METHOD AND COMPOSITION FOR H2S SCAVENGING COMPRISING AN IMINE

Technical Field of the Invention The invention relates to a method of scavenging hydrogen sulfide from a liquid, such as from a hydrocarbon liquid. The invention also relates to a composition comprising a liquid, such as a hydrocarbon liquid, and an imine compound.

Background to the Invention

It is commonly known that many liquids, such as hydrocarbon liquids, typically contain hydrogen sulfide and other sulfur based species that can liberate hydrogen sulfide (i.e. hydrogen sulfide precursors). For example, hydrocarbon liquids such as crude oil, petroleum liquids and refinery liquids may contain hydrogen sulfide and other sulfide species that can liberate hydrogen sulfide. Hydrogen sulfide is toxic and corrosive and so it is desirable to scavenge it from liquids containing hydrogen sulfide.

Various methods of scavenging hydrogen sulfide (and optionally other sulfur based species when present) from liquids such as hydrocarbon liquids containing hydrogen sulfide are known. One of the most common methods is to use hydrogen sulfide scavengers, which react with hydrogen sulfide and remove it or reduce its amount, in the liquid.

For example, hydrogen sulfide scavengers may be used at various stages of crude oil production and/or processing operations. In this case, the hydrogen sulfide scavenger may be added to the crude oil whilst downhole, during production, during above ground processing, during transportation or storage, i.e. at any point prior to entering the refinery for processing. Hydrogen sulfide scavengers may also be used at the refinery for example, on receipt of the oil, during storage, during the refining process or to treat finished products or waste streams. Thus, it is well known to use hydrogen sulfide scavengers to scavenge hydrogen sulfide from hydrocarbon liquids. Examples of commonly used organic hydrogen sulfide scavengers include non amine scavengers such as aldehydes and protected aldehydes like acetals, and nitrogen based scavengers such as amines, triazines and imine compounds. US 5169411 discloses the use of certain hindered monoimines as hydrogen sulfide scavengers in the sulfur containing complex media of crude oils, petroleum residues and fuels.

Whilst hydrogen sulfide scavengers are known, it would be desirable to provide further hydrogen sulfide scavengers, for example which are more effective at removing or reducing amounts of hydrogen sulfide in hydrocarbon liquids than current hydrogen sulfide scavengers. In particular it would be desirable to provide imine based hydrogen sulfide scavengers which react more quickly than known scavengers and/or can consistently achieve low levels of hydrogen sulfide at low treat rates.

Summary of the Invention

According to a first aspect of the present invention, there is provided a method of scavenging hydrogen sulfide from a liquid, the method comprising adding to the liquid an imine compound represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group.

According to a second aspect of the present invention, there is provided a method of scavenging hydrogen sulfide from a hydrocarbon liquid, the method comprising adding to the hydrocarbon liquid an imine compound represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group.

According to a third aspect of the present invention, there is provided a composition comprising a liquid and an imine compound represented by the formula R ¹ -C(CH ₃ ) ₂ -N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group.

According to a fourth aspect of the present invention, there is provided a composition comprising a hydrocarbon liquid and an imine compound represented by the formula R ¹ - C(CH ₃ ) ₂ -N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group.

According to a fifth aspect of the present invention, there is provided the use of an imine compound represented by the formula R ¹ -C(CH ₃ ) ₂ -N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group, to scavenge hydrogen sulfide from a liquid.

According to a sixth aspect of the present invention, there is provided the use of an imine compound represented by the formula R ¹ -C(CH ₃ ) ₂ -N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group, to scavenge hydrogen sulfide from a hydrocarbon liquid.

According to a seventh aspect of the present invention, there is provided a liquid product obtainable by (or obtained by) a method according to the first aspect of the present invention.

According to an eighth aspect of the present invention, there is provided a hydrocarbon liquid product obtainable by (or obtained by) a method according to the second aspect of the present invention. Detailed Description of the Invention

Unless otherwise stated, the following terms used in the specification and claims have the meanings set out below.

As used herein, the term“liquid” means a liquid at the conditions when the imine compound is added. In many cases the liquid may also be a liquid at ambient temperature (typically 20 to 25°C) and pressure (about 100 kPa), but this is not essential. In some cases, the imine may be added to a liquid at an elevated temperature and/or pressure, for example when adding the imine compound downhole, the temperature may be over 170°C.

As used herein, the term “hydrocarbon liquid” means any liquid which is substantially hydrocarbon in nature, i.e. which contains predominantly carbon and hydrogen, for example less than 20 wt% of other atoms such as sulfur.

For example, the liquid or hydrocarbon liquid is a liquid that contains hydrogen sulfide (and optionally other sulfur containing species such as hydrogen sulfide precursors), i.e. wherein it is desirable to remove or reduce the amount of hydrogen sulfide therein. As used herein, the term“crude oil” means unrefined oil. Crude oil is typically composed of a complex mixture of organic (predominantly hydrocarbon) and inorganic compounds.

As used herein, the term“scavenging” means removing or lowering the amount of hydrogen sulfide present in a liquid.

As used herein, the term“alkyl” includes both straight and branched chain alkyl groups. The term “alkyl” does not include aryl groups. References to individual alkyl groups such as “propyl” are specific for the straight chain version only and references to individual branched chain alkyl groups such as“isopropyl” are specific for the branched chain version only. For example,“(1-5C)alkyl” includes (1-2C)alkyl, propyl, isopropyl and tert-butyl.

Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components. The term“consisting essentially of” or“consists essentially of means including the components specified but excluding other components except for components added for a purpose other than achieving the technical effect of the invention. The term“consisting of or“consists of means including the components specified but excluding other components. Whenever appropriate, depending upon the context, the use of the term “comprises” or “comprising” may also be taken to include the meaning“consists essentially of or“consisting essentially of, and may also be taken to include the meaning“consists of or“consisting of.

The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each exemplary embodiment of the invention, as set out herein are also applicable to any other aspects or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each aspect or embodiment of the invention as interchangeable and combinable between different aspects of the invention.

Method

In a first aspect, the present invention provides a method of scavenging hydrogen sulfide from a liquid, the method comprising adding to the liquid an imine compound represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group.

The liquid may be a hydrocarbon liquid. Thus, in a second aspect, the present invention provides a method of scavenging hydrogen sulfide from a hydrocarbon liquid, the method comprising adding to the hydrocarbon liquid an imine compound represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ , wherein R ¹ represents a (1-5C)alkyl group.

In the method of the first aspect, the liquid (prior to addition of the imine compound) may, for example, contain up to 5000 mg of hydrogen sulfide per L (litre) of the liquid, for example up to 1000 mg of hydrogen sulfide per L (litre) of the liquid, or for example up to 500 mg/L. In some embodiments, the liquid may contain up to 200 mg, or up 150 mg, of hydrogen sulfide per L of liquid. For example, the liquid may contain 0.1 to 150 mg, such as 0.5 to 100 mg, of hydrogen sulfide per L of liquid. In some aspects, the liquid may contain 10 to 50 mg of hydrogen sulfide per L of liquid. In other aspects, the liquid may contain 0.1 to 10 mg of hydrogen sulfide per L of liquid. Such amounts refer to the amount of hydrogen sulfide present in the liquid in the liquid phase.

In the method of the second aspect, the hydrocarbon liquid (prior to addition of the imine compound) may, for example, contain up to 5000 mg of hydrogen sulfide per L (litre) of the hydrocarbon liquid, for example up to 1000 mg of hydrogen sulfide per L (litre) of the hydrocarbon liquid, or for example up to 500 mg/L. In some embodiments, the hydrocarbon liquid may contain up to 200 mg, or up 150 mg, of hydrogen sulfide per L of hydrocarbon liquid. For example, the hydrocarbon liquid may contain 0.1 to 150 mg, such as 0.5 to 100 mg, of hydrogen sulfide per L of hydrocarbon liquid. In some aspects, the hydrocarbon liquid may contain 10 to 50 mg of hydrogen sulfide per L of hydrocarbon liquid. In other aspects, the hydrocarbon liquid may contain 0.1 to 10 mg of hydrogen sulfide per L of hydrocarbon liquid. Such amounts refer to the amount of hydrogen sulfide present in the hydrocarbon liquid in the liquid phase.

It is common for levels of hydrogen sulfide to be measured in the gas phase such as in the head space of a tank. Such measurements in the gas phase are commonly quoted as parts per million (ppm). There is no direct correlation between the amount of hydrogen sulfide present in the gas phase (as measured in ppm) and the amount of hydrogen sulfide present in the liquid phase (as measured in mg of hydrogen sulfide per L of liquid). The ratio of these two measures, or partition coefficients, is affected by many factors, such as the temperature of the liquid, the viscosity of the liquid etc. As a very rough guide, 1 mg of hydrogen sulfide in 1 L of in hydrocarbon liquid in the liquid phase may typically result in a level of 1 to 500 ppm of hydrogen sulfide in the gas phase. Thus, the method of the first aspect may be used to treat liquids which have hydrogen sulfide present in the gas phase in amounts of up to 100,000 ppm or more. The method of the second aspect may be used to treat hydrocarbon liquids which have hydrogen sulfide present in the gas phase in amounts of up to 100,000 ppm or more.

The method of the first aspect of the invention comprises adding an imine compound represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group, to a liquid. The method of the second aspect of the invention comprises adding an imine compound represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group, to a hydrocarbon liquid. The imine compound is added in the first and second aspects of the invention in an amount that is effective to scavenge the hydrogen sulfide present.

The particular treat rate of imine compound (i.e. amount of imine compound added to the liquid, for example hydrocarbon liquid) will depend on several factors including, for example, the amount of hydrogen sulfide present in the liquid; the desired final level of hydrogen sulfide to be achieved; the exact imine compound being used; the desired reaction time to achieve the desired level of hydrogen sulfide; the temperature, pressure, water content, or pH of the liquid; the mixing efficiency of the liquid and imine compound; and the variability in any of these parameters. For example, one mole of imine compound may react with one mole of hydrogen sulfide. For example, 141 mg of tert-octylimine per L of hydrocarbon liquid may be required to treat 34 mg of hydrogen sulfide per L of hydrocarbon liquid. Higher treat ratios may be desirable in some circumstances, for example to achieve faster reaction times, or to provide a safety margin ensuring very low levels of hydrogen sulfide in the treated fuel. Lower treat ratios may be desirable in some circumstances for example to achieve a reduction in hydrogen sulfide levels without completely removing the hydrogen sulfide. For example, in some circumstances 0.1 to 100 or 0.5 to 20 or 0.8 to 10 molar equivalents of imine compound may be used.

Suitably, in the methods of the first and second aspects some or all of the hydrogen sulfide present in the liquid (for example hydrocarbon liquid) is converted to a less corrosive, reactive and/or toxic form, for example through chemical reaction with the imine compound. For example, the imine compound may react with the hydrogen sulfide (and optionally sulfur based species) to product a nitrogen containing compound, such as an amine residue of the imine and a hydrogen sulfide aldehyde adduct.

In the first aspect, the treat rate of imine compound may be from 1 to 20000 mg, for example from 1 to 5000 mg, for example from 1 to 2500 mg, such as from 1 to 1000 mg, of imine compound per L of liquid. Typically, the treat rate of imine compound may be from 1 to 500 mg of imine compound per L of liquid.

In the second aspect, the treat rate of imine compound may be from 1 to 20000 mg, for example from 1 to 5000 mg, for example from 1 to 2500 mg, such as from 1 to 1000 mg, of imine compound per L of hydrocarbon liquid. Typically, the treat rate of imine compound may be from 1 to 500 mg of imine compound per L of hydrocarbon liquid.

The treat rate/ratio of imine compound:hydrogen sulfide present in the liquid may be from 40:1 to 1 :10, preferably from 10:1 to 1 :2, more preferably from 6:1 to 1 :1 and most preferably from 5:1 to 2:1 . Such treat rate ratios are on a weight basis. For example, a treat rate of 40 mg imine compound per L of liquid when used to treat an amount of 1 mg of hydrogen sulfide per L of liquid would be a ratio of 40:1 .

Suitably, the method of the first aspect of the invention scavenges hydrogen sulfide so as to remove or lower the amount of hydrogen sulfide present in a liquid. For example, the method of the first aspect suitably lowers the amount of hydrogen sulfide present in a liquid to an amount of less than 20 mg of hydrogen sulfide per L of liquid, preferably less than 15 mg of hydrogen sulfide per L of liquid, such as less than 10 mg or less than 5 mg of hydrogen sulfide per L of liquid.

By“removing hydrogen sulfide” we mean that the hydrogen sulfide is substantially removed, for example such that 1 L of the treated liquid would contain less than 5 mg, such as less than 4 mg, preferably less than 3 mg, less than 2 mg or less than 1 mg, of hydrogen sulfide. The treat rate/ratio of imine compound:hydrogen sulfide present in the hydrocarbon liquid may be from 40:1 to 1 :10, preferably from 10:1 to 1 :2, more preferably from 6:1 to 1 :1 and most preferably from 5:1 to 2:1 . Such treat rate ratios are on a weight basis.

Suitably, the method of the second aspect of the invention scavenges hydrogen sulfide so as to remove or lower the amount of hydrogen sulfide present in a hydrocarbon liquid. For example, the method of the second aspect suitably lowers the amount of hydrogen sulfide present in a hydrocarbon liquid to an amount of less than 20 mg of hydrogen sulfide per L of hydrocarbon liquid, preferably less than 15 mg of hydrogen sulfide per L of hydrocarbon liquid, such as less than 10 mg or less than 5 mg of hydrogen sulfide per L of hydrocarbon liquid.

By“removing hydrogen sulfide” we mean that the hydrogen sulfide is substantially removed, for example such that 1 L of the treated hydrocarbon liquid would contain less than 5 mg, such as less than 4 mg, preferably less than 3 mg, less than 2 mg or less than 1 mg, of hydrogen sulfide.

The imine compound may also react with other sulfur species present in the hydrocarbon liquid, such as HS and S ² when present.

The imine compound used in the method of the first and second aspects of the invention is represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ also shown as:

wherein R ¹ represents a (1 -5C)alkyl group.

References to“an imine compound represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group” are intended to refer to one or more of such imine compounds selected from this formula. Thus, mixtures of two or more imine compounds having the formula R ¹ -C(CH ₃ ) ₂ -N=CH ₂ may be used.

Examples of suitable imine compounds for use in the method of the first and second aspects of the present invention are as follows:

Mixtures of imine compounds having the formula R ¹ -C(CH ₃ )2-N=CH ₂ may also be used. Suitably, in the formula R ¹ -C(CH ₃ )2-N=CH ₂ , R ¹ represents a methyl group or a 5C alkyl group, more particularly R ¹ represents a 5C alkyl group. For example, the imine compound that is used in the method of the first and second aspects of the invention may be tert-butylimine or tert-octylimine or mixtures thereof. More particularly the imine compound that is used in the method of the first and second aspects of the invention may be tert-octylimine.

Suitably, the imine compound used in the method of the first and second aspects of the invention may be an imine compound prepared from tert-butyl amine and formaldehyde or paraformaldehyde. Suitably, the imine compound used in the method of the first and second aspects of the invention may be an imine compound prepared from tert-octyl amine and formaldehyde or paraformaldehyde. Preparation of imines from amines and aldehydes is well known to those skilled in the art. When the aforementioned imine compounds are used to scavenge hydrogen sulfide from a liquid (for example hydrocarbon liquid), the imine compound reacts with the hydrogen sulfide, and may also react with other sulfur based species such as HS and S ² when present (which species can liberate hydrogen sulfide). The imine compound(s) does not remove sulfur from the liquid, but it changes the hydrogen sulfide into a different form of sulfur compound (which form is more readily tolerated).

It is believed that the particular imine compounds used in the method of the first and second aspects of the present invention are especially effective at scavenging hydrogen sulfide (and optionally other sulfur based species when present), for example compared to other known hydrogen sulfide scavengers.

The first and second aspects of the invention may further comprise a method wherein the hydrogen sulfide is substantially removed, such that 1 L of the treated liquid or hydrocarbon liquid contains less than 5 mg of hydrogen sulfide.

The methods of the first and second aspects of the invention may comprise any further suitable steps, such as mixing (for example by stirring) the mixture of the liquid or hydrocarbon liquid with the imine compound and optionally heating.

In all aspects of the invention, the liquid (for example hydrocarbon liquid) may be any liquid, for example that comprises hydrogen sulfide to be scavenged. The liquid may also comprise other sulfur species, such as HS and S ² . The liquid may be a hydrocarbon liquid.

Hydrocarbon Liquid

The hydrocarbon liquid may be any hydrocarbon liquid, for example that comprises hydrogen sulfide to be scavenged. For example, the hydrocarbon liquid may comprise petroleum liquids. The hydrocarbon liquid may comprise refinery liquids. By the term“refinery liquids”, we mean any hydrocarbon liquid that enters or leaves (for example following processing) a refinery. For example, the hydrocarbon liquid may comprise refinery liquids which may themselves be blends of various refinery streams.

Suitably, the hydrocarbon liquid may comprise any one or more liquids selected from crude oil, crude oil emulsions, oil field condensate, petroleum residuals, bunker fuel oil, asphalt, bitumen, mineral oils, lubricating oils, refined fuel, distillate fuel, fuel oil, heating oil, diesel fuel, gasoline and/or jet fuel.

In one aspect, the hydrocarbon liquid does not comprise crude oil. For example, in this aspect, the hydrocarbon liquid may comprise any one or more liquids selected from oil field condensate, petroleum residuals, bunker fuel oil, asphalt, bitumen, mineral oils, lubricating oils, refined fuel, distillate fuel, fuel oil, heating oil, diesel fuel, gasoline and/or jet fuel.

In some preferred aspects, the hydrocarbon liquid is selected from one or more of petroleum residuals, bunker fuel oil, asphalt, bitumen, mineral oils, lubricating oils, refined fuel, distillate fuel, fuel oil, heating oil, diesel fuel, gasoline and jet fuel.

In another aspect, the hydrocarbon liquid may comprise crude oil and/or crude oil emulsions. Composition

A third aspect of the present invention provides a composition comprising a liquid and an imine compound represented by the formula R ¹ -C(CH ₃ ) ₂ -N=CH ₂ , wherein R ¹ represents a (1-5C)alkyl group.

A fourth aspect of the present invention provides a composition comprising a hydrocarbon liquid and an imine compound represented by the formula R ¹ -C(CH ₃ ) ₂ -N=CH ₂ , wherein R ¹ represents a (1-5C)alkyl group.

As discussed above in relation to the first and second aspects, examples of suitable imine compounds for including in the composition of the third and fourth aspects of the present invention are as follows:

Mixtures of imine compounds having the formula R ¹ -C(CH ₃ )2-N=CH ₂ may also be used. Suitably, in the formula R ¹ -C(CH ₃ )2-N=CH ₂ , R ¹ represents a methyl group or a 5C alkyl group, more particularly R ¹ represents a 5C alkyl group. For example, the imine compound that is included in the composition of the third or fourth aspect of the invention may be tert-butylimine or tert-octylimine or mixtures thereof. More particularly, the imine compound may be tert- octylimine.

Suitably, the imine compound that is included in the composition of the third or fourth aspect of the invention may be an imine compound prepared from tert-butyl amine and formaldehyde or paraformaldehyde. Suitably, the imine compound that is included in the composition of the third or fourth aspect of the invention may be an imine compound prepared from tert-octyl amine and formaldehyde or paraformaldehyde.

Immediately after addition of the imine compound, the composition of the third or fourth aspect comprises the imine compound in an amount that is effective to scavenge the hydrogen sulfide present. Suitable treat rates are as described in relation to the first and second aspects.

It will be appreciated that on reaction with hydrogen sulfide, the imine compound will form a nitrogen containing compound, such as an amine residue as above. Thus, the composition of the third or fourth aspect may additionally comprise a nitrogen containing derivative of the imine compound, such as an amine residue of the imine compound.

Suitably, the composition of the third aspect may comprise a liquid and from 1 to 20000 mg, for example from 1 to 5000 mg, such as from 1 to 1000 mg, preferably from 1 to 500 mg, of an imine compound represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ , wherein R ¹ represents a (1 - 5C)alkyl group, and from 5000 to 1 mg, such as from 1000 to 1 mg, preferably from 500 to 1 mg of an amine residue thereof, per L of liquid.

Suitably, the composition of the fourth aspect may comprise a hydrocarbon liquid and from 1 to 20000 mg, for example from 1 to 5000 mg, such as from 1 to 1000 mg, preferably from 1 to 500 mg, of an imine compound represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group, and from 5000 to 1 mg, such as from 1000 to 1 mg, preferably from 500 to 1 mg of an amine residue thereof, per L of hydrocarbon liquid.

The particular imine compound(s) included in the composition of the third or fourth aspect of the present invention are especially effective at scavenging hydrogen sulfide (and optionally other sulfur based species when present) from a liquid or hydrocarbon liquid, for example compared to other known hydrogen sulfide scavengers.

A fourth aspect of the invention may provide a composition comprising a hydrocarbon liquid and an imine compound represented by the formula R ¹ -C(CH ₃ ) ₂ -N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group, and wherein the hydrocarbon liquid does not comprise crude oil or a crude oil emulsion.

A fourth aspect of the invention may provide a composition comprising a hydrocarbon liquid and an imine compound represented by the formula R ¹ -C(CH ₃ ) ₂ -N=CH ₂ , wherein R ¹ represents a (1 -5C)alkyl group, and wherein the hydrocarbon liquid comprises refinery liquids. A fourth aspect of the invention may provide a composition comprising a hydrocarbon liquid and an imine compound represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ , wherein R ¹ represents a (1-5C)alkyl group, and wherein the hydrocarbon liquid comprises petroleum liquids.

A fourth aspect of the invention may provide a composition comprising a hydrocarbon liquid and an imine compound represented by the formula R ¹ -C(CH ₃ )2-N=CH ₂ , wherein R ¹ represents a (1-5C)alkyl group, and wherein the hydrocarbon liquid comprises any one or more liquids selected from crude oil, crude oil emulsions, oil field condensate, petroleum residuals, bunker fuel oil, asphalt, bitumen, mineral oils, lubricating oils, refined fuel, distillate fuel, fuel oil, heating oil, diesel fuel, gasoline and/or jet fuel.

A fourth aspect of the invention may provide a composition comprising a hydrocarbon liquid and an imine compound represented by the formula R ¹ -C(CH ₃ ) ₂ -N=CH ₂ , wherein R ¹ represents a (1-5C)alkyl group, and wherein the hydrocarbon liquid comprises any one or more liquids selected from oil field condensate, petroleum residuals, bunker fuel oil, asphalt, bitumen, refined fuel, distillate fuel, fuel oil, heating oil, diesel fuel, gasoline and/or jet fuel.

The composition of the third or fourth aspect of the invention may comprise further additional components. Such additional components are typical additives known in the petroleum industry.

Brief Description of Drawings

For a better understanding of the invention, and to show how exemplary embodiments of the same may be carried into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:

Figure 1 shows a comparison of hydrogen sulfide scavenging efficiency for Scavenger C and Scavenger A according to Example 1 , with the concentration of hydrogen sulfide remaining (in mg/L) on the y axis and time (in minutes) on the x axis.

Figure 2 shows a comparison of hydrogen sulfide scavenging efficiency for Scavenger C and Scavenger A according to Example 2, with the concentration of hydrogen sulfide remaining (in mg/L) on the y axis and time (in minutes) on the x axis.

Figure 3 shows a comparison of hydrogen sulfide scavenging efficiency for Scavengers C, D and E according to Example 4, with the concentration of hydrogen sulfide remaining (in mg/L) on the y axis and time (in minutes) on the x axis. Examples The invention will now be described with reference to the following non-limiting examples.

Scavenger A is a terminal imine formed by the reaction of Primene 81 R Amine and formaldehyde (or paraformaldehyde) and is a known commercial hydrogen sulfide scavenger. Primene 81 R is a primary aliphatic amine in which the amino nitrogen is linked to a tertiary carbon and the total number of carbon atoms is in the C12 -C14 range. Thus Scavanger A is a compound of the formula R ² -N=CH ₂ , wherein R ² - represents an alkyl group having 12-14 carbon atoms. Scavenger A is described in example 10 of US5169411.

Preparative Example Scavenger A (Comparative; example 10 of US 5169411)

Primene 81 R amine (10 g, 50.3 mmol) was dissolved in toluene (50 ml). Paraformaldehyde (1.81 g, 60.3 mmol) was added and the mixture heated to reflux for 1 hour with a Dean Stark trap in place to capture the water produced. After cooling to room temperature, the organic phase was concentrated in vacuo to afford Scavenger A (9.52 g, 45.1 mmol, 90 %) as a yellow oil. Preparative Example Scavenger B (Comparative; example 8 of US 5169411)

tert-Butylamine (6.96 g, 95.2 mmol) was dissolved in toluene (20 ml). 2-Ethyl hexanal (9.76 g, 76.1 mmol) was added and the mixture stirred at room temperature for 1 hour, then at 60 °C for 4 hours. After cooling to room temperature, the solution was then partitioned between water (50 ml) and EtOAc (50 ml). The aqueous phase was separated and the organic phase washed with water (100 ml), 0.5 M aq. HCI (100 ml) then water (100 ml), dried over MgS0 ₄ and concentrated in vacuo to afford Scavenger B (12.8 g, 69.9 mmol, 92 %) as a yellow oil.

Preparative Example Scavenger C (Inventive; tert-octylimine)

Paraformaldehyde (0.94 g, 31.1 mmol) was added to in EtOAc (20 ml) to form a suspension. tert-Octylamine (4.03 g, 31 .1 mmol) was added and the mixture stirred at room temperature for 1 hour, then at 60 °C for 1 hour. After cooling to room temperature, the aqueous phase was separated and the organic phase dried over MgS0 ₄ and concentrated in vacuo to afford tert- octylimine, Scavenger C (3.43 g, 24.3 mmol, 78 %) as a colourless oil. Preparative Example Scavenger D (Comparative; N-(2,6-dimethylphenyl)methanimine)

Paraformaldehyde (2.44 g, 81.2 mmol) and 2,6-dimethylaniline (9.84 g, 81.2 mmol) were combined and heated to 60°C for 1 hour, with stirring. The temperature was increased to 80 °C for a further 2 hours, then the reaction mixture was cooled to room temperature. The resulting oil was dissolved in ethyl acetate (50 ml_). The organics were dried (MgS0 ₄ ) and filtered. The filtrates were concentrated in vacuo to afford Scavenger D as a colourless oil.

Preparative Example Scavenger E (Comparative; N-(2.6-diisopropylphenvDmethanimine) Paraformaldehyde (1 .59 g, 53 mmol) and 2,6-diisopropylaniline (9.4 g, 53 mmol) were combined and heated to 60°C for 1 hour, with stirring. The temperature was increased to 80°C for a further 2 hours, then the reaction mixture was cooled to room temperature. The resulting oil was dissolved in ethyl acetate (50 ml_). The organics were dried (MgS0 ₄ ) and filtered. The filtrates were concentrated in vacuo to afford Scavenger E as a colourless oil.

Example 1 : Hydrogen sulfide scavenging efficiency

Caromax 20 (20 ml) was placed into a reaction vessel containing a stirrer bar and the system sealed. A stock solution of Caromax 20/H ₂ S (4 ml, about 525 mg/L H ₂ S) was added to the reaction vessel and the mixture heated to 75°C with stirring. Once the temperature had stabilised the time = 0 liquid H ₂ S content was determined (in mg H ₂ S/L). Hydrogen sulfide scavenger (415 mg/L) was then injected into the system and the liquid H ₂ S content determined at the following time points after injection; 1 , 5, 10, 20 and 30 minutes. The results are shown in Figure 1.

The hydrogen sulfide scavengers tested were: Scavenger C and Scavenger A.

Figure 1 shows that for the same scavenger treat rate, Scavenger C reduces the amount of hydrogen sulfide in the system considerably faster and more effectively than Scavenger A.

Example 2: Hydrogen sulfide scavenging efficiency

Crude oil (20 ml) was placed into a reaction vessel containing a stirrer bar and the system sealed. A stock solution of Caromax 20/H2S (1 .3 ml, about 525 mg/L H2S) was added to the reaction vessel and the mixture heated to 49°C with stirring. Once the temperature had stabilised the time = 0 liquid H2S content was determined (in mg H2S/L). A hydrogen sulfide scavenger (Scavenger A or Scavenger C) (525 mg/L) was then injected into the system and the liquid H2S content determined at the following time points after injection; 1 , 5, 10, 20 and 30 minutes. The results are shown in Figure 2.

Figure 2 shows that for the same scavenger treat rate, Scavenger C reduces the amount of hydrogen sulfide in the system considerably faster and more effectively than Scavenger A. Example 3: Hydrogen sulfide scavenging efficiency

Performance of Scavenger B A series of tests were performed to study the effectiveness of Scavenger B. In these tests,

2ml of a stock solution containing 0.6 mg/ml of Na ₂ S in MeOH was added to 8 ml of Caromax and the vessel sealed. Hydrogen sulfide was generated in situ by injecting 0.07 ml of 0.5M HCI (2 molar equivalents). Thus, the solution contained approximately 50 mg/L of hydrogen sulfide. Scavenger B was then injected in an amount as shown in Table 1. The mixture was heated to 75°C for 30 minutes and then allowed to cool. The presence of hydrogen sulfide remaining was assessed using a colourimetric test which tests positive if >1 mg/L of hydrogen sulfide is present in the liquid phase. Thus, a positive test indicates a failure to reduce the hydrogen sulfide concentration to <1 mg/L. Multiple tests were performed over an extended period of time (several weeks) using different batches of Scavenger B and the results are summarised in Table 1.

Table 1

The results show that at a treat rate of 2 moles of Scavenger B per mole of hydrogen sulfide, only 25% of tests resulted in hydrogen sulfide levels <1 mg/L. Even at treat rates of 20 moles of Scavenger B per mole of hydrogen sulfide, the target hydrogen sulfide level was not achieved in all cases.

Performance of Scavenger C

A similar series of tests to those discussed above for Scavenger B were performed where Scavenger C was used instead of Scavenger B. Again, multiple tests were performed over an extended period of time (several weeks) using different batches of Scavenger C and the results are summarised in Table 2 Table 2

The results show that at treat rates at or above 1 mole of Scavenger C per mole of hydrogen sulfide, all tests resulted in hydrogen sulfide levels <1 mg/L.

Example 4: Hydrogen sulfide scavenging efficiency

The H ₂ S scavenging efficiency of Scavengers C, D and E was compared using a slightly modified procedure. Caromax 20 (20 mL) was charged to a reaction vessel fitted with a stirrer bar. A stock solution of Na ₂ S.xH ₂ 0 (1000 mg/L in methanol, 2 mL) was added and the reaction vessel tightly sealed. A solution of HCI (1 M in diethyl ether, 0.035 mL) was injected and the reaction mixture was heated to 30°C with stirring. After stabilisation of the temperature, the starting H ₂ S content (t = 0) was determined (mg H ₂ S/L). The H ₂ S scavenger under test (5 mol eq relative to H ₂ S) was injected into the system and the solution H ₂ S content determined at the following time points after injection; 1 , 5, 10 and 20 minutes. The results for scavengers C, D or E are shown in Figure 3.

Figure 3 showed that for the same scavenger treat rate, t-octyl imine (Scavenger C) reduced the amount of hydrogen sulfide in the system considerably faster and more effectively than the comparative compounds N-(2,6-dimethylphenyl)methanimine (Scavenger D) or N-(2,6- diisopropylphenyl)methanimine (Scavenger E).