HEAVY PETROLEUM RESIDUE DERIVED IRON INCORPORATED SP2 CARBON NANOGRANULES FOR IMPROVED SYNTHESIS OF LIGHT OLEFINS

Abstract

Present invention relates to sp.sup.2 carbon nanogranules with iron incorporated in it from heavy petroleum residue of a refinery and thereby utilizing the materials for improved synthesis of light olefins (C.sub.2-C.sub.4) from syngas in a single step Fischer Tropsch synthesis to lower olefins, (FTO). The efficient iron incorporated carbon nanogranules derived from low value heavy petroleum residue are very attractive as catalytic system for direct synthesis of light olefin (C.sub.2-C.sub.4) from syngas at CO conversion up to 30%.

Claims

1. (canceled)

2. (canceled)

3. The process of claim 11, further comprising, prior to step (i): iv. dissolving heavy petroleum residue or vacuum residue in a solvent along with iron precursor to prepare a homogeneous solution; v. pumping the homogeneous solution as obtained in step (iv) at flow range of 0.5 mL/min to 5 mL/min to a quartz reactor tube placed in a furnace and spraying the solution to a reactor tube in presence of nitrogen flow in the range of 100 to 300 mL/min for a time period of 10 minute to 60 minutes to obtain carbon deposited on tube surface; vi. cooling the tube and collecting the carbon deposits from the surface as obtained in step (v.) of the reactor tube followed by washing with solvent to remove any unconverted residue; and vii. drying the carbon deposits as obtained in step (vi) and calcining at temperature in the range of 400 to 700 C. for a period in the range of 1 to 6 hours under nitrogen flow at 50 to 150 mL/min to obtain iron incorporated carbon nanogranules (Fe/CNG).

4. The process as claimed in claim 3, wherein the heavy petroleum residues used is vacuum residue from refinery consisting of polyaromatic hydrocarbons (PAH).

5. The process as claimed in claim 3, wherein the solvent used in step (iv or v) is an aromatic solvent selected from the group consisting of light naphtha, petroleum ether, benzene, toluene, xylene and ethylbenzene.

6. The process as claimed in claim 3, wherein the iron precursor used is an organometallic compound of iron.

7. The process as claimed in claim 3, wherein the iron precursor used is ferrocene.

8. (canceled)

9. The process as claimed in claim 3, wherein the weight composition of the heavy petroleum residue or vacuum residue used is in the range of 5 to 20%

10. The process as claimed in claim 3, wherein weight composition of the iron precursor used is in the range of 5 to 20%.

11. A process for the direct synthesis of lower olefins from syngas using an iron incorporated sp.sup.2 carbon nanogranules (Fe/CNG) catalyst, the catalyst comprising (a) iron in the form of Fe(0), in bulk phase, (b) iron in the form of Fe(0) along with the Fe.sub.3C phase, and (c) trace amounts of Fe(II) and Fe(III), where (a), (b) and (c) are collectively present in the range from 5 to 20 w/w % of the sp2 carbon nanogranules, and wherein the trace amounts of Fe(ii) and Fe(III) are found on a surface of the sp2 carbon nanogranules, the process comprising the steps of: i. reducing the Fe/CNG catalyst under hydrogen or diluted hydrogen under pressure of atmospheric to 10 bar_g at a temperature in the range of 350 to 500 C. for a period in the range of 2 to 12 hours; ii. cooling the catalyst followed by heating under the flow of syngas and nitrogen with H.sub.2 to CO mole ratio is in the range of 0.5:1 to 2:1 at GHSV of 2000 to 5000 mLh.sup.1g.sup.1 at a temperature in the range of 300 to 380 C. under atmospheric pressure; and iii. pressurizing the bed at 5 to 30 bar to obtain lower olefins.

12. The process as claimed in claim 11, wherein CO conversion efficiency is up to 30% and selectivity of light olefins is up to 50%.

13. The process as claimed in claim 11, wherein the light olefins from syngas obtained at lower rate of methanation of 15 to 17% and reduced conversion of CO to CO.sub.2 at 12 to 15% with respect to the hydrocarbons.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0058] FIG. 1 represents the synthesis scheme of Fe/CNGs from heavy petroleum residues wherein 1. Homogeneous solution of CNG precursor and organometallic iron precursor in a solvent, 2. High pressure nitrogen (UHP grade) cylinder, 3. Reciprocating pump, 4. Double stage gas regulator, 5. Mass flow controller, 6. Check valve, 7. Sprayer, 8. Quartz reactor tube, 9. Three zone tubular split furnace, 10. Flask for collecting Fe/CNGs, 11. Stand for holding the furnace, 12. Gas stream from CNG collector.

[0059] FIG. 2 is schematic representation of high pressure continuous flow fixed bed reactor setup for carrying out performance evaluation of Fe/CNGs for conversion of syngas to light olefins in a direct F-T route; wherein 1: Cylinder pressure regulator, 2: Needle valve, 3: Pressure gauge, 4: Mass flow controller (MFC), 5: Check Valve, 6: Gas mixer, 7: Gas preheater, 8: Pressure safety relief valve, 9: Reactor tube, 10: Single zone tubular split furnace, 11: Heating zone of furnace, 12: Temperature sensor for catalyst bed inside the reactor, 13: Temperature sensors for the skin of the reactor tube, DTC: Digital Temperature Controller, 14: Condenser separator, 15: Back Pressure Regulator (BPR), 16: Three way valve, 17: Bubble gas flow meter, 18: Gas stream for GC, RGA: Refinery Gas Analyzer.

[0060] FIG. 3 represents the chromatography of the hydrocarbons (C.sub.1-C.sub.6) and permanent gases with their respective retention times (RT, min in x-axis) required to find out the composition of both the feed and product streams in the conversion of syngas in presence of Fe/CNGs as catalysts.

[0061] FIG. 4 shows the X-ray diffraction patterns of Fe/CNGs e.g., Fes/CNG, Fe.sub.10/CNG and Fe.sub.12/CNG synthesized from varying composition of iron precursor in the homogeneous solution.

[0062] FIG. 5A represents the X-ray Photoelectron spectroscopy (XPS) spectra of surfaces of Fes/CNG, Fe.sub.10/CNG and Fe.sub.12/CNG in Fe.sub.2p region. FIG. 5B represents XPS spectra of surfaces of Fes/CNG, Fe.sub.10/CNG and Fe.sub.12/CNG in O1s region. FIG. 5C represents XPS spectra of surfaces of Fes/CNG, Fe.sub.10/CNG and Fe.sub.12/CNG in C1s region. FIG. 5D represents the H.sub.2-TPR profile of the Fe/CNGs.

[0063] FIGS. 6A, 6B and 6C represent the SEM image of Fes/CNG, Fe.sub.10/CNG and Fe.sub.12/CNG particles respectively. FIGS. 6D, 6E and 6F represent the TEM image of Fes/CNG, Fe.sub.10/CNG and Fe.sub.12/CNG particles respectively.

[0064] FIG. 7 represents the time on stream activity profile of the Fe/CNG catalysts for the selective synthesis of lower olefins for a period of 25 hours.

[0065] FIG. 8 represents the Anderson-Schulz-Flory (ASF) model for the calculation of chain growth probability (a) based on the distribution of hydrocarbons in the invented catalyst system for the single step conversion of syngas to light olefins.

DETAILED DESCRIPTION OF THE INVENTION

[0066] The present invention provides a process for the synthesis of sp.sup.2 carbon nanogranules with iron incorporated in it from low value refinery residue preferably vacuum residue and thereof utilization of the carbon nanogranules as efficient catalyst system for improved synthesis of lower olefins (C.sub.2-C.sub.4) from syngas in direct single step Fischer Tropsch process (FTO). The designed materials catalyze to synthesize light olefins at a lower methanation rate with reduced CO.sub.2 formation in comparison to the other reported costlier carbon catalytic materials. The steps comprises dissolution of heavy petroleum residue in an aromatic solvent along with a desirable amount of iron precursor to prepare a homogeneous solution, spraying the solution with the aid of nitrogen to a quartz tube reactor operated at high temperature at atmospheric pressure, scratching out the carbon deposits from the surface of the reactor tube and washing with aromatic solvent to remove any unconverted residue, drying the carbon materials and calcining under nitrogen to obtain desirable iron incorporated carbon nanogranules (Fe/CNG), treating the Fe/CNGs under hydrogen or diluted hydrogen atmosphere and finally carrying out hydrogenation of carbon monoxide (CO) in presence of Fe/CNGs as catalyst system.

[0067] The process of the present invention involves a practical approach for the synthesis of sp.sup.2 carbon nanogranules with iron content from low value heavy petroleum residue of refinery and thereby utilizing the carbon materials for efficient synthesis of lower olefins from syngas by direct F-T process. In synthesizing the carbon nanogranules, firstly heavy petroleum residue preferably vacuum residue to a weight composition of 5 to 20% preferably 10 to 15% is dissolved in an aromatic solvent preferably toluene along with an organometallic compound of iron preferably ferrocene as iron precursor to weight composition of 5 to 20% to prepare a homogeneous solution. The solution is then pumped at the flow range of 0.5 mL/min to 5 mL/min preferably 1 mL/min to 2 mL/min with the aid of a reciprocating pump (flow range: 0.01-10 mL/min) to a heated quartz reactor tube (Diameter: 60 mm, Length: 1200 mm) kept through a three zone tubular split furnace with heating capacity up to 1200 C. having adjustable diameter and length of 900 mm. The upper zone of the furnace is maintained at 450 to 750 C. preferably 500 to 600 C. while the middle and the lower zones are at 800 to 1200 C. preferably 900 to 1000 C. The solution is sprayed to the reactor tube with the aid of nitrogen gas flow in the range of 100 to 300 mL/min preferably 200 to 250 mL/min for a time period of 10 minutes to 60 minutes preferably 20 minutes to 40 minutes. Then the tube is cooled down to room temperature under nitrogen flow and the carbon deposits are collected from the reactor tube. The carbon materials are then purified by washing with toluene followed by drying in oven at 80 to 110 C. Finally the iron incorporated carbon nanogranules are synthesized by calcining the purified carbon materials under the flow of nitrogen at 50 to 150 mL/min preferably 70 to 100 mL/min at the condition of temperature in the range of 400 to 700 C. preferably at 500 to 600 C. for 1 to 6 hours preferably 3 to 5 hours. The same experiment is repeated with the aromatic solvent used for preparing the homogeneous solution in blank to find the distinction of yield amount in comparison to heavy hydrocarbons.

[0068] For the measurements of catalytic activity, the Fe/CNG samples are crushed, pelletized, sieved (20 to 30 mesh) and diluted with SiC granules. About 2.0 g of each catalyst after dilution are loaded in the reactor in each of the experiments. The catalyst bed is initially flushed with nitrogen and heated up to temperature range of 350 to 500 C. preferably 400 to 450 C. at heating rate of 1 to 10 C./min preferably 2 to 5 C. and kept for a time period of 2 to 12 hours preferably 4 to 8 hours under hydrogen atmosphere or diluted hydrogen atmosphere with nitrogen with flow of nitrogen at 60 to 65 mL/min and hydrogen 20 to 25 mL/min to reduce the catalyst under condition of pressure of atmospheric to 10 bar_g preferably atmospheric to 5 bar_g. After the reduction, the bed is cooled down and again kept on heating under the flow of syngas and nitrogen with H.sub.2:CO mole ratio at 0.5:1 to 2:1 preferably 1:1 to 1.5:1 at GHSV of 2000 to 5000 mLh.sup.1g.sup.1 preferably 2500 to 3500 mLh.sup.1g.sup.1 till the temperature of the bed reaches to 300 to 380 C. preferably 320 to 350 C. under atmospheric pressure. Once the temperature is attained, the bed is pressurized by turning the knob of BPR to the value of gauge at 5 to 30 bar preferably 10 to 15 bars. The Fe/CNGs were tested for a time of stream of 25 hours to determine the activity towards selective synthesis of light olefins in a single step.

To check the activity of the Fe/CNGs following were calculated:

Co Conversion:

[0069] [00001]$X_{\mathrm{CO}}\left(\%\right)=\frac{\mathrm{mole}.Math..Math.\mathrm{of}.Math..Math.\mathrm{CO}.Math..Math.\mathrm{in}-\mathrm{mole}.Math..Math.\mathrm{of}.Math..Math.\mathrm{CO}.Math..Math.\mathrm{out}}{\mathrm{mole}.Math..Math.\mathrm{of}.Math..Math.\mathrm{CO}.Math..Math.\mathrm{in}}100$

Selectivity for Hydrocarbon y:

[0070] [00002]$S_y\left(\%\right)=\frac{\mathrm{mole}.Math..Math.\mathrm{of}.Math..Math.\mathrm{CO}.Math..Math.\mathrm{converted}.Math..Math.\mathrm{to}.Math..Math.y}{\mathrm{mole}.Math..Math.\mathrm{of}.Math..Math.\mathrm{CO}.Math..Math.{\mathrm{reacted}}^{*}}100.Math..Math.{[}^{*}.Math.\mathrm{excluding}.Math..Math.\mathrm{conversion}.Math..Math.\mathrm{to}.Math..Math.{\mathrm{CO}}_2.Math..Math.\mathrm{and}.Math..Math.H_2.Math.O].Math.$

Selectivity for CO.SUB.2.:

[0071] [00003]$S_{{\mathrm{CO}}_2}\left(\%\right)=\frac{\mathrm{mole}.Math..Math.\mathrm{of}.Math..Math.\mathrm{CO}.Math..Math.\mathrm{converted}.Math..Math.\mathrm{to}.Math..Math.{\mathrm{CO}}_2}{\mathrm{mole}.Math..Math.\mathrm{of}.Math..Math.\mathrm{CO}.Math..Math.\mathrm{converted}.Math..Math.\mathrm{to}.Math..Math.\mathrm{hydrocarbon}}100$

Value for ASF Model:

[0072] The chain growth probability () factor for the present catalyst system is evaluated as per FIG. 8 to identify the deviation of component distribution in hydrocarbon product from the conventional ASF model.

[0073] Heavy petroleum refinery residue preferably vacuum residue is utilized. However, the scope of invention is not limited to these streams only and other feeds containing at least polyaromatic hydrocarbons may be used.

[0074] FIG. 1 represents the synthesis scheme of Fe/CNGs from heavy petroleum residues wherein 1. Homogeneous solution of CNG precursor and organometallic iron precursor in a solvent, 2. High pressure nitrogen (UHP grade) cylinder, 3. Reciprocating pump, 4. Double stage gas regulator, 5. Mass flow controller, 6. Check valve, 7. Sprayer, 8. Quartz reactor tube, 9. Three zone tubular split furnace, 10. Flask for collecting Fe/CNGs, 11. Stand for holding the furnace, 12. Gas stream from CNG collector.

[0075] Prior to synthesis, the reactor tube 8 is initially purged with nitrogen gas (99.999%) from cylinder 2 and heated by a three zone split tubular furnace 9 kept upright with the help of a stand 11 at the desired temperature under an inert atmosphere of nitrogen. A homogeneous solution 1 comprising of heavy petroleum residue or vacuum residue or polyaromatic hydrocarbon or in suitable combination along with organometallic iron precursor is pumped by a reciprocating pump 3 and sprayed by sprayer 7 to the quartz tube reactor 8 placed at the heated zone of furnace with the aid of controlled flow of nitrogen by mass flow controller 5. The pressure of nitrogen in upstream of mass flow controller (MFC) is controlled by the double stage cylinder regulator 4 while that in downstream by the check valve 6 ensuring forward flow of nitrogen gas up to the outlet 12. The reactor tube is later on allowed to cool down under the constant flow of nitrogen. The carbon layers from the reactor tube are then separated and collected in the flask 10 and washed with an aromatic solvent to purify. Finally, the purified carbon materials are calcined under the flow of nitrogen to obtain Fe/CNGs.

[0076] FIG. 2 is schematic representation of high pressure continuous flow fixed bed reactor setup for carrying out performance evaluation of Fe/CNGs for conversion of syngas to light olefins in a direct F-T route; wherein 1: Cylinder pressure regulator, 2: Needle valve, 3: Pressure gauge, 4: Mass flow controller (MFC), 5: Check Valve, 6: Gas mixer, 7: Gas preheater, 8: Pressure safety relief valve, 9: Reactor tube, 10: Single zone tubular split furnace, 11: Heating zone of furnace, 12: Temperature sensor for catalyst bed inside the reactor, 13: Temperature sensors for the skin of the reactor tube, DTC: Digital Temperature Controller, 14: Condenser separator, 15: Back Pressure Regulator (BPR), 16: Three way valve, 17: Bubble gas flow meter, 18: Gas stream for GC, RGA: Refinery Gas Analyzer.

[0077] All gas lines connected to the reactor tube 9 were made of stainless steel tubing. Three mass flow controllers (Brooks) 4 equipped with a four-channel control panel are used to adjust the flow rate of the inlet gases (CO+N.sub.2, H.sub.2 and N.sub.2 with purity of 99.99%). The gases with proper flow rate at first undergo intensive mixing in a mixer 6. The mixed gas then passes into the preheater 7 followed by reactor tube 9 which is placed inside a single zone split tubular furnace 10 capable of producing temperature up to 800 C. and is controlled by a digital temperature controller (DTC). The reactor tube is made of stainless steel having internal diameter of 20 mm capable of sustaining pressure up to 80 bar at temperature 800 C. The reactor tube consists of three zone 11: preheating zone which is filled with SiC granules (1-2 mm), zone temperature up to 250 to 300 C.; catalysts bed zone which is situated almost in the middle of the reactor, contains mixture of catalyst particles (20 to 30 mesh) mixed with SiC granules (20 to 30 mesh) to a volume ratio of 1:(3 to 5), zone temperature 300 to 450 C.; product dispersion zone which is filled with porcelain beads of internal diameter of 1 mm and outer diameter of 2.5 mm, zone temperature up to 250 C. The product stream from the reactor then moves downward to the condenser separator 14 where separation of gas and liquid takes place. The liquid product from the separator bottom is then collected through a pressure trap system while the gas from the separator comes out through a BPR 15. The BPR is capable to maintain pressure inside the reactor to a desired value up to 100 bar at the reactor operating condition. The gas stream post BPR is taken through a three way ball valve 16 either to a bubble flowmeter 17 for calculating flow or to a gas chromatography (GC) 18 [Agilent, 7890B, equipped with two FID for hydrocarbons C.sub.1-C.sub.12, HPAl.sub.2O.sub.3/KCL column (25 m0.320 mm; 5 apm) & CP-SIL 2CB column (25 m0.320 mm; 1.2 jpm) and one TCD for the permanent gases H.sub.2, CO.sub.2, N.sub.2, CO, Hayesep Q column (6 ft2 mm)] for identifying and quantifying the composition.

[0078] FIG. 3 represents the chromatography of the hydrocarbons (C.sub.1-C.sub.6) and permanent gases with their respective retention times (RT, min in x-axis) required to find out the composition of both the feed and product streams in the conversion of syngas in presence of Fe/CNGs as catalysts.

[0079] FIG. 4 shows the X-ray diffraction patterns of Fe/CNGs e.g., Fes/CNG, Fe.sub.10/CNG and Fe.sub.12/CNG synthesized from varying composition of iron precursor in the homogeneous solution. X-ray diffraction (XRD) patterns were obtained on a Bruker D8 advance X-ray diffractometer using monochromatic CuK (=1.5418 ) radiation in 20 range from 10 to 80 with a step size 0.040.

[0080] Major peaks at 26, 43.5 (2) corresponding to the reflection of 002 and 101 hkl planes, represent the graphite form of carbon with hexagonal phases (JCPDS card No. 75-1621), whereas the broad peaks with sample Fe.sub.10/CNG possibly because of the presence of carbon in amorphous form. The peaks at 44.7 in all the Fe/CNG samples confirm the presence of iron [Fe(0)]. The presence of iron in the Fe/CNG samples were also confirmed by ICP-AES and calcining the samples at 700 to 1000 C. preferably at 800 to 950 C. under air. The CNG samples are therefore named as per the iron content in it, e.g., Fe.sub.10/CNG represents the carbon nanogranules with iron content of 10% by weight. There are no characteristic peaks of iron oxide [Fe(II) or Fe(III)] appeared in XRD pattern of all the synthesized CNGs. This confirms the prepared Fe/CNG catalysts unanimously have [Fe(0)] in bulk phase.

[0081] FIG. 5A represents the XPS spectra of surfaces of Fes/CNG, Fe.sub.10/CNG and Fe.sub.2/CNG in Fe.sub.2p region. X-ray Photoelectron spectroscopy (XPS) analyses of the materials were carried out on model: S/N-10001, Prevac Poland, with a VG Scienta-R3000 hemispherical energy analyser. The Fe2p3/2 binding energy peak at 706.6 eV in all the samples prove the presence of [Fe(0)] which is in concomitant with XRD analyses. Nevertheless, the peak at 708.5 eV in Fes/CNG and Fe.sub.10/CNG belongs to surface Fe.sub.2O.sub.3 and peak at 709.5 eV in Fe/CNG pellets belongs to surface FeO, while peak at 710.1 eV in Fe.sub.10/CNG belongs to Fe(III) oxides and peak at 711.8 eV in Fe.sub.12/CNG belongs to surface iron oxo-hydroxo (FeOOH) species due to air exposure. The CNG samples are reduced in-situ prior to the reaction. The XPS of O1s were fitted for the three samples as shown in FIG. 5B. The peak at 529.6 eV corresponds to the binding energy of O.sup.2. The other peaks at 531.4 eV and 532.5 eV could be assigned as O1s in [OH.sup.]. Here the oxygen species present in the samples are similar to the oxygen species present on iron. In the C1s spectrum of the three samples as shown in FIG. 5C, the peak at 284.8 eV confirms sp.sup.2 hybridization of graphitic carbon, the deconvoluted peak at 283.5 eV is correspond to surface Fe.sub.3C species and 286.0 eV corresponds to CO species.

[0082] H.sub.2-Temperature-programmed reduction (H.sub.2-TPR) of the carbon nanogranules were performed using a Chemisorption analyser, Autochem 2920 (Micromeritics, USA) equipped with a conventional atmospheric quartz flow reactor (5 mm ID). Prior to the reduction studies, pre-treatment of samples (70 mg) inside the reactor were carried out at temperature of 350 C. under flow of helium (99.995%) at 50 mL/min for 3 hours. The reactor was then cooled down to room temperature under the flow of helium and the TPR studies were carried out by heating the reactor from 50 C. to 1000 C. at a rate of 10 C./min under the flow of 10% H.sub.2/Ar (on mole basis) at 30 mL/min. the TPR profiles were recorded by using the response of the thermal conductivity detector (TCD) of the effluent gas.

[0083] The H.sub.2-TPR profile of the Fe/CNGs according to the FIG. 5D, also confirms the requirement of Fe/CNGs to reduce prior to the reaction. The single broad peak area at 435-440 C. in the TPR profiles corresponding to the reduction of Fe.sub.2O.sub.3 phase to Fe(0). The shifting of the peak in comparison to the pure Fe(0) evidences the strong metal support interaction in prepared catalyst system.

[0084] FIGS. 6A, 6B, 6C, 6D, 6E and 6F represent the structure and morphology of synthesized Fe/CNGs analyzed by SEM and TEM. Morphological information of the catalyst samples were obtained by FEI Quanta 200F scanning electron microscope (SEM) system equipped with energy-dispersive X-ray (EDX) spectroscopy. Transmission electron microscopic (TEM) analyses were performed on FEI model no. Technai G220 S-TWIN instrument.

SEM and TEM image of Fe/CNGs prepared show spherical granular shape of the particles. According to the images, the Fes/CNG and Fe.sub.12/CNG particles have diameter less than 300 nm (FIGS. 6a & 6c) while Fe.sub.10/CNG has diameter more than 400 nm (FIG. 6b). The TEM images of Fe.sub.10/CNG indicate the particle size of less than 50 nm (FIG. 6 d-f).

[0085] FIG. 7 represents the time on stream activity profile of the Fe/CNG catalysts for the selective synthesis of lower olefins for a period of 25 hours. The figure shows that Fe/CNGs are attractive catalyst system providing a stable activity pattern for conversion of syngas to lower olefins.

[0086] FIG. 8 represents the Anderson-Schulz-Flory (ASF) model for the calculation of chain growth probability (a) based on the distribution of hydrocarbons in the invented catalyst system for the single step conversion of syngas to light olefins. The a value enables to predict the deviation from the conventional distribution of product components in F-T synthesis that is required to develop process for short chain olefins.

EXAMPLES

[0087] The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention.

Example 1

[0088] A homogeneous solution containing 10% Vacuum residue (VR-550+) and 10% ferrocene dissolved in toluene was pumped at flow rate of 1 mL/min and sprayed through the heated zone of furnace with the aid of flow of nitrogen at 200 mL/min for 30 minutes. After that, the reactor tube was allowed to cool down under the constant flow of nitrogen. The carbon layers from the reactor tube were then separated and washed with toluene to purify. Finally, the purified carbon materials were calcined at 600 C. for 3 hrs under the flow of nitrogen at 80-90 mL/min to obtain Fe/CNGs. The Fe/CNG is named as Fes/CNG as it contain 8% of iron by weight as per ICP-AES analysis. The XRD, XPS and SEM images of the Fes/CNG are represented in the FIG. 4, FIG. 5 and FIG. 6 respectively.

Example 2

[0089] A homogeneous solution containing 10% Vacuum residue (VR-550+) and 15% ferrocene dissolved in toluene was used for the synthesis of Fe/CNG as given in example 1 and the resulted Fe/CNG is termed as Fe.sub.10/CNG consisting of 10% iron by weight. The XRD, XPS and SEM & TEM images of the Fe.sub.10/CNG are represented in the FIG. 4, FIG. 5 and FIG. 6 respectively.

Example 3

[0090] A homogeneous solution containing 10% Vacuum residue (VR-550+) and 20% ferrocene dissolved in toluene was used for the synthesis of Fe/CNG as given in example 1 and the resulted Fe/CNG is termed as Fe.sub.12/CNG consisting of 12% iron by weight. The XRD, XPS and SEM images of the Fe.sub.2/CNG are represented in the FIG. 4, FIG. 5 and FIG. 6 respectively.

Example 4

[0091] The synthesized Fe/CNGs in examples 1-3 were crushed and pelletized to 20-30 mesh size and loaded in the fixed bed reactor setup for analyzing the activities for synthesis of light olefin from syngas. The catalyst bed was initially treated at the temperature of 400 C. for 8 hours under continuous flow of hydrogen of 20 mL/min and nitrogen 65 mL/min in order to reduce the Fe/CNGs. Hydrogenation of carbon monoxide was then conducted over the catalysts bed at temperature of 340 C., pressure of 15 bar__g, GHSV of 3000 mL h.sup.1g.sup.1 and H.sub.2:CO mole ratio of 1.15:1 for 25 hours of time on stream. Following table represents the performance of the Fe/CNGs in the hydrogenation of CO in the synthesis of lower olefins in a direct F-T route.

TABLE-US-00001 TABLE 1 Experimental data for single step conversion of syngas to hydrocarbons using catalysts described in examples 1-3 Catalyst X.sub.co S.sub.CO.sub.2 S.sub.CH.sub.4 S.sub.C2-C4.sup.= S.sub.C2-C4.sup.paraffin S.sub.C5+ Fe.sub.8/CNG 13.5 14.60 14.99 51.88 9.76 23.37 0.5 Fe.sub.10/CNG 24.3 12.73 17.02 49.12 12.48 21.39 0.53
(X.sub.CO=conversion of CO in the hydrogenation reaction; S.sub.CO2=selectivity of CO conversion to CO.sub.2 in comparison to the hydrocarbons; S.sub.CH4, S.sub.C2-C4.sup.=, S.sub.C2-C4.sup.paraffin, S.sub.C5+=selectivity of formation of methane, C.sub.2-C.sub.4 olefins, C.sub.2-C.sub.4 paraffins and hydrocarbons heavier than C.sub.4 respectively from CO upon hydrogenation; =ASF factor in the formation of hydrocarbons)

[0092] The time on stream analyses of the Fe/CNGs have been shown in the FIG. 7 representing stable activity pattern for a time of run of 25 hours.

Example 5

[0093] As in example 4, the hydrogenation of CO is carried out over Fe.sub.10/CNG catalyst at condition of pressure of 20 bar_g.

TABLE-US-00002 TABLE 2 Hydrogenation of CO over Fe.sub.10/CNG catalyst at 20 bar_g Catalyst X.sub.co S.sub.CO.sub.2 S.sub.CH.sub.4 S.sub.C2-C4.sup.= S.sub.C2-C4.sup.paraffin S.sub.C5+ Fe.sub.10/CNG 19.9 12.10 25.41 45.40 10.74 18.45 0.5

Example 6

[0094] As depicted in example 4, the direct F-T reaction is carried out over Fe.sub.10/CNG catalyst at condition of temperature of 320 C.

TABLE-US-00003 TABLE 3 Hydrogenation of CO over Fe.sub.10/CNG catalyst at 320 C. Catalyst X.sub.co S.sub.CO.sub.2 S.sub.CH.sub.4 S.sub.C2-C4.sup.= S.sub.C2-C4.sup.paraffin S.sub.C5+ Fe.sub.10/CNG 21.2 11.91 17.60 47.23 13.43 21.73 0.52

Advantages of the Invention

[0095] The present invention provides an efficient pathway of utilization of low value refinery residue for the synthesis of high value olefins by;

a) synthesizing sp.sup.2 carbon nanogranules with iron incorporated in it from heavy petroleum residue having polyaromatic hydrocarbon content
b) conducting direct F-T synthesis of light olefins in fixed bed reactor over the Fe/CNGs as catalyst system

[0096] The main advantages of the present invention are: [0097] Synthesis of lower olefins utilizing the iron incorporated carbon nanogranules derived from low cost heavy petroleum residues in a direct F-T route with selectivity of up to 50% at CO conversion of up to 30%. [0098] Reduced methanation and CO.sub.2 formation in the selective synthesis of light olefins in a single step hydrogenation of carbon monoxide. [0099] Provides an attractive pathway for creating wealth from waste refinery residues