Title of Invention

A process for making impregnating pitch from FCC recycle stocks of waxy crudes.

Abstract

The present invention relates to a process for making impregnating pitch from FCC recycle stocks of waxy crudes. Process steps comprises; solvent extraction of waxy FCC recycle stocks using solvent such as NMP/furfural to prepare pitch feedstock by removing large amount of undesired paraffinic hydrocarbons at temperature gradient of 5 to 20°C to increase the Bureau of Mines Correlation Index (BMCI) to obtain aromatic rich extract, thermal soaking of the said aromatic rich extract at a temperature in the range of 350 to 450°C for a period more than 10 hrs in an inert atmosphere to get pitch suitable for graphite electrode impregnation.

Full Text

The present invention relates to a process for making impregnating pitch from FCC recycle stocks of waxy crudes. Pitch is a solid, fusible product of pyrolysis of organic compounds. It is a complex mixture of polynuclear aromatic hydrocarbons (PAHs) and their heterocyclic analogous. Pitch is an important raw material for the manufacture of carbon and graphite artifacts used in metallurgy, electrochemistry, and mechanical and electrical engineering. Some important examples are ultra high power (UHP) graphite electrodes for steel industry and high modulus carbon fibers for aerospace applications. Impregnating pitch, a special type of pitch, is a vital constituent for making low thermal expansion coefficient graphite electrodes. Graphite electrodes are fabricated by kneading calcined needle coke, after sizing with binder pitch, extruding as a cylinder of the paste, baking of the extruded material at 1000°C, impregnating with pitch, rebaking and finally graphitising at 3000°C. Impregnating pitches differ from binder pitches in respect of their low softening point and low quinoline insoluble (QI) matters. Impregnating pitches are used for increasing apparent density, mechanical strength and electrical conductivity of baked or graphitised carbon electrodes. As is well known to those skilled in the art, pitches are produced by thermal soaking of aromatic rich coal and petroleum based feedstocks (US patent 3,140, 248, July 7, 1964; US patent 3,510, 328 May 5, 1970; German patent 3,702, 720, Aug. 11, 1988). Currently, use of coal based feedstocks for making pitch has been decreasing slowly because of their inconsistent quality, inadequate availability and inferior impregnating characteristics. Coal tar is a byproduct of coal carbonization and is used for pitch making. In recent years, poor availability of coal tar is caused by closure of numerous coke ovens in many parts of the world as a result of stringent environmental regulations imposed by Environmental Protection Agency (EPA) on benzene emission from coking oven equipments (Velasco, Preps. Div. Fuel Chem. ACS 37(2) 590 (1992). Most common method for pitch making is thermal soaking of aromatic rich feedstock. Thermal soaking is generally carried out at temperature in the range of 350-500°C at atmospheric pressure in an inert atmosphere (US patent 4,080, 283, March 21, 1978). Main chemical reactions take place during thermal soaking are dealkylation of alkyl aromatics, aromatisation of hydroaromatics and polymerisation and condensation of aromatics. These reactions proceed via free radical mechanism under the influence of thermal energy. In addition, Dolmatov (Solid Fuel Chemistry, 23 109, 1989) describes thermal soaking under elevated pressure. However, elevated pressure conditions gives better yield but has some practical operational problems due to pressure assemblies. In addition, US patent 3,995, 014, Nov. 30, 1976 describes thermal soaking under reduced pressure. Although this process gives desired quality of pitch but it suffers lower yield due to more volatilisation of high boiling aromatic hydrocarbons. In addition Mochida et.al. (Carbon, 1_5 239 1997) describes use of A1C13 as a catalyst for polymerisation of aromatic hydrocarbons into pitch and finally into coke. However, removal of AlCl3 from pitch completely is very difficult, which deteriorates product quality. Further, AlCl3 is not recyclable also. In addition, US patent 2,884, 469, April 8, 1969 describes the use of HF/BF3 as a super Bronsted catalyst for making pitch at relatively lower temperature range i.e. 180- 300°C. However, this route produces a pitch having fluorine substituted aromatic hydrocarbons, resulting poor pitch quality. In addition an Indian patent 692/DEL/94, describes a process for making impregnating pitch from pyrolysis tar, a petrochemical by-product stream, generated during olefin production, according to this process pyrolysis tar was first prefractionated to remove low boiling aromatic hydrocarbons and then thermally soaked at the temperature in the range of 300-350°C at atmospheric pressure under continuous purging of nitrogen but these experimental conditions are not suitable for petroleum refinery based feedstocks particularly those which are rich is paraffins or waxes. All the above mentioned processes deals with thermal soaking of aromatic rich feedstocks under different operating conditions for making pitch. These processes are suitable for those feedstocks, having aromaticity more than 100 Bureau of Mines Correlation Index (BMCI) which are easy to convert into pitch. Conversion of waxy/paraffinic feedstocks into pitch by only thermal soaking is very difficult because paraffins first undergoes aromatistion which take large reaction period and then finally be converted into pitch. So from the practical point of view it is necessary to remove paraffins from the feed first and then thermal soak, to get a quality pitch. Keeping this in view, the present invention is designed which consist of two steps: first -preparation of aromatic rich high Bureau of Mines Correlation Index (BMCI) feedstock and second thermal soaking for making impregnating pitch. The primary object of the present invention is to provide a process for making impregnating pitch from Fludized Catalytic Cracking (FCC) recycle stocks of waxy crudes. Another object of the present invention is to provide a process for making impregating pitch from FCC recycle stocks which are rich in wax/paraffins and are not suitable for direct conversion into pitch. Still another object of the present invention is to provide a two step process for preparation of aromatic rich feedstock in first step and preparation of impregnating pitch in second step. The above objects accomplished by solvent extraction of waxy FCC recycle stocks using N-methyl pyrrolidone (NMP)/furfural as solvents followed by thermal soaking of aromatic rich portion at atmospheric pressure and under inert atmosphere. Accordingly the present invention provides a process for making impregnating pitch from Fluidized Catalytic Cracking (FCC) recycle stocks of waxy crudes which comprises; a) solvent extraction of waxy FCC recycle stocks using solvent such as herien described to prepare pitch feedstock by removing large amount of undesired paraffmic hydrocarbons in glass packed extraction column at temperature gradient of 5 to 20°C to increase the Bureau of Mines Correlation Index (BMCI) more than 50 and preferably more than 80 and most preferably more then 100 to obtain aromatic rich extract, b) thermal soaking of the said aromatic rich extract at a temperature in the range of 350 to 450°C for a period more than 10 hrs in an inert atmosphere at a nitrogen flow rate in the range of 200 to 800 ml/min. to get pitch suitable for graphite electrode impregnation. In an embodiment of the present invention feedstock may be obtained from fluid catalytic cracking (FCC) operation of petroleum refining and aromaticity of feedstock may be as low in the range of 30 to 60 BMCI. In another embodiment of the present invention solvent extraction of waxy feedstock may be carried out using N-methyl pyrrolidon (NMP) or furfural as solvent. In yet another embodiment of the present invention temperature gradient for solvent extraction may be taken in the range of about 5 to about 20°C and preferably in the range of about 10 to about 15 °C. In yet another embodiment of the present invention solvent to feed (S/F) ratio for solvent extraction may be taken in the range of about 0.5 to about 1.2 and preferably in the range of about 0.7 to about 1.0. In yet another embodiment of the present invention thermal soaking of aromatic rich portion may be performed at temperature in the range of about 350 to about 450°C and preferably in the range of about 370 to 430°C. In yet another embodiment of the present invention thermal soaking of aromatic rich portion obtained from solvent extraction may be carried out for a period more than 10 hrs. and preferably in the range of about 15 to about 80 hrs. In yet another embodiment of the present invention during thermal soaking inert gas purged may be such as nitrogen, helium or argon. In yet another embodiment of the present invention, inert gas flow rate may be in the range about 200 to about 800 ml/min and preferably in the range of about 300 to about 700 ml/min for 1000 gms of charged feedstock. To carryout the present process into effect, waxy feedstock (FCC recycle stock) is first subjected to solvent extraction to separate aromatics. Solvent extraction is brought into effect in a glass packed column of 2 meter height. Temperature gradient of column is kept in the range of about 5 to about 20°C. The operation mode is counter current as the solvent (NMP/mrfural) flows downward under gravity from top, while feedstock enters in the lower end of column by pumping. Solvent to feed (S/F) ratio is kept in the range of about 0.5 to about 1.2. After the equilibrium stage achieved in column, samples of aromatic rich portion collected, which after making solvent free is used as pitch feedstock for thermal soaking. Thermal soaking is carried out taking aromatic rich portion in a glass reactor consisting of two subsequent overhead water condensers followed by an ice cooled trap to collect maximum amount of condensable liquid from effluent gases generated at temperature in the range about 350 to about 450°C for a period of about 10 to about 80 hrs. under continuous purging of nitrogen at the ate of about 200 to about 800 ml/min Residual portion of thermal soaking was treated as pitch. Scientific explanation of each step of the present invention may be summarised as given below: As pitch is a complex mixture of highly polymerised aromatic hydrocarbons, pitch feedstock must contain sufficient amount of aromatics compounds. Aromatic structures, preferably of 3-5 membered rings are best suited due to their easy polymerisation and conversion into pitch. Paraffinic type hydrocarbons are undesirable due to their slow conversion into aromatics because a series of steps are involved like formation of alkenes, cyclisation of alkenes (Diels Alder reaction) and aromatisation. The whole sequence takes fairly large reaction period and is not of commercial importance. Keeping this basic chemistry in view it is appropriate to remove paraffinic type hydrocarbons from the feed before it is subjected to thermal soaking. Generally distillation scheme is used to remove paraffins from aromatics but as in present case where feedstock contains substantial amount of waxes, solvent extraction scheme is more advantageous. Solvent extraction is a physical separation based on interaction between aromatic and solvent molecules. During such separation no change in chemical structure occurs Thermal soaking is one of the important means for making pitch from aromatic feedstocks. During thermal soaking homolytic cleavage of C-C and C-H bond of hydrocarbon molecules take place which gives very reactive free radicals. Polymerisation and condensation of these free radicals leads to formation of large polynuclear aromatic hydrocarbons or pitch. The following examples are given by way of illustration of the present invention and should not be constructed to limit the scope of the present invention. EXAMPLES Example-1 : Preparation of pitch feedstock Pitch feedstock was prepared by solvent (NMP/furfural) extraction of FCC recycle stock in a glass packed column at a temperature gradient of 10°C (Top temp 65°C Bottom temp 55°C). solvent to feed (S/F) ratio was kept at 0.93 v/v. Yield of aromatic extract was 29.5 %wt with aromaticity of 108 BMCI. Example-2: Preparation of pitch feedstock Run was repeated under same condition except a temperature gradient of 12°C (Top temperature 65 and bottom temperature 53°C) and solvent to feed ratio was 0.84 v/v. Aromatic extract yield was 27.7 %wt with aromaticity of 116 BMCI. Example - 3 : Preparation of Impregnating Pitch Impregnation pitch was prepared by thermal soaking of aromatic extract (481.02 gms) in a glass reactor at 400°C for a period of 60 hrs. During entire experiment nitrogen gas was purged at the rate of 300 ml/min. The resulting pitch has softening point 112°C and coking value 51.30 %wt. Examplle-4 : Preparation of Impregnating Pitch In an another run 200.31 gm aromatic extract was charged in reactor and thermal soaked at 410°C under similar conditions for 36 hrs. A pitch of relatively low softening point 108 and coking value 44.75 %wt. was obtained. Example-5 : Preparation of Impregnating Pitch In an another run 200.8 gm aromatic extract was charged in glass reactor and thermally soaked at 390°C for 16 hrs and nitrogen flow rate was kept constant at 500 ml/min. A pitch of low softening point 70°C and low coking value 33.14 %wt was obtained. From the above experiments it is apparent that the process according to present invention is suitable for making quality impregnating pitch from waxy FCC recycle stocks which was not possible from prior art processes. The main advantages of the present invention are: 1. This invention provides a process for making impregnating pitch from waxy petroleum feedstocks. 2. This process provides a better utilisation of FCC recycle stocks which are presently used as a low value fuel oil blending component. 3. This process provides waxy reffinate as a by-product, which can be used as a source of recovery of good quality waxes. 4. This process provides waxy reffinate which can also be used as a recycle stock for producing improved quality middle distillates (Diesel fuel) 5. This process provides an another byproduct during thermal soaking which is a good quality carbon black feedstock. Claim: 1. A process for making impregnating pitch from Fluidized Catalytic Cracking (FCC) recycle stocks of waxy crudes which comprises; a) solvent extraction of waxy FCC recycle stocks using solvent such as herien described to prepare pitch feedstock by removing large amount of undesired paraffinic hydrocarbons in glass packed extraction column at temperature gradient of 5 to 20°C to increase the Bureau of Mines Correlation Index (BMCI) more than 50 and preferably more than 80 and most preferably more then 100 to obtain aromatic rich extract, b) thermal soaking of the said aromatic rich extract at a temperature in the range of 350 to 450°C for a period more than 10 hrs in an inert atmosphere at a nitrogen flow rate in the range of 200 to 800 ml/min. to get pitch suitable for graphite electrode impregnation. 2. A process as claimed in claim 1 wherein FCC recycle stock used is of aromaticity within the range of 30 to 60 BMCI. 3. A process as claimed in claims 1 to 2 wherein aromatic extraction is done by using N-methyl pyrrolidone (NMP) or furfural as solvent. 4. A process as claimed in claims 1 to 3 wherein temperature gradient used in solvent extraction is preferably within the range of 10 to 15°C. 5. A process as claimed in claims 1 to 4 wherein solvent to feed ratio (S/F) used in aromatic extraction is preferably within the range of 0.5 to 1.2. 6. A process as claimed in claims 1 to 5 wherein pitch feedstock used is of aromaticity preferably within the range of 100-116 BMCI. 7. A process as claimed in claims 1 to 6 wherein thermal soaking of aromatic extract is carried out preferably within the temperature range of 370 to 430°C. 8. A process as claimed in claims 1 to 7 wherein thermal soaking is carried out is an inert atmosphere using nitrogen, helium or argon gas. 9. A process as claimed in claims 1 to 8 inert gas flow rate is preferably within the range of 300 to 700 ml/min. 10. A process for making impregnating pitch from Fluidized Catalytic Cracking (FCC) recycle stocks of waxy crudes substantially as herein described with reference to the examples accompanying this specifications.

Documents:

3835-del-1998-abstract.pdf

3835-del-1998-claims.pdf

3835-del-1998-complete specification (granted).pdf

3835-del-1998-correspondence-others.pdf

3835-del-1998-correspondence-po.pdf

3835-del-1998-description (complete).pdf

3835-del-1998-form-1.pdf

3835-del-1998-form-19.pdf

3835-del-1998-form-2.pdf