Adsorbtion of Nitrogen Compounds from Hydrocarbon Liquids by Using Fixed Packed Bed Activated Carbon

The Extraction behavior of nitrogen compounds (quionoline, indole, and pyridine) from a liquid hydrocarbon (nonane, C9) was studied by using batch and fixed bed activated carbon experiments. The adsorption isotherm curves and the extraction percentage were determined in batch experiments in the conditions of initial concentration 20,40,60,80,and 100 ppm of either of quionoline, indole, and pyridine, fuel/(AC) ratio of 20 wt/wt, room temperature 30 ± 1°C , and stirring time of 2h. In the fixed bed experiments the breakthrough curves were determined as a function of the following variables:  Bed height of activated carbon 3, 5, and10 cm.  Initial concentration of nitrogen compounds 50, 75, and100 ppm.  Flow rate of the feed (15, 25, and35) ml/min.  Particle Diameter of activated carbon 1.5, 1.2, and1 mm. The adsorption capacity increases with increasing equilibrium concentration of the nitrogen compounds in the liquid phase, which is a very favorable isotherm irreversible adsorption. Also the activated carbon has very high affinity for the nitrogen compounds in the order indole < quinoline < pyridine and the conversion values were (50, 46, Journal of Petroleum Research & Studies E 114 and42) % respectively. In fixed bed experiments the time to breakthrough point decreases with:  Decreasing in bed height.  The increase in flow rate.  The increase in initial concentration of nitrogen compounds.  There is no effect of varying the particle diameter of the activated carbon because the experimental values of the activated carbon lies in the region of the large particle size and macrospore volume and there is no gradient in the particle size.

 The increase in initial concentration of nitrogen compounds.
 There is no effect of varying the particle diameter of the activated carbon because the experimental values of the activated carbon lies in the region of the large particle size and macrospore volume and there is no gradient in the particle size.

Introduction
Adsorption is a process of accumulation substances that are found in the solution, called solute, on a suitable interface [1].
Adsorption is the most commonly used process because it is fairly simple and convenient unit operation and that the cost for its application is relatively low compared to other treatment processes.
Adsorption can be equally effective in removing trace component from the liquid phase and may be used either to recover the component or simply to rid an industrial effluent of a noxious substance [2].
In recent years, the removal of nitrogen compounds (NCs) has received great attention [3]. Due to the relative difficulties and costs of the catalytic removal of NCs through hydrodenitrogenation (HDN),

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researchers worldwide are seeking alternative approaches to achieve deep denitrogenation of liquid hydrocarbon streams [3].
A great attention has been paid to use of adsorbents for selective removal of NCs in recent years, which can be beneficial not only for nitrogen reduction, but also for achieving the desired sulfur level in the subsequent HDS Process [4].
Batch and fixed bed absorber are the most efficient arrangement in the adsorption process [5]. It is necessary to know the adsorption capacity to design adsorption equipment. Adsorption capacity is usually expressed by an isotherm based on measured data. Also the breakthrough curves under specific operating condition must be predictable to design and operate a fixed bed adsorption process successfully [5][6][7]. In fixed bed granular adsorbents the most effectively used in columns where the liquid to be purified is passed through a stationary bed of the adsorbent, and to achieve a very large surface area for adsorption per unit volume. [8]. Activated carbons (AC) remain the most used adsorbents, mainly due to their superior physical and chemical properties, such as highly developed porous structure, large specific surface area, good mechanical properties, biocompatibility and chemical stability, as well as their low cost and great accessibility. They are produced from a wide variety of carbonaceous precursors such as lignite, coal, wood.etc) [9].
Typically breakthrough is said to have occurred when the effluent concentration reaches 5 percent of the influent value.

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Exhaustion of the adsorption bed is assumed to have occurred when the effluent concentration is equal to 95% of influent concentration [1].
Several studies were developed to have a good selectivity for the removal of nitrogen compounds; some of the scientist used promoted and unpromoted M O O 3 /alumina with coker kerosene and find the difference between them [10]. The others studied the adsorption of benzene and toluene vapours using fixed bed activated carbon [9].
Denitrogenation of the liquid hydrocarbons using metal ions and metal salts had reported good results [11].
Several types of activated carbon from different sources were tested to have the best denitrogenation of the liquid hydrocarbons using batch technique [3].

Aim of the Present Work
The objective of the present study is to:  Understand the adsorption mechanism of different types of nitrogen compounds on activated carbon through the evaluation of the adsorption capacity, and the adsorption isotherm curves.
 Study the effects of various important parameters such as the height of the bed, inlet nitrogen ions concentration, flow rate, and size of the adsorbent particles on (breakthrough curves,) of the adsorption denitrogenation process using fixed bed activated carbon techniques.

Materials Adsorbate:
A model diesel fuel (MDF), containing various molar concentrations of either Indole or Quinoline or pyridine, was prepared using nonane (C 9 ) as a solvent.

Adsorbent:
Granulated activated carbon (GAC) was used as an adsorbent in the present work. It was supplied from the Iraqi commercial markets.
The physical properties were measured by the oil research and development center and were coincided with that supplied by the manufacturer. These physical properties are listed in Table (1). In order to compare the adsorption selectivity, a model diesel fuel was prepared by adding 20, 40, 60, 80,100 ppm of either In dole or Quinoline or pyridine into liquid alkane (nonane (C 9 )).All compounds added in MDF were purchased from Aldrich chemical co.

Effect of Bed Height:
The bed depth is one of the major parameters in the design of fixed bed adsorption column. The effect of bed height on the breakthrough curve was studied for indole, quinoline, and pyridine respectively for adsorption onto activated carbon at constant flow rate, constant concentration, and constant particle size are presented in Figs. (4)(5)(6). These figures show that as the bed height increases the time of breakthrough point and the residence time will increase. It is clear from these figures that at smaller bed height the effluent metal ion concentration ratio increases more rapidly than at a higher bed height. Furthermore at smaller bed height the bed is saturated in less time compared with the higher bed height. Smaller bed height means lesser amount of activated carbon than for the higher one.

Effect of Initial Concentration:
The effect of initial nitrogen concentration on the breakthrough curves for nitrogen compounds was investigated for all the systems.
The change in initial nitrogen concentration will have a significant effect on the breakthrough curves. Figs. (7)(8)(9) show the experimental breakthrough curves at different initial nitrogen concentrations at constant flow rate, constant bed height, and constant particle size of activated carbon. the rate of adsorption is controlled by the concentration gradient, it takes a longer time to reach equilibrium for the case of low value of initial solute concentration.

Effect of Flow Rate:
The contact time is an important variable in the design of a fixed bed adsorption column; therefore the flow rate is one of the major design parameter [14]. The effect of varying flow rate on breakthrough curve was studied for all the systems. Figs. (10)(11)(12) show the experimental breakthrough curves for quinoline, indole, and pyridine respectively obtained for different flow rates and at constant bed height, constant concentration, and constant particle size of activated carbon, in term of C e /C i versus time:

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It is clear from the above figures that there is no effect of varying the particle size of the activated carbon because the experimental values of the activated carbon lies in the reign of the and macrospore volume and there is no gradient in the particle size.
Also the macrospore surface area is not a key factor for removal of the nitrogen compounds in the tested activated carbons. It is expected that the oxygen functionality of the activated carbons may play a more important role in determining the adsorption capacity for the nitrogen compounds since the adsorption capacity for nitrogen compounds increases with increase in the oxygen concentration of the activated carbons, and the type of the oxygen-functional groups may be crucial in determining their selectivity for various nitrogen compounds (Selective adsorption).

Conclusions:
In the present work the adsorption of nitrogen compounds named quinoline, indole, and pyridine onto activated carbon for single component system lead to the following conclusions: 1. The adsorption capacity increases with increasing equilibrium concentration of the nitrogen compounds in the liquid phase, which is limiting case of a very favorable isotherm irreversible adsorption.

2.
The activated carbon has very high affinity for the nitrogen compounds in the order indole < quinoline< pyridine. And the conversion values of quinoline, indole, pyridine were