OBJECTIVE

The aim of this experiment is to determine the vapor pressure of gasoline and white spirit.

1.0 INTRODUCTION

Vapor pressure is the pressure of a vapor in equilibrium with its condensed phase. The

equilibrium vapor pressure is an indication of a liquids evaporation rate. If the vapor

pressure is higher, the sample will be more volatile and will more readily evaporate.

Unlike distillation data, vapor pressure provides a single value that reflects the combined

effect of the individual vapor pressure of the different petroleum fractions in accordance

with their mole ratios. It is thus possible for two wholly different products to exhibit the

same vapor pressure at the same temperature - provided the cumulative pressures exerted

by the fractions are the same.

Temperature affects vapor pressure. According to Le Chatelier's principle a system disturbed

by rise in temperature will react to relieve this stress. A liquid will boil, when the

temperature is increased enough to raise the vapor pressure to atmospheric pressure. The

liquid will boil much more when the atmospheric pressure is zero as in a vacuum system.

This is the basis for obtaining pure samples of liquid with high boiling points in a vacuum

distillation process .The presence of dissolved substances in liquid or solid also affects vapor

pressure.

A setavap 2 vapor pressure tester is used to determine vapor pressure of gasoline and

other similar solvents. A vacuum pump is attached to the equipment to ensure that the

solvent is tested under a complete vacuum.

2.0 Literature Review

EXPERIMENTAL DESCRIPTION

Solvent

Gasoline consists of aliphatic hydrocarbons obtained by the fractional distillation of

petroleum, enriched with iso-octane or the aromatic hydrocarbons toluene and benzene

to increase its octane rating.

White spirit - A transparent organic solvent used for cleaning, degreasing and also as solvent

in aerosol, paints, varnishes et al. It is mixture of saturated aliphatic and alicyclic with a

maximum of25% of seven carbon atom to twelve carbon atoms alkyl aromatic Hydrocarbon.

Vacuum Pump

This is attached to the vapor pressure tester. It drains out all the liquid in the tester and

evacuates the air so that a vacuum exist in the vacuum tester.

Setavap Tester

The Setavap 2 Vapour Pressure Tester is an automated instrument used for the

measurement of the vapour pressure of gasoline, solvents, light crude oils, etc.

It consist of a chamber centrally located (cylinder of 15ml) and an electrical register which

displays the pressure. Fully evacuated chamber technology guarantees that the sample is

tested under a full vacuum.

A two button keypad and a rotary control allow access to all functions. The digital display

points the operator through the test sequence, displays the instrument status and the test

results. If an action is required from the operator, an audible prompt is sounded. Then a

sample gasoline/white spirit is injected through a septum into a fixed volume chamber

which is maintained at 37.8°C ± 0.1°C and the vapour to liquid ratio is 4:1. At one minute

intervals, the pressure is automatically measured until three Readings are within 0.1 k Pa,

which determines the end of the test. The test results can be displayed as total pressure

(Ptot), dry vapour pressure equivalent (DVPE), EPA requirements.

Septum Holder

A screw at the top of the vapor pressure tester which allow access to the tester cylinder. It is

used to hold the septum.

Septum

A small round rubber attached to the top of the screw nub which helps to guarantee

complete vacuum.

Silicon grease

An ointment used to lubricate the septum

Hamilton micro litre syringe

A syringe used to siphon and measure the solvent.

Fig I: A Setavap Tester

3.2 Experimental Procedure

The waste container was placed under the drain.

The vacuum pump and the setavap tester were powered on.

At the instruction of the display unit, the septum was removed by unscrewing the

septum holder.

The button was tuned and the top line of the tester displayed "Draining 10",

which allowed the system to drain for I Osecs.

After 10seconds, the message displayed "purging 120" and counted down to zero.

After 120 seconds, an audible warning (beep) was heard. The "insert new septum" display came up.

A new septum was fitted into the septum holder and silicon grease was smeared on

the exposed surface.

The septum holder was firmly screwed into the Setavap Tester to give a vacuum

tight" seal.

The start button was taped and the system was automatically evacuated for 300 minutes.

At the end ofthe evacuation process an audible warning (beep) was heard.

On the instruction of the Setavap tester the sample was prepared by siphoning

3.5ml of sample into a properly cleaned syringe.

NOTE: The needle is a side-exit type. Take care to avoid spill to yourself or

colleagues.

The sample was drained to 3.0ml to expel air.

The button on the Setavap was tuned and it displayed" inject sample".

The sample was injected into the septum holder until the syringe was in contact

with the bottom of the septum holder.

The button was tuned to put the test in progress.

The Setavap Tester originally took reading at one minute interval

The readings were recorded.

When three consecutive readings were within 0.1Kpa the test was automatically

terminated.

A warning beep sound was heard and the test result displayed

The ptot, DVPE, EP A were read from the display unit by tuning the knob.

The same procedure was followed for the white spirit and results were recorded .

4.0 RESULTS

The white spirit sample was tested at the following conditions; Test

Conditions: Temperature of vacuum = 37.8°C

Pressure of vacuum = 0.2Kpa

The following results were obtained from the vapor pressure experiment for white spirit.

Table 1: Vapor pressure measurement for White Spirit Test

Time 1st pressure (kpas) 2nd pressure (Kpas)0 4.5 3.9

20 4.5 440 4.5 460 4.5 480 4.6 4

100 4.6 4120 4.6 4140 4.6 4160 4.6 4.1180 4.6 4.1200 4.6 4.1220 4.6 4.1

Table 2: DVPE and EPA for White Spirit

Vapor Pressure (kpa)P-tot DVPE EPA

Test No.1 4.6 0.7 2.0Test No.2 4.1 0.2 1.5

The white spirit sample was tested at the following conditions. Test Conditions: Temperature of vacuum = 37.8°C

: Pressure of vacuum = O.2kpa

The following results were obtained from the vapor pressure experiment for gasoline.

Table 3: Vapor pressure measurement for Gasoline TestTime 1st pressure (kpas) 2nd pressure (Kpas)

0 61 5320 62.2 54.140 62.4 54.660 62.6 54.880 62.7 55.1

100 62.8 55.2120 62.9 55.3140 63.1 55.4160 63.1 55.5180 63.2 55.6200 63.3 55.6220 63.3 55.7240 63.3 55.7260 63.4 55.8280 63.4 55.8300 63.4 55.8320 63.4 55.8340 63.4 55.8

360 63.4 55.8380 63.4 55.8

Vapor Pressure (kpa)P-tot (kpas) DVPE (kpas) EPA (kpas)

Test No.1 63.4 57.4 58.3Test No.2 55.8 50.1 51.0

Fig.2 : Gasoline plot showing Vapor pressure Vs Time Fig.3 : White Spirit plot showing Vapor pressure Vs Time Fig.4: Gasoline & White spirit plot showing Vapor pressure Vs Time 5.0 DISCUSSION OF RESULTS. SOURCES OF ERROR

Error due to parallax in measuring the quantity ofthe solvent Error due to inadequate smearing silicon grease over the septum, thereby

compromising the existence of complete vacuum.

CONCLUSIONS Gasoline has a vapor pressure of 13.1kpas and white spirit is 5.kpas

The vapor pressure for gasoline is higher than that of white spirit an indication that whit

spirit is less volatile than gasoline

White spirit and gasoline have different vapor pressures because they are different

solvents and have different cumulative pressure.

6.0 RECOMMENDATION Appropriate personal protective equipment must be worn before performing this

experiment.

All instructions concerning the tester must be followed 0 obtain accurate results

The setavap tester should be connected to its data logger or printer