Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF IMPREGNATING TYPE ELECTRODE PITCH"

Abstract

Preparation of impregnating type pitch by prefractionating the petroleum base having 100+ BMCI upto a temp. 250 deg C at ambient pressure and nitrogen purge rate , subjecting the said residual/modified/ processed feed in the presence of free radical initiator at a temp rise ranges of 1-4 deg C at a cascading temp of 280 - 350 deg C under ambient pressure & nitrogen purge for a period of 2 - 4 hrs.

Full Text

This invention relates to an improved process for the preparation of impregnating type electrode pitch. More specially this process is an improvement and further development of our earlier developed process disclosed in our copending patent application No. 692/DEL/94. I Pitch is a highly carbonaceous material which consists primarily of a complex mixture of Polynuclear Aromatic Hydrocarbons (PAHs) and their heterocyclic analogues. One of the industrially significant uses of pitch is as binder and impregnator in the manufacture of various carbon electrodes. The most important outlet for petroleum derived impregnating pitch is the graphite electrode industry where it is used to densify porous graphite electrodes and nipples through impregnation. Pitch impregnation also improves the mechanical strength of baked or graphitised electrodes and increased the electrical and thermal conductivity of final carbon/graphite product. Such high density graphite electrodes are the vital constitutent of ultra high power (UHP) arc furnaces used in the production of special alloys and stainless steel. Impregenation is carried out by placing baked carbon electrodes, which have 10-20% porosity, in vacuum chamber to open the mouths of the closed pores and then molten impregnating pitch is allowed to penetrate the electrode body under pressure. The impregnated carbon electrodes are rebaked for the conversion of pitch into coke and thereafter subjected to final graphitisation. Earlier, impregnating pitch used in the manufacture of graphite electrodes was processed from coal tar, which is a by-product of high temperature carbonisation of coal. ! Now the situation has changed because of declining coal oven capacity. Recent strict environmental regulations imposed by Environmental Protection Agency (EPA) on carcinogenic benzene emissions from coke ovens led to closures of several coke ovens in many advanced countries [L. Velasco, Pre[. ACS Div. Fuel Chem. 37(2) 590 (1992)] resulting in decline of coke ovens capacity and less availability of coal tar pitch for conversion into impregnating pitch. With the result petroleum impregnating pitches have : ,| come on to the scene a an alternate. Petroleum based impregnating pitch with satisfactory performance for industrial uses have been prepared by thermal soaking of aromatic rich feed stocks [Stokes et.al. Erdol Und Khole Erdgas Petrochemie, 38 31 (1985)]. Being a commercial product very limited information is available on pitch preparation methods in open literature, most of the informations are trade secretes of companies in the form of patents. Stepwise procedure reported in many patents is the distillation petroleum based feed stocks followed by thermal soaking [R.D. Archakova, USSR Patent Su 1, 383, 685; CA 107: 220359s (1987)]. Thermal soaking is usually carried out at 300 to 4200C temp, under atmosphere of nitrogen [Komine et al. Jpn Patent, JP 0302298; CA 115: 34285e (1991) i & G Dickakian, ACS Symp. Ser. 303 (1986); CA:104: 209650x (1986)] for the period of 10-12 hrs. In alternate procedures thermal soaking is carried out under pressure [L.V. Dolmatov, Solid Fuel Chem. 23(4) 109 (1989)] or reduced pressure [Turner et al? Fuel, 66 1481 (1987)]. But there are some major drawbacks in above mentioned procedures e.g. in former case, long thermal soaking period (10-12 hrs) make it more energy it consuming arid in later case precise temperature control and other of operational problems arising due to pressure assemblies. The main object of the present invention is to provide an improved process for the i p preparation of impregnating type electrode pitch which is commercially feasible, energy-efficient and time saving. The present modified process sharply cuts soaking period to about 2-3 hrs against the 10-12 hrs of our previously developed processes with almost same product yield and quality. The improved process is based on the basic understanding of chemical reactions taking place during the conversion of aromatic rich petroleum base feed stocks into pitch. The process of pitch formation is a controlled growth of aromatic clusters under the influence of temperature and time. The \ main :t reactions in the pitch formation are delakylation of aromatic structures and subsequent polymerisation through condensation. Keeping in view that thermal reactions are >ased on free radical mechanism [M.L. Poutsma, Energy & Fuels, 4 113 (1990)]. our present invention is related to addition of free radical initiator for enhancing the rate of polymerisation reactions and, in turn obtain quality product in much shorter jl time. i ; Although in similar type of studies for conversion of aromatic precursor into pitch, A1C13 was used as an additive [Mochida et al., Carbon 15, 9 & 239 (1977), Fuel Processing Technol. 3 207 (1980)] but use of organic free radical initiators proposed in the process of the present invention is more advantageous because due to the absence of metals .there is no chance of contamination and deterioration of product quality as these initiators gets converted into CO2 andH2O. The main advantage of the improved process of the present invention is a small thermal soaking period (1-3 hrs) which makes the process more energy and time efficient thus commercially more acceptable. The process of the present invention provides petroleum pitch of almost same quality in one fourth of the thermal soaking duration as compared to previously developed process without any change in other variables of process viz. heat treatment temperature and nitrogen purge rate etc. The present invention provides an improved process for the preparation of petroleum base impregnating pitch. The key element of which is the addition of free radical initiator in appropriate concentration during the thermal soaking step. Accordingly, the present invention provides an improved process for the preparation of impregnating type electrode pitch which comprises of prefractionating the petroleum base selected feed stocks having 100+ Bureau of Mines Correlation i| O Index (BMCI) value upto a temperature of 250 C under ambient i pressure and appropriate nitrogen purge rate in the range of 60-100 ml/minute, characterised in that subjecting the said o residual/modified/processed feed (250 C+) in the presence of free radical initiator at a temperature rise in the range of o 1-4 C/min at a cascading temperature in the range of 280 to o 350 C, under ambient pressure and nitrogen purge rate in the range of 100 ml to 1 lit/minute for a period of 2 to 4 hrs. The whole process comprises of two steps; first prefraction-ation of pyrolysis tar to upgrade the feed quality by .removing low boiling hydrocarbons, mostly aromatics through distillation due to their slow/little conversion into pitch1. The operating conditions of this step are same a,s disclosed in our pending application no 692 DEL94 namely the temperature 250xC, N2 purge rate 100 ml/min for 100 gm feeds and at atmospheric pressure. The residual portion which accounts for 78-80 wt% of starting material is termed as 'processed feed'/"modified feed' and is the starting material for second step. The second step is the thermal soaking of 'processed feed1 in presence of free radical initiators such as hydroperoxides, peroxides, peroxyacids, peroxyesters, diacyl peroxides and aza-arenes [M. Sato et al., 17th biennial conf. on Carbon, ACS, pp 326 ff(1985)]. The concentration of the initiator range from 1 to 5 wt%. Thermal soaking is carried out under very controlled conditions of temperature (1-40C/min rise) in a cascading modes from 250-3500C and well calibrated nitrogen gas purge rate (50-100 ml/min per 100 gm feed). The thermal soaking temperature was kept constant for the period of 2-3 hrs during which 'processed feed1 is converted into impregnating pitch of well defined properties. Heavy distillate is collected as by-product. Progress of conversion of feed into defined quality of pitch was carefully monitored by using 1H NMR spectroscopy. Notable features of this process are rigorous temperature control, thermal soaking duration, concentration, mode and temperature of addition of free radical initiators which governs the reaction kinetic and extent of condensation/polymerisation reaction resulting in pitch formation of desired quality. Additional advantage of the process of the present invention is that the two by-products viz. light and heavy distillates generated during prefractionation and thermal soaking steps respectively, are further utilizable. Light distillate being rich in naphthelene is a potential source of its production while heavy distillate having sufficiently high aromaticity and Bureau of Mines Correlation Index (BMCI = 125) a valuable feed for carbon black industry. The utilisation of by-product streams improves the process economics. The invention as described in details in the examples given below, which illustrate the process and should not be construed to limit the scope of the invention. Important properties of interest such as softening point and coking value of pitch, are also reported in respective examples. These properties are comparable with widely accepted A-240 petroleum pitch. In all the examples (except example 3) the feed used is pyrolysis tar. STEP I: Preffactionation (is common to all examples) The process parameters for prefractionation are: Temperature 2500C, N2 flow rate 100 ml/min for 100 gm feed Material Balance: Gas + loss l-2%wt; light distillate 18-20 %wt. Residue 78-80% wt (BMCI 154) STEP II: Thermal Soaking EXMAPLE-1 FEED: Residue of Step I + 0.9 wt% of benzyol peroxide PROCESS PARAMETERS: - Thermal soaking temp. 3400C - Temp, rise l-20C/min - Thermal soaking duration 3 hrs - Nitrogen purge rate 65 ml/min for 100 gm feed MATERIAL BALANCE: Gas + Loss, %wt 1.97 I Distilalte %wt 56.94 Pitch (residue) %wt 41.09 PRODUCT QUALITY: Softening ppint 0C 134 Coking value (CCR) %wt 46.52 EXMAPLE-2 FEED: Residue of Step I + 1.1 wt% of benzyol peroxide PROCESS PARAMETERS: - Thermal soaking temp. 3350C -Temp, rise l-30C/min - Thermal soaking duration 2 hrs 40 minutes - Nitrogen purge rate 60 ml/min for 100 gm feed . MATERIAL BALANCE: Gas + Loss %wt 2.62 Distilalte %wt 5604 Pitch (residue) %wt 41.34 PRODUCT QUALITY: Softening point 0C 130 Coking value (CCR) %wt 45.38 EXMAPLE-3 FEED: Residue of Step 1+1.5 wt% of benzyol peroxide PROCESS PARAMETERS: - Thermal soaking temp. - Temp, rise - Thermal soaking duration - Nitrogen purge rate MATERIAL BALANCE: Gas + Loss %wt Distilalte %wt 3340C l-30C/min 2 hrs 30 minutes 60 ml/min for 100 gm feed 0.50 52.86 Pitch (residue) %wt 46.62 PRODUCT QUALITY: Softening point 0C 120 Coking value (CCR) %wt 44.88 The advantages of this improved process are: 1. The raw material used in the process invention of the patent is a low value by-products of petrochemical plants with sufficient BMCI value > 120. 2. he process operates at ambient pressure and moderate temperature (3350C). Experimental set up is distillation assembly without any machine work. 3. The process of the present invention in more time and energy efficient to get the same product (impregnating pitch) yield and quality as compared to the process disclosed in our corresponding patent Application No. 692/DEL/94. 4. Other benefits of the process of the present invention are the utilisation of by-product streams for the manufacture of high value products namely naphthalene and high BMCI feed stock for carbon black industry. We claim: 1. An improved process for the preparation of impregnating type electrode pitch which comprises of prefractionating the petroleum base selected feed stocks having 100+ Bureau of Mines Correlation Index (BMCI) value upto a temperaturex of o 250 C under ambient pressure and appropriate nitrogen purge rate in the range of 60-100 ml/minute, characterised in that o subjecting the said residual/modified/processed feed (250 C+) in the presence of free radical initiator at a temperature o rise in the range of 1-4 C/min at a cascading temperature in o the range of 280 to 350 C, under ambient pressure and nitrogen purge rate in the range of 100 ml to 1 lit/minute for a period of 2 to 4 hrs. 2. An improved process as claimed in claim 1 wherein the petroleum base feed material used preferably has Bureau of Mines Correlation Index (BMCI) value in the range of 110 to 130. ^Wt/W^J 3. An improved process as ^clausee in claim 1 & 2 wherein the initiator used is selected from hydro-peroxides, peroxides, peroxy-acids, peroxy-esters di-aryl-peroxides and azo arenes. 4. An improved process for the preparation of impregnating type electrode pitch substantially as herein described with reference to the examples.

Documents:

498-del-1995-abstract.pdf

498-del-1995-claims.pdf

498-del-1995-correspondence-others.pdf

498-del-1995-correspondence-po.pdf

498-del-1995-description (complete).pdf

498-del-1995-form-1.pdf

498-del-1995-form-2.pdf

498-del-1995-form-4.pdf

498-del-1995-form-5.pdf

498-del-1995-form-6.pdf

498-del-1995-form-9.pdf