Synthesis and Characterization of Co- -Alumina Catalyst from local Kaolin clay for Hydrodesulfurization of Iraqi Naphtha

This work deals with the hydrodesulfurization of three types of naphtha feedstocks; mixed naphtha (WN), heavy naphtha (HN) & light naphtha (LN) with a sulfur content of 1642.1, 1334.9 & 709 ppm respectively, obtained from Missan refinery using prepared Co-Mo/ -Al2O3 catalyst. The Iraqi white kaolin was used as a starting material for the preparation of -Al2O3 support, transferring kaolin to meta-kaolin was studied through calcination at different temperatures and durations, kaolin structure was investigated using X-Ray diffraction techniques. -Al2O3 with a surface area of 129.91 m /gm, pore volume 0.9002 cm/g was synthesized by extraction of Iraqi kaolin with H2SO4 at different acid to clay weight ratios, acid concentrations & leaching time. Ethanol was used as precipitating agent; the resultant gel was dried and calcined at 70C, 10 hrs & 900 C, 2 hrs respectively. The effects of different parameters on the average crystallinity and extraction % of synthesized -Al2O3 were studied like; acid: clay ratio, sulfuric acid concentration, leaching time, leaching temperature & kaolin conversion to metakaolin. Al2O3 & Co-Mo catalyst were achieved by X-ray diffraction, FTIR-spectra, texture properties & BET surface area, BJH N2 adsorption porosity, AFM, SEM, crush strength & XRF tests.


Introduction
In refinery, high sulfur levels lead to deactivate the catalysts that promote desired chemical reactions in certain refining processes and releases emissions of sulfur compounds to air [1,2].
The main objective of environmental legislation is to reduce sulfur dioxide, nitrogen oxides, aromatics, and vapor and soot particulate emissions from both refineries and its products after combustion. [3].
Hydrotreating catalysts are used extensively for enhancing the conversion rate of heavy feedstock and for improving the purity of final products. It also plays an important key in pretreating streams for some chemical processes such as catalytic reforming, fluid catalytic cracking (FCC) and hydrocracking. Sulfided Co and Ni promoted Mo on gamma-alumina catalysts are active for hydrodesulphurization [4,5].
Conventional systems include CoMo and NiMo mixed sulfide catalysts supported on gamma alumina, CoMo specifically being used when a large Hydrodesulphurization (HDS) duty is demanded, NiMo for hydrodenitrogenation (HDN) operations [6,7] -Al 2 O 3 is widely used as a support in heterogeneous catalysis because it is thermally stable and allows the dispersion of active phases due to its high surface area [8].
Alumina is used as a catalyst and catalyst support material in many industries and different processes such as hydrotreating processes, the low cost of kaolin has been identified as a potential raw material for the production of zeolite and in addition for the production of alumina ( -Al 2 O 3 ) [9,10].
Gamma alumina can be formed from several methods such as sol-gel, hydrothermal processing, and controlled precipitation. While the others are produced from inorganic aluminum salts, alkoxides, metallic powders, waste alumina and kaolin [11].
The traditional synthesis of promoted MoS2/Al 2 O 3 catalyst is by simultaneous or successive impregnation of molybdenum and promoter salts onto alumina, followed by calcination (producing oxides), and sulfidation prior to use [12,13] The active component is normally molybdenum sulfide, although tungsten containing catalysts are also used (though seldom, and that generally for special applications such as lube oil processing). For molybdenum catalysts both cobalt (CoMo) and nickel (NiMo) are used as promoters. The promoter has the effect of substantially increasing the activity of the active metal sulfide.
Preparation of molybdenum -based supported catalyst with higher concentration of active metals on the exterior surface and high dispersion still represents a synthetic challenge in advanced catalysis [14]. Many researchers studied working with HDS catalyst of relatively high metals oxides loading and gain the sulfide active phase at low pre-sulfiding temperature to avoid sintering of the catalyst associated at elevated temperatures [15].
The performance, in terms of desulfurization level, activity, and selectivity, depends on the properties of the specific catalyst used concentration of the active species, support properties, synthesis route, the reaction conditions sulfidizing protocol, temperature, and partial pressure of hydrogen and H 2 S, the nature and concentration of the sulfur compounds present in the feed stream, and the reactor and process design [  6. The mixture of kaolin and acid was cooled to room temperature and filtered to remove l each residue, which is containing silica.
7. The filtered clear leach liquor then was added dropwise at a rate of 6.0 ml/min into 600-750 ml of ethanol with continuous stirring by a magnetic stirrer, a white precipitate of aluminum sulfate was directly seen, and the precipitate is gradually changed to a thick gel, which typically is the aluminum sulfate.
8. The precipitate was filtered using a Buchner set under vacuum, then it was washed with sufficient amount of ethanol and distilled water.
9. The resulted gel was air dried overnight then oven dried at 70°C for 10 hrs and finally c alcined at 900°C for 2 hrs in an electric furnace to get gamma alumina powder.

Preparation of Co--Al 2 O 3 Catalyst
The Co--Al 2 O 3 was prepared using dry impregnation technique for loading the cobalt oxide to ensure obtaining the desired loading percentage while incipient wetness impregnation technique was used for loading molybdenum oxide, the active metals loading was carried out as in the following steps: 1.
-Al 2 O 3 support was pre-heated at temperature of 250 0 C for 30 min to 1 hr. using an electrical oven to ensure eliminating moisture and undesired impurities from the support internal pores, and preconditioning for impregnation stage by using the impregnation apparatus which is consisting of a two-neck round flask 500 ml connected to a separating funnel on the top to control the flow of the active metal solution on the catalyst support, the round flask is connected to a vacuum pump on the side to ensure an efficient impregnation. 4. The impregnated support was then dried at 120 0 C for 1 hr to prepare it for the next impregnation, then it was moved to the round flask and subjected to the vacuum and reimpregnated again which is known as sequential impregnation with additional amount of cobalt nitrate hexa-hydrate 3.6 gm as in the previous.

Purity of produced -Al 2 O 3
The main composition of the prepared alumina is given in Table (

Texture Properties: Surface Area and porosity measurements
Surface area and pore volume play a very important role for the activity of the catalyst support, because high surface area leads to high active sites causes increasing in activity. which is close to the Nano scale, where particles of sizes in the range of 1 to 100 nm are classified as Nano materials [21], this could be attributed to the use of ethanol alcohol as surfactant and precipitating agent. The bar charts of particle size distribution of prepared sample are shown in Figure (10), while the surface shape can be seen in Figure (11) which is for the morphology of prepared gamma alumina that was studied to show the images of AFM on two-dimensional surface profile at calcination temperature 900 o C, which represents the twodimension surface morphology of the prepared sample with irregular hexagonal structure.

Scanning Electron Microscopy (SEM)
The morphology of the synthesized gamma-alumina is tested by scanning electron microscopy -alumina of irregular hexagonal shape particles associated with gamma-alumina at 900 O C calcination temperature.
SEM images of the prepared -alumina sample of best conditions are shown in Fig. 12 (a-c) at different magnification degrees revealing an evidence of transfer from the amorphous phase to -alumina showed relatively high crystallinity, which is also consistent with XRD profile. SEM images showed that -alumina is consisting of clusters of irregular shape.

Fourier Transform Infrared Spectroscopy (FTIR)
FTIR spectra tests were done by FTIR-600 Biotech Spectrometer for some of the prepared gamma alumina samples and prepared CoMo\ -alumina catalyst with wave range between (400-4000) cm -1 , the sample pressed to disk shape after added 1% -alumina to 99% KBr, FTIR spectum are shown in Figure (13) which shows large bands in the region between 400--1000 cm-1 represent the stretching vibration of Al-O-Al bands. The broad bands between 500-750 cm-1 refer to gamma alumina as mentioned by [22,23]. mesoporous alumina synthesized can be distinguished by two bands in the region of 4000 cm -1 1500 cm -1 .
The broad band around 3450 3500 cm -1 may be attributed to the adsorbed water molecules, the broad band shown for the adsorbed water is a characteristic of porous materials which are usually found in zeolites and mesoporous materials [24].    LHSV of the through a catalytic packed bed reactor is the reciprocal of time therefore it reflects the residence time of the reaction [25]. So, as the LHSV increases the residence time of the reactants in the reactor is decreased or in other words the feed flow rate is high so that there is not enough time for the reaction. By this, the value of LHSV of 4 hr-1 causes lower sulfur removal efficiency than that at LHSV of 2 hr-1 for all types of feed and at different temperatures.
Also, it can be seen that the value of sulfur removal at LHSV of 2 hr-1 is higher than that at LHSV of 1 hr-1 which can be explained by that the feed flow rate at 1 hr-1 is could not cover all the catalyst area or channeling may be occurred due to a bad distribution of the feed at this low flow rate at LHSV. The decrease in LHSV means that lesser quantity of feed contacting the same quantity of catalyst per time, while increasing in LHSV provides for a greater quantity of naphtha through the reaction per unit of time, these observations agree well with the results of Steiner and Blekkan [26].

Conclusions
Nominate the following issues were concluded that Iraqi raw kaolin is a promising source for