DESC:FIELD
The present disclosure relates to a process for preparing mixed xylenes and C9 aromatic compounds from heavy aromatics.
DEFINITION
As used in the present disclosure, the following term is generally intended to have the meaning as set forth below, except to the extent that the context in which it is used indicate otherwise.
The term “distilled cut” refers to cuts at predetermined points during a distillation run where a stiller will separate products coming from the still into separate containers/fractions resulting in different fractions of product.
BACKGROUND
Xylene or dimethylbenzene, is present in any of the three isomeric forms - ortho-xylene, meta-xylene and para-xylene. These xylenes are the principal precursors of terephthalic acid and dimethyl terephthalate, which are further used in the production of polyethylene terephthalate (PET) plastic bottles and polyester clothing. Xylene is also used as a solvent and is a common component of ink, rubber, adhesives, thinning paint, and varnishes. Mixed xylenes are considered to be industrially significant petrochemicals as each of its components, namely ortho, meta and para xylene find multifarious applications in different fields.
The process of catalytic reforming of naphtha converts the naphtha feedstock containing C6 to C12 non-aromatic hydrocarbons to a reformate product containing C6 to C8 aromatics (benzene, toluene, xylenes), paraffins and heavier aromatics (C9 to C12 aromatics). Similarly, steam cracking of hydrocarbons produces a cracked naphtha product commonly referred to as pyrolysis gasoline, which typically consists of C6 to C8 aromatics, heavier aromatics (C9 to C12 aromatics) and non-aromatic cyclic hydrocarbons containing 6 or more carbon atoms (such as naphthenes).
Conventionally used catalyst composition for mixed xylene and C9 aromatic compounds typically comprises different combinations of catalytic moieties such as molecular sieves, metal oxides, and zeolites. However, use of such complex catalyst compositions is often associated with disadvantages such as high energy input, requirement of carrying out the process at high temperature-pressure conditions, lengthy time periods, and use of expensive catalysts.
Therefore, there is need for preparing mixed xylenes (C8 aromatic compounds) and C9 aromatic compounds from heavy aromatics (C10-C13 aromatic compounds) which mitigates the drawbacks associated with the conventional processes.
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.
Another object of the present disclosure is to provide a process for preparing mixed xylenes and C9 aromatic compounds.
Still another object of the present disclosure is to provide a process for preparing mixed xylenes and C9 aromatic compounds, which is economical.
Yet another object of the present disclosure is to provide a process for preparing mixed xylenes and C9 aromatic compounds, which is environmentally friendly, requires low energy input, and does not cause corrosion of the reactor.
Another object of the present disclosure is to provide a process for preparing mixed xylenes and C9 aromatic compounds, which works at milder reaction conditions including milder temperature and autogeneous pressure.
Yet another object of the present disclosure is to provide a process for preparing mixed xylenes and C9 aromatic compounds, which requires less time for completion of reaction as compared to the conventional process in batch mode.
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 preparing mixed xylenes and C9 aromatic compounds. The process includes the step of reacting a cut of heavy aromatics (C10 – C13 aromatic compounds) with toluene in a weight ratio ranging from 1:2 to 1:12, in the presence NMP-AlCl3 (N-methyl pyrrolidone-aluminium chloride ionic liquid catalyst) at a temperature ranging from 180 oC to 250 oC and at an agitation speed in the range of 600 rpm to 700 rpm for a predetermined time period to obtain a reaction mixture. The amount of NMP-AlCl3 used in the process of present disclosure ranges from 5 wt% to 15 wt% with respect to the total weight of reaction mixture (heavier aromatics and toluene). The so obtained reaction mixture is cooled to a temperature ranging from 25 oC to 30 oC to obtain a biphasic mixture comprising a heavier phase and a supernatant liquid. Further, the heavier phase is separated from the supernatant component by a known method such as decantation. The so obtained heavier phase is washed 2-3 times with water to obtain a hydrocarbon phase containing mixed xylenes, C9 aromatic compounds, and unreacted heavy aromatics. Typically, heavy aromatics are usually C10 to C13 aromatic hydrocarbons and are a result of the catalytic reformation of naphtha. The predetermined time period is in the range of 0.5 hour to 7 hours, typically 3 hours.
DETAILED DESCRIPTION
The present disclosure provides a process for preparing mixed xylenes and C9 aromatic compounds from heavy aromatics. The process is described in detail.
From the heavier aromatics, a distilled cut is obtained. The distilled cut of heavy aromatics is reacted with toluene in a weight ratio ranging from 1:2 to1:12, in the presence of NMP-AlCl3 as an ionic liquid catalyst to obtain a reaction mixture. The amount of NMP-AlCl3 used in the process of present disclosure ranges from 5 wt% to 15 wt% with respect to the total weight of reaction mixture (heavier aromatics and toluene).
In the present disclosure, the distilled cut of heavy aromatics is typically C10 to C13 aromatics and/or naphtha feedstock.
In an exemplary embodiment, the weight ratio of the distilled cut of heavy aromatics and toluene is 1:3; and the amount of the ionic liquid catalyst used in the process of the present disclosure is 10 wt% with respect to the total weight of the reaction mixture.
The temperature maintained during this step ranges from 180 oC to 250 oC for a predetermined time period and the agitation speed is in the range of 600 rpm to 700 rpm. In an exemplary embodiment, the temperature maintained during the reaction is 220 oC and agitation speed is 700 rpm. The predetermined time period is in the range of 0.5 hour to 7 hours, typically 3 hours.
The reaction mixture obtained in the above step is cooled to a temperature ranging from 25 oC to 30 oC to obtain a biphasic mixture. The step of cooling the reaction mixture helps to settle the reaction mixture into two components - a heavier phase and a supernatant liquid.
The so obtained heavier phase is then separated from the supernatant liquid by any method of separation known to a person skilled in the art, to obtain separated heavier phase. In an exemplary embodiment, the step of separation is carried out by decantation. The so obtained heavier phase comprises mixed xylenes C8 aromatic compounds, C9 aromatic compound and unreacted heavy aromatics C10 to C13.
The separated heavier phase is washed 2-3 times with water to remove the acidity associated with the hydrocarbons. The heavier phase, after washing with water, separates into two layers. The upper layer contains hydrocarbon and the lower layer (aqueous layer) comprises water and the catalyst (ionic liquid).
The hydrocarbon layer comprises the mixture containing mixed xylenes (C8 aromatic). In one embodiment the hydrocarbon layer also contains C9 aromatic compounds, and unreacted heavy aromatics along with mixed xylenes. C9 aromatic compounds are formed as a major co-product along with mixed xylenes. C9 aromatic compounds can be recycled back to the reactor to generate mixed xylenes. In chemical industries, C9 aromatic compounds can be reacted with toluene in a Pyrex process to obtain xylenes.
In one embodiment, the separation of mixed xylenes and C9 aromatic is carried out by simple distillation and then analyzed by gas chromatography.
The process of the present disclosure is associated with many advantages such as the process is economical, environmentally friendly, requires low energy input, and does not cause corrosion of the reactor. The process works at milder reaction conditions including milder temperature and autogenous pressure. The process requires less time for completion as compared to the conventional process in batch mode.
The present disclosure is further described in light of the following laboratory scale experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The experiments provided herein below can be scaled up to industrial/ commercial scale.
Experimental Details:
All the experiments were carried out in batch operation by using a 100 ml Parr autoclave reactor equipped with a pitch blade turbine impeller for agitation. The temperature was maintained at +/- 1 ºC of the desired value by a PID controller (proportional–integral–derivative controller).
Experiment 1: Preparation of mixed xylenes C8 and C9 aromatic compounds in accordance with the process of the present disclosure
The autoclave reactor was charged with a distilled cut of heavy aromatics and toluene in 1:3 weight ratio and 10 wt% of NMP-AlCl3 (catalyst) was loaded into the reactor. The reactor was heated to 220 ºC and agitated at 700 rpm for 3 hours. After the completion of the reaction, the reactor was cooled to room temperature and the reaction mass was separated. The reaction mass was washed with water and analyzed by Gas Chromatography (GC). The results are presented in Table 1.

Table 1:
Experiment No. Ionic liquid Mixed xylenes C8 Yield (%) C9 Yield (%)
1 NMP-AlCl3 48.2 33.1

Experiment 2: Optimization of the temperature parameter
The effect of temperature on the heavy aromatic conversion and yield of mixed xylenes C8 and C9 aromatic compounds was studied and the results obtained are presented in Table 2. The reactor was charged with a distilled cut of heavy aromatics and toluene in 1:3 weight ratio and 10 wt% of a catalyst (NMP-AlCl3) was loaded into the reactor. The resulting reaction mixture was agitated at 700 rpm and the reactor was heated to 180 oC (Trial 1), 200 oC (Trial 2), 220 oC (Trial 3), 230 oC (Trial 4), 240 oC (Trial 5) and 250 oC (Trial 6) for 3 hours each. The reactor was then cooled to room temperature after each trial and the step of washing the reaction mass with water was repeated after each trial. The hydrocarbon layer was separated after each trial and the layer obtained from each trial was analyzed by Gas Chromatography.
Table 2:
Trial No. Temperature (0C) Mixed xylenes
C8 Yield (%) C9 Yield (%)
1 180 15.6 42.3
2 200 30.4 37.6
3 220 48.2 33.1
4 230 45.7 31.8
5 240 45.0 31.4
6 250 42.4 33.5

From the results shown in table 1, it is observed that increasing the reactor temperature to 220 oC results in increased yield of mixed xylene. However, after 220 oC, a decrease in the yield of mixed xylenes is observed.
Further, the reaction was continued for 45 hours at a temperature of 220 °C using NMP-AlCl3 as a catalyst. No corrosion was observed in the reactor even after the continuous use of NMP-AlCl3 as the catalyst.

Experiment 3: Optimization of heavy aromatics: toluene weight ratio
The weight ratio of heavy aromatics and toluene used in the process of preparing mixed xylenes was optimized, which is given in Table 3.
The reactor was charged with distilled cut of heavy aromatics and toluene in varying weight ratios such as 1: 2 (Trial 1), 1:3 (Trial 2), 1:5 (Trial 3), 1:7 (Trial 4), 1:10 (Trial 5), 1:12 (Trial 6) and 10 wt% catalyst (NMP-AlCl3) was loaded into the reactor. The reactor was heated to 220 0C while agitating the mixture at 700 rpm for 3 hours. After 3 hours, the reactor was cooled to room temperature to obtain a biphasic mixture containing a heavier component and a supernatant liquid. The heavier phase was separated by decantation and washed with water to obtain a hydrocarbon layer and an aqueous layer. The separated hydrocarbon was analyzed by GC.
Table 3:
Trial No. Weight ratio (Heavy aromatics: Toluene) w/w Mixed xylenes C8 Yield (%) C9 Yield (%)
1 1:2 38.2 36.8
2 1:3 48.2 33.1
3 1:5 49.7 32.2
4 1:7 51.8 27.8
5 1:10 54.7 25.7
6 1:12 54.9 25.4

From the results shown in Table 3, it is observed that increasing the quantity of toluene increases the yield of mixed xylene. However, it is also observed that beyond the weight ratio of 1:10, a significant increase in the yield of mixed xylenes is not observed.

Experiment 4: Optimization of the weight ratio of loading catalyst:
The effect of loading of the catalyst in the reactor, on the yield of mixed xylene (C8 compounds) and C9 aromatic compounds was studied and the results obtained are given in Table 4.
The reactor was charged with a distilled cut of heavy aromatics and toluene 1:10 (w/w) ratio. Varying amounts of the catalyst such as 5 wt% (Trial 1), 10 wt% (Trial 2), and 15wt% (Trial 3) were loaded in the reactor. The resulting reaction mixture was agitated at 700 rpm and the reactor was heated to 220 0C for 3 hours. The reactor was then cooled to room temperature to obtain biphasic mixture containing a heavier component and a supernatant liquid. The heavier phase was separated by decantation and washed with water to obtain a hydrocarbon layer and an aqueous layer. The separated hydrocarbon was analyzed by GC.
Table 4:
Trial No. Catalyst loading wt% Mixed xylenes C8 Yield (%) C9 Yield (%)
1 5 25.7 38.6
2 10 54.7 25.7
3 15 56.9 24.4

From the results shown in Table 4, it is observed that increasing the quantity of catalyst increases the yield of mixed xylene. However, it is observed that beyond 10 wt% of catalyst loading, a significant increase in the yield of mixed xylenes is not observed.

Experiment 5: Optimization of the reaction time:
The effect of reaction time on the yield of mixed xylene (C8 compounds) and C9 aromatic compounds was studied and the results obtained are given in Table 5. The reactor was charged with distilled cut of heavy aromatics and toluene 1:10 (w/w) ratio. The resulting reaction mixture was agitated at 700 rpm and the reactor was heated to 220 0C for different reaction time period, such as 30 min (Trial 1), 60 min (Trial 2), 120 min (Trial 3), 180 min (Trial 4), 240 min (Trial 5), 300 min (Trial 6), 420 min (Trial 7). The reactor was then cooled to room temperature to obtain a biphasic mixture containing a heavier component and a supernatant liquid. The heavier phase was separated by decantation and washed with water to obtain a hydrocarbon layer and an aqueous layer. The separated hydrocarbon was analysed by GC.
Table 5:
Trial No. Reaction time in (min) Mixed xylenes C8 Yield (%) C9 Yield (%)
1 30 37.4 34.6
2 60 42.8 32.2
3 120 49.7 29.5
4 180 54.7 25.7
5 240 54.1 24.9
6 300 52.1 24.5
7 420 50.7 24.7

It is seen from Table 5 that as the reaction time increases, the mixed xylene yield also increases, up to 180 minutes. However beyond 180 minutes, self-cracking of mixed xylene was observed and hence a decrease in the mixed xylene yield was observed after 180 minutes.

TECHNICAL ADVANCEMENTS AND ECONOMIC SIGNIFICANCE
The process for preparing mixed xylenes and C9 aromatic compounds of the present disclosure has several technical advancements that include, but are not limited to, the realization of: a process
- that is an economical, and environmentally friendly;
- that requires low energy input and does not cause corrosion of the reactor;
- that includes milder reaction conditions including milder temperature and autogenous pressure; and
- that requires of less time for completion of the reaction as compared to the conventional process in batch mode.
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.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments 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.
,CLAIMS:WE CLAIM:
1. A process for preparing mixed xylenes and C9 aromatic compounds from a distilled cut of heavy aromatics, said process comprising the following steps:
i. reacting the distilled cut of heavy aromatics with toluene in a weight ratio ranging from 1:2 to 1:12 in the presence of N-methyl pyrrolidone-aluminium chloride catalyst (NMP-AlCl3) at a temperature ranging from 180 oC to 250 oC and at an agitation speed in the range from 600 rpm to 700 rpm for a predetermined time period to obtain a reaction mixture;
ii. cooling the reaction mixture to a temperature ranging from 25 oC to 30 oC to obtain a biphasic mixture comprising a heavier phase and a supernatant liquid; and
iii. separating the heavier phase and washing the heavier phase with water to obtain a hydrocarbon phase comprising mixed xylenes and C9 aromatic compounds.

2. The process as claimed in claim 1, wherein the heavy aromatics are C10 to C13 aromatic hydrocarbons.

3. The process as claimed in claim 1, wherein the weight ratio of said distilled cut of heavy aromatics and said toluene is 1:3.

4. The process as claimed in claim 1, wherein the amount of said N-methyl pyrrolidone-aluminium chloride catalyst (NMP-AlCl3) used is in the range of 5 wt% to 15 wt% with respect to the total weight of the reaction mixture.

5. The process as claimed in claim 1, wherein the temperature maintained during step (i) is in the range of 200 oC to 250 oC.

6. The process as claimed in claim 1, wherein the predetermined time is in the range of 0.5 hour to 7 hours, preferably 3 hours.