View of LIQUID-LIQUID EQUILIBRIUM STUDIES ON MODEL HYDROCARBONS REPRESENTING HEART CUT FOR CYCLOHEXANE USING INDUSTRIAL SOLVENTS

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ACCENT JOURNAL OF ECONOMICS ECOLOGY & ENGINEERING Available Online: www.ajeee.co.in Vol.01, Issue 01, May 2016, ISSN -2456-1037 (INTERNATIONAL JOURNAL)

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LIQUID-LIQUID EQUILIBRIUM STUDIES ON MODEL HYDROCARBONS REPRESENTING HEART CUT FOR CYCLOHEXANE USING INDUSTRIAL SOLVENTS

Dr. R.K. Joshi¹ and Dr. M.S. Panwar²

1Department of chemistry, Govt P.G.College, Dakpathar, (Dehradun)

2Department of Chemistry, Govt. P.G.College, Agastyamuni, (Rudraprayag)

Abstract- Solvent extraction depends on the physical and chemical properties of a solvent when used for separation of complex liquid mixtures such as the recovery of valuable products and removal of contaminants in effluent streams. The separation potential and feasibility of solvents for commercial applicability are dependent on the physical properties such as boiling point, thermal stability, density and viscosity, ease of recovery, toxicity and corrosive nature of the solvent. Liquid liquid equilibrium studies on cyclohexane, n- heptane with N-methyl pyrrolidone (NMP) and cyclohexane, n-hexane with N-formyl morpholine (NFM) were carried out. Water was used as antisolvent. Selectivity of the solvent is the important component in characterizing a solvent. The data so obtained have been predicted for effect of solvent and temperature on selectivity and solubility.

Keywords: Liquid liquid equilibrium, selectivity, solubility.

1 INTRODUCTION

Liquid-liquid equilibria are of interest in extraction operations and are useful for developing thermodynamic predictive and correlative method. Light petroleum fraction like naphtha and natural gas liquid (NGL) contain valuable naphthenic products such as cyclopentane and Cyclohexane. The separation of cyclohexane from their appropriate boiling range cuts is considered to be difficult separation step. Such appropriate cuts are generally required first to be made aromatic free before separation of these naphthenes from their corresponding boiling range paraffins. Simple distillation cannot be used as the boiling points overlap. Moreover, these components form azeotropes in between. Azeotropic mixtures are difficult to separate due to closeness of the boiling points of the compounds that are present in such mixture. It is, therefore, difficult to represent such petroleum fractions by a single binary model hydrocarbon mixture.

Moreover, such typical model compounds are not readily available. Basic liquid- liquid equilibrium (LLE) data for hydrocarbons in this carbon number range are required to be generated for each of these types of hydrocarbon classes (1). The data thus generated would be used subsequently to represent a particular fraction for design and simulation of the solvent-extraction process for removal/recovery of aromatics in these fractions. Solvent extraction depends on the physical and chemical properties of a solvent when

used for separation of complex liquid mixtures such as the recovery of valuable products and removal of contaminants in effluent streams. The separation potential and feasibility of solvents for commercial applicability are dependent on the physical properties such as boiling point, thermal stability, density and viscosity, ease of recovery, toxicity and corrosive nature of the solvent. Selectivity of the solvent is the important component in characterizing a solvent (2-4). The solvent should have low solubility in one of the components, and separation in the two phase region should be large. These denote a larger composition range in which the solvent can be used. The solvent should have low toxicity from vapour inhalation or skin contact. When extraction is used as a pre-treatment for waste water before being finally discharged to a stream, low toxicity to aquatic life is vital. Another important factor which determines the economic viability of solvent extraction potential of prospective solvent is its ease of availability and unit cost.

The most common liquid solvents reported for separation of cyclohexane from paraffins includes N-alkyl-2- pyridone (methyl-, ethyl- and isopropyl) (5), N-methyl pyrrolidone (NMP) and NMP with water (6), N-mercaptoethyl-2- pyrrolidone and cyclohexanol (7), a mixuture of NMP and ethylene glycol or tetra ethylene glycol (8), N-methyl-2- thiopurrolidone (9). Liquid liquid equilibrium data for the system {water + propionic acid + isobutyl acetate} at T =

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2 (298.2, 303.2, 308.2 and 313.2) K and atmospheric pressure. It was reported that the studied ternary system exhibit the type-1 behavior of LLE. For the investigated temperature range, it was noted that the separation factor changed little with temperature. Their findings confirmed that organic solvents has relatively high separation factor, indicating the ability of solvent to extract acid from water. The experimental LLE data was correlated using the universal- quasi-chemical (UNIQUAC) method of Abrams and Prausnitz and the Non- Random, Two Liquid (NRTL) model of Renon and Prausnitzat at each temperature. The reliability of experimental tie-line data was determined by applying Othmer-Tobias and hand correlations (10). Hence design of extraction column for systems containing these higher fractions makes it essential to generate equilibrium data on synthetic mixtures of known hydrocarbons with industrial as well as new solvents.

Estimation of binary NRTL or UNIQUAC parameters also requires the availability of experimental LLE or infinite dilution activity coefficient data.

Present studies report LLE data generated only on cyclohexane, n-heptane with N-methyl pyrrolidone (NMP) and cyclohexane, n-hexane with N-formyl morpholine (NFM). Water was used as antisolvent. Such a combination of solvents is reported to give the advantages of lower consumption or energy, lower solvent to feed ratio, with a consequent in the dimension of the column. The studies reveal effect of temperature, carbon number, structure of solvent and effect of anti solvent and co-solvent on extraction of the aromatics.

2 MATERIALS AND METHODS

Cyclohexane-hepatne and cyclohexane- hexane were chosen as model hydrocarbons to present the heartcut for cyclohexane. The liquid-liquid equilibrium (LLE) studies on these models were carried out with N-methyl pyrolli done (NMP) and N-formyl morpholine (NFM).

Water was used as antisolvent. Analysis method was used for determination of these compositions of equilibrium phases.

In order to get the tie-lines, single stage batch equilibrium runs were carried out in a jacketed mixer-settler of about 200 ml capacities. The mixer-settler was

provided with a thermometer pocket and a syringe stirrer and was maintained at the run temperature within +0.05^oC with the help of a thermostatic bath. The solvent and the hydrocarbon feed mixture of known composition and weights were taken in the mixer-settler and stirred well.

The stirring was done for 10 minutes, which is sufficient time for the establishment of equilibria in the present set-up. After mixing, the phases were allowed to settle for about the same time, at the same time temperature and then withdrawn separately, weighed and analysed (11). Solvent was removed from the raffinate phase by water-washing and from the extract phase by azeotropic distillation with water. The equilibrium phase depends on variables such as temperature, pressure, chemical nature and concentration of the various substances involved. Phase equilibrium thermodynamics seeks to establish the relationship between the various properties when the system is at equilibrium and it is related quantitatively to the intensive properties, that is, temperature and pressure which describe the equilibrium state of two or more homogenous phases (12).

3 RESULTS AND DISCUSSION

The generated experimental data was correlated using the Othmer-Tobias correlations and NRTL modelling and the latter model was also used to calculate the phase compositions and component interactions of the studied mixtures.

Overall experimental LLE data collected on these systems at various temperatures are presented in Table 1-2. Solubility or solvent power and selectivity are the key properties based on which solvent be screened and evalutaed for extraction application. High solubility for naphthenes (cyclohexane) would lead to lower solvent to feed (S/F) ratio. In practice the requirements of high raffinate yield, high purity extract at low S/F are met by clever choice of solvent and antisolvent. LLE studies were done on cyclohexane, n-heptane with N-methyl pyrrolidone (NMP), cyclohexane and n- hexane with N-formyl morpholine (NFM).

Water was used as antisolvent. The data were presented in Table- Selectivities and solubilities were also calculated and compared for these solvents. The result shows increasing selectivities and

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decreasing solubilities with increase in water content of the solvent.

Table-1 Liquid-liquid Equilibrium Studies at 40^oC Cyclohexane-n-hexane-NMP (Pure)

S.

No. Cyclohexane in feed, Wt%

S / F

Extract phase composition,

wt% Raffinate phase

composition, wt%

Solubility Selectivity Cyclohexa

ne

n- Hexan

e NMP Cyclohexa ne

n- Hexa

ne NMP

1 11.2 1 2.6 13.8 83.6 8.7 76.9 14.4 16.4 1.6

2 41.3 1 11.2 12.4 76.4 31.9 48.6 19.5 23.6 1.4

3 55.2 1 16.8 11.3 71.9 40.6 36.5 22.9 28.1 1.3

4 69.0 1 25.9 10.0 64.1 48.0 22.3 29.7 35.9 1.2

Cyclohexane-n-hexane-NMP + 5% Water S.

No. Cyclohexane

in feed, Wt% S/F Extract phase composition, wt% Raffinate phase composition, wt% Solu bilit y

Selec t Cyclohexane n-Hexane NMP Cyclohexane n-Hexane NMP y

1 10.9 1 1.2 5.7 93.1 9.2 83.4 7.4 6.9 2.0

2 41.5 1 5.4 4.4 90.2 36.1 54.2 9.7 9.8 1.9

3 54.5 1 7.1 3.5 89.4 47.6 41.8 10.6 10.

6 1.8

4 70.1 1 9.8 2.4 87.8 61.8 27.1 11.1 12.

2 1.7 Cyclohexane-n-hexane-NMP + 10% Water

S.

No. Cyclohexane in feed, Wt%

S / F

Extract phase

composition, wt% Raffinate phase composition, wt%

Solubi

lity Selectiv ity Cyclohexan

e

n- Hexa

ne NMP Cyclohexane n- Hexan

e NMP

1 10.2 1 0.7 2.9 96.4 9.0 85.9 5.1 3.6 2.2

2 39.6 1 2.5 1.8 95.7 36.9 58.1 5.0 4.2 2.1

3 55.0 1 3.8 1.5 94.7 50.2 43.2 6.6 5.3 2.1

4 70.4 1 4.9 1.0 94.1 64.6 28.6 6.8 5.9 1.7

Table-2 Liquid-liquid Equilibrium Studies at 40^oC Cyclohexane-n-heptane-NMP (Pure) S.

No. Cyclohexane in feed, Wt% S/

F

wt% Raffinate phase composition,

wt% Solub

ility Selecti vity Cyclohexane n-

Heptane NMP Cyclohexane n-

Heptane NMP

1 10.4 1 2.4 14.9 82.7 8.4 76.0 15.6 17.3 1.5

2 40.4 1 10.9 13.1 76.0 31.6 48.5 19.9 24.0 1.3

3 55.8 1 17.7 12.0 70.3 41.4 34.6 24.0 29.7 1.2

4 68.8 1 27.6 11.9 60.5 45.4 21.6 33.0 39.5 1.1

Cyclohexane-n-heptane-NMP + 5% Water S.

F

wt% Raffinate phase

composition, wt% Solubi

lity Selectivi Cyclohexane n- ty

Hepta

ne NMP Cyclohexane n- Heptan

e NMP

1 10.2 1 1.1 4.7 94.2 9.1 84.1 6.8 5.8 2.2

2 41.4 1 4.2 3.6 92.2 37.3 55.0 7.7 7.8 1.7

3 54.0 1 5.6 2.9 91.5 49.2 42.2 8.6 8.5 1.6

4 70.0 1 8.6 2.4 89.0 62.4 27.4 10.2 11.0 1.6

Cyclohexane-n-heptane-NMP + 10% Water S.

F

wt% Raffinate phase composition,

wt% Solub

ility Selectivi Cyclohexane n-Heptane NMP Cyclohexane n-Heptane NMP ty

1 10.2 1 0.8 2.9 9

3 9.3 85.3 5.

4 3.7 2.4

2 41.4 1 2.8 2.0 9.

2 38.5 55.4 6.

1 5.0 2.0

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3 55.2 1 3.7 1.6 9.

7 50.7 42.7 7.

0 4.3 1.9

4 69.8 1 4.7 1.1 9.

2 64.7 28.8 6.

5 5.8 1.9

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