U.S. patent application number 12/576680 was filed with the patent office on 2010-04-15 for use of zinc ferrite-based solids in a process for deep desulfurization of hydrocarbon fractions.
This patent application is currently assigned to IFP. Invention is credited to Celine BABE, Arnaud Baudot, Delphine Bazer-Bachi, Carole Bobin, Christophe Geantet, Thierry Huard, Anthony Tanguy.
Application Number | 20100089799 12/576680 |
Document ID | / |
Family ID | 40637234 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100089799 |
Kind Code |
A1 |
BABE; Celine ; et
al. |
April 15, 2010 |
USE OF ZINC FERRITE-BASED SOLIDS IN A PROCESS FOR DEEP
DESULFURIZATION OF HYDROCARBON FRACTIONS
Abstract
The invention relates to a process for desulfurization of a
non-oxidized hydrocarbon feedstock, comprising organic sulfur
compounds, by adsorption, especially chemisorption of sulfur on a
composition in bulk form consisting essentially of 70% by weight of
zinc ferrite and optionally iron oxides or zinc oxides. The process
is performed in the presence of hydrogen at a temperature of
between 200.degree. C. and 450.degree. C.
Inventors: |
BABE; Celine; (Villeurbanne,
FR) ; Baudot; Arnaud; (Vernaison, FR) ;
Bazer-Bachi; Delphine; (Saint-Genis-Laval, FR) ;
Bobin; Carole; (Grezieu La Varenne, FR) ; Geantet;
Christophe; (Miribel, FR) ; Huard; Thierry;
(Saint Symphorien D'Ozon, FR) ; Tanguy; Anthony;
(Lyon, FR) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
2200 CLARENDON BLVD., SUITE 1400
ARLINGTON
VA
22201
US
|
Assignee: |
IFP
Rueil-Malmison Cedex
FR
|
Family ID: |
40637234 |
Appl. No.: |
12/576680 |
Filed: |
October 9, 2009 |
Current U.S.
Class: |
208/217 |
Current CPC
Class: |
B01J 20/3458 20130101;
C10G 2400/08 20130101; B01J 20/0229 20130101; B01J 20/0244
20130101; B01J 20/28059 20130101; B01J 2220/56 20130101; C10G
2300/1055 20130101; C10G 2300/202 20130101; B01J 20/3433 20130101;
C10G 2300/1051 20130101; B01J 20/06 20130101; C10G 2300/4006
20130101; C10G 2300/70 20130101; C10G 2400/02 20130101; C10G
2400/04 20130101; C10G 2300/1044 20130101; C10G 2300/104 20130101;
C10G 2300/4018 20130101; B01J 20/28004 20130101; B01J 2220/42
20130101 |
Class at
Publication: |
208/217 |
International
Class: |
C10G 45/00 20060101
C10G045/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2008 |
FR |
08/05.623 |
Claims
1. A process for desulfurization of a hydrocarbon feedstock
comprising sulfur compounds, comprising subjecting said feedstock,
in the presence of hydrogen at a temperature of between 200.degree.
C. and 450.degree. C., to chemisorption on a bulk adsorption agent
consisting essentially of zinc ferrite.
2. A process according to claim 1, conducted under a pressure of
between 0.2 and 3.5 MPa.
3. A process according to claim 1, conducted with an hourly
volumetric flow rate of the feedstock to be treated of between 0.1
h.sup.-1 and 10 h.sup.-1.
4. A process according to claim 1, conducted with a
hydrogen/hydrocarbon feedstock volumetric ratio of between 5 and
400.
5. A process according to claim 1, in which the hydrocarbon
feedstock is a gasoline, kerosene or diesel fraction.
6. A process according to claim 1, in which the hydrocarbon
feedstock is a diesel fraction.
7. A process according to claim 1, in which the hydrocarbon
feedstock comprises cyclic sulfur compounds.
8. A process according to claim 1, in which the bulk adsorption
agent comprises more than 80% by weight of zinc ferrite.
9. A process according to claim 1, in which the bulk adsorption
agent comprises more than 98% by weight of zinc ferrite.
10. A process according to claim 2, in which the pressure is
between 0.5 and 3 MPa.
11. A process according to claim 1, further consisting essentially
of zinc oxide and/or iron oxide.
12. A process according to claim 1, wherein the hydrocarbon
feedstock is a non-oxidized feedstock.
13. A process according to claim 11, wherein the hydrocarbon
feedstock is a non-oxidized feedstock.
14. A process according to claim 1, wherein the bulk adsorption
agent is a free flowing mass of powder having a particle size of
between 80 and 125 microns wherein the zinc ferrite consists
essentially of crystallites having a size between 20 and
5000.degree. .ANG..
15. A process according to claim 14, wherein the size of the
crystallites is between 100 and 1000 .ANG..
16. A process according to claim 15, in which the bulk adsorption
agent comprises more than 98% by weight of zinc ferrite.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is related to a concurrently filed
application entitled "Use of Solids Based on Zinc Ferrite In a
Process For Deep Desulphurizing Oxygen-Containing Feeds" by Arnaud
Baudot et al., attorney docket number PET-2552, based on French
Priority application Ser. No. 08/05.624. Same related application
has been incorporated by reference herein.
[0002] The future specifications on automobile fuels call for a
great reduction of the sulfur content in the fuels. European
legislation defines the specifications of gas-oil fuels that have
had 50 ppm of sulfur since 2005 and will have 10 ppm of sulfur in
2009. The evolution of the specifications of the sulfur content in
the fuels requires the improvement of existing catalytic
hydrotreatment processes or the development of new processes for
deep desulfurization of gas oils.
[0003] Among the new methods for desulfurization of gas oils, the
processes for purification by adsorption of sulfur compounds on a
selective adsorbent offer an advantageous alternative to the
standard hydrodesulfurization processes. This invention relates to
a process for deep desulfurization on a zinc ferrite.
[0004] It is recalled that a standard hydrodesulfurization unit
transforms the essential part of the sulfur compounds that are
contained in a distillate into H.sub.2S under temperature
conditions that are close to 450.degree. C., and pressures between
20 and 60 bar. However, a portion of the sulfur compounds is called
"refractory" in hydrodesulfurization because their transformation
into H.sub.2S requires clearly higher pressure and temperature
conditions. These refractory molecules are a part of the family of
alkylated dibenzothiophenic compounds. The content of
post-hydrodesulfurization refractory compounds to be treated
depends on several parameters, including pressure level and
hydrodesulfurization unit temperature, the quantities of catalysts
involved, and the hourly volumetric flow rate that is implemented.
The content of refractory compounds in the effluent of a
hydrodesulfurization unit is in general greater than 15 ppmS and in
general less than 500 ppmS, and even 350 ppmS, and even 50
ppmS.
[0005] During purification by adsorption, as considered in this
invention, the refractory compounds will react selectively in the
presence of hydrogen with the solid, releasing the organic molecule
without the sulfur atom, which remains trapped in the adsorbent in
a sulfide form. This adsorption with modification of molecules and
adsorbent is called a reactive chemisorption. The fact that the
sulfur is directly trapped on the oxide makes it possible to shift
the balance of the reaction very greatly and is particularly
suitable for purification treatment. As a result, contrary to the
conventional hydrodesulfurization processes with which it is
necessary to increase the partial pressure of hydrogen to increase
the release of sulfur in H.sub.2S form of the organic sulfur
compounds, the purification by adsorption does not require the use
of a high hydrogen pressure. This leads to a reduction of the
investment and operating costs, in particular on the level of
hydrogen compressors, in the equipment concerned. In addition,
whereby the sulfur is trapped in the oxide, the hydrogen that exits
from the reactor where the desulfurization stage takes place does
not contain sulfur (in particular in H.sub.2S form). It is
therefore unnecessary to treat the hydrogen again so as to remove
its sulfur from it.
PRIOR ART
[0006] The patent application US 2006/0191821A1 describes a process
for desulfurization on a zinc oxide that is optionally promoted by
an iron or copper oxide that is supported on a porous substrate
based on silica and/or alumina.
[0007] The patent application WO 2007/021084 describes mixed zinc
and aluminum oxides used in desulfurization processes. These solids
are reduced before use.
[0008] Document WO 01/70393 A1 by Khare describes the binding of
zinc ferrite particles with a binder such as alumina. The resultant
solid reduced zinc ferrite-alumina particles can be used to remove
sulfur from a cracked gasoline or diesel fuel stream.
[0009] The U.S. Pat. No. 4,985,074 describes the use of coked
feedstocks and naphtha feedstocks of solids based on copper-zinc
oxides or copper-zinc-alumina oxides that are obtained by
co-precipitation. A reduction of the solid under hydrogen before
the desulfurization stage is carried out.
SUMMARY DESCRIPTION OF THE INVENTION
[0010] The invention relates to a process for desulfurization of a
non-oxidized hydrocarbon feedstock, comprising organic sulfur
compounds, by collection of sulfur on a bulk compound that consists
essentially of more than 70% by weight of zinc ferrite and
optionally iron oxides or zinc oxides. The process is performed in
the presence of hydrogen at a temperature of between 200.degree. C.
and 450.degree. C.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The invention relates to a process for desulfurization of a
preferably non-oxidized hydrocarbon feedstock, preferably a
gasoline, kerosene or diesel fraction, preferably a diesel
fraction, comprising organic sulfur compounds, preferably cyclic
sulfur compounds, by collection of sulfur on a bulk compound that
consists essentially of more than 70% by weight of zinc ferrite,
preferably more than 80% by weight of zinc ferrite, more preferably
more than 98% by weight of zinc ferrite, even more preferably more
than 99.5% by weight of zinc ferrite and optionally iron oxides
and/or zinc oxides, whereby said process is performed in the
presence of hydrogen at a temperature of between 200.degree. C. and
450.degree. C.
[0012] The pressure is generally between 0.2 and 3.5 MPa,
preferably between 0.5 and 3 MPa, and even preferably between 0.5
and 1.5 MPa. The hourly volumetric flow rate of the feedstock to be
treated is generally between 0.1 h.sup.-1 and 10 h.sup.-1,
preferably between 0.5 h.sup.-1 and 5 h.sup.-1. The hourly
volumetric flow rate or VVH of treated liquid feedstock is defined
as the volumetric flow rate of treated liquid feedstock on the
solid bulk compound volume. The hydrogen/hydrocarbon feedstock
volumetric ratio is generally between 5 and 400, preferably between
50 and 300. The hydrogen flow rates and that of liquid feedstock to
be treated are taken up under normal conditions.
[0013] The zinc ferrite-type mixed oxide according to the invention
is very active even under mild operating conditions relative to the
conventional hydrodesulfurization conditions and to "high-pressure"
hydrodesulfurization conditions designed to reach sulfur contents
in the fuels that are set by the most recent standards promulgated
in developed countries. While operating at hydrogen pressures of
between 0.5 and 3 MPa, it makes it possible to reduce the
refractory sulfur compounds to contents that are similar to that
which is reached by the high-pressure hydrodesulfurization units
that operate at 6 MPa and more.
[0014] The process according to the invention makes it possible to
produce a desulfurized hydrocarbon fraction with contents that are
less than or equal to 10 ppm of sulfur, preferably less than 5 ppm
of sulfur, and even preferably less than 1 ppm of sulfur. This
process is particularly effective for eliminating the refractory
sulfur compounds with conventional hydrodesulfurization treatments
such as dimethyldibenzothiophene in gas-oil fractions.
[0015] The process according to the invention constitutes a simple
alternative to the "high-pressure" hydrodesulfurization process
that makes it possible to revamp at lower cost "low-pressure"
conventional hydrodesulfurization units to reach the sulfur
contents set by the most recent standards.
[0016] The iron- and zinc-based mixed oxide of this invention can
also be used in multicycling by making sulfur adsorption stages and
solid regeneration stages alternate by oxidizing means.
[0017] In general, increasing the temperature makes it possible to
desulfurize the most refractory sulfur compounds. In the case of
sulfur compounds such as thiophene, the zinc ferrite is active from
150.degree. C., whereas in the case of benzothiophenic compounds,
it is active from 200.degree. C., and in the cases of particularly
refractory sulfur compounds of alkylated dibenzothiophene
compounds, the zinc ferrite is active from 300.degree. C.
[0018] An adsorption cycle that uses standard adsorbents consists
of a series of recurring stages: [0019] Stage 1: Activation phase
of the solid. This pre-reduction stage is difficult to operate
industrially in a stationary bed because of the exothermicity of
this reaction. [0020] Stage 2: Adsorption phase: The evaporated
feedstock is brought into contact with the hydrogen on the
adsorbent. Once the solid is saturated with sulfur or once the
sulfur specifications of the effluent are no longer observed, the
solid is to be regenerated. [0021] Stage 3: Draining and
immobilization phase of the adsorption column. This involves a
stripping phase with an inert gas to eliminate the partially
converted hydrocarbons and the gases that are present in the pore
volume. The purpose is actually to prevent any mixing of hydrogen
that is used in the adsorption phase with the oxygen that is used
in the regeneration phase. [0022] Stage 4: Stage for regenerating
the adsorbent. The regeneration is carried out in general by a mild
oxidation by using, for example, greatly diluted oxygen to control
the combustion. [0023] Stage 5: Draining phase of the adsorbent bed
with an inert gas for eliminating any trace of residual oxygen in
the pore volume.
[0024] Over the entire cycle, Stage No. 2 constitutes the single
productive stage in the desulfurization process whereas the other
stages, although necessary, constitute a non-productive down time
in the desulfurization process. As a result, the operator of this
type of separation operation should aim at maximizing the
proportion of the duration of the phase No. 2 relative to the total
cycle time.
[0025] This invention has a certain technological advantage since
the implementation of the zinc ferrite does not require an
activation stage. As a result, the "adsorption phase duration/total
cycle duration" ratio is greatly improved. The productivity of the
desulfurization operation by zinc ferrite according to the
invention is still greater than that of the standard processes.
[0026] Another advantage resides in the fact that whereby the
activation stage is exothermic, it is necessary that it regulate
its behavior very precisely, without which irreversible mechanisms
of structural modifications of the adsorbent, induced by the
temperature (sintering, phase shift, . . . ) can take place. In the
absence of this stage, the behavior of the zinc ferrite according
to the invention for the deep desulfurization of hydrocarbon
feedstocks is easier than that of standard adsorbents, such as
those claimed in the prior art.
[0027] The process for preparation of a zinc ferrite-type mixed
oxide generally comprises: [0028] A stage for co-precipitation of a
mixture of precursor salts of zinc II and iron III, in the presence
of a base, at a pH of between 6.1 and 6.9 and at a temperature of
between 30.degree. C. and 50.degree. C. [0029] A filtration stage
of the precipitate that is obtained [0030] A drying stage for a
duration of between 12 and 24 hours at a temperature of between
125.degree. C. and 175.degree. C. [0031] A calcination stage in the
presence of oxygen at a temperature of between 600.degree. C. and
700.degree. C. for a duration of between 1 hour and 3 hours.
[0032] The zinc ferrite of formula ZnFe.sub.2O.sub.4 generally has
a franklinite-type crystalline structure.
[0033] The size of the zinc ferrite crystallites is generally
between 20 and 5000 .ANG., and preferably between 100 and 1000
.ANG..
[0034] The specific surface area of the zinc ferrite is generally
between 2 and 100 m.sup.2/g. The zinc ferrite is active even for
specific surface areas that are less than 10 m.sup.2/g. The zinc
ferrite can be used in the form of free flowing powder, balls or
extrudates. The zinc ferrite is preferably run in a fixed bed, but
it is also possible to run it in a circulating bed.
[0035] The zinc ferrite-type mixed oxide is generally obtained by a
co-precipitation followed by a calcination. The preparation process
does not require an intermediate stage of impregnation of a second
phase that acts as a promoter. The zinc ferrite mixed oxide is
active even with specific surface areas that are less than 10
m.sup.2/g. The synthesis according to the invention of an active
zinc ferrite-based mass does not require a sophisticated protocol
whose purpose is to develop a large specific surface area that is
necessary for a high reactivity of this solid with regard to sulfur
molecules. The process for preparation does not require a reduction
stage so as to make the oxide active nor a promoter dispersion
stage (for example, an iron oxide or copper oxide) on the oxide.
Such a reduction stage, for example with hydrogen, is generally
difficult to operate industrially in a fixed bed due to the
exothermicity of the reaction.
EXAMPLES
Example No. 1
(According to the Invention): Preparation of a Zinc Ferrite
[0036] A foot of water is introduced into a double-envelope
borosilicate glass reactor and then heated at 40.degree. C. under a
stifling power of about 150 W/m.sup.3 released by a rotor with
axial flow rate of the propeller type with blades.
[0037] The precursors are aqueous solutions of zinc (II) nitrate
and iron (III) nitrate. The bulk concentrations of zinc and iron
are respectively 13 g/l and 22.5 g/l.
[0038] The base is an aqueous ammonia solution. The bulk
concentration of ammonia is 225 g/l.
[0039] The precursors and the base are introduced into the reactor
via a pumping system that makes it possible to regulate the
introduction flow rates and the duration of the synthesis. The
management of the pH is ensured by the flow rate of the basic pump:
it is kept constant at 6.5.+-.0.2 throughout the
co-precipitation.
[0040] During the reaction, a stirring power of about 75 W/m.sup.3
is applied in the reaction medium, and a temperature of 40.degree.
C..+-.2.degree. C. is maintained in the reactor via a thermostated
bath.
[0041] The precipitate is hot-filtered in a Buchner flask. The wet
cake that is obtained after 45 minutes of filtration is dried in
the oven for 18 hours at a temperature of 150.degree. C.
[0042] The solid that is obtained is then calcined in the presence
of molecular oxygen at a temperature of 650.degree. C. for 2
hours.
[0043] The solid that is obtained is characterized by X-ray
diffraction via a Bragg-Brentano-type powder diffractometer in a
.theta.-.theta. configuration. The recording conditions are as
follows: an anticathode voltage adjusted to 35 kV, the intensity in
the anticathode filament set at 35 mA, the sampling span equal to
0.05.degree.2.theta., the counting time by span set at 5 s, and an
angular domain that ranges from 2 to 72.degree.2.theta.. On the
experimental diffractogram that is obtained on our solid, the
position of the lines is similar to that of a known
crystallographic structure that is listed in the database "Powder
Diffraction File" corresponding to the franklinite
ZnFe.sub.2O.sub.4 (PDF No. 00-022-1012).
[0044] The positions of the most intense experimental lines are as
follows for our solid:
29.93.degree.2.theta.-35.27.degree.2.theta.-56.61.degree.2.theta.-62.15.d-
egree.2.theta.. For the franklinite, they are
29.92.degree.2.theta.-35.26.degree.2.theta.-56.63.degree.2.theta.-62.21.d-
egree.2.theta..
[0045] As for the mesh parameter (a=b=c in the case of a cubic
system), it is identical, i.e., equal to 8.44 .ANG.. For our solid,
the mean size of zinc ferrite crystallites is 410.+-.40 .ANG..
[0046] A semi-quantitative analysis by X fluorescence has also been
carried out on the synthesized solid. The contents that are
obtained after correction of a fire loss carried out at 550.degree.
C., 4 h (PAF=0.3%) leads to the following contents: % by weight of
Fe=42.48.+-.0.74% and % by weight of Zn=23.18.+-.0.78%.
[0047] Finally, the specific surface area developed by the solid
has been estimated by a low-temperature nitrogen volumetric
analysis according to the ASTM Standard D 3663-84 or NFX 11-621: it
is equal to 6.+-.1 m.sup.2/g.
Example No. 2
(According to the Invention): Desulfurization Test by Chemisorption
on Zinc Ferrite with a Model Diesel-Type Feedstock that Contains a
Refractory Sulfur Compound
[0048] The second example describes the use of the solid in a
fixed-bed-type reactor. 12 grams of solid in powder form is
introduced into a column with an inside diameter of 1 cm and a
useful volume of 9 cm.sup.3. The column is placed in a ventilated
oven that operates at 380.degree. C. The regulation of the
temperature is an external regulation with measurement of the
column wall temperature, which makes it possible to work without a
thermowell and to eliminate any preferred path in the column.
[0049] The temperature of the output effluent is maintained and
sampled by means of a sampling loop for an analytical online
follow-up. The compounds are analyzed by gas-phase chromatography
equipped with an FID detection and a PFPD analyzer.
[0050] A model liquid feedstock that consists of dodecane and that
contains 50 ppmS by mass of 2,4 dimethyldibenzothiophene is fed
with a VVH of 4 h.sup.-1 by means of a Gilson syringe pump, and
then evaporated in the presence of hydrogen by means of a dedicated
device before being injected into the reactor. The pressure in the
reactor is 12 bar, and the hydrogen/hydrocarbon molar ratio at the
inlet of the reactor is equal to 200.
[0051] Upon the contact of the feedstock with the solid, an almost
immediate drop in the sulfur content in the effluent of the reactor
to values that are lower than 5 ppm by mass is observed. The sulfur
profile based on time at the outlet of the reactor is thus kept
constant and less than 5 ppm before the piercing (breakthrough)
phenomenon that corresponds to a rise in the sulfur concentration
until reaching the sulfur concentration value at the inlet when the
adsorbent is completely saturated with sulfur. Before piercing, no
trace of sulfur can be detected by the PFPD detector of the gas
phase chromatograph.
[0052] It is possible to distinguish two parameters that represent
the performance levels of the solid that is based on zinc ferrite:
[0053] The dynamic capacity that corresponds to the sulfur content
that is trapped in the adsorbent just before the piercing. Under
the operating conditions that are used, the dynamic sulfur capacity
of the adsorbent based on zinc ferrite is 6.8% by mass. [0054] The
saturation capacity that corresponds to the maximum sulfur capacity
of the adsorbent that is measured after saturation. Under the
operating conditions that are used, the sulfur capacity with
saturation of the zinc ferrite-based adsorbent is 13.4% by
mass.
Example No. 3
(According to the Invention): Desulfurization Tests by
Chemisorption on Zinc Ferrite of a Polycyclic Sulfur Compound in
Vapor Phase
[0055] The adsorption reaction of pure dibenzothiophene (DBT) has
been studied by pressurized vapor phase in an open reactor with a
flushed bed. The test unit that is used consists of three parts:
[0056] The device for introducing reagents, [0057] The reaction
device, [0058] The analysis device.
[0059] The device for introducing reagents makes it possible to use
hydrogen and DBT. The H.sub.2 flow rate is regulated by means of a
bulk flowmeter of the Brooks trademark (0-100
cm.sup.3min.sup.-1).
[0060] The vapor pressure of the DBT is regulated using a
saturator-condenser system. The hydrogen bubbles in the DBT that is
contained in the saturator and is kept at the temperature T.sub.S.
The gas mixture then passes through a coil (the condenser) that is
kept at the temperature T.sub.C, less then T.sub.S, which allows a
recondensation of the DBT. Using this system, the vapor pressure of
the DBT is absolutely stable within the remainder of the device.
The systems for reaction and analysis should be kept at a
temperature that is higher than T.sub.C. The H.sub.2-DBT flow is
then introduced into the reactor that contains the solid.
[0061] The reaction device consists of a Pyrex glass tube that has
a 12 mm diameter with a frit that is inserted into a stainless
steel reactor with a slightly larger diameter. A graphite Teflon
seal ensures the air-tightness and can withstand temperatures of
300.degree. C. The reaction temperature is identified at the frit
with a thermowell that allows the passage of a thermocouple. After
the reactor, a needle valve makes it possible to regulate the
pressure in the device and to ensure the stress relief at
atmospheric pressure.
[0062] After the reaction and the stress relief at atmospheric
pressure, the gas mixture is analyzed in a chromatogram (Hewlett
Packard 5890 Series II) with detection by flame ionization (FID).
These analyses make it possible for us to obtain breakthrough
curves that represent the evolution of the DBT concentration at the
outlet based on time.
[0063] 280 mg of solid (in the form of sieved powder between 80 and
125 .mu.m) that is manufactured according to the description of
Example No. 1 is introduced into the reactor and heated under
N.sub.2 at 350.degree. C. with a temperature slope of 10.degree.
C./minute. When the temperature is stable, the H.sub.2/DBT gas
mixture is sent to the solid with a flow rate of 70 ml/minute and a
pressure of 7.10.sup.5 Pa (partial pressure of DBT=195 Pa).
[0064] When the DBT concentration at the outlet of the reactor is
stable (or equal to that of the inlet), a bypass of the reactor is
carried out. Then, the unit is flushed under H.sub.2 so as to
eliminate the DBT that is present in the unit. The unit and the
reactor are then flushed under N.sub.2 for about 1 hour, and then
the heating of the reactor is stopped.
[0065] Under these conditions, it has been shown that the DBT
content was zero in hydrogen at the outlet of the reactor before
piercing and that the dynamic sulfur capacity of the zinc ferrite
was 8.8% by mass. Its sulfur capacity at saturation is equal to
15.3% by mass.
Example No. 4
(According to the Invention): Desulfurization by Chemisorption on
Zinc Ferrite of a Model "Heavy Gasoline"-Type Feedstock
[0066] The device and the quantity of zinc ferrite used in this
example are similar in all respects to what is described in Example
No. 2.
[0067] A model liquid feedstock that consists of 80% decane and 20%
toluene containing 50 ppmS by mass of 3-methylbenzothiophene is fed
with a VVH of 4 h.sup.-1 by means of a Gilson syringe pump, then it
is evaporated in the presence of hydrogen by means of a dedicated
device and then injected into the reactor. The pressure in the
reactor is 15 bar, and the hydrogen/hydrocarbon molar ratio at the
inlet of the reactor is 200.
[0068] Upon the contact of the feedstock with the adsorbent, an
almost immediate drop in the sulfur content in the effluent of the
reactor to values of less than 5 ppm by mass is observed. The
sulfur profile based on time at the outlet of the reactor is thus
kept constant and less than 5 ppm before the piercing phenomenon.
Before piercing, no trace of sulfur was detected by the PFPD
detector of the gas phase chromatograph. Under the operating
conditions that are described in this patent, the dynamic sulfur
capacity of the adsorbent with a zinc ferrite base is 9.8% by mass,
and its sulfur capacity at saturation is 14.8% by mass.
Example No. 5
(Comparison Test with a Zinc Ferrite-Based Oxide Supported on an
Alumina)
[0069] Starting from zinc ferrite and boehmite powders, a solid is
prepared by mixing-extrusion. The percentages by mass of zinc, iron
and aluminum are respectively 5.4%, 9.3% and 21.2%. The oxide
powders are mixed in a mixer in the presence of acidified water.
After mixing for 30 minutes, at 25 rpm, the paste that is obtained
is extruded on a piston extruder with a shift of the piston of 10
mm/minute, through a die with a 3 mm diameter. The rods are finally
dried for one night at 80.degree. C. in the oven and calcined at
650.degree. C. for 2 hours in air. After this calcination stage,
the solid was analyzed by DRX and scanning electronic microscopy,
and it showed the presence of phases that are for the most part
zinc ferrite and alumina.
[0070] The solid has a specific surface area of 200 m.sup.2/g,
whereby the alumina greatly contributes to providing this
property.
[0071] The device and the quantity of solid used in this example
are similar in all respects to what is described in the Example
Nos. 2 and 4.
[0072] Under these conditions, it was shown that the piercing
(breakthrough) time is faster than in the case of zinc ferrite
alone and that the dynamic sulfur capacity of the adsorbent drops
to 1.5% by mass for a total capacity of 1.8% by mass. If the zinc
ferrite that is deposited on alumina is compared, it appears very
clearly that its sulfur capacity, either dynamic or with
saturation, is extremely reduced relative to the zinc ferrite
alone. The very large specific surface area offered by this
composite relative to the zinc ferrite alone (specific surface area
of the zinc ferrite/alumina/specific surface area of the zinc
ferrite alone>20) therefore does not make it possible to
compensate for the dilution effect of the zinc ferrite by
alumina.
[0073] The preceding examples can be repeated with similar success
by substituting the generically or specifically described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
[0074] The entire disclosures of all applications, patents and
publications, cited herein and of corresponding French application
Ser. No. 08/05.623, filed Oct. 10, 2008 are incorporated by
reference herein.
[0075] In claim 1, the term "consisting essentially of" is meant to
preclude additional components which would materially lower the
sulfur capacity of the bulk adsorbent and in particular is meant to
preclude the presence of binders as mentioned in WO 01/70393 by
Khare.
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