WO2014002115A2

WO2014002115A2 - A system and a method for measurement of adsorption isotherms and kinetics of hydrocarbons

Info

Publication number: WO2014002115A2
Application number: PCT/IN2013/000385
Authority: WO
Inventors: Satish D. SHEWALE; Vijayalakshmi R. PURANIK; Raksh Vir Jasra
Original assignee: Reliance Industries Limited
Priority date: 2012-06-27
Filing date: 2013-06-21
Publication date: 2014-01-03
Also published as: WO2014002115A3

Abstract

There is disclosed a system comprising an adsorbent charging vessel, an adsorber and a sample tube. The system is useful for measuring adsorption isotherms and kinetics of hydrocarbons in a liquid phase. A method for measuring adsorption isotherm and kinetics of hydrocarbon at plant operating conditions of temperature and pressure is also provided.

Description

A SYSTEM AND A METHOD FOR MEASUREMENT OF ADSORPTION ISOTHERMS AND KINETICS OF HYDROCARBONS

FILED OF THE DISCLOSURE:

The present disclosure relates to an apparatus for measuring adsorption isotherm and kinetics of hydrocarbons in liquid phase. In another aspect the present disclosure also relates to a method for determining the adsorption isotherm and kinetics of hydrocarbons in liquid phase.

BACKGROUND:

Though several method and systems for measuring an amount of gas adsorbed on or desorbed from a solid and for analyzing adsorption and desorption characteristics by measuring the adsorption isotherms under various conditions have been disclosed in various patents such as US6595036, JP2004333447, JP2009002878, JP2008203154, JP2011090015, KR2002062233, EP444246, JP2000292246, US5637810, BE757533, ES2024309A6, CZ199603252, and US5058442, systems and method for determining the adsorption isotherms for liquids under various conditions have- still not been adequately developed and disclosed till date. Set-ups, systems and customized apparatus for determining the adsorption isotherm for liquids using various adsorbents under varying conditions of temperature and pressure are not commercially available and these are very rarely mentioned in the public domain.

Apparatus for measuring adsorption of a first material by a second material in a liquid under pressure for determining adsorption isotherms is disclosed in O1999063336. It is particularly useful in the determination of the adsorption isotherms of formulations for pressurized metered dose inhalers. There is disclosed a methylene blue adsorption measurement equipment in JP 11094745 which is useful for measuring the quantity of methylene blue adsorbed on a given adsorbent which is coal ash.

The measurement of adsorption isotherm is very critical for identifying various adsorbents and catalysts for various purification and separation processing during the processing of the petrochemicals. However, the adsorption behavior is always governed by conditions such as pressure and temperature under which the adsorption process is carried out. The usual purification and separation processes in the petrochemical industry are carried out at relatively higher temperatures ranging between 50°C to 300°C. It therefore becomes imperative to study adsorption characteristics of various hydrocarbons with respect to the different adsorbents under such operative plant conditions.

The presently known method employs stirred basket reactor for measuring the adsorption of a liquid on an adsorbent. The adsorbent is placed in the basket and it comes in contact with the liquid once it is stirred and the data generated through such set up is used for model prediction of batch kinetics and finding out the intra-particle molecular diffusivity.

Minceva and Rodrigues et al have disclosed the details of the experiments on "Adsorption of Xylenes on Faujasite-Type Zeolite: Equilibrium and Kinetics in Batch Adsorber" in Chemical Engineering Research and Design; Volume 82, Issue 5, May 2004, Pages 667-681. They employed a-stirred basket reactor for performing liquid phase adsorption equilibrium -and ^* kinetic experiments. According to the arrangement as disclosed by Minceva and Rodrigues et al, an adsorbent is placed in the basket and tied to the impeller. Initially, ?the impeller is held in the vapor head space of the adsorber. Once the solution attains the requisite temperature, during stirring, the impeller is lowered and the adsorbent containing basket comes in contact with the liquid. The sampling of liquid in the adsorber is automatic. One of the outlets of the adsorber is connected to the 0.1 μΐ, liquid sampling valves (Valco, USA). The samples are further analyzed with online gas chromatograph (GC).

However, the above mentioned known set up and the method suffer from numerous shortcomings. Firstly, during the initial stage, even though the adsorbent containing basket is not in direct contact with the liquid, it comes in contact with the vapors thereby resulting in adsorption of such vapors. Secondly, the volume of the adsorber is required to be sufficient enough to accommodate the basket containing adsorbent. Thirdly, though the sample collection is automatic, the assembly does not provide for flushing of dip tube after sample collection and injection into GC, which is essential to avoid mixing of samples, and to obtain correct sample and reliable experimental data.

There is therefore exists a need for a system and a method that can be used to perform adsorption equilibrium/kinetics experiments to generate correct adsorption isotherm data for liquids under varying conditions of temperature and pressure that resemble to the actual plant operating conditions.

OBJECTS:

Some of the objects of the present disclosure are described herein below:

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. It is another object of the present disclosure to provide an apparatus to perform adsorption isotherm and kinetic experiments with various hydrocarbon liquid mixtures at plant operating conditions.

It is an object of the present disclosure to provide a method to measure the adsorption isotherm and kinetics of various hydrocarbon liquid mixtures at plant operating conditions.

It is still another object of the present disclosure to provide an apparatus to measure the adsorption isotherm and kinetics of various hydrocarbon liquid mixtures at plant operating conditions, which is cost effective and which provides reliable data with error margins well within the accepted international standards.

Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.

DEFINITIONS:

As used in the present specification, the following words and phrases are generally intended to have the meanings as set forth below, except to the extent that the context in which they are used to indicate otherwise.

The term adsorption isotherm means relationship between adsorbed phase - concentration and liquid phase concentration of adsorbate at equilibrium. For gaseous adsorption it is the relationship between adsorbed phase concentration and partial pressure of adsorbate in bulk phase.

The term liquid hydrocarbon means a compound constituting carbon and hydrogen elements. The term sample means a small part of liquid phase in adsorber and is collected outside the adsorber. It must have same concentration as that of liquid phase in adsorber at the time of collection. .

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.

When an amount, concentration, or other value or parameter is given as a range, or a list of upper and lower values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper and lower range limits, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It, is not intended that the scope of the present disclosure be limited to the specific values recited when defining a range.

When the term "about" is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to. SUMMARY:

In accordance with the present disclosure there is provided a system for measuring adsorption isotherms and kinetics of hydrocarbons in a liquid phase, said system comprising:

- an adsorbent charging vessel adapted to maintain an adsorbent contained therein at a predetermined pressure;

- an adsorber functionally coupled to said adsorbent charging vessel and comprising a hydrocarbon solution contained therein, said adsorber adapted to facilitate charging of said adsorbent by facilitating direct contact of said adsorbent with said hydrocarbon solution and by using pressure difference between said adsorbent charging vessel and said adsorber; and

- a sample tube functionally connected to said adsorbent charging vessel and said adsorber, said sample tube comprising a jacketed type condenser, said sample tube adapted to collect a sample of said liquid phase from said adsorber and maintain temperature of said sample to a

- pre-determined temperature.

Typically, the absorbent charging vessel is connected to the adsorber by means of a valve.

Typically, adsorber comprises a stirrer.

In accordance with one embodiment of the present disclosure the system further comprises a dip tube functionally connected to said adsorber and said sample tube. -

Typically, an end of said dip tube that is positioned inside said adsorber is fitted with a wire mesh at an operative lower end thereof to avoid entrainment of said adsorbent towards said sample tube.

In accordance with another aspect of the present disclosure there is provided a method for determining an isotherm of a liquid hydrocarbon with respect to an adsorbent, said method comprising the following steps: charging a predetermined amount of liquid hydrocarbon into an adsorber functionality;

- increasing the pressure of the adsorber functionality ranging between 1 to 50 bar by introducing nitrogen in and stirring the contents of the

\ adsorber functionality;

- charging a predetermined amount of adsorbent in an adsorbent charging vessel and maintain pressure in adsorbent charging vessel to predetermined value ;

- heating the contents of adsorber to attain predetermined temperature and pressure conditions;

- releasing predetermined amount of the adsorbent from the adsorbent charging vessel to the adsorber functionality through a valve;

- collecting a sample from the adsorber functionality at predetermined time intervals; and

- subjecting the samples to analysis for determination of concentration of adsorbate in solution.

BRIEF DESCRIPTION OF THE DRAWING:

Figure 1 illustrates a system to perform adsorption equilibrium experiments to generate adsorption isotherm and perform kinetic experiments to get intra- particle diffusivity and adsorption rate constants for liquids under high temperature and pressure conditions in accordance with the present disclosure. Fig. 2 provides variation in p-xylene concentration with respect to time in blank run.

Fig. 3 shows the change in liquid phase concentration of p-xylene and calculated adsorbed phase concentration due to adsorption on faujasite zeolite at 180 °C and 10 kg/cm².

Fig. 4 provides shows adsorption isotherm of p-xylene (Graph of Q_e against C_e) at 180 °C and 10 kg/cm². Fig. 5 shows adsorption isotherm of p-xylene at 180 °C and 10 kg/cm². DETAILED DESCRIPTION

Referring to Figure 1, a schematic representation of a system 100 for measuring adsorption isotherms and kinetics of hydrocarbons in liquid phase is disclosed. The system 100 includes an adsorbent charging vessel 102, an adsorber 104 and a sample tube 106.

The adsorbent charging vessel 102 is adapted to maintain an adsorbent contained therein at a predetermined pressure. In one embodiment, the predetermined pressure is lOkg/cm². However, the present disclosure is not limited to any particular predetermined pressure.

The adsorber 104 is functionally coupled to the adsorbent-charging vessel 102 and includes a hydrocarbon solution contained therein. In one embodiment, the absorbent charging vessel 102 is connected to the adsorber 104 by means of a valve VI. In one embodiment, the valve VI is a ball valve of 1/4" diameter. However, the present disclosure is not limited to any particular type of valve or any particular dimension of the valve VI. Before charging adsorbent, pressure in, the adsorbent charging vessel 102 is higher (by around 10%) than that in the adsorber 104. For charging, adsorbent valve .VI- is opened and adsorbent is introduced to the solution in the adsorber 104 by gravity.

If pressure in the adsorbent charging vessel 102 is lower than that in the adsorber 104, then vapors from vapor head space rush into adsorbent charging vessel thereby delaying the time required for charging the adsorbent.

In one embodiment, the adsorber 104 includes a stirrer 108. The stirrer 108 is adapted to facilitate stirring of the mixture of the adsorbent and the hydrocarbon contained in the adsorber 104. In one embodiment, the system 100 includes a dip tube 110 functionally connected to the adsorber 104 and the sample tube 106. More specifically, an operating lower end of the dip tube 110 is disposed in the mixture of the adsorbent and the hydrocarbon contained in the adsorber 104. Further, an upper end of the dip tube 110 is connected to the sample tube 106 by means of a valve V2. In one embodiment, the valve V2 is a needle valve of 1/4" diameter. However, the present disclosure is not limited to any particular type of valve or any particular dimension of the valve V2. In one embodiment, the operative lower end of the dip tube 110 is fitted with a wire mesh to avoid entrainment of the adsorbent towards the sample tube 106.

The sample tube 106 functionally connected to the adsorbent charging vessel 102 and the adsorber 104. In one embodiment, the sample tube 106 functionally connected to the adsorbent charging vessel 102 by means of a valve V4. In one, embodiment, the valve V4 is a three way valve of 1/4" diameter. However, the present disclosure is not limited to any particular type of valve or any particular dimension of the valve V4. The valve V4 facilitates entry of nitrogen gas into the sample tube 106. The sample tube 106 includes a jacketed type condenser. The sample tube 106 is adapted to maintain temperature of the sample collected_e from the adsorber 104 to a pre-determined temperature. The jacketed type" condenser facilitates maintaining of temperature of the sample collected from the adsorber 104 to a pre-determined temperature. In one embodiment, the predetermined temperature is 5 C. However, the present disclosure is not limited to any particular pre-determined temperature. The alphabet "I" denotes flow of chilled water inside the jacketed type condenser and the alphabet "O" represent flow of water after the heat exchange operation.

A valve V3 illustrates exhausts of the sample from the sample tube 106. In one embodiment, the valve V3 is a needle valve of 1/4" diameter. However, the present disclosure is not limited to any particular type of valve or any particular dimension of the valve V3.

In one aspect of the present disclosure, there is provided a system designed to generate high quality data required for characterizing various adsorbents used■ in chemical industry both for separation and purification processes.

The inventors of the present disclosure have developed the present system indigenously by utilizing an autoclave of Paar (make). The system of the present disclosure allows isotherm generation at various temperatures and pressures ranging between ambient and 300°C and from atmospheric to 50 bar respectively. Most of the separation and purification process in refinery and petrochemical processes operate in this range.

The system of the present disclosure for measuring adsorption isotherms and kinetics of hydrocarbons in a liquid phase comprises an adsorbent charging vessel, an adsorber functionally coupled to the adsorbent charging vessel through a valve and a sample tube.

The adsorbent charging vessel is connected to the adsorber 104 through a valve (VI).

Liquid hydrocarbon is charged into adsorber 104, and then adsorber is closed. The adsorber. 104 (Parr make) typically comprises a Vessel and a lid fitted with a temperature sensor, a pressure gauge, a stirrer with magnetic drive and a dip tube. After charging liquid into the vessel, a lid is fitted to the vessel through split ring with cap screws. Once the adsorbent is released through a valve (VI) it comes in direct contact with the liquid hydrocarbon- present in the adsorber functionality. The adsorber functionality is also provided with a stirrer that ensures a better contact of the adsorbent with the liquid hydrocarbon. Also connected with the adsorber functionality and the adsorbent charger is a sample tube that comprises a jacketed type condenser. The jacket type condenser helps to maintain the temperature of the sample to a predetermined temperature. For both adsorption equilibrium experiments for isotherm and adsorption kinetic experiments it is needed to collect sample of liquid phase in the adsorber, which is at high temperature and pressure. During sample collection liquid at high temperature and pressure will rush into sampling tube which is at atmospheric pressure; hence flashing (or partial vaporization) of liquid hydrocarbon will occur in sample tube. This sample must be immediately cooled so that sample should be correct representative of liquid phase at time of sampling, which is achieved by means of cooling jacket around sample tube. The sample tube is used for collecting a sample.of the liquid phase from the adsorber/ reactor.

In accordance with embodiment of the present disclosure there is provided a dip tube functionally connected to the adsorber functionality and the sample tube. Typically, the end of the dip tube is fitted with a wire mesh at an operative lower end to avoid entrainmerit of said adsorbent particle towards said sample tube.

In accordance with a second aspect of the present disclosure there is provided a method for determining an isotherm of a liquid hydrocarbon with respect to an adsorbent, said method comprising the following steps:

^■ charging a predetermined amount of a liquid hydrocarbon into the adsorber functionality;

^■ increasing the pressure of the adsorber functionality 1 bar to 50 bar by introducing nitrogen in the adsorber and stirring the contents of the adsorber functionality; ■ charging a predetermined amount of adsorbent in an adsorbent charging vessel, wherein the adsorbent is preferably pre-heated and charged in hot condition ;

• heating the contents of adsorber to attain predetermined temperature and pressure conditions;

■ releasing predetermined amount of the adsorbent from the adsorbent charging vessel to the adsorber functionality through a valve;

■ collecting a sample from the adsorber functionality at predetermined time . intervals for adsorption kinetic experiment; and after sufficient contact time for attaining adsorption equilibrium for adsorption isotherm experiments; and -

■ subjecting the samples to analysis for determining the concentration of •adsorbate in the solution.

Typically, the adsorbed phase concentration is determined using following equation,

where, Q and C_t are liquid phase concentration (mass fraction) at t=0 and any time t respectively. M_soi_n is the mass of the solution charged in the adsorber. M_ads is the mass of adsorbent.

The isotherm data i.e. graph between adsorbed phase concentration and liquid phase concentration at equilibrium indicates the maximum adsorption capacity and adsorption affinity of desired molecule toward a given adsorbent. Furthermore, the isotherm measured at varied temperatures using the system of the present disclosure also indicates the heat of adsorption, an important parameter that is useful in carrying out the desorption of the molecule. The kinetics of adsorption gives us the idea of intra-particle diffusivity of molecules into the micro and macropores of the adsorbent. The data collected from this system is highly useful in adsorbent screening for bulk separation and purification of various hydrocarbons.

The inventors of the present disclosure carried extensively experimentation and analyzed the results for various liquid hydrocarbons. It has been found that the system of the present disclosure provides reproducible data with a very high level of accuracy as prescribed by the International norms.

Very high level of reproducibility and accuracy of the results obtainable using the system of the present disclosure are attributed to numerous distinct advantages associated with the system and the method of the present disclosure. The system of the present disclosure allows the introduction of the adsorbent at high temperature and pressure ranging between ambient and 300°C; and between 1 and 50 bar, respectively. The sample can be withdrawn at predetermined time intervals without flashing of hydrocarbons. The adsorbent does not even come in contact with the vapors of the liquid hydrocarbon prior to the start of the kinetic run thereby ensuring high level of accuracy. The adsorbent is introduced to the liquid hydrocarbon and is in the form of a suspension under stirring during both isotherm and kinetic run which ensures a better contact between the liquid hydrocarbon and the adsorbent.

The system of the present disclosure is useful to check the suitability of new adsorbents for the existing separation. It is also useful for checking the regeneration of the spent adsorbent. The data generated by the system of the present disclosure is useful for plants in trouble shooting.

The system of present disclosure can also be used for catalyst screening and reaction kinetics in liquid phase heterogeneous/ homogeneous catalysis i

examples Friedel-craft alkylation, isomerization of alkyl-aromatics, oligomerization of olefins, hydrogenation of aromatic aldehydes and olefins.

The present disclosure will now be described with the help of the following non-limiting examples:

Example 1 :

Blank run (180 °C and 10 kg/cm ) was performed with solution of p-xylene in i- octane, which is non-adsorbing solvent. Variation in p-xylene concentration with respect to time in blank run (i. e. adsorption kinetics experiment without adsorbent) is shown in Fig. 2. Average sample weight is 0.75 g and % error in p-xylene concentration in all samples is ± 3 %. In absence of adsorbent, liquid phase concentration- is approximately constant. This shows- that system of sample withdrawal - at high temperature and pressure is reliable and reproducible.

Example 2:

Adsorption kinetic experiment (180 °C and 10 kg/cm²) was performed with p-

I

xylene as model adsorbate and faujasite zeolite as adsorbent. Change in liquid phase concentration of p-xylene and calculated adsorbed phase concentration due to adsorption on faujasite zeolite at 180 °C and 10 kg/cm is shown in Fig. 3.

Example 3:

Adsorption equilibrium experiments were performed for different initial concentrations of p-xylene in the liquid phase with one type of faujasite adsorbent at 180 °C and 10 kg/cm . From each experiment one data point for adsorption isotherm was obtained. Values of adsorbed phase concentration at equilibrium (Q_e) and liquid phase concentration at equilibrium (C_e) from several adsorption equilibrium experiments yields adsorption isotherm i.e. graph of Q_e against C_e. Adsorption isotherm graph is given in Figure 4.

Example 4:

Adsorption equilibrium experiments ^* were performed for different initial concentrations of p-xylene in the liquid phase with other faujasite adsorbent at 180 °C and 10 kg/cm². From each experiment one data point for adsorption isotherm was obtained. Values of adsorbed phase concentration at equilibrium (Q_e) and liquid phase concentration at equilibrium (C_e) from several adsorption equilibrium experiments yields adsorption isotherm i.e. graph of Q_e against C_e. Adsorption isotherm graph is given in Figure 5.

Claims

Claims:

1. A system for measuring adsorption isotherms and kinetics of hydrocarbons in a liquid phase, said system comprising:

• an adsorbent charging vessel adapted to maintain an adsorbent contained, therein at a predetermined pressure;

• an adsorber functionally coupled to said adsorbent charging vessel and comprising a hydrocarbon solution contained therein, said adsorber adapted to facilitate charging of said adsorbent by facilitating direct contact of said adsorbent with said hydrocarbon solution and by using pressure difference between said adsorbent charging vessel and said adsorber; and

• a sample tube functionally connected to said adsorbent · charging vessel and said adsorber, said sample tube comprising a jacketed type condenser, said sample tube adapted to collect a sample of said liquid phase from said adsorber and maintain temperature of said sample to a predetermined temperature.

2. The system as claimed in claim 1, wherein said absorbent charging vessel is connected to the adsorber by means of a valve.

3. The system as claimed in claim 1, wherein said adsorber comprises a stirrer.

4. The system as claimed in claim 1, further comprising a dip tube functionally connected to said adsorber and said sample tube.

5. The system as claimed in claim 5, wherein an end of said dip tube that is positioned inside said adsorber is fitted with a wire mesh at an operative lower end thereof to avoid entrainment of said adsorbent towards said sample tube.

6. A method for determining an isotherm of a liquid hydrocarbon with respect to an adsorbent, said method comprising the following steps:

^■ charging a predetermined amount of liquid hydrocarbon into an adsorber functionality;

^■ increasing the pressure of the adsorber functionality ranging between 1 to 50 bar by introducing nitrogen in and stirring the contents of the adsorber functionality;

^■ charging a predetermined amount of adsorbent in an adsorbent charging vessel and maintain pressure in adsorbent charging vessel to predetermined value ;

^■ heating the contents of adsorber to attain predetermined temperature and pressure conditions;

^■ releasing predetermined amount of the adsorbent from the adsorbent charging vessel to the adsorber functionality through a valve;

^■ collecting a sample from the adsorber functionality at predetermined time intervals; and

^■ subjecting the samples to analysis for determination of concentration of adsorbate in solution.