Scholarly article on topic 'Adsorptive desulfurization of kerosene and diesel oil by Zn impregnated montmorollonite clay'

Adsorptive desulfurization of kerosene and diesel oil by Zn impregnated montmorollonite clay Academic research paper on "Chemical sciences"

CC BY-NC-ND
0
0
Share paper
Academic journal
Arabian Journal of Chemistry
OECD Field of science
Keywords
{"Adsorptive desulfurization" / Montmorollonite / π-Complexation / Impregnation / "Clay adsorbents"}

Abstract of research paper on Chemical sciences, author of scientific article — Waqas Ahmad, Imtiaz Ahmad, Muhammad Ishaq, Khudija Ihsan

Abstract In the present research work, desulfurization of kerosene and diesel oil has been carried out by selective adsorption through metals impregnated montmorollonite clay (MMT). Different metals were impregnated on MMT by wet impregnation method which included Fe, Cr, Ni, Co, Mn, Pb, Zn and Ag. The adsorption study was carried out in batch operation initially for 1h time and at room temperature (25°C). The results show that high desulfurization was brought about by Zn-MMT. In the case of kerosene highest desulfurization of 76% and in the case of diesel maximum desulfurization of 77% was achieved with adsorption through Zn-MMT. Conditions were also optimized for the desulfurization process. Highest yield of desulfurization was obtained at 1-h stirring period, at room temperature (25°C) and using oil to adsorbent ratio of 20:1.5. Under optimized conditions the adsorbent was found to adsorb about 81% of DBT from the model oil containing 1000ppm DBT dissolved in cyclohexane. EDX, Surface characterization and SEM analysis of the adsorbents used in the study were conducted to evaluate their mineralogical nature and textural behavior. Results show that the surface area, pore size and pore volume of the MMT has been found to be increased many fold with Zn impregnation. Also the surface morphology of the MMT has also been improved with Zn impregnation.

Academic research paper on topic "Adsorptive desulfurization of kerosene and diesel oil by Zn impregnated montmorollonite clay"

Arabian Journal of Chemistry (2014) xxx, xxx-xxx

King Saud University Arabian Journal of Chemistry

www.ksu.edu.sa www.sciencedirect.com

ORIGINAL ARTICLE

Adsorptive desulfurization of kerosene and diesel oil by Zn impregnated montmorollonite clay

Waqas Ahmad a,% Imtiaz Ahmad b, Muhammad Ishaq b, Khudija Ihsan b

a Department of Chemistry,University of Malakand, Chakdarra, Lower Dir, KPK, Pakistan b Institute of Chemical Sciences, University of Peshawar, 25120 KPK, Pakistan

Received 15 July 2012; accepted 24 December 2013

KEYWORDS

Adsorptive desulfurization;

Montmorollonite;

p-Complexation;

Impregnation;

Clay adsorbents

Abstract In the present research work, desulfurization of kerosene and diesel oil has been carried out by selective adsorption through metals impregnated montmorollonite clay (MMT). Different metals were impregnated on MMT by wet impregnation method which included Fe, Cr, Ni, Co, Mn, Pb, Zn and Ag. The adsorption study was carried out in batch operation initially for 1 h time and at room temperature (25 °C). The results show that high desulfurization was brought about by Zn-MMT. In the case of kerosene highest desulfurization of 76% and in the case of diesel maximum desulfurization of 77% was achieved with adsorption through Zn-MMT. Conditions were also optimized for the desulfurization process. Highest yield of desulfurization was obtained at 1-h stirring period, at room temperature (25 °C) and using oil to adsorbent ratio of 20:1.5. Under optimized conditions the adsorbent was found to adsorb about 81% of DBT from the model oil containing 1000 ppm DBT dissolved in cyclohexane. EDX, Surface characterization and SEM analysis of the adsorbents used in the study were conducted to evaluate their mineralogical nature and textural behavior. Results show that the surface area, pore size and pore volume of the MMT has been found to be increased many fold with Zn impregnation. Also the surface morphology of the MMT has also been improved with Zn impregnation.

© 2014 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.

1. Introduction

Desulfurization of liquid fuels is a challenging task for the refiners, because of the undesirable effects of the sulfur

compounds in petroleum, which not only hampers the refining operations but also causes serious environmental degradation. The current worldwide stringent environmental regulations intensify more to produce liquid fuels with ultralow levels of sulfur (Gang et al., 2011). At the present, catalytic hydrodesul-furization (HDS) is the sole process commercially used for the desulfurization of petroleum products. HDS is however an expensive process in terms of utilizing expensive operating conditions i.e. high temperature, high pressure of hydrogen gas and expensive catalyst, as well as it is inefficient to eliminate the sterically hindered sulfur compounds and thereby cannot achieve ultralow levels of sulfur in the product fuels (Campos-Martin et al., 2010). An alternative to HDS process is

* Corresponding author. Tel.: (0945) 762355 6; fax: (0945) 761626. E-mail addresses: waqasaswati@gmail.com, waqasaswati@yahoo. com (W. Ahmad).

Peer review under responsibility of King Saud University.

^jjfl I

Elsevier I Production and hosting by Elsevier

1878-5352 © 2014 King Saud University. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.arabjc.2013.12.025

the desulfurization through adsorption, wherein sulfur compounds are selectively removed through adsorption on the solid adsorbent leaving behind sulfur free fuel. However the process is in the juvenile stage and in order to be recognized as a commercially acceptable process researchers are striving to increase its efficiency. Variety of adsorbents have been used for this purpose such as modified composite oxides (Seredych and Bandosz, 2010), activated carbon (Marin-Rosas et al., 2010), mesopourous and microporous zeolites such as SBA-15, MCM-41, Fujasite (McKinley and Angelici, 2003; Mingels et al., 1988; Salem, 1994) 5-A, 13-X, ZSM-5 and Y-Zeolite, etc. (Salem and Hamid, 1997; Weitkamp et al., 1991; Velu et al., 2003). We have also investigated the removal of sulfur compounds from crude petroleum, kerosene and diesel oil by reactive adsorption using metal oxide, it was found that PbO2 and MnO2 were most effective in the desulfurization of all the three fractions for 1 and 3 h reaction times in batch operation adsorption experiments (Shakirullah et al., 2009).

Recent research studies revealed that reactive adsorption is superior to ordinary physical adsorption, because it involves p complexation between aromatic sulfur compounds and the adsorbent, which is stronger than van der waals interaction. However p complexation can be broken easily by heating or decreasing pressure, thereby it is easy to regenerate the adsorbent (Hernandez and Ralph, 2003). Different metal cations supported on various supports have been used as reactive adsorbents for the desulfurization of liquid fuels. Yang et al. investigated the removal of thiophene from the simulated feedstock using Cu(I)-Y and Ag-Y zeolites (Hernandez and Ralph, 2003). McKinley et al. employed Ag-I/SBA-15 and Ag-I/SiO2 as adsorbents for the selective removal of DBT and 4,6-DMDBT from Model oil (McKinley and Angelici, 2003). Metals halides, CuCl2 and PdCl2 supported on activated carbon (Wang et al., 2006; Wang and Yang, 2007) and PdCl2 supported on SBA-15 and MCM-41 have also been found to be effective for desulfurization of jet fuel (Wang et al., 2008a,b). Desulfurization of jet fuel oil has also been studied with Cu2O supported on SBA-15 and MCM-41, which have shown that the adsorbent with MCM-41 was more effective than the one with SBA-15 support, the adsorbent could be regenerated by heating in air and reused (Wang et al., 2008a,b).

Mineral clays is a group of adsorbents which is enjoying rapid popularity in the petroleum industry for various separations and adsorption processes e.g. for the removal of objectionable color from lube oil, separation of different hydrocarbon groups and the removal of sulfur compounds from petroleum products (Mikhail 1970; Occelli et al., 1984). Mikhail et al. investigated the selective adsorption of dimethyl disulfide from cyclohaxane using acid activated kaolinite, acid activated bentonite, charcoal, petroleum coke and cement kiln dust (Occelli et al., 1984; Mikhail et al., 2002), they reported that adsorption efficiency of acid activated bentonite and charcoal was superior to all other adsorbents studied. Li Shi et al. investigated the removal of mercaptans from model oil through adsorptive desulfurization using bentonite modified with Cu + 2, Cu + 1, Fe + 3 and MnO^1, they concluded from their findings that high desulfurization capacity of bentonite modified with Fe + 3 and MnO4 could be attributed to the oxidation of marcaptans, and that of Cu impregnated bentonite was because of p complexation (Tang et al., 2011).

In the present study we have investigated the selective adsorption of sulfur compounds prevalent in commercial

kerosene and diesel over different metals loaded with acid modified montmorollonite clay. The effect of various variables such as time, temperature and concentration on the efficiency of adsorptive desulfurization has also been studied.

2. Experimental

Samples of Kerosene and Diesel oil were collected from Attock oil refinery, Rawalpindi. The material was brought in the metal cans. The samples were characterized by determining its various physico-chemical parameters including specific gravity, API gravity, kinematic viscosity, aniline point, flash point, fire point, ash contents, conradson carbon residue and total sulfur by employing the standard procedures of ASTM and IP. A sample of montmorollonite/bentonite clay was provided by the Material Research Laboratory (MRL), Department of Physics, University of Peshawar. All chemicals used were of Analytical grade.

2.1. Acid modification of clay

Before the clay was used for adsorption, it was modified with acids in order to remove the organic materials and increase adsorption capacity. The sample was cleaned, desilted and then modified with HCl solution. 50 g of the clay sample was taken in the round bottomed flask and 250 ml of the 0.1 N HCl solution was added to it and refluxed for 2 h. The clay slurry was then filtered through vacuum filtration and washed with excess of deionized water. The sample was then dried in the oven at 120 0C for 6 h. The dried clay was ground to fine powder and then screened through a 200 micron mesh sieve. Finally the clay sample was activated by heating at 600 0C in the Muffle furnace for 5 h and the stored in a vacuum desiccator.

2.2. Preparation of adsorbent

Adsorbent used for desulfurization was metal impregnated montmorollonite/bentonite clay, which was prepared by the wet impregnation method reported elsewhere (S. Mikhail et al., 2002). In a typical procedure stoichiometric amounts of 0.2 M solution of different metals precursors i.e. Ni(NO3)2, Ag(NO3)2, Fe(NO3)3, ZnCl2, MnCl2, Cr(NO3)2, Pb(NO3)2 and Co(NO3)2 was mixed with 3 g of modified clay. The slurry was stirred via magnetic stirrers for 2 h at 60 0C and then dried in an oven at 90 0C for 24 h. The dried solid mass was ground to fine powder, which was screened via a 200 micron mesh sieve. The adsorbent was calcined at 750 0C for 4-5 h and then stored in a vacuum dissicator.

2.3. Desulfurization of kerosene and diesel oil

The kerosene and diesel oil (sulfur contents of 0.0542 and 1.041 wt.%, respectively) was provided by the Attock Oil Refinery for the adsorptive desulfurization study. The Adsorbents used were various metals impregnated on montmorollonite and charcoal. Adsorption was carried out in batch operation initially at room temperature and for one hour. Later on the process conditions were also optimized. In a typical procedure, 20 ml of the sample was taken in the Erlenmeyer flask and 1 g of clay or adsorbent was added to it. The mixture was stirred with the help of a magnetic stirrer for about one hour at room

temperature. After each time interval of 10 min the mixture was given a rest of 2 min, the mixture was then filtered through Wattman No. 42 filter paper. The filtrate was reserved for sulfur analysis and the charged clay was kept for further examination. The same procedure was carried out with other adsorbents for different time intervals i.e. 1, 3 and 6 h at different temperatures i.e. room temperature (25 °C), 60 and 100 °C, and also with different concentrations of adsorbent i.e. 0.5, 1 and 1.5 g .

2.4. Desulfurization of model oil

Desulfurization of model oil was carried out following the same procedure as mentioned in section 2.3. The model oil used consisted of dibenzothiophene (DBT) dissolved in cyclo-hexane (1000 ppm DBT solution). Oil to adsorbent ratio was 10:0.5, adsorption was investigated at room temperature for different time intervals i.e. 10, 15, 30, 45 and 60 min.

2.5. Sulfur analysis

Quantitative analysis of total Sulfur in the original sample and treated oil samples was carried out with software controlled CHNS analyzer (Leco SC-144DR carbon sulfur analyzer). The concentration of DBT in model oil was determined by UV-visible Spectrophotometer (Schimadzu, 2010, Japan) at a wave length of 320 nm.

2.6. Surface area, pore volume and pore diameter

The surface area, pore volume and pore diameter of the clay samples was determined with surface area analyzer (Quanta-chrome Nova station A), using BJH model and nitrogen gas as adsorbent.

2.7. Scanning electron microscopy (SEM)

The morphology of the clays used in the adsorption study was examined by scanning electron microscope Model No. JEOL-Jsm-5910; Japan. For this purpose, the powdered samples were mounted on the sample stubs and placed in the sample carrier of the machine. The samples were then automatically analyzed using computer software.

2.8. Energy dispersive X-rays (EDX) analysis

The mineralogical composition of the clays used in the adsorption study was examined by Energy Dispersive X-rays

Spectrometer (EDX Model Inea 200, UK Company Oxford).

3. Result and discussion

In the current study desulfurization of the kerosene and diesel was carried out using metals impregnated montmorollonite clay and activated charcoal. The effect of time, temperature and concentration of adsorbent on desulfurization was also studied. The results of desulfurization are discussed below.

3.1. Characterization of the petroleum fractions

Before processing for desulfurization samples of kerosene and diesel oil were characterized physico-chemically. Various physico-chemical properties like specific gravity, kinematic viscosity, relative density, API gravity, carbon residue, ash contents, flash point, and aniline point of the kerosene and diesel oil, were determined. The physico-chemical properties of the various fractions are summarized in the Table 1.

Data in the table show that, values of specific gravity for kerosene and diesel, is 0.7879 and 0.8729 respectively, while API gravity is 48.0913 and 30.7706, respectively. In the case of kerosene and diesel the specific gravity increases gradually as with an increase in their boiling points. On the other hand, their API gravity decreases gradually, because the structural complexity of the molecules increases with increase in the boiling points of the fractions. Kinematic viscosity is a function of the chemical nature of any fraction. In the case of kerosene the kinematic viscosity is 2.1808 cst, while in the case of diesel it is 3.5136 cst. The reason is that with the increase in the boiling point, the complexity of the molecular structures contained in that fraction also increases.

Aniline point, flash point and fire point have also showed an increase in the same manner. The values of aniline point, flash point and fire points for kerosene are, 58 °C, 42 °C and 45 °C, respectively, while for diesel these are 62 °C, 48 °C and 50 °C respectively. Thus in the case of diesel oil the given parameters increase due to complexity of prevailing hydrocarbon molecules. Conradson carbon residue is also related to the nature of the hydrocarbons. For kerosene and diesel, the value of Conradson carbon residue was 0.13% and 1.14%, respectively, i.e. the value gradually increases. The ash content in kerosene and diesel oil was found to be 0.002 and 0.003 wt% respectively. Sulfur contents also increase with the increase of the boiling range of the fractions, as sulfur compounds exist in different forms at different boiling ranges. In the case of

Table 1 Physicochemical characteristics of kerosene and diesel oil.

Characteristics Method used Kerosene Diesel

Specific gravity IP-160/87 0.7879 0.8720

API gravity - 48.091 30.077

Kinematic viscosity cSt @ 100 F ASTM-D 455-04 2.1808 3.5136

Aniline point (°C) ASTM-D 611-04 58 62

Flash point (°C) IP-34/87 42 48

Ash contents (wt%) ASTM-D 482-03 0.002 0.003

Conradson carbon residue (wt%) IP-13/92 0.13 0.14

Total sulfur (wt%) ASTM D 129-83 0.0542 1.041

Table 2 Surface area, Pore Volume and Pore diameter of the adsorbent clay.

Sample Surface area BET model (m2/g) BJH Model (m2/g) Pore volume (cc) Pore diameter (Ao)

Montmorollonite 89.87 155.65 0.46 125.56

Zn-Montmorollonite 124.29 420.85 1.35 128.40

kerosene sulfur content were 0.0542% while in diesel the sulfur content were up to 1.04% by wt.

3.2. Characterization of adsorbent

The adsorbents were characterized by determining its surface area, pore diameter and pore volume, SEM and EDX in order to know about the nature of the adsorbents. Discussion on these parameters is given as follows.

3.2.1. Surface area and pore dimensions

The results of surface area and pore dimensions are given in the Table 2. It is clear from the table that according to the BET and BJH models, the surface area of the original clay is 89.87 and 155.65 m2/g whereas that of Zn-impregnated montmorollonite is 124.29 and 420.85 m2/g, respectively. The result shows that the surface area of the clay has been increased due to Zn impregnation on the clay. Similarly the pore volume and pore diameter of the virgin clay is 0.46 cc/ g and 125.56 A, while that of Zn-impregnated montmorollo-nite is 1.35 cc/g and 128.40 A, which indicates that during impregnation treatment the pore dimensions of the clay were raised significantly.

3.2.2. Scanning electron microscopy

In order to examine the surface morphology of the clay adsorbents, scanning electron microscopic analysis of the samples was carried out, SEM images of the clay samples are displayed in Fig. 1. SEM micrographs of montmorollonite clay (Fig. 1a) clearly show the porous and layered but non-uniform textural surface of the clay. The particles size is somewhat non-uniform. Major fissures and channels are evident. The layered surface can be seen clearly. The SEM micrographs of Zn-impregnated montmorollonite clay (Fig. 1b) indicate that fissures and channels on the surface are present. Also the layered structure with larger pores can be seen. The surface is mainly comprised of irregularities and plateaus. The textural non-uniformity is evident in both magnifications. The particle size however seems of uniform size as compared to the original clay. It shows that Zn cations are uniformly dispersed on the entire surface of the clay, and hence successfully impregnated.

3.2.3. EDX analysis

The EDX analysis of the virgin and Zn-impregnated clays was carried out in order to know their mineralogical nature and chemical composition. The EDX profile (Fig. 2) of montmoroll-onite or bentonite having chemical formula of (Na, Ca)0.33

(a)1000 x magnification (b) 2000 x magnification

(a)1000 x magnification (b) 2000 x magnification

Figure 1 SEM images of Clay adsorbents, (a) virgin clay and (b) Zn-Montmorollonite.

(Al, Mg)2 Si4Oio (OH). n H2O, which belongs to subgroup Smectite shows that the percentage of Al and Si in the sample is 8.90% and 22.53%, respectively. Whereas the percentages of other metals like Fe, Ca, K, Mg and O is 3.19%, 4.05%, 2.74% and 54.11%, respectively. The major constituents of the clay are aluminum, silicon, magnesium, iron, oxygen and calcium, which correspond to its chemical formula.

The EDX analysis of the Zn-MMT shows that its mineral-ogical composition is almost same as that of virgin, except the %wt of Zn is 18.14%, which is close to the theoretical value of 20%.

3.3. Desulfurization through adsorption with clays

Fig. 2 display the results of total desulfurization carried out by adsorption in the case of kerosene oil and diesel oil through charcoal activated and metals impregnated with montmorollo-nite at 40 0C. The adsorption process was carried out for one hour. The desulfurization efficiency and effect of time were studied for each adsorbent.

3.3.1. Desulfurization of kerosene

The desulfurization efficiency of variously metals impregnated MMT in kerosene and diesel oil is displayed in the Fig. 2. In the case of kerosene oil, untreated MMT and charcoal shows desulfurization activity of about 16% and 21.98%, respectively. Out of metal impregnated clays, the highest desulfuriza-tion has been shown by Zn-MMT, i.e. 60%, followed by Mn-MMT i.e. 45.33%, Co-MMT i.e. 40%, and Ni-MMT i.e. 41%, while for the other adsorbents desulfurization efficiency is fairly low. The results show that desulfurization efficiency of the MMT clay has been increased with metals impregnation.

3.3.2. Desulfurization of diesel

In the case of diesel oil the desulfurization trend is similar to that of kerosene. Desulfurization of diesel with montmorollo-nite shows the value of 43.96% while that of charcoal is up to 27.80%. However the in case of metal impregnated clays desul-furization efficiency was enhanced. Among these, the highest desulfurization yield is obtained with Zn-MMT that is 62.48%, followed by Pb-MMT i.e. 55.7%, Ni-MMT i.e.

55.9%, whereas for the rest of adsorbent the desulfurization yield was not much appreciable. Desulfurization of model and real oil has been investigated by many researchers using various transition metals exchanged/supported adsorbents, out of which adsorbents containing Ag, Ni, Cu etc. have been used and found to be effective. In the present case, it is clear from the results that the desulfurization yield of Zn based adsorbent is superior to others, which exhibit high desulfuriza-tion efficiency in the case of both kerosene and diesel oil.

3.4. Optimization of conditions

Desulfurization of kerosene and diesel with Zn-MMT as adsorbent was carried out at different conditions of time, temperature and concentrations in order to find the optimum set of conditions. The effects of different parameters studied are given below.

3.4.1. Effect of temperature

Adsorptive desulfurization of kerosene and diesel was carried out with Zn-MMT at different temperatures i.e. room temperature (25 0C), 40, 60 and 100 0C. Results for % desulfurization of kerosene and diesel are given in the Fig. 3. The data show that in the case of kerosene the % desulfurization at room temperature was 62%, whereas at 40, 60 and 100 0C it was, 61%, 55% and 45% respectively. Similarly for diesel at room temperature the% desulfurization was 63%, and at a temperature of 40, 60 and 100 0C it was 61%, 58% and 46%, respectively. Hence the highest desulfurization is obtained at room temperature in the case of both kerosene and diesel. From the results it is concluded that with an increase in temperature the rate of desorption increases, that is why the decline in desulfurization has been observed, hence the optimum temperature for adsorptive desulfurization is room temperature i.e. 25 0C. Similar results are also reported by Majid et al., they used Ni-loaded Y type zeolite for adsorptive desulfurization of gasoline, they found that with the increase in temperature from 25 to 60 0C, the adsorption capacity of the adsorbent decreased from 0.55 to 0.65 mg(S)/g (Majid and Seyedeyn-Azad, 2010). It may be attributed to the exothermic nature of the process, which is hampered with the rise in temperature.

3O 2O lO O

Kerosene Diesel

M лг ci

¡Ü I

s 3 Í

■fí i

* s й

////// / , <f ^ </ О* сГ 4й У

Adsorbents

Figure 2 % Desulfurization with different absorbents in kerosene and diesel oil.

TG б0 SG 40 30

Kerosene

Diesel

4G б0

Temperature oC

Figure 3 Effect of temperature on desulfurization of kerosene and diesel oil.

3.4.2. Effect of time

Fig. 4 shows the effect of time on desulfurization of kerosene and diesel on Zn-MMT adsorbent. In the case of both fractions i.e. kerosene and Diesel, the desulfurization increases with increase in reaction time. In kerosene, % desulfurization increases from 62% to 69%, while in diesel the desulfurization increases from 64% to 71% with an increase in reaction time from 1 to 6 h. Hence the highest desulfurization is attained at 6 h. It may be concluded that desulfurization occurs through multilayer adsorption, hence as time passes multilayer adsorption progresses and completes at 6 h time. Effect of time was also studied by Majid et al. using Ni/y zeolite, which showed that desulfurization increases with time and completes at 4 h (Majid and Seyedeyn-Azad, 2010), however Tang et al. reported that using Ga-Y zeolite, desulfurization of model gasoline completes at 6 h (Tang et al., 2008).

3.4.3. Effect of adsorbent quantity

The desulfurization of kerosene and diesel was also carried out with different quantities of Zn-MMT i.e. 0.25, 0.5, 1 and 1.5. Effect of concentration of adsorbent on desulfurization is shown by Fig. 5. Increasing the oil to adsorbent ratio from 20:0.25 to 20:0.5, 20:1 and 20:1.5 the % desulfurization in the case of kerosene increased from 57% to 71%, 73% and

76%, respectively, likewise in the case of diesel it was raised from 57% to 73%, 75% and 77%, respectively. The increase in the desulfurization yield with an increase in adsorbent concentration may be attributed to the availability of a larger surface area and hence larger p complexation sites for the sulfur compounds. Using high concentration of adsorbents provides more absorption sites for sulfur compounds, and hence the desulfurization yield is high.

3.5. Desulfurization of model oil

Desulfurization of model oil containing DBT as model sulfur compounds dissolved in cyclohexane (1000 ppm) was investigated through adsorption over Zn-MMT under room temperature at different adsorption times. Results indicated in Fig. 6, show that at different adsorption times studied i.e. 15, 30, 45, and 60 min, the % removal of DBT was 75%, 78%, 79% and 81%, respectively. It can be seen from the data that the rate of DBT adsorption increases with an increase in adsorption time, however beyond 30 min adsorption there is very little increase in the adsorption. This indicates that unlike kerosene and diesel oil, in the case of model oil, after 30 min the adsorbents becomes saturated with the DBT. In the case of kerosene and

б0 SG 4G 3G 2G

0.25 0.5 1 1.5

Concentration of Adorbents (g)

Figure 5 Effect of quantity of adsorbent on desulfurization of kerosene and diesel oil.

izati бб ri

á б4

б2 б0 S8 S6

Kerosene

Diesel

Time (h)

l o TG

В 6S e

# 60 SS

Time (min)

Figure 4 Effect of time on desulfurization of kerosene and diesel oil.

Figure 6 % Removal of DBT from model oil through adsorption using Zn-MMT.

diesel oil the sulfur removal is favored by increasing the adsorption time. It may be suggested that as in the case of model oil the concentration of DBT is higher than kerosene and diesel oil therefore adsorbent saturation occurs at less adsorption time.

4. Conclusion

The following conclusions can be drawn from the current study,

• Montmorollonite clay, which is locally available, can be efficiently used for adsorptive desulfurization.

• Metals impregnation on MMT clay increases its adsorption characteristics.

• The surface area, pore size and pore volume of the MMT has been found to be increased many fold with Zn impregnation.

• The surface morphology of the MMT has also been improved with Zn impregnation.

• Metal impregnated MMT has more high desulfurization efficiency than the original MMT.

• Zn impregnated MMT shows better adsorption efficiency for sulfur compounds.

• The selective adsorption of the sulfur compounds using Zn-MMT is found to be higher at 1 h adsorption time, at 25 0C (room temperature) and 1.5 g concentration of adsorbent.

Acknowledgements

The authors acknowledge the cooperation of the Material Research Laboratories (MRL), Department of Physics, University of Peshawar for providing the Clay samples, the Centralized Resources Laboratories (CRL) University of Peshawar for facilitating the analytical work and the Attock Oil Refinery, Rawalpindi Pakistan, for providing the oil samples for this study. The authors also acknowledge the contribution of late Professor Dr. M. Shakirullah, ICS University of Peshawar.

References

Gang, W., Yaoshun, W., Jingxin, Fan., Chunming, Xu., Jinsen, Gao., 2011. Reactive characteristics and adsorption heat of Ni/ZnO, SiO2, Al2O3 adsorbent by reactive adsorption desulfurization. Ind. Eng. Chem. Res. 50, 12449-12459. Campos-Martin, J.M., Capel-Sanchez, M.C., Perez-Presas, P., Fierro, J.L.G., 2010. Oxidative processes of desulfurization of liquid fuels. J. Chem. Technol. Biotechnol. 85, 879-890. Seredych, M., Bandosz, T.J., 2010. Adsorption of dibenzothiophenes on nanoporous carbons: identification of specific adsorption sites governing capacity and selectivity. Energy Fuels 24, 3352-3360.

Marin-Rosas, C., Ramirez-Verduzco, L.F., Murrieta-Guevara, F.R., Hernandez-Tapia, G., Rodriguez-Otal, L.M., 2010. Desulfurization of low sulfur diesel by adsorption using activated carbon: adsorption isotherms. Ind. Eng. Chem. Res. 49, 4372-4376.

McKinley, S.G., Angelici, R.J., 2003. Deep desulfurization by selective adsorption of dibenzothiophenes on Ag+/SBA-15 and Ag+/SiO2. Chem. Commun., 2620-2621.

Mingels, W., Enody, E.M., Vansant, E.F., 1988. Eur. Pat. Appl., 275855.

Salem, A.B.S.H., 1994. Naphtha desulfurization by adsorption. Ind. Eng. Chem. Res. 33, 336-340.

Salem, A.B.S.H., Hamid, H.S., 1997. Removal of sulfur compounds from naphtha solutions using solid adsorbents. Chem. Eng. Technol. 20, 342-347.

Weitkamp, J., Schwark, M., Ernst, S., 1991. Removal of thiophene impurities from benzene by selective adsorption in zeolite ZSM-5. J. Chem. Soc., Chem. Commun., 1133-1134.

Velu, S., Ma, X., Song, C., 2003. Selective adsorption for removing sulfur from jet fuel over zeolite-based adsorbents. Ind. Eng. Chem. Res. 42, 5293-5304.

Shakirullah, M., Ahmad, I., Ishaq, M., Ahmad, W., 2009. Study on the role of metal oxides in desulphurization of some petroleum fractions. J. Chin. Chem. Soc. 56, 107-114.

Hernandez, M., Ralph, T.Y., 2003. Desulfurization of liquid fuels by adsorption via p complexation with Cu(I)—Y and Ag—Y Zeolites. Ind. Eng. Chem. Res. 42, 123.

Wang, Y., Yang, F.H., Yang, R.T., Heinzel, J.M., Nickens, A.D., 2006. Desulfurization of high-sulfur jet fuel by p-complexation with copper and palladium halide sorbents. Ind. Eng. Chem. Res. 45, 7649-7655.

Wang, Y., Yang, R.T., 2007. Desulfurization of liquid fuels by adsorption on carbon-based sorbents and ultrasound-assisted sorbent regeneration. Langmuir 23, 3825-3831.

Wang, Y., Yang, R.T., Heinzel, J.M., 2008a. Desulfurization of jet fuel by-complexation adsorption with metal halides supported on MCM-41 and SBA-15 mesoporous materials. Chem. Eng. Sci. 63, 356-365.

Wang, Y., Yang, R.T., Heinzel, J.M., 2008b. Desulfurization of jet fuel JP-5 light fraction by MCM-41 and SBA-15 supported cuprous oxide for fuel cell applications. Ind. Eng. Chem. Res. 48, 142-147.

Mikhail, S., 1970. Evaluation of Egyptian clays in petroleum refining by adsorption. Cairo University, Cairo.

Occelli, M.L., Landau, S.D., Pinnavaia, T.J., 1984. Cracking selectivity of a delaminated clay catalyst. J. Catal. 90, 256-260.

Mikhail, S., Zaki, T., Khalil, L., 2002. Desulphurization by economically adsorption technique. Appl. Catal. A General 227, 265-278.

Tang, X.-L., Meng, X., Shi, L., 2011. Desulfurization of model gasoline on modified bentonite. Ind. Eng. Chem. Res. 50, 75277533.

Majid, D., Seyedeyn-Azad, F., 2010. Desulfurization of gasoline over nanoporous nickel-loaded Y-type zeolite at ambient conditions. Ind. Eng. Chem. Res. 49, 11254-11259.

Tang, K., Song, L.j., Duan, L.h., Li, X.Q., Gui, J.Z., Sun, Z.l., 2008. Deep desulfurization by selective adsorption on a heteroatoms zeolite prepared by secondary synthesis. Fuel Proc. Technol. 89, 1-6.