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1. Introduction

The ash point (FP) is one of the most important

ammability characteristics of liquids and low-melting

substances. Knowledge of the ash points is important

for classication of materials according to the classesdened in each particular regulation [1,2] and has great

practical signicance in handling, transport, storage and

packaging of these materials. The ash point is dened

as the lowest temperature (corrected to a pressure of

101.3 kPa) at which the application of anignition source

causes the vapors of a sample specimen to igniteunder

specied testing conditions [3].

Flash points are determinedexperimentally by heating

the liquid in a container and thenintroducing a smallame

just above the liquid surface. Thetemperature at which

there is a ash/ignition is recorded as the ash point.

Two general methods are called closed-cupand open-

cup [4,5]. The closed-cup method prevents vapors from

escaping and therefore usually results in a ash point

that isa few degrees lower than in an open cup. Because

the twomethods give different results, one must always

list thetesting method when listing the ash point.

Flash points of common pure chemical substances

are widely reported,but very limited data are available

for mixtures.

Since the experimental measurement of ash point

is expensive and time consuming, predictive theoretical

methods are required to estimate the ash points of both

pure components and mixtures.

Several prediction models are presented in the

literature for the prediction of mixture ash point.Wickey et al. [6] reported a method for calculating the

ash point of miscible, ideal solutions of petroleum

blends. Catoire and Paulmer [7] proposed a model for

total miscible combustible solvent blends. McGovern

studied a method [8] for estimating the ash points of

mixtures of oxygenated and hydrocarbon solvents and

petroleum distillates. Affens and McLaren [9] suggested

the model for ideal solution by the lower ammability limit

(LFL) temperature dependence assumption; White [10]

simplied the Affens model by ignoring the temperature

dependence of LFL. Liaw et al. [11-15] have reported a

series of models, which could be used for predicting theash points for ideal and non ideal solutions. The basic

assumption in these models is that the liquid phase is in

equilibrium with the vapor. The non-ideality of the liquid

phase is accounted by liquid-phase activity coefcients by

means of thermodynamic models. The activity coefcient

is a dimensionless parameter that measures the deviation

from ideality in a mixture. Some of the models that can

be used to obtain the activity coefcients are: Margules

Central European Journal of Chemistry

Flash point of organic binary mixtures

containing alcohols: experiment and prediction

* E-mail: [email protected]

Received 11 August 2012; Accepted 1 November 2012

Abstract:

Versita Sp. z o.o.

Keywords:Flash point Binary mixture Pensky-Martens Prediction

University of Chemical Technology and Metallurgy,1756 Soa, Bulgaria

Mariana Hristova1*, Dimitar Damgaliev

Research Article

The ash points of three organic binary mixtures containing alcohols were measured in the present work. The experimental data was

obtained using the Pensky-Martens closed cup tester. The experimental data were compared with the values calculated by the Liawmodel. Activity coefcients were calculated by the Wilson equation and NRTL equation. The accuracy of predicted ash point values is

dependent on the thermodynamic model used for activity coefcient.

388

Cent. Eur. J. Chem. 11(3) 2013 388-393

DOI: 10.2478/s11532-012-0171-6

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M. Hristova, D. Damgaliev

[16], Van Laar [17], Wilson [18], NRTL [19], UNIFAC [20]and UNIQUAC [21]. The rst four models for calculating

the activity coefcients depend on experimental binary

interaction parameters (BIPs). The UNIQUAC model

requires only pure component molar volumes as well

as surface area and volume parameters. By contrast,

predictive models such as the UNIFAC do not need

experimental BIPs. The contributions due to molecular

interactions are obtained from a database using a wide

range of experimental results.

In general, Liaw et al.s model is the most frequently

used, but accuracy of predicted mixture ash points

depends on the reliability of input data.The ash points of three binary mixtures, 1-propanol

+ 1-pentanol, 4-methyl-2-pentanone (MIBK)+1-butanol

and ethanol + aniline, were measured by Pensky-

Martens closed cup tester, and compared with the

values calculating by using Liaw`s model. The activity

coefcients were estimated by using the Raoults law,

Wilson and NRTL equations.

2. Experimental procedure

The experimental data was obtained using the Pensky-

Martens closed cup tester (Fig. 1) model PM 1, SUB

(Berlin, Germany).The closed cup tester was operated

according to the standard test method, EN ISO 2719

[22].

The mixture was heated at a rate of 1.5C min-1with

continual stirring. The temperature control was sustained

by electrical heating. Tester thermometer having a range

from -7 to +110 C was used. The ambient barometric

pressure was observed and recorded at the time of

the test. When the pressure differed from 760 mm Hg

(101.3 kPa), the ash point was corrected as follows:

Corrected ash point = T0+0.25(101.3 P)

where T0is the observed ash point (C); P is barometric

pressure (kPa).

The mole fraction of each component was determined

by measuring the mass using a Sartorius digital balance

(sensitivity 0.0001 g, maximum load 100 g). The sample

was prepared and transferred to the cup of the apparatus

at least 10C below the expected ash point. The sample

was not stirred while the ame was lowered into the cup.

The ash point was the temperature at which the test

ame application caused a distinct ash in the interior

of the cup. The measured value was the mean of two

measurements which do not differ by more than 2C.

All materials used in this study were purchased from

Merck and Fluka. Purities were at least 99.5% (analytical

grade) for all compounds used for these experimental

ash point determinations.

3. Results and discussion

The ash point of a binary mixture can be estimated by

the model developed by Liaw et al. [11]:

(1)

where ix , ,sat

iP andsat

fpiP, are the mole fraction,activity coefcient, vapour pressure at temperature T,

and vapour pressure at the ash point temperature ofthe mixture components, respectively.

If the mixture is an ideal, Eq. 1becomes:

(2)

The temperature that satises Eqs.1or 2is the ash

point temperature of the mixture.

The vapour pressure,sat

iP , can be estimated froman equation, such as Antoines equation, if the required

constants are known:

i

ii

sat

i

CT

BAP

+

=log (3)

where Ai, B

i and C

i are the parameters of compound

i. This correlation should not be used outside the

temperature range at which the parameters were

obtained.The parameters for the Antoine equation can

be obtained from different collections [23,24].

The activity coefcients, , were estimated by the

Wilson equation and the NRTL equation.The estimated

activity coefcients were subsequently used to predict the

corresponding ash points. In addition, it is necessary to

input the ash points of the pure components into such

Figure 1. Photograph of the experimental apparatus.

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a model to predict the ash point of a mixture. The pure

compound data are listed in Table 1.

The parameters of the Wilson and NRTL equations

were also from the literature [25-27]. It is well known

that these parameters are obtained by regression of

the experimental data for such binary mixtures and are

listed in Table 2.

The measured ash points of studied binary mixtures

and those predicted by Liaws model are presented in

Tables 3-5respectively, where Tfp= |T

experimental T

predicted|.

In Figs. 2-4, the ash point variation between

the model predictive curves and the experimentally-

derived data for the binary solutions are compared.

Most liquid mixtures made of members of homologous

series are practically ideal. The propanol-pentanol

mixture exhibits no deviation from ideal behavior

and no azeotropes are present [27]. This mixture

has properties that can be predicted with a simple

mixing rule that ignores interactions among theindividual components because these chemicals are

very similar.

Fig. 2 shows that predicted results by the Wilson

equation and as ideal solution (Raoults law; activity

coefcients equal unity) are in excellent agreement with

the experimental data. On the other hand, the NRTL

model predicts ash points which differ considerably

from experimental data even if the mixture exhibits

minimum ash point behavior.

Similar results can also be seen for ethanol-aniline

mixture (Fig. 3). Experimental data for the ethanol-

aniline mixture were taken from the literature [28].

The Wilson and NRTL predicted values are lower

than the experimental values measured. As indicated

in Fig. 3, the values in the complete set of ash point

experimental data are lower than those calculated for

the corresponding ideal mixture. This indicates the

positive deviation of the mixture from ideal behavior. In

other words, the volatility of this mixture is higher and

its boiling point lower than the corresponding values

estimated for ideal mixtures of the same components.

The formation of this mixture is associated with the

predominance of repulsive interactions. Nevertheless,

Table 1.Antoine coefcients, ash points and molecular volume for pure components.

Substance CASnumber

Antoine coefcients* [23] ViL

(cm3 mol-1)FP (C)

Exp.A B C

Aniline

Ethanol

1-Butanol

1-Propanol

1-Pentanol

MIBK

62-53-3

64-17-5

71-36-3

71-23-8

71-41-0

108-10-1

7.2418

8.2133

7.4768

7.6192

7.1776

6.9920

1675.30

1652.05

1362.39

1375.14

1314.56

1365.03

200.01

231.48

178.73

193.01

168.16

215.90

91.60

58.60

91.51

75.09

108.29

124.89

700.5

130.7

370.5

230.9

490.5

140.8

*CCT

BAmmHgP

+=

)()(log

0

Table 2.VLE parameters of the Wilson and NRTL equations for the studied systems*.

Mixtures Wilson NRTL Ref.

A12

(J mol-1)

A21

(J mol-1)

A12

(J mol-1)

A21

(J mol-1)

4-methyl-2-pentanone (1)+1-butanol (2)

1-propanol (1)+1-pentanol (2)

Ethanol (1)+aniline (2)

-323.39

-1472.74

862.9016

1666.30

4557.2

598.5729

1118.87

6478.94

679.8036

203.72

-3523.07

538.0489

0.30

0.30

0.29

[26]

[27]

[25]

Wilson: ; NRTL:

Figure 2. Comparison of the ash point prediction curves withexperimentally derived data for 1-propanol (1) +

1-pentanol mixture.

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Table 3.Experimental ash points and predictions for 1-propanol (1) + 1-pentanol mixture.

X1

Exp. (C) Ideal DTfp/ oC Wilson DT

fp/ oC NRTL DT

fp/ oC

0 49.5 49.5 0.0 49.5 0.0 49.5 0.0

0.1 42.5 43.8 1.3 43.9 1.4 23.3 19.2

0.2 39.0 39.7 0.7 39.8 0.8 19.8 19.2

0.3 35.5 36.3 0.8 36.3 0.8 19.2 16.3

0.4 33.0 33.6 0.6 33.4 0.4 19.4 13.6

0.5 29.5 31.2 1.7 30.8 1.3 19.9 9.6

0.6 28.0 29.2 1.2 28.6 0.6 20.5 7.5

0.7 25.5 27.4 1.9 26.8 1.3 20.9 4.6

0.8 25.0 25.8 0.8 25.2 0.2 21.2 3.8

0.9 23.5 24.3 0.8 24.0 0.5 21.2 2.3

1.0 23.0 23.0 0.0 23.0 0.0 23.0 0.0

Table 4.Experimental ash points and predictions for Ethanol (1) Aniline (2).

X1


fp/ oC NRTL DT

fp/ oC

0 70.0 70.0 0.0 70.0 0.0 70.0 0.0

0.1 32.7 48.9 16.2 27.2 5.5 11.3 21.4

0.2 - 38.7 - 20.8 - 8.9 -

0.3 22.3 32.2 9.9 18.3 4.0 9.2 13.1

0.4 19.8 27.5 7.7 17.0 2.8 10.5 9.3

0.5 - 23.9 - 16.2 - 11.3 -

0.6 17.5 21.0 3.5 15.7 1.8 12.4 5.1

0.7 - 18.6 - 15.2 - 13.1 -0.8 15.5 16.5 1.0 14.7 0.8 13.5 2.0

0.9 13.3 14.6 1.3 14.0 0.7 13.6 0.3

1.0 13.0 13.0 0.0 13.0 0.0 13.0 0.0

Table 5.Experimental ash points and predictions for 4-methyl-2-pentanone (1) +1-butanol (2).

X1


fp/ oC NRTL DT

fp/ oC

0 37.0 37.0 0.0 37.0 0.0 37.0 0.0

0.1 31.0 33.5 2.5 31.4 0.4 31.4 0.4

0.2 28.0 30.4 2.4 27.5 0.5 27.5 0.5

0.3 25.5 27.5 2.0 24.6 0.9 24.6 0.9

0.4 23.0 24.9 1.9 22.3 0.7 22.3 0.7

0.5 19.5 22.7 3.2 20.5 1.0 20.5 1.0

0.6 19.0 20.6 1.6 18.5 0.5 18.9 0.1

0.7 17.0 18.7 1.7 17.6 0.6 17.6 0.6

0.8 16.5 17.0 0.5 16.4 0.1 16.3 0.2

0.9 15.0 15.4 0.4 15.2 0.2 15.2 0.2

1.0 14.0 14.0 0.0 14.0 0.0 14.0 0.0

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this effect is not strong enough to cause ash point

values to be lower than the value obtained for the pure

light component. The Wilson equation better represents

the experimental data. The largest difference in the ash

point values from experimental data and predicted by

the Wilson equation is approximately 5C.

The ash point predictions for 4-methyl-2-

pentanone +1-butanol mixture are presented in

Fig. 4. All thermodynamic models agree in their ash

point predictions. The ideal solution model predicts

higher but acceptable ash point values.

Table 6includes average absolute deviation (A.A.D.)

for three binary solutions:

(4)

A.A.D. is a measure of agreement between the

experimental data and the calculated values.

In the prediction model, it was assumed that the

vapour phase and liquid phase of a solution are in

equilibrium. The predicted data was only adequate for

the data determined by the closed cup test method, and

may not be appropriate to apply to the data obtained

from the open cup test method because of its condition

of having deviated from the vapour-liquid equilibrium.

4. Conclusions

The ash points of binary mixtures containing alcohols,

1-propanol + 1-pentanol, 4-methyl-2-pentanone (MIBK)

+1-butanol and ethanol + aniline, were measured by

Pensky-Martens closed cup tester. The experimental

data were compared with values calculated by using

Liaw`s model. The activity coefcients were estimated

by the Wilson equation and the NRTL equation. For

the 4-methyl-2-pentanone + 1-butanol mixture, all the

predictions agree with the experimental data. Signicantdeviations were observed for the other two mixtures

when Wilson and NRTL models are used. However,

the calculated values based on the Wilson equation

were found to be better than those based on the NRTL

equation.

Table 6. Average absolute deviation (A.A.D.) between calculated and experimental ash points.

Solution Ideal Wilson NRTL

1-propanol (1) + 1-pentanol 0.61 0.51 8.73

Ethanol (1) Aniline (2) 6.6 2.6 8.53

4-methyl-2-pentanone (1) +1-butanol (2) 1.47 0.44 0.51

Figure 3.Comparison of the ash point prediction curves withexperimentally derived data forEthanol (1) Aniline (2).

Figure 4. Comparison of the ash point prediction curves with

experimentally derived data for 4-methyl-2-pentanone (1)+1-butanol (2).

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