Claims:1. A process for obtaining hydrogen of purity greater than 95% from a feed stream comprising hydrogen in the range of 40 to 70% w/w and C1-C12 hydrocarbons in the range of 30 to 60% w/w, said process comprising the following steps:
a) compressing the feed stream to a pressure in the range of 10 bar to 25 bar to obtain a pressurized feed stream;
b) reforming the pressurized feed stream by reacting with steam to obtain a reformed stream comprising hydrogen, carbon monoxide and carbon dioxide; wherein the amount of hydrogen in the reformed stream is in the range from 50 to 80% w/w;
c) performing a water gas shift reaction on the reformed stream to obtain a hydrogen-rich stream containing hydrogen and carbon dioxide; wherein the amount of hydrogen in the hydrogen-rich stream is in the range from 60 to 90% w/w; and
d) contacting the hydrogen-rich stream with an adsorbing medium to form a complex of hydrogen and the adsorbing medium, and generate an effluent stream containing carbon dioxide; and desorbing hydrogen from the complex to obtain hydrogen of purity greater than 95%.
2. The process as claimed in claim 1, wherein the feed stream is tail gas from a continuous catalytic reformer pressure swing adsorption (CCR-PSA) unit, wherein the tail gas from CCR-PSA unit comprises hydrogen in the range of 40 to 70% w/w and C1-C3 hydrocarbons in the range of 30 to 60% w/w.
3. The process as claimed in claim 1, wherein the feed stream is a mixture of tail gas from a continuous catalytic reformer pressure swing adsorption (CCR-PSA) unit and a hydrocarbon stream.
4. The process as claimed in claim 3, wherein the hydrocarbon stream is at least one selected from the group of streams consisting of a naphtha stream, a desulfurized naphtha stream, a natural gas stream and a desulfurized natural gas stream.
5. The process as claimed in claim 1, involves the step of desulfurizing the feed stream prior to reforming.
6. The process as claimed in claim 1, wherein the step of reforming is carried out in a single reformer or multiple reformers.
7. The process as claimed in claim 1, wherein the step of adsorption is carried out by pressure swing adsorption. , Description:FIELD
The process of the present disclosure relates to obtaining hydrogen from refinery off-gases.
BACKGROUND
There is huge demand for hydrogen of high purity in refineries for hydroprocessing applications such as hydrotreating and hydrocracking.
Some refinery off-gas streams contain hydrogen, and these streams can be a potential source of hydrogen. However, the hydrogen content of these refinery off-gas streams is low. Further, the separation of hydrogen from refinery off-gas streams involves costly separation techniques. Furthermore, refinery off-gas streams may require separation of light end fraction and high end fraction prior to hydrogen recovery, which further increases the cost of the process. Still further, obtaining hydrogen of high purity is challenging.
There is, therefore, felt a need to develop an inexpensive process for obtaining hydrogen of high purity from refinery off-gas streams.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a process for obtaining hydrogen of high purity from a refinery off-gas stream.
Another object of the present disclosure is to provide a process for obtaining hydrogen of high purity from a refinery off-gas stream that is economical.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure provides a process for obtaining hydrogen of purity greater than 95% from a feed stream comprising refinery off-gas stream. The feed stream contains hydrogen in the range of 40 to 70% w/w and C1-C12 hydrocarbons in the range of 30 to 60% w/w.
The feed stream is first compressed to a pressure in the range of 10 bar to 25 bar to obtain a pressurized feed stream. The pressurized feed stream is reformed by reacting with steam, without separating light end fractions and high end fractions. A water gas shift reaction is performed on the reformed stream to obtain a hydrogen rich stream. Hydrogen from the hydrogen rich stream is then adsorbed in a pressure swing adsorption (PSA) unit to form a complex, followed by desorption to obtain hydrogen.
During the process of the present disclosure, the hydrocarbons present in the feed stream are utilized for the preparation of hydrogen during the steps of reforming and the water gas shift reaction.
The feed stream can be a refinery off-gas stream such as tail gas from a continuous catalytic reformer pressure swing adsorption (CCR-PSA) unit. The feed stream can be a mixture of CCR-PSA unit tail gas, and a hydrocarbon stream, such as a naphtha stream or a natural gas stream.
The process of the present disclosure provides hydrogen having a purity of greater than 95%.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING: The process of the present disclosure will now be described with the help of the accompanying drawing, in which:
Figure-1 illustrates a schematic flow-chart of the process of the present disclosure for obtaining hydrogen from a feed stream comprising tail gas from a continuous catalytic reformer pressure swing adsorption (CCR-PSA) unit and a naphtha stream, wherein, the feed stream is desulphurized prior to feeding to the reformer.
Figure-2 illustrates another schematic flow-chart of the process of the present disclosure for obtaining hydrogen from a feed stream comprising tail gas from a CCR-PSA unit and a desulphurized naphtha stream.
Figure-3 illustrates yet another schematic flow-chart of the process of the present disclosure for obtaining hydrogen from a feed stream comprising tail gas of a CCR-PSA unit.

DETAILED DESCRIPTION
There is a demand for hydrogen of high purity in refineries. This disclosure envisages obtaining hydrogen from refinery off-gas streams.
In one aspect, the present disclosure provides a process for obtaining hydrogen of purity greater than 95% from a feed stream comprising hydrogen in the range of 40 to 70% w/w and C1-C12 hydrocarbons in the range of 30 to 60% w/w.
The process of the present disclosure involves the following steps:
First, the feed stream is compressed to a pressure in the range of 10 bar to 25 bar to obtain a pressurized feed stream.
The pressurized feed stream is reformed by reacting with steam to obtain a reformed stream comprising hydrogen, carbon monoxide and carbon dioxide. The amount of hydrogen in the reformed stream is in the range from 50 to 80% w/w.
During the step of reforming, the hydrocarbons react with water molecules in the steam and produce hydrogen, carbon monoxide and carbon dioxide. Due to the production of hydrogen during reforming, the total amount of hydrogen in the reformed stream is greater than the amount of hydrogen in the feed stream.
In accordance with the embodiments of the present disclosure, the step of reforming is carried out at a temperature in the range of 450 ?C to 1100 ?C.
In accordance with the embodiments of the present disclosure, the step of reforming can be carried out in a single reformer or multiple reformers.
In the next step, a water gas shift reaction is performed on the reformed stream to obtain a hydrogen-rich stream containing hydrogen and carbon dioxide. The amount of hydrogen in the hydrogen-rich stream is in the range from 60 to 90% w/w.
During the water gas shift reaction, the carbon monoxide reacts with water molecules in the steam to produce hydrogen and carbon dioxide, thereby increasing the hydrogen content of the stream.
The next step involves contacting the hydrogen-rich stream with an adsorbing medium to form a complex of hydrogen and the adsorbing medium, and generate an effluent stream containing carbon dioxide; and hydrogen is desorbed from the complex to obtain the hydrogen of purity greater than 95%.
In accordance with the embodiments of the present disclosure, the step of adsorbing hydrogen is carried out by pressure swing adsorption (PSA). Other techniques such as membrane separation, solvent extraction, catalytic purification, can also be used for adsorption of hydrogen in the process of the present disclosure.
In accordance with the embodiments of the present disclosure, the adsorbing medium is at least one selected from the group consisting of activated carbon, zeolite, alumina silicate, and activated alumina.
In accordance with one embodiment of the present disclosure, the adsorbing medium is activated carbon.
In accordance with one embodiment of the present disclosure, the feed stream is tail gas from a continuous catalytic reformer pressure swing adsorption (CCR-PSA) unit. The tail gas from CCR-PSA unit comprises hydrogen in the range of 40 to 70% w/w and C1-C3 hydrocarbons in the range of 30 to 60% w/w.
In accordance with another embodiment of the present disclosure, the feed stream is a mixture of tail gas from a CCR-PSA unit and a hydrocarbon stream.
The hydrocarbon stream is at least one selected from the group of streams consisting of a naphtha stream, a desulfurized naphtha stream, a natural gas stream and a desulfurized natural gas stream.
The hydrocarbon stream used in the process of the present disclosure contains C1 to C12 hydrocarbons. Other hydrocarbon streams can also be used.
The feed stream may be desulfurized before the step of reforming.
Thus, during the process of the present disclosure, the hydrocarbons present in the feed stream are utilized for obtaining hydrogen during the steps of reforming and water gas shift reaction. Due to the hydrogen thus produced, the amount of hydrogen obtained from the process is higher as compared to the amount of hydrogen in the feed stream. Thus, the process of present disclosure provides hydrogen in large quantities.
In the process of the present disclosure, the feed stream is used without separating light end fractions and high end fractions.
The process of the present disclosure is simple and economical.
An exemplary embodiment of the process of the present disclosure is provided in Figure-1. A mixture comprising tail gas obtained from a continuous catalytic reformer pressure swing adsorption (CCR PSA) unit (10) and a naphtha stream (20) is desulfurized in a desulfurizer (A) to obtain a feed stream (100). The feed stream (100) is compressed in a compressor (B) to a desired pressure in the range of 10 bar to 25 bar to obtain a pressurized feed stream (110). The pressurized feed stream (110) fed to a steam reformer (C) which can be a combination of single or multiple reactors. The feed stream reacts with steam to obtain a reformed stream (120) comprising hydrogen, carbon monoxide and carbon di-oxide. A water gas shift reaction is performed on the reformed stream (120) in a shift reactor (D) to obtain a hydrogen-rich stream (130). Hydrogen from the hydrogen rich stream (130) is adsorbed in a pressure swing adsorption unit (E) to form a complex of hydrogen and the adsorbent bed; and an effluent stream containing carbon dioxide (150), which is vented off. Desorption of hydrogen from the complex containing adsorbed hydrogen in the pressure swing absorption unit (E) provides hydrogen of purity greater than 95% (140).
Another exemplary embodiment of the process of the present disclosure is provided in Figure 2. A naphtha stream (20) is desulfurized in desulfurizer (A) to obtain desulfurized naphtha stream (20A). The desulfurized naphtha stream (20A) and tail gas (10) obtained from a continuous catalytic reformer pressure swing adsorption (CCR PSA) unit are mixed in mixer (M) to obtain a feed stream (100). The feed stream (100) is compressed in a compressor (B) to a desired pressure in the range of 10 bar to 25 bar to obtain a pressurized feed stream (110). The pressurized feed stream (110) is fed a steam reformer (C) which can be a single reformer or multiple reformers. The feed stream reacts with steam to obtain a reformed stream (120) comprising hydrogen, carbon monoxide and carbon di-oxide. A water gas shift reaction is performed on the reformed stream (120) in a shift reactor (D) to obtain a hydrogen-rich stream (130). Hydrogen from the hydrogen-rich stream (130) is adsorbed in a pressure swing adsorption unit (E) to form a complex comprising hydrogen and adsorbent bed. An effluent stream containing carbon dioxide (150) is generated, which is vented out. Desorption of hydrogen from the complex containing adsorbed hydrogen in pressure swing adsorption unit (E) is carried out to obtain hydrogen of purity greater than 95% (140).
Yet another exemplary embodiment of the process of the present disclosure is provided in Figure 3. The tail gas obtained from a continuous catalytic reformer pressure swing (CCR PSA) unit (10) is desulfurized in desulfurizer (A) to obtain a feed stream (100). The feed stream (100) is compressed in a compressor (B) to a desired pressure in the range of 10 bar to 25 bar to obtain a pressurized feed stream (110). The pressurized feed stream (110) is fed to a steam reformer (C) which can be a single reformer or multiple reformers. The feed stream reacts with steam to obtain a reformed stream (120) comprising hydrogen, carbon monoxide and carbon di-oxide. A water gas shift reaction was performed on the reformed stream (120) in a shift reactor (D) to obtain a hydrogen rich stream (130). Hydrogen from the hydrogen rich stream (130) is adsorbed in a pressure swing adsorption unit (E) to form a complex comprising hydrogen and adsorbent bed, and an effluent stream containing carbon dioxide (150) is generated, which is vented off. Desorption of hydrogen from the complex containing adsorbed hydrogen in a pressure swing absorption unit (E) is carried out to obtain hydrogen of purity greater than 95% (140).
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
Experiments:
Experiment 1:
A feed steam was passed through the processing unit described in Figure-1. The operating data obtained from a commercial processing unit was collected and utilized for simulation studies. The results are shown in Table-1.
Table 1:
Case-I Case-II
Units Kg/hr Kg/hr
Naphtha Feed 7724 7724
Tail gas stream from a CCR-PSA unit 0 1106
Hydrogen production 1813 2246

Hydrogen content of tail gas stream from a CCR-PSA was 63 % w/w. A feed stream, comprising a naphtha stream at flow rate of 7724 Kg/hr and the tail gas from a CCR-PSA unit at flow rate of 1106 Kg/hr, was introduced in the desulfurizer (A). Hydrogen was produced at a rate of 2246 Kg/hr with purity of 99.99%.
Comparative example (Case-I) showed that hydrogen was produced at a rate of 1813 Kg/hr when the feed stream is a naphtha stream at flow rate of 7724 Kg/hr. Thus, due to the presence of tail gas from a CCR-PSA unit in the feed stream, the amount of hydorgen produced has increased by by 433 Kg/hr.
Experiment 2:
A feed steam was passed through the processing unit described in Figure-2. The operating data obtained from a commercial processing unit was collected and utilized for simulation studies. The results are shown in Table-2.
Table 2:
Case-I Case-II
Units Kg/hr Kg/hr
Naphtha as Feed 7724 7724
Tail gas stream from a CCR-PSA unit 0 1661
Hydrogen production 1813 2546

Hydrogen content of tail gas stream from a CCR-PSA was 63 % w/w. A feed stream comprising a desulfurized naphtha stram at flow rate of 7724 Kg/hr and the tail gas stream from a CCR-PSA unit at flow rate of 1661 Kg/hr) was introduced in the mixer (M). Hydrogen was produced at a rate of 2546 Kg/hr with purity of 99.99%.
Comparative example (Case-I) showed that hydrogen was produced at a rate of 1813 Kg/hr when the feed stream is the desulfurized naphtha stream at flow rate of 7724 Kg/hr. Thus, due to the presence of tail gas from a CCR-PSA unit in the feed stream, the amount of hydorgen produced has increased by by 733 Kg/hr.

Experiment 3:
A feed steam was passed through the processing unit described in Figure-3. The operating data obtained from a commercial processing unit was collected and utilized for simulation studies. The results are shown in Table-3.
Table 3:
Case-I
Units Kg/hr
Tail gas stream from a CCR-PSA unit 1661
Tail gas Equivalent Naphtha as Feed saved 2222
Hydrogen production 768

The feed stream comprising a tail gas stream from a CCR-PSA unit having 63 % w/w of hydrogen was introduced in the desulfurizer (A). The results showed hydrogen was produced at flow rate of 768 Kg/hr with purity of 99.99%, when feed stream comprising tail gas from a CCR-PSA unit at flow rate of 1661 Kg/hr was introduced.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for obtaining hydrogen of high purity, that:
- is economical;
- produces hydrogen from feed stream comprising refinery off-gas such as CCR-PSA tail gas; and
- uses refinery off gas such as CCR PSA tail gas stream directly without separating high end fractions and light end fractions.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.