Generation of TBP data using ASTM distillation LABORATORY PROJECT GUIDED BY : DR. H.K. MOHANTA

BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE, PILANI

1

Acknowledgement

2

3

TABLE OF CONTENTS

1. INTRODUCTION ……………………………………………………………5

2. TBP APPARATUS…………………………………………………………..6

3. ASTM METHODS FOR CRUDE CHARACTERISATION……..7

4. PRINCIPLES INVOLVED…………………………………………………8

5. APPARATUS…………………………………………………………………10

6. PROCEDURE……………………………………………………………….12

7. OBSERVATION…………………………………………………………….14

8. CALCULATION……………………………………………………………..16

9. RESULTS………………………………………………………………………18

10. CONCLUSION…………………………………………………………..20

11. REFERENCES……………………………………………………………22

4

Having in mind that crude oil cost accounts for more than 80% of

refinery expenditure the proper operation of crude distillation unit has

great impact on refinery profitability. In order to find the adequate

technological regime that provides maximum yields of high value

products in a crude distillation unit the process engineer needs to have

laboratory analyses data of crude oil that is processed in the unit.

Distillation characteristics of a crude are assessed by performing a

preliminary distillation called ‘True Boiling Point’ analysis (TBP). This

pulse test enlightens the refiners with all possible information regarding

the percentage quantum of fractions, base of crude and the possible

difficulties beset during treatment operations etc. Information supplied

by this distillation forms the basis of design of distillation columns and

thus represents the veridity of crude distillation.

The basic methods for determining the TBP data for a sample are: (1) To

actually perform a TBP distillation, which is time consuming procedure

( 2 ) to perform single theoretical plate distillation (designated by the

American Society for Testing and Materials as Method D-86 for

atmospheric distillations , and Method D-11602 for vacuum

distillations), and converting the data mathematically with help of

5

correlations. (3) Simulated distillation by gas chromatography. (4)

Equilibrium Flash Vaporization (4) Humpel distillation

Unfortunately the TBP analyses are costly and time consuming, a TBP

analysis takes about 48 hours. That is why it is impractical to use it as a

tool for daily monitoring of the crude distillation unit operation. For

refineries, which often switch the crude oils, the lack of information

about the crude oil quality could negatively impact the optimum

operation and in this way the profitability of the crude distillation unit.

6

To ameliorate these inconveniences other quicker methods have been

developed. One such method, used for almost all petroleum fractions,

except for heavy fractions, is the ASTM D86 method. In this test, the

sample is boiled and the vapors are collected and condensed as they are

produced. Vapor temperatures are then recorded as a function of

cumulative liquid volume collected. Because no reflux is used and there

is only one equilibrium stage, the initial boiling point of this assay is

larger and the final point is lower than the one in the TBP curve. Test

results are commonly expressed as percent evaporator percent, recovered

versus corresponding temperature, either in a table or graphically, as a

plot of the distillation curve.

7

This basic test method of determining the boiling range of a petroleum

product by performing a simple batch distillation has been in use as long

as the petroleum industry has existed. It is one of the oldest test methods

under the jurisdiction of ASTM Committee D02, dating from the time

when it was still referred to as the ENGLER DISTILLATION. Since

the test method has been in use for such an extended period, a

tremendous number of historical data bases exist for estimating end-use

sensitivity on products and processes.

Here ASTM D-86 method is used to generate the TBP curve. After

performing the experiment, we got the temperature versus fractional

volume distilled data. Now to interconvert ASTM D-86 distillation to

TBP distillation we use Riazi-Daubert method which is based on a

generalized correlation in the following form:

TBP= a(ASTM D-86)b

8

Here a, b depend on the fraction distilled as shown in the table and

temperature is used in Kelvin.

One can safely extrapolate distillation curve from a set of data that

does not cover the full distillation range of an oil by using Riazi’s

distribution model.

Regardless of the method for distillation used, Riazi’s model can easily

approximate the boiling point distribution.

The model contains two set of equations:

(Ti - To)/ To = [Atln(1/(1-xi))/Bt]1/

Bt

(1)

Y= C1 + C2.X (2)

%Volume

Distilled

Coefficient

a

Coefficient

b

range a, oC

0 0.9177 1.0190 20-320

10 0.5564 1.0900 35-305

30 0.7617 1.0425 50-315

50 0.9013 1.0176 55-320

70 0.8821 1.0226 65-330

90 0.9552 1.0110 75-345

95 0.8177 1.0355 75-400

9

Where Y= ln[(Ti-To)/ To] ; X=lnln[1/(1-xi)]

Bt=1/ C2 ; At= Btexp(C1. Bt)

To = initial boiling point in K; Ti = temperature at which i percent

is distilled in K; xi = volume or weight part of distillate.

Thus, the TBP curve is generated by plotting the obtained

temperature versus % volume distilled.

Here, ASTM D-86 apparatus is used. The basic components of the

distillation unit are the distillation flask, the condenser and associated

cooling bath, a metal shield or enclosure for the distillation flask, the

heat source, the flask support, the thermometer, and the receiving

cylinder to collect the distillate.

10

11

We are generating TBP curve for hexane and diesel here using

ASTM D-86 apparatus.

In this test 100 ml of the sample is distilled in a standard flask. The

distillate is condensed in a brass tube condenser, surrounded by water

bath kept at 0 oC by ice-water mixture.

First drop from the condenser must be available in 5 mins for

Hexane and 10 mins for Diesel after heating started, at which the

recorded temperature is mentioned as Initial Boiling Point (IBP) of the

sample.

The vapor temperature is recorded at each successive 10 ml

distillate collected in the measuring cylinder.

The test continues in the same way till 95% of fraction is

condensed.

At this point the heat intensity can be increased to obtain the

maximum boiling point also known as End Point (EP).

12

Fluctuation in temperatures is common when last 2-3 ml of sample

are distilled. When bottom of the flask shows dryness, the temperature

corresponds to final boiling point. The distillate collected should be

greater than 95 ml and the difference is accounted as loss; usually

ascribed to light ends.

To reduce evaporation loss of the distillate, cover the receiving

cylinder with a piece of blotting paper, or similar material, that has been

cut to fit the condenser tube snugly. If a receiver deflector is being used,

start the distillation with the tip of the deflector just touching the wall of

the receiving cylinder. If a receiver deflector is not used, keep the drip

tip of the condenser away from the wall of the receiving cylinder. Note

the start time. Observe and record the IBP to the nearest 0.5°C (1.0°F).

If a receiver deflector is not being used, immediately move the receiving

cylinder so that the tip of the condenser touches its inner wall.

13

VOLUME

in ml

TEMPERATURE

In Kelvin

(ASTMD-86)b TBP=

a(ASTMD-

86)b

0 483.15 543.3498376 498.6321459

10 513.15 899.8421311 500.6721618

20 523.15 792.0183019 521.9796619

30 543.15 709.8292227 540.6769189

40 553.15 668.7523888 556.0676113

50 563.15 629.5570221 567.419744

60 593.15 674.3807141 601.3452828

70 603.15 697.0484161 614.8664078

80 613.15 682.9640656 627.4049388

85 617.15 674.8032484 632.2400335

14

VOLUME

in ml

TEMPERATURE

In Kelvin

(ASTMD-86)b TBP=

a(ASTMD-

86)b

0 328.15 366.3344693 336.1851424

10 339.15 572.9636698 324.5266226

20 341.15 502.056977 330.8806507

30 342.15 438.4506795 333.9678826

40 343.15 408.9547883 340.0459065

50 343.65 380.8482777 343.2585527

60 343.65 386.4490881 344.5966519

70 343.65 392.1322648 345.8998708

80 344.15 379.6340311 348.7508027

85 345.15 374.3571973 350.7446171

90 347.15 376.5566817 352.805369

95 357.15 387.5567261 363.1115856

100 363.15 394.1588159 369.2972486

15

As mentioned earlier in ‘Principles’ the temperature observed in

ASTM distillation experiment is converted into TBP data by

using Riazi – Daubert correlation , which is:

TBP= a(ASTM D-86)b

The values of coefficient a and b are taken as per table

mentioned earlier.We also observe that data for volumes 85-100

ml is not given in the observation table of Diesel. Due to

limitation of the thermometer, distillation was performed for

temperature not higher than 350 oC.

So, we use Riazi’s Distribution Model to extrapolate the data

obtained and get TBP data for 90, 95, 100 ml.

Plotting :

Y= C1 + C2.X

Where Y= ln[(Ti-To)/ To] ; X=lnln[1/(1-xi)]

Bt=1/ C2 ; At= Btexp(C1. Bt)

To = initial boiling point in K; Ti = temperature at which i

percent is distilled in K; xi = volume fraction of distillate.

16

The graph obtained is:

Using linear regression we get the straight line and hence the constants

Bt=1/ C2 = -3.0988883 ; At= Btexp(C1. Bt)= -52.27953 .

y = -0.2507x - 0.9118

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

-2.5 -2 -1.5 -1 -0.5 0 0.5 1

17

Diesel:

Initial Boiling Point obtained is around 498 K.

End Point obtained is around 666 K.

True Boiling Point Plot is as shown:

450

480

510

540

570

600

630

660

690

0 10 20 30 40 50 60 70 80 90 100

T

e

m

p

e

r

a

t

u

r

e

(

K)

Volume(ml)

Series1

18

Hexane:

Initial Boiling Point obtained is 336 K.

End Point obtained is around 370 K.

True Boiling Point Plot is as shown:

320

330

340

350

360

370

380

0 10 20 30 40 50 60 70 80 90 100

T

e

m

p

e

r

a

t

u

r

e

(K)

Volume (ml)

Series1

19

In the current economic climate, refineries face the heavy task of

improving the efficiency of individual units. The lack of crude oil

distillation data may result in wide swings in product qualities. The

single and most important laboratory analysis is true boiling point

distillation, which tends to separate individual mixtures sharply and thus

give a very good approximation of the expected separation. Obtaining

TBP data is costly and time consuming, however, requiring use of

expensive laboratory equipment. A single TBP distillation can take up to

48 hr, which makes it impractical for daily monitoring of refinery crude

quality. The Engler distillation (ASTM D-86) is a fast and low cost

method for measuring distillation characteristics of oils. It is performed

at atmospheric pressure, and for that reason the maximum temperature at

which the distillation is terminated is about 360o C. Hence, a full-range

distillation curve can be generated from an incomplete distillation data

set. Specifically, the full-range crude true boiling point (TBP) curve can

be generated from only the atmospheric part of the crude distillation

analysis.

An improvement in the speed of generating the full-range crude

TBP curve can be achieved by converting the ASTM D-86 distillation

data of the crude fraction into TBP and applying Riazi's boiling point

distribution model. With this approach, the crude oil curve TBP can be

20

generated in 45 min instead of the 48 hr typically necessary for crude oil

TBP analysis.

The method can be used in refineries that frequently run on

different crudes for generating the full crude oil TBP curve from the

simple and quick ASTM D-86 analysis of the distillation characteristics

of the crude fraction.

21

1.B.K. Bhaskara Rao, Modern Petroleum Refining Process , Department of

Chemical Engineering IIT Kharagpur.

2. Angel Nedelchev, Dicho Stratiev, Atanas Ivanov, Georgy Stoilov ,BOILING

POINT DISTRIBUTION OF CRUDE OILS BASED ON TBP AND ASTM D-86

DISTILLATION DATA, Lukoil Neftochim Bourgas – Chief Process Engineer

Department, 8104 Bourgas, Bulgaria

3. ASTM D86: Standard Test Method for Distillation of Petroleum Products at

Atmospheric Pressure.

4. Dr. Khalid Farhod Chasib Developed Equation for fitting ASTM Distillation

curves, Chemical Engineering Department - University of Technology.