|Title of Invention||
"A PROCESS FOR THE PREPARATION OF PETROLEUM PITCH FROM PETROLEUM REFINERY EXTRA VACUUM RESIDUE
|Abstract||The present invention provides a process for the preparation of petroleum pitch from petroleum refinery "extra vacuum residue". To carry out the present process into effect extra vacuum residue was made asphaltene free to prepare pitch feedstock. Asphaltenes were precipitated form extra vacuum residue (EVR) by addition of n-pentane, n-hexane, n-heptane and mixtures thereof at dilution ratio in the range of 30 to 60 ml of solvent/gm of EVR. This mixture was subjected to Soxhlet extraction for 50 to 60 hrs and then allowed to rest at ambient temperature for 24 hours. Asphaltene were recovered as a solid phase from Whatman thimble and washed several times with fresh solvent. The asphaltene free oil was made solvent free by distillation and stripping and used as feed for making pitch. Pitch was prepared by thermal soaking of asphaltenes free oil.|
|Full Text||Field of invention
The present invention relates to a process for the preparation of petroleum pitch from petroleum refinery extra vacuum residue. More particularly, the present invention relates to a process for the preparation of high quality petroleum pitch by the combination of deasphalting and thermal soaking of petroleum refinery extra vacuum residue.
Background of the invention
Pitch is a black colored solid. Chemically, it is a complex mixture of poly - nuclear aromatic hydrocarbons (PAHs) and their heterocyclic analogues. Some times aliphatic side chains are also attached to aromatic molecules depending on feed source. The molecular weight distribution (MWD) of pitch ranges from 300 to 3000.
Pitch is an important raw material for making a wide variety of industrial carbon materials. In graphite electrode industry pitches are used as 'binder' and 'impregnator'. Binder pitches are generally coal derived. 'Petroleum pitches' are mainly used as 'Impregnating Pitch'. Petroleum derived impregnating pitches have special properties such as low softening point, low Quinoline Insolubles (Ql) and high coking value and are in high demand as compared to coal derived pitches. In recent years, the use of petroleum pitches for making carbon fibers, activated carbon spheres, carbon foam, mesocarbon microbeads, needle coke etc has gained considerable commercial acceptance also.
Originally, pitches were prepared from coal tar, a by-product of coke ovens. Recently, very stringent environment regulations have a lot of pressures on coke oven operators either to improve existing coking technology or to close the coking units because there is a lot of emissions of carcinogenic substances. With the result, coal tar supply became inadequate for making pitches. Further, many times quality of coal-derived pitches is not on specs. Therefore, pitch producers are looking for alternate sources of coal tar. Petroleum derived feedstocks offer a good alternate to coal tar for making pitches. Some other advantages of petroleum derived pitches are, they are better pitches - being very low or almost zero in Ql -as compared to coal tar pitches, consistent in quality and environmentally relatively more safe. Low level of quinoline insolubles in petroleum pitch make them ideal for impregnation purpose. Besides these advantages petroleum pitches also have some paraffinic type hydrocarbons, which are easy to stabilize during processing
of carbon fibers. Petroleum pitch particularly has a high market value and can be worth from 3 to 5 times the value of its feedstock component.
Generally, heavy aromatic oils (HAOs) are used for making pitch, which are the byproducts of petroleum refining, petrochemical manufacturing and coal coke production (C.A. Stockes and V.J. Guercio; Erdol und Kohle - Erdgas - Petrochemie 38(1) 31 (1985). These HAOs have high carbon contents - due to presence of polynuclear aromatics such as naphthalenes, anthracenes, chrysenes and pyrenes - and are good feedstocks for making pitches. Some major sources of heavy aromatic oils are: Clarified oils from Fluid Catalytic Cracking (FCC) of gas oils, Pyrolysis tars from steam cracking of naphtha and gas Oils, Aromatic extracts from lube refining. These feedstocks are generally boiling in the range of 125 - 540°C, The prime requirement for suitability of feedstock for making pitches is it should be quite aromatic and free from hetro-atoms. From economic point of view feedstocks containing more than 70wt% of 350°C+ boiling materials are preferred. These two characteristics in combination lead to high coke yield of petroleum pitches during product making. In petroleum refining, a vacuum residue is obtained during vacuum distillation of crude oil and contains enough amounts of 350°C+ materials. In recent years there is an enormous interest in further utilization of low value petroleum refinery residues to upgrade them into high value products. This is also a need of the hour because petroleum refineries will have to deal with much heavier crudes and deeper distillation in the future decades.
According to current refinery practice 'vacuum residue' obtained from vacuum distillation unit (VDU) is further processed in various petroleum refinery processes. For example, in lube refinery, it is used for making high viscosity lube base oils called as 'bright stocks'. For making bright stocks, vacuum residue is subjected to first propane de-asphalting followed by solvent extraction, solvent dewaxing and hydro-finishing (Lubricating Oils 1 : Manufacturing Processes by A . Sequeira, Jr. in Encyclopedia of Chemical Processing and Design, John. J. McKetta(Ed.) Page 347-375 Vol.28 Year 1988). Asphalt, which is produced as by-product of propane de-asphalting is mainly used for making paving grade bitumen or roofing or specialty coatings (US 6,048,447, April 2000; US 6,296,912, October 2001).
In fuel refinery, 'vacuum residue' is sent to Visbreaking', a relatively inexpensive and mild thermal cracking process. The visbreaking (US 5,925,236, July 1999) produces gas, gasoline, middle distillates and stable fuel oil or fuel oil components, lower in viscosity than the feed. Visbreaking is employed to increase refinery distillates yield by converting residue and/or by reducing volume of expensive cutter stock needed for fuel oil blending. Moreover, the use of these residues as fuel oil has been inhibited because of sulphur, which is normally high in petroleum feedstocks, producing sulphurous acid gas resulting in atmospheric pollution. Hence, the market of fuel oil is shrinking.
Alternately, vacuum residue is subjected to delayed coking (US 6,048,448, April 2000) - a severe thermal cracking process - to produce gas, gasoline, and middle distillates. This process essentially rejects metals and residual carbon (as coke) completely and concentrates them in coke. In this process coke is produced as by-product. This coke is generally of low value, which goes to thermal power stations. Since the 'Vacuum residue' contains substantial amount of asphaltenes (polynuclear aromatics embedded with hetroatoms) the products obtained from vacuum residues are of inferior quality for blending with straight run products like gasoline, kerosene and middle distillates.
Recently, some of the petroleum refineries have installed the short path distillation facility to recover more distillates (upto 50%) from vacuum residues. The residue of short path distillation, which is termed as extra vacuum residue (EVR) still contains some high boiling valuable oil components.
The main limitation of upgradation of vacuum residue or extra vacuum residue is the presence of asphaltenes. During upgrading process of residues, asphaltenes form sludge due to their flocculation, which reduces the flow and plug down stream separators, exchangers and towers. They are also bad actors in poisoning and reducing the activity of cracking catalyst with their high hetero-atoms contents, trace metals and high tendency to coke formation. Thus, upgradation of vacuum residue through catalytic processes is not possible due to poisoning of precious metal containing catalyst. During thermal process asphaltenes progressively aggregates and polymerize to large units called asphaltenes cores. These asphaltenes core then further polymerizes and lead to formation of less valuable macroscopic coke.
Petroleum asphaltenes are n- pentane or n- heptane insolubles organic material of crude oil or the bottom from a vacuum still. These are the heaviest fraction of crude oil. The amount and structure of asphaltenes are source dependent. The asphaltenes are highly polar, high molecular weight compounds and consist of highly condensed aromatic ring system with nitrogen, sulfur, oxygen and metal contents. Asphaltenes are precipitated in low molecular weight aliphatic hydrocarbons like propane, n-butane, n-pentane, n-hexane and n-heptane and appear as dark brown or black solid. The structure of asphaltenes may be defined as a loose network of condensed poly nuclear aromatic flat sheets and saturated chains, and these sheets are loosely held together by n - n bonds with a dissociation energy of about 58 KJ Mol-1. Since, asphaltenes are the main source of hetro-atoms and metals (Ni & V) their up-gradation into value added transportation fuel is not possible by catalytic route. Further, conversion of vacuum residue into high value graphite products - by non-catalytic route is also not possible, because presence of hetro-atoms and metals in asphaltenes causes hindrance in the growth of mesophase formation and will create defect in graphitic structure. Thus, for the upgradation of residues it is essential to get rid of asphaltenes.
In the prior art in US patent No 4,518,483, May 21, 1985 a process has been disclosed for making pitch from aromatic asphaltenes fractions of steam cracker tar, cat cracker tar and coal tar. The asphaltenes fraction present in the tars is primarily aromatic in nature and is composed of 7 or more polynuclear aromatic rings. These have high coking components and thus it is good starting materials for making pitch. However, asphaltenes present in the vacuum residue or extra vacuum residue are of different nature from naphtha cracker bottom, cat cracker bottom, coal tar etc. Asphaltenes present in the vacuum residue or extra vacuum residue are composed of polynuclear aromatics linked by polymethylene bridges many containing hetro-atoms and are undesirable molecules for making pitches, mesophase pitch and graphite articles.
Keeping the above situation in view this process was developed to prepare a high quality, zero Ql petroleum pitch by using high boiling components boiling above 650°C obtained from extra vacuum residue (EVR) of extra high vacuum distillation of vacuum residues.
In the prior art, pitches are produced by 'thermal soaking' of aromatic rich petroleum derived feedstocks (US 4,080,293, March 1978). In case of feedstock, which are not rich or lean in
aromatics 'solvent extraction' is coupled before 'thermal soaking' (US 3,140,248, July 1964; US 4,271,006, June 1981). Some times, rate of polymerization and condensation reactions that take place during 'thermal soaking' are promoted by adding some reactions promoters like AICI3, CuCI2, ZnCI2, HF3/BF3 (Carbon, 15 39 (1997); US 415,494,567; US 2,884,469).
The present invention provides a new feed stock and a novel route for making petroleum derived pitches from 'Extra Vacuum Residue' obtained from petroleum refinery. Before this invention no one used components of 'Extra Vacuum Residue' boiling above 650 °C to make pitches. The present invention is a combination of de-asphalting and thermal soaking for making zero Ql petroleum pitch.
Objectives of the invention
The main object of the present invention is to provide a process for the preparation of petroleum pitch from petroleum refinery "extra vacuum residue".
Another object of the present invention is to provide a process for making zero Ql petroleum pitch from extra vacuum residue which provides an efficient utilization of second heaviest part of the crude oil for making petroleum pitch.
Yet another object of the present invention is to provide a process for making petroleum pitch, which can be used either as impregnating pitch for graphite electrodes or as precursor for making advance carbon materials such as carbon fibers, activated carbon spheres or needle coke.
Still another object of the invention is the precipitation of asphaltenes from extra vacuum residue followed by 'thermal soaking' of asphaltenes free oil at atmospheric pressure and under inert atmosphere.
Summary of the invention
Accordingly the present invention provides a process for making petroleum pitch from extra vacuum residue which comprises 'precipitation of asphaltenes' from extra vacuum residue(boiling above 650°C) by using n-pentane, n-hexane, n-heptane and mixtures thereof as solvent by soxhlet extraction, in a solvent-to-feed ratio in the range of 5 to 60 and preferably 10 to 50 and 'thermal soaking' of asphaltenes free oil in absence or presence of organic catalyst in the range of 1 to 7% preferably 2 to 3% at a temperature in the range
of about 320 to about 450 °C preferably from 370 to 425 °C for a period of 6 to 20 hrs, preferably in the range of 9 to 16 hrs in the atmosphere of non oxidizing gas at a flow rate in the range of 250 to 800 ml/ min and preferably in the range of 300 to 700 ml/min.
In an embodiment of the present invention feedstock for pitch may be obtained as residue from extra vacuum distillation in petroleum refining.
In another embodiment of the present invention asphaltene precipitation from extra vacuum residue may be carried out using n-pentane, n-hexane, n-heptane or mixtures thereof as solvent.
In yet another embodiment of the present invention solvent-to-feed (S/F) ratio for asphaltene precipitation may be taken in the range of 5 to 60 and preferably 10 to 50.
In yet another embodiment of the present invention thermal soaking of asphaltene free oil may be carried out at a temperature in the range of 320 to 450 °C, preferably at 370-425 °C.
In yet another embodiment of the present invention thermal soaking of asphaltene free oil may be carried out for a period of 6 to 20 hrs, preferably for a period of 9 to 16 hrs.
In yet another embodiment of the present invention thermal soaking may also be carried out in presence of organic catalyst such as peroxides, hydro-peroxides, peroxy-acids, peroxy esters, and di-aryl peroxides in concentration in the range of 1 to 7 wt% preferably 2 to 3 wt%.
In yet another embodiment of the present invention during entire thermal soaking step inert gas such as nitrogen, helium or argon may be purged.
In still another embodiment inert gas flow rate may be in the range of 200 to 800 ml/min and preferably in the range of 300 to 700 ml/min.
Detailed description of the invention
In the present invention extra vacuum residue obtained from a commercial unit was used as pitch feed stock. This extra vacuum residue contains some hydrocarbons boiling above 650°C and asphaltic materials. To carry out the present process into effect extra vacuum residue was made asphaltene free to prepare pitch feedstock. Asphaltenes were precipitated form extra vacuum residue (EVR) by addition of n-pentane, n-hexane, n-heptane and mixtures thereof at dilution ratio in the range of 30 to 60 ml of solvent/gm of
EVR. This mixture was subjected to Soxhlet extraction for 50 to 60 hrs and then allowed to rest at ambient temperature for 24 hours. Asphaltene were recovered as a solid phase from Whatman thimble and washed several times with fresh solvent. The asphaltene free oil was made solvent free by distillation and stripping and used as feed for making pitch.
Pitch was prepared by thermal soaking of asphaltenes free oil. Thermal-soaking experiment was carried out at atmospheric pressure. During entire thermal soaking operation, a continuous stream of nitrogen gas was purged in the feedstock for sweeping-off low boiling hydrocarbons, to keep reaction atmosphere inert and to provide sufficient agitation in the reaction mixture. Thermal soaking temperature was monitored carefully throughout the experimental runs within the accuracy of ± 1°C. For thermal soaking run, asphaltene free oil was charged in the reactor and heated at a rate 10°C/minute till the final temperature is achieved. At this point- considered to be zero time - gas purging (N2) was started at a constant flow rate. Thermal soaking was continued for a period required for getting pitch of desired softening point and other key characteristics. At the end of run residual mass was used as 'pitch'. Characterization of feedstocks and pitches were carried out following standard ASTM/IP/BIS test procedures. Properties of extra vacuum residue are given in
The following examples are given by the way of illustration and therefore should not be construed to limit the scope of the present invention
EXAMPLE -1 PREPARATION OF PITCH FEEDSTOCK
Pitch feedstock was prepared by precipitation of asphaltenes from extra vacuum residue using n-pentane as solvent in solvent-to-feed ratio 40. The other operational conditions are given in Table-2 The yield of asphaltene free oil is 59.20. Some other properties of the same are given in Table- 3.
(Table Removed) OF PETROLEUM PITCH
Petroleum pitch was prepared by thermal soaking of asphaltene free oil obtained in Example - 1 in a glass reactor at a temperature of 400 °C for a period of 9 hrs. During entire
experiment non-oxidizing gas such as nitrogen was purged at a rate of 300 ml/min to make reaction atmosphere inert. When thermal soaking was completed, the resulting pitch was cooled under nitrogen and collected. The physico chemical properties of pitch are given in
From the above experiments, it is apparent that the process according to present invention is suitable for making quality zero Ql petroleum pitch from extra vacuum residue which was not possible from prior art processes.
The main advantages of the present invention are:
1 This invention provides a process for making zero Ql petroleum pitch from oil obtained
from extra vacuum residue. This material is never used before for value addition by
converting into pitch.
2 The asphaltenes free components of extra vacuum residue boiling above 650 °C are
useful for making petroleum pitch.
3 Zero Ql petroleum pitch is suitable for its use as impregnator in graphite electrode
4. The by-product of the process like asphaltenes can be utilized for making bitumen.
1. A process for the preparation of petroleum pitch from petroleum refinery extra
vacuum residue, which comprises precipitating asphaltenes from extra vacuum
residue by using an organic solvent with a solvent to feed ratio in the range of 5 to
50 (v/w), at a temperature in the range of 25-35 °C to obtain the asphaltenes free oil,
thermal soaking the above said asphaltenes free oil, optionally in the presence of
organic catalyst, at a temperature in the range of about 320 to 450 °C, for a period of
6 to 20 hrs, in an inert atmosphere, with an inert gas flow rate of 200 to 800 ml/
minute to obtain the desired petroleum pitch.
2. A process as claimed in claim 1, wherein the organic solvent used is selected from
the group consisting of n-pentane, n-hexane, n-heptane and mixtures thereof.
3. A process as claimed in claims 1, wherein the organic solvent to feed ratio used is
preferably in the range of 10 to 50 (v/w).
4 A process as claimed in claim 1, wherein the organic catalyst used is selected from
the group consisting of peroxides, hydro-peroxides, peroxy-acids, peroxy esters, and
5 A process as claimed in claim 1 and 4, wherein the concentration of organic catalyst
used is 1 to 7%, preferably 2 to 3%.
6. A process as claimed in claim 1, wherein the temperature used for thermal soaking of
asphaltene free oil is preferably in the range of 370 - 425 °C.
7. A process as claimed in claim 1, wherein the time period used for thermal soaking of
asphaltene free oil is preferably in the range of 9-16 hrs.
8 A process as claimed in claims 1, wherein the inert gas used is selected from the
group consisting of helium, nitrogen and argon.
9 A process as claimed in claims 1, wherein the flow rate of inert gas used preferably in
the range of 300 to 700 ml/min.
10 A process for the preparation of petroleum pitch from extra vacuum residue
substantially as herein described with reference to the examples accompanying this
|Indian Patent Application Number||787/DEL/2006|
|PG Journal Number||40/2013|
|Date of Filing||22-Mar-2006|
|Name of Patentee||COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH|
|Applicant Address||ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI - 110 001, INDIA.|
|PCT International Classification Number||C10C 3/00|
|PCT International Application Number||N/A|
|PCT International Filing date|