Fractional Distillation of Indigenous Coal Tar

                       ZULIFQAR ALI DHAKAN*, MUHAMMED IBRAHIM PATHAN**,

              AND HAFEEZ-UR-REHMAN MEMON***

ABSTRACT

Pakistan being a developing country is facing difficulty in the supply of energy and utilization of industrial by products. At present a considerable foreign exchange has been spent on import of chemical based components of coal tar. The experimental studies were carried out for the fractional distillation of indigenous coal tar produced by Pakistan Steel Mills Karachi from carbonization of coal. For the present work, a 200 kg capacity distillation unit was constructed and operated at a temperature of 450°C. The distillation products obtained were included banzole, carbolic, creosote, anthracene oil and pitch. The quality and quantity of the products obtained were very much encouraging.

The rapid growth in industrialization has increased the use of natural resources available. The constant use of these natural resources has depleted them. Some of these natural resources e.g. oil and coal are expected to be depleted in the next 40-50 years. In view of this situation, the consumption of these natural resources should be minimized, finding alternatives, making efficient use of them and recycling the residue.

Coal tar is a mixture of many chemical compounds mostly aromatics, which vary widely in their composition. The coal tar is available in abundance in Pakistan as a by-product recovered during carbonization of coal in the coke oven batteries at Steel Mills, Karachi.

A few studies have been carried out for the development of methods regarding distillation/separation of chemical based coal tar components. In 1983, Memon and his colleagues' [1] produced a comprehensive report on feasibility of coal tar distillation plant. About 11 gallons of coal tar can be produced from one ton of carbonized coal. The precious products extracted from coal tar include phenol, naphthalene, anthracene oil and pitch. As these products are of considerable importance in terms of their wide application like manufacturing of perfumes, dyes, drugs, timber, fungi, termite, enamel and coating pipes, it is important to study the experimental process for maximum fractional distillation of indigenous coal tar.

Eysymontted et.al [2] developed a method for distillation/ separation of group components of coal tar from black coal, A sample of coa! tar weighing 300 grams was heated in a distillation flask at a pressure of 5.2 kPa and temperature up to 320 °C for the time period ranged between 2-4.5 hours. Naphthalene, anthracene, pyrene, acctonaphthalene and floranthene were reported as the distillation products at these temperatures and pressures.

Yu Qiching et.al [3] investigated the gasification of coal tar separation into five fractions between temperature range of 170-350°C. The composition was analyzed by GLC (Gas Liquid Chromatography) coupled with mass spectrometer, fluorescent spectrometry and liquid solid Chromatography. They have discovered about 200 compounds in distillates. Off which 77 were aromatic hydrocarbon, 48 species paraffin's, 31 species olefins, 29 species oxygen containing compounds, 12 species are nitrogen-containing compounds, while 3 species were sulfur containing compounds. A detailed chemical analysis of black coal tar was also carried out by Jastrzebsic, et. al. [4] by applying NMR.

spectroscopy. They have concluded that proposed analysis methods are suitable for analysis, quality assessment of liquid products and evaluation of influenced coking parameters.

A method of separating primary hydrocarbon from low temperature carbonization tar of Here Zovsk brown coal in conditions was developed by Platonov, et. al. [5]. They have made it possible to isolate concentration of tritarpenes, starenes, azolenes and tarpenes. The compounds obtained were analyzed using infrared and ultraviolet spectroscopy, mass spectroscopy and capillary chromatography.

Platonov, et. al., [6] investigated organic compounds in primary tar obtained from brown coal with the help of 1 0% solution of H₂SO₄ saturated with NaSO₄. The data obtained has shown that organic mass in brown coal tar is a complex material of aromatic, hydro-aromatic and heterocyclic compounds. The method developed has made it possible to obtained sub-fraction and separate compounds differing in molecular mass, structures and distribution of oxygen and nitrogen containing fractional group. At present the coal tar based chemicals are being imported in the country. It was with this objective in mind to extract precious organic chemicals from coal tar. The precious products that can be obtained from it include phenols, naphthalene oil, anthracene oil and pitch. As these products are of considerable importance in term of their wide range application, it was necessary to study the distillation of indigenous coal tar. The coal tar for this study was obtained from Steel Mills, Karachi and the experimental work was carried out in PCSIR Laboratory Complex, Karachi. The quality and the quantity of recovered products were very much encouraging.

2.  EXPERIMENTAL   APPARATUS   AND PROCEDURE

2.1         Apparatus

A coal tar distillation pilot plant as shown in Figure 1, was constructed and operated at PCSIR Laboratories Complex, Karachi and is explained well by Dhakan, [7]. Batch distillation was the process of separating specific quantity of a liquid mixture. Material was charged into reaction vessel and then brought to boiling temperature. The vapors were collected and condensed in a reservoir or receiving tank.

A vertical type distillation vessel was used for separation of fractions consisting of many parts. As can be seen in figure, it consists of a pot, inlet for feeding and out let for discharge, safety valve, thermocouples and vessel insulated with asbestos and plaster of Paris, clay and liquid binding refractory material along with supporting legs on floor. The reaction vessel was vertical type with the capacity of 200 Kg with 3.0-ft dia and 6.0 ft height, The material used for construction of these vessels was mild steel sheet of 1/4 " and 3/4 " thickness. The entire reaction vessel was insulated with asbestos rapes, plaster of Paris, fire clay and liquid binding refractory material. The inlet pipe dia was 2,0" and outlet dia was 1.0" for flue gases and 2.0" for vapors, which was fitted with pressure gauge and safety valve. A dial thermometer with flexible stainless steel steam readable upto 500°C was also fitted. The entire vessel was supported on four pipes. The reaction vessel was contacted to a recovery tank by piping network, which was served as natural air cooling condenser. Four-inch dia mild steel pipe of schedule 40 was connected with the reaction vessel at one end and other was connected with receiving tank at a distance of 10 ft. The receiving tank having dia of 1.6". height 2.0" and flat top and bottom was also vertical type with a capacity of 25 kg. Same material was used for construction of reaction vessel.

2.2 Procedure

Raw coal tar was feeded in an insulated distillation vessel. It was heated upto 450°C. Initially 100 kg of coal tar was poured into the distillation vessel designed capacity of which was 200 kg. The vessel was fixed in a furnace with the arrangement of exhaust gases outlet. Natural gas is burned with oxygen of air with the help of blower according to the calculated feed rate. However, 50% excess gas is consumed initially instead of theoretical calculation with the calorific value of 950 Btu/hr obtained from Sui Southern Gas Company (SSGC), Total time required for distillation of 100 kg was 8 hrs. The first fraction started to fall after 40 minutes of the firing of furnace and collected at 100°C which was water. The temperature was observed with the help of temperature recorder and thermocouple. Second fraction started to fall after 50 minutes of the first fraction. This fraction was obtained between 100 - 170°C and was continued upto 35 minutes. Third, fourth, fifth and sixth fractions were obtained at 171 - 230°C, 231 - 270^DC, 271 -320°C and 321 - 380°C during 35, 25, 50 and 45 minutes respectively. At 230°C soft pitch was obtained. The residue was hard pitch obtained at 380°C. All separated fractions were tested physically and in the light of physical properties. The fractions obtained were including benzole, carbolic, creosote, anthracene light oil and anthracene heavy oil and residue pitch with respect to their boiling temperatures

3. EXPERIMENTAL RESULTS

Thirty experimental runs were conducted. Each run was consisting of 100 kg of raw coal tar. The results reported here are the average of the ten runs (I st, 2nd, and 3rd batch

of Ten Test) as it is inconvenient to report all thirty runs. They are given in Tables 1-3, showing minimum and maximum percentage of the recovery of products. While Fig. 2 shows comparison of differint products of coal tar distillation obtained from 1st, 2nd and 3rd batch of Ten Tests (Average Value) at 100 kg feeding rate.

Benzole (light oil) was obtained at 100 - 170°C. The range of benzole production was between 1.510 kg-1.970 kg/100 kg of coal tar processed. The carbolic (middle oil) was obtained at 171-230ⁿC. Its amount of recovery was 0.138 kg/100 kg of coal tar processed. The creosote (heavy oil) was obtained at 231-270°C. The amount of recovery was 6.140 kg -11.950 kg/100 kg of coal tar processed. While anthracene (light oil) was obtained at 271-320°C. The amount of recovery was 7.780 kg/100 kgs of coal tar processed. The anthracene (heavy oil) was obtained between 321 -380°C. The quantity recovered was 21.57 kgs/ 100 kgs of coal tar processed. However, the pitch was obtained at 381-400°C. Its quantity recovered was 40.70-57.250 kgs per 100 kgs of coal tar processed.

The variation in the production of above chemicals was mainly due to the variation in ths rate because of variation in the natural gas supply line. There may be mixing of various products because the products were manually collected.

4. DISCUSSION

The light oils were obtained at 170°C. These are first crudely fractionated and agitated at low temperatures with concentrated H₂SO₄, neutralized with caustic soda and redistilled, furnishing, benzene C6H6, toluene C6H5CH3

TABLE 1 FRACTIONS OF COAL TAR DISTILLATION FROM "FIRST BATCH OF TEN TEST"

CARRIED OUT AT 100 kg.

TABLE 2. FRACTIONS OF COAL TAR DISTILLATION FROM "SECOND BATC OF TEN TESTS

CARRIED OUT AT 100 kg.

TABLE 3. FRACTIONS OF COAL TAR DISTILLATION FROM "THIRD BATC OF TEN TESTS

CARRIED OUT AT 100 kg.