Sulfur Reduction in Naphtha produced from Al-Qayarah Refinery Units by the Simplest Possible and Economically Feasible Methods

Production of low sulfur content of untreated naphtha from Al -Qayarah Refinery units has been studied in this research by using oxidation, oxidation-adsorption, and adsorption methods. The influence of time, temperature, sorbent type on sulfur reduction was investigated. The results showed that oxidationadsorption was an efficient method for the desulfurization of naphtha where high removal efficiencies of about 93% were obtained. Also, it was concluded that by increasing temperature (up to 60C), and time (up to 5 hr) led to decreasing sulfur content from 1194ppm to about 76ppm. The results indicated that the best 2O3 2O3.

Introduction directly react with the metal. Active sulfur includes sulfur, hydrogen sulfide and mercaptan.
Non-active includes sulfide, carbon disulfide, thiophene (TH). The presence of sulfur in crude oil reduces its price in the world market, and sulfur compounds will appear in the petroleum fractions after distillation, which will cause corrosion in pipelines and equipment and after burning, it will pollute the environment (1, 2).
Sulfur containing compounds are undesirable in gasoline and diesel fuels because of the emission of sulfur dioxide (SOx) gases. In order to protect the human health and reduce the environmental hazards, environmental regulation that tend to limit the sulfur levels to very low ones have already been introduced in many countries during the last few decades. Also sulfur must be removed from the petroleum fractions as it causes poisoning of catalysts, corrosion of surfaces, and air pollution (3,4) Deep desulfurization of refinery streams becomes possible when the severity of the HDS process increased. Unfortunately, more severe conditions result not only in a higher level of desulfurization but also in undesired side reactions. When FCC gasoline is desulfurized at higher pressure, many olefins are saturated and the octane number decreases. Higher temperature processing leads to increased coke formation and subsequent catalyst deactivation (5,6).
Various methods were suggested for the desulfurization and deep desulfurization of the oil and refinery streams. These strategies include:-1. Hydrodesulfurization (HDS).

Precipitation dmkllesulfurization.
Among these methods, Oxidative desulfurization (ODS) has been demonstrated to be a promising method for ultra-deep desulfurization technology because of its mild operation conditions, i.e. no hydrogen required and low cost of operation. During the process, the organ sulfur compounds are oxidized to their corresponding sulfoxides or sulfones. The process is carried out in the presence of a catalyst and an oxidant agent, and the oxidized sulfur compounds are subsequently removed by extraction, adsorption, distillation, or decomposition (7,8).
ADS has become a promising approach in the ultra-deep desulfurization, A crucial issue in a successful adsorption process is to identify and develop a novel adsorbent, which has high adsorptive capacity, high selectivity and good regenerability(9). The objective of this work is to study the desulfurization of untreated naphtha from Al-Qayarah units. Two processes were adopted: Oxidation adsorption and adsorption using different adsorbents. Activated Carbon (AC), gamma alumina and nickel loaded on both materials.

Experimental Work
Materials Naphtha Naphtha was supplied from the North Refineries Company -Baiji Refinery (Qayarah Refinery). Some properties of naphtha are listed in Table (1). Total 100

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Gamma alumina -Al2O3) Formulated Spherical shape of gamma alumina was used as a carrier for the prepared catalyst; -Al2O3 are shown in Table (2).

Activated carbon (AC)
Granular activated carbon AC of industrial grade used in the present work. The AC dried in an oven at 120 o C for 3 hr to remove any moisture and stored in desiccators, physical properties of AC are shown in Table (3).

Chemicals
The chemical compounds which used in this research are listed in Table (4).

Oxidation Experiments
Untreated Naphtha (100 ml) was introduced into a three necked round bottom flask reactor equipped with condenser, stirred continuously at constant mixing speed (550 rpm) and heated to a temperature of 60 o C using magnetic stirrer heater. When the mixture reached the desired temperature, 4ml of hydrogen peroxide as oxidant and Acetic Acid (1ml) as homogenous catalyst were added to the reaction mixture. These amounts were fixed following the results of previous studies (10) . Then, the solution was allowed to settle in a 100 ml separating funnel, where clear distinguishable phases were obtained. After that sample was withdrawn from the organic phase and it sent for analysis or to the next adsorption step. The experimental setup is shown in figure (1).

Adsorbent Preparation
Preparation of Ni/ -Al2O3 Catalyst Nickel loaded on gamma alumina was prepared by the impregnation method shown in Figure   (2). Trials were made to obtain the desired loading percent of 7.5% (11) , 50g of -Al2O3 was soaked in 60 wt% Ni/ (NO3)2.6H2O aqueous solution in a 500 ml round flask The mixture was stirred for 48 hr. Next to the impregnation step was the filtration using Buchner funnel with a vacuum pump, followed by overnight drying in an oven at 110 °C and finally calcinations in a programmable electrical furnace at 550°C for 5 hrs.

Preparation of Ni/AC Catalyst
Nickel loaded on activated carbon (AC) was prepared. 46 g of AC was impregnated in the solution prepared by dissolving 18.8g of Ni/ (NO3)2.6H2O in 100ml distilled water. Other steps were the same as described in the previous section except that 350 o C was the calcination temperature. Experimental setup is shown in Figure (2).
Preparation of Co/AC Catalyst impregnation (very low loading was obtained may be because of bad storage of cobalt nitrate material) so, it was not used in the next steps. 44.88 g of cobalt nitrate hexahydrate was dissolved in distilled water (complete volume to 100 ml) with continuous stirring. After that 20 g of AC was placed in a flask and the prepared solution was added gradually to AC with shaking for (24) hours. This process was done at ambient temperature and then filtered by filter paper in Buchner funnel. The apparatus used for impregnation was shown in Figure (2).
The impregnated AC was dried at 120°C in an oven for 2 hr to eliminate water and crystallize the salt in the pore surface. The dried catalyst was calcined at (400)°C in a furnace for (4) hr to convert the salt to oxides over catalysts support and to acquire the catalyst physical and chemical properties.  Fig(1 A) but changing the condition as suitable for adsorption. The total sulfur content in samples before and after adsorption was measured by sulfur analyzer XRF.

Tests
All tests were made at petroleum research and development center (PRDC). Sulfur content in Naphtha was measured by sulfur analyzer (XRF) at refining and gas researches department which is shown in Figure (3), PONA analysis and metals content were measured by laboratory E48 analysis department. Surface area, pore volume, and bulk density of catalyst were measured by catalyst center section.

Results and Discussion
The experiments were carried out for desulfurization of naphtha in two methods testing, Oxidation and adsorption. Batch method was used for Oxidation and adsorption runs at different conditions.

Effect of time
The effect of increasing the oxidation time was found to enhance the desulfurization of naphtha as the sulfur content decreased from 1194 ppm of feed to 139, 128.5, and 125.2 after 1, 3, and 5 hr. respectively. This is shown in Table (5) and Figure (4). This is explained by E49 that, when increasing the reaction time there is more chance for sulfur compounds to react with H2O2 and to be oxidized to sulfones. This reaction like any other reactions needs enough time for completion and is promoted as time goes on. Maximum sulfur removal of 89.5% was obtained after 5 hours, however the removal of 89.2% after 3 hours can also be considered as a good result and the small difference may be due to the experimental error.

After oxidation
This step is a complementary to the oxidation step. Sulfone, as being produced from the oxidation reaction, will be removed by adsorption. In order to investigate the role of sorption, -Al2O3 2O3 as sorption materials. A comparison of sulfur removal from naphtha with these sorption materials are shown in Figure (5) and Table (6). Figure (5) shows the differences in sulfur content with sorption materials, keeping all other variables constant (feed volume=50ml, sorbent amount=1gm, Temp. =20 o C, time=3hr, stirring speed=750 rpm). The results indicate the 2O3 2O3. Activated carbon has high surface area and pore volume, therefore, it is found to have the highest removal efficiency among other adsorbents as this result agrees with many studies in literature (11).
A small improvement in sulfur removal was obtained from 92.79% to 93.6% in case of using -Al2O3. Many past studies had shown the effect of loading nickel (and cobalt) in improving the catalytic activity and selectivity of the adsorbent materials (10,12). Table (7) shows the effect of time on PONA content in the oxidation-adsorption process at the condition, feed volume=50ml, activated Carbon=1gm, Temp=20 o C, time=(3hr,and 5hr),stirring speed=750 rpm. This table shows that a decrease in the percentage of n-paraffin and increase in aromatics had occurred, which may be attributed to the adsorption of nparaffin into activated carbon. This is considered as a benefit for better quality of such fuel.        2. Oxidation process reduces sulfur content from 1194 ppm to 128.5 ppm corresponding to 89.2% removal using operating conditions, 60º C, 4 ml of H2O2 and 3hr, 3. Further removal of sulfur compounds is achieved by adsorption process using Ni/AC which ha -Al2O3 -Al2O3obtaining 93.2%.Sulfur in Al-Qayarah naphtha after this step is reduced to 76.4ppm.
4. Adsorption desulfurization (without oxidation) achieved 30% removal of sulfur compounds for the sulfur content reduced to 835ppm using a temperature of 60 o C in a batch mode operation. 5.
-Al2O3 must be reviewed to select the most economic adsorbent for some differences were noticed which may be ignored if it affects the economy of the process as the higher removal is obtained using the oxidation process.