FIELD
The present disclosure relates to a method of modifying coal-tars, more particularly it relates to a method of decreasing and/or modifying the quinoline insoluble content therein.
BACKGROUND
Coal tar is a valuable by product generated while processing coking coal into metallurgical coke in a coke oven plant. Coal tar accounts for around 2.4-3.6 wt.% of coke produced. The increase in production of steel is one of the factors that led to the increase in the production of coke. Many valuable products are recovered from coal tar such as benzene, toluene, xylene, naphthalene. The final product is the coal tar pitch (CTP) which has got high amount of polycyclic aromatic compounds. This can be used in the manufacturing of mesocarbon micro beads, needle coke, carbon foam and carbon fibres (for example, see patent literature 1 & 2 and non-patent literature 1 & 2). CTP can also be used in the production of impregnated pitches (pitches having very low QI content).
The solid content in the coal tar which is insoluble in quinoline is termed as quinoline insoluble or QI. This insoluble material exists as a colloidal dispersion of sub-micron to multi-micron spheres and sphere cluster. The presence of QI blocks the pores of the carbon electrodes and decreases the efficiency of the electrodes. The graphite properties such as flexural

strength, apparent density and electrical conductivity depend on nature of QI. In the mesosphere formation, sphere generation is delayed due to the presence of QI. The coal tar pitch having a low QI content is the most feasible source for the production of needle coke having low coefficient of thermal expansion. Hence, removal of QI is important for further utilisation of coal tar into valuable products.
Coal tar has very high viscosity at room temperature which makes it difficult to process the coal tar for subsequent use. There are two methods of viscosity reduction, by increasing the temperature and by adding solvent in the coal tar. The reduced viscosity of coal tar makes it easy in separating the QI content of coal tar. Extraction technique can be carried out with coal tar using solvents such as hexane, heptanes, cyclohexane, petroleum spirit, quinoline etc. QI free tar can be obtained by supercritical extraction at 250-300°C and at a pressure of 10-15 MPa and liquid extraction at 150-200°C. The extraction method is energy intensive hence; it is a very costly process. High QI content in coal tar also fetches lower margins to the plant when sold in the market. Hence, it is necessary to reduce the QI content as much as possible from the coal tar to get the better price in the market.
These are widely used techniques for the removal of QI content from coal tar. Gravitational settling can be carried out by using an appropriate solvent. The gravitational technique doesn’t require any power but it requires very longer periods of time and even separation is difficult because we can’t distinguish easily. Filtration is suitable technique for the removal of QI but

the major drawbacks are high temperature, pressure and every time the filter paper has to be changed. Continuous flow filtration technique can be used for producing solids free tar and concurrently the QI rich tar. Continuous flow filtration also results in membrane fouling. Addition of solvents can reduce the viscosity but in order to separate the QI, coal tar has to be heated up to 60-70 °C. The heating of coal tar incurs additional operation cost. Thus, a process is desired to separate QI from coal tar at low temperature, and low viscosity.
PRIOR ART:
Now, reference may be made to the following prior arts discussing state of the art techniques.
United States Patent US4029749 provides process is disclosed for manufacturing needle coke, which process involves the steps of comminuting a coal, dispersing it in a suitable solvent, subjecting the dispersion to hydrogenolysis liquefaction at 360-480°C and 1-150 kg/cm2 H2 pressure, distilling the resultant ashless coal solution at 250-600°C to remove impurities, and unreacted coal, and coking selected distillate fractions in a conventional coker.
United States Patent US4116815 provides a process for preparing needle coal pitch coke by mixing coal tar and/or coal tar pitch with aromatic and aliphatic solvents under atmospheric pressure and at temperatures between

15° C and 140° C. The mixing ratio of the aromatic and aliphatic solvents and their quantities of addition to coal tar and/or coal tar pitch are adjusted so that insoluble substances precipitate in a zone selected from the group consisting of a slurry zone and a crystal zone. By distilling a supernatant solution obtained by separating the insoluble substances occurring in the slurry or crystal zone, hydrocarbons consisting substantially of aromatic compounds and free of the insoluble substances are obtained. The obtained hydrocarbons are processed into coke.
United States Patent US4259171 provides that Quinoline-insoluble components are separated from coal tar pitch by treating the coal tar pitch which has a softening point of greater than 60° C. (according to the method of Kraemer-Sarnow) with a solvent mixture comprising at least one solvent with paraffinic characteristics and at least one tar solvent, wherein the treatment is carried out at a temperature in the range of 200° to 270° C.
United States Patent US4436615 provides a process for removing solids from coal tar for the preparation of a coal tar pitch containing liquid comprising (1) centrifuging the coal tar at a suitable viscosity to separate a large particle size solids fraction from a first liquid fraction containing pitch and small particle size solids, and (2) filtering the large particle size fraction while maintaining the solids fraction at a suitable viscosity to thereby produce a second pitch containing liquid fraction which is substantially free of solids, and a densified readily handleable large particle size solid material. The liquid

fractions are useful for making electrodes, needle coke or carbon fibers whereas the densified solid material is readily utilized.
OBJECTS DISCLOSURE
The objective of the present disclosure is to provide a process for reducing
QI or Quinoline insoluble content in coal tar.
Another objective is to achieve low viscosity for coal tar in the
aforementioned process.
Another objective is to achieve the aforementioned process at low cost.
Another objective is to achieve the aforementioned process at low or room
temperature.
SUMMARY
The present disclosure relates to a process for reducing QI or Quinoline insoluble content in coal tar. The process includes mixing the coal tar and a wash oil in ratio 2:1 - 20:1 to obtain a mixture; heating the mixture at 50-100 degree Celsius or adding toluene in the mixture in 1 - 30% ratio of the wash oil by volume; centrifuging the mixture to separate QI from the coal tar; and decanting the coal tar.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this disclosure will be more apparent from the ensuing description when read in conjunction with the accompanying drawings of the exemplary embodiments and wherein:

Figure 1 shows: A process 100 for reducing QI or Quinoline insoluble content in coal tar in accordance with an embodiment of the present disclosure.
Figure 2 shows: Percentage QI variation with different coal tar to wash oil (SWO) ratio.
The figure(s) depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT DISCLOSURE WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
The present disclosure, now be described more specifically with reference to the following specification.
It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various

arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
The present disclosure provides a process of producing low quinoline insoluble (QI) content coal tar by mixing wash oil (discarded by coke by-product plant) in it, centrifuging it at above room temperature, separating the supernatant liquid and measuring the QI content in supernatant liquid. In the present disclosure, wash oil is taken from the coke by-product plant. The by-product plant discards the wash oil after using it for sufficient number of time in the process. The coal tar is also taken from the coke by-product plant, being one of the by-products from the coke plant. The coal tar thus produced contains QI particles and also has high viscosity, which makes it difficult to use in the subsequent process. The present disclosure provides the aforementioned process for reducing QI content in coal tar.

These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
Coke oven plant produces coke oven gas when carbonizing the coal samples to coke. This coke oven gas contains impurities such as coal tar, naphthalene, ammonia, hydrogen sulphide and BTX etc. The naphthalene is removed by scrubbing the coke oven gas with wash oil. This absorbed naphthalene is stripped by steam in a stripper and wash oil is recycled back to scrubber. The recycled wash oil decreases its absorption property after some time and hence, it is discarded. The discarded wash oil is called spent wash oil (SWO) and it cannot be used anywhere.
In the coke oven plant, coal blend sample is converted to cake by stamping with the help of hammer in the stamping machine. The cake formed is charged in the coke oven battery and kept inside the battery for long hours till the carbonization is completed. The volatile matter comes out from the oven during the carbonization makes the coke oven (termed as CO) gas. The coke oven gas contains hydrogen (50-55 wt.%) and methane (20-25 wt. %) on dry basis. The CO gas also contains many impurities such as coal tar, hydrogen sulphide, ammonia, BTX, naphthalene etc. These impurities are

removed one by one in a by-product plant. The naphthalene is removed using wash oil by combination of scrubber and stripper. The wash oil is sprayed on ascending CO gas. The wash oil absorbs the naphthalene from the CO gas. The rich liquid (containing naphthalene in wash oil) is again sprayed in stripper and interacts with ascending steam. The steam strips the naphthalene and the lean wash oil is recycled back to scrubber.
At certain point of time the wash oil is discarded from the plant. This discarded wash oil is called spent wash oil (SWO). The by-product plant cannot use the SWO anymore. This SWO has got no use except burning. At the same time coal tar is also removed from the CO gas which has high QI content and also high viscosity. In an embodiment, the SWO is used for viscosity and QI reduction of the coal tar. The SWO is mixed with coal tar in different ratio and heated at different temperature. The viscosity of the mixture is determined by the viscometer. The said mixture is then put into centrifuge to get the separation of QI particles from the coal tar. The supernatant liquid contains less QI than feed coal tar.
The present disclosure provides a process 100 to use the wash oil for coal tar QI reduction. In alternative embodiment, the wash oil can be spent wash oil. The proposed process 100 flow diagram is presented in the Figure 1. As per Figure 1, at step 102 the process 100 includes mixing the coal tar and wash oil to obtain a mixture. The coal tar having high QI content was taken for the study and it was mixed with the wash oil in mixer in different proportions. In the mixer, the coal tar and SWO were mixed thoroughly to

make the sample homogenous. Here, SWO was mixed in different proportions. At step 104 of the process 100, the said mixture is heated at different temperatures in the heater to observe the viscosity reduction. The increased temperature reduces the viscosity. At step 106 of the process, the heated mixture is fed to centrifuge, which rotates at high RPM. The rpm and the time were varied in the centrifuge to get the optimum separation. The QI particles were separated in the centrifuge because of the force applied during the operation. Further, at step 108 of the process 100 includes decanting the coal tar, wherein the coal tar containing low QI is separated from the QI particles in a separation unit. The separation unit separates the low QI content coal tar from QI particles.
The disclosure further provides that the process 100 is performed at room temperature. In case of using SWO, heating of the coal tar and SWO mixed sample is done at 60-70 °C as per Figure 1. The heating of the sample increases cost of the production. So, second solvent, for example toluene, is added in small quantity to do experiments at room temperature. The maximum drop in viscosity was achieved with toluene. So, toluene was mixed as second solvent in 1% to 30% concentration in the coal tar and SWO mixture. It was found that just 2% addition of toluene gave better results at room temperature condition.
The present disclosure provide solution for problems existing traditionally. First problem is to identify the solution for wash oil discarded in the plant. Second problem is the high QI content in the coal tar produced from the by-

product plant. The coal tar and these wash oils were mixed in different proportions one by one and tested for viscosity. The wash oil mixing ratio was optimized. The wash oil gave the better results compare to other wash oils. The wash oil was mixed in the coal tar at optimum ratio and then the mixture was heated to 60-70 °C and centrifuging was done. The supernatant liquid was separated from the settled particles. The QI was determined for supernatant liquid. The feed coal tar QI content was reduced by more than 50%. These processes were done at high temperature, which had additional cost. In order to reduce the temperature, second solvent, i.e. toulene was added for better QI separation at room temperature. The ratio of second solvent addition was also optimized. The SWO and toluene were added in coal tar in optimum condition and then processed in centrifuge as mentioned above. The supernatant liquid was separated and QI was determined.
An exemplary analysis based on the process 100 will now be explained with reference to Tables 1-3 and Figure 2 as described in the foregoing description.

In an example, the coal tar and the wash oil are analysed and characterized. Table 1 shows properties of the coal tar, and Table 2 shows properties of the wash oil. As evident from Table 1 and Table 2, the kinematic viscosity of coal tar at 35 °C was 103.5 cSt and 14.5, 12.9 and 8.7 cSt for fresh, recycle and spent wash oil respectively. The viscosity of coal tar and three (3) wash oils were measured at different temperatures. Maximum drop in viscosity was found between 60-70 °C. The coal tar viscosity dropped from l03.5 cSt to 25 cSt.
The wash oils viscosity was dropped from 14.5, 12.9 and 8.7 cSt to 7.5, 6.7, and 5 for fresh, recycle and spent wash oil respectively. Spent wash oil was mixed with coal tar in different proportion ranging from 2:1 to 20:1 (where first part is coal tar and second part is solvent) more preferably between 6:1 to 12:1. This mixture of coal tar and solvent was heated to 60- 70 °C since maximum drop in viscosity was occurred at this temperature. This was then put into centrifuge to separate the coal tar having low QI and QI particles. The centrifugation time was varied from 1 min to 10 min and more preferably between 3 min to 7 min. The centrifuge RPM was varied from 1000 to 5000 more preferably between 4000 and 5000. The supernatant liquid is taken out after the centrifugation and sent for QI determination. The coal tar taken for the study was having 3.07% QI content. The results are presented in Figure 2. The QI content in the supernatant liquid was less than one in most of the ratios till 10:1 after that it increased close to 1.5.

Further in an example, in order to operate at low temperature or at room temperature, the second solvent (toluene) was added along with spent wash oil (SWO) in the coal tar. The percentage of toluene was varied from 1 to 30% and more preferably from 1 to 5%. For example, in 6:1 coal tar to solvent ratio; first part is coal tar and second part is mixed solvent. In the mixed solvent, toluene content was varied from 1 to 30%. So, 5% toluene means, the mixed solvent contains 95% SWO and 5% toluene. The SWO and toluene in desired ratio was mixed in the coal tar. This mixture is then centrifuged at rpm between 4000 and 5000 for 2 to 7 min. The supernatant liquid is poured separately and QI content is determined. The QI results for three different ratios is shown in the Table 3. The QI was reduced to less than one for 10:1 coal tar to mixed solvent ratio having 2% toluene. The coal tar QI was reduced more than fifty percentage using SWO. This way the spent wash oil could be used in the coal tar QI reduction. The addition of SWO in coal tar has many advantages apart from QI reduction such as reduction in viscosity of coal tar, reduction of steam consumption for coal tar heating, and decrease in pumping cost.
It is to be noted that the present disclosure is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this disclosure are intended to be within the scope of the present disclosure, which is further set forth under the following claims.

WE CLAIM:
1. A process (100) for reducing QI or Quinoline insoluble content in a
coal tar, the process comprising steps of:
mixing the coal tar and a wash oil in ratio 2:1 - 20:1 to obtain a mixture;
heating the mixture at 50-100 degree Celsius or adding toluene in the mixture in 1 - 30% ratio of the wash oil by volume;
centrifuging the mixture to separate QI from the coal tar; and decanting the coal tar.
2. The process (100) as claimed in claim 1, wherein the wash oil is a solvent from coke by-product plant.
3. The process (100) as claimed in claim 1, wherein the addition of toluene to the mixture enables the process (100) to be carried out at low or room temperature.
4. The process (100) as claimed in claim 1, wherein the coal tar has a density (@30 degree Celsius) of approx. 1.2 g/cc, kinematic viscosity (@35 degree Celsius) of approx. 103.5 cSt, carbon (in wt.%) approx. 92.19, hydrogen (in wt.%) approx. 5.131, nitrogen (in wt.%) approx. 1.7, sulphur (in wt.%) approx. 0.989.

5. The process (100) as claimed in claim 1, wherein the wash oil has density (30 degree Celsius) of approx. 0.9506 g/cc, kinematic viscosity (35 degree Celsius) of approx. 8.7cSt, initial boiling point (IBP) - 158 degree C, final boiling point (FBP) >200° C, carbon (in wt.%) approx. 83.14, sulphur (in wt.%) approx. 1.815, hydrogen (in wt.%) approx. 12.115, nitrogen (in wt.%) approx. 0.42, mean relative Molecular mass (in wt.%) approx. 475.
6. The process (100) as claimed in claim 1, wherein the mixture is centrifuged between 1000 to 5000 rpm.
7. The process (100) as claimed in claim 1, wherein the mixture is centrifuged for 1 to 7 min.