Description:FIELD OF THE INVENTION
The present invention relates to a process for the removal of sulfur compounds and selective hydrogenation of di-olefins and the simultaneous conversion of olefins from hydrocarbon feed stocks through a selective hydrogenation route, in a hydrogenation reactor, in the presence of Ni-Mo based catalyst, with minimum or no loss of total olefins and minimum loss of valuable olefins such as isobutene and butene-1.

BACKGROUND OF THE INVENTION
Olefinic C4/ liquefied petroleum gas (LPG) obtained from cracking units such as thermal and catalytic cracking processes such as delayed coking, steam cracking, fluid catalytic cracking (FCC), visbreaking etc. are upgraded to motor gasoline in gasoline upgradation units such as dimerization, alkylation, etherification etc. or sent for the recovery of petrochemical feedstocks like butene-1 and isobutene or sent to the LPG pool. Most of the catalysts used in these gasoline production processes are sensitive to the impurities present in the olefinic C4/LPG such as di-olefins, basic nitrogenous compounds, metals and sulfur compounds. Also, in the recovery of petrochemical feedstocks, the product should be free of these impurities.

Conventionally, lighter mercaptans are removed from the olefinic C4 or LPG streams by treatment with alkali solutions such as caustic, however the spent caustic generated in these processes are significant, which in turn causes environmental issues in the refinery. Moreover, heavier mercaptans are difficult to remove in these processes. The di-olefins present in these streams causes the faster deactivation of the catalyst in the downstream processing units. Few prior arts described the selective hydrogenation of di-olefins, and methods of removal and reduction of sulfur from the feed streams are mentioned below.

Franklin et. al. (2016) has studied the catalytic performance of Al2O3-supported monometallic and bimetallic catalysts in selective hydrogenation of 1,3-butadiene in the presence of 1-butene under liquid phase conditions. The study revealed that the increase in Ni/Pd atomic ratio suppressed n-butane formation at relatively long contact time, increasing the recovery of 1-butene at middle conversion of 1,3-butadiene and an improved catalytic performance of the bimetallic catalysts being highest in the case of the 1NiPd/Al2O3.

JP2009536216A discloses a process for the selective hydrogenation of butadiene contained in a C4 fluid comprising a concentration of catalyst poison and a C4 olefin containing 1-butene, and further comprising the process of 1-butene in a C4 olefin fluid using a nickel-based catalyst. The process provides a product comprising a minimum butadiene concentration and a reduced concentration of 1-butene.

AU2001291009B2 discloses a method for decreasing sulfur levels in a previously hydrodesulfurized mercaptan sulfur containing olefinic naphtha feed stream. The mercaptans are decomposed to olefins and H2S in the process. The reactions are carried out in presence of a fixed bed catalyst comprises a Group VIIIB metal promoted Group VIB catalyst.

EP1517979B1 discloses a process for the selective hydrodesulfurization of an olefin stream to reduce sulfur content of a cracked olefinic stream, while minimizing the hydrogenation of olefins present in the said streams using non-reactive compounds selected from N2, C1-C4 saturated hydrocarbons, group VIII A noble gases and mixtures thereof.

KR20040019984A discloses a hydrogenation process and conditions for removing mercaptan from gasoline comprises a step of contacting gasoline supply raw materials with a hydrogenated mercaptan removing catalyst wherein the gasoline supply raw materials are whole fractions or some of the whole fractions of fluidized catalytic cracking gasoline, deep catalytic cracking gasoline, straight-run gasoline, coker gasoline, pyrolysis gasoline, thermal cracking gasoline or a mixture thereof. The hydrogenated mercaptan removing catalyst comprises one or more of non-precious metals supported onto amorphous alumina or amorphous alumina silicate and selected from group VIB and/or group VIII on the periodic table.

US6495030B1 discloses a process for concurrently fractionating and hydrotreating of a full range naphtha stream. The process subjects a full boiling range naphtha stream containing organic sulfur compounds and di-olefins is fractionated in a first distillation column reactor with a Group VIII metal hydrogenation catalyst under conditions to form sulfides. The heavier bottoms from first distillation column reactor and hydrogen are fed to a second distillation column reactor containing a hydrodesulfurization catalyst. The heavy naphtha from second distillation column reactor and hydrogen are preferably fed to a third distillation column reactor containing a hydrodesulfurization catalyst.

US7244352B2 discloses a process for producing naphtha having a decreased amount of sulfur by selective hydroprocessing a petroleum feedstream comprising cracked naphtha to reduce its sulfur content with minimum loss of octane. The process utilizes mercaptan reversion process and the product of the HDS unit, which will have a mercaptan reversion sulfur content well above the desired specification but an acceptable non-mercaptan sulfur level (pre-determined), are sent to a mercaptan removal step where at least a portion of the mercaptan reversion sulfur compounds will be selectively removed, thereby, producing a product that meets specification.

US8236172B2 discloses a process for reducing the sulfur content of a hydrocarbon stream, including feeding hydrogen and a hydrocarbon stream including sulfur compounds to a catalytic distillation reactor having one or more hydrodesulfurization reaction zones.

US10280376B2 discloses a process for reducing the sulfur content of a hydrocarbon stream. The process claimed a full range cracked naphtha is contacted with a hydrogenation catalyst to convert at least a portion of the dienes and mercaptans to thioethers and to hydrogenate at least a portion of the dienes. The full range cracked naphtha is fractionated into a light naphtha fraction, a medium naphtha fraction, and a heavy naphtha fraction. The heavy naphtha fraction is hydrodesulfurized. The medium naphtha fraction is mixed with hydrogen and gas oil to form a mixture, which is contacted with a hydrodesulfurization catalyst to produce a medium naphtha fraction having a reduced sulfur concentration.

US7550636B2 discloses a process for the hydrotreatment of an olefinic gasoline comprising a selective hydrogenation stage to reduce at least the di-olefinic and acetylenic compounds content and simultaneously carry out an at least partial conversion of sulphur products comprised in the feedstock so as to increase the molecular weight of said sulphur products. The selective hydrogenation catalyst comprising, on an inert support, at least a sulphide of an element of the group of iron, cobalt and nickel.

Although few prior arts described the selective hydrogenation of di-olefins, however, there is significant loss of olefins in these processes particularly for the lighter streams up to C4 components. Moreover, conversion of mercaptans from a hydrocarbon stream is reported in few prior arts but none of the prior arts describe a process to remove the converted sulfur compounds from the hydrocarbon stream without further hydrodesulfurization which further loses valuable olefins.

Hence there is a requirement of a process for selective hydrogenation of di-olefins from the olefinic C4 and liquefied petroleum gas (LPG) streams prior to routing the streams to the dimerization, alkylation, etherification etc. There is also requirement of a process for the removal of sulfur compounds to meet the desired specification of end products from the said processes.

SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended to determine the scope of the invention.

The present invention provides a process for the removal of sulfur compounds and selective hydrogenation of di-olefins and the simultaneous conversion of olefins from an olefinic C4/LPG feed by co-processing it with a naphtha stream in a hydrogenation reactor, the process comprising the steps of:
(i) mixing the olefinic C4/LPG feed with the naphtha stream to form a combined hydrocarbon feed stream;
(ii) treating the combined hydrocarbon feed stream with a hydrogen stream comprising a recycled hydrogen and a make-up hydrogen in the presence of a catalyst in a hydrogenation reactor zone to form a reactor effluent;
(iii) sending the reactor effluent to a separator and separating a hydrocarbon stream and a hydrogen stream containing hydrogen sulfide from the reactor effluent;
(iv) sending the hydrogen stream containing hydrogen sulfide from the separator to a H2S absorption section;
(v) passing an absorbent amine from the H2S absorption section to obtain a recycled hydrogen after H2S removal and sending a spent absorbent obtained from the H2S absorption section to an absorbent regeneration section;
(vi) sending the recycled hydrogen stream along with a make-up hydrogen to the hydrogenation reactor zone;
(vii) sending the hydrocarbon stream from the separator to a debutanizer zone to separate a clean olefinic C4/LPG stream and a treated naphtha stream;
(viii) sending the clean olefinic C4/LPG stream to upgradation units, petrochemical feedstock recovery section or final liquefied petroleum gas (LPG) product pool; and
(ix) sending the treated naphtha stream to a naphtha hydrotreating (NHT) unit reaction section based on the nature of naphtha used.

OBJECTIVES OF THE PRESENT INVENTION
The main objective of the present invention is to provide a process for the removal of sulfur compounds from an olefinic C4/LPG feed.

Another objective of the present invention is to provide a process for selective hydrogenation of di-olefins in an olefinic C4/LPG feed.

Another objective of the present invention is to increase aromatic content of naphtha stream and reducing the conversion of valuable olefins such as butene-1 and isobutene in an olefinic C4/LPG feed.

Yet another objective of the present invention is selective conversion of olefins based on the use of olefinic C4/LPG feed in the downstream processes such as preparing feed stocks for recovery of petrochemicals or gasoline upgradation processes like alkylation, etherification or dimerization.

BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1 depicts the flow diagram for the selective hydrogenation process for selective conversion of olefins and simultaneous removal of impurities from hydrocarbon feed stocks.

DETAILED DESCRIPTION OF THE INVENTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated process, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The process, and examples provided herein are illustrative only and not intended to be limiting.

The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.
Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference.

The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.

The present invention provides a process for the removal of sulfur compounds and selective hydrogenation of di-olefins and the simultaneous conversion of olefins from an olefinic C4/LPG feed by co-processing it with a naphtha stream in a hydrogenation reactor, the process comprising the steps of:
(i) mixing the olefinic C4/LPG feed (1) with the naphtha stream (2) to form a combined hydrocarbon feed stream (3);
(ii) treating the combined hydrocarbon feed stream (3) with a hydrogen stream comprising a recycled hydrogen (13) and a make-up hydrogen (16) in the presence of a catalyst in a hydrogenation reactor zone (4) to form a reactor effluent (5);
(iii) sending the reactor effluent (5) to a separator (6) and separating a hydrocarbon stream (7) and a hydrogen stream containing hydrogen sulfide (11) from the reactor effluent (5);
(iv) sending the hydrogen stream containing hydrogen sulfide (11) from the separator (6) to a H2S absorption section (12);
(v) passing an absorbent amine (14) from the H2S absorption section (12) to obtain a recycled hydrogen (13) after H2S removal and sending a spent absorbent (15) obtained from theH2S absorption section (12) to an absorbent regeneration section;
(vi) sending the recycled hydrogen (13) stream along with a make-up hydrogen (16) to the hydrogenation reactor zone (4);
(vii) sending the hydrocarbon stream (7) from the separator (6) to a debutanizer zone (8) to separate a clean olefinic C4/LPG stream (9) and a treated naphtha (10) stream;
(viii) sending the clean olefinic C4/LPG stream (9) to upgradation units, petrochemical feedstock recovery section or final liquefied petroleum gas (LPG) product pool; and
(ix) sending the treated naphtha (10) stream to a naphtha hydrotreating (NHT) unit reaction section based on the nature of naphtha used.

In an embodiment of the present invention, the olefinic C4/LPG feed is selected from a mixed olefinic C4/LPG or a mixture of paraffinic C4/LPG and olefinic C4/LPG; wherein the mixture has the olefinic C4/LPG in a range of 5 - 50 wt%.

In an embodiment of the present invention, the olefinic C4/LPG feed comprises compounds selected from a group consisting of di-olefins and sulfur compounds comprising mercaptans such as methyl & ethyl mercaptans or C3 & C4 mercaptans etc., wherein di-olefins and sulfur compounds are impurities.

In an embodiment of the present invention, the olefinic C4/LPG feed comprises a compound selected from a group consisting of n-butane, iso-butane, trans-2-butene, cis-2-butene, 1-butene, isobutene propane, propylene and butadienes; wherein butadienes are 1, 2 butadiene and 1, 3 butadiene.

In an embodiment of the present invention, the naphtha is selected from paraffinic naphtha, olefinic naphtha or cracked gasoline derived from straight run (SR) naphtha, hydrocracking, delayed coking, steam cracking, fluid catalytic cracking (FCC), visbreaking etc. The naphtha has a final boiling point (FBP) up to 210 ?.

In an embodiment of the present invention, the naphtha stream comprises paraffins, isoparaffins, olefins, naphthenes, aromatics, and combination thereof.

In an embodiment of the present invention, the naphtha stream is derived from straight run (SR) naphtha, hydrocracking, delayed coking, steam cracking, FCC, and visbreaking.

In an embodiment of the present invention, the naphtha is taken as treated or untreated naphtha before the treatment in any treating unit. The naphtha stream is termed as treated naphtha stream as obtained from the process after the treatment.

In an embodiment of the present invention, the catalyst is Ni-Mo based catalyst.

In an embodiment of the present invention, the olefinic C4/LPG feed to naphtha stream in step (i) has a volume ratio in a range of 1-5, preferably 1-3.

In an embodiment of the present invention, the hydrogen to hydrocarbon ratio in step (ii) is in a range of 10-50 Nm3/m3, preferably 10-30 Nm3/m3.

In an embodiment of the present invention, the hydrocarbon stream is treated with the hydrogen stream in the reaction zone at a temperature in a range of 150-200 ?.

In an embodiment of the present invention, the hydrocarbon stream is treated with the hydrogen stream in the reaction zone at a pressure in a range of 16-20 bar.

In an embodiment of the present invention, the absorbent amine is selected from a group consisting of monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA).

In an embodiment of the present invention, the hydrocarbon stream is treated with the hydrogen stream in the reaction zone at a liquid hourly space velocity (LHSV) in a range of 3.0-5.0 hr-1.

In an embodiment of the present invention, the combined hydrocarbon stream in step (i) has a total sulfur content is in a range of 300 to 1000 ppmw.

In an embodiment of the present invention, the clean olefinic C4/LPG stream is free of di-olefins and mercaptan sulfur compounds, the clean olefinic C4/LPG stream has a total sulfur content of less than 10 ppmw.

In an embodiment of the present invention, the Ni-Mo based catalyst selectively saturates di-olefins and converts mercaptans to hydrogen sulfide and other heavier sulfides using hydrogen.

In an embodiment of the present invention, the flow diagram for the selective hydrogenation process for selective conversion of olefins and simultaneous removal of impurities from hydrocarbon feed stocks is depicted in Figure 1.

In an embodiment, the present invention provides a general reaction scheme for the conversion of the sulfur compounds to heavier sulphur compounds as presented below:

In another embodiment, the present invention provides a general reaction scheme for selective hydrogenation as presented below:

In an embodiment of the present invention, the process converts up to 100% of the mercaptan sulfur compounds and removes up to 50% of the di-olefins in C4 / LPG.

In an embodiment of the present invention, the clean olefinic C4/LPG stream has a minimum or no loss of total olefins and minimum loss of valuable olefins selected from isobutene and butene-1.

In an embodiment of the present invention, the treated naphtha stream has an aromatic content selectively increases up to 50% when an olefinic naphtha/FFC gasoline is used for co-processing and a butene-1 conversion is reduced.

In an embodiment of the present invention, the clean olefinic C4/LPG stream has a butene-2 content selectively increases up to 40 wt%.

In an embodiment of the present invention, the process utilizes selective hydrogenation approach, there is no caustic consumption step as that of used in a conventional process to remove mercaptans. Also, the process of present invention removes the gaseous sulfur compounds (H2S) and heavier sulfur compounds converted from lighter sulfur compounds present in the olefinic C4/LPG feed whereas in the conventional sweetening process mercaptans are converted into sulfides and remains in the feed itself.

In one embodiment of the present invention, mercaptans such as methyl & ethyl mercaptans or C3 & C4 mercaptans etc., present in the olefinic combined hydrocarbon feed stream is hydrotreated to form olefins and hydrogen sulfide. Newly formed hydrogen sulfide further reacts with di-olefins to form heavier sulfide compounds and with olefins to form heavier mercaptans. Heavier sulfides compounds depends on mercaptan compound and olefin/diolefin compounds in the reaction as given in the reaction scheme above. Heavier mercaptans are defined as mercaptans comprising carbon C5 and above. In an exemplary embodiment heavier mercaptans containing C5 is formed when C1 mercaptan reacts with C4 olefins as given in the reaction scheme above.

In other embodiment of the present invention, lighter mercaptans present in the combined hydrocarbon feed stream and heavier mercaptans formed in the reaction zone reacts with olefins to form heavier mercaptans. Lighter mercaptans are defined as C1-C4 mercaptans such as methyl & ethyl mercaptans or C3 & C4 mercaptans etc., which are generally present in LPG/C4 streams.

In another embodiment of the present invention, lighter mercaptans present in the combined hydrocarbon feed stream and heavier mercaptans formed in the reaction zone reacts with di-olefins to form heavier sulfide compounds. Such heavier sulfides compounds depends on mercaptan compound and olefin/diolefin compounds in the reaction as given in the reaction scheme above.

In yet another embodiment of the present invention, di-olefins present in the combined hydrocarbon feed stream are selectively saturated to olefins in the hydrogenation reactor zone.

In other embodiment of the present invention, the sulfur compounds present in the olefinic C4/LPG stream, reacts in the reaction zone and either shifted to gaseous phase and separated along with the hydrogen stream in the separator or shifted to heavier sulfur compounds boils in the range of higher than that of olefinic C4/LPG feed. The heavier sulfur compounds are separated from the olefinic C4/LPG feed in the debutanizer along with the naphtha stream.

In another embodiment of the present invention, treated naphtha stream is free of di-olefins and containing heavier sulfur compounds are sent to any of the existing naphtha hydrotreater in the refinery for removal of sulfur. As the naphtha stream is already treated in the reaction zone and free of di-olefins, the stream can be directly routed to the HDS reactor without any preprocessing.

In another embodiment of the present invention, the naphtha stream can be reused or recycled before or after removal of sulfur.

In another embodiment of the present invention, the process converts pure olefinic components such as butene-1 through isomerization to produce mixed olefinic components comprising isobutene and butene-2.

EXAMPLES:
The present disclosure with reference to the accompanying examples describes the present invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. It is understood that the examples are provided for the purpose of illustrating the invention only and are not intended to limit the scope of the invention in any way.

Example-1: This example shows the composition of olefinic C4/LPG feed and clean olefinic C4 stream when different types of naphtha streams are used for co-processing as given in Table 1.

Table 1
Components C4 Compositions, %
Type of Naphtha used for co-processing Feed C4 n-Hexane Heavy SRN Light SRN FCC GASOLINE
I-Butane 31.22 30.86 31.32 31.23 31.67
n-Butane 7.82 8.25 8.33 8.06 7.96
Iso-Butene 18.48 18.10 18.26 17.33 16.94
Trans-2-Butene 17.95 25.23 24.59 24.92 20.19
Cis-2-Butene 11.51 11.64 11.57 11.93 11.96
1-Butene 10.74 3.66 3.72 4.25 8.99
1,3 Butadiene 0.08 0.00 0.00 0.00 0.00
Propane 1.71 1.79 1.73 1.79 1.80
Propylene 0.49 0.47 0.49 0.48 0.49
Total Olefins 59.17 59.10 58.62 58.92 58.57
% Saturation of olefins 0.11 0.92 0.42 1.00
% Conversion of mercaptans 98.89 99.92 99.43 99.82

Example-2: This example shows the composition of product LPG (mixed C3 and C4 components) when SR LPG is used as feed. In this case the SR LPG is mixed with olefinic C4 in different compositions and doped with 400 ppmw of ethyl mercaptan before sending to the reactor. N-hexane is used as co-processing naphtha component. No mercaptans were observed in the product LPG. The composition of feed and product LPG are shown in Table 2.

Table 2
wt% of olefinic C4 in SR LPG SR LPG Feed Olefinic C4 feed 5% 10% 20% 35% 50%
Compositions, wt%
Propane 18.38 1.50 17.36 16.30 14.72 12.66 9.34
Propylene 0.03 0.54 0.14 0.07 0.11 0.19 0.77
I-Butane 19.30 31.88 20.17 21.10 22.45 23.90 25.87
n-Butane 61.59 6.88 58.76 55.56 50.90 43.75 35.23
Iso-Butene 0.39 19.48 1.18 2.01 3.58 6.30 9.10
Trans-2-Butene 0.11 14.10 1.37 2.79 4.69 7.57 11.24
Cis-2- Butene 0.09 10.98 0.77 1.55 2.58 4.16 6.23
1-Butene 0.10 11.33 0.25 0.61 0.99 1.48 2.24
1,3 Butadiene 0.00 0.16 0.00 0.00 0.00 0.00 0.00
% conversion of mercaptans Complete conversion of mercaptans

Example-3: This example shows the effect of temperature as given in Table 3. This example shows that, when all other conditions are kept same, the conversion of isobutene and saturation of olefins increases with temperature. Further, the formation of central olefin (butene-2) decreases with temperature. However, at all the experimental temperatures between 150-200 ?, complete conversion of mercaptans and di-olefins are observed.

Table 3
Temperature, ? 150 170 200
% Conversion of isobutene 39.43 49.41 66.55
% Increase in butene-2 36.25 25.00 1.13
% Saturation of total olefins 7.49 15.13 31.31
% Conversion of butadiene Complete conversion of butadiene
% Conversion of mercaptans Complete conversion of mercaptans

Example-4: This example shows the effect of pressure as given in Table 4. This shows that lower pressure is preferable to suppress the saturation of olefins and conversion of isobutene. However, below 16 bar pressure is not preferable to carry out the reaction at liquid phase condition.

Table 4
Pressure, bar 16 20
% Conversion of isobutene 32.72 47.04
% Increase in butene-2 23.77 20.70
% Saturation of total olefins 11.95 16.61
% Conversion of butadiene Complete conversion of butadiene
% Conversion of mercaptans Complete conversion of mercaptans

Example-5: This example shows the effect of liquid hourly space velocity (LHSV) as given in Table 5. Complete conversion of mercaptans and butadiene are observed even at higher space velocity up to 4.5 hr-1. Further, saturation of olefins is suppressed by increasing LHSV which is shown in this example.

Table 5
LHSV, h-1 2.0 3.0 4.5
% Conversion of isobutene 32.72 14.78 12.57
% Conversion of butene-1 67.94 65.29 63.05
% Increase in butene-2 23.77 31.53 35.50
% Saturation of total olefins 11.95 3.23 -1.30
% Saturation of butadiene Complete conversion of butadiene
% Conversion of mercaptans Complete conversion of mercaptans

Example-6: This example shows the effect of olefinic C4/LPG feed to naphtha stream ratio as given in Table 6.

Table 6
Olefinic C4/LPG feed to Naphtha stream ratio (v/v) 0.89 1.02 2.06 2.67 3.00 C4 only*
% Conversion of isobutene 33.57 32.72 35.54 24.22 17.11 27.50
% Conversion of butene-1 66.00 67.94 79.69 72.17 72.30 78.71
% Increase in butene-2 21.28 21.93 27.91 6.40 3.21 0.83
% Saturation of total olefins 14.37 11.95 16.49 17.75 18.61 18.70
% Saturation of butadiene Complete conversion of butadiene
% Conversion of mercaptans Complete conversion of mercaptans
*Complete conversion of mercaptans. However, total sulphur remains constant as there is no naphtha stream to carry over the heavier sulphur compounds.

Example-7: This example shows the composition of naphtha stream in terms of paraffins, isoparaffins, olefins, naphthenes and aromatics (PIONA) before and after co-processing with olefinic C4/LPG feed as given in Table 7. This example shows significant increase in aromatics content in case of FCC gasoline used for co-processing with olefinic C4/LPG feed.

Table 7
Attributes n-Hexane Heavy SRN Light SRN FCC GASOLINE
Feed Product Feed Product Feed Product Feed Product
Paraffins, % 100.00 97.64 14.84 14.98 26.32 18.79 4.22 4.10
Isoparaffins, % 0.00 1.45 22.23 24.23 50.89 53.76 31.63 29.12
Olefins, % 0.00 0.74 0.04 1.00 0.13 0.63 32.044 22.57
Naphthenes, % 0.00 0.13 41.26 38.12 19.37 25.41 5.97 7.40
Aromatics, % 0.00 0.05 21.06 21.66 3.28 1.40 24.39 36.82

Example-8: This example shows the composition of product having mixed C4 components when pure Butene-1 is co-processed with n-hexane as naphtha stream which is pre-doped with 800 ppmw of ethyl mercaptan as given in Table 8. This example shows that although pure Butene-1 is used as the feed, mixed C4 components which were converted from Butene-1 in the process are obtained in the product.

Table 8
Components Product C4 composition, wt%
I-Butane 3.96
n-Butane 16.18
Iso-Butene 2.40
Trans-2-Butene 44.78
Cis-2- Butene 23.35
1-Butene 8.69
Propane 0.00
Propylene 0.45

Advantages of the present invention over the prior art:
• The advantage of the present invention is the removal of sulfur specifically mercaptan sulfur and di-olefins such as 1,2 butadiene and 1, 3 butadiene from C4/LPG stream with minimum or no saturation of olefins.

• Another advantage of the present invention is the co-processing of the C4 /LPG feed along with a paraffinic or olefinic naphtha stream.

• Another advantage of the present invention is the conversion of mercaptans to other sulfides and removal of di-olefins from the naphtha stream also.

• Yet another advantage is that the process of present invention operates at moderate temperature (150-200 ?) and moderate pressure (16-20 bar).

• Yet another advantage of the present invention is that the converted sulfur compounds from C4/LPG feed removed along with the naphtha stream which can be further treated in any of the existing unit such as naphtha hydrotreating (NHT) unit or Gasoline hydrodesulfurization (HDS).

• Yet another advantage of the present invention is the process removes impurities from straight run (SR) C4/LPG or any other paraffinic C4/LPG streams by mixing with cracked/olefinic C4 or cracked/olefinic LPG in the range of 5- 50% prior to co-processing with said naphtha stream. Hence this process is applicable for the purpose of removal of impurities from SR C4/LPG or any paraffinic LPG.

• One advantage of the present invention is that the process increases aromatic content and research octane number (RON) of naphtha /gasoline stream when olefinic naphtha / gasoline is used for co-processing.

• Yet another advantage of the present invention is that there is minimum conversion of butene-1 when olefinic naphtha/gasoline is used for co-processing.

• Another advantage of the present invention is that there is no change in hydrocarbon matrix of naphtha in terms of PIONA when paraffinic naphtha is used for co-processing.

• Yet, another advantage of the present invention is that the process utilizes selective hydrogenation approach, hence there is no caustic consumption as that of conventional process to remove mercaptans.

• Yet another advantage of the present invention is very low consumption of hydrogen as there is minimum saturation of olefins.

• Yet another advantage of the present invention is that the process of present invention removes the sulfides converted from mercaptans in the C4/LPG stream whereas in the conventional sweetening process mercaptans are converted into sulfides and remains in the feed itself.

• Yet another advantage is that, in the present invention process condition is optimized in such a way that the di-olefins are saturated selectively along with conversion of mercaptans to heavier sulfides with minimum or no loss of valuable olefins.

• Yet another advantage of the present invention is that the process converts pure olefinic components such as butene-1 through isomerization to produce mixed olefinic components comprising isobutene & butene-2. , Claims:1. A process for the removal of sulfur compounds and selective hydrogenation of di-olefins and the simultaneous conversion of olefins from an olefinic C4/LPG feed by co-processing it with a naphtha stream in a hydrogenation reactor, the process comprising the steps of:
(i) mixing the olefinic C4/LPG feed with the naphtha stream to form a combined hydrocarbon feed stream;
(ii) treating the combined hydrocarbon feed stream with a hydrogen stream comprising a recycled hydrogen and a make-up hydrogen in the presence of a catalyst in a hydrogenation reactor zone to form a reactor effluent;
(iii) sending the reactor effluent to a separator and separating a hydrocarbon stream and a hydrogen stream containing hydrogen sulfide from the reactor effluent;
(iv) sending the hydrogen stream containing hydrogen sulfide from the separator to a H2S absorption section;
(v) passing an absorbent amine from the H2S absorption section to obtain a recycled hydrogen after H2S removal and sending a spent absorbent obtained from the H2S absorption section to an absorbent regeneration section;
(vi) sending the recycled hydrogen stream along with a make-up hydrogen to the hydrogenation reactor zone;
(vii) sending the hydrocarbon stream from the separator to a debutanizer zone to separate a clean olefinic C4/LPG stream and a treated naphtha stream;
(viii) sending the clean olefinic C4/LPG stream to upgradation units, petrochemical feedstock recovery section or final liquefied petroleum gas (LPG) product pool; and
(ix) sending the treated naphtha stream to a naphtha hydrotreating (NHT) unit reaction section based on the nature of naphtha used.

2. The process as claimed in claim 1, wherein the olefinic C4/LPG feed is selected from a mixed olefinic C4/LPG or a mixture of paraffinic C4/LPG and olefinic C4/LPG; wherein the mixture has the olefinic C4/LPG in a range of 5 - 50 wt%.

3. The process as claimed in claim 1, wherein the olefinic C4/LPG feed comprises a compound selected from a group consisting of di-olefins and sulfur compounds comprising mercaptans, wherein the mercaptan is selected from methyl mercaptan, ethyl mercaptan, C3 mercaptan or C4 mercaptan; wherein di-olefins and sulfur compounds are impurities.

4. The process as claimed in claim 1, wherein the naphtha is selected from paraffinic naphtha, olefinic naphtha or cracked gasoline derived from straight run (SR) Naphtha, hydrocracking, delayed coking, steam cracking, fluid catalytic cracking (FCC), and visbreaking; the naphtha has a final boiling point (FBP) up to 210 ?.

5. The process as claimed in claim 1, wherein the catalyst is Ni-Mo based catalyst.

6. The process as claimed in claim 1, wherein the olefinic C4/LPG feed to naphtha stream in step (i) has a volume ratio in a range of 1-5.

7. The process as claimed in claim 1, wherein the hydrogen stream to the hydrocarbon stream in step (ii) has a ratio is in a range of 10-50 Nm3/m3.

8. The process as claimed in claim 1, wherein the hydrocarbon stream is treated with the hydrogen stream in the reaction zone at a temperature in a range of 150-200 ?.

9. The process as claimed in claim 1, wherein the hydrocarbon stream is treated with the hydrogen stream in the reaction zone at a pressure in a range of 16-20 bar.

10. The process as claimed in claim 1, wherein the hydrocarbon stream is treated with the hydrogen stream in the reaction zone at a liquid hourly space velocity (LHSV)in a range of 3.0-5.0 hr-1.

11. The process as claimed in claim 1, wherein the combined hydrocarbon stream in step (i) has a total sulfur content is in a range of 300 to 1000 ppmw.

12. The process as claimed in claim 1, wherein the absorbent amine is selected from a group consisting of monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA).

13. The process as claimed in claim 1, wherein the clean olefinic C4/LPG stream is free of di-olefins and mercaptans, the clean olefinic C4/LPG stream has a total sulfur content of less than 10 ppmw.

14. The process as claimed in claim 1, wherein the clean olefinic C4/LPG stream has a minimum or no loss of total olefins and minimum loss of valuable olefins selected from isobutene and butene-1.

15. The process as claimed in claim 1, wherein the treated naphtha stream has an aromatic content selectively increases up to 50% when an olefinic naphtha/FFC gasoline is used for co-processing.

16. The process as claimed in claim 1, wherein the clean olefinic C4/LPG stream has a butene-2 content selectively increases up to 40 wt%.