Molecular sieve abstract
The present invention relates to a process for the production of
high-octane gasoline from straight run light naphtha on Pt containing
HZSM-5 molecular sieve catalyst. The preparation of the catalyst
for the process does not involve the steps of steaming and acid
leaching before the actual catalytic application. The mentioned
catalyst is environmentally friendly as the preparation does not
involve the use of hazardous mineral acids, viz., HCl, HNO.sub.3
etc.
Molecular sieve claims
We claim:
1. A process for the production of high-octane gasoline from straight
run light naphtha over a Pt containing HZSM-5 molecular sieve catalyst
which comprises (i) impregnating 0.1-2.0 wt % of Pt from tetramine
platinum chloride on a HZSM-5 zeolite extrudate, (ii) drying the
zeolite extrudate followed by calcination, (iii) loading the Pt
impregnated zeolite extrudate in a high pressure reactor and reducing
it (iv) cooling the Pt impregnated zeolite bed and then increasing
the bed temperature (v) passing light naphtha through the bed to
obtain a mixture of high octane gasoline and LPG and separating
the gasoline from the mixture.
2. A process as claimed in claim 1 wherein in step (ii) the zeolite
extrudate is dried at a temperature of about 110.degree. C. and
for a period of 10-12 hrs and then calcined at a temperature in
the range of of 400-600.degree. C. for a period of 1-4 hrs in static
air.
3. A process as claimed in claim 1 wherein the treated Pt impregnating
zeolite extrudate is reduced inside the high pressure reactor in
step (iii) by passing hydrogen for a period in the range of 2-5
hours at a temperature in the range of 400-500.degree. C. and at
a flow rate in the range of 8-12 l/h into the reactor.
4. A process as claimed in claim 1 wherein in step (iv) the Pt
impregnated zeolite bed is first cooled to a temperature of about
300.degree. C. under nitrogen atmosphere and the bed temperature
thereafter increased to a range of 300-600.degree. C.
5. A process as claimed in claim 1 wherein in step (v) of the process,
light naphtha is passed through the bed at a weight hourly space
velocity in the range of 1 to 8 hrs.sup.-1 and at a pressure in
the range of 1 to 25 kg/cm.sup.2 and in the absence of nitrogen.
6. A process as claimed in claim 1 wherein the light naphtha feedstock
comprises light naphtha containing C.sub.6 to C.sub.8 range paraffins
and naphthenes.
7. A process as claimed in claim 1 wherein the reaction temperature
is in the range of 400-500.degree. C.
8. A process as claimed in claim 1 wherein the reaction pressure
is in the range of 1-10 kg/cm.sup.2.
9. A process as claimed in claim 1 wherein the weight hourly space
velocity of light naphta is in the range of 2-8 hrs.sup.-1.
10. A process as claimed in claim 1 wherein the Research Octane
Number (RON) of straight light naphtha fraction is increased from
64 to 97 in the product with gain of 34 units.
11. A process as claimed in claim 1 wherein the platinum impregnated
ZSM-5 zeolite composite used is prepared by incipient wetness method.
12. A process as claimed in claim 1 wherein the catalyst used is
regenerated by oxidative combustion.
13. A process as claimed in claim 1 wherein the total amount of
platinum metal added into HZSM-5 molecular sieve is in the range
of 0.1 to 1.1 wt %.
14. A process as claimed in claim 1 wherein the catalyst used results
in the reduction of the sulfur content in light naphtha feed stock
from 50 ppm level sulfur to 10 ppm level sulfur in the obtained
product.
15. A process as claimed in claim 1 wherein the pressure is varied
to in order to increase the aromatic content and decrease the LPG
in product mixture.
16. A process for the production of high-octane gasoline from straight
run light naphtha on Pt containing HZSM-5 molecular sieve catalyst
which comprises (i) impregnating 0.1-2.0 wt % of Pt from tetramine
platinum chloride on HZSM-5 zeolite extrudate, (ii) drying the zeolite
extrudate at a temperature of about 110.degree. C. for a period
of 10-12 hrs followed by calcination at a temperature of 400-600.degree.
C. for a period of 1-4 hrs in static air, (iii) loading the treated
Pt impregnated zeolite extrudate in a high pressure reactor and
reducing it by passing of hydrogen for a period of 2-5 hours at
a temperature of 400-500.degree. C. at a flow rate of 8-12 l/h into
the reactor (iv) cooling the Pt impregnated zeolite bed to a temperature
of about 300.degree. C. under nitrogen atmosphere and increasing
thereafter further bed temperature to 300-600.degree. C. (v) passing
light naphtha through the bed at weight hourly space velocity ranging
from of 1 to 8 hrs.sup.-1 at a pressure in the range of 1 to 25
kg/cm.sup.2 in the absence of nitrogen to obtain a mixture of high
octane gasoline and LPG and separating the gasoline from the mixture.
Molecular sieve description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for the production
of high-octane gasoline from straight run light naphtha on Pt containing
HZSM-5 molecular sieve catalyst. More particularly the present invention
relates to a process for the utilization of straight run light naphtha
feedstock available from various refineries, into value added aromatics
with low amounts of benzene which can be used as blending stocks
for improvement of octane number in gasoline fuel. In addition to
high-octane gasoline liquid product, some amounts of gas by-product
are also obtained which can be used as domestic fuel (LPG).
BACKGROUND OF THE INVENTION
[0002] The fast growing automobile population as well as increasing
pressure from environmental legislators has resulted in demand for
good quality gasoline in the country. The focal point for the improvement
of gasoline quality, at present is centered around benzene content
of 5% (V/V) with already lead free gasoline available in India (Ref.
Report of Sub-group on the Refining for IX.sup.th plan 1996). It
is stated that some of the refiners will be unable to meet the specification
of benzene leading to gasoline production loss. To address the benzene
problem in gasoline it is suggested to increase IBP of reformer
feed by adjusting naphtha splitter cut point which leads to substantial
loss in gasoline production volume and increased quantities of light
naphtha. As a result increasing interest is shown in the development
of new catalysts and processes, which allow production of gasoline
with sufficiently high octane numbers, making use of unconventional
low value feed stock such as light naphtha into standard gasoline
production. In addition to this, the demand for LPG is also growing
much faster in India at growth rate of 12 to 13 percent per year.
The corresponding deficit of LPG in 2000-01 is 4 million tons and
expected to increase up to 7.8 million tons by the year 2010-2011
(Sundar Rajan Committee Report on Hydrocarbon perspective 1996
Ref LPG News of India, March '96 p 17).
[0003] Light naphtha is one of the least viable petroleum feed
stocks treated today. Projected production of straight run light
naphtha cut (IBP-130) other than catalytic reforming feed in India
indicates 1-1.25 MMTPA (million metric tons) of light naphtha is
available from various refineries in 1996-97. Light naphtha mainly
contains C.sub.5 and C.sub.6 hydrocarbons (30 to 40 wt %) depending
upon the source. Due to high percentage of n-paraffins in light
naphtha it has lower research octane number (RON) and high RVP (Reid
Vapour Pressure) due to n- and i-pentanes, hence it cannot be used
directly for gasoline blending. Thus, the conversion of light naphtha
into other petroleum and petrochemical products gains significance
in this scenario.
[0004] Conventionally, gasoline is being produced from the Catalytic
reforming process of naphtha and Fluid catalytic cracking units
from various refineries. The indigenous gasoline production by refineries
with low benzene content will be inadequate to meet the demands
in future like at present. The catalyst used for reforming process
is monometallic Pt/Al.sub.2O.sub.3 or PtRe/Al.sub.2O.sub.3 bimetallic
catalyst. Although these processes are used all over the world,
there are number of limitations in the use of these catalysts. The
conventional catalyst is not effective in promoting aromatization
of light naphtha rich in C.sub.5 hydrocarbons. The catalyst is also
not very effective in promoting the aromatization of straight chain
paraffins such as n-hexane and n-heptane present in the feed that
remain unconverted. On the other hand, LPG production either from
refineries or from gas fields is not enough to meet the demands.
The import situation is also not encouraging, as only a few private
entrepreneurs have actually created facilities for import market.
Therefore the increasing demand for good quality gasoline and increasing
gap between LPG deficit and import capacity also indicates the need
to develop novel processes for the production of gasoline as well
as LPG from cheaply available feed stocks, viz., light naphtha.
[0005] There are reports in the literature on the conversion of
these straight chain paraffins into aromatics, using zeolites and
metal-doped zeolites as catalyst.
[0006] Reference is made to a process developed by Mobil researchers
(Ind. Eng. Chem. Process. Design Dev., 25 (1986) wherein the preparation
of aromatics from variety of feedstock such as pyrolysis gasoline,
unsaturated gases from catalytic cracker, paraffinic naphtha and
LPG have been described. Reference is also made to (Patent of Russia
Federation No 1141704 Appl. 17.06.1983) wherein method of producing
gasoline fractions from gas condensate over HZSM-5 catalyst has
described. The limitation of this process is that it utilizes long
range naphtha (80-180.degree. C.) which is also a feedstock for
catalytic reforming unit.
[0007] Reference is made to (Hydrocarbon Processing September 1989
p 72) wherein a process developed jointly by UOP Inc. and British
Petroleum based on gallium doped zeolite catalyst has been reported.
In this process LPG was converted into BTX aromatics and the process
has been demonstrated in a large-scale pilot plant of the British
Petroleum Grangemouth refinery in Scotland. Reference is also made
to U.S. Pat. No. 5026938 dated 25 Jun. 1991 wherein a process
for converting a gaseous feed stock containing C.sub.3-C.sub.5 paraffins
into aromatics hydrocarbons by contacting the feed with gallosilicate
molecular sieve catalyst has been described.
[0008] The draw back of all these processes is that these are mainly
related to the production of aromatics from paraffins of C.sub.3-C.sub.5
range which are in high demand as LPG in India.
[0009] Reference is made to U.S. Pat. No. 5125415 dated June
1992 wherein the use of Pt--Sn-ZSM-5 catalyst for the production
of mono-alkyl aromatics from C.sub.8 n-paraffins containing feed
stocks has been described. The limitation of the above process is
production of xylenes from C.sub.6-C.sub.8 hydrocarbons. Reference
is also made to Indian Patent Application No. 010/DEL/2001 dated
May 1 2001 wherein a process for the conversion of natural gas
liquid (NGL) into liquefied petroleum gas (LPG) and high-octane
gasoline over modified ZSM-5 zeolite has been reported. The limitation
of above process is that zeolite catalyst was modified by steaming
method and it produces more LPG (55 wt %) than aromatics (22 wt
%).
[0010] Reference is made to Indian Patent Application No. 2627/DEL/96-dated
29 Nov. 1996 wherein a process for the preparation of a novel modified
ZSM-5 zeolite has been reported. In this process zeolite catalyst
was modified by steaming method followed by acid leaching to remove
the extra framework alumina.
[0011] The limitations of the above process are firstly formation
of high quantity (8-12 wt %) of dry gas (C.sub.1+C.sub.2) during
the n-heptane conversion which will be a loss to the economy of
the process. Secondly the preparation of ZSM-5 catalyst in this
process involves acid leaching step which involves the use of hazardous
mineral acids viz. HCl.
OBJECTS OF THE INVENTION
[0012] The main object of the invention is to provide a process
for the production of high-octane gasoline from straight run light
naphtha on platinum containing HZSM-5 molecular sieve catalyst,
which obviates the drawbacks as detailed above.
[0013] Another object of the invention is to provide a process
for the conversion of light naphtha into high octane low benzene
content unleaded gasoline as a blender to boost the octane number
along with LPG as by product by using a catalyst system containing
platinum supported ZSM-5 zeolite composite.
[0014] Another object of the present invention is to provide a
process for the preparation of platinum metal modified ZSM-5 zeolite
catalyst by impregnation method with out acidity modification by
steaming and acid leaching steps.
[0015] Yet another object of the invention is to provide a process,
which utilizes the straight run light naphtha containing up to 35
hydrocarbon components for the production of high-octane gasoline
unlike the other existing processes.
[0016] Still another object of invention is to convert C.sub.5-C.sub.7
paraffinic and C.sub.6-C.sub.8 naphthenic components efficiently
to produce high-octane gasoline.
[0017] Another object of invention is to provide a process that
produces in addition to n-paraffinic and naphthenic components,
isoparaffins; benzene and other aromatics present in the feed also
can be effectively converted to give high octane gasoline with low
benzene content and LPG.
SUMMARY OF THE INVENTION
[0018] Accordingly the present invention provides a process for
the production of high-octane gasoline from straight run light naphtha
over a Pt containing HZSM-5 molecular sieve catalyst which comprises
[0019] i) impregnating 0.1-2.0% wt % of Pt from tetramine platinum
chloride on a HZSM-5 zeolite extrudate,
[0020] ii) drying the zeolite extrudate followed by calcination,
[0021] iii) loading the Pt impregnated zeolite extrudate in a high
pressure reactor and reducing it
[0022] iv) cooling the Pt impregnated zeolite bed and then increasing
the bed temperature
[0023] v) passing light naphtha through the bed to obtain a mixture
of high octane gasoline and LPG and separating the high octane gasoline
from the mixture.
[0024] In one embodiment of the invention, in step (ii) the zeolite
extrudate is dried at a temperature of about 110.degree. C. and
for a period of 10-12 hrs and then calcined at a temperature in
the range of 400-600.degree. C. for a period of 1-4 hrs in static
air.
[0025] In another embodiment of the invention, the treated Pt impregnating
zeolite extrudate is reduced inside the high pressure reactor in
step (iii) by passing hydrogen for a period in the range of 2-5
hours at a temperature in the range of 400-500.degree. C. and at
a flow rate in the range of 8-12 l/h into the reactor.
[0026] In yet another embodiment of the intention, in step (iv)
the Pt impregnated zeolite bed is first cooled to a temperature
of about 300.degree. C. under nitrogen atmosphere and the bed temperature
thereafter increased to a range of 300-600.degree. C.
[0027] In a further embodiment of the invention, in step (v) of
the process, light naphtha is passed through the bed at a weight
hourly space velocity in the range of 1 to 8 hrs.sup.-1 and at a
pressure in the range of 1 to 25 kg/cm.sup.2 and in the absence
of nitrogen.
[0028] In another embodiment of the invention the light naphtha
feedstock comprises light naphtha containing C.sub.6 to Cg range
paraffins and naphthenes.
[0029] In another embodiment of the invention the reaction temperature
is in the range of 400-500.degree. C.
[0030] In yet another embodiment of the invention the pressure
is in the range of 1-10 kg/cm.sup.2.
[0031] In another embodiment of the invention the weight hourly
space velocity of light naphta is in the range of 2-8 hrs.sup.-1.
[0032] In another embodiment of the invention the Research Octane
Number (RON) of straight light naphtha fraction is increased from
64 to 97 in the product with gain of 34 units.
[0033] In another embodiment of the invention the platinum impregnated
ZSM-5 zeolite composite used is prepared by incipient wetness method.
[0034] In another embodiment of the invention the catalyst used
is regenerated by oxidative combustion.
[0035] In another embodiment of the invention the total amount
of platinum metal added into HZSM-5 molecular sieve is in the range
of 0.1 to 1.1 wt %.
[0036] In another embodiment of the invention the catalyst used
results in the reduction of the sulfur content in light naphtha
feed stock from 50 ppm level sulfur to 10 ppm level sulfur in the
obtained product.
[0037] In another embodiment of the invention the pressure is varied
to in order to increase the aromatic content and decrease the LPG
in product mixture.
DETAILED DESCRIPTION OF THE INVENTION
[0038] In the present invention, preparation of the catalyst for
the process does not involve the steps of steaming and acid leaching
before the actual catalytic application. The mentioned catalyst
is environmentally friendly as the preparation does not involve
the use of hazardous mineral acids, viz., HCl, HNO.sub.3 etc.
[0039] The detailed steps of the process are:
[0040] About 18 cc of the catalyst (13 g) in extruded form of 1.5
to 2 mm diameter is loaded in a fixed bed, down flow, high pressure
reactor. Before the test runs, the catalyst is reduced at 450.degree.
C. with H.sub.2 gas for 4 hours with flow rate of 10 l/h. It is
cooled down to 300.degree. C. in N.sub.2 flow and heated again to
desired reaction temperature. The light naphtha is pumped by plunger
type feed pump and N.sub.2 flow was stopped totally. Reactor effluents
are cooled before being fed to high-pressure separator. The vapors
from separator are purged, while the liquid phase is sent to stabilizer
column.
[0041] Regeneration of the deactivated catalyst in reactor is carried
out by conventional procedure using air and nitrogen mixture. The
liquid product is analyzed using a gas Chromatograph fitted with
Tetra Cyano Ethoxy Propionitrile column and FID detector. The gaseous
products are analyzed using Squalane column.
[0042] The process conditions controls the C.sub.1+C.sub.2 (dry
gas) yield, which is not desired in the gasoline process. In order
to reduce the duration of regeneration of the catalyst thereby to
improve the catalyst life against the coke lay down, 0.4 wt % of
platinum metal is doped on HZSM-5 catalyst. The process can operate
for maximization of LPG as well by simply altering process parameters.
The catalyst used in present process is a novel platinum supported
HZSM-5 zeolite in which parent ZSM-5 zeolite composite was procured
from Zeolyst international (Lot No. 1822-43). The zeolite to binder
ratio of HZSM-5 extrudates was 80:20. These extrudates were impregnated
with 0.4 wt % of Pt from tetraamine platinum chloride (Aldrich)
solution. These extrudates were oven dried at 110.degree. C. for
12 hrs and then processed to calcination at 500.degree. C. for 3
hrs in static air.
[0043] The Physico-chemical properties of the zeolite catalyst
are as follows:
[0044] Characteristics of Parent HZSM-5:
[0045] Si--Al ratio (SAR): 100; XRD Crystallinity: 99%; Catalyst:
Pt/HZSM-5; Shape: Cylindrical form; Diameter: 1.5-2.0 mm; Bulk Density:
0.7-0.75 gm/cc; BET Surface Area: 350400 m.sup.2/g.
[0046] The composition of straight run light naphtha used in this
process has been analyzed by GC is shown below.
[0047] Light naphtha Feed Composition (wt %):
1 Carbon No. n-paraffin i-paraffin Naphthenes Aromatics C.sub.4
0.4 0.1 -- -- C.sub.5 4.5 5.5 1.5 -- C.sub.6 4.7 7.2 11.5 2.3 C.sub.7
5.0 7.5 21.5 5.9 C.sub.8 4.0 3.6 11.5 3.2
[0048] The following examples are given by way of illustration
and therefore should not be construed to limit the scope of the
present invention.
EXAMPLE--1
[0049] This example describes the characteristics of the high-octane
gasoline liquid product and LPG obtained in the present process
from light naphtha feed stock. Yields of individual product components
that are obtained are given. Analysis is based on GC fitted with
Tetra Cyano Ethoxy Propionitrate column and FID detector.
2TABLE 1 Characteristics of Feed and Liquid Products of this process
Process conditions: Catalyst: Pt/HZSM-5; Feed: light naphtha of
Numaligharh refinery; Reaction Temperature: 450.degree. C.; Pressure:
3 kg/cm.sup.2; WHSV: 6 hr.sup.-1; TOS: 24 hrs; Reactor: Micro Reactor
of 25 gm-catalyst capacity. Light naphtha Liquid Component Feed
(wt %) Product (wt %) Dry Gas 0 1.0 LPG (C.sub.3 + C.sub.4) 0 13.5
Total Paraffins* 42.6 11.3 Total Aromatics 11.4 60.0 Benzene content
2.3 8.6 Density of the Liquid (g/cc) 0.7230 0.7498 Research Octane
No. (RON) 64.4 97.4 Sulphur (ppm) 43.3 10.2 RVP of liquid (kPa at
38.degree. C.) 41.2 67.6 Existent gum (g/m.sup.3) -- 17.0 Potential
gum (g/m.sup.3) -- 89.0 Distillation a. Initial Boiling Point(.degree.
C.) 44.1 46.3 b. Recovery up to 70.degree. C.(% vol) 20.0 20.0 c.
recovery up to 100.degree. C. 70.0 50.0 d. recovery up to 180.degree.
C. nil 95.0 e. Final boiling point(.degree. C.) 132.4 210.5 f. Residue
(% vol) 1.2 3.3 *excluding C.sub.6-C.sub.8 naphthenes of 46 wt %
[0050] Table 1 shows conversion of light naphtha feed stock having
RON of 64 into aromatics rich (60%) liquid product with low benzene
content having RON 97.4. 85 wt % of high-octane gasoline was produced
from low value feedstock, which also met environmental regulations
on gasoline in terms of low benzene content and low sulphur level.
EXAMPLE--2
[0051] This example illustrates the results of effect of temperature
on product distribution of aromatics (BTX) in liquid product, LPG
and dry gas. Gaseous and liquid products were analyzed by same method
mentioned in example 1.
3TABLE 2 Effect of Temperature on Product Yields Process conditions:
Catalyst: Pt/HZSM-5; Feed: light naphtha; Pressure: 20 kg/cm.sup.2;
WHSV: 6 hr.sup.-1; TOS: 24 hrs Temperature (.degree. C.) 400 450
500 Ex-reactor yield (Wt % based on the feed) Dry gas 2.5 2.0 3.5
LPG 24.4 21.5 31.6 C.sub.3 14.4 14.1 20.9 C.sub.4 10.0 7.4 10.6
C.sub.5-C.sub.8 (Sat) 51.6 50.5 13.6 Aromatics (BTX) 16.4 20.8 43.4
C.sub.9+ 5.1 5.2 7.9 RON 80.0 90.4 9
[0052] Table-2 shows that yield of aromatics (BTX) increases with
increase of temperature and optimum temperature for the present
process was chosen as 450.degree. C. due to formation of less coke
during reaction.
EXAMPLE--3
[0053] This example includes results of effect of pressure on yields
and composition of aromatics and LPG. The product analysis is presented
in table-3.
4TABLE 3 Effect of Pressure on Product Yields Process conditions:
Catalyst: Pt/HZSM-5; Feed: Straight run light naphtha; Temperature:
450.degree. C.; WHSV: 6 hr.sup.-1; TOS: 24 hrs Pressure (kg/cm.sup.2)
20 3 Ex-Reactor Yields (Wt % based on the feed) Dry gas 2.0 1.0
LPG 21.5 13.5 C.sub.3 14.1 8.0 C.sub.4 7.4 5.5 C.sub.5-C.sub.8 (Sat)
50.5 21.7 Aromatics (BTX) 20.8 60.0 C.sub.9+ 5.2 3.8 RON 90.4 97.4
[0054] The experimental results reported in table-3 shows that
the decrease of pressure increases the BTX production with decrease
in yields of LPG. The optimum pressure for this process was fixed
at 3 Kg/cm.sup.2 due to more aromatic formation.
EXAMPLE --4
[0055] This example illustrates effect of weight hourly space velocity
on yield and composition of high-octane gasoline and LPG. The product
analysis presented in Table-4.
5TABLE 4 Effect of Weight Hourly Space Velocity on Product Yields
Process conditions: Catalyst: Pt/HZSM-5; Feed: Straight run light
naphtha; Temperature: 450.degree. C.; Pressure: 3 kg/cm.sup.2; TOS:
24 hrs WHSV (hr.sup.-1) 6.0 2.0 Ex-Reactor Yields (Wt % based on
the feed) Dry gas 1.0 1.3 LPG 13.5 38.4 C.sub.3 8.0 22.1 C.sub.4
5.5 16.3 C.sub.5-C.sub.8 (Sat) 21.7 11.8 Aromatics (BTX) 60.0 37.4
C.sub.9+ 3.8 11.1 RON 97.4 94.8
[0056] From the above table-4 it is shown that the increase of
WHSV to 6 decreases the LPG yield and increases aromatic yields
with similar dry gas yields. |