GB2356404A

GB2356404A - Process for deacidifying crude oils and a device therefore

Info

Publication number: GB2356404A
Application number: GB0025667A
Authority: GB
Inventors: Guy Rousseau; Gilbert Bayle; Jean Louis Crolet
Original assignee: Elf Exploration Production SAS
Current assignee: Elf Exploration Production SAS
Priority date: 1999-10-22
Filing date: 2000-10-19
Publication date: 2001-05-23
Anticipated expiration: 2020-10-19
Also published as: FR2800090B1; NO20005243L; FR2800090A1; GB2356404B; OA11690A; NO330099B1; GB0025667D0; NO20005243D0

Abstract

A process is described for deacidifying crude oil comprising a desalting step, a step in which naphthenic acids are neutralised with an amine containing 0 to 6 carbon atoms, preferably ammonia, and a step in which the naphthenates thus formed are extracted by separation using an alcohol containing 1 to 6 carbon atoms, preferably methanol. Apparatus is also described for deacidifying crude oil, together with a specific solvent composition.

Description

2356404 PROCESS FOR DEACIDIFYING CRUDE OILS AND DEVICE IMPLEMENTING THIS

PROCESS The present invention relates to a novel process for deacidifying crude oils, and a device for carrying out this process.

Crude oils or factions thereof having a high acid content, such as those containing naphthenic acids, create a risk of corrosion of the devices and equipment used to transport such crude oils or factions thereof or of devices and equipment for treating them, at the oilfield or at the refinery. Crude oil acidity is conventionally measured by the TAN (total acid number) index, measured according to ASTM D664. Thus, a discount is applied to crude oils having a TAN index greater than 0.6. The majority of crude oils currently produced are naturally acid. A treatment for such crude oils using a process able to provide a TAN index lower than 0.6 by extracting the naphthenic acids would avoid such crude oils being downgraded and would boost profit margins. It would be preferable to be able to carry out this process at the oilfield. Additionally, naphthenic acids have several applications such as the wood fungicide field, paints, lubricants. It would consequently be advantageous to provide a process enabling the naphthenic acids to be recovered in order to put them to economic use.

Numerous efforts have been made in recent years in an attempt to develop such a crude oil deacidification process.

Among the various approaches adopted, one which has been particularly studied is neutralization by nitrogen compounds, optionally associated with the use of a solvent, as mentioned in United Sbates Patents 2,769,768, 2,850,435, 3,176,041, 2,911,360, 4,634,519, or 5,550, 296.

United States Patent 2,769,768 discloses the use of a straight chain or branched primary alcohol having 4 to 7 carbon atoms with a mixture of methanol and ammonia for removing heavy naphthenic acids from a de-paraffinated hydrocarbon oil (base oils for lubrication or residues thereof). Example 7 shows that by associating methanol with ammonia and water, only 23% of 2 naphthenic acids can be extracted (as against 60% using the method and solvent compositions claimed in the present invention). The process employs an oil:solvent volume ratio of 1:1 which cannot be employed industrially in view of the amounts involved and even less at the oilfield, for treating an extracted crude oil.

United States Patent 2,850,435 discloses a process also applying to de-paraffinated lubricant oils employing a solvent mixture consisting this time of a methanol: ammonia: water mixture, in which the ammonia content is from 5 to 7% and the water content does not exceed 0.4%. The operating conditions are adapted as a function of the amount of oil to be treated; the greater the viscosity of the oil the more severe the conditions and the higher the oil:solvent volume ratio (varying between 0.2 and 2, and temperatures varying from 60 to 900C).

This process cannot be applied industrially to crude oil.

United States Patent 3,176,041 discloses trapping of naphthenic acids of crude oil by contact with a clay impregnated with a volatile amine having a boiling point below 1000C, notably ammonia. This process cannot be applied at the crude oil production field as it requires a contact temperature greater than 2000C for 20-75 minutes and the extremely complex daily regeneration of several hundreds of tons of clay.

United States Patent 2,911,360 discloses a process applying to crude oil. The crude oil is deacidified in the liquid phase by bringing it into contact with a base in the presence of an alcohol, followed by distillation. The base can be ammonia while the solvent phase is an aqueous solution containing from to 50% by weight of alcohol. The naphthenic acids are regenerated after sulphuric acid acidification of the extraction solvent. This process is complex as it involves two treatments, one in the liquid phase and the other in the vapour phase. Additionally, it is only applicable in the refinery as it involves atmospheric distillation and vacuum distillation of the treated crude oil.

United States Patent 4,634,519 discloses a process for deacidifying petroleum cuts using a specific solvent mixture comprising water, methanol and ammonia. It is indicated that the specific ratios are critical for effective extraction of the naphthenic acids. The methanol:water weight ratio should 3 notably be comprised between 0.2:1 and 3:1. The example states that the decantation time is 16 hours, which is not compatible with continuous deacidification on the oilfield. This process applies solely to petroleum cuts, as is clearly indicated.

Application of this treatment to crude oil leads to a stable emulsion rendering extraction solvent recovery practically impossible.

United States Patent 5,550,296 discloses ketone synthesis but also discloses a process for oil deacidification directly at the outlet from the well (before stabilisation), using liquid ammonia for neutralising the naphthenic acids. Such a process is very difficult to implement at an oilfield.

None of the above documents teaches nor suggests the invention.

Thus, the invention provides a process making it possible to produce a deacidified crude oil having a TAN index below 0.6, corresponding to a crude oil substantially free of naphthenic acids and naphthenates.

The invention also provides an industrial deacidification process which is both effective on all types of crude oil, can be implemented at any oil field,. including platforms at sea, and which allows the reagents used for deacidifi cation to be, recycled, and which, by simple heating, allows recovery of the naphthenic acids with a view to sale or synthesis of new products.

The invention also provides a device for implementing this process, as well as a solvent composition used in the process.

In a first aspect, the invention is a process for deacidifying crude oils comprising the following steps:

(i) desalting by washing with soft water; (ii) neutralization of naphthenic acids by liquid/liquid mixing with an amine containing 0-6 carbon atoms; (iii) extraction by separation of the naphthenates formed at step (ii) using a solvent comprising a C1 to C6 alcohol; in order to produce a flow of deacidified crude oil and a flow of extraction solvent.

To facilitate description of the invention, we shall consider that ammonia is an amine containing 0 carbon atoms.

4 According to one embodiment of the process, the neutralization and extraction steps are carried out simultaneously.

According to a f urther embodiment of the process, the neutralization and extraction steps consist of a mixing phase immediately followed by a separation phase.

According to one embodiment of the process, the neutralization and extraction steps are carried out with a solvent composition comprising, in percent by weight based on the composition:

from 80 to 98.5% of a C1 to C6 alcohol; from 0.5 to 5% of an amine containing 0-6 carbon atoms; and from 0 to 15% water.

According to a further embodiment of the process, the crude oil:solvent volume ratio is comprised between 5:1 and 15:1.

According to a further embodiment of the process, the amine:acid molar ratio is comprised between 1:1 and 50:1.

According to one embodiment of the process, the temperature of the neutralization and/or extraction step is comprised between 20 and 950C, preferably between 50 and 900C.

According to a further embodiment of the process, the separation is performed by gravitational decantation and/or by coalescence and/or electrostatically.

According to one embodiment, the process additionally comprises the step of:

(iv) washing deacidified crude oil with water, preferably soft water.

In a second aspect, the invention is a device for deacidifying crude oil comprising:

(i) a desalting unit for said crude oil to give a stabilised crude oil leaving by a desalted crude oil removal conduit; (ii) at least a primary mixer in which stabilised crude oil leaving said desalted crude oil removal conduit is mixed with an amine containing 0-6 carbon atoms and, optionally, a C1 to C6 alcohol and, optionally, water; and, optionally, a secondary mixer in which the mixture leaving said primary mixer is mixed with a Cl to C6 alcohol and, optionally, water; (ii!) a f irst separator connected to said primary mixer or said secondary mixer from which deacidif ied crude oil is removed by a deacidif ied crude oil removal conduit and f rom. which naphthenate extraction solvent is removed by a naphthenate extract removal conduit.

According to one embodiment, the device comprises:

(ii) a primary mixer in which stabilised crude oil leaving said desalted crude oil conduit is mixed with an amine containing 0-6 carbon atoms, a Cl to C6 alcohol and water; wherein (ii!) the first separator is directly connected to said primary mixer.

According to another embodiment, the device further comprises:

(iv) a second mixer in which deacidified crude oil leaving said deacidified crude oil removal conduit is mixed with water leaving a washing water feed conduit; (v) a second separator directly connected to said second mixer from which washed deacidified crude oil is removed by a washed deacidified crude oil removal conduit and from which washing water is removed by a washing water removal conduit.

According to another embodiment, the device additionally comprises:

(vi) a first extraction column fed with the 6 extraction solvent leaving said naphthenate extract removal conduit and, if appropriate, washing water from said washing water removal conduit, f rom. the head of which a mixture is removed by a f irst recycle conduit and optionally recycled to said primary mixer and f rom. the bottom of which there is removed a mixture containing naphthenic acids and water, by a third separator f eed conduit; (v) a third separator supplied with the mixture from said third separator feed conduit and f rom the head of which naphthenic acids are removed by a naphthenic acids removal conduit and from the bottom of which water is removed by a second recycle conduit, optionally recycled to said primary mixer and/or said second mixer.

According to a further embodiment, the device additionally comprises:

(vi) a second extraction column supplied by washing water leaving said washing water removal conduit, from the bottom of which water and, optionally, alcohol is removed by a fourth recycle conduit for optional recycling to the primary mixer and/or the second mixer and f rom the head of which a mixture of alcohol and amine is removed by a third recycle conduit for optional.

recycling to said primary mixer, or for delivery to the middle of said first column.

7 According to still a further embodiment, the said separator or separators is/are one or a plurality of gravitational decanters or coalescers, optionally electrostatic.

According to an embodiment, the device is intended for carrying out the process according to the invention.

The invention also provides a solvent composition comprising, by percentage in weight based on said composition:

from 80 to 98.5% of a C1 to C6 alcohol; from 0.5 to 5% of an amine containing 0-6 carbon atoms; and from 0.5 to 15% water.

The solvent composition preferably comprises, in percentage by weight based on said composition:

from 83 to 87% of a C1 to C6 alcohol; from 3.5 to 4.5% of an amine containing 0-6 carbon atoms; and less than 11% water.

In one embodiment of the solvent composition, the C1 to CG alcohol is methanol; the amine is ammonia.

The invention will now be described in detail below, with reference to the attached drawings, in which:

- figure 1 is a diagram of a first embodiment of the invention; - f igure 2 is a diagram of a second embodiment of the invention; f igure 3 is a diagram of a third embodiment of the invention; - figure 4 is a diagram of a fourth embodiment of the invention.

Desalting step During this first step, the salts (including, notably, bivalent cations) are eliminated from the crude oil. It is desired to obtain a desalted crude oil the salt content of which is less than 120 mg/l, preferably less than 60 mg/l, and/or of which the bivalent cation content is less than 40 mg/kg, preferably less than 20 mg/kg.

8 This desalting step is carried out conventionally by washing with soft water preferably containing a de-emulsifying agent, followed by separation. washing and separation are carried out under conventional conditions, for exampleunder I- 15 bar and at 50 to 950C. Separation can for example be carried out in a gravitational decanter, an electrostatic separator or a coalescer. The person skilled in the art can refer to the publication "Proc6d6 et traitement des p6troles bruts sai6s', Technip, 1976, page S9 et seq.

The results of measuring TAN, implementing neutralization- extraction using a methanol: water: ammonia (93:6-1 by weight) solvent composition, on Dalia crude oil having a TAN of 1.85, with and without prior desalting, are given in the table below.

Characteristxcs ot without prxor witti -prior desaltl-iig- treated crude oil desalting [salts] (mg/1) 625 60 [Cal (mg/kg) crude 113 34 oil after deacidification Residual TAN of 0.93 0.51 crude oil after deacidification Thus, this prior desalting step is required in the present process for obtaining the desired value of TAN.

Without wishing to be bound by this, the applicant believes that the presence of bivalent cations would lead, during subsequent steps, to the formation of naphthenates which would remain in the crude oil, with impairement of the TAN index.

In the case of a process where the water is recycled (notably a desalter) without the salts being eliminated, if the crude oil were not to be desalted, the final TAN index would not cease to increase as a result of salt concentration (notably bivalent cation concentration) in the recirculation loop.

Additionally, this step aims at producing a stabilised crude oil, in other words one the characteristics of which are preferably the following:

Salt content < 60 mg/1 Water content < 0.5 per cent 9 Vapour tension < 76 kPa Neutralization and extraction steps The second step is a step of crude oil deacidification by neutralising naphthenic acids using a nitrogenous compound, followed by the third step of extracting the naphthenates formed using an alkanol- type solvent.

The term nitrogenous compound should be taken to mean amines containing up to 6 carbon atoms (the chain being straight or branched), notably any volatile amine such as ammonia or the alkyl amines such as monomethyl amine, monoethyl amine, dimethyl amine, diethylamine, trimethylamine, triethylamine, diisopropyl amines, and amino-2 butane, preferably ammonia or the amine having a maximum of 2 carbon atoms in total, advantageously ammonia. These amines have low solubility in the crude oil (this solubility increases with the total number of carbon atoms), and is even practically zero in the case of ammonia. This amine is also, generally, soluble in alcohol, and notably methanol, and can be readily regenerated. 20 For practical reasons of packaging, transport, storage and security, it is possible to use the amine in aqueous solution, for example ammonia in the form of ammonium hydroxide in aqueous solution, for example at 20 or 25% by weight NH, concentration. 25 The amount of ammonia or amine is in general sufficient to completely neutralise the naphthenic acids, consequently in an amine molar ratio or NH3:RCOOH ratio of 1:1 to 50: 1. The solvent used for extracting the amine naphthenates, preferably ammonium, formed during the neutralization reaction is a (straight chain or branched) volatile alcohol having 1 - 6 carbon atoms, preferably 1-3 carbon atoms, and more preferably is methanol.. Methanol is preferred in view of its low solubility in the crude oil.

Thus, a Dalia crude oil was deacidified using a 0.1N trimethyl amine alcoholic solution (i.e. by weight, 99.3 per cent alcohol and 0.7 per cent amine) at ambient temperature with a crude oil: solvent volume ratio of 1:1. The results are summarised in the table below:

Example 1 -Example Z Exampl-673- Alcohol methanol ethanol isopropanol employed Number of 1 2 3 carbon atoms Residual TAN 61 0.67 0.75 0.52 crude oil after washing Volume % of 0.03 0.17 0.42 alcohol in the crude oil The basis of the present deacidification process is consequently a neutralization by amine, notably ammonia, followed by extraction of the amine or ammonium naphthenates formed by an alcohol, notably methanol.

The extraction step cannot follow the neutralization step. It is, of necessity, implemented subsequent to or -simultaneously with neutralization. This is clear from the series of cross-trials the results of which are summarised in the table below. The crude oil was a Dalia crude oil having an initial TAN of 1.85; the crude oil:solvent volume ratio was 1:1, and the temperature 501C.

___T_e_sU__ step Solvent intermedi-ate tinal TAN TAN Ex. 1 neutralization 10 0 % NH40H 1.17 0.43 followed by (0. SN in NHO extraction then 100% MeOH Ex. 2 extraction 100% MeOH 1.3 0.9 followed by then 100% neutralization NH40H (0. 5N in NH 3) Ex. 3 simultaneo s MeOH: water: 0.44 neutralization NH3 (93: 6: 1 and extraction in weight%) Washing of this crude oil with ammonia in the first step, after separation and centrifuging, led to a crude oil having a residual TAN of 1.17; the ammonium naphthenates formed by the neutralization reaction remained, in the majority, solubilised in the crude oil. The take-up of this crude oil by the methanol allowed the majority of the ammonium naphthenates to be selectively extracted thereby giving a crude oil with a residual TAN < 0.6.

The same result is obtained with simultaneous separation and extraction.

if the steps are reversed by firstly washing with methanol, only the naphthenates or light naphthenic acids present from the outset in the crude oil are extracted and, in the second step, washing with ammonia does indeed provide for neutralization of the naphthenic acids but without being able to cause the naphthenates to pass into the aqueous phase which would have made it possible to bring the TAN down to below 0. 6.

The neutralization was performed by bringing the crude oil into contact with the amine (or the latter in the solvent). Contact is achieved by liquid/liquid mixing for from one second up to several tens of minutes, preferably from one second to one minute. Mixing can be performed, for example, in a static mixer, a turbine, or, preferably, a mixing valve. In the case of the ammonia, a solvent is employed (for example water or alcohol), whereas this is not necessary for the other amines which are liquid at the treatment temperatures adopted.

Neutralization and extraction can also be implemented simultaneously, in one embodiment. For example, this can be a mixing phase as implemented in a mixing valve (immediately) followed by a separation phase.

The alcohol, notably methanol, consequently allows the amine, notably ammonium, naphthenates to be extracted, but also makes it possible to achieve rapid separation (for example by simple decanting) of the oil phase and a solvent phase given the difference in density existing between alcohol and crude oil. By way of example, methanol has a density of 0.79 and Dalia crude oil a density of 0.92.

For good crude oil:water separation, the density differential will generally only be at least about 0.1.

In the case of a crude oil having a density of 0. 92 and in the case of a methanol:NH40H solvent system, a density of 0. 82 for the solvent system will consequently be. looked for. Thus,.

the density of methanol being 0.79, the water content (density 1) to obtain the value of 0.82 will be around a maximum of 1S%, preferably between 1 and 11%. This preferred maximum value of water content (when the latter is present) consequently varies 12 as a function of the alcohol chosen and the crude oil to be treated.

The separation can also be reversed; in the case of a very light crude, a heavy solvent, for example water possibly 5 containing a minor portion of alcohol, will be adopted.

The table below gives the results of separation for a methanol: water: NH, (1% by weight NH,) solvent system.

Test 16 water 3-n the % oil separated A oij. separated solvent system in 15 minutes in 60 minutes Example 1 6 94 100 Example 2 8 101 101 Example 3 12 103 103 Example 4 15 60 105 Example 5 80 0 55 A value of greater than 100% indicates that a small portion of solvent is to be found in the oil phase in the form of an emulsion, thus increasing volume.

This series of tests carried out at 501C highlights the influence of water content of the solvent system on the separation speed, a content too high having a negative effect.

The separation step is carried out at a mixture temperature of between 20 and 950C and, preferably, between 50 and 900C. The pressure is for example comprised between 1x105 and 5x105 Pa.

The table below gives the results of tests carried out with a crude oil:solvent volume ratio of 1:1, on a Dalia. crude oil, with, as the solvent composition, methanol:water: NH3 (96.6:3:

0.4 by weight).

Increasing contact temperature only slightly improves crude oil deacidification yield but makes it possible to significantly reduce the time needed for crude oil:solvent Test temperature % ol I % 02.1 res:LCLUaJL (OC) separated separated TAX of oil in 1 min in 15 min treated Example 1 40 0 100 0.40 Example 2 so 0 100 0.43 Example 3 60 20 105 0.40 Example 4 70 80 100 0.25 Example 5 90 100 100 0.32 13 separation making it possible to employ, for deacidification, a separator of reduced size in line with the short dwell time The last point to take into account when dimensioning a separator is the crude oil:water (or crude oil:solvent) volume 5 ratio. In the context of a crude oil production of the order of 1325m3/h, a crude oil:solvent volume ratio of 1:1 with a dwell time of 15 min would require a separator of 5 m diameter and 40 m length, which is unthinkable for industrial production, notably in the field.

The invention makes it possible to employ crude oil:solvent volume ratios distinctly higher than 1:1. The crude oil:solvent volume ratio will in general be comprised between 5:1 and 15:1.

The table below gives the results for a series of tests performed on a Dalia crude oil, at 500C, with a methanol:water:

NH, (92:7:1 by weight) solvent composition.

example I example 2. example 3 example 4 crude 3:1 5:1 9:1 12:1 oil:solvent volume ratio % oil 100 100 0 0 separated in 30 min % oil 100 100 95 90 separated in 60 min average 0.57 0.55 0.50 0.60 residual TAN By increasing temperature, it is possible to further increase separation speed.

At the end of these neutralization and extraction steps, a deacidified crude oil is obtained having a TAN index less than 0.6 (or a value very close) and an extraction solvent containing naphthenates.

14 Washing step The crude oil, deacidified at the preceding step, still generally contains residual methanol (for example of the order of 1%) and generally has a fairly pronounced smell of ammonia.

The water washing step can f or example be carried out at a pressure comprised between jX105 and 5xl 05 Pa, and at a temperature comprised, for example, between 20 and 750C.

This step makes it possible to eliminate residues of reagents possibly still present and, additionally, also contributes to reducing TAN.

The table below illustrates this latter effect (the oil is a Dalia crude oil, deacidified as previously) examp-Le I example -2 example 3 Crude oil:water 5:1 9:1 12:1 vol ratio TAN of unwashed 0.55 0.50 0.60 crude oil TAN of washed 0.40 0.38 0.50 crude oil % MeOH in 1.0 1.7 1.3 unwashed crude oil MeOH in 0.03 0.01 < 0.01 washed crude oil one f or example separates the water used for washing and the methanol and ammonia by distillation, thereby favouring their elimination. This separated washing water is also preferably deionized prior to recycling.

final desalting step On the assumption that the deacidified and washed crude oil has a salt content above specification, a fourth step consisting in desalting can be envisaged with passage through a conventional desalter of the type described in the framework of the first step (allowing soft water washing).

Recycling of reagents and valorization of the naphthenic acids The naphthenates (in general ammonium naphthenates) extraction solvent can be sent to an extraction column (ie a distillation column). This distillation column is for example operated at 1000C to thermally decompose the naphthenates (here ammonium naphthenates) according to the reaction:

A RCOONH4 - - > RCOOH + NH3 The naphthenic acids are recovered at the bottom of the column, with the water, from which they are subsequently separated. The naphthenic acids thus produced have a mean molecular weight of the order of 300 which is completely comparable with that of commercially available naphthenic acids such as those f rom Fluka, or Iso Chemie GmbH and can consequently be sold as such or transformed subsequently into esters or metal salts to increase their value.

At the head of the column, the other constituents of the extraction solvent are recovered, viz alcohol, amine, light hydrocarbons (these light C3 to C6 hydrocarbons are carried with the solvent at the time of naphthenate extraction from the crude oil), with, possibly, a small amount of water. These constituents can then be recycled to the neutralization/extraction steps.

The table below gives an example of operating conditions and results with distillation of the extraction solvent. The solvent system is methanol: water: NH3 (92: 7: 1 by weight) exampi e 1 example 2.

Crude oil:solvent volume ratio 5:1 12:1 Temperature (OC) 50 50 % light HC in extraction solvent 3.4 2.6 Distillation temperature (OC) 100 100 Heating time (min) 30 30 TAN of regenerated acids 184 182 % light HC in the naphthenic acids 0.01 0.07 mean mol wt of acids 305 309 Application to all crude oils The invention applies to all crude oils. The nature of the naphthenic acids is specific to one type of crude oil. Thus, Heidrun crude oil, when distilled, concentrates 85% of its acidity in residues, and contains heavy naphthenic acids. Dalia crude oil, on the contrary, concentrates its acidity in light 16 cuts having a boiling point below 4000C. The deacidification process has been tested on Dalia and Heidrun crude oils under the same conditions, i.e. at a temperature of 700C, a crude oil:solvent volume ratio of 1:1 and with methanol:water:NH3 (94.S: 5: 0.5 by wt) as the solvent composition. The results are given in the table below:

Test crude V6 Oil ---- residual TAN ot separated in 1 deacidified minute crude oil Example 1 Dalia 80 0.25 Example 2 Heidrun 100 0.60 Even if the deacidification yield seems slightly less good for Heidrun crude oil, the process of the invention does indeed make it possible to deacidify crude oils containing varying molecular weight naphthenic acids. The deacidified crude oil from Heidrun crude oil could then be washed in order to further reduce the TAN index, in order to obtain a f inal TAN index less than 0. G.

Device implementing the process according to the invention In figure 1, the Dalia crude oil is brought from the source 1, preferably directly at the production field, via conduit 2 to a -desalting unit 3. Desalting is carried out under the following conditions: 14 bars, SOOC, with soft water containing a de-emulsifying additive.

A stabilised crude oil having the specifications given above is obtained at desalted crude oil removal conduit 4. Its temperature is typically 600C.

This stabilised crude oil is sent to primary mixer MI. Mixer Ml can be a static or simple mixing valve or turbine mixer. The stabilised crude oil is mixed with a solvent composition arriving from solvent feed conduit 5. This solvent composition consists, for example, of 85 to 98.5% by weight methanol and preferably 850-. by weight methanol, less than 15% andpreferably less than 11% water, with an amount of ammonia such that the NH3:naphthenic acid molar ratio is from 1:1 to 50: 1. The crude oil:employed solvent volume ratio is comprised between S-1 and 15: 1. The mixing is for example done at a temperature comprised between 17 and 950C and, preferably, between 50 and 900C, and for example at a pressure of 1.105 to 5.10-5 Pa for a time that can be between one second and several minutes.

Mixer MI is preferably a mixing valve.

one could conceive a staged reagents feed, mixing being done at several mixers /extractors (separators). In this case, for example, the amine flow is mixed at primary mixer M1 and the alcohol (with, optionally, water) is mixed at a secondary mixer M'1.

This crude oil:solvent mixture is then decanted into a separator S1. This decantation is for example done at a temperature comprised between 20 and 950C and, preferably, between 50 and 900C, and under a pressure of for example f rom. 10-5 to 5.105 Pa f or a time of from several minutes up to several tens of minutes, generally from 5-15 minutes. The crude oil, now deacidified, of a higher density is drawn off via a deacidified crude oil removal conduit 6, while the lower density naphthenate extraction solvent is drawn off via a naphthenate extract removal conduit 7. This solvent contains water, methanol, ammonium naphthenates, in general ammonia (generally in excess with respect to the acids), as well as, in general, only light hydrocarbons (of the order, for example, of a few percent).

Figure 2 shows the apparatus of Figure 1 with the 18 addition of a supplementary washing unit.

The deacidif ied crude oil is brought, via conduit 6, to a second mixer M2. This second mixer M2 is of the same type as primary mixer M1 and operates under similar conditions. The deacidified crude oil is mixed with water arriving from washing water feed conduit 8. This water is preferably soft water thereby avoiding introducing salts (notably bivalent cation salts) into the deacidified crude oil. The mixture is then decanted into second separator S2. This separator S2 is of the same type as first separator S1 and operates under similar conditions. The washed deacidified crude oil is thus purified of residual methanol and ammonia; the naphthenic acid content is additionally further reduced.

This washed deacidified crude oil is drawn off by washed deacidified crude oil removal conduit 9. It has a methanol content generally less than 0.1% and has a TAN index below 0.6. This deacidified and washed crude oil can optionally be desalted again if its salt content specification was not achieved.

The washing water, charged with methanol and ammonia, is drawn off by washing water removal conduit 10.

Figure 3 shows the device of Figures 1 and 2, with the addition of a unit for recycling components of the 19 solvent mixture.

The naphthenate extraction solvent drawn of f by conduit 7 is sent towards first column C1. This flow can thus be combined with ammonia and methanol-charged washing water drawn of f by a conduit 10 (embodiment shown).

In the column C1, the ammonium naphthenates are thermally decomposed at a temperature of around 1000C into naphthenic acids and ammonia.

The methanol, light hydrocarbons, ammonia and a small amount of water leave the column head via f irst recycle conduit 11, for condensation and recycling towards mixer M1 (and then separator SI).

A mixture of water and naphthenic acids leaves the bottom of column Cl via third separator feed conduit 12.

This mixture of water and naphthenic acids is then separated in a third separator S3, the acids being insoluble in water. The naphthenic acids, being lighter, leave the top portion via naphthenic acids removal conduit 13 and are sent for storage while the water is recycled via second recycle conduit 14 towards mixer MI and/or M2 (here, mixer M2 is shown).

In Figure 4, the device of Figure 3 is shown with the addition of a second recycling column.

The washing water containing a small amount of methanol and ammonia is sent via conduit 10 no longer to column C1 together with the extraction solvent but rather to an independent column C2. In this second column C2, the methanol and ammonia are separated from the water at a temperature of the order of 750C and at atmospheric pressure. The methanol (or a portion thereof) and the ammonia leaving the column head are condensed and introduced, via third recycle conduit 15., at the mid point of column C1 (for example at the level of conduit 7). The water (with, possibly, the remainder of the methanol) leaves the bottom of column C2 and is recycled via fourth recycle conduit 16 to mixer M1 and/or M2 (here, mixer M2 is shown).

The use of the second column C2 for summarily separating the methanol and ammonia from the washing water and directing them towards column C1 gives around a 30% gain in energy balance. one can however perfectly well just use column C1, to which all or part of the fluid transported by line 10 will be directed.

one could also not connect column C2 to column Cl; in this case, the head fraction leaving through conduit is recycled, for example towards mixer M1 by conduit 11.

The invention is not limited to the embodiments described but may be the object of numerous variations accessible to those skilled in the art; for example, a mixture of reagents could be employed.

21

Claims

I. A process for deacidifying crude oils comprising the following steps:

(i) desalting by washing with soft water; (ii) neutralization of naphthenic acids by liquid/liquid mixing with an amine containing 0-6 carbon atoms; (iii) separation of the naphthenates formed at step (ii) by extraction using a solvent comprising a C1 to C6 alcohol; in order to produce a flow of deacidified crude oil and a flow of extraction solvent.
2. A process according to claim 1, in which the neutralization and extraction steps are carried out simultaneously.
3. A process according to claim 1, in which the neutralization and extraction steps consist of a mixing phase immediately followed by a separation phase.
4. A process according to claim 2 or 3, in which the neutralization and extraction steps are carried out with a solvent composition comprising, in percent by weight 22 based on the composition:

from 80 to 98.5% of a C1 to C6 alcohol; from 0.5 to 5% of an amine, containing 0-6 carbon atoms; and from 0 to 15% water.
5. A process according to any one of claims I to 4, in which the crude oil: solvent volume ratio is from 5:1 to 15:1.
6. A process according to any one of claims 1 to 5, in which the amine:acid molar ratio is from 1:1 to 50:1.
7. A process according to any one of claims 1 to 6, in which the temperature of the neutralization and/or extraction step is from 20 to 950C.
8. A process according to claim 7, in which the temperature of the neutralization and/or extraction step is from 50 to 900C.
9. A process according to any one of claims 1 to 8, in which the separation is performed by gravitational decantation and/or by coalescence and/or electrostatically.

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10. A process according to any one of claims 1 to 9, additionally comprising the step of:

(iv) washing deacidified crude oil with water, preferably soft water.
11. A device for deacidifying crude oil comprising:

(i) a desalting unit for said crude oil to give a stabilised crude oil leaving by a desalted crude oil removal conduit; (ii) at least a primary mixer in which stabilised crude oil from said desalted crude oil removal conduit is mixed with an amine containing 0-6 carbon atoms and, optionally, a Cl to C6 alcohol and, optionally, water; and, optionally, a secondary mixer in which the mixture leaving said primary mixer is mixed with a Cl to C6 alcohol and, optionally, water; (iii) a first separator connected to said primary mixer or said secondary mixer from which deacidified crude oil is removed by a deacidified crude oil removal conduit and from which naphthenate extraction solvent is removed by a naphthenate extract removal conduit.
12. A device according to claim 11, comprising:

(ii) a primary mixer in which stabilised crude oil leaving said desalted crude oil removal conduit is mixed 24 with an amine containing 0-6 carbon atoms, a C1 to C6 alcohol and water; wherein (iii) the first separator is directly connected to said primary mixer.
13. A device according to claim 12, additionally comprising:

(iv) a second mixer in which deacidified crude oil leaving said deacidified crude oil removal conduit is mixed with water from a washing water feed conduit; (v) a second separator directly connected to said second mixer from which washed deacidified crude oil is removed by a washed deacidified crude oil removal conduit and from which washing water is removed by a washing water removal conduit.
14. A device according to claim 12 or 13, further comprising:

(vi) a first extraction column fed with the extraction solvent from said naphthenate extract removal conduit and, if appropriate, washing water leaving said washing water removal conduit, from the head of which a mixture is removed by a first recycle conduit and optionally recycled to said primary mixer and from the bottom of which there is removed a mixture containing naphthenic acids and water, by a third separator f eed conduit; (v) a third separator supplied with the mixture leaving said third separator f eed conduit and from the head of which naphthenic acids are removed by a naphthenic acids removal conduit and f rom the bottom of which water is removed by a second recycle conduit, and optionally recycled to said primary mixer and/or said second mixer.
15. A device according to claim 13 or 14, additionally comprising:

(vi) a second extraction column supplied by washing water leaving said washing water removal conduit, from the bottom of which water and, optionally, alcohol is removed by a fourth recycle conduit for optional recycling to the primary mixer and/or the second mixer and f rom the head of which a mixture of alcohol and ainine is removed by a third recycle conduit for optional recycling to said primary mixer, or for delivery to the middle of said first column.
16. A device according to any one of claims 12 to 15, in which the said separator or separators is/are one or a plurality of gravitational decanters or one or a 26 plurality of coalescers, optionally electrostatic.
17. A device according to any one of claims 11 to 16, for carrying out the process according to any one of claims 1 to 10.
18. A solvent composition comprising, by percentage in weight based on said composition:

from 80 to 98.5% of a Cl to C6 alcohol; from 0.5 to 5% of an amine containing 0-6 carbon atoms; and from 0.5 to 15% water.
19. A solvent composition according to claim 18, comprising, in percentage by weight based on said composition:

from 83 to 87% of a C1 to C6 alcohol; from 3.5 to 4.5% of an amine containing 0-6 carbon atoms; and less than 11% water.
20. A solvent composition according to claim 18 or 19, in which the C1 to C6 alcohol is methanol; the amine is ammonia.

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2 1. A method of deacidif ying crude oils substantially as described herein with reference to any one of Figures 1 to 4 of the drawings.
22. Apparatus for deacidifying crude oils substantially as described herein with reference to any one of Figures I to 4 of the drawings.
23. A solvent composition substantially as described 10 herein.