds of solid base were prepared and the removal capacities for H2S were tested. The results are shown in Fig. 1. As can be seen from Fig. 1, the solid base SB14 has the highest capacity for absorption of hydrogen sulfide. It is known that there is a competitive between physical adsorption and chemical adsorption. Therefore, the removal capacity of the solid base for hydrogen sulfide was the sum of physical and chemical adsorptions. Different solid base has different surface area and chemical center, so the capacity for hydrogen sulfide removal is alternative. It is concluded that SB14 has the best chemical components for removal of hydrogen sulfide. 3.2. The effect of vacuum filtration time during preparation of solid base on the removal of H 2S Experiments examine the effect of time of vacuum filtration during preparation of the solid base on the removal of hydrogen sulfide. In the preparation process of solid base SB14, a series of solid bases were obtained with different vacuum filtrated time. The removal of hydrogen sulfide with different solid bases was tested, and the results are demonstrated in Fig. 2.
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Fig. 1. The adsorption capacity of different solid bases. *The preliminary concentration of hydrogen sulfide is 674 Ag/g.
Fig. 2 shows that the adsorption capacity of the solid base for hydrogen sulfide firstly increased and then decreased with the increase of the vacuum filtration time during the preparation of the solid base. As a result, the time of vacuum filtration is a factor to effect the hydrogen sulfide removal ability of the solid base; the optimum time of vacuum filtration should be 60 min. 3.3. The effect of drying time during preparation of solid base on the removal of H2S A series of solid bases were made with different drying time. And the removal of hydrogen sulfide of these solid bases was also examined. The experimental results are shown in Fig. 3.
Fig. 2. The adsorption capacity of the solid bases obtained at different times of vacuum filtration. *The preliminary concentration of hydrogen sulfide is 622 Ag/g.
Y. Duan et al. / Fuel Processing Technology 86 (2004) 237–244
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Fig. 3. The adsorption capacity of the solid base made at different drying time. *The preliminary concentration of hydrogen sulfide is 660 Ag/g.
It can be seen from Fig. 3 that the adsorption ability of the solid base for hydrogen sulfide is firstly increased then decreased with the time of drying prolonged in the preparation of the solid base. It is well known that the shorter the time of drying is, the higher the water content of the solid base is. Therefore, the higher water content of the solid base reduced the physical adsorption of hydrogen sulfide on the solid base when the drying time is less than 3 h. With the further increase of drying time, the water is too less in the solid base to provide the polar environment for the chemical adsorption. Consequently, the chemical adsorption quantity of hydrogen sulfide on the solid base was decreased greatly. It was found that the optimum time of drying for the solid base with good properties for removal of hydrogen sulfide should be 2 h.
Fig. 4. The adsorption capacity of the solid base for H2S with different amount of additive. *The preliminary concentration of hydrogen sulfide is 945 Ag/g.
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Fig. 5. The removal curves of hydrogen sulfide at different liquid hourly space velocity. *The preliminary concentration of hydrogen sulfide is 584 Ag/g.
3.4. The effect of additive on the removal of H2S with solid base It is believed that the function of polar compound is to serve as a proton transfer medium in the chemical adsorption of hydrogen sulfide on the solid base. Especially, the compounds are selected from the group consisting of water, alcohols, esters, ketones, diols and mixtures thereof [8]. A group of polar compounds was chosen as the additive for removal of H2S with the solid base. Experiments were carried out for measuring the adsorption capacity of the solid base SB14 with different quantities of the additive; the results were shown in Fig. 4. It was found from Fig. 4 that the removal of H2S greatly increased when the additive was added to the feedstock. The adsorption ability of the solid base for hydrogen sulfide firstly increased and then decreased with the increase of the quantity of additive. This
Fig. 6. The removal curves of hydrogen sulfide with the additive.
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Table 2 The adsorption capacity of solid bases for hydrogen sulfide LHSV [h 1]
The adsorption capacity of solid base [mg g 1]
1 2 2* 4
98.4 85.9 119.2 76.5
*Solid base with additive.
indicated that low additive content increased the polar environment of the solid base and improved the adsorption for hydrogen sulfide. However, high excess of additive content is detrimental to the adsorption of hydrogen sulfide on the solid base. The reason is not clear up to now. 3.5. Dynamic adsorption of solid base for H2S removal Three glass columns were installed and each was loaded with 10 g of SB14; the same feedstock was pumped through every column at liquid hourly space velocity (LHSV) of 1, 2 and 4 h 1, respectively. The removal curves of hydrogen sulfide at different liquid hourly space velocity are collected in Fig. 5. In addition, one experiment was also carried out at the mentioned experimental conditions (with LHSV, 2 h 1) with an additive added to the feedstock. The results are shown in Fig. 6. The adsorption capacities of solid base for H2S are summarized in Table 2. From Figs. 5 and 6 and Table 2, it can be seen that the adsorption capacity of solid base for hydrogen sulfide decreased with increase of LHSV. The additive evidently improved the adsorption capacity for hydrogen sulfide, which was in accordance with the results of stationary adsorption test at Section 3.4.
4. Conclusions 1. Preparation factors of the solid base play an important role for removal ability of hydrogen sulfide on the solid base. The preparation factors include mainly the components of solid base, the time of vacuum filtration and the time of drying. 2. The adsorption capacity of the solid base for hydrogen sulfide was the sum of physical and chemical adsorptions. 3. Addition of a group of polar compounds to the feedstock can promote significantly the removal of hydrogen sulfide on the solid base. 4. The adsorption capacity of solid base for hydrogen sulfide decreased with increase of LHSV.
References [1] F. Cavani, F. Trifiro, A. Vaccari, Catalysis Today 11 (1991) 173. [2] P. Ansquer, J.-M. Orgebin, US P5,382,354 (1995).
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[3] [4] [5] [6] [7] [8]
J.J. Alcaraz, B.J. Arena, R.D. Gillespie, J.S. Hollmgren, Catalysis Today 43 (1998) 89. D.-E. Jiang, G. Pan, B. Zhao, G. Ran, Y. Xie, E. Min, Applied Catalysis. A, General 201 (2000) 169. T.J. Bandosz, Q. Le, Carbon 36 (1998) 39. T.J. Bandosz, A. Bagreev, F. Adib, A. Turk, Environmental Science & Technology 34 (2000) 1069. A. Turk, K. Mahmood, J. Mozaffari, Water Science and Technology 27 (1993) 121. B.J. Arena, J.S. Holmgren, US P5,232,887 (1993).
Removal of hydrogen sulfide from light oil with solid base Yongfeng Duan, Yuzhi Xiang, Daohong Xia* State Key Laboratory of Heavy Oil Processing, College of Chemistry and Chemical Engineering, University of Petroleum, 257061 Dongying Shandong, China Accepted 1 December 2003
Abstract A novel solid base with activated carbon as supporter and alkali and earth-alkali compounds as active components has been developed for removal of hydrogen sulfide from light oils. The experimental results indicated that the solid base has excellent adsorption capacity for hydrogen sulfide. In addition, an additive added to feedstock that can promote significantly the removal of hydrogen sulfide for the solid base was also developed. The adsorption capacity of the solid base for hydrogen sulfide was evaluated with dynamic testing. D 2004 Elsevier B.V. All rights reserved. Keywords: Hydrogen sulfide; Removal; Solid base; Adsorption; Additive
1. Introduction Sulfur compounds such as mercaptan and hydrogen sulfide exist in various light oils made from petroleum, which cause foul odors and deteriorate the finished products. Due to their acidity, they are corrosive to metals, which is harmful for storage and use of oil products. Therefore, it is necessary to remove them. In the oil refining industry, a water solution of base such as sodium hydroxide or ammonia is employed to fulfil the purpose of removal of acidic compounds. Although its effectiveness and the low cost of fresh caustic are the reasons for its wide use, the water solution of base, especially sodium hydroxide, always causes some problems, such as spending many caustic materials, and discarding lots of hazardous waste. So environ-
* Corresponding author. Tel.: +86-546-839-2280; fax: +86-546-1971. E-mail address: [email protected] (D. Xia). 0378-3820/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2003.12.008
238
Y. Duan et al. / Fuel Processing Technology 86 (2004) 237–244
mental agencies around the world have tightened the regulations aimed at controlling its disposal. Solid bases merge as an ideal alternative to the aqueous bases to overcome the environmental and economic problems. The reported researches concerning solid base are mostly concentrating in mercaptan oxidation; these solid bases are selected from the group consisting of magnesium, nickel, zinc, copper, aluminum, iron oxides and mixtures thereof [1– 4]. However, as far as we know, the report concerning solid base on removal of hydrogen sulfide was hardly reported. In addition, activated carbon has been widely employed as one of the main sorbents for the hydrogen sulfide removal. Its application mainly aimed at hydrogen sulfide removal in various gases [5– 7]. This paper reports the effects of preparation of solid base for removal of hydrogen sulfide at ambient temperature. The objective is to select the optimum factors for preparation of the solid bases having better abilities for removal of hydrogen sulfide in light oil, and investigate the adsorption capacity of solid base for hydrogen sulfide removal with additive, at different liquid hourly space velocity.
2. Experimental 2.1. Preparation of solid base Activated carbon marked by DV-01 produced in China was used as supporter in this study. Physical properties of the activated carbon are listed in Table 1. The activated carbon was calcined at high temperature for 6 h, then impregnated with an aqueous solution of some mixed metallic salt materials at ambient temperature; after that, caustic solution was added and alkali compounds were produced on the carbon. The saturated activated carbon was filtrated in vacuum for a period of time, then dried for another period of time at 120 jC. 2.2. Experimental oil Petroleum ether (boiling point 90– 120 jC) with 800– 1000 Ag/g hydrogen sulfide concentration was used as experimental oil. 2.3. Capability test of solid base for H2S removal One gram of solid base was loaded in a 200-ml flask, and 100-ml experimental oil was added, then the solution was electromagnetically stirred at ambient temperature with
Table 1 Physical properties of activated carbon BET surface area/m2 g 1 Bulk density/g ml 1 Pore volume/ml g 1 Particle size/mesh
945.8 0.707 0.72 6 – 16
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239
protection of nitrogen; the stirred speed was 350 rpm. The hydrogen sulfide concentration in light oil was analyzed with period by the method of GB/T1792-88. 2.4. The dynamic adsorption of solid base for H2S removal The dynamic test was carried out to evaluate the capacity of solid base for H2S removal. Ten grams of solid base was loaded in a glass column (length 150 mm, diameter 2.5 mm). A petroleum ether feedstock containing 580 Ag/g hydrogen sulfide was processed at a steady liquid hourly space velocity; the test was stopped when outlet concentration of hydrogen sulfide reached 100 Ag/g. The experiments were carried out at ambient temperature. 2.5. Calculation of adsorption quantity The adsorption quantity of hydrogen sulfide by solid base is as follows: Xg ¼ ðC0 Ct ÞqV 103 =M Xg: adsorption quantity of hydrogen sulfide, mg/g; C0: concentration of hydrogen sulfide in pre-adsorption oil, Ag/g; Ct: concentration of hydrogen sulfide in oil at t hour, Ag/g; q, V: density, vol. of oil, g/ml, ml; M: quality of the solid base used, g.
3. Results and discussion 3.1. The effect of different chemical components of solid base on the removal of H2S With different alkaline materials, six kinds of solid base were prepared and the removal capacities for H2S were tested. The results are shown in Fig. 1. As can be seen from Fig. 1, the solid base SB14 has the highest capacity for absorption of hydrogen sulfide. It is known that there is a competitive between physical adsorption and chemical adsorption. Therefore, the removal capacity of the solid base for hydrogen sulfide was the sum of physical and chemical adsorptions. Different solid base has different surface area and chemical center, so the capacity for hydrogen sulfide removal is alternative. It is concluded that SB14 has the best chemical components for removal of hydrogen sulfide. 3.2. The effect of vacuum filtration time during preparation of solid base on the removal of H 2S Experiments examine the effect of time of vacuum filtration during preparation of the solid base on the removal of hydrogen sulfide. In the preparation process of solid base SB14, a series of solid bases were obtained with different vacuum filtrated time. The removal of hydrogen sulfide with different solid bases was tested, and the results are demonstrated in Fig. 2.
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Fig. 1. The adsorption capacity of different solid bases. *The preliminary concentration of hydrogen sulfide is 674 Ag/g.
Fig. 2 shows that the adsorption capacity of the solid base for hydrogen sulfide firstly increased and then decreased with the increase of the vacuum filtration time during the preparation of the solid base. As a result, the time of vacuum filtration is a factor to effect the hydrogen sulfide removal ability of the solid base; the optimum time of vacuum filtration should be 60 min. 3.3. The effect of drying time during preparation of solid base on the removal of H2S A series of solid bases were made with different drying time. And the removal of hydrogen sulfide of these solid bases was also examined. The experimental results are shown in Fig. 3.
Fig. 2. The adsorption capacity of the solid bases obtained at different times of vacuum filtration. *The preliminary concentration of hydrogen sulfide is 622 Ag/g.
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Fig. 3. The adsorption capacity of the solid base made at different drying time. *The preliminary concentration of hydrogen sulfide is 660 Ag/g.
It can be seen from Fig. 3 that the adsorption ability of the solid base for hydrogen sulfide is firstly increased then decreased with the time of drying prolonged in the preparation of the solid base. It is well known that the shorter the time of drying is, the higher the water content of the solid base is. Therefore, the higher water content of the solid base reduced the physical adsorption of hydrogen sulfide on the solid base when the drying time is less than 3 h. With the further increase of drying time, the water is too less in the solid base to provide the polar environment for the chemical adsorption. Consequently, the chemical adsorption quantity of hydrogen sulfide on the solid base was decreased greatly. It was found that the optimum time of drying for the solid base with good properties for removal of hydrogen sulfide should be 2 h.
Fig. 4. The adsorption capacity of the solid base for H2S with different amount of additive. *The preliminary concentration of hydrogen sulfide is 945 Ag/g.
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Fig. 5. The removal curves of hydrogen sulfide at different liquid hourly space velocity. *The preliminary concentration of hydrogen sulfide is 584 Ag/g.
3.4. The effect of additive on the removal of H2S with solid base It is believed that the function of polar compound is to serve as a proton transfer medium in the chemical adsorption of hydrogen sulfide on the solid base. Especially, the compounds are selected from the group consisting of water, alcohols, esters, ketones, diols and mixtures thereof [8]. A group of polar compounds was chosen as the additive for removal of H2S with the solid base. Experiments were carried out for measuring the adsorption capacity of the solid base SB14 with different quantities of the additive; the results were shown in Fig. 4. It was found from Fig. 4 that the removal of H2S greatly increased when the additive was added to the feedstock. The adsorption ability of the solid base for hydrogen sulfide firstly increased and then decreased with the increase of the quantity of additive. This
Fig. 6. The removal curves of hydrogen sulfide with the additive.
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243
Table 2 The adsorption capacity of solid bases for hydrogen sulfide LHSV [h 1]
The adsorption capacity of solid base [mg g 1]
1 2 2* 4
98.4 85.9 119.2 76.5
*Solid base with additive.
indicated that low additive content increased the polar environment of the solid base and improved the adsorption for hydrogen sulfide. However, high excess of additive content is detrimental to the adsorption of hydrogen sulfide on the solid base. The reason is not clear up to now. 3.5. Dynamic adsorption of solid base for H2S removal Three glass columns were installed and each was loaded with 10 g of SB14; the same feedstock was pumped through every column at liquid hourly space velocity (LHSV) of 1, 2 and 4 h 1, respectively. The removal curves of hydrogen sulfide at different liquid hourly space velocity are collected in Fig. 5. In addition, one experiment was also carried out at the mentioned experimental conditions (with LHSV, 2 h 1) with an additive added to the feedstock. The results are shown in Fig. 6. The adsorption capacities of solid base for H2S are summarized in Table 2. From Figs. 5 and 6 and Table 2, it can be seen that the adsorption capacity of solid base for hydrogen sulfide decreased with increase of LHSV. The additive evidently improved the adsorption capacity for hydrogen sulfide, which was in accordance with the results of stationary adsorption test at Section 3.4.
4. Conclusions 1. Preparation factors of the solid base play an important role for removal ability of hydrogen sulfide on the solid base. The preparation factors include mainly the components of solid base, the time of vacuum filtration and the time of drying. 2. The adsorption capacity of the solid base for hydrogen sulfide was the sum of physical and chemical adsorptions. 3. Addition of a group of polar compounds to the feedstock can promote significantly the removal of hydrogen sulfide on the solid base. 4. The adsorption capacity of solid base for hydrogen sulfide decreased with increase of LHSV.
References [1] F. Cavani, F. Trifiro, A. Vaccari, Catalysis Today 11 (1991) 173. [2] P. Ansquer, J.-M. Orgebin, US P5,382,354 (1995).
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Y. Duan et al. / Fuel Processing Technology 86 (2004) 237–244
[3] [4] [5] [6] [7] [8]
J.J. Alcaraz, B.J. Arena, R.D. Gillespie, J.S. Hollmgren, Catalysis Today 43 (1998) 89. D.-E. Jiang, G. Pan, B. Zhao, G. Ran, Y. Xie, E. Min, Applied Catalysis. A, General 201 (2000) 169. T.J. Bandosz, Q. Le, Carbon 36 (1998) 39. T.J. Bandosz, A. Bagreev, F. Adib, A. Turk, Environmental Science & Technology 34 (2000) 1069. A. Turk, K. Mahmood, J. Mozaffari, Water Science and Technology 27 (1993) 121. B.J. Arena, J.S. Holmgren, US P5,232,887 (1993).