Preparation of Some Mercurated Dowex Resins and Study of Their Industrial Applications For Desulfurization

During this research some chemical modifications especially )mercuration) have been done on Dowex resin. It is known that the sulfur dioxide gases are the main source of acid rain and air pollution, result from the conversion of fuels containing sulfur compounds in combustion engines. As a result of environmental impact, strict requirements on low sulfur content in fuels are becoming prominent throughout the world. This study was carried out to remove dibenzothiophene from model light oil (benzene containing DBT, 3080 ppm. sulfur content) by using the mercurated Dowex.The analysis of the resulting treated DBT solution to know the sulfur concentration was obtained by using atomic absorption The mercurated polymers were identified spectroscopicaly using infrared spectroscopy.


Introduction
Crude oil is the largest and most widely used as source of energy in the world. However, such crudes contain sulfur, typically in the form of organic sulfur compounds. The sulfur content and the API gravity are two properties which have a great influence on the value of the crude oil. The sulfur content has been determine as a percentage of sulfur by weight and varies from less than 0.1% to more than 5% depending on the type and source of crude oils [1].
The most abundant heterocyclic sulphur compounds identified in petroleum includes sulfides, thiophenes, benzothiophenes and naphthobenzothiophenes.
During the partial or complete combustion of a sulfur-containing residual oil, the sulfur gets converted to SO2 and SO3 (typically referred to as SOx). During the combustion or pyrolysis process, the sulfur emissions from a typical high sulfur residual oil can be extremely high; additional processes such as flue gas desulfurization are needed to clean up these emissions and bring the SOx content of effluent gases to acceptable levels. This requires an additional investment of capital, as well as additional operating expense, to continue operating industrial units that use the sulfur-containing residual oil [2]. One of the easily and fast method to remove sulfur from diesel oil is the adsorption desulfurization process [3].It is one of the methods which can be used to achieve ultra-low sulfur content in diesel fuel. It is considered the most effective method for the removal of the trace amounts of residual sulfur in fuels after hydro desulfurization treatment [4]. Chemical modification of polymers is one of the methods used to synthesize new polymeric compounds. It is the most active fields of research in polymer sciences for the past 30 years and enables us to introduce functional or reactive groups into polymers, to alter polymer surfaces, to provide side chain substituents. Important products of polymer modification include polymeric reagents, functionalised resins, catalyst and media for trapping reaction intermediates organometallic polymers acid carrier for active molecules [5]. The mercuration of polymers is a suitable method for the preparation of selective adsorbents [6].More particularly, the invention relates to a new class of homo and copolymers which contain mercuric ions aromatically bound therein. The products produced in accordance with this invention find utility as carries in biopolymer applications, i.e. as carrier gels for removing sulfur-containing groups from mixtures, in tracing studies, as carrier for biologically active substances and the like [7].

Materials and instruments
All the chemicals used have been supplied by Fluka and Aldrich.
Infrared spectra have been recorded by shemadzue FT-IR-8400 s Fourier transform Infrared spectrophotometer in the range between (4000-250 cm -1 ).
Varian-AA-240FS Fast Sequential Atomic Absorption Spectroscopy, Australian, used for measuring the concentration of mercury and sulfur ions in solutions in N.G.C / Kirkuk-Iraq.
All the samples have been dried under reduced pressure at 50-65 C o .

Mercuration of Dowex(-SO 3 Na) Using Mercury acetate in Dioxan (C-1)
(2.0620 g) of Dowex (-SO 3 Na) were added to (10 ml) of Dioxan in a (250 ml) flask with stirring for (30 min) at room temperature, then (3.1868 g) of mercury acetate and (2 ml) acetic acid were added to the reaction mixture. The content was refluxed for (24 hrs) and the resulting mixture poured into a (200 ml) of water. The polymer were collected and washed with excess of water until the removal of unreacted mercury and then with methanol. The weight of product after drying was (2.4076 g).

Acidification of Dowex(-SO 3 Na) (C-2)
(10 ml) of (18%) HCl was added to (10 g.) of Dowex (-SO 3 Na) in round bottomed flask. The reaction mixture was refluxed in a water bath at (50 C o ) with constant stirring for (2 hrs). The resultant mixture was filtered and washed well with distilled water several times until the removal of acidity. The weight of product after drying was (8.4925 g).

Desulfurization (Using Different Conditions)
Time:-(10 ml) Solution of (Dibenzothiophene in Benzene) (3083 ppm sulfur) was mixed with This step is to choose the proper amount of absorbent that gives highest sulfur removal.

.Results and Discussion
Scheme (1): Expected chemical structure of modified polymers prepared from Dowex.

Mercuration of Dowex(-SO 3 Na) Using Mercuric acetate (C-1)
Mercuration of Dowex(-SO 3 Na) by using mercuric acetate was achieved when Dowex was mixed with dioxane and added to mercuric acetate with reflux for (24 hrs.), as shown in scheme (1) .
The IR spectrum of free Dowex (-SO 3 Na) (sodium-poly-p-vinylbenzylsulfonate) and mercurated Dowex can be compared with each other to check spectral changes.
The IR-spectrum of nitrated Dowex showed the characteristic absorption bands of nitro groups at 1531 cm -1 for (N=O) asymmetric stretching vibration and at 1361 cm -1 for (N=O) symmetric stretching vibration in addition to the (-SO 3 H) bands.

Mercuration of Nitrated Dowex Using Mercury oxide (C-5)
Nitrated Dowex is also mercurated by treating the nitrated Dowex with mercuric ions to produce a mercurated resin, as shown in scheme (1) .
The IR spectrum of nitrated Dowex and mercurated resin can be compared with each other to check spectral change. An important spectral change observed in the spectra of nitrated Dowex (-SO 3 H) and the mercurated resin investigated here is the shifting of a band observed at 1531 cm -1 in nitrated Dowex to higher wave number at 1537 cm -1 . Also it was observed an increase in the weight of product, which indicates the entry of mercury in the copolymer structure. Percent mercury was equal to (5.33%), as it shown in Table (3-1).

Desulfurization
All mercurated Dowex resins were used to desulfurize the solution of (dibenzothiophene in benzene 3083 ppm sulfur).

Time:-
The desulfurization time was (4,8,12,16,20,24 hrs),almost all polymers which were used for desulfurization gave the proper contact time that gives highest sulfur removal at room temperature was (24 hrs), as shown in Table (3-2), so the best time that uses for desulfurization was (24 hrs). It was found that the stirring for (24 hrs) is enough to get reasonable sulfur removal.
Temperature:-By raising the temperature of desulfurization from room temperature to (35 C o ) and (50 C o ). It was observed a better desulfurization, as shown in Table (3-3).