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Research Papers

# Finding of Optimum Effective Parameters on Sweetening of Methane Gas by Zinc Oxide NanoparticlesOPEN ACCESS

[+] Author and Article Information
Farshad Farahbod

Department of Chemical Engineering,
Firoozabad Branch,
Islamic Azad University,
P.O. Box 74715-117,
Firoozabad, Fars, Iran
e-mail: mf_fche@iauf.ac.ir

Sara Farahmand

School of Chemical and Petroleum Engineering,
Shiraz, Iran
e-mail: sfarahmand2005@gmail.com

Mohammad Jafar Soltanian Fard

e-mail: soltanianfardm.j@gmail.com

Mohammad Nikkhahi

e-mail: nikkhahi92@gmail.com
Department of Chemical Engineering,
Firoozabad Branch,
Islamic Azad University,
Firoozabad, Fars, Iran

1Corresponding author.

Manuscript received July 8, 2013; final manuscript received September 13, 2013; published online October 7, 2013. Assoc. Editor: Roger Narayan.

J. Nanotechnol. Eng. Med 4(2), 021003 (Oct 07, 2013) (6 pages) Paper No: NANO-13-1040; doi: 10.1115/1.4025467 History: Received July 08, 2013; Revised September 13, 2013

## Abstract

Nanocatalysts are adapted in this research to remove $H2S$ as the toxic, corrosive, and pyrophoric contaminant. The important feature which is considered is to enhance the adsorption efficiency of hydrogen sulfide from hydrocarbon fuels such as methane gas by applying the zinc oxide nanocatalyst. In general, the optimum conditions to eliminate the hydrogen sulfide from methane gas are evaluated in this paper, experimentally. In this study, zinc oxide nanoparticles are synthesized and are contacted with flow of sour methane. The synthesized nanoparticles are characterized by SEM. The process performance of $H2S$ removal from methane gas on zinc oxide nanoparticles is illustrated by the ratio of outlet concentration per feed concentration. The effects of operating conditions such as operating temperature, pressure, the occupied volume of bed, the amount of $H2S$ concentration in feed stream, feed superficial velocity, size of nanocatalyst, and the bed height are studied in this paper. Also, the cost estimations are presented for different operating pressures and temperatures. This work studies the adsorption of $H2S$ from natural gas with an emphasis on the influence of the operating parameters on process efficiency and cost evaluation. Finally, results introduce the amount of pressure 15 atm, temperature 300 °C, bed height 70 cm, and 35 nm in diameter nano zinc oxide as the optimum properties. Therefore, the amount of $C/C0$ is decreased to 0.022. In addition, this is confirmed that the increase in the feed concentration of $H2S$ and feed superficial velocity, also the decrease in the diameter of zinc oxide catalyst enhances the process efficiency.

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## Introduction

Nanotechnology (sometimes shortened to “nanotech”) is the manipulation of matter on an atomic and molecular scale. The earliest, widespread description of nanotechnology has been referred to the particular technological goal of precisely manipulating atoms and molecules for fabrication of macro scale products, also now is referred to as molecular nanotechnology [1]. A more generalized description of nanotechnology was subsequently established by the National Nanotechnology Initiative, which defines nanotechnology as the study and application of fine particles which are sized from 1 to 100 nm in all of the science fields [2].

Sulfur compounds in fuels such as methane gas cause problems on two fronts: they release toxic gases during combustion, and they damage metals and catalysts in engines and fuel cells [3]. They usually are removed using a liquid treatment that adsorbs the sulfur from the methane gas, but the process is cumbersome and requires that the gas be cooled and reheated, making the fuel less energy efficient [4]. To solve these problems, researchers have turned to solid metal oxide adsorbents, but those have their own sets of challenges [5]. While they work at higher temperatures, eliminating the need to cool and re-heat the fuel, their performance is limited by stability issues. They lose their activity after only a few cycles of use [6].

Previous studies found that sulfur adsorption works best at the surface of solid metal oxides [7]. So, the authors set out to create a material with maximum surface area. The solution seems to be tiny grains of zinc oxide nanoparticles, uniting high surface area, high reactivity, and structural integrity in a high-performance sulfur adsorbent [8]. ZnO has been numerously used for removing of hydrogen sulfide from gas streams in processes like reforming [9,10], integrated gasification combined cycle [11], and fuel cell [11-14]. Although ZnO has been well evaluated with hydrogen sulfide feed stocks, the performance of zinc oxide nanostructure with different operating conditions and structural characteristics in $H2S$ removal has not been specially evaluated in details. This work is devoted to using experimental design methodology to identify the optimum conditions for $H2S$ removal by nano zinc oxide catalysts. Clearly, the nanosized ZnO is more reactive than the same material in bulk form, enabling complete sulfur removal with less material, allowing for a smaller reactor. The nanoparticles stay stable and active after several cycles [10].

Thermal swing regeneration is a common industry process used for sweetening natural gas. In that process, chemical sponges called sorbents remove toxic and flammable gases, such as rotten-egg smelling hydrogen sulfide from natural gas.

The gas must first be treated with a solution of chemical sorbents that are dissolved in water. That solution must then be heated up and boiled to remove the hydrogen sulfide, in order to prepare the sorbent for future use. Once the hydrogen sulfide is boiled off, the sorbent is then cooled and ready for use again. The repeated heating and cooling requires a lot of energy and markedly reduces the efficiency of the process, scientists say.

In the adsorption process by nano zinc oxide, sweetening of natural gas is occurred with minimum heat flux comparing with the other sweetening methods. Also, about 70–80% of the initial amount of hydrogen sulfide is removed from the methane by the proposed adsorption process. Also, zinc oxide catalyst is produced due to feasible method and is not expensive comparing with the other catalysts. So, this method is beneficial. Undoubtedly, the zinc oxide nanoparticles as sorbents have large active surface. So, they can be reused again and again. This method will be developed as soon as possible and will be applied in industrial scale.

In this work, a fixed bed reactor is set up which is equipped by nano zinc oxide catalysts. Some experiments have been held to investigate the effect of different operating pressure, temperature, catalyst diameter, bed height on the performance of $H2S$ removal. Also, the capability of nanocatalysts is surveyed toward changing the amount of $H2S$ in feed stream and also changing feed superficial velocity. The results are illustrated as the ratio of outlet $H2S$ concentration per inlet $H2S$ concentration. In addition, this work contains the cost estimations for the various operating pressures and temperatures. Consequently, the optimum conditions are introduced.

## Materials and Methods

Zinc oxide nanoparticle is a common ingredient and has a huge variety of applications. Zinc is an essential mineral and is nontoxic in low concentration [11].

###### Synthesis Method of Nanosized ZnO.

Zinc metal is used to make a solution containing one molar $Zn2+$ion. At first, this solution is purified, and then a type of surface-active reagent (zinc acetate dehydrate) 0.05 M is added. At the next step, approximately, 10% of ethanol is added under the ultrasonic conditions. The produced solution is agitated for 25–30 min. The obtained solution will be homogenized after this time interval. Same reagents are added to $Na2CO3$, 1 M solution under the same conditions. Then another surface active reagent (folic acid) is added. The solution is agitated for 30 min again. In the next step, filtering and washing of the solution is done several times by ethanol and distilled water alternately under the ultrasonic action. The produced substance is prepared to dry for 50 min at 80 °C. Then, it roasted at 450 °C for 45 min to obtain zinc oxide nanoparticles. The obtained produced substance has light yellow color, and can been characterized by XRD and TEM. Produced spherical particles with the average diameter of 35–55 $nm$ in size are observed approximately, and finally the crystal is pure zinc oxide with hexahedral structure. Figure 1 shows SEM photos of nanoparticles in two different visions (a) in the scale of 5 $μm$ and (b) in the scale of 500$nm$.

###### Set Up Description.

One laboratory cylindrical vessel equipped with the nanosized ZnO catalytic fixed bed is applied for $H2S$ adsorption process, in this work. The process temperature is adjusted by one steam jacket around the vessel. Methane stream from a tank reservoir is mixed by $H2S$ and is fed into the bed containing zinc oxide nanoparticles. The inside diameter and the height of the vessel is 10 $cm$ and 130$cm$, respectively. All the instruments and equipments are made of stainless steel.

Figure 2 shows briefly the mentioned adsorption experimental setup constructed to remove hydrogen sulfide from methane gas by using zinc oxide nanocatalyst.

Methane gas flow rate is controlled by the flow meter and adjusted by valve after passing a filter, then is mixed by the adjusted amount of hydrogen sulfide and compressed to the reactor. The bed height of catalyst can be verified by some separate smaller metallic beds which are located in the vessel. Measuring the hydrogen sulfide concentration in the feed and the discharge flow, defines the performance of the process.

## Results and Discussion

Anyone knows, the hydrogen sulfide is corrosive and toxic, severely. Meanwhile, this component is in several industrial. We know the current technologies use huge resources of energy for removing the hydrogen sulfide component. Therefore, the researchers try to enhance the performance of sweetening process. So, in this paper the zinc oxide is applied as nanocatalysts for removal of $H2S$. This metal oxide is not expensive comparing with the other metal oxides. So, several experiments are designed to evaluate the performance of sweetening process in this paper, operationally and economically. These experiments were tested to determine operational conditions that would optimize the amount of H2S removed from gas in order to gas sweetening.

Some major parameters are considered experimentally in the gas sweetening process by nanoparticles. The effects of operating conditions, properties of catalytic bed and zinc oxide catalyst are investigated on the process performance. The ratio of $H2S$ concentration in the product stream on the initial concentration in the input stream ($C/C0$) represents the process performance. The purpose of the experiments is to decrease the amount of hydrogen sulfide below the 4 ppm in the outlet stream. Experimental results are presented in the following figures.

###### The Effect of Operating Temperature.

Both, temperature and pressure are two important parameters in separation processes. Five 100 °C, 200 °C, 300 °C, 400 °C, and 500 °C are examined during different pressures and the amount of $C/C0$ is measured. So, to find the best operating temperature, the operating pressure is changed from 5 atm to 20 atm using 35 nm in diameter catalyst. The feed contains 100 ppm $H2S$ with 1.67 $μm3/s$ flow rate and the reactor has a bed with 70 cm height. Figure 3 shows that the 5 atm operating pressure is not effective even at 500 °C temperature, since the amounts of $C/C0$ are higher than 0.04. Also, the amount of $C/C0$ reaches below the 0.04 just when 500 °C and 300 °C are adjusted as the operating temperatures when 10 atm and 15 atm is the operating pressure, respectively. The operating pressure 20 atm decreases the amount of $C/C0$ below the 0.04 at all experimental operating temperatures. However, this is risky to handle the process under high pressure as high as 20 atm. So, running the process under 15 atm seems to be more feasible than 20 atm. According to the results in Fig. 3, providing operating temperatures above the 300 °C is effective on decreasing the amount of hydrogen sulfide. Although the outlet concentration is the same at 300 °C and 400 °C, but the consumed energy in steam jacket to provide the operating temperature of 400 °C and 500 °C is considerable comparing with 300 °C. So, the temperature of 300 °C and pressure of 15 $atm$ are considered as the best operating conditions.

Then, experiments are held for two different 35 $nm$and 55 $nm$ nanocatalysts at 15 $atm$ and different temperatures. Again, bed height is adjusted 50 cm and the amount of $H2S$ in feed is 100 ppm. Figure 4(a) shows the decrease in the outlet $H2S$ concentration by the temperature augmentation. Temperature varies from 100 °C to 500 °C. The values of $C/C0$ are changed from 0.067 to 0.003 and from 0.057 to 0.001 when catalyst with 55 $nm$ and 35 $nm$ in diameter are used, respectively. The adsorption progress is obtained by temperature rise. The amount of $C/C0$ is higher than 0.04 when the reactor operates at 100 °C and 200 °C, for both 55 $nm$ and 35 $nm$ catalysts. So these are not the proper as operating temperatures. Although the $H2S$ removes perfectly at 500 °C but the required heat energy provided by the steam jacket is much, so the temperature 300 °C seems to be the best. The $H2S$ content in the outlet stream is receivable at 300 °C.

Figure 4(b) shows the cost of production of required steam to hold the reactor temperature and the process performance versus the temperature variations. The performance of process is determined by the amount of $C/C0$ for 35 $nm$ zinc oxide catalysts. At 300 °C, 400 °C, and 500 °C the final $H2S$ concentration meets the determined specification and is below than 4 ppm. However, the cost of produced steam at 300 °C, is lower than the price related to the 400 °C and 500 °C. As indicated in Fig. 4(b) the optimum temperature is 300 °C.

###### The Effect of Operating Pressure.

Generally, the high values of pressure improve the adsorption processes. In this part, the effect of this major operating parameter is investigated experimentally on the $H2S$ removal for two types of nanocatalyst. The feed with 1.67 $μm3/s$flow rate and 100 ppm $H2S$ enters into the reactor with 70 cm height of bed at 300 °C. Figure 5(a) shows a sudden decrease in the outlet $H2S$ when the pressure increases from 5 $atm$ to 10 $atm$ while both 35 $nm$ and 55 $nm$ nanocatalysts are applied. So, the pressure rise improves the $H2S$ removal. Also, 35 $nm$ in diameter catalysts remove $H2S$ more effectively. As mentioned before, the amount of final concentration of hydrogen sulfide, $C$, should be decreased as 4 ppm. This objective is reached at the pressures 15 $atm$ and 20 $atm$. However, the cost of reactor vessel which sustains high pressure and operates at 300 °C and 20 $atm$ is considerable. Figure 5(b) shows the estimated price of stainless steal reactor vessel and also the process performance versus the operating pressure. The best process performance is reached if the final concentration of hydrogen sulfide decreases less than 4 ppm. As shown in Fig. 5(b) the optimum process performance is at 15 atm with the acceptable price.

###### The Effect of Feed Superficial Velocity.

The performance of the adsorption process is studied in different feed flow rates hence different superficial velocities in Fig. 6. The diameter of the experimental zinc oxide catalytic bed is 0.1 m. So, feed superficial velocity varies by changing feed flow rates. Figure 6 shows that, the rise in superficial velocity emerges the bed higher content of input $H2S$ so, the amounts of $C/C0$ increase. However, the bed contains 35 $nm$ catalysts removes $H2S$ more effectively. The results are obtained at 300 °C and 15 $atm$ with 70 cm bed height while the feed contains 100 ppm of hydrogen sulfide.

###### The Effect of Bed Height.

The height of the catalytic bed changes between 30$cm$ and 110$cm$. The optimum height of the nanocatalytic bed is studied in this section. Operating temperature and pressure is adjusted at 300 °C and 15 $atm$, respectively. Results are shown in Fig. 7. Totally, the increase in the height of catalytic bed improves the $H2S$ removal when both 35 $nm$ and 55 $nm$ catalyst is used. Figure 7 shows that the decrease in the amounts of $C/C0$ is considerable when the height of the bed changes from 30 $cm$ to 110$cm$. However, the slighter decrease in values of $C/C0$ is obtained at heights more than 70$cm$. So, using extra catalytic bed more than 70 cm has not considerable effect in decreasing the acid gas. Also, nanocatalyst with 35 $nm$ in diameter removes $H2S$ more effectively. This result is predictable since the height of the catalytic bed is adjusted 70 cm to find the optimum temperature and pressure, at first.

###### The Effect of Occupied Volume.

The zinc oxide catalytic bed is set up in a cylinder shape with 10 cm inside diameter and can be filled to 110 $cm$ in height. In this section, the effect of catalyst volume occupied the bed is studied on the amount of $H2S$ removal. The operating conditions are adjusted at 300 °C, 15 $atm$ and with 70 $cm$ bed height. The initial concentration, $C0$, is 100 ppm and the feed flow rate is 1.67 $μm3/s$. Figure 8 illustrates that the increase in the volume which is occupied by zinc oxide catalyst, improves the process performance. Also, the better results are obtained by using the 35 $nm$ in diameter catalyst.

###### The Effect of Amount of Input Hydrogen Sulfide.

The effect of $H2S$ content in feed stream on the process performance is studied in Fig. 9. Each experiment is held at 300 °C and 15 $atm$. The feed flow rate is adjusted 1.67 $μm3/s$. This is indicated that the capability of nanocatalysts is fixed and the active sites decreased.

###### The Effect of Catalyst Size.

In this section, nano zinc oxide catalysts with five different diameters are applied in separate experiments. According to the results which are obtained above, the optimum operating temperature, 300 °C, pressure 15 $atm$, and bed height of 70 $cm$ is considered in the experiments. The amount of initial $H2S$ and feed flow rate are adjusted 100 ppm and 1.67 $μm3/s$, respectively. Figure 10 shows the different capabilities of nanocatalysts in $H2S$ adsorption. Lower diameter 35 nm removes $H2S$ more effectively comparing with the other catalysts with higher diameters. The value of $C/C0$ is 0.022 and 0.036 for usage of 35 $nm$ and 55 $nm$ catalysts, respectively.

###### The Effect of Catalyst Surface Area.

The effective surface area for the catalysts is a function of the methods which they are prepared. On the other hand, the effective surface area depends on the catalyst diameter. All catalysts used in this study are produced by the same method. So, different diameters make different effective surface area, $(m2/gr)$ for the catalysts. The lower diameter of zinc oxide catalyst, 35 $nm$ shows the larger surface area, 60 $m2/gr$ and consequently removes much more $H2S$ in adsorption process. Figure 11 shows the results. Also, the decreasing tendency of $C/C0$ values is obvious by increasing the catalytic surface area. The experiments are held under the optimum conditions 300 °C and 15 $atm$ with 100 ppm initial concentration of hydrogen sulfide.

## Conclusions

Nanotechnology has been developed in various fields and also is applied in many industries, gradually. Nanocatalytic gas sweetening is not utilized yet, industrially. This work proposes the optimum operating conditions for hydrogen sulfide removal with ZnO nanocatalyst. Investigation to find optimum operating conditions in different process has been considered all the time. Since if the process is designed due to the optimum conditions then it will be performed automatically and precisely. So, this work propose the optimum operating conditions for gas sweetening by ZnO nanocatalyst with lower required heat comparing with the common sweetening methods such as thermal swing regeneration.

This work surveys the effects of operating parameters, zinc oxide catalyst characteristics and bed properties on methane sweetening, experimentally. The optimum amounts of the investigated parameters are presented, finally. The process performance is considered as the ratio of the outlet concentration of $H2S$ per the inlet concentration and is presented as value of $C/C0$. Experimental results are held on a cylindrical reactor with 10 cm inside diameter which is packed with zinc oxide nanocatalysts. The feed flow stream contains 100 $ppm$$H2S$ with $5.3×10-5m/s$ superficial velocity, initially. The effect of catalyst diameter and surface area, bed height and occupied volume, operating pressure and temperature on the $H2S$ removal are evaluated. In addition, the curves are presented which illustrate the economical estimations of the process in different pressures and temperatures.

The experimental results indicate that the optimum adsorption performance is obtained at 300 °C and 15 atm operating conditions by 35 $nm$ zinc oxide catalysts. This size of catalyst has 60 $m2/gr$ surface areas. When the bed height is fixed 70 cm and the feed flow rate is about 1.67 $μm3/s$.

Also, the changes in adsorption performance are considered at five different bed heights 30, 50, 70, 90, and 110 cm. The optimum bed height is obtained 70 $cm$ because the amounts of $C/C0$ decreases slightly at the larger heights than 70$cm$.

Inlet feed which contains 50, 75, 100, 150, and 200 $ppm$$H2S$ are imposed in the catalytic bed, respectively. Also, superficial velocity of feed is changed by imposing different feed flow rates in the vessel. The results confirmed that, the capability of nano zinc oxide catalysts decreases by the increase in the initial concentration of $H2S$ and also by the increase in the feed superficial velocity. Results show the efficiency of sweetening process is very high in optimum conditions. Undoubtedly, this performance is feasible. Economical evaluations which are presented in Figs. 4(b) and 5(b) confirm this fact, also.

## References

Yuxiao, N., Mingyang, X., Baozhu, T., and Jinlong, Z., 2012, “Improving the Visible Light Photocatalytic Activity of Nano-Sized Titanium Dioxide Via the Synergistic Effects between Sulfur Doping and Sulfation,” Appl. Catal., B, 115–116(5), pp. 253–260.
Corrie, L. C., and Kenneth, J. K., 2002, “Unique Chemical Reactivities of Nanocrystalline Metal Oxides Toward Hydrogen Sulfide,” Chem. Mater., 14(4), pp. 1806–1811.
Rao, M., Song, X., and Cairns, E. J., 2012, “Nano-Carbon/Sulfur Composite Cathode Materials With Carbon Nanofiber as Electrical Conductor for Advanced Secondary Lithium/Sulfur Cells,” J. Power Sources, 205(1), pp. 474–478.
Zhang, Y., Zhao, Y., Konarov, A., Gosselink, D., Soboleski, H. G., and Chen, P., 2013, “A Novel Nano-Sulfur/Polypyrrole/Graphene Nanocomposite Cathode With a Dual-Layered Structure for Lithium Rechargeable Batteries,’’ J. Power Sources, 241(1), pp. 517–521.
Hosseinkhani, M., Montazer, M., Eskandarnejad, S., and Rahimi, M. K., 2012, “Simultaneous in Situ Synthesis of Nano Silver and Wool Fiber Fineness Enhancement Using Sulphur Based Reducing Agents,” Colloids Surf., A, 415(5), pp. 431–438.
Christoforidis KonstantinosC., Figueroa Santiago, J. A., and Fernández-García, M., 2012, “Iron–Sulfur Codoped TiO2 Anatase Nano-Materials: UV and Sunlight Activity for Toluene Degradation,” Appl. Catal., B, 117–118(18), pp. 310–316.
Balouria, V., Kumar, A., Samanta, S., Singh, A., Debnath, A. K., Mahajan, A., Bedi, R. K., AswalD. K., and Gupta, S. K., 2013, “Nano-Crystalline Fe2O3 Thin Films for ppm Level Detection of H2S,” Sens. Actuators B, 181, pp. 471–478.
Eow, J. S., 2004, “Recovery of Sulfur From Sour Acid Gas: A Review of the Technology,” Environmental Prog., 21, pp. 143–162.
HabibiR., RashidiA. M., Towfighi DaryanJ., AlizadehA., 2010, “Study of the Rod–Like and Spherical Nano ZnO Morphology on H2S Removal From Natural Gas,” Appl. Surf. Sci., 257, pp. 434–439.
Novochimskii, I. I., Song, C. H., Ma, X., Liu, X., Shore, L., Lampert, J., and Farrauto, R. J., 2004, “Low Temperature H2S Removal From Steam Containing Gas Mixtures With ZnO for Fuel Cell Application. 2. Wash-Coated Monolith,” Energy Fuels, 18, pp. 584–589.
NovochimskiiII., Song, C. H., Ma, X., Liu, X., Shore, L., Lampert, J., and Farrauto, R. J., 2004, “Low Temperature H2S Removal From Steam Containing Gas Mixtures With ZnO for Fuel Cell Application. 1. ZnO Particles and Extrudates,” Energy Fuels, 18, pp. 576–583.
Arthour, L. K., and Richard, B., 1997, Gas Purification, Nielsen edition, Gulf Publishing Company, Houston, TX.
Habibi, R., Towfighi Daryan, J., and Rashidi, A. M., 2009, “Shape and Size-Controlled Fabrication of ZnO Nanostructures Using Noveltemplates,” J. Exp. Nanosci., 4(1), pp. 35–45.
Farahbod, F., Bagheri, N., and Madadpour, F., 2013, “Effect of Solution Content ZnO Nanoparticles on Thermal Stability of Poly Vinyl Chloride,” ASME J. Nanotechnol. Eng. Med., 4, p. 021002.
Copyright © 2013 by ASME
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## References

Yuxiao, N., Mingyang, X., Baozhu, T., and Jinlong, Z., 2012, “Improving the Visible Light Photocatalytic Activity of Nano-Sized Titanium Dioxide Via the Synergistic Effects between Sulfur Doping and Sulfation,” Appl. Catal., B, 115–116(5), pp. 253–260.
Corrie, L. C., and Kenneth, J. K., 2002, “Unique Chemical Reactivities of Nanocrystalline Metal Oxides Toward Hydrogen Sulfide,” Chem. Mater., 14(4), pp. 1806–1811.
Rao, M., Song, X., and Cairns, E. J., 2012, “Nano-Carbon/Sulfur Composite Cathode Materials With Carbon Nanofiber as Electrical Conductor for Advanced Secondary Lithium/Sulfur Cells,” J. Power Sources, 205(1), pp. 474–478.
Zhang, Y., Zhao, Y., Konarov, A., Gosselink, D., Soboleski, H. G., and Chen, P., 2013, “A Novel Nano-Sulfur/Polypyrrole/Graphene Nanocomposite Cathode With a Dual-Layered Structure for Lithium Rechargeable Batteries,’’ J. Power Sources, 241(1), pp. 517–521.
Hosseinkhani, M., Montazer, M., Eskandarnejad, S., and Rahimi, M. K., 2012, “Simultaneous in Situ Synthesis of Nano Silver and Wool Fiber Fineness Enhancement Using Sulphur Based Reducing Agents,” Colloids Surf., A, 415(5), pp. 431–438.
Christoforidis KonstantinosC., Figueroa Santiago, J. A., and Fernández-García, M., 2012, “Iron–Sulfur Codoped TiO2 Anatase Nano-Materials: UV and Sunlight Activity for Toluene Degradation,” Appl. Catal., B, 117–118(18), pp. 310–316.
Balouria, V., Kumar, A., Samanta, S., Singh, A., Debnath, A. K., Mahajan, A., Bedi, R. K., AswalD. K., and Gupta, S. K., 2013, “Nano-Crystalline Fe2O3 Thin Films for ppm Level Detection of H2S,” Sens. Actuators B, 181, pp. 471–478.
Eow, J. S., 2004, “Recovery of Sulfur From Sour Acid Gas: A Review of the Technology,” Environmental Prog., 21, pp. 143–162.
HabibiR., RashidiA. M., Towfighi DaryanJ., AlizadehA., 2010, “Study of the Rod–Like and Spherical Nano ZnO Morphology on H2S Removal From Natural Gas,” Appl. Surf. Sci., 257, pp. 434–439.
Novochimskii, I. I., Song, C. H., Ma, X., Liu, X., Shore, L., Lampert, J., and Farrauto, R. J., 2004, “Low Temperature H2S Removal From Steam Containing Gas Mixtures With ZnO for Fuel Cell Application. 2. Wash-Coated Monolith,” Energy Fuels, 18, pp. 584–589.
NovochimskiiII., Song, C. H., Ma, X., Liu, X., Shore, L., Lampert, J., and Farrauto, R. J., 2004, “Low Temperature H2S Removal From Steam Containing Gas Mixtures With ZnO for Fuel Cell Application. 1. ZnO Particles and Extrudates,” Energy Fuels, 18, pp. 576–583.
Arthour, L. K., and Richard, B., 1997, Gas Purification, Nielsen edition, Gulf Publishing Company, Houston, TX.
Habibi, R., Towfighi Daryan, J., and Rashidi, A. M., 2009, “Shape and Size-Controlled Fabrication of ZnO Nanostructures Using Noveltemplates,” J. Exp. Nanosci., 4(1), pp. 35–45.
Farahbod, F., Bagheri, N., and Madadpour, F., 2013, “Effect of Solution Content ZnO Nanoparticles on Thermal Stability of Poly Vinyl Chloride,” ASME J. Nanotechnol. Eng. Med., 4, p. 021002.

## Figures

Fig. 1

(a) SEM photographs of zinc oxide nanoparticles on 5 μm scales and (b) SEM photographs of zinc oxide nanoparticles on 500 nm scales

Fig. 2

The experimental set up to remove hydrogen sulfide by nano zinc oxide

Fig. 3

The effect of pressure and temperature on H2S removal for 35 nm in diameter catalysts

Fig. 4

(a) Process performance versus the operating temperature. (b) The process performance and price of steam production versus the operating temperatures for 35 nm in diameter catalysts.

Fig. 5

(a) The process performance versus the operating pressure. (b) The process performance and reactor vessel cost versus the operating pressures for 35 nm in diameter catalysts.

Fig. 6

The process performance versus the feed superficial velocity

Fig. 7

The effect of zinc oxide bed height on the adsorption performance

Fig. 8

The effect of catalyst volume on the process performance

Fig. 9

The effect of initial concentration of H2S on the process performance

Fig. 10

The adsorption performance due to the various diameters of the zinc oxide

Fig. 11

The effect of catalyst surface is on the process performance

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