A PROCESS FOR ADSORPTIVE DESULPHURIZATION OF NAPHTHA

FIELD

The present disclosure relates to a process for adsorptive desulphurization of naphtha.

DEFINITIONS As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.

Desulphurization: The term“desulphurization” also known as“desulfurization” refers to a chemical process for the removal of sulphur from a material/molecule or removal of sulphur compounds from a mixture such as oil refinery streams.

Reactive adsorption desulphurization (RADS): The term “reactive adsorption desulphurization (RADS)” refers to reactive adsorption of sulphur wherein the sulphur compounds in fuel are removed by chemical interaction between the fuel and the sorbent material. BACKGROUND

The background information herein below relates to the present disclosure but is not necessarily prior art.

Sulphur is an important hetero-element found in crude oil and causes a significant detrimental effect on refining of the crude oil. It poisons catalyst and corrodes refining equipment. The combustion of sulphur products from automobiles impairs the emission control technology designed to meet the nitrogen oxides (NOx) and particulate emission standards which leads to environmental pollution. It contributes to the deterioration of air quality and affects public health and the ecosystem.

Most of the sulphur found in gasoline comes from naphtha produced from a fluid catalytic cracking (FCC) unit. FCC naphtha is the primary blending stock of gasoline in conventional petroleum refineries. The sulphur content of FCC naphtha typically varies from 150 to 3,000 ppm depending on the sulphur concentration of the feed and the end boiling point of the gasoline product.

Sulphur compounds found in crude oil are divided into aliphatic (mercaptans, sulfides, disulfides) and aromatic refractory group (thiophene derivatives). In a typical FCC naphtha, sulphur compounds range from l¾S to the derivatives of dibenzothiophene. Typically FCC naphtha has an end boiling point of 220 °C. The complexity of the sulphur compounds increases with increase in end boiling point of naphtha.

Further, most of the sulphur present in FCC naphtha is in the form of thiophenic derivatives, however the most complex sulphur compound is considered to be benzothiophene. The naphtha product must be subjected to desulphurization treatments to meet the downstream production and marketing needs. The desulphurization methods mainly cover hydro desulphurization, oxidative desulphurization and adsorptive desulphurization. The hydro desulphurization reaction conditions tend to result in some hydrogenation of olefins, which results in loss of octane number rating as much as 3 to 8 number loss for full-range naphtha feed. The oxidative desulphurization (ODS) enables achievement of ultra-low sulphur content in diesel fuels by oxidation of refractory sulphur compounds in the presence of catalyst, that are difficult to remove with hydrodesulphurization. The oxidative desulphurization brings about the sulphur content to below 10 mg kg ^-1 . The major disadvantages of ODS are: one, appropriate oxidant may cause unwanted side reactions with other components in the fuel that are of interest and second, solvent selection is critical because undesirable solvents may extract other components of the fuel that will affect the overall quality of the product.

Conventionally, the adsorptive desulphurization process uses adsorbents such as molecular sieves, activated carbon, ion exchange resins, and activated carbon fibers. In adsorptive desulphurization, the adsorbents need to be effective, selective, and apt for sulphur removal. There is always scope for developing a new method for desulphurization of naphtha.

Therefore, there is felt a need to develop a process for adsorptive desulphurization of naphtha.

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 adsorptive desulphurization of naphtha.

Another object of the present disclosure is to provide a simple, cost effective and rapid process for adsorptive desulphurization of naphtha.

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 relates to a process for adsorptive desulphurization of naphtha. The process comprises contacting the naphtha having sulphur impurities greater than 200 ppm, with at least one adsorbent at an ambient temperature and at a predetermined pressure for a predetermined time to obtain treated naphtha having reduced sulphur impurities. The adsorbent used in the present disclosure is a combination of ferric chloride and aluminum hydroxide. The molar ratio of the ferric chloride to the aluminum hydroxide is 2: 1. The treated naphtha has less than 100 pm of reduced sulphur impurities.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The present disclosure will now be described with the help of the accompanying drawing, in which:

Figure 1 illustrates the process of reduction of content of organic sulphur compounds in a test hydrocarbon feed in accordance with an embodiment of the present disclosure; and

Figure 1 illustrates the process for reduction of content of organo- sulphur compounds in naphtha by semi-continuous process in accordance with an embodiment of the present disclosure; and

DETAILED DESCRIPTION Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.

Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail. The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising,"“including,” and“having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.

Adsorption occurs when a solid surface is exposed to a liquid or a gas that tend to adhere to the unoccupied spaces in solid particles due to the presence of unsaturated molecular forces within a solid material. The principle of adsorption is based on the removal of certain substances called adsorbate (liquid or gas) by an adsorbent (solid material). There are two different types of adsorption: physiosorption, which is reversible, and chemisorption that is irreversible. There are three principal forces responsible for adsorption which includes: van der Waal’s forces, chemical affinity, and electrostatic attraction. The present disclosure envisages a simple, rapid, and cost-effective process for adsorptive desulphurization of naphtha without the use of hydrogen.

In an aspect, the present disclosure provides a process for adsorptive desulphurization of naphtha. The process is described in detail below: The naphtha containing hydrocarbon feed having sulphur impurities greater than 200 ppm is contacted with at least one adsorbent at an ambient temperature and at a predetermined pressure for a predetermined time period to obtain a treated hydrocarbon feed having reduced sulphur content.

In accordance with the present disclosure, the naphtha containing hydrocarbon feed prior to treatment with adsorbent comprises sulphur impurities in the range of 200 ppm to 800 ppm.

In accordance with the present disclosure, the adsorbent is selected from the group consisting of ferric chloride, aluminium hydroxide, and combination thereof. In one embodiment, the adsorbent is ferric chloride. In another embodiment, the adsorbent is aluminium hydroxide. In still another embodiment the adsorbent is a mixture of ferric chloride and aluminium hydroxide.

In an embodiment the molar ratio of ferric chloride to aluminium hydroxide is 2: 1. The adsorbent is prepared by mixing the predetermined quantity of ferric chloride and aluminium hydroxide under a nitrogen atmosphere at room temperature. The adsorbent used in the process of the present disclosure is in the form of powder or pellets. In accordance with the present disclosure, the sulphur impurities present in the Naphtha containing hydrocarbon feed, are at least one of, benzothiophene (BT), 2,5- dimethylthiophene (2,5-DMT) and 2-methyl thiophene (2-MT). In one embodiment, the sulphur impurity is benzothiophene (BT). In another embodiment, the sulphur impurity is 2,5-dimethylthiophene (2, 5 -DMT). In still another embodiment, the sulphur impurity is 2- methyl thiophene (2-MT). In an exemplary embodiment the sulphur impurity is a combination of benzothiophene (BT), 2,5-dimethylthiophene (2,5-DMT) and 2-methyl thiophene (2-MT). The amount of sulphur impurities present in the treated hydrocarbon feed is below 100 ppm. In one embodiment the sulphur impurity present in the treated hydrocarbon feed is in the range of 1 ppm to 100 ppm.

In accordance with the present disclosure, the ambient temperature can be in the range of 30 °C to 55 °C. In one embodiment, the ambient temperature is 50 °C. In accordance with the present disclosure, the predetermined pressure can be in the range of 1 atm to 4 atm. In one embodiment, the predetermined pressure is 1 atm.

In accordance with the present disclosure, the predetermined time can be in the range of 15 minutes to 60 minutes. In one embodiment, the predetermined temperature is 30 minutes.

The process for adsorptive desulphurization of naphtha can be continuous process or semi- continuous process.

In one embodiment the process of the present disclosure is a continuous process. During the continuous process, the powder adsorbent bed can be made stationary during a continuous flow of hydrocarbon. For making the adsorbent bed stationary during continuous process, the adsorbent is sandwiched between Si(¾ layers. Initially, some amount of Si(¾ is taken in a reactor column followed by addition of required amount of powder adsorbent and further addition of some amount of Si(¾. In an embodiment, silica beads are used on the top of Si(¾ layer. The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

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.

EXPERIMENTAL DETAILS:

Experiment 1:

Reduction of content of organic sulphur compounds in a test hydrocarbon feed: A test hydrocarbon feed was prepared by solubilizing organo sulphur compounds, such as 41.94 mg of benzothiophene (BT), 35.2 mg of 2,5-dimethylthiophene (2,5-DMT) and 30.68 mg of 2-methyl thiophene (2-MT) in 50 gm of iso-octane so as to obtain a test hydrocarbon feed having sulphur content of 205 ppm in each sample. Mixed solution was prepared by dissolving the above mentioned quantity of BT, 2,5-DMT, and 2-MT in 150 gm of iso-octane so that mixed solution has 205 ppm of sulfur in the solution.

The adsorbent used in this experiment was a mixture of 5.0 gm of ferric chloride and 1.2 gm of aluminium hydroxide in a mole ratio of 2:1. The adsorbent (10 mass % i.e. 5 g) was added to the test hydrocarbon feed (50 g) to obtain a mixture. The mixture was stirred at 50 °C under 1 atmospheric pressure for 30 minutes at 300 rpm to obtain a treated mixture. After 30 minutes the treated test hydrocarbon layer was separated from solid adsorbent in the treated mixture. The treated test hydrocarbon was analyzed for total sulphur content using a total sulphur total nitrogen analyzer (TSTN analyzer). It was observed that the content of benzothiophene (BT) 2,5-dimethylthiophene (2,5-DMT), 2-methyl thiophene (2-MT) and mixture of sulphur were reduced by 85%, 92%, 95% and 94% respectively. The treated hydrocarbon feed had sulphur impurity of benzothiophene (BT) 2,5-dimethylthiophene (2,5- DMT), 2-methyl thiophene (2-MT) and mixture were 30, 16, 10 and 12 ppm as depicted in Figure 1. Thus, the adsorbent of the present disclosure is found to be effective in reducing the content of organo sulphur compounds in the test hydrocarbon feed.

Experiment 2:

Reduction of content of organo- sulphur compounds in naphtha by semi-continuous process. The experiment was performed by continuously passing the naphtha samples by Syrris syringe pump through the fixed bed reactor containing solid adsorbent. The flow of the naphtha was controlled by a programmable flow controller and flow was continuous due to the presence of two syringes in series. The adsorbent layer was sandwiched between the Si(¾ layers to avoid the deformation of adsorbent bed during the experiments. Glass beads were also used to avoid the channeling of fluid. The samples were collected at time intervals of 15 min, and treated naphtha samples were analysed for total sulphur content using a total sulphur total nitrogen analyser (TSTN analyzer).

Two different experiments were carried out by using naphtha feed having initial sulphur concentration of 205 and 381 ppm. Liquid hourly space velocity (LHSV) of the semi- continuous process was set to 6.25 h ¹ . The experiments were carried out at ambient temperature and atmospheric pressure. It has been observed that activity of adsorbent is directly proportional to concentration of sulphur present in naphtha. The treated naphtha sample A had sulphur impurity of 1.2 ppm at sample collection on 15 min and 71.27 ppm at sample collection on 300 min as depicted in Figure 2. Further, the treated naphtha sample B had sulphur impurity of 1.2 ppm at sample collection on 15 min and 70 ppm at sample collection on 170 min as depicted in Figure 2. Overall, treated naphtha has sample impurity of less than 100 ppm.

TECHNICAL ADVANCEMENTS The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a simple, cost-effective and rapid process for adsorptive desulphurization of naphtha.

The embodiments as described herein above, and various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description.

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 disclosure to achieve one or more of the desired objects or results. The foregoing description of specific embodiments so fully reveal the general nature of the embodiments herein, that others can, by applying current knowledge, readily modify and/or adapt for various applications of such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Further, 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.

Having described and illustrated the principles of the present disclosure with reference to the described embodiments, it will be recognized that the described embodiments can be modified in arrangement and detail without departing from the scope of such principles.

While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other modifications in the nature of the disclosure or the preferred embodiments 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.