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Title:
METHOD FOR REDUCING AND/OR INHIBITING ALDOL CONDENSATION IN GAS SCRUBBERS
Document Type and Number:
WIPO Patent Application WO/2018/046606
Kind Code:
A1
Abstract:
The present invention relates to the use of at least one ketone as inhibitor for aldol condensation of at least one aldehyde present in a gas scrubbing solution, in particular an acid gas scrubbing solution.

Inventors:
DICKE RENÉ (AT)
REGUILLO CARMONA REBECA (AT)
Application Number:
PCT/EP2017/072481
Publication Date:
March 15, 2018
Filing Date:
September 07, 2017
Export Citation:
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Assignee:
BOREALIS AG (AT)
International Classes:
B01D53/14; C10G53/12; C10G75/04
Domestic Patent References:
WO1996035501A11996-11-14
WO1996037279A11996-11-28
WO1996037279A11996-11-28
WO1996035501A11996-11-14
Foreign References:
US5194143A1993-03-16
US5879534A1999-03-09
CN102872708B2015-05-13
CN102531822B2014-05-21
EP1102063A12001-05-23
US5527447A1996-06-18
Attorney, Agent or Firm:
MAIKOWSKI & NINNEMANN PATENTANWÄLTE PARTNERSCHAFT MBB (DE)
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Claims:
Claims

1 . Use of at least one ketone as inhibitor for aldol condensation of at least one aldehyde present in a gas scrubbing solution, in particular an acid gas scrubbing solution, wherein the at least one ketone is selected from a group of compounds of the general formulae (I)

R1-CO-CHR2R3 wherein the moiety R1 is selected from a group comprising linear or branched C1-C10 alkyl, C3-Cio-cycloalkyl and linear or branched Ci-Cio-alkyl substituted C3-C10- cycloalkyl,,

wherein the moieties R2 and R3 are selected from a group comprising H, linear or branched C1-C10 alkyl, C3-Cio-cycloalkyl and linear or branched Ci-Cio-alkyl substituted C3-Cio-cycloalkyl, and

wherein R1, R2 and R3 can be the same or different, or

wherein R1 and R2 form together a C4-C10 cycloalkyl ring.

2. Use according to claim 1 , characterized in that the moietiy R1, is selected from the group comprising linear or branched C1-C5 alkyl and C3-C7-cycloalkyl, in particular ethyl, propyl, isopropyl, butyl or iso-butyl.

3. Use according to claim 1 and 2, characterized in that, the moieties R2 and R3 are selected from a group comprising H, linear or branched C1-C5 alkyl and C3-C7- cycloalkyl, in particular H, ethyl, propyl, isopropyl, butyl or iso-butyl.

4. Use according to one of the preceding claims, characterized in that the at least one ketone is acetone, butan-2-one, pentan-2-one, pentan-3-one, hexan-2-one, hexan-3- one, 2-methyl-pentan-3-one, 2,2-dimethylpentan-3-one, 3-methyl-butanone, 3,3- dimethyl-butanone, cyclopentanone, cyclohexanone, 2-methyl-cyclohexanone.

5. Use according to one of the preceding claims, characterized in that the at least one aldehyde is at least one low molecular weight aldehyde and/or higher molecular weight aldehydes.

6. Use according to one of the preceding claims, characterized in that the at least one aldehyde is acetaldehyde, propanaldehyde, butanaldehyde, hexanal, heptanal, octanal nonanal and/or decanal.

7. Use according to one of the preceding claims, characterized in that the at least one ketone is used as inhibitor for at least one ester, preferably an ester comprising at least one double bond, in particular preferably at least one vinyl ester.

8. Use according to one of the preceding claims, characterized in that the at least one ketone is added to the gas scrubbing solution in stoichiometric amount in respect to the at least one aldehyde in the gas scrubbing solution.

9. Method for inhibiting aldol condensation of aldehydes, in particular low molecular weight aldehydes, in a gas scrubber solution, in particular an acid gas scrubber solution, characterized in that at least one ketone is fed to the gas scrubbing solution, in particular to the acid gas scrubbing solution.

10. Method according to claim 9, characterized in that the at least one ketone is a ketone as defined in one of the claims 1 -4.

1 1. Method according to claim 9 or 10, characterized in that the at least one ketone is fed to the gas scrubbing solution in a molar amount that is at least substantial the same as the molar amount of the at least one aldehyde in the gas scrubbing solution.

12. Method according to one of the claims 9 to 1 1 , characterized in that the at least one ketone is fed to the gas scrubbing solution in a basic media.

13. Method according to one of the claims 9 to 12, characterized in that the at least one ketone is fed to the gas scrubbing solution in a NaOH containing solution.

14. Method according to one of the claims 9 to 13, characterized in that the at least one ketone is fed at different feeding points to the gas scrubber and/or gas scrubber solution.

Description:
Method for reducing and/or inhibiting aldol condensation in gas scrubbers

The present invention relates to the use of at least one ketone as inhibitor of aldol condensation and a method for reducing and/or inhibiting aldol condensation.

Description

The occurrence of so-called red oil polymers is common for caustic towers in steam cracking units. The primary cause for red oil formation are aldehydes and conjugated vinyl monomers such acetaldehyde and vinyl acetate present in the crack gas. Aldehydes such as acetaldehyde present in the gas feed react with the caustic in the solution via aldol condensation reaction giving rise to the so-called red oil polymer. The chemical mechanism of this reaction is shown below:

The progression of the condensation reaction yields long chain and high molecular weight polymeric molecules. These compounds are called red oils. They have a highly undefined structure and have a yellowish to brownish/red color depending on their molecular weight and double bond system. As the reaction progresses, the color of the solution will become darker until an oily, viscous hydrocarbon liquid phase is produced. If left unchecked, an aldehyde resin material is formed. This is the fouling material that composes deposits found in many acid gas scrubber systems, especially the so called caustic towers. The majority of the red oil formation occurs in the lower section of the caustic tower and can adversely impact the caustic tower operation mostly through deposition of polymers and mechanical blocking - e.g. in the down corner areas and on the trays.

The problems associated with red oil formation in acid gas scrubbers or caustic towers are normally addressed by adding commercial anti-red oil additives. Anti-red oil additives are chemical substances that react with the red oil precursors inhibiting the polymerization reaction. This chemical treatment consists usually but is not limited to an amine or amine derivate. It reacts with the active aldehyde group to form an inert product, generally an oxime. The product (oxime) formed is soluble in water and in caustic solutions, thus, the spent caustic blowdown removes the oxime product from the tower. The chemical reaction between the carbonyl group of acetaldehyde and a typical amine-type carbonyl scavenger is shown below:

This chemical reaction is stoichiometric and requires 1 :1 equivalents of scavenger per acetaldehyde. The predominant anti-red oil additives are usually generic primary, secondary or tertiary amines, although ammonium salts can be also used for this purpose. Commercially available anti-red oil additives are listed below in Table 1.

Formulas Structures

Amines

Primary amines

Monoethanolamine (MEA) H2NCH2CH2OH

Diglycolamine (DGA) H2NCH2CH2OCH2CH2OH

2-amino-2-methyl-1 -

propanol (AMP)

Secondary amines

Diethanolamine (DEA) HN[CH 2 CH 2 OH] 2

Table 1 : Typical anti-red oil products

The use of other kind of additives has also been reported, like Si-based products (EP1 102063 A1 , US 5,527,447) or oxidizing agents such as hydroperoxides or hydrogen peroxide (WO 96/37279 A1 , WO 96/35501 A1 )

The major problems associated with these kind of additives is the interaction of the remaining commercial products with downstream units in the ethylene plant. Although these additives are typically soluble in water, it may occur that when hydrocarbon-water phase separation is not efficient (due to emulsion formations, presence of rag layers, etc) or additive overdose happens (feeding system failure, miscalculation of additive amount, etc), part of these products end up in downstream units where they can cause damage or malfunction (e.g. deactivation of hydrogenation catalysts, additive carried over in the pygas stream recirculated to the primary fractionator, etc.).

Furthermore, the so-formed red oil polymer accumulates in the bottom part of the caustic towers and needs to be removed on a regular basis. A too high amount of formed solid aldol polymer can lead to operational issues for instance due to viscosity increase or mixing issues. Therefore, the operators have to invest additional time for pumping the polymer layer into the downstream vessels. Thus, there is a need for alternative methods for reducing and inhibiting red oil formation in a gas scrubber, in particular in an acid gas scrubber.

The object of the present invention is to provide an alternative method for reducing and/or inhibiting red oil formation in a gas scrubber.

This object is being solved by the use of at least one ketone according to claim 1 and a method for inhibiting and/or reducing aldol condensation in a gas scrubber according to claim 8. Accordingly, at least one ketone is used as an inhibitor for aldol condensation of at least one aldehyde present in a gas scrubbing solution, in particular an acid gas scrubbing solution in a gas scrubber.

According to the invention, the at least one ketone applied as inhibitor for aldol condensation comprises the structural unit -CO-CH-. Thus, the ketone used as red oil inhibitor comprises at least one H-atom on the ocarbon atom to the carbonyl group.

The at least one ketone is selected from a group of compounds of the general formulae (I) R 1 -CO-CHR 2 R 3 wherein the moiety R 1 is selected from a group comprising linear or branched C1-C10 alkyl, C3-Cio-cycloalkyl and linear or branched Ci-Cio-alkyl substituted C3-Cio-cycloalkyl, wherein the moieties R 2 and R 3 are selected from a group comprising H, linear or branched C1-C10 alkyl, C3-Cio-cycloalkyl and linear or branched Ci-Cio-alkyl substituted C3- Cio-cycloalkyl, and

wherein R 1 , R 2 and R 3 can be the same or different, or

wherein R 1 and R 2 form together a C4-C10 cycloalkyl ring. The linear or branched Ci-Cio-alkyl, C3-Cio-cycloalkyl, Ci-Cio-alkylsubstituted C3-C10- cycloalkyl may be in each case interrupted by one or multiple oxygen atoms, sulphur atoms and/or substituted nitrogen atoms and/or by one or multiple groups of the type -C(0)0-, - OC(O)-, -C(O)- and/or -OC(0)0- and/or can be functionalized by one or multiple hydroxyl groups, amino groups, in particular primary amino groups or secondary amino groups, mercapto groups and/or halids, in particular CI or Br. It is to be understood that acetoacetyl is exempted from that list. It is also to be understood that none of the moieties R 1 , R 2 , R 3 comprises an aryl moiety, in particular R 1 does not comprises an aryl moiety and therefore ketones such as benzophenone, acetophenone and alike are not included, also not as part of a mixture. Besides, the water solubility of ketones like benzophenone and acetophenone is too low for use in a water phase of any scrubber.

The use of ketones according to formulae (I) as inhibitor of aldol condensation in gas scrubbing solutions has several advantages: Ketones like acetone are soluble in water and solvent phase and can react with formed redoil oligomers in both phases; If ketones are reacting with redoil oligomers, the formed blocked redoil compounds stays soluble in the reactors and can be easily further transported to next vessels; ketones like acetone help to reduce foaming and other issues, like rag layer formation, in downstream units.

In a further embodiment the moieties R 1 , R 2 and R 3 are selected from the group comprising H (in case of R 2 and R 3 ), linear or branched C1-C5 alkyl and C3-C7-cycloalkyl. The moieties R 1 , R 2 and R 3 are in particular selected from a group comprising H (in case of R 2 and R 3 ), ethyl, propyl, isopropyl, butyl or / ' so-butyl.

In a yet further embodiment the moieties R 1 , R 2 and R 3 are selected from the group of linear or branched C1-C5 alkyl and C3-C7-cycloalkyl substituted with at least one hydroxy group or at least one amino group, in particular at least one primary amino group or secondary amino group, such as hydroxy-C1 -C3, (monoethylamino)-C1 -C3,(diethylamino)-C1 -C3.

In another embodiment the moieties R 1 and R 2 or R 1 and R 3 are part of a Cs-Cs cyclic ring system. Thus, in this case a cyclic ketone is used as inhibitor.

In a most preferred embodiment the at least one ketone is acetone, butan-2-one, pentan-2- one, pentan-3-one, hexan-2-one, hexan-3-one, 2-methyl-pentan-3-one, 2,2-dimethylpentan-3- one, 3-methyl-butanone, 3,3-dimethyl-butanone, cyclopentanone, cyclohexanone, 2-methyl- cyclohexanone, hydroxyacetone, 4-hydroxy-butan-2-one, (diethylamino)-acetone, (monoethylamino)-acetone, (monomethyl)-acetone.

In a further embodiment a mixture comprising at least two ketones according to general formula (I) may be used. It is in particular preferred if a mixture comprising a water soluble ketone and a ketone with a reduced water solubility and increased solubility in hydrocarbons (or certain hydrocarbon soluble property) is used. Such a mixture of ketones with different solubilities allows the inhibition of red-oil formation not only in a aldehyde monomer containing water phase but also in the hydrocarbon phase comprising soluble red-oil oligomers / polymers, where other ketones containing the moiety -CO-CHR- can also been solubilized, and fouling reaction stopped. Such an inhibitor formulation is in particular suitable for flexible crackers, where hydrocarbon phase (and therefore aldehydes and oxygenate groups) is constantly changing regarding composition, aromaticity, aliphatic character etc. Furthermore, this allows for a tailor-made formulation of aldol-condensation inhibitor according to the specific needs and solubility requirements of the water and hydrocarbon phases in the acid gas scrubber.

In one embodiment a mixture comprising acetone and at least one of the ketones selected from the group comprising

- aliphatic ketones such as butan-2-one, pentan-2-one, pentan-3-one, hexan-2-one, hexan-3-one, 2-methyl-pentan-3-one, 2,2-dimethylpentan-3-one, 3-methyl-butanone, 3,3- dimethyl-butanone, cyclopentanone, cyclohexanone, 2-methyl-cyclohexanone, hydroxyacetone, 4-hydroxy-butan-2-one, (diethylamino)-acetone, (monoethylamino)-acetone, (monomethyl)-acetone, ;

- ketones containing a double bond in at least one of their R groups, such as 5-hexen- 2-one, 5-methyl-5-hexen-2-one, 1 ,8-nonadien-5-one,

- ketones containing conjugated double bonds in at least one of their R groups, such as 1 -acetyl-1 -cyclohexene, beta-ionone, 3-buten-2-one,4-(1 -cyclohexen-1 -yl)-, pseudoionone;

- ketones containing heteroatoms such as 2-acetylpyrrole, 2-acetyl-1 -methylpyrrole, 4- (3,4-dimethyl-1 H-pyrrol-2-yl)-3-buten-2-oneis provided. The preferred mixtures comprise acetone as the first ketone and butan-2-one and/or 5-hexen- 2-one and/or beta-ionone and/or 2-acetylpyrrole as the second ketone. The most preferred mixtures are acetone / buntan-2-one, acetone / 5-hexen-2-one, acetone / beta-ionone, acetone / 2-acetylpyrrole. In a further embodiment the at least one aldehyde causing the red oil formation is at least one low molecular weight aldehyde, in particular acetaldehyde, propanaldehyde, butanaldehyde, or a higher molecular weight aldehydes, preferably hexanal, heptanal, octanal nonanal, decanal, and/or C15-C20 aldehydes. Esters compounds, in particular unsaturated ester compounds, may also cause or may be involved in red oil formation. Typical esters are for example compounds comprising at least one double bound that is preferably in conjugation to the -CO- group. Such ester may be arise from the reaction of an olefin and the corresponding acid, such as ethylene and acetic acid. A preferred ester is a conjugated vinyl monomer, such as vinyl acetate.

The aldol condensation reaction, which leads to the red oil formation, takes place by self- condensation of aldehydes, ketones and/or unsaturated esters In order to initiate the aldol condensation reaction in basic media the presence of a hydrogen atom in oposition to the carbonyl group is required:

The first step of the aldol condensation reaction takes place by condensation through the methylene group in a- position to the carbonyl group of one aldehyde with the aldol group of another aldehyde molecule:

For the red oil polymer to be formed, the aldol condensation proceeds by reaction of the remaining aldehyde with the aldol groups of the intermediate products:

When a ketone, such as acetone is present, the aldol condensation reaction cannot proceed further after the first reaction step due to the fact that the resultant intermediate product is a ketone and not an aldehyde: further reaction possible

In this way, by the presence of a ketone, such as acetone in the reaction mixture, a major part of the aldehyde, such as acetaldehyde molecules will be compromised in the reaction with acetone, and will not be available for further reaction to produce long-chain red oil polymer. This will be translated in a low to none formation of red oil polymer in the reaction media.

As mentioned above, the use of acetone as inhibiting agent is particularly preferred since acetone is highly soluble in water. Thus, a carry over with the hydrocarbon phase is very unlikely. In addition to that, it has less impact in downstream units than other additives (e.g. less to no harm to catalysts or primary fractionator). In particular the possibility of influencing downstream units is an advantage of using ketons like acetone, because foaming and rag- layer formation can be suppressed. Furthermore, acetone can be used as anti- red oil additive and depending on the fed amount of acetone the chain length of the aldol polymer can be regulated so that probably the foaming tendency is influenced positively.

Additionally, by controlling the chain length of the red oil polymer the viscosity of the processed solution can be controlled, so that an operator can manage the process more efficiently. The object of the invention is also solved by a method for reducing and/or inhibiting aldol condensation of aldehydes, in particular low molecular weight aldehydes, in a gas scrubber solution, in particular an acid gas scrubber solution (caustic towers), wherein at least one ketone is fed to the gas scrubbing solution, in particular to the acid gas scrubbing solution. The at least one ketone used in the present method is a ketone as defined previously.

In a further embodiment the at least one ketone as inhibitor for aldol condensation can be used as mixture with other process additives like anti-red-oil agents, anti-oxidants, or antifoaming agents.

In an embodiment of the present method the at least one ketone is fed to the gas scrubbing solution in a molar amount that is at least substantial the same as the molar amount of the at least one aldehyde in the gas scrubbing solution. Thus, the amount of the at least one ketone added to the gas scrubber solution should be sufficient to inhibit the aldol condensation of the at least one aldehyde.

In a variant the at least one ketone is fed to the gas scrubbing solution in a basic media. In particular, the at least one ketone is fed to the gas scrubbing solution in a NaOH containing solution.

In a further embodiment of the present method the at least one ketone is fed at different feeding points to the gas scrubber and/or gas scrubber solution. It is possible that the at least ketone as red oil inhibitor can be injected in the caustic tower through different feeding lines at multiple different points.

In a first variant the at least one ketone is fed into the fresh caustic stream that is subsequently fed to the caustic tower.

In a second variant the at least one ketone is fed into one or more of the recirculating caustic lines of the different sections in the caustic tower.

There may be one feeding point for the at least one ketone at one line or multiple feeding points at multiple lines transporting the recirculating caustic from different sections of the caustic tower. For example, there may be at least one feeding point for the at least one ketone at the line for recirculation the caustic compound from and into the lower section of the caustic tower. There also may be at least one feeding point for the at least one ketone at the line for recirculation the caustic compound from and into the middle and/or upper section of the caustic tower.

In yet a third further variant the at least one ketone is fed into the feed line of the hydrocarbon product entering the caustic tower. In general a combination of two or all feeding variants is also possible and conceivable.

The present invention is explained in more detail in the following examples with reference to the figures. It shows: Figure 1 a process scheme of a scrubber unit; and Figure 2 a diagram showing comparative experimental results.

In the general scheme of Figure 1 a scrubber unit with a caustic tower 10 is illustrated. The scheme depicts the gas scrubber (caustic tower) as part of the refinery section.

In an embodiment of the present method the at least ketone as red oil inhibitor can be injected in the caustic tower through a feeding line at multiple different points 1 , 2, 3. The first feeding point 1 for the red oil formation inhibitor, such as acetone, is provided at a suitable location along the feeding line for the fresh caustic stream fed from the fresh caustic storage 1 1 to the caustic tower. Here the inhibitor is directly fed into the fresh caustic stream that is subsequently fed to the caustic tower 10. The second feeding point 2 for the red oil inhibitor may be provided at any suitable location of one or more recirculating caustic lines. There may one feeding point at one or multiple feeding points at multiple lines transporting the recirculating caustic from different sections of the caustic tower. One second feeding point 2a for the inhibitor is provided at the line for recirculation the caustic compound from and into the lower section 10a of the caustic tower 10. Further second feeding points 2b, c for the inhibitor may be located at the line for recirculation the caustic compound from and into the middle and/or upper section of the caustic tower 10 b,c. The third feeding point 3 for the inhibitor is provided at the line for the hydrocarbon feed (such as ethylene) into the caustic tower 10. In particular, the inhibitor is fed into the hydrocarbon feed coming from the compressor 12 and preheater 13, i.e. after compressor 12 and preheater

13.

A combination of the different feeding points 1 -3 is also possible. Example: a) Test method The test method ASTM D1500 covers the visual determination of the colour of a wide variety of petroleum products, such as lubricating oils, heating oils, diesel fuel oils, and petroleum waxes. Using a standard light source, a liquid sample is placed in the test container (e.g. a standard UV-vis cuvette) and optically compared with colour standards, ranging in value from 0.5 to 8.0 ( see Table 2).

Chromaficlty Coordinates' 1 Luminous Trans-

ASTM {RGB USC system)" miftance (CIEF C

Color Standard Source C)

Red Green Blue r,„

0.5 0,482 0.473 0.065 0,86 ± 0.06

1.0 0.489 0.475 0.036 0.77 ± 0,06

1 ,5 0.521 0.464 0.015 0.67 ± 0.06

2.0 0,552 0.442 0.006 0,55 ± 0.06

2.5 0.582 0,416 0.002 0.44 ± 0.04

3.0 0.611 0,388 0.001 0.31 ± 0.04

3.5 0.640 0.359 0.001 0.22 ± 0.04

4.0 0.671 0.328 0.001 0,152 ± 0.022

4.5 0.703 0.296 0,000 0.109 ± 0.018

5.0 0.736 0.264 0.000 0.081 ± 0.012

5.5 0,770 0,230 0,000 0,058 * 0.010

6.0 0,805 0.195 0,000 0,040 ± 0,008

6.5 0.841 0.159 0.000 0 026 ± 0 006

7.0 0.877 0.123 0,000 0,016 ± 0.004

7.5 0.915 0.085 0.000 0.0081 ± 0.0016

8.0 0.956 0.044 0,000 0.0025 ± 0,0006

Λ Tolerances on the chromaticity coordinates are ±0.008.

° Judd, D. B.. "A Maxwell Triangle Yielding Uniform Chrornaticity Scales, ' * Journal of Research of the National Bureau of Standards, Vol 14, 1935, p. 41 , (HP 758);

Journal of the Optical Society of America, Vol 25, 1935, p. 24,

c Commission Internationale de t'Echairage {International Commission on

Illumination).

Table 2: ASTM D1500 colour standards.

The comparison with the standards can be made automatically by using software tools compatible with lab scale spectrophotometers. For these tests, IPT has used the Spectrophotometer ColorLite sph850, a color measuring instrument suitable for a wide range of applications. The software controlling the equipment gives the colour difference to the standards specified in ASTM D1500 (see Table 2).

For the purpose of these experiments, this method has been used for the monitoring the polymerization reaction of acetaldehyde in basic aqueous media. This reaction is a model for the study of red oil formation in acid gas scrubbers in cracker plants. As the polymerization reaction progresses, the colour of the solution will evolve from colourless to yellow and finally to red/brown. The solutions are often turbid due to the dispersion of the polymers in the liquid phase. The final colour will depend on the red oil's molecular weight and chemical structure. If the reaction is left unattended for several weeks, an aldehyde resin (solid) material is finally formed. b) Sample preparation

In order to prove the validity of the method, a calibration curve of the concentration of red oil against the ASTM D1500 values was done. A known amount of dry red oil residue (5 g) from a steam cracker was diluted until saturation in 250 mL of toluene. Several dilutions of these solutions were then used to obtain the colorimetric data according to ASTM D1500 (see Table 3).

Table 1 : Red oil concentration vs. ASTM D1500 colour value c) Experimental results: Acetone inhibited vs non inhibited solution Experiments were done preparing three batch solutions of 500 mL of NaOH at 8 wt% in distilled water. The first solution was kept as blank.

The second solution (uninhibited solution, i.e. without the addition of any inhibitor) was prepared by adding to the blank solution 1000 ppm (0.1 wt%) acetaldehyde. The third solution (acetone inhibited solution; i.e. acetone was added as inhibitor) was prepared by adding to the blank solution 1000 ppm (0.1 wt%) acetaldehyde and the same weight equivalent acetone, 1000 ppm (0.1 wt%).

The three batch samples were allowed to stand without stirring at room temperature during the whole experiment time. Samples from each of these batches were taken once per day during at least ten days for their colour analysis according to ASTM D1500. The colour of each sample was evaluated according to ASTM D1500 - Standard Test Method for ASTM Color of Petroleum Products (ASTM Color Scale).

The measured results are shown in Table 4:

* 8 wt% NaOH in distilled water; ** 8 wt% NaOH, 0.1 wt% acetaldehyde in distilled water; *** 8 wt% NaOH, 0.1 wt% acetaldehyde, 0.1 wt% acetone in distilled water . Samples stored at RT.

Table 4: Colour scale values of solutions based on ASTM D 1500

The colour test results according to ASTM D 1500 are shown in the diagram of Fehler! Verweisquelle konnte nicht gefunden werden.2. In addition, illustrative pictures of the visual appearance of the solutions on selected days are also shown. The results show clearly that the addition of acetone effectively decreases the red oil polymer formation. d) Experimental results: Acetone vs commercial red oil inhibitor

Experiments with and without red oil inhibitor (an ammonium sulfate was used here) were done preparing three batch solutions of 500 ml. of NaOH at 8 wt% in distilled water.

The first solution (uninhibited solution) was prepared by adding to the first batch solution 1000 ppm (0.1 wt%) of acetaldehyde (red oil precursor). The second solution (commercial inhibitor solution) was prepared by adding to the third batch solution 1000 ppm (0.1 wt%) of acetaldehyde (red oil precursor) and the same weight equivalent of a commercial inhibitor for this specific application, 1000 ppm (0.1 wt%; red oil inhibitor).The third solution (acetone inhibited solution) was prepared by adding to the second batch solution 1000 ppm (0.1 wt%) of acetaldehyde (red oil precursor) and the same weight equivalent of acetone, 1000 ppm (0.1 wt%; red oil inhibitor). The three samples were allowed to stand without stirring at room temperature during the whole experiment time. Samples from each of these batches were taken once per day during at least seven days for their colour analysis according to ASTM D1500. The colour of each sample was evaluated according to ASTM D1500 - Standard Test Method for ASTM Color of Petroleum Products (ASTM Color Scale).

The measured results are shown in *8 wt% NaOH in distilled water ; ** 8 wt% NaOH, 0.1 wt% acetaldehyde in distilled water; *** 8 wt% NaOH, 0.1 wt% acetaldehyde, 0.1 wt% acetone in distilled water . Samples stored at RT.

Table 5:

* 8 wt% NaOH, 0.1 wt% acetaldehyde in distilled water; ** 8 wt% NaOH, 0.1 wt% acetaldehyde, 0.1 wt% commercial additive in distilled water ** 8 wt% NaOH, 0.1 wt% acetaldehyde, 0.1 wt% acetone in distilled water. Samples stored at RT.

Table 5: Colour scale values of solutions based on ASTM D1500