298.15K에서의 Methanol(1)+Hexadecane(2)+Heterocyclic Nitrogen-Containing Compounds(3) 삼성분계의 액-액 평형

원동복  한규진  오종혁  박소진  김철중*

충남대학교 공과대학 화학공학과

*SK, R&D Center

Liquid-Liquid Equilibria for Methanol(1)+Hexadecane(2)+ Heterocyclic Nitrogen-Containing Compounds(3) at 298.15K

Dong-Bok Won·Kyu-Jin Han·Jong-Hyeog Oh·So-Jin Park

Cheol-Joong Kim*

Department of Chemical Engineering, Chungnam National Univ.

*SK, R&D Center

INTRODUCTION

The oil industry is under increasing pressure from the automobile company and the environmental protection agencies to improve the quality of diesel fuel with a view to reduce NOx content in the exhaust gas in the combustion of diesel fuel. Tighter sulfur specifications for diesel fuel have been therefore introduced in many countries in the last few years, and further tightening of sulfur specifications is planned over the next few years[1,2]. Until now, the hydrodesulfurization(HDS) process is most commonly used to reduce sulfur content in diesel fuel by converting sulfur compounds into hydrogen sulfide[3∼5], however this process has some problems to use directly for the ultra-low sulfur diesel (< 50 ppm sulfur) manufacture. Recently, there are some reports that HDS process will successfully applied for producing of ultra-low sulfur diesel, if heterocyclic nitrogen-containing compounds, which are inhibitor for desulfurization process, in the middle distillate feedstock removed effectively. Adsorption and solvent extraction could be one of the solutions to remove these nitrogen-containing compounds from middle distillates. Solvent extraction may have some advantages to the adsorption for removing nitrogen compounds, because it will be operated at the condition of atmospheric pressure and moderate temperature ranges. Besides it needs not additional catalyst.

In this study, tie-line end compositions for 6 different heterocyclic compounds containing systems, methanol(1)+hexadecane(2)+nitrogen-containing compounds(3) were experimentally determined at 298.15K. N-hexadecane(cetane) was taken as the model compound for diesel fuel and quinoline, pyridine, acridine, indole, pyrrole and aniline were taken as the basic and non-basic heterocylic nitrogen-containing compounds in the middle distillate feedstock.

EXPERIMENTAL

Materials Methanol was provided by Duksan chemical co, Korea and hexadecane and acridine were obtained from Aldrich. Quinoline was from Junsei and the others were from Kanto chemical Co. The contents of volatile impurities were checked by gas chromatographic analysis. Their impurities were less than 0.3 mass% except acridine( < 2.0% ) and indole( < 1.0% ). All chemicals were used without further purification and were stored in a desicator with a drying agent before the use.

Apparatus and procedure End point determinations of the tie lines were performed in ca. 50 ml equilibrium cell by using stirring method. This method was based upon the independent analysis of the separate phases that were regarded as being in equilibrium state. In general, shaking and stirring method [6,7] are most commonly used to measure liquid-liquid equilibria. In this study, self-designed simple stirring apparatus was used. The experimental set up is consisted of three parts, equilibrium cell, thermostat(Lauda MD 20 with DLK15 cooler) with precision temperature measuring system and Corning PC-320 magnetic stirrer. Ternary mixtures for each system with compositions within the heterogeneous gap were prepared and then introduced into the thermostatted equilibrium cell. The sample mixtures were prepared with adding nitrogen compound to mother solution of hexadecane and methanol, which mass ratio was 1:1. Under given temperature condition, first stirring (about 8h) and then by allowing to settle (about 24h) at constant temperature brought the mixture into equilibrium. The temperature during the experiment was monitored with IBM PC and Lauda A R46 temperature measuring system. Temperature fluctuation was less than 0.02 ℃. Equilibrated samples in an equilibrium cell were collected from the lower and upper layer by using sampling syringe equipped with a needle. Analysis has been carried out using gas chromatography(Hewlett Packard, 5890 ser. Ⅱ). HP-FFAP(Hewlett-Packard, polyethylene glycol-TPA modified, 50m x 0.2mm x 0.3m) capillary column and thermal conductivity detector were used for analysis.

RESULTS AND DISCUSSION

The experimental tie line data for the ternary systems, methanol(1)+hexadecane(2)+nitrogen-containing compounds(3) at 298.15K were measured and measured tie line data were correlated using NRTL[8] model.

The corresponding sets of binary parameters were determined by minimizing the differences between the experimental and calculated mole fractions for each of the components over all the measured tie lines of the ternary systems[9]. The simplex function in ASPEN software package was applied for the minimization procedure. The object function (F) used was

[eqn: F``=``min SUM from { { i}} SUM from { { j}} SUM from { { k}} LEFT ( X_ijk`````` - {{X}^c}_ijk RIGHT ) ^2]	(1)

Where X and Xc are the experimental and calculated mole fractions, respectively. The subscripts i, j and k denote component, phase and tie line respectively. The parameters calculated were shown in Table 1, together with the root mean square deviation (RMSD) values between experimental and calculated data, defined as:

[eqn: R MSD``=`` LEFT [ SUM from { { i}} SUM from { { j}} SUM from { { k}} LEFT ( X_ijk`````-``{X^c}_ijk RIGHT )^2 ``/ ``6N RIGHT ] ^1/2]	(2)

Where N is the number of tie lines

Treyball[10] classified the ternary liquid-liquid equilibria according to the number of heterogeneous phases, into three types; type 1 to type 3. If only one binary system is immiscible, which categorized as type 1 and if two binary systems are immiscible, which is categorized as type 2.

Methanol(1)+hexadecane(2)+quinoline(3) or +pyridine(3) systems have only one partially miscible system, which are belong to type 1 system and other systems have two binary immiscible systems belong to type 2.

Experimental and calculated tie lines and calculated binodal curves for ternary systems, containing quinoline, pyridine as type 1 are presented on triangular diagrams in Fig. 1 and 2. The solid line is calculated tie line. The experimental and calculated data are agreed well as shown in the figures. The slopes of the tie lines presented in figures show that quinoline, pyridine are more soluble in methanol phase than in hexadecane phase. And the consistency of experimental tie lines was carried out. Bachman-Brown and Othmer-Tobias equations were used to estimate consistency. The results are presented in Fig. 3 and 4.

CONCLUSIONS

All the measured ternary systems have one or two partially miscible phases, are considered to be category type 1 or 2. The methanol(1)+hexadecane(2)+qui

noline(3) or +pyridine(3) systems have only one partially miscible binary system, while the others have two partially miscible binary systems. The measured end compositions of tie lines were well correlated using the NRTL equation.

According to experimental selectivity, methanol could be used for the extraction of heterocyclic nitrogen-containing compounds from hexadecane, model compound of the middle distillates.

REFERENCE

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Table 1. NRTL parameters methanol(1)+hexadecane(2)+nitrogen-containing  compounds(3) at 298.15K

Nitrogeng- containing compounds	g11	g22	g33	g12	g13	g23	□12	□13	□23	RMSD
Quinoline	1.0	1.0	1.0	1.0691	1.0606	0.6642	-0.002	0.0017	0.2517	0.027
Pyridine	1.0	1.0	1.0	1.1844	3.1621	0.4256	-0.003	-0.8304	0.1780	0.006
Acridine	1.0	1.0	1.0	1.1459	0.2675	1.9080	-0.001	0.5203	-0.5311	0.015
Indole	1.0	1.0	1.0	1.0749	1.1734	1.0529	-0.001	-0.0500	0.0092	0.004
Pyrrole	1.0	1.0	1.0	1.0800	1.2655	1.1528	-0.001	-0.1459	0.0108	0.018
Aniline	1.0	1.0	1.0	1.1199	0.7838	1.7634	-0.001	-0.0403	-0.3920	0.009

Fig. 1. Liquid-Liquid Equilibria for methanol(1)+hexadecane(2)+quinoline(3) at 298.15K.	Fig. 2. Liquid-Liquid Equilibria for methanol(1)+hexadecane(2)+pyridine(3) at 298.15K.
Fig. 3. Bachman-Brown correlation for methanol(1)+hexadecane(2)+nitrogen-containing compounds(3) system at 298.15K.	Fig. 4. Othmer-Tobias correlation for methanol(1)+hexadecane(2)+nitrogen-containing compounds(3) system at 298.15K.