CA2297094A1 - Treatment of fluids - Google Patents

Abstract

Fluids are treated to remove undesirable chemical species such as sulphur by bringing the fluid into contact with an adsorbent (10) having a crystal structure, such as an SbSn intermetallic; neucleophilic polar heads (13) are attracted to defect sites (12) in the adsorbent surface.

Description

"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.

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.

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.

WO 99104898 PCTIIE98I0006t 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.

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;

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.

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 _g_ 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 _g_ 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%.

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 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 w~ 9y~~g8 PCTIlE98/00061 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.

- t3 -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.

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 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".

-l5-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 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 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 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.

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 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 WO 99/04898 PCTlIE98100061 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) 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.

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

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.

WO 99/04898 PGT/1~98/00061 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.

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.

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 __ .__._ . , _. ,. . .~..~ , ., . . . . .,... . .

treated to remove undesirable constituents. Also it is envisaged that contaminated waste water and sea water may be effectively treated.

Claims (39)

-29-

1. 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 undesirable chemical species of the fluid onto the filter.

2. A method as claimed in claim 1, wherein the filter comprises defect sites on the surface adjacent electron-deficient atoms.

3. A method as claimed in claims 1 or 2, wherein the filter comprises an intermetallic.

4. A method as claimed in claim 3, wherein the intermetallic metals are Sb and Sn.

5. A method as claimed in any preceding claim, wherein the fluid contains water.

6. A method as claimed in claim 5, wherein the fluid is a liquid and is an emulsion.

7. A method as claimed in claim 6, wherein one of the emulsion phases is an electrolyte.

8. A method as claimed in claim 7, wherein the emulsifying agent is a surfactant.

9. A method as claimed in claim 8, wherein the surfactant is of the type which acts to reverse micelles containing heterocyclic - containing groups so that these groups are orientated towards the outside.

10. A method as claimed in claim 9, wherein the surfactant is of the type in which the hydrophobic group is the long chain and the hydrophilic group is a carboxylate.

11. A method as claimed in any preceding claim, wherein a magnetic field is applied to the fluid as it is brought into contact with the filter.

12. A method as claimed in any preceding claim, wherein an electrical potential is applied to the filter.

13. A method as claimed in any preceding claim, wherein the method comprises the further steps of rejuvenating the filter by washing with a water solution.

14. A method as claimed in any preceding claim, wherein the fluid is a hydrocarbon oil feedstock.

15. A method as claimed in 14, wherein viscosity is reduced.

16. A method as claimed in claims 14 or 15, wherein turbidity is increased.

17. 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.

18. A method as claimed in claim 17, wherein the adsorbent is an intermetallic.

19. A method as claimed in claim 17, wherein the emulsifying agent is a surfactant.

20. A method as claimed in claim 19 wherein the surfactant is of a type which acts to reverse micelles so that adsorbate species face outwardly.

21. A method as claimed in claim 20 wherein the surfactant contains calcium.

22. A method as claimed in claims 20 or 21 wherein the surfactant contains sodium.

23. A method as claimed in any of claims 20 to 22 wherein the surfactant is of the type in which the hydrophobic group is the long chain and the hydrophilic group is a carboxylate.

24. A method as claimed in any of claims 17 to 23 wherein electrical energy is applied to the adsorbent and the emulsion.

25. A method as claimed in claim 24, wherein the energy is applied as a magnetic field around the adsorbent.

26. A method as claimed in claim 24 wherein the energy is applied as a direct voltage applied to the adsorbent.

27. A method as claimed in claim 26, wherein the applied voltage is in the range 0.8 V to 2.0 V.

28. 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.

29. A method as claimed in claim 28, wherein the adsorbent has a crystal structure.

30. A method as claimed in claim 29, wherein the adsorbent comprises defect sites on its surface adjacent electron-deficient atoms.

31. 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.

32. A method as claimed in claim 31, wherein the adsorbent comprises defect sites on its surface adjacent electron-deficient atoms.

33. A method as claimed in claim 32, wherein the adsorbent is an intermetallic.

34. A method as claimed in claim 33, wherein the adsorbent is an SbSn intetmetallic.

35. A fluid filter 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.

36. A filter as claimed in claim 35, wherein the adsorbent comprises defect sites on the surface at adjacent electron-deficient atoms.

37. A filter as claimed in claims 35 or 36, wherein the adsorbent is an intermetallic.

38. A filter as claimed in claim 37, wherein the intermetallic is an SbSn intermetallic.

39. A filter as claimed in any of claims 35 to 38, further comprising means for applying electrical energy to enhance adsorption.