Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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"Treatment of Fluids"
INTRODUCTION
Field of the Invention
The invention relates to treatment of fluids to remove undesirable
constituents, more
particularly chemical species.
Prior Art Discussion
Such fluid treatment arises to a large extent in the hydrocarbon fuel
processing
industry, for example, reduction of sulphur in an oil refinery. One approach
to such
treatment is generally referred to as a hydrotreating process in which the
feedstock is
subjected to high temperatures and pressures. This approach involves a large
energy
input and equipment is expensive.
A different approach is proposed in EP 254781 (Chevron) which involves
contacting
the feedstock with a sorbent having a metal such as sodium, potassium, barium
or
calcium. EP 332324 (ICI) proposes removal of hydrogen sulphide by passing the
feedstock through a zinc oxide-containing absorbent. The absorbent may be
regenerated using a water-containing gas stream. It appears that absorption as
a
treatment method suffers from the problems of being effective only for gaseous
feedstreams, and of allowing a limited feedstream throughput.
Therefore, the invention is directed towards achieving treatment of fluids in
a simpler
manner.
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According to the invention, there is provided a method of treating a fluid
having an
undesirable chemical species, the method comprising the step of bringing the
fluid
into contact with a filter having a surface crystal structure to facilitate
adsorption of
undesireable chemical species of the fluid onto the filter.
In one embodiment, the filter comprises defect sites on the surface adjacent
electron-
deficient atoms. This provides a very effective adsorption mechanism.
In one embodiment, the filter comprises an intermetallic, and the
intermetallic may
contain Sb and Sn.
In one embodiment, the fluid contains water.
In one embodiment, the fluid is a liquid and is an emulsion, and preferably
one of
the emulsion phases is an electrolyte.
Preferably the emulsifying agent is a surfactant.
In one embodiment, the surfactant the surfactant is of the type which acts to
reverse
micelles containing heterocyclic - containing groups so that these groups are
orientated towards the outside.
Preferably, the surfactant is of the type in which the hydrophobic group is
the long
chain and the hydrophilic group is a carboxylate.
In another embodiment, a magnetic field is applied to the fluid as it is
brought into
contact with the filter. In the latter embodiment, an electrical potential may
be
applied to the filter.
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In one embodiment, the method comprises the further steps of rejuvenating the
filter
by washing with a water solution.
In one embodiment, the fluid is a hydrocarbon oiI feedstock.
In one embodiment, viscosity is reduced.
In one embodiment, turbidity is increased.
The invention also provides a method of treating an emulsion in which one
phase is
an electrolyte, by bringing the emulsion into contact with an adsorbent having
a
surface crystal structure.
Preferably, the adsorbent is an intermetallic.
In one embodiment the emulsifying agent is a surfactant.
Preferably, the surfactant is of a type which acts to reverse micelles so that
adsorbate
species face outwardly.
Preferably, the surfactant contains calcium.
Preferably, the surfactant contains sodium.
In one embodiment, the surfactant is of the type in which the hydrophobic
group is
the long chain and the hydrophiiic group is a carboxylate.
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In one embodiment, electrical energy is applied to the adsorbent and the
emulsion.
The energy may be applied as a magnetic filed around the adsorbent. The energy
may be applied as a direct voltage applied to the adsorbent.
The applied voltage may be in the range 0.8 V to 2.0 V.
According to another aspect, the invention provides a method of treating a
liquid
comprising the steps of forming an emulsion in which one phase is an
electrolyte and
the emulsifying agent is a surfactant which acts to reverse micelles so that
heterocyclic-containing functions are oriented towards the outside, and
bringing the
emulsion into contact with an adsorbent.
Preferably the adsorbent has a crystal structure.
In one embodiment, the adsorbent comprises defect sites on its surface
adjacent
electron-deficient atoms.
The invention also provides a method of desulphurising a hydrocarbon
feedstream
comprising the steps of bringing the feedstream into contact with an adsorbent
having a surface crystal structure until sulphur species adsorb onto the
adsorbent
surface.
Preferably, the adsorbent comprises defect sites on its surface adjacent
electron-
deficient atoms.
In one embodiment, the adsorbent is an intermetallic.
In another embodiment, the adsorbent is an SbSn intermetallic.
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The invention also provides a fluid filter comprising having comprising having
an
adsorbent with surface crystal structure to facilitate adsorption of
undesireable
chemical species onto the filter when the fluid containing the adsorbate comes
into
contact with it.
In one embodiment, the absorbent comprises defect sites on the surface at
adjacent
electron-deficient atoms.
Preferably, the adsorbent is an intermetallic.
In another embodiment, the intermetallic is an SbSn intermetallic.
Preferably, the filter filter comprises means for applying electrical energy
to enhance
adsorption.
DETAILED DESCRIPTION OF THE INVENTION
Brief Description of the Drawinss
The invention will be more clearly understood from the following description
of
some embodiments thereof, given by way of example only with reference to the
accompanying drawings, in which:
Fig. 1 is a diagram showing reversal of an asphaltene micelle in an adsorbate
fluid;
Fig. 2 is a diagram illustrating sulphur adsorption;
Fig. 3 shows scanning electron micrographs of SbSn filter samples sintered in
100% hydrogen atmospheres;
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Fig. 4 is an X-ray diffraction pattern of sintered SbSn powder;
Fig. 5 is an optical micrograph of the surface of SbSn filters;
Figs. 6 and 7 are cyclic voltammogram plots indicating reactions of a fluid
with a filter;
Fig. 8 is a diagram showing an experimental set-up for treatment of
hydrocarbon liquids; and
Figs. 9, 10, and 11 are plots indicating adsorption of inorganic Sulphur on an
intermetallic filter.
petailed Description of the Invention
The invention provides filtration of fluids by adsorption of undesirable
species of
fluids onto a filter surface.
The filtration medium material has a well defined crystalline structure with
surface
cavities and defects generally in the nano-scale, 2nm to 100nm.
It has been found that, to be effectively treated, the fluid preferably has
the following
properties:-
(a) if a liquid, it is preferably an emulsion in which one phase is an
electrolyte such as water containing small quantities of ionic salts for
ionic conduction, or
(b) if a gas, it preferably contains moisture.
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For an emulsion, the emulsifying agents are preferably surfactants which form
layers
containing vesicles and micelles. The general types of surfactant found to be
suitable
are anionic, ionic and Zwitterionic surfactants.
Preferably, in the surfactant the hydrophobic group is the long chain (e.g.
fatty acid)
and the hydrophilic group is a carboxylate . Na and Ca are preferably present
as
salts. Such surfactants are naturally-occurring in petroleum resin and
asphaltene
fractions.
Such surfactants act' to reverse micelles containing undesirable species. An
example
is given in Fig. 1 in which the asphaltene in native petroleum is reversed.
The
micelle reversal arises by membrane mimetic chemistry action in which the
heterocyclic containing functions (S,N,O) are orientated towards the outside
from
the micelles. Consequently, chemical reactions such as destructive adsorption
are
facilitated.
Where the fluid is a gas, it must contain moisture and the molecules
preferably have
low molecular weights, below 200. An example is natural gas in which the
Sulphur
species may be HzS, RiS, or RSH. All of these have low molecular weights and
are
volatile, and may therefore undergo surface adsorption.
For filtration, a liquid feedstock containing adsorbate species is brought
into contact
with the filter. An electrical potential arises in the fluid causing
electrokinetic (or
"zeta") potential. Alternatively a potential may be caused by an externally-
induced
electrical field. This potential, in an environment in which the micelles are
reversed
by the surfactants, causes the polar adsorbtate species to interact with the
filter
surface. This action is a type of destructive adsorption in which bonds with
the fluid
are broken, for example an S-C bond. The nucleophilic atoms attack electron
deficient cavities in the filter. In the case of asphaltenes, adsorbent
destruction cracks
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the asphaltene into resins or aromatics. The diagram of Fig. 2 gives an
illustrative
example.
Referring to Fig. 2, the SbSn intermetallic structure is identified as 10. The
Sb atoms
form the electron deficient cavities 12 in the filter surface, and these
attract
nucleophilic polar sulphur heads 13 . By this action, the long chain tail part
14 of the
fluid molecule is broken by vibrational and rotational forces, and thus
elemental
sulphur is removed from the liquid.
The following sets out one example of how an SbSn filter is produced. Words
which
are used in headings of subsequent parts of the description are underlined.
Initially, there is melt vrevaration in which an equiatomic composition of tin
and
antimony is melted in a graphite crucible using an induction heater. True
atomic
intermixing occurs in the molten state. The melt is held for 10 minutes at
500°C
with a hydrogen gas cover to avoid oxidation.
The melt is bottom poured into an atomisation nozzle operated with high
pressure
nitrogen at a plenum pressure of 2.5 MPa for gas atomisation. Nitrogen escapes
through an annular gap surrounding the melt stream, causing formation of
droplets.
The adiabatic expansion of the gas rapidly cools the droplets and accelerates
them
away from the melt source. During the subsequent flight, the droplets freeze
into
SbSn intermetallic crystalline particles with an average size of 10~m. The
particles
are collected in a container containing nitrogen gas.
These particles may be directly used because the microscopic size of the
particles
provides a high surface area for contact with the fuel. For example, the
particles may
be loose packed in a column. The particles may also be used when bonded to a
substrate. Further, it is envisaged that a substrate having a porous structure
may be
used onto which the composition is coated, instead of providing an integral
porous
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structure. In this case, a ceramic or metallic substrate may be used, and the
composition may be coated by chemical or physical vapour deposition
techniques, of
by plasma spray coating.
Alternatively, the powder may be used as follows to produce a porous structure
through which fuel passes for surface contact.
The powder is loose packed into a machined graphite mould to form a disc with
the
addition of approximately 2% by weight stearic acid as a pore former. The
graphite
is heated in a hydrogen ~jnt~_tering atmosphere to bond the particles at
370°C for 30
minutes.
By sintering in this manner, a porous filter having an optimal balance between
bonding and porosity is formed.
The filter thus produced has the following properties:-
Porosity: 40-50%
Permeability: 10-"mz
Pore size: 251xm
'The following description sets out alternative ways of implementing steps of
the
process.
Melt Preparation
The materials used could in addition include other metals such as platinum,
gold or
palladium. The formulation need not be equiatomic. The end-product
intermetallic
preferably has a tin atomic percentage in the range of 39.5 to 57%.
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The melt may be at any temperature at which it does not absorb and/or react
with
oxygen.
It is envisaged that the materials need not necessarily be melted. For
example,
separate powders could be mechanically alloyed with sufficient energy such
that the
metals physically combine into a single powder.
Gas Atomisation
The gas atomisation pressure is dependent on the desired particle size, while
being
sufficient to provide the necessary high cooling rate. It is estimated that
this is at
least 10' °C/s.
For example, a lower pressure of 0.7 MPa may be used, providing a larger
particle
size of 20 Vim.
The atomisation gas may alternatively be hydrogen, argon, helium or any other
inert
gas or any mixture of such gases.
Sintering Atmosphere
It is not essential that a hydrogen atmosphere be used. Due to the problems
associated with using a lower temperature hydrogen furnace, sintering
behaviour has
been studied in nitrogen and nitrogen-hydrogen atmospheres. It was found that
sintering of filters in either complete nitrogen or a combination of hydrogen
and
nitrogen atmospheres resulted in a black coating on the surface. This was due
to the
deposition of carbon on the surface of the filter. Stearic acid is a
hydrocarbon
consisting of several C-H bonds and was used as a pore-forming additive. Bum
out
of stearic acid is facilitated by the breaking of carbon-hydrogen and the
formation of
simple gases using a reducing atmosphere. Hydrogen is a reducing atmosphere
and
helps in the burnout of stearic acid as well as in the sintering of the
powders. The use
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of a nitrogen atmosphere does not cause these two processes because of its non-
reducing behaviour.
The carbon deposition on the surface also hampered the sinterability of the
powders.
The samples sintered using the hydrogen/nitrogen combination were black on the
surface and were very fragile. The carbon coating was found only on the
surface and
not on the other sides of the filter. The discoloration may also be due to
carbon
deposition.
An interesting phenomenon noticed was that carbon deposition was prevented
when
the powder samples were covered by a graphite plate over the mould. Also, the
powders covered by the graphite plate and sintered in a nitrogen atmosphere
showed
the same sintering behaviour as the powders sintered in hydrogen atmospheres.
The
covering plate (which was made of graphite) would have caused the formation of
carbon monoxide which is a reducing atmosphere. It is envisaged that a plate
other
than graphite could be used, provided some part of the mould is carbon when
using a
nitrogen atmosphere.
Figure 3 shows fractographs of samples sintered in full hydrogen and full
nitrogen
atmospheres. They have a similar pore structure. The permeability, density and
shrinkage of the filters sintered in 100% nitrogen and 100% hydrogen
atmosphere are
shown in Table 1.
Table 1
Atmosphere Permeability Density % Shrinkage % Shrinkage % Mass Loss
(m=) (%) in ht. in dia.
100% HZ 1x10'" 58 20 11 3.3
100% NZ 7x10'~Z 61 17 9.5 3.1
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The X-ray diffraction patterns of the samples also show that the filters
sintered using
the nitrogen and hydrogen atmosphere form the same intermetallic phase SbSn
(refer
to Fig. 4).
In conclusion, powders mixed with 2 wt. % stearic acid showed the maximum
permeability and pore size. The powders can be sintered in both I00% hydrogen
as
well as 100% nitrogen atmospheres, but for sintering in 100% nitrogen, the
samples
are covered at the top by a graphite boat to provide a reducing atmosphere.
The
samples sintered in 100% nitrogen atmosphere also formed the same
intermetallic
SbSn phase.
Sintering may be carned out by heating graphite to 370°C in a
graphite boat
arrangement. In this case, oxygen reacts with the graphite to form CO gas,
further
oxidation reactions leading to formation of COZ . Both reactions remove oxygen
or
oxides from the sintering environment. There is a continual consumption of
graphite
as it is transformed into a vapour over time.
Any suitable reducing atmosphere could be used. Examples are use of methane,
CO,
HZ, N~- HZ mixes, NH3, and dissociated ammonia. Suitable combinations of the
above gases could be used by endothermic or exothermic burning processes. In
particular, the use of HZ-N~ is aaractive because at low HZ levels of a few
percent, the
atmosphere is non-explosive, yet still reducing.
Additional Step - Sintering Additives
The process may have the additional step of adding an additive to the
intermetallic
powder to dilate the pores during sintering to provide a larger catalyst
surface area.
This is briefly referred to above and is described in more detail in this
section.
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In one example, stearic acid was chosen as a binder to be added to the powder
to
increase the permeability. The stearic acid used was Industrene 5016
manufactured
by Witco. The reason for choosing stearic acid was that it completely burns
out
before reaching the sintering temperature of 370°C. Stearic acid and
the powder
were mixed in a grinder to form a uniform blend of the powder and the binder.
The
total time of grinding was approximately 2 minutes. The grinding was done in
short
time intervals of 20 seconds so as to prevent melting of stearic acid caused
by heat
generated in the grinder.
The sintering experiments were carried out in a retort in both nitrogen and
hydrogen
atmospheres. The permeability experiments were conducted using permeability
measuring equipment using air as the flow medium and mercury as the reference
liquid in a column. The Archimedes method was used to measure the final
density.
Table 2 below compares the % density and permeability of filters sintered by
mixing
powders with different weight percentages of stearic acid at 370°C in
HZ atmosphere.
Table 2
Wt. % binder Permeability (mz) Pore diameter (pm) Density (%)
0 5x10''3 20 61
0.5 9x10''z 37 65
1 9x10''z 35 65
1.5 7x10''z 50 62
2 2x10'" 53 58
In Table 2, all of the measurements were made for powders sintered in a cavity
made
of graphite boat, 19 mm in diameter and 4.3 mm in height and were not of the
size of
the actual filter.
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The powder mixed with 2 wt.% stearic acid gave a maximum permeability of 2x10-
"
m~ and was approximately 50 times more permeable than the powders mixed with
1.5 and 1 wt.% binder showed an increase in density while the powders mixed
with
1.5 and 2 wt.% showed a decxease in density. Powders mixed with stearic acid
showed better sintering behaviour than the powders that were not mixed with
binders. The initial increase in density could be attributed to this
behaviour. The
decrease in density for powders mixed with more than 1 wt.% was due to the
excessive pores created by the burnout of stearic acid. The powder mixed with
2
wt.% stearic acid and sintered had a maximum pore size of 52 pm and the
highest
porosity. Figure 5 shows optical micrographs of the surface of filters
sintered from
powders with 0 and 2 wt.% stearic acid.
In general, any suitable agent which occupies space during heating but burns
our
1 S during sintering may be used. Clean burnout at relatively low temperatures
is
desired. Stearic acid in powder form has been found to be suitable at a
particle size
of 100pm or less. The powder may be added upon vibration of the intermetallic
powder to allow a lower packing density, giving a dilated structure with a
higher
permeability after sintering.
Any suitable pore forming agent which has these general properties could be
used,
for example, ammonium carbonate, camphor, naphtha, ice, monostearates, and
also
low molecular weight waxes and organic gels. It is also envisaged that a pore
forming agent which acts to provide a reducing atmosphere could be used, for
example paraffin wax, which forms methane on burnout.
It is also envisaged that the filter could be formed from one or a number of
layers so
that the desired properties are obtained using the layers as "standard parts".
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The filter could have physical properties which are different from those
outlined
above. The following are desirable parameter value ranges:-
Porosity: 30 to 50%
Permeability: 1 to 400 x 10'"mZ
Pore size: 2 to 300 lcm
The above is a description of one method of producing an SbSn intermetallic.
However, such an intelmetallic may be produced by alternative techniques such
as
by physical vapour deposition. This depends on the structure of the filter,
which in
tum depends on the particular operating conditions and type of feedstream
being
treated.
It has been found that an SbSn intelmetallic is particularly effective. It is
expected
that other materials having similar crystal structures would also be
effective. For
example, CuZn and CuZr have close lattice parameter matches and an identical
Pearson space group.
Operation of Filter
Irrespective of the physical arrangement of the filter, it is used to treat a
fluid by
bringing the fluid into contact with it, causing undesirable chemical species
to be
adsorbed onto its surface. The filter acts as an adsorbent, the fluid species
which is
removed being the adsorbate.
The adsorption depends on the nature of the fluid being treated and on the
filtration
process employed. Many different fluids may be treated, including many
polymeric
and hydrocarbon fluids.
The filtration may be enhanced by use of a magnetic field in the fluid.
Alternatively,
or in addition, an electrical potential may be applied to the filter itself.
Such electrical
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and /or magnetic fields provide an attraction gradient towards the filter.
Such a field
may also allow selectivity of the species adsorbed.
The filtration action provides beneficial effects for some fluids in addition
to removal
of undesirable species. One such effect is reduction of viscosity of fluids
such as non-
Newtonian fluids including crude oil or condensate. Another such effect is
very
quick destabilisation of an emulsion by virtue of a reaction with surfactants.
This
action is particularly effective if the emulsifying agents are surfactants
including Na
and/or Ca ions. If water is to be introduced to the fluid to improve the
filtration
effect, the artificial surfactants should include Na and/or Ca ions. A further
effect is
an increase in turbidity.
When the filter ceases to be effective, a clean filter is substituted and the
original is
cleaned. Cleaning involves application of an electric field to the filter,
possibly with
a wash using a strongly alkaline cleaning fluid. However, in some instances
the filter
may be cleaned with a wash only.
Regarding the SbSn intermetallic filter, in more detail, cycfic voltammagram
tests
carried out with electrodes of tin only, antimony only, and the intermetallic
(INI)
indicate that the intermetallic action is not simply a sum of the actions of
tin and
antimony separately. Also, these tests demonstrate that more than one reaction
occurs as the voltage is varied. This indicates that if a voltage is applied,
filtration
may be tuned for selectivity.
Referring to Fig. 6, cyclic voltammogram plots are shown for an infiltrated
intermetallic filter in an equal crude oil/water mixture. The scan rate was
lOmV/s,
although this parameter is of little importance because response was found to
be
independent of the scan rate. As is clear from these plots, there are peaks at
c. -1.2 to
-1.3 V. This indicates that a specific reaction occurs involving adsorption of
a species
onto the filter at a particular voltage bias. It also indicates that the
process is not
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reversible because of lack of activity for forward bias. A subsequent set of
tests
carried out with the water portion of the above mixture revealed the plots
shown in
Fig. 7. There are again reaction peaks at c. -1.2 to -1.3 V, but also two
other less
pronounced reaction peaks, including one at a forward bias. This confirms that
the
reaction is irreversible and therefore a solvent wash would be required for
filter
cleaning. They also indicate that presence of water is important, and that the
active
adsorbates are preferably water soluble such as inorganic salts. These latter
conclusions were borne out by further tests with the oil portion alone which
resulted
in lower significant reactions.
The following examples illustrate the filtration method. Tests were carried
out to
analyse effectiveness of the filter in various adsorbate fluids. The tests
were also
carried out with a filter of another material - stainless steel.
Tests With Fnel Oils
The invention finds particular application in treatment of combustible fuels
such as
oil and natural gas because of the major impact these fuels have on the
environment.
In such fluids on undesirable constituent is Sulphur, which is usually present
in the
range of 100 to 1000 ppm. Sulphur not only pollutes the atmosphere itself, but
it also
poisons conventional catalysts for cleaning exhaust gases. Sulphur also
damages
engine parts such as turbine blades - causing major design and maintenance
problems in the avionics field for example. Sulphur takes different forms, for
example, thiophene, benzothiophene or dibenzothiophene.
In the existing art, hydrotreating processes are used for removal of Sulphur
and these
are effective for reduction to below 50 ppm. These processes are based on high
pressure and temperature treatment with hydrogen to remove HZS. The collected
streams of H2S at the refinery are then further treated to remove and recover
elemental Sulphur. However, these processes involve not only very expensive
and
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complex plant and control methods, but also a high energy input - again
adversely
affecting the environment. These processes also reduce some of the unsaturated
organic compounds present, consuming more Hydrogen than needed to treat the
Sulphur.
Various tests have been carried out which indicate the beneficial effect of
oil filtration
according to the invention.
Tests involved pumping the oiI in a dynamic rig through a housing containing
SbSn
intermetallic, providing a contact time of 1 to 5 seconds. Other tests were
static - the
filter being introduced into the oil in powder form.
For cxude oil, an effect is de-emulsification by removal of natural
surfactants. This
effect depends on the stability of the emulsion and/or the total energy input
into the
emulsion. The following improvements were observed:-
(i) Substantially high levels of inorganic sulphide species were removed
from the water phase.
(ii) The pH value in the water considerably improved.
(iii) SARA analyses demonstrated decreases in asphaltene and resin
content, and increases in aromatic content.
(iv) In the oil phase, the viscosity was greatly reduced.
It was found that if a magnetic field was applied to the liquid emulsion,
separation
was delayed. In this case, high levels of organic S were removed and
selectivity of
the adsorbed species was achieved by adjusting the magnetic field. A similar
effect
was observed if an electrical potential was applied to the filter.
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Referring to Fig. 8 an experimental apparatus 10 is illustrated. The apparatus
comprises a feed flask 11 from which the feedstock is drawn by a pump 12
through a
powder bed 13 containing SbSn intermetallic. Valves 14 allow direction of the
feedstock either (a) in a single-pass flow to a sampling bottle 15 or (b) in a
re-cycling
flow. A power supply I6 feeding a coil 17 provide an induced magnetic field in
the
powder bed 13, when activated.
Tests were carried out with a crude oil having a sulphur concentration as set
out in
Table 3 below, as determined by GC spectra.
Table 3~
Sulphur Species Isomer
Peak Relative
Ht. Conc.(%)
Thiophene 14.4 0.0063 0.0063
C 1 Thiophene 11.0 0.0048 0.0048
C2 Thiophene Isomer -1 18.5 0.0080
Isomer -2 22.5 0.0098 0.0238
Isomer - 3 13.7 0.0060
Benzvthiophene 20.0 0.0087 0.0087
C1 Benzothiophene Isomer-1 23.8 0.0103
Isomer - 2 28.8 0.0125
Isomer - 3 34.6 0.0150 0.0864
Isomer - 4 56.7 0.0246
Isomer - S 55.0 0.0239
C2 Benxothiophene Isomer -1 33.5 0.0146
Isomer - Z 142.0 0.0617
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Isomer - 3 91.0 0.0395
Isomer - 4 74.0 0.0322 0.2043
Isomer - 5 68.8 0.0299
Isomer - 6 60.8 0.0264
Dibenzothiophene 66.1 0.0287 0.0287
C 1 DibenzothiopheneIsomer -I 79.9 0.0343
Isomer - 2 93.2 0.0405 0.1136
Isomer - 3 89.2 0.0388
C2 DibenzothiopheneIsomer -1 98.0 0.0426
Isomer - 2 96.0 0.0417
Isomer - 3 105.6 0.0459
Isomer - 4 104.9 0.0456 0.2673
Isomer - 5 107.5 0.0467
Isomer - 6 103.0 0.0448
C3 DibenzothiopheneIsomer -1 107.5 0.0467
Isomer - 2 103.0 0.0448
Isomer - 3 102.5 0.0445
Isomer - 4 95.2 0.0414 0.2410
Isomer - 5 87.5 0.0380
Isomer - 6 58.8 0.0256
Benzonaphathathiophene 35.0 0.0152 0.0152
In a fast stage, the crude oil was pumped in the recycling circuit for 30
minutes. The
sample size was 600m1 and it had a ratio of 3 parts oil to 2 parts water by
volume.
'The flow rate was 20 - 25 mI/min. the quantity of SnSb intermetallic powder
was
40% of the weight of the sample feedstock.
In a second stage a voltage of 1.2 V was applied to create a magnetic field
and the
emulsified effluent from the first stage (about 300m1) was pumped through the
powder bed (adjusted to remain at 40% of sample weight) in a single pass to
the
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sampling bottle 15. The voltage level should be in the range 0.8 V to 2.0 V
and is
preferably approximately I.2 V.
For sampling after bath stages, the effluent was allowed to de-emulsify and
the
samples were analysed by the modified Eschka method (ASTM 3177-89) for total
sulphur determination and by the Thin Layer Chromatography ('TLC) Method for
SARA analysis.
The following are the results for removal of total sulphur.
Tabl
Sulphur ContentRemoval EfficiencyTotal Removal
(%) - (%) EfflClenCy (%)
Original 3.06
Sample
First Stage 1.70 44.4
Second Stage0.99 41.8 (Relative67.6
to
first stage)
Table S below sets out the SARA analysis.
Table 5
Saturates Aromatics Resins % Asphaltenes
% %
Original 33.0 41.1 7.7 18.2
Sample
First Stage 31.3/-5.2a47.0/+14.4 6.7/-13.0 15.0/-17.6
Second Stage30.3/-3.2b43.0/-8.5 7.2/+7.5 19.5/+30.0
(-8.2)c (+4.6) (-6.5) (+7.1)
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Notes:-
(a) Figures to left of / are % of original and to the right are the % change.
(b) Figures to left of / are % of sample relative to the first stage, and to
right are
the % change.
(c) The figures in parentheses are total % change relative to the original
sample.
These results demonstrate that the composition of the crude oil has been
changed by
the intermetallic. Regarding the SARA composition, the objective is to
increase
saturates and aromatics and to reduce resins and asphaltenes. This benefits
downstream processing in the refinery. The results indicate that if the
sequence is
changed to incorporate an applied voltage initially and then subsequently
repeating
without a voltage, the resin and asphaltenes would be significantly reduced.
Regarding elemental sulphur. Eleven organo species were identified.
Desulphurisation by the filter, with and without an applied voltage occurred
uniformly across the species. The level reached 67.6%. It is anticipated that
by
incorporating multiple filter units and by increasing surface area of the
intermetallic,
levels of sulphur reduction will exceed those achieved in these experiments.
The following test were also carried out with the crude oil of Table 3, as
follows:
A Continuous flow with a flowrate of 20 - 25 ml/min in a recycling
circuit and without applied voltage, as for the first stage above.
B Continuous flow with a flowrate of 20 - 25 ml/min without recycling
and with an applied voltage. This is similar to the second stage above,
except the sample is fresh and not the effluent from test A.
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A SARA analysis demonstrated:
(i) For test-type A,
- asphaltene content reduced by 27%, resin content reduced by 30%,
aromatics content increased by 40% and saturates content decreased
slightly.
(ii) For test type B,
- asphaltene content increased by 18%, resin content increased by 8%,
aromatics content decreased by 20% and saturates content increased by
6%.
Other tests were carried out using the apparatus 10 and the crude oil as set
out in
Table 3. The total S content of emulsified samples before and afrer reactions
were
1 S measured in the oil phase, which was separated from the re-emulsified
samples by a
modified Eschka method, and in the water phase by the Titrimetric Method and
the
Turbidimetric Method.
These methods were also used for analysis of the separate phases after
treatment.
The following are the results.
Table 6
Water Phase
Sulphate Sul 'de
InitialFinal % Initial Final
ContentContentReductionContent ContentReduction
(PPm) (PPm) (PPm) (PPm)
Test Type 2800 2800 0% 248 96 61
A
Test Type 2800 2800 0% ~ 248 ~ 104 ( 58.1%
B
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Qil Phase
Total Initial Total Final % Reduction
Sulphur Content Sulphur Content
(%) (%)
Test Type A 3.12 1.55 50.3
Test Type B 3.12 1.39 55.4
Tests With Model Solutions
Tests were carried out using an Sb/Sn intermetallic filter as a powder in 40
ml
distilled water having a fixed concentration of sodium sulphide (NazS) of 348
mg-
S/1. Adsorption was measured for different concentrations of intermetallic and
a
fixed contact time of 30 hrs. To avoid interference from dissolved oxygen, the
distilled water was stripped for 3 hrs. There was a controlled pH of 3 ~ 0.5.
The
result is shown in Fig. 9, from which it will be seen that the inorganic
Sulphur
concentration decreased by about 11% for 5g of intermetallic.
Tests were then carried out with different initial Na2S concentrations, a
fixed contact
time of 30 hours, a fixed amount of intermetallic (15% w/w), and a controlled
pH of
3 t 0.5. The deionised water was again stripped for 3 hours. The results are
shown
in Figs. 10 and 11. Fig. 10 indicates that with increasing concentration of
sulphide,
the adsorption capacity of the intermetallic increases. Fig. 11 indicates that
the
adsorption behaviour of inorganic sulphide can be described well by using the
Freundtich equation.
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Further tests carried out both with and without HCl in solution indicated a
higher
Sulphur adsorption efficiency with HCI. This indicates that there may be
selective
adsorption of Na prior to S, and that there is much better adsorption in an
acidic
solution (pH = 3.0).
In another test the fluid was dibenzothiophene emulsified with distilled water
(40%
by vol.) by addition of surfactant (Span 20). The results were as follows:-
Table 8
Initial Sulphur Final Sulphur % Reduction
Content (mg/1) Content (mg/1)
Test Type A 978 872 I0.8
Test Type B 1778 1253 29.5
These results are very significant because dibenzothiophene is particularly
difficult to
remove.
Tests with partly refined feels.
Tests were also carried out with partly-refined oil, naphtha, in which the
predominant S-containing compounds were substituted thiophenes,
benzothiophenes, and a small fraction of dibenzothiophenes. The tests were
dynamic - the oil being pumped through a housing containing polymer Raschig
rings
coated with Sb/Sn intermetallic.
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It.was found that the presence of water was necessary to obtain significant
Sulphur
reduction with optimum results being obtained when the full naphtha was
emulsified
with water and then filtered. Water washing prior to treatment gave reductions
between 10% and 30%. Emulsification of the full naphtha with water using an
added
surfactant gave an improved performance. Tests have demonstrated a reduction
from 1700 ppm to 700 ppm Sulphur.
Tests with diesel fuel have shown a reduction in the Sulphur levels by 40%
without
water treatment. Gasoline has shown significant improvements when treated
without water treatment.
These tests indicate that a possible strategy for filtration is in several
stages, first to
treat the crude on arrival at a refinery, intermediate treatment during the
refining
I 5 process (naphtha), and finally a last stage treatment of the final
product.
It is lrnown that the organic Sulphur species in lighter petroleum (gasoline,
diesel and
naphtha) are different from those in heavy petroleum (high Sulphur containing
crude
oil and heavy oil). The lighter petroleum contains mostly polar and
polarizable
Sulphur compounds such as mercaptans and hydrogen sulphide, but heavy oils
contain poiarizable Sulphur compounds such as dibenzothiophenes. There is more
effective removal of polar or polarizable sulphide compounds from petroleum
products than from crude petroleum.
It has been observed in the naphtha tests that the presence of water was in
many
instances essential for the intermetallic to effectively either remove the
natural or
artificial surfactants and completely separate the two liquids from an
emulsified state
or efficiently remove Sulphur species, other than in crude oil.
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Further it has been shown that the water portion of natural emulsions is an
active
component in the reaction. Furthermore, these reactions appear to occur at
specific
voltages and current densities. By replicating these conditions it has been
shown that
by fine tuning the voltage, specific elements can be removed from the crude
oil
without affecting the emulsified state of the liquid.
R~'nvenation of Filter
For commercial application of the invention, it is important that the filter
can be
cleaned repeatedly for re-use. A filtration system would comprise a control
system
which moves filters out of the flow conduit, cleans the filters and
subsequently moves
them back into the flow conduit.
It has been found that the surface of the filter is cleaned by immersion in a
cleaning
liquid and application of a voltage. In one example, cyclic voltammogramms
were
carried out with a scan range of -1.5 V vs. SCE to 1.5 V vs. SCE. The cleaning
liquids were water, Alconox detergent, and again water. It was observed that
current
levels returned to the same range as for the initial water test, indicating
that the
detergent was removing significant quantities of Sulphur. An XPS analysis of
one
filter demonstrated a reduction of 6 atomic % S to approximately zero.
Filtration of Other Flnids
The filtration method of the invention may be used with other fluids. For
example
gases such as natural gas, combustion products or contaminated gases may be
treated.
In one example, it is envisaged that blood may be treated, in which case
undesirable
polar molecules may be removed. More generally, food or medical products may
be
__ .__._ . , _. ,. . .~..~ , ., . . . . .,... . .
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treated to remove undesirable constituents. Also it is envisaged that
contaminated
waste water and sea water may be effectively treated.
