Claims:1. A process for treatment of off-gases from a hydro-desulfurization (HDS) unit, said process comprising:
feeding the off-gases comprising hydrogen (H2) gas and C1-C5 hydrocarbon gases to a membrane module at a feeding side of the membrane module, said membrane module housing a polymeric membrane selective to permeation of the hydrogen gas as compared to the C1-C5 hydrocarbon gases;
withdrawing a permeate stream from the membrane module at a permeate side of the membrane module, said permeate stream being a hydrogen (H2) gas rich stream; and
withdrawing a retentate stream from the membrane module at a retentate side of the membrane module, said retentate stream being a hydrogen (H2) gas depleted stream,
wherein said polymeric membrane is an asymmetric polymeric hollow fiber membrane, and wherein a pressure drop across the feeding side and the permeate side of the membrane module ranges from 5 psi to 90 psi.
2. The process as claimed in claim 1, wherein the off-gases comprise hydrogen (H2) gas in an amount ranging from 40% to 90% v/v.
3. The process as claimed in claim 1, wherein the permeate stream comprises hydrogen (H2) gas in an amount ranging from 50% to 99% v/v.
4. The process as claimed in claim 1, wherein the retentate stream comprises hydrogen (H2) gas in an amount ranging from 1% to 49% v/v.
5. The process as claimed in claim 1, wherein the polymeric membrane is made of polysulfone.
6. The process as claimed in claim 5, wherein the polymeric membrane has a wall thickness ranging from 25-100 µm and an outer diameter ranging from 90-500 µm.
7. The process as claimed in claim 1, wherein pressure on the feeding side ranges from 30 to 725 psi.
8. The process as claimed in claim 1, wherein pressure on the permeate side ranges from 20 to 705 psi.
9. The process as claimed in claim 1, wherein the membrane module comprises a plurality of polymeric membranes selective to permeation of the hydrogen gas as compared to the C1-C5 hydrocarbon gases.
10. The process as claimed in claim 9, wherein the membrane module comprises a plurality of polymeric membranes arranged in a series such that a retentate stream from a first polymeric membrane is fed to a second polymeric membrane.
11. The process as claimed in claim 9, wherein the membrane module comprises a plurality of polymeric membranes arranged in parallel allowing simultaneous feeding of the off-gases to said polymeric membranes.

, Description:TECHNICAL FIELD
[0001] The present disclosure pertains to the technical field of treatment of off-gases. In particular, the present disclosure relates to a process for treatment of off-gases from a hydro-desulfurization (HDS) unit that affords efficient recovery and/or recycling of hydrogen (H2) gas from the off-gases in an economical manner.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Hydrogen is an important gas for producing clean and low sulphur fuel. Due to stringent environmental regulations for production of sulphur free fuels, hydrogen requirement in refinery and petrochemical plants has increased over the past few years. In addition, more hydrogen is needed to enhance the capacity of refinery processes. Hence, more recently, focus has been on recovering and reusing the leftover hydrogen from refinery off-gas or fuel gas streams. The impetus for hydrogen recovery in the petroleum refineries is of three-fold, as hydrogen rich gas routing to fuel gas header or PSA tail gas or waste gaseous stream: (a) first, the demand of hydrogen gas in the refinery/petrochemical plant is substantially very high, (b) secondly, it is desirable to reduce the production of hydrogen and enhance the reuse of left over gas, which also helps in reducing the environment emissions, and (c) lastly, the process for recovery of hydrogen from unrecovered area has attractive ROI, as the hydrogen is one of the most costly gas in refinery/petrochemical plants.
[0004] A wide variety of processes and techniques have been proposed to separate/enrich hydrogen from hydrocarbon gaseous mixture streams in refineries. For example, U.S. Pat No 4,238,204 describes permeabilities and separation factor for H2, CO, CH4 and H2/CO, H2/CH4 respectively. A feed gas (i.e. regenerating gas) is collected in the holding tank at about 2.4 bar pressure before passing to the membrane unit. These gas is then compressed to 21 bar and fed to the membrane unit for achieving hydrogen enrichment from 82 mol. % to 97 mol. %. The differential in pressure between compressed regenerating gas and the permeated gas is maintained at about 13.6 bar.
[0005] U.S. Pat No 4,654,063 discloses a hybrid cryogenic/membrane process and stand-alone cryogenic or membrane system for achieving the higher purity hydrogen as product from hydrocracker off-gas. The maximum hydrogen purity in a stand-alone membrane process is achieved about 89 mol% and hydrogen recovery of 61.6% at the expense of 2.4 time higher power consumption compared with hybrid cryogenic/membrane process. Whereas in another example, the maximum purity and recovery of hydrogen using a stand-alone membrane process is achieved about 97.3 mol% from 86.9 mol% and 64.11% respectively. To achieve such separation, it required higher pressure drop (~48 bar) and partial pressure difference (~31 bar) across the membrane module.
[0006] U.S Pat. No 7,947,117B2 illustrates a purification process using polymeric membrane technique applicable for downstream section of stream reforming process where the gaseous mixture consist of mainly carbon monoxide, hydrogen and carbon dioxide (commonly known as syngas). Three combination of membranes were used to come down CO by 100ppm and simultaneously enriched hydrogen purity at 99% with a recovery more than 85%.
[0007] Similarly, U.S. Pat No 5,634,354 related to fluid catalytic cracker off-gas for recovery of hydrogen from mixture of hydrocarbon gases in combination with refrigeration and membrane techniques. A non-condensed gases from separator is introduced to the series of polymeric membranes (supplied by permea Inc, St Louis) operated at lower pressure drop i.e. 125 psi and enriched hydrogen stream (permeate) withdrawn at 25 psia with 90 mol% purity. Further, these permeate stream is compressed to 250-600 psia and fed to the second membrane for achieving higher purity of hydrogen up to 98 mol%.
[0008] However, the methods proposed in these documents and such other documents suffers from several fold disadvantages, key disadvantage being requirement of maintaining high pressure drop between the feeding side and the permeate side mandating usage of one or more compressors to compress the off-gases/gaseous mixture before it can be subjected to the recovery, which dramatically increases the capital expenditure as well as the operating costs making the overall process non-viable on an industrial scale.
[0009] The present invention satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the state-of-art. Particularly, the present disclosure provides an economically viable process for an efficient recovery of hydrogen from the multi-component hydrocarbon gases (C1-C5) mixture present in fuel gas (or off-gas) stream of hydro-desulfurization unit.
[0010] All publications referred to hereinabove are incorporated in their entirety by way of reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

OBJECTS
[0011] It is an object of the present disclosure to provide a process for treatment of off-gases from a hydro-desulfurization (HDS) unit that overcomes one or more disadvantages of the processes known in the art.
[0012] Another object of the present disclosure is to provide a process for treatment of off-gases from a hydro-desulfurization (HDS) unit that is economical and industrially viable.
[0013] Another object of the present disclosure is to provide a process for treatment of off-gases from a hydro-desulfurization (HDS) unit that precludes the requirement of usage of compressors.
[0014] Another object of the present disclosure is to provide a process for treatment of off-gases from a hydro-desulfurization (HDS) unit that can operate at a minimal pressure drop.
[0015] Another object of the present disclosure is to provide a process for treatment of off-gases from a hydro-desulfurization (HDS) unit that affords recovery of hydrogen (H2) gas of requisite purity grade.
[0016] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the exemplary embodiments of the invention.

SUMMARY
[0017] The present disclosure pertains to the technical field of treatment of off-gases. In particular, the present disclosure relates to a process for treatment of off-gases from a hydro-desulfurization (HDS) unit that affords efficient recovery and/or recycling of hydrogen (H2) gas from the off-gases in an economical manner.
[0018] An aspect of the present disclosure relates to a process for treatment of off-gases from a hydro-desulfurization (HDS) unit, said process comprising: feeding the off-gases comprising hydrogen (H2) gas and C1-C5 hydrocarbon gases to a membrane module at a feeding side of the membrane module, said membrane module housing a polymeric membrane selective to permeation of the hydrogen gas as compared to the C1-C5 hydrocarbon gases; withdrawing a permeate stream from the membrane module at a permeate side of the membrane module, said permeate stream being a hydrogen (H2) gas rich stream; and withdrawing a retentate stream from the membrane module at a retentate side of the membrane module, said retentate stream being a hydrogen (H2) gas depleted stream, wherein said polymeric membrane is an asymmetric polymeric hollow fiber membrane, and wherein a pressure drop across the feeding side and the permeate side of the membrane module ranges from 5 psi to 90 psi.
[0019] In an embodiment, the off-gases comprise hydrogen (H2) gas in an amount ranging from 40% to 90% v/v. In an embodiment, the permeate stream comprises hydrogen (H2) gas in an amount ranging from 50% to 99% v/v. In an embodiment, the retentate stream comprises hydrogen (H2) gas in an amount ranging from 1% to 49% v/v. In an embodiment, the polymeric membrane is made of polysulfone. In an embodiment, the polymeric membrane has a wall thickness ranging from 25-100 µm and an outer diameter ranging from 90-500 µm. In an embodiment, pressure on the feeding side ranges from 30 to 725 psi. In an embodiment, pressure on the permeate side ranges from 20 to 705 psi. In an embodiment, the membrane module comprises plurality of polymeric membranes selective to permeation of the hydrogen gas as compared to the C1-C5 hydrocarbon gases. In an embodiment, the membrane module comprises plurality of polymeric membranes arranged in a series such that a retentate stream from a first polymeric membrane is fed to a second polymeric membrane. In an embodiment, the membrane module comprises plurality of polymeric membranes arranged in parallel allowing simultaneous feeding of the off-gases to said polymeric membranes.
[0020] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0022] FIG. 1 illustrates an exemplary schematic showing integration of the method of the present disclosure with existing hydro-desulfurization unit in refinery in accordance with an embodiment of the present disclosure.
[0023] FIG. 2A illustrates an exemplary schematic showing a membrane module with a plurality of polymeric membranes (M1 and M2) arranged in a series in accordance with an embodiment of the present disclosure.
[0024] FIG. 2B illustrates an exemplary schematic showing a membrane module with a plurality of polymeric membranes (M1 and M2) arranged in parallel in accordance with an embodiment of the present disclosure.
[0025] FIG. 3 illustrates a schematic showing the flow scheme of experimental set up in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0026] The following is a detailed description of embodiments of the present invention. The embodiments are in such detail as to clearly communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
[0027] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0028] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability.
[0029] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0030] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0031] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0032] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[0033] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
[0034] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0035] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0036] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0037] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0038] The present disclosure pertains to the technical field of treatment of off-gases. In particular, the present disclosure relates to a process for treatment of off-gases from a hydro-desulfurization (HDS) unit that affords efficient recovery and/or recycling of hydrogen (H2) gas from the off-gases in an economical manner.
[0039] An aspect of the present disclosure relates to a process for treatment of off-gases from a hydro-desulfurization (HDS) unit, said process comprising: feeding the off-gases comprising hydrogen (H2) gas and C1-C5 hydrocarbon gases to a membrane module at a feeding side of the membrane module, said membrane module housing a polymeric membrane selective to permeation of the hydrogen gas as compared to the C1-C5 hydrocarbon gases; withdrawing a permeate stream from the membrane module at a permeate side of the membrane module, said permeate stream being a hydrogen (H2) gas rich stream; and withdrawing a retentate stream from the membrane module at a retentate side of the membrane module, said retentate stream being a hydrogen (H2) gas depleted stream, wherein said polymeric membrane is an asymmetric polymeric hollow fiber membrane, and wherein a pressure drop across the feeding side and the permeate side of the membrane module ranges from 5 psi to 90 psi.
[0040] In an embodiment, the off-gases comprise hydrogen (H2) gas in an amount ranging from 40% to 90% v/v.
[0041] In an embodiment, the permeate stream comprises hydrogen (H2) gas in an amount ranging from 50% to 99% v/v, preferably, ranging from 55% to 99% v/v, more preferably, ranging from 60% to 99% v/v and most preferably, ranging from 70% to 99% v/v.
[0042] In an embodiment, the retentate stream comprises hydrogen (H2) gas in an amount ranging from 1% to 49% v/v, preferably, ranging from 2% to 44% v/v, more preferably, ranging from 3% to 40% v/v and most preferably, ranging from 5% to 35% v/v.
[0043] In an embodiment, the polymeric membrane is made of polysulfone. In an embodiment, the polymeric membrane is made of polysulfone and one or more additives such as citric acid, maleic acid and tartatic acid. Alternatively, the polymeric membrane made of any other material that exhibits requisite selectivity towards hydrogen in comparison to the hydrocarbons may be used.
[0044] In an embodiment, the polymeric membrane has a wall thickness ranging from 25-100 µm, preferably, ranging from 35 to 65 µm, more preferably, ranging from 45 to 95 µm and most preferably, ranging from 55 to 100 µm.
[0045] In an embodiment, the polymeric membrane has an outer diameter ranging from 90-500 µm, preferably, ranging from 100 to 450 µm, more preferably, ranging from 100 to 400 µm and most preferably, ranging from 150 to 350 µm.
[0046] In an embodiment, pressure on the feeding side ranges from 30 to 725 psi, preferably, ranging from 35 to 650, more preferably, ranging from 35 to 500, and most preferably, ranging from 40 to 400.
[0047] In an embodiment, pressure on the permeate side ranges from 15 to 705 psi, preferably, ranging from 20 to 705 psi, more preferably, ranging from 20 to 550 psi, and most preferably, ranging from 30 to 350 psi.
[0048] FIG. 1 illustrates an exemplary schematic showing integration of the method of the present disclosure with existing hydro-desulfurization unit in refinery. As can be seen from FIG. 1, a combination of VGO (stream 1) and pure hydrogen (stream 2) can be fed to the hydro-desulfurization reactor (3). After the reaction, the product can be separated in a high pressure separator unit (4) and a low pressure separator unit (5). The gaseous stream from the separator unit (5) can then be fed to a cold flash unit (6), gaseous stream emitted wherefrom typically contain hydrogen in about 79-82 vol%, which conventionally is routed to the fuel gas header (10). The dotted line indicates integration of the membrane unit (7). The membrane can be operated at the same pressure and temperature condition as of the cold flash unit (6). A feed gas stream (9) i.e. the off-gases, for example, containing 79-82 vol% hydrogen, 8-10 vol% methane, 3-5 vol% ethane, 1-2 vol% propane, 0.5-1.5 vol% n-butane, 0.1-0.2 vol% moisture and 0.02-0.05 vol% H2S having temperature in the range of 30-45? can be fed to the membrane unit (7) on its feed side. The membrane unit (7), can include a hollow fiber polymeric membrane, for example, made up of polysulfone, defining two outlet streams i.e. permeate and retentate sides. The permeate stream is hydrogen rich stream and the retentate stream is hydrogen depleted stream. Membrane selectively affords permeation of hydrogen. In an embodiment, the membrane exhibits a hydrogen/methane selectivity of about 30-50. The hydrogen depleted stream can be combined with existing/conventional fuel gas header (10) for further usage of heavier hydrocarbon molecules. The hydrogen rich stream (11), free from impurities and primarily including the recovered hydrogen from stream (9) can be withdrawn at appropriate pressure. The hydrogen rich stream (11) can be combined with the existing ultrapure hydrogen header, and the same may be used as input feed to the existing compressor or other process streams in the refinery (13). The amount of recovered hydrogen from the stream (9) can be utilized in the reactor (3) without additional requirement of compressor.
[0049] In an embodiment, the membrane module comprises plurality of polymeric membranes selective to permeation of the hydrogen gas as compared to the C1-C5 hydrocarbon gases. Alternatively, one can use a plurality of membrane modules each containing one or more polymeric membranes selective to permeation of the hydrogen gas as compared to the C1-C5 hydrocarbon gases.
[0050] In an embodiment, the membrane module comprises plurality of polymeric membranes arranged in a series such that a retentate stream from a first polymeric membrane is fed to a second polymeric membrane. FIG. 2A illustrates an exemplary schematic showing a membrane module with a plurality of polymeric membranes (M1 and M2) arranged in a series such that a retentate stream from a first polymeric membrane (M1) is fed to a second polymeric membrane (M2). With this configuration, the hydrogen recovery can be increased as compared to the performance of single membrane module; however, throughput of the membrane may be reduced (e.g. by about 50-55%) as compared to the single membrane module, plausibly owing to the flow resistance offered by second membrane, which may ultimately reduce the overall feed throughput in the membranes arranged in series.
[0051] In an embodiment, the membrane module comprises plurality of polymeric membranes arranged in parallel allowing simultaneous feeding of the off-gases to said polymeric membranes. FIG. 2B illustrates an exemplary schematic showing a membrane module with a plurality of polymeric membranes (M1 and M2) arranged in parallel allowing simultaneous feeding of the off-gases to said polymeric membranes (M1 and M2). This configuration affords independent operation of each of the plurality of membranes. In an exemplary embodiment, the permeate stream (i.e. hydrogen gas of requisite purity) from each of the membranes is withdrawn at requisite pressure and combined together. In an embodiment, the retentate stream is available (withdrawn) at the same pressure as that of the feed. With this configuration, the feed throughput can be amplified by about 40-45% as compared to the configuration wherein, the plurality of membranes are arranged in series; however, with this configuration, the hydrogen recovery may be reduced by about 2% while retaining the same purity of hydrogen.
[0052] Accordingly, the present invention provides an efficient process for recovering hydrogen from mixture of heavier hydrocarbon gases using hollow fibre polymeric membrane selectively permeating hydrogen molecules and restricting other hydrocarbon gas molecules based on diffusivity and permeation rate of each molecules. The process can be useful for the recovering hydrogen from different streams in the refineries such as recovering hydrogen from PSA off-gas, fuel gas header, hydrocracker, hydrotreater off-gas and the likes. Preferably, for efficient working of the method of the present disclosure, the hydrogen should be present in range of 20-90 vol.% (in the off-gas) at a minimum operating pressure of 30-70 psig. A skilled artisan would appreciate that the operating condition may vary depending upon the source of streams from various processes in the refinery. In an exemplary embodiment, the feed gas operating pressure, temperature and hydrogen concentration are in range of 30-520 psig, 15-65? and 20-90 vol%, respectively. The advantageous method of the present disclosure can be employed and/or integrated in any refinery or petrochemical or chemical industry process, irrespective of the feed pressure. Simply put, the process of the present disclosure may be used when feed pressure is at lower range for example, 30-50 psig or at a higher range for example, 500-1000 psig.
EXAMPLES
[0053] The dope solution for hollow fiber membrane spinning was prepared by adding 320 g of polysulfone in a stirred tank containing 340 g of N,N-dimethyl acetamide, 50 g of ethanol, 250 g of tetrahydrofuran and 40 gm of tartaric acid. The stirring was continued at ambinet for 20 hours. The solution was allowed to settle for 24 hours. The formed dope solution was used to make hollow fiber membranes by a conventional dry-jet/wet spinning process. Water was used as the bore fluid as well as external coagulant at 30 ?C. The dope solution pressure was 45 psi and the bore fluid pressure was 10 psi. The formed membranes were washed with water for 48 hours and then dried at 60°C. The membrane modules were prepared by using conventional two-component glue and SS-316 as housing. The membrane module so prepared was used for further experiments.
[0054] FIG. 3 illustrates a schematic showing the flow scheme of experimental set up, wherein all necessary ancillary instrumentation for pressure, temperature, flow rate measurements and necessary control for process safety were used. The feed pressure was maintained by a pressure regulator installed in the source of gas stream. Both permeate and retentate flow rates were measured after expansion to atmospheric pressure using wet gas meter. The feed gas enters the shell (feed) side at high pressure and flows inside the membrane in a co-current or counter current mode and available at lower pressure (compared to feed pressure) at permeate side of membrane. The composition of each gas stream was analyzed by Refinery gas analyzer (make Agilent 7890A) Gas Chromatograph equipment.
[0055] EXAMPLES 1-3
[0056] Membrane bench scale unit was equipped with provision for testing the polymeric membrane module, inclusive of a separate permeate and retentate line followed by the flow measuring device i.e. wet gas meter. The composition of gas was kept the same as per the fuel gas stream available in typical VGO-HDS plants. The feed gas was used at room temperature i.e. around 35?. The membrane module contained hollow fibrous membranes with effective surface area varying from 0.5-1 m2. The membrane module can withstand pressures and temperatures of about 1000 psig and about 120 °C, respectively, while it can handle gas stream flows of up to 0.5- 40 NL/min.
[0057] The membrane unit treated the off-gas from the separator, corresponding to the total flow of 2.26 kg/hr of gas containing almost 0.467 kg/hr of hydrogen being utilized in the fuel gas stream of refinery as shown below in Table 1, 2 and 3, respectively. The operating conditions were kept at minimum feed pressure at about 21.75, 65.25 and 104.4 psig, withdrawing permeate at constant pressure of 14.5 psig in all the examples. The permeate purity of hydrogen is enriched from 80 mol% to 92.18, 96.15 and 98.40 a feed to permeate pressure drop of 7.25, 50.75 and 89.99 psig, respectively. Detailed process parameters are also provided in the Table 1, 2 and 3.

Table 1: Process parameters for treatment of the off-gas (Feed Pressure: 21.75 psig)
Components/Parameters CFD off-gas Permeate stream Retentate stream
Mass flow rate (Kg/hr) 2.26 0.56 1.69
Temperature ? 35-38 35-38 35-38
Pressure , psig 21.75 14.5 19.75
Composition (mol%)
Hydrogen 80.00% 92.18% 11.65%
Methane 8.00% 4.18% 16.14%
Ethane 5.00% 2.02% 20.43%
Propane 2.50% 0.78% 15.85%
n-Butane 2.50% 0.46% 22.50%
Composition (Kg/hr)
Hydrogen 0.4672 0.2700 0.1972
Methane 0.3701 0.0969 0.2732
Ethane 0.4337 0.0878 0.3459
Propane 0.3180 0.0498 0.2683
n-Butane 0.4192 0.0383 0.3809
Total (Kg/hr) 2.01 0.54 1.47

Table 2: Process parameters for treatment of the off-gas (Feed Pressure: 65.25 psig)
Components/Parameters CFD off-gas Permeate stream Retentate stream
Mass flow rate (Kg/hr) 2.26 0.43 1.83
Temperature ? 35-38 35-38 35-38
Pressure , psig 65.25 14.5 63.25
Composition (mol%)
Hydrogen 80.00% 96.15% 10.12%
Methane 8.00% 2.06% 17.61%
Ethane 5.00% 0.99% 21.33%
Propane 2.50% 0.38% 16.04%
n-Butane 2.50% 0.22% 21.88%
Composition (Kg/hr)
Hydrogen 0.4672 0.2820 0.1852
Methane 0.3701 0.0478 0.3223
Ethane 0.4337 0.0433 0.3904
Propane 0.3180 0.0245 0.2935
n-Butane 0.4192 0.0189 0.4003
Total (Kg/hr) 2.01 0.42 1.59

Table 3: Process parameters for treatment of the off-gas (Feed Pressure: 104.4 psig)
Components/Parameters CFD off-gas Permeate stream Retentate stream
Mass flow rate (Kg/hr) 2.26 0.35 1.91
Temperature ? 35-38 35-38 35-38
Pressure , psig 104.4 14.5 102.4
Composition (mol%)
Hydrogen 80.00% 98.40% 9.35%
Methane 8.00% 0.85% 18.36%
Ethane 5.00% 0.41% 21.79%
Propane 2.50% 0.16% 16.14%
n-Butane 2.50% 0.09% 21.56%
Composition (Kg/hr)
Hydrogen 0.4672 0.2888 0.1784
Methane 0.3701 0.0199 0.3502
Ethane 0.4337 0.0180 0.4157
Propane 0.3180 0.0102 0.3078
n-Butane 0.4192 0.0079 0.4114
Total (Kg/hr) 2.01 0.34 1.66

[0058] During the series of experiments, it could be noted that the process of the present disclosure can afford recovery of the hydrogen to the tune of about 59 wt% with the optimised stage cut.
[0059] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES
[0060] The present disclosure provides a process for treatment of off-gases from a hydro-desulfurization (HDS) unit that is economical and industrially viable.
[0061] The present disclosure provides a process for treatment of off-gases from a hydro-desulfurization (HDS) unit that precludes the requirement of usage of compressors.
[0062] The present disclosure provides a process for treatment of off-gases from a hydro-desulfurization (HDS) unit that affords recovery of hydrogen (H2) gas of requisite purity grade.