PROCESS FOR ISOMERIZATION OF C5-C7 HYDROCARBONS IN LIGHT NAPHTHA RANGE

Abstract

The present invention is related to the isomerization process in which a light naphtha stream comprising of paraffinic (mono and single branched), naphthenic and aromatic hydrocarbons in the range of C.sub.5-C.sub.7 is contacted with the solid catalyst in multiple reaction zones and in presence of hydrogen to produce high octane gasoline predominantly comprising of paraffins (single and di-branched) and naphthenes. The process scheme comprises of more than one isomerization reaction section operating at different temperatures and other operating conditions. The catalyst employed in these reaction sections is a high coordination sulfated mixed metal oxide catalyst which contains at least one noble metal and sulfated zirconia in addition to the other components. The process of the present invention also comprises more than one fractionation section and recycling of a particular stream to the reaction zone for improving the isomerization of light naphtha.

Claims

1. A process for isomerization of C.sub.5-C.sub.7 hydrocarbons in light naphtha range, the process comprising: a) feeding a light naphtha hydrocarbon feed to a fractionation column for separating into an i-pentane comprising stream, a stream predominantly comprising of n-pentane, n-hexane, mono and di-branched isomers of n-hexane and some methyl cyclopentane, and stream predominantly comprising of methyl cyclopentane, cyclohexane, benzene and C.sub.7 paraffinic/naphthenic hydrocarbons; b) mixing the stream with a recycle stream, and hydrogen, and feeding to a first isomerization reactor provided with a mixed metal oxide type catalyst; c) passing an effluent obtained from the first isomerization reactor through a separator to separate hydrogen and a liquid stream after cooling; d) feeding the liquid stream to a stabilizer for separating dissolved light gases, and bottom stream and sending the stream to a fractionation column to produce a top stream, a middle stream and a bottom stream; e) recycling the middle stream to the first isomerization reactor; and f) mixing stream from fractionating column with hydrogen and feeding to a second isomerization reactor provided with a mixed metal oxide type catalyst to produce an effluent which is passed through a separator to remove hydrogen and obtain a liquid stream after cooling, wherein in step a) light naphtha hydrocarbon feed in the fractionation column is optionally separated into only two streams: stream predominantly comprising of i-pentane, n-pentane, n-hexane, mono and di-branched isomers of n-hexane and some methyl cyclopentane and stream predominantly comprising of methylcyclopentane, cyclohexane, benzene and C.sub.7 paraffinic/naphthenic hydrocarbons and wherein stream before being feed to the first isomerization reactor is fed to a deisopentanizer, along with stream to obtain i-pentane containing stream and stream predominantly comprising of n-pentane, n-hexane, mono branched isomers of n-hexane and some methyl cyclopentane; and wherein the bottom stream in step d) is optionally fed to C.sub.5/C.sub.6 splitter for separating into top C.sub.5 containing stream predominanently consisting of i-pentane and n-pentane, which is recycled back to the inlet of deisopentanizer, and bottom C.sub.6 containing stream, which is fed to fractionation column to produce a top stream, a middle stream and a bottom stream.

2. The process as claimed in claim 1, wherein the mixed metal oxide catalyst is a high coordination sulfated mixed metal oxide catalyst, wherein a composition of the catalyst before high temperature treatment, comprising mixtures of: a) alumina and zirconia in weight ratio of 1:3 to 1:5; and b) α-amino acids, having molecular weight ≤250, wherein the α-amino acids are a combination of α-amino acids with non-polar side chain and basic side chain; and wherein the particle size of (a) is less than 37 μm.

3. The process as claimed in claim 1, wherein the α-amino acid with non-polar side chain is selected from Glycine, Alanine, Valine, Leucine, Isoleucine, Methionine, Proline and Phenylalanine with a molar concentration in the range of 1 to 2M; and wherein the α-amino acid with basic chain is selected from Lysine, Arginine and Histidine, with molar concentration in the range of 2 to 3M.

4. The process as claimed in claim 1, wherein the hydrogen used in the first isomerization reactor is a combination of make-up hydrogen and recycled hydrogen.

5. The process as claimed in claim 1, wherein the hydrogen used in the second isomerization reactor is a combination of make-up hydrogen and recycled hydrogen.

6. The process as claimed in claim 1, wherein the hydrogen from the separator is passed to a compressor and recycled to the first isomerization reactor.

7. The process as claimed in claim 1, wherein the hydrogen from the separator is passed to a compressor and recycled to the second isomerization reactor.

8. The process as claimed in claim 1, wherein the stream consists of predominantly C.sub.6 paraffinic di-branched isomers, n-pentane, and i-pentane.

9. The process as claimed in claim 1, wherein the stream consists of predominantly C.sub.6 paraffinic di-branched isomers.

10. The process as claimed in claim 1, wherein the isomerate product, obtained after mixing streams, has an improved octane number by 2 to 3 units.

11. The process as claimed in claim 1, wherein the isomerate product, obtained after mixing streams, has an improved octane number by 2 to 3 units.

12. The process as claimed in claim 1, wherein the stream predominantly consists of cyclohexane and methyl cyclopentane.

13. The process as claimed in claim 1, wherein the stream consists of n-hexane and mono branched isomers.

14. The process as claimed in claim 1, wherein the first isomerization reactor is operated at a temperature in a range of 180-210° C.; and wherein the second isomerization reactor is operated at a temperature in a range of 140-180° C.

15. The process as claimed in claim 1, wherein the liquid stream from the separator consists of cyclohexane, methyl cyclopentane, and other C.sub.7 hydrocarbons free from benzene.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1: is a diagrammatic representation of scheme 1 of the present invention.

[0046] FIG. 2: is a diagrammatic representation of scheme 2 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0047] For promoting an understanding of the principles of the present disclosure, reference will now be made to the specific embodiments of the present invention further illustrated in the drawings and specific language will be used to describe the same. The foregoing general description and the following detailed description are explanatory of the present disclosure and are not intended to be restrictive thereof. It will nevertheless be understood that no limitation of the scope of the present disclosure is thereby intended, such alterations and further modifications in the illustrated composition, and such further applications of the principles of the present disclosure as illustrated herein being contemplated as would normally occur to one skilled in the art to which the present disclosure relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinarily skilled in the art to which this present disclosure belongs. The methods, and examples provided herein are illustrative only and not intended to be limiting.

[0048] In the present invention, the light naphtha hydrocarbon feed is first separated by fractionation column into three streams; wherein the first stream of hydrocarbon predominantly consists of i-pentane; second stream of hydrocarbons consist of n-pentane, n-hexane and its isomers, and some methyl cyclopentane; and third stream consist of naphthenes mainly cyclohexane and methyl cyclopentane, benzene, and other heavier C.sub.7 hydrocarbons. The first stream of hydrocarbon is directly blended with isomerate, the final product from this process. The second stream is fed to the first isomerization reactor employing high coordination sulfated mixed metal oxide catalyst operated at high temperature in the range of 180-210° C. after the addition of hydrogen. The third stream is fed to the second isomerization reactor operated at low temperature also employing high coordination sulfated mixed metal oxide catalyst operated at low temperature in the range of 140-180° C. after addition of hydrogen.

[0049] In another preferred embodiment of the present invention, the light naphtha hydrocarbon feed stream is separated by fractionation column into two streams; the first stream predominantly consists of i-pentane, n-pentane, n-hexane, mono and di-branched isomers of n-hexane, and some methyl cyclopentane; and the second stream predominantly consists of methylcyclopentane, cyclohexane, benzene and C.sub.7 paraffinic/naphthenic hydrocarbons. There may be some component overlap between these streams, which is frequent when fractionation is used to separate components.

[0050] In an embodiment of the present invention, there is a reduction in the undesired conversion of methyl cyclopentane to n-hexane and subsequently to mono branch C.sub.6 paraffins, since a portion of methyl cyclopentane, present in the feed of the first isomerization reactor, will be converted to cyclohexane and equilibrium between these two naphthene isomers will be maintained, thereby reducing the availability of methyl cyclopentane for undesirable conversion into n-hexane.

[0051] In another embodiment of the present invention, additional conversion of low octane paraffins to high octane branched paraffins. The feed of the first isomerization reactor, operating at high temperature, doesn't contain benzene and thereby no benzene saturation reaction takes place in the reactor which is a highly exothermic reaction. Thus, there is no possibility of excessive temperature rise which usually happens with feedstock containing benzene. Thus, favoring the formation of paraffin isomers due to favourable equilibrium at lower temperature.

[0052] In another preferred embodiment, the present process produces high octane isomerate, as the low operating temperature in the second isomerization reactor inhibits the conversion of methyl cyclopentane (having high octane number) to n-hexane and subsequently to mono branch C6 paraffins (low octane number). This methyl cyclopentane is either present in the feed of the second isomerization reactor or formed through isomerization of cyclohexane. This leads to increase in product octane number.

[0053] In another embodiment of the present invention, aromatic components present in the feed of the second isomerization reactor e.g., benzene saturates in the second reactor, thereby increasing the reactor bed temperature required for isomerization of cyclohexane to methyl cyclopentane. This contributes to an increase in octane number.

[0054] In another embodiment of the present invention, the coke formation reduces in the first isomerization reactor operating at high temperature due to the absence of C.sub.7 hydrocarbons in the feed thereby enhancing the catalyst life.

[0055] In yet another embodiment of the present invention, a high coordination sulfated mixed metal oxide catalyst, wherein a composition of the catalyst before high temperature treatment, comprising mixtures of: [0056] a) alumina and zirconia in weight ratio of 1:3 to 1:5; and [0057] b) α-amino acids, having molecular weight ≤250; [0058] wherein the α-amino acids are a combination of α-amino acids with non-polar side chain and basic side chain.

[0059] In another preferred embodiment of the present invention, particle size of (a) is less than 37 μm.

[0060] In another preferred embodiment of the present invention, the α-amino acid with non-polar side chain is selected from Glycine, Alanine, Valine, Leucine, Isoleucine, Methionine, Proline and Phenylalanine; with molar concentration in the range of 1 to 2M.

[0061] In another preferred embodiment of the present invention, the α-amino acid with basic chain is selected from Lysine, Arginine and Histidine, with molar concentration in the range of 2 to 3M.

[0062] Process Description

[0063] The process scheme of the present invention is shown in FIG. 1. As per the process scheme as depicted in FIG. 1, the light naphtha hydrocarbon feed stream (10) fed to fractionation column (12) is separated into three streams; stream (11) predominantly consists of i-pentane; stream (13) predominantly consists of n-pentane, n-hexane, mono & di-branched isomers of n-hexane, and some methyl cyclopentane; stream (14) predominantly consists of methyl cyclopentane, cyclohexane, benzene and C.sub.7 paraffinic/naphthenic hydrocarbons. There is a possibility of slight overlap of components among these streams, which is common in separation of components using fractionation. Stream (11) is used for blending in the product isomerate. The stream (13) after mixing with recycle stream (29) and hydrogen (make up, 19, and recycle, 22) is fed to first isomerization reactor (16) operating at high temperature usually in the range of 180-210° C. Hydrogen is removed from the reactor effluent (17) through separator (20) after cooling. The liquid stream (21) from the separator is fed to stabilizer (23) to remove dissolved light gases which are removed from top (24). The bottom stream (25) from stabilizer is fed to fractionation column (26). The top stream (27) from the column predominantly consists of di-branched isomers along with C.sub.5 hydrocarbons both n-pentane and i-pentane, having high octane number and used for blending in the product isomerate. The middle stream (29) predominantly consists of n-hexane and its mono branched isomers, having low octane number is recycled back to first isomerization reactor for further conversion. The bottom stream (28) predominantly consists of cyclohexane and methyl cyclopentane, along with other heavier components is used for blending in the product isomerate. The bottom stream (14) from fractionating column (12) which consists of predominantly benzene, methyl cyclopentane, cyclohexane and heavier C.sub.7 hydrocarbons is fed to second isomerization reactor (30) operating at lower temperature in the range of 140-180° C. after contacting with hydrogen (make up, 31, and recycle, 34). The reactor effluent (32) is passed through separator (33) to remove hydrogen after cooling. The liquid stream (35) from the separator (33) consists of naphthenic hydrocarbon, predominantly cyclohexane and methyl cyclopentane, and other C.sub.7 hydrocarbons free from benzene. Since very less cracking will takes place at a lower temperature in the reaction zone, stream (35) is directly used for blending in the product isomerate. Further, instead of two separate compressors (18 and 18′) only one compressor can be used with the distribution of the hydrogen stream in both reactors as per the requirement.

[0064] The process scheme of the present invention as per the second embodiment is shown in FIG. 2. The light naphtha hydrocarbon feed stream (10) is fed to fractionation column (12) is separated into two streams; stream (11a) predominantly consists of i-pentane, n-pentane, n-hexane, mono and di-branched isomers of n-hexane, and some methyl cyclopentane; and stream (14) predominantly consists of methylcyclopentane, cyclohexane, benzene and C.sub.7 paraffinic/naphthenic hydrocarbons. There may be some component overlap between these streams, which is frequent when fractionation is used to separate components. The stream 11a is fed to another fractionating column, deisopentanizer (43), after mixing with stream (41) to remove the i-pentane from the top stream (44). Stream (44) is used for blending in the product isomerate. The bottom stream (13) consists of other components predominantly normal paraffins in the range of C.sub.5 and C.sub.6 alongwith the other components. The stream 13 after mixing with recycle stream (29) and hydrogen (make up, 19, and recycle, 22) is fed to first isomerization reactor (16) operating at high temperature usually in the range of 180-210° C. Hydrogen is removed from the reactor effluent (17) through a separator (20) after cooling. The liquid stream (21) from the separator is fed to stabilizer (23) to remove dissolved light gases which are removed from top (24). The bottom stream (25) from stabilizer is fed to fractionation column, C.sub.5/C.sub.6 splitter, (40). The top stream (41) of this column is recycled back to the inlet of deisopentanizer (43). This stream consists C.sub.5 components i.e. predominantly i-pentane and n-pentane. The bottom stream (42) of this column consists of C.sub.6 and heavier components. This bottom stream is fed to fractionation column (26). The top stream (27a) from the column predominantly consists of C6 paraffinic di-branched isomers, having high octane number and used for blending in the product isomerate. The middle stream (29) consists of n-hexane and its' mono branched isomers, having low octane number is recycled back to first isomerization reactor for further conversion. The bottom stream (28) predominantly consists of cyclohexane, and methyl cyclopentane along with other heavier components is used for blending in the product isomerate. The bottom stream (14) from fractionating column (12) which consists of predominantly methylcyclopentane, benzene, cyclohexane and heavier C.sub.7 hydrocarbons is fed to second isomerization reactor (30) operating at lower temperature in the range of 140-180° C. after contacting with hydrogen (make up, 31, and recycle, 34). The reactor effluent (32) is passed through a separator (33) to remove hydrogen after cooling. The liquid stream (35) from the separator (33) consists of naphthenic hydrocarbon, predominantly cyclohexane and methyl cyclopentane, and other C.sub.7 hydrocarbons free from benzene. Since very less cracking will takes place at lower temperature in the reaction zone, stream (35) is directly used for blending in the product isomerate. Further, instead of two separate compressors (18 and 18′) only one compressor can be used with the distribution of the hydrogen stream in both reactors as per the requirement.

[0065] In the above embodiments, both first and second isomerizartion reactors may operate at the same or different process conditions such as pressure in the range of 15-35 bar, weight hour space velocity in the range of 1.25-4.0 h.sup.−1 and hydrogen to hydrocarbon ratio in the range of 0.5-4.0 mol/mol.

[0066] Following examples, as given below, will substantiate the performance of the reactors using a high coordination sulfated mixed metal oxide catalyst at different temperatures as proposed in the scheme. The catalyst used in the below examples is prepared as per the method given in Indian Patent Application no. 202021007171, details of which are incorporated herein by way of reference.

EXAMPLE 1

[0067] Feed Composition:

TABLE-US-00001 Component Wt % Cyclopentane 1.20 i-Pentane 0.54 n-Pentane 6.72 22DMB 2.70 23DMB 5.92 n-Hexane 20.41 2MP 25.19 3MP 17.68 Benzene 2.22 Cyclohexane 3.97 Methyl cyclopentane 11.14 C7+ 2.32

TABLE-US-00002 Temper- Pres- n-pentane n-hexane Δ RON ature, sure, WHSV, conversion, conversion, (Product − ° C. bar h.sup.−1 wt % wt % Feed) 200 20 1.5 53.6 41.8 9.1 200 20 2.0 48.7 40.4 8.4

[0068] This example shows that the activity of the high coordination sulfated mixed metal oxide catalyst towards the conversion of n-pentane and n-hexane, and RON improvement in a once-through operation at 200° C. which is the operating temperature of the first isomerization reactor using light naphtha stream.

EXAMPLE 2

[0069] Feed Composition:

TABLE-US-00003 Component Wt % Cyclopentane 1.21 i-Pentane 0.53 n-Pentane 6.69 22DMB 2.69 23DMB 5.92 n-Hexane 20.44 2MP 25.15 3MP 17.68 Benzene 2.24 Cyclohexane 3.96 Methyl cyclopentane 11.16 C7+ 2.34

TABLE-US-00004 Temper- Pres- Benzene n-pentane n-hexane ature, sure, WHSV, conversion, conversion, conversion, ° C. bar h.sup.−1 wt % wt % wt % 140 32 1.5 100 3.22 3.06 180 20 2.0 100 19.6 29.2

[0070] The experiments were conducted at different temperatures in the range of 140-180° C. at H.sub.2/HC ratio of 2.5 mol/mol using the light naphtha stream as per the above mentioned composition. This example shows the activity of the high coordination sulfated mixed metal oxide catalyst towards the benzene saturation takes place in the second isomerization reactor operating in the temperature range of 140-180° C. at different process conditions using light naphtha stream. The above results indicate complete saturation of benzene present in the light naphtha stream and substantially lower activity in terms of n-pentane and n-hexane conversion in the temperature range of 140-180° C.

EXAMPLE 3

[0071] Feed Composition:

TABLE-US-00005 Component Wt % 2MP 19.5 Cyclohexane 80.5

TABLE-US-00006 (Methyl Temper- Pres- Gas cylopentane + Δ RON ature, sure, WHSV, yield, Cyclohexane) in (Product − ° C. bar h−1 wt % the product, wt % Feed) 160 20 2.6 0.11 77.86 0.35 180 20 2.6 0.45 75.55 0.09 200 20 2.6 1.36 70.70 −0.40

[0072] The experiments were conducted at different temperatures in the range of 160-200° C. at H.sub.2/HC ratio of 3.0 mol/mol using the synthetic feed as per the above mentioned composition. The above example shows that if the feed predominantly contains naphthenic hydrocarbons then the gas yield (C.sub.1-C.sub.4) increases with an increase in temperature which consequentially decreases the isomerate yield. The experimental results further indicate the decrease in sum of methylcyclopentane and cyclohexane, in the product with the increase in the temperature which results in a decrease in the product RON. These results substantiate that the conversion of methylcyclopentane, formed through isomerization of cyclohexane in the feed, to n-hexane and subsequently to mono branch paraffins increases with an increase in the temperature.

EXAMPLE 4

[0073] Feed Composition:

TABLE-US-00007 Component Wt % Benzene 11 Cyclohexane 67 n-heptane 22

TABLE-US-00008 Gas yield Temperature, Pressure, WHSV, (C.sub.1-C.sub.4), ° C. bar h.sup.−1 wt % 160 20 1.5 0.29 170 20 1.5 0.58 200 20 1.5 9.36

[0074] The experiments were conducted at different temperatures in the range of 160-200° C. at H.sub.2/HC ratio of 2.5 mol/mol using the synthetic feed as per the above mentioned composition. The experimental results show that if the feed contains a substantial amount of benzene, C.sub.7 and naphthenic hydrocarbons then the gas yield (C1-C4) formed due to undesired cracking reactions substantially increases with increase in temperature specifically in the operating temperature of first isomerization reactor which in-turn decreases the isomerate yield. These results corroborate that it is advantageous to process the feed containing benzene, naphthenic and C.sub.7 hydrocarbons at a lower temperature i.e. operating temperature of the second isomerization reactor as per the present invention to avoid the cracking reaction.

EXAMPLE 5

[0075]

TABLE-US-00009 Composition, Wt % Component Feed X Feed Y n-pentane 80 89 Cyclohexane 10 0 Methyl cyclopentane 10 11

TABLE-US-00010 Feed X Feed Y paraffinic-C6 (n-hexane + mono 4.39 3.25 branch isomers) in the product, wt % ΔRON (Product − Feed) 11.92 14.12

[0076] The experiments were conducted at 200° C., 20 bar using the synthetic feed in a mixture of n-hexane and methylcyclopentane with and without cyclohexane at WHSV of 1.5 h.sup.−1 and H.sub.2/HC ratio of 2.6 mol/mol. From the experimental results, a reduction of 1.14 wt % in the formation of n-hexane and mono branch C.sub.6 paraffins in the product and an increase in the ΔRON of 2.2 units are observed when using feed without cyclohexane. This example shows the reduction in the formation of n-hexane and subsequently to mono branch C.sub.6 paraffins from methyl cyclopentane in the feed without cyclohexane in comparison with the feed with cyclohexane as anticipated in the present invention where the feed of the first isomerization reactor does not contain cyclohexane.

EXAMPLE 6

[0077] Feed Composition:

TABLE-US-00011 Composition, Wt % Component Feed A Feed B Feed C n-Pentane 25 45.5 0 n-Hexane 30 54.5 0 Benzene 5 0 11 Cyclohexane 30 0 67 C7+ 10 0 22

TABLE-US-00012 Product RON Conventional process scheme Experimental results using Feed-A (at 200° C.) 79.71 Process scheme as per the present invention Experimental results using Feed-B as per first 84.80 isomerization reactor conditions (at 200° C.) Experimental results using Feed-C as per second 80.46 isomerization reactor conditions (at 170° C.) Combined product after blending product 82.91 obtained after processing Feed-B and C Benefit in terms of RON improvement of new 3.20 process scheme over the conventional scheme

[0078] This example shows the once-through experimental results at 20 bar, WHSV of 1.5 h−1 and H.sub.2/HC ratio of 2.6 mol/mol with the synthetic feed using a single reaction zone operating at high temperature as per the conventional process scheme and the two reaction zones operating at different process conditions as per the present invention. Feed-A which is a mixture of paraffinic, napthenic and aromatic hydrocarbons in the light naphtha range is used in experiments to estimate once through RON as per the conventional scheme. While, Feed-B and Feed-C, which are representative of the cuts obtained after the separation of Feed-A, are used in the experiments with two reactions zone as per the present invention. The experimental results indicate an increase in the RON in the final product as compared to the conventional process.

[0079] Advantages of the Present Invention:

[0080] An improved process for the production of high octane isomerate using two reactors employing the same genre of catalyst.

[0081] Production of high octane isomerate consisting of i-paraffins and naphthenes free from aromatic hydrocarbons like benzene.

[0082] Reduction in cracking of C.sub.7 paraffins to less valuable C.sub.1-C.sub.4 gases, leading to increased liquid yield; and reduction in the undesired conversion of methyl cyclopentane to n-hexane.

[0083] Conversion of low octane paraffins to high octane branched paraffins.