Title of Invention

"AN IMPROVED PROCESS FOR THE PRODUCTION OF PURE LIGHT AROMATICS"

Abstract The present invention relates to a process for the production of pure light aromatics from reformats and hydrogenated pyrolysis gasoline containing 45 to 50% of aromatics by using synergistic extraction solvent mixture in which sulpholane and N methyl pyrolidine is used as a solvent and co-solvent to get maximum purity and recovery of the product. Moreover, by adding the co-solvent to sulpholane increases the feed throughput without affecting the purity.
Full Text This invention relates to an improved process for the production of pure light aromatics This invention particularly relates to an improved process for the production of pure light aromatics such as benzene, toluene & xylenes. More particularly this invention relates to an improved process for the production of pure aromatics by solvent extraction from reformates and hydrogenated pyrolysis gasoline containing 45-80% aromatics.
Benzene produced in this manner is essential raw material for production of polystyrene, nylon, terylene etc. It is the basic raw material used by most chemical manufacturing companies and the base chemical for almost all dyes and dye intermediates. It is used for pharmaceuticals, pesticides, cosmetics, paints, detergents. About 90% of the organic industry is based on benzene or its derivatives.
In India, there are five units producing benzene. Gujarat Refinery, Baroda which uses tetraethyleneglycol. Other four units uses sulpholane extraction process these include : Indian Petrochemicals Corporation Limited, Baroda, National Organic Chemical Limited , Bombay, Bharat Petroleum Corporation Limited, Bomaby and Cochin Refineries Limited, Cochin. The latter two use Indian Institute of Petroleum (IIP)-Engineers India Limited (EIL) process Reference may be made to IIP report on " Process development for aromatics extraction with sulpholane" Vol-1.
The demand for benzene is expected to increase at the rate of 5-7% per year while overall benzene supply will not increase significantly as a result of the impending restriction on benzene in the reformulated gasoline pool.
Thus significant additional benzene production capacity must be built over the years to come to keep pace with the expected growth in demand.
The selection of solvent forms the basis of solvent extraction process. The solvent should have a good compromise between selectivity and capacity. However, capacity is most important property that affects the economics of the process as it affects the solvent rate and total throughput which, in turn, affects the efficiency of the column.

Union Carbide has developed a new process for aromatics extraction ( Patent No. US 4,498,980 Feb 1985) where the use of glycol ether type solvent has been used as co-solvent with tetraethylene glycol to increase the capacity of the solvent.
For getting maximum purity and recovery of benzene in an extraction process, sulpholane is found to be the best solvent by the researchers and users and because of this there are maximum units in commercial operation based on this solvent. Directionally the ideal solvent is one which gives required purity and recovery at minimum solvent to feed ratio. Already 99.97% purity and 99.9% recovery of benzene is achieved with sulpholane and as such there is little scope to improve further these two key requirements. Since sulpholane has high inherent selectivity purity is not a problem. The question, therefore, is whether it is possible to lower the solvent to feed ratio by adding a cosolvent to sulpholane in such a way that without affecting the purity, feed throughput is increased.
The main objective of the present invention is to provide an improved process for the production of pure light aromatics which obviate the drawbacks as detailed above.
Another objective of the present invention is to provide a process for the production of pure aromatics such as benzene, toluene and xylenes.
Yet another objective of the invention is to provide a process wherein solvent extraction from reformate and hydrogenated pyrolysis gasoline containing 45-80% aromatics to obtain pure light aromatics.
Still another objective is to use solvent and cosolvent to obtain synergism resulting in lower solvent to feed ratio with increased thruoghput.
In the present invention therefore the aromatics are separated from the no-aromatics by extraction using mixed extraction solvent. The term mixed extraction solvent here means a solvent mixture comprising a solvent and co-solvent. The solvent used here is sulpholane while the co-solvent is N-methylpyrolidone
(NMP).

Accordingly, the present invention provides an improved process for the production of pure light aromatics which comprises:
(f) contacting rich aromatic feed containing less than 3% of naphthalenes with a
synergistic extraction solvent mixture of the kind such as herein described at a
temperature in the range of 30-80°C to obtain extract phase and raffmate phase;
(g) stripping the extract phase of non-aromatics by conventional methods as herein
described;
(h) recovering the aromatics from the stripped extract phase obtained in step (b) by known methods as herein described;
(i) recovering the solvent mixture from the raffmate phase by known methods as herein described;
(j) recycling the recovered solvent mixture containing less than 2% water obtained in steps (c) & (d).
In an embodiment of the present invention, the rich aromatic feed containing less than 3% naphthalenes used may be such as reformate, hydrogenated pyrolysis gasoline containing 45 to 80% aromatics.
In another embodiment of the present invention, the synergistic extraction solvent mixture used may be a mixture of solvent such as sulpholane and 5 to 30% of co solvent such as N-methyl pyrrrolidone (NMP).
In yet another embodiment of the invention ratio of solvent mixture to aromatic feed may be in range of 0.5 to 5% by wt.
In still another embodiment the contacting of rich aromatic feed and mixed extraction solvent may be effected counter currently in a contacting zone at a temperature on the range of 30 to 80°C.
In yet another embodiment of the invention the conventional method used for stripping the extract phase may be such as extractive distillation at atmospheric pressure at a temperature in the range of of 120-165°C.

Accordingly, the invention provides a improved process for the production of pure
light aromatics which comprises
a) Contacting rich aromatic feed containirk less than 3% of naphthalenes with a svnereistic extraction solvent mixture of the kind ruler as herein discribed a temp in the range of 30-80 C at to obtain extract phase and raffinate phase)
b)Stripping the extract phase of non-aromatics by conventional method
c) Recovering the aromatics from the stripped extract phase obtained in step b) by known methods-

d)Recovering the solvent mixture from the raffinate phase by known methods;
e) Recycling the recovered solvent mixture containing less than 2% water
obtained in steps c) and d),
In an embodiment of the present invention the rich aromatic feed containing less than 3% naphthalenes used may be such as reformate, hydrogenated pyrolysis gasoline containing 45-80% aromatics
In another embodiment of present invention the synergistic extraction solvent mixture used may be a mixture of solvent such as sulpholane and 5-30% of cosolvent such as N-methylpyrrolidone (NMP)
In yet another embodiment of the invention ratio of solvent mixture to aromatic feed may be in range of 0.5 to 5% by wt.
hi still another embodiment the contacting of rich aromatic feed and mixed extraction solvent may be effected counter currently in a contacting zone at a temperature in the range of 30-80°C
hi yet another embodiment of the invention the conventional method used for stripping the extract phase may be such as extractive distillation at atmospheric pressure at a temperature in the range of 120-165°C

In another embodiment the recovery of aromatics from the stripped extract phase may be effected using conventional method such as distillation at reduced pressure at temperature in the range of 120-200°C.
Recovery of solvent from raffinate phase may be done by known method such as water washing at a temperature in the range of 30-40°C
The flow diagram of an embodiment of the process of the present invention is shown in Fig-1 of the drawing accompanying this specification.
The feed stream is introduced through line (1) into the contact zone (A) and lean solvent (mixed solvent) is introduced via line (2) where the two streams meet countercurrently. The contact zone may comprise either a packed column or plate or a rotating disc contactor. The raffinate and extract phase, thus produced, are separately withdrawn through (3) and (4) respectively.
The top raffinate phase which leaves the contacting zone (A) via line (3) is water washed in raffinate wash column (D). The solvent free raffinate is withdrawn through line (5). The wash water containing solvent from line (6) is recycled to solvent recovery column (C).
The extract phase obtained from the contact zone (A) is introduced via line (4) hi the distillation column (B) for stripping-off the non-aromatics from the extract phase. The bottom mixed solvent phase containing mainly the aromatic hydrocarbons is introduced via line (7) in the second distillation column (C) for solvent recovery from where solvent-free extract is withdrawn through line (8) and recovered solvent is withdrawn through line (9) and joined to line (2) for recycling. A slip-stream of solvent is taken from line (10) and fed to the solvent regeneration column (E) from where the regenerated mixed solvent is taken through line (11) and put back into the mixed solvent recycle line (2).

The process of the invention is illustrated by the use of the following examples which should not be construed to limit the scope of the invention.
EXAMPLE-1
The liquid-liquid equilibrium data were generated with benzene-heptane model mixture containing 75.6 wt% benzene, which was admixed with an equal weight of mixed solvent containing 80% sulpholane and 20% N-methylpyrolidone (NMP) at 40°C. The liquid phases under equilibrium were formed. Each phase was separated made solvent free and analysed. Benzene was reduced to 43.49 wt% in the raffinate phase. The solvent-free extract obtained contains 80.1 wt% of benzene. The solubility of the extract hydrocarbons being 45.93 wt% in the mixed solvent phase.
EXAMPLE- 2
The benzene-heptane model hydrocarbon mixture containing 51.6 wt% benzene was fed into the bottom of a packed liquid-liquid extraction column at a rate of 2.65 kg/hr where it was contacted countercurrently with the mixed solvent stream of sulpholane containing 20% NMP flowing in from the top of the extraction column at a rate of about 4.99 kg/hr. The temperature in the column was maintained at 40°C. The resulting raffinate stream was withdrawn from the top of the column at a rate of 1.025 kg/hr and extract stream was withdrawn from the bottom at a rate of 6.72 kg/hr.
The raffinate stream from the extraction column which contains about 0.98 wt% of the solvent was water washed in the raffinate wash column (RWC) with 25% water. The water washed raffinate stream was withdrawn from the top of RWC at the rate of 1.01 kg/hr. The total benzene in the washed raffinate was 0.18 wt%. The wash water containing solvent from the bottom of RWC was fed into the solvent recovery column (SRC) as stripper water for recovery of hydrocarbons.
The extract phase from the bottom of the extraction column contains about 25.35 wt% of hydrocarbons out of which 87.1 by weight is benzene, was fed into a distillation column (stripper) to strip-off the heptane at the reboiler temperature of

160°C. The bottom phase contains about 6.65 wt% of hydrocarbons , thus obtained was fed into another distillation column (Solvent Recovery Column) operating with bottom temperature of 170°C and top temperature Of 80°C. Wash water from the RWC was also fed into the column at a point below the entry point. The overhead vapours on condensation gave a hydrocarbon layer and a water layer. The hydrocarbon layer was withdrawn as benzene containing 50-115 ppm of heptane alongwith increase in percent recovery of benzene as compared to that obtained with sulpholane solvent. The water layer was recycled to the RWC and a part of water layer was returned to the distillation column top as reflux. The bottom product from the SRC contains no hydrocarbons and was recycled back to the extractor as lean solvent.
The main advantages of the present invention over the sulpholane extraction process are increased solvent capacity, with increase in throughput and mass transfer rates. The raffinate produced contains less aromatics simultaneously increasing the recovery of aromatics with increased purity. Moreover, the reboiler temperature of solvent recovery column is also lowered as boiling point of the cosolvent is less than that of sulpholane, resulting in less solvent degradation. Additional advantage is the ease of handling of solvent as the melting point of the combination solvent is lowered.





WE CLAIM:
1. An improved process for the production of pure light aromatics which comprises:
(a) contacting rich aromatic feed containing less than 3% of naphthalenes with a
synergistic extraction solvent mixture of the kind such as herein described at a
temperature in the range of 30-80°C to obtain extract phase and raffmate phase;
(b) stripping the extract phase of non-aromatics by conventional methods as herein
described;
(c) recovering the aromatics from the stripped extract phase obtained in step (b) by
known methods as herein described;
(d) recovering the solvent mixture from the raffmate phase by known methods as
herein described;
(e) recycling the recovered solvent mixture containing less than 2% water obtained in
steps (c) & (d).

2. An improved process as claimed in claim 1, wherein rich aromatic feed
containing less than 3% naphthenes used is such as reformate, hydrogenated
pyrolysis gasoline containing 45-80% aromatics.
3. An improved process as claimed in claiml, wherein synergistic extraction solvent
mixture used is a mixture of solvent such as sulpholane and 5-30% of co-solvent
as N-methyl pyrolidone.
4. An improved process as claimed in claiml, wherein the ratio of solvent mixture
and aromatic feed is in the range of 0.5 to 5 by weight.

5. An improved process as claimed in claim 1, wherein the stripping of extract phase
is done utilizing extractive distillation at atmospheric pressure at a temperature in
therange of120-165°C.
6. An improved process as claimed in claim 1, wherein recovery of aromatics from
the stripped extract phase is effected using conventional methods.
7. An improved process as claimed in claiml, wherein recovery of solvent from
raffmate phase is effected by water washing at a temperature in the range of 30-
40°C.
8. An improved process for the production of pure light aromatics substantially as
herein described with reference to the examples and drawing accompanying
specification.





Documents:

1677-del-1998-abstract.pdf

1677-del-1998-claims.pdf

1677-del-1998-correspondence-others.pdf

1677-del-1998-correspondence-po.pdf

1677-del-1998-description (complete).pdf

1677-del-1998-drawings.pdf

1677-del-1998-form-1.pdf

1677-del-1998-form-19.pdf

1677-del-1998-form-2.pdf


Patent Number 216246
Indian Patent Application Number 1677/DEL/1998
PG Journal Number 13/2008
Publication Date 28-Mar-2008
Grant Date 11-Mar-2008
Date of Filing 18-Jun-1998
Name of Patentee COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110 001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 BACHAN SINGH RAWAT, INDIDN INSTITUTE OF PERTOLEUM, DEHRADUM-248005,INDIA,
2 SNEH KIRAN CHOPRA INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005, INDIA,
3 TURUGA SUNDARA RAMA PRASADA RAO INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIAN,
4 MOHAN KRINSHAN KHANNA, INDIA INSTIITUTE OF PETROLEUM, DEHRADUN-248005, INDIA
5 GUR PARSAD, INDIA INSTITUTE OF PETROLEUM, DEHRADUN-248005, INDIA,
6 SHRIKANT MADHUSUDAN NANOTI, INDID INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA,
7 DHARAM PAUL, INDIAN INSTITUTE OF PEROLEUM, DEHRADUN-248005, INDIA,
8 SHRI KRISHNA GUPTA, INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005, INDIA,
PCT International Classification Number C10G 35/04
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA