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DETERMINATION

OF T H E Q U A L I T Y

OF T H E R E F I N E D P R O D U C T

AT THE E X I T OF THE E X T R A C T I O N

C O L U M N IN U N I T S

FOR THE S E L E C T I V E P U R I F I C A T I O N

OF OILS W I T H FURFURAL

(UDC 665.54) A. A. K y a z i m o v , a n d M. I . Y u r i n

Z. B. K h a l d e i ,

Yu. I. Khar'kovski/,

"Twelfth Meeting of the Communist Party of the Soviet Union" 13aku Plant, Oil Research and Design Institute "Neftekhimavtomat" Translated from Khimiya i Tektmologiya Topliv i Masel, No. i, pp. 24-26, January, 1965

In the selective purification of oils the undesirable components are extracted from the distillate in an extraction column. The refined product leaving the extraction column does not change in quality on its way through the other parts of the unit, which includes a regenerator for the solvent vapor from the refined product solution. Figure 1 shows a diagram of part of the unit used for the selective purification of oils with furfural in the "Twelfth Meeting of the Communist Party of the Soviet Union" Baku oil refinery. The refined product solution withdrawn from the top of the extraction column 1 enters the solution container 2, passes through the heat exchanger 3, the tubular furnace 4, the solvent regeneration column 5, re-enters the heat exchanger 3, and, finally, leaves the unit through the cooler 6. Refined product samples for analysis are taken only at the exit of cooler 3, which causes delays of 2.5-3.0 h in the adjustment of the oil purification process, since the operator cannot change the technological regime of the extraction column before he knows the results of the laboratory analysis. Since it takes about 1 h before the refined product quality at the extraction column exchange changes after transition to a new regime, it is clear that an incorrect action of the operator will cause the unit to produce a wrong product for 4 h. For this reason, the quality of the refined product should be determined directly in the refined product solution leaving the extraction column. In the plant the quality of the refined product is determined from the density. The furfural has to be evaporated from the solution sample taken at the extraction column exit before the density of the refined product can be determined; this evaporation takes much time; hence, direct determination of the density of the refined product leaving the extraction column is impossible. The furfural content in the refined product solution varies between 12 and 25%. Examining the possibility of determining the quality of the refined product directly in the refined product solution, we found that the refractive index of refined product solutions containing no more than 30 weight % furfural equals the refractive index of the pure refined product. To check whether the furfural concentration does not Solvent vapor affect the refractive index of refined product solutions, we artificially prepared samples of the refined product with a definite value of the refractive index and various furfural 6 concentrations.

Solven%[~ t Distillai~

2 ~

@

~

s" T Fig. 1. Diagram of the technological unit for the selective purification of oil with furfural,

The furfural content in the solution was determined from the weights of the refined product and the furfural added. Before determination of the refractive index of refined product solutions, the test tubes filled with the ground samples were placed in a water bath and heated at 70-80~ To achieve complete solution of fuffural in the refined product, the test tubes were shaken. Then, the refractive index of the refined product solution was measured in an IRF-22 refractometer. 29


TABLE I

Refractive index of the refined product solution

Furfural content in the refined product soln.

Refractive index of the refined product n 20 D 1.4920 1.4940 1.4942 1.4931 1.4911 1.4924 1,4959 1.4951

1.4921 1.4939 1.4941 1.4929 1.4909 1.4921 1.4958 1.4952

23.0 22.8 12.5 15.2 28.3 19.3 27.2 16.4

TABLE 2

Refractive index of the refined product solution 20

nD 1.4920 1.4938 1.4932 1.4920 1.4921 1.4931 1.4923 1.4909 1.4915 1.4911 1.4949 1.4946

Refractive index of the refined 9-0 product n D

Density of the refined product

1.4921 1.4936 1.4931 1.4918 1.4918 1.4931 1.4925 1.4911 1.4917 1.4913 1.4952 1.4945

0.9019 0.9032 0.9031 0.9014 0.9015 0.9036 0.9034 0.8994 0.9002 0.9013 0.9057 0.9050

Furfural content, weight

%

Density of the refined product found from the plot, Fig. 2

24.4 27.2 14.8 22.6 21.9 k

21.4 21.1 20.0 18.7 25.1 24.2

0.9013 0.9041 0.9032 0.9013 0.9014 0.9030 0.9029 0.8996 0.9005 0.9009 0.9058 0.9053

The measurements yielded the following values for the refractive index as a function of the furfural content in the refined product solutions. Refractive index nz0 D 1.4940 1.4942 1.4941 1.4940

............ ............ ............ ............

Furfural content, weight % 0.00 13.65 19.50 26.00

Table 1 gives the refractive index of solutions composed of various refined products and up to 30% furfural. Further tests were done in refined solution samples taken directly from the top of the extraction column. The refractive index was measured and furfural was driven out; then, the refractive index and the density of the refined and furfural-f~ee product were measured. The results of these tests are reported in Table 2. A linear relationship was found to exist between the refractive index and the density of the refined products produced by the unit e x a m i n e d (Fig. 2). The densities of the refined products obtained by expulsion of the furfural and the values read from the plot in Fig. 2 are also given in T a b l e 2. As is evident from the data in this table, the density can be quite satisfactorily determined by measuring the refractive index.

30


/,z~80

In laboratory practice all measurements of the refractive index of any oil product are reduced to a definite temperature by using the following formula

o o t

/

1,4970~

o

o

n~ = nb -- 9 q -- 20 ~

o

where c~ denotes the correction coefficient; for oils and fats this c o efficient equals 0.0004 per ~ t is the temperature of the m e a s u r e ment.

g,

o

t4gso~

The a p p l i c a b i l i t y of this formula for temperature corrections in the determination of the refractive index of refined product solutions was checked in the temperature range between 15 and 30~

o

I'~91~!~,,9~'~o,.,, o,9o2o

o,m6n

o,gzoo t

Density p ~ Fig. 2. Refractive index of the refined product as a function of the density. TABLE 3. Refractive Index 15 ~

20 ~

1.4922 1.4949 1.4959 1.5001 1.4950 1.4940 1.4971 1.4941

1.4910 1.4921 1.4928 1.4980

25 o 1.4892 1.4900 1.4908

1.4931 1.4920

1.4960 1.4910 1.4902

1.4950 1.4920

1.4929 1.4901

80 ~

1.4871 1.4881 1.4983 1.4939 1.4891 1.4880 1.4910

The measured data are reported in Table 3, From T a b l e 3, it is evident that the results obtained are in fair agreement with the above formula. The finding that the refined solution and the product obtained from this solution have the same refractive index m a y be explained as follows. The refined solution withdrawn from the top of the extraction column contains 12-25% furfural and is homogeneous at the t e m p e r ature of 105-115~ (the c r i t i c a l solution temperature). At the t e m perature at which the refractive index is determined (15-a0~ the refined solution is a heterogeneous system in which the furfural is finely dispersed ha the oil.

An oil layer forms on the surface of the prism of the IRF-22 refractometer when the refined solution is deposited for determination of 1.4883 the refractive index. The principle of this determination in an IRF-22 refractometer is that the l i m i t i n g refraction angle, viz., the angle at which the ray skims along the prism surface and is refracted into the oil layer formed, is measured in a thin layer of the product to be examined. CONCLUSIONS 1. It is shown that the quality of the refined product can be determined at the exit from the extraction c o l umn by measuring the refractive index of the refined solution in an IRF-22 type refractometer. 2. Determination of the product quality at the exit from the extraction column allows us better to control the extraction process in the unit.

31

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