CHAPTER 3 EXPERIMENTAL SET UP AND PROCEDURE

Size: px

Start display at page:

Download "CHAPTER 3 EXPERIMENTAL SET UP AND PROCEDURE"

Sherilyn Kelley
5 years ago
Views:

1 16 CHAPTER 3 EXPERIMENTAL SET UP AND PROCEDURE 3.1 DETERMINATION OF VAPOUR LIQUID EQUILIBRIA Iso baric vapor liquid equilibria data have been obtained, using a Smith and Bonner (1949) type still, a modified design of Othmer still. It is very simple in design, construction and operation. The still design was further modified to suit the systems containing salt. The fabrication details are shown in Figure DESCRIPTION OF THE APPARATUS Modified Smith and Bonner type still, used for the experiment is shown in the Figure 3.1. The still was modified to prevent or minimize, as far as possible, the errors due to the different sources identified by Ellis (1960) The still consists of 3-necked 500 ml flask (A) with a stopcock at the bottom of the still to collect the sample of the bottom product. Through one of the neck heater is introduced to heat if required. Another neck is used for measuring temperature of the liquid in the still. The center neck (B) is used to collect vapors, which are produced during the heating. The center neck is connected to a condenser to condense the vapor produced during heating. A stopcock is provided at the bottom of the condenser to collect the top product sample. A slight modification at the bottom of the still in the entry of the condensed liquid greatly reduces both the axial and radial concentration gradient in the bulk of the liquid as pointed out by Ellis (1960) and provided

2 17 TO ATMOSPHERE ICE COOLED WATER J~ICONDENSATE CHAMBER M2 OUTLET SAMPLE Figure 3.1 Schematic diagram of the experimental set-up for the determination of Vapour - Liquid Equilibrium (Smith and Bonner Type)

3 18 for accurate equilibrium composition The entire setup was completely lagged using asbestos magnesia mixture to minimize the heat loss. A Magnetic Stirrer (MS) was used to maintain sufficient homogeneity of the liquid mixture to improve salt dissolution. At the same time it decreased the irregularities in the boiling behavior such as blanketing, chugging and sputtering. This apparatus is thus suited, not only for miscible systems, but also for Partially miscible systems as it was possible to keep the partially miscible systems always in an emulsion form, with the help of the magnetic stirrer. The performance of this still was ascertained by measuring the vapor liquid equilibrium data for the binary systems Methanol Water system. The data were compared with the literature data (Ciparis 1966) and there was good agreement (Figure A1.1). 3.3 PROCEDURE FOR DETERMINING EXPERIMENTAL VLE DATA The raw equilibrium data were obtained at atmospheric pressure kpa using the modified Smith and Bonner type still (Figure 3.1). The still was charged with 300ml of mixture of desired composition containing dissolved salt at a particular mole fraction. The reboiler electric voltage was adjusted in such a way that approximately 5 to 8 ml of condensate was collected per minute. At this rate no entrainment was observed. The jacket heater was adjusted to give 2 to 3 o C of super heat. The equilibrium was attained within 45 minutes as indicated by the constancy of equilibrium vapor temperature recorded by the standard mercury thermometer. However the condensed vapor phase was circulated for 2.5 to 3 hrs before samples were drawn for analysis.

4 19 The vapour phase, being free of salt, was analyzed for its composition y 1, by gas chromatographic method using established procedures. The details of the analytical procedures adopted in this investigation are discussed in Appendix 3. The liquid sample at the end of each run was analyzed for its Composition on a salt free basis by first separating it quantitatively into salt and solvent fractions by a total distillation technique or evaporating to dryness. The equipment used for the evaporation is similar to the one used by Hashitani et al (1962). The liquid phase composition, x 1 was then analyzed for composition and the results were determined on salt free basis. 3.4 MATERIAL USED All the solvents used in this investigation were obtained from M/s.Merck (India) Ltd, The hydrocarbons were assayed by gas chromatography and exceeded 99.5 percent purity and some of them were used after further purification. The purities of the solvents were checked by comparing the measured boiling points, densities and refractive indices with those reported in the standard chemical engineers hand books (1973). Anhydrous Reagent grade salts, calcium chloride, calcium bromide, calcium iodide, calcium acetate, calcium oxalate have been purchased from BDH (Glaxo) Laboratories and E. Merck (India ) Ltd, Bombay. All salts were dried before use.

5 DETAILS OF THE SYSTEMS STUDIED UNDER THE PRESENT INVESTIGATION System Studied i) Acetone (1) Methanol (2) ii) Methanol (1) Benzene (2) iii) Methanol (1) Ethylacetate (2) iv) Methanol (1) Hexane (2) v) Isopropanol (1) Water (2) Salts employed i) Calcium chloride (Fused) ii) Calcium Bromide iii) Calcium Iodide iv) Calcium acetate v) Calcium Oxalate Mixed salts i) Calcium chloride + Calcium acetate ii) Calcium chloride + Calcium oxalate iii) Calcium bromide + Calcium acetate iv) Calcium bromide + Calcium oxalate v) Calcium Iodide + Calcium acetate vi) Calcium Iodide + Calcium oxalate. Salt concentration : 0, 2, 3, 4, 8 mole percent depending upon the solubility in each case. In the case of mixed salt 1:1 mole ratio is used.

EXPERIMENTAL SETUP AND PROCEDURE

CHAPTER 3 EXPERIMENTAL SETUP AND PROCEDURE 3.1 Determination of vapour-liquid equilibria Isobaric Vapour-Liquid Equilibria date have been obtained, using a Smith and Bonner [39] type still which is a modified