Field method – Aniline Solubility method for Aromatics in Naphtha

- April 07, 2019

Field method – Aniline Solubility method for Aromatics in Naphtha

Following properties of Aniline has been used to derive a simple field method to determine Aromatics content in naphtha.

The aniline point is useful as an aid in the characterization of pure hydrocarbons and in the analysis of hydrocarbon mixtures.

Aromatic hydrocarbons exhibit the lowest, and paraffins the highest values. Cycloparaffins and olefins exhibit values that lie between those for paraffins and aromatics.

In homologous series the aniline points increase with increasing molecular weight. Although it occasionally is used in combination with other physical properties in correlative methods for hydrocarbon analysis, the aniline point is most often used to provide an estimate of the aromatic hydrocarbon content of mixtures.

Field Method:

1. Scope:-

1.1 The method is studied for Naphtha Samples having,

a) Aromatics = Max 22% Vol

b) Naphthenes = Max 40% Vol

c) Olefins = Max 1 % Vol

d) Paraffins = Balance of 100%

1.2 Boiling range (ASTM D 86) of Naphtha = 30 – 200⁰C

2 Significance:

2.1 Aniline solubility method indicates the composition of Naphtha. Lower the Aniline point – Higher solubility of Naphtha – also suggest higher aromatics or/and naphthenes or lower paraffins and vice-versa.

3 Summary of the method:

3.1 An appropriate volume of Naphtha sample (see table 1) and 5 ml of Aniline is taken in conical flask. This mixture is either cooled or heated slightly and the temperature at which the mixture is completely soluble is noted. Aromatics is calculated from the empirical equation given below.

4 Apparatus and Chemicals:

4.1 Burette (25 or 50 ml capacity)

4.2 Graduated Pipette (10 ml capacity)

4.3 Conical flask (100 ml capacity)

4.4 Aniline point tubes

4.5 Aniline (check purity giving aniline point of n-heptane 69.3 +/- 0.2 ⁰C as per ASTM D611/IP 2)

5 Procedure:

5.1 Place 5 ml of Aniline in a 100 ml conical flask. Add appropriate volume of naphtha sample (table 1) from burette to the flask. Keep a thermometer (IP-39 or IP-64C) to measure temperature of the mixture. Cool or heat the mixture of flask with swirling,

5.2 Note the miscibility temperature in above step 5.1, similar as the aniline point method. For the table 1 naphtha sample volume, this temperature is usually around 27 ⁰C.

5.3 Table 1 for sample size. (see note 4 for Expected Aromatics%).

Expected Aromatic % V	Sample size, ml
0 - 6	70
7 - 11	50
12 - 15	40
16 - 22	20

5.4 Determine the aniline point of the sample as per ASTM D611. If aniline point is more than 60⁰C, do not use this value and use equation 6.1 for calculation of Aromatics.

6 Calculation:

Calculate the aromatics in naphtha using one of the following equation:

6.1 Aromatics %V = 24 – 0.29V – 0.5*(T-27)… If Ar%V is less than 6.

6.2 Aromatics %V = 23.5 + A.P. – 0.69V – 1.31*T .. If Ar%V is between 6 and 15.

6.3 Aromatics %V = 28.2 + A.P. – 0.89V – 1.23*T .. If Ar%V is more than 15.

Where V = size of the sample

A.P.= Aniline Point as per ASTM D 611

T = miscibility Temperature as per 5.2 above.

7 Precision :

From the data generated by us and round robin done, results obtained by this method is similar to the standard test method of Aromatics - ASTM D1319 Standard Test Method for Hydrocarbon Types in Liquid Petroleum Products by Fluorescent Indicator Adsorption.

7.1 Repeatability = 1.0 % V

7.2 Reproducibility = 2.0 % V

Notes :

1 . Heating/cooling process should be very slow ( max 1 deg C per minute.

2. Avoid as far as possible heating/cooling by water bath.

3. Aniline/Naphtha mixing is an endothermic process.

4. Approx. aromatics %V for the sample size as per serial number 5.3 can be predicted by using one of the following empirical equations.

Aromatics % V = 0.55 ( 70 – A.P.) or

Aromatics % V = 225 ( 1.47*D – 1.0) where

A.P. = Aniline point and D = Density of sample at 15 ⁰C.

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