CA1329164C - Method for controlling fouling in fcc slurry loop - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

FCC slurry compositions have a tendency to foul during heat exchange processes. Treatment of these slurries with a combination of a Mannich reaction product, a polyalkenylthio phosphonic acid compound and a succinic acid-polyamine reaction product provided significant improvement in the fouling rates.

Description

132ql64 F~565 METHOD FOR CONTROLLING
FOULING IN FCC SLURRY LOOP

.

~ACKGROUND OF THE INVENTION

Th;s invention relates to a method of controlling fouling ' 5 in a FCC Slurry Loop and FCC Main Fractionator Bottoms.
, The Fluid Catalytic Cracking IFCC) Unit is one of the most , important refinery operating units. These units, common to mostsl refiner~es, experience process side fouling which affects operations and reduces operating profît. In most FCC Units, the slurry loop has historically been the most severe fouling system in the unit.
Factors which affect fouling in the slurry system include feed composition, main fractionator bottoms temperature, slurry system viscosity, the slurry settling system, and catalyst loading.

In the processing of petroleum hydrocarbons and feedstocks such as petroleum processing intermediates, e.g., gasZ oils and .~ reformer stocks, the hydrocarbons are commonly heated to temperatures of 100 to 1000F. Similarly, such petroleum hydrocarbons are frequently employed as heating ~ediums on the "hot side" of heating and heat exchange systems. In both instances, the ~jr ,, . ~ 1, . . . . . . .

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petroleum hydrocarbon liquids are subjected to elevated temperatures which produce a separate phase known as fouling deposits, within the petroleum hydrocarbon. In all cases, these deposits are undesirable by-products. In many processes, the deposits reduce the bore of conduits and vessels to impede process throughput, impair thermal transfer, and clog filter screens, valves and traps. In the case of heat exchange systems, the deposits form an insulating layer upon the available surfaces to restrict heat transfer and necessitate frequent shut-downs for cleaning. Moreover these deposits reduce throughput, which of course, results in a loss of capacity with a drastic effect in the yield of finished product. Accordingly, these deposits have caused considerable concern to the industry.

~ hile the nature of the foreqoing deposits defies precise analysis, they appear to contain a combination of carbonaceous phases which are coke-like in nature, polymers or condensates formed ; from the petroleum hydrocarbons or impurities present therein and salt formations which are primarily composed of magnesium, calcium and sodium chloride salts. The catalysis of such condensates has been attributed to metal compounds such as copper or iron which are present as impurities. For example, such metals may accelerate the , hydrocarbon oxidation rate by promoting degenerative chain , branching, and the resultant free radicals may initiate oxidation 1 and polymerization reactions which form gums and sediments. It -~ further appears that the relatively inert carbonaceous deposits areentrained by the more adherent condensates or polymers to thereby contribute to the insulating or thermal opacifying effect.

'i Historically, the major area of fouling within the Fluid Catalytic Cracking Unit is the main fractionator bottoms and the slurry loop. Attempts to reduce this fouling have included , ~ . .
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! mechanical changes, operational changes, and chemical treatment.
Often, these have met with limited success. Factors which have an effect on the slurry fouling within this system would include the stream properties, main fractionator bottoms temperature, catalyst loadinq, velocity, and viscosity.

Slurry properties and composition are greatly dependent upon the feedstock processed in the unit, the type of catalyst used, and the severity of the cracking operation. Feedstock to the FCC
Unit may consist of heavy gas oils, vacuum gas oils, and residuum.
These feedstocks may or may not be hydrotreated, which greatly affects the unit operation. It has been shown that hydrotreated feedstocks generalty are less prone to cause fouling in the slurry , system due to better conversion, lower Conradson carbon, and reduced ' metals content. It is known that when resids are charged to the un;t, fouling in the slurry loop will increase. Usually, the higher the resid feedrate, the greater the fouling tendency in the system.
Resids are much higher in solids and in asphaltene levels which are both primary contributors to a feedstock fouling tendency.
,., l Catalyst types, which are the commonly used zeolites:,i3 20 either as such or modified, also seem to affect fouling in the slurry loop - especially when cracking residuum. Higher activity catalysts will generally crack heavier molecules more efficiently, thereby reducing the amount of slurry yield, increasing the gravity and the solids loading in the main fractionator bottoms and, in ~`~ 25 turn, increasing the fouling tendency.

j The FCCU main fractionator bottoms temperature is usually controlled between 650 and 700F in order to maintain optimum product separation and to reduce coking in the fractionator~ The . s ,, ~, ' : . , :' , ~. ~
~:', ~ ~ .; ' -t'~ ' ~ ~, . ' ' ' t 3~ 1 64 ma~ior method of controlling this temperature is by cooled slurry recycle. Therefore, it is most important to maintain a clean slurry exchanger system. As the slurry recycle temperature increases, the bottoms temperature also increases promoting a greater fouling rate in the slurry system which further increases the column temperature and reduces production rates. A major method of cooling the slurry is by generating steam where the heat from the slurry (650-700 F) heats the water to ~roduce the steam, thereby in turn effectively cooling the slurry.

ln In the process relating to the slurry loop, FCC reactor vapors which are being discharged from the FCC unit are introduced into a fractionating column. The vapors are composed of a wide range of hydrocarbons from the light fractions represented by methane, ethane, ethylene and the like to the heavy fractions such as the high molecular weight aromatics.

In the fractionating column the heaviest components of the mixture condense and are withdrawn from the fractionator. Since the temperature of the condensed heavy fraction is still quite high9 the fraction, which itself must be cooled for storage or transportation, is used as a heat source in process heat exchangers, reboilersy steam generators and the like. As is apparent, the system of utilizing residual heat of the heavy fraction improves the economies ' and operations production efficiencies.

However, it appears ~hat because the mixture is composed . ~5 of the very heavy fractions in combination with the residual unremoved FCC catalyst, there is a tendency for fouling to occur.

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~ 5 --' , In the past, additives and different chemistries including .~ two of the ingredients of the present invent;on have been utilized with varying degrees of success in treatin~ heavy hydrocarbon FCC
slurry mixtures after the fractionators (distillation columns).
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As will be established by the following case studies, topping ~he combination treatment with the third component provided I~ much superior run times.

; DESCRIPTION OF THE INVENTION

The present inventor discovered that if the high molecular ' 10 wei~ht hydrocarbon - FCC catal~yst slurry was treated with a cnmbination of reaction products after or during removal from the fractionator, that fouling and deposition could be controlled to an `? acceptable degree.

The treatment combination is comprised of three reaction products tProducts I, II, and III~ which are described and prepared ~s follows.

Product I is a Mannich-type product formed via reaction of :
the reactants tA), (B), and (C); wherein (A) is an alkyl substituted ~;, phenol of the structure ` 20 OH FORMULA (A) ,~ I .
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where;n R and Rl are the same or different and are ;ndependently selected from alkyl, aryl, alkaryl, or aralkyl of From about 1 to 20 carbon atoms, x is O or l; wherein (B) is a polyamine ` of the structure H2N(CH-(CH2)y ~CH-NH)z -H FORMULA (B) wherein z is a positive integer, R2 and R3 may be the same or different and are independently selected from H, alkyl, aryl, ~, 10 aralkyl, or alkaryl hav~ng from 1 to 20 carbon atoms, y may be O or l; and wherein (C) is an aldehyde of the structure `J
o FORMULA (C) ,~,~ 11 wherein R~ is selected from hydrogen and alkyl having from 1 to 6 carbon atoms.
, As to exemplary compounds falling within the scope of Formula A supra, p-cresol, 4-ethylphenol, 4-t-butylphenol~

4-t-amylphenol, 4-t-octylphenol, 4-dodecylphenol, 2,4-di-t-butylphenol, 2,4-di-t-amylphenol, and 4-nonylphenol may be :~ mentioned. ~t present, it is preferred to use 4-nonylphenol as the ;J Formula A component.
'1 Exemplary polyamines which can be used in accordance with Formula B include ethylenediamine, propylenediamine, diethylene-triamine, triethylenetetramine, tetraethylenepentamine and the like,with ethylenediamine being preferred.
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132ql64 The aldehyde component can comprise, for example formaldehye, acetaldehyde, propionaldehyde, butyraldehyde, hexaldehyde, heptaldehyde, etc. with the most preferred being formaladehyde which may be used in its monomeric form, or, more conveniently, in its polymeric form (;.e., paraformaldehyde).

As is conventional in the art, the condensation reaction may proceed at temperatures from about 50 to 200C, with a preferred temperature range being about 75-175 C. As is stated in ! U S. Pat. No. 4,166,726, the t;me required for completion of the reaction usually varies from about 1-8 hours, varying of course with the specific reactants chosen and the reaction temperature.

As to the molar range of components (A):(B):(C) which may be used, this may fall within 0.5-5:1:0.5-5.

Product I, which is described and taught as a transition 15 metal deacti~ator in U.S. Patent No. 4,749,468, the Specific Embodiment which follows, was prepared utilizing molar ratios of 2:1:2 of p-nonylphenol, ethylenediamine and formaldehyde.
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Product II is a polyalkenylthiophosphonic acid rompound or alcohol/polyglycol esters thereof. The methods of preparation of ~0 these type compounds are described in U.S. Patents 3,281,359;
4,578,178; and 4,775,458 the latter of which also establishes the use of the compounds as antifoulnts.
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As is expressed in the patents, the polyalkenyl-P2Ss reaction products may be prepared by reacting alkenyl polymers such as polyethylene, polypropylene, polyisopropylene, polyisobutylene, ~' . .
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polybutene or copolymers comprising such alkenyl repeat unit moieties with P2Ss (at about 5-40 wt. percent of the reaction mass) at a temperature of from about 100 to about 320 C in the presence of between about 0.1-5.0 wt. percent sulfur.

The resulting reaction mixture ;s then diluted with mineral oil and is then steam hydrolyzed. If desired, the hydrolyzed polyalkenyl-P2Ss reaction product may then be esterified~
by further reaction with lower alkyl lCl-C5) alcohols such as methanol, ethanol, propanol, butanol, etc. or with a polyglycol such ln as hexylene glycol or pentaerythritol.
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As the '359 patent states, it is highly desirable to employ, as a precursor material, an alkenyl polymer having an averaqe molecular weight of between about 600 and 5,000.

The reaction product preferred for use is the 15 pentaerythritol ester of polyisobutenylthiophosphonic acid which was used in the Specific Embodiments and use studies below. This particular ester is com~ercially available and is hereinafter referred to as PETPA. The polyisobutenyl moiety of PETPA has been reported as having an average molecular weight of about 1300. The , 20 product is sold as a 40 vol 7O solution in mineral oil. It has a J specific gravity of 0.92 at 60F, and a viscosity of 63.9 CST at } 210 F
;l, PETPA is prepared by mixing polyisobutene (average molecular weight of 750-2000) with P2Ss (po1ybutene-P2Ss molar ratio of 0.9-1.25) in the presence of sulfur at 300-600F until the reaction product is soluble in n-pentane. The product is di luted with paraffin base distillate, steamed for 4-10 hours at 350-375F~

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g then dried with N2 at 350-375F. The product is extracted with 50-100~0 by volume of methanol at 75-150F to leave a lubricating oil raffinate containing a polyisobutenylthiophosphonic acid. This material is reacted with pentaerythritol to yield PETPA.

Product III is an alkyl or alkenyl substituted succinimide which is prepared by reacting a substituted succinic anhydride having the following formula:

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Rs - CH - CH2 or a substituted succinic acid having the following formula:

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t Rs - CH - CH2 in which Rs is an alkyl or alkenyl radical having from 30 to ~00 carbon atoms in the carbon chain with a polyamine of the formula:

' 20 H2N - (CnH2n - N~m H
H

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in which n is an integer between 2 and 10 inclusive, m is an integer between 1 and 10 inclusive, and CnH2n is a straight chain hydrocarbon group.

' 5 In the above reaction, from 1/2 to 2 chemical equivalents ; of polyamine are used for 1 chemical equivalent of succinic compound.

The preferred Product III is obtained by reaction of triethylenetetramine with polyisobutenyl succinic anhydride. This product was incorporated in the formulation tested in the Specific ;~10 Embodiment, The preparation and use of Product III type compounds ~'as antifoulants are described in U.S. Patent No.'s 3,271,295 and j 3,271,296.

;The combination product of the invention may be dispersed ¦within the petroleum hydrocarbon slurry within the range of about 0.5-10,000 ppm based upon one million parts hydrocarbon slurry.
Preferablv, the product is added in an amount of from about 1 to 500 ppm.

The exact combination of the specific ingredients and the A,~ effective dosage rates for the combination product will depend upon ~-20 the severity of the fouling problem. The relative weight ratios of ~- Products I to II to III which would appear to be effective are 6:1:12 to 40:12:1.

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As earlier indicated, both Product II and Product III have heen used ;ndependently and in co~binat;on ;n FCC hydrocarbon slurry applications as a dispersant or antifoulant, with minor success being experienced in each instance.

SPECIFIC EMBODIMENTS

The treatment as specified below was tested in accordance with the test procedure, set forth to establish the fouling inhibitory capacity of the inventive mixture.

Pressurized Hot Filament Fouling Test A weighed nickel chromium wire was suspended between two electrodes in an autoclave. 500 mL of FCC slurry and the appropriate amount of treatment was added to the vessel. Stirring was started, the vessel was pressurized with nitrogen and a current of 10 amps was applied across the wire for 24 hours. The wire was then removed, washed, dried and weighed.

FCC SLURRY FOULING RESULTS

Treatment Deposit Weight (mg) ~ l None (Blank*) 92 (average~

i 2 Inventive Treament: 10 , , 20 250 ppm comprised of 40qo '; weight active Product I
~ ~100 npm active) : ,, .

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Treatment Deposit Weight (mg) and 750 ppm of a combination comprised of 19% weight active Product III (142,5 ppm active) and 1.8X weight active Product II
~13.5 ppm active)**

3 None (~lank ~ 2-1/2 wt. ~ 395 spent catalyst) 10 * ~lank slurry contained 49.7 lb. of zeolite catalyst per thousand BBL of Hydrocarbon ** weight ratio of Products I:II:III=8:1:12 Case History No. 1 Fouling in the FCC slurry loop of a Texas refinery became 15 so severe that exchanaer run lengths were reduced to 2-3 weeks.
~ecause of this fouling problem, a Composition X was fed to determine whether the heat exchanger run lengths could be increased. Composition X, which was a 2570 by weight Product II
(earlier described) in 75% solvent was fed at a level of 200 ppm to ' 20 the slurry. The treatment resulted in a doubling of exchanger run¦ lengths (4-6 weeks) between cleanin~s.

j Since the first treatment was considered to be successful~ to a degree, the refinery agreed to the treatment of the slurry I system with another composition, Composition Y, to see whether even 25 longer run lengths were possible. Composition Y, which was a combination of 19% by weight Product III and 1.8% by weight Product remainder solven~) was fed at 200 ppm to the slurry.
Performance with the treatment using Composition Y was essentially the same as that obtained with Composition X.

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1 32q 1 64 Again, in order to establish whether run lengths could be lengthened, the refinery agreed to a third evaluation. However, iprior to the third evaluation, several slurry characterizations were made to establish what mechanisms could be involved which might be resulting in the shortened run lengths. The characterizations of the slurry follow.

Although it was not clear just what phenomena which might be occurring to establish the fouling problem3 it was decided that perhaps the addit;on of a third component to the treatment might have some effect. At that time, Product I in the form of Composition Z ~40~ by weight Product I with 60~o solvent) was used at `I50 ppm to the slurry in con~iunction with Composition Y at 200 ppm.
(Molar ratio of Product I to Product II to Product III was 6:1:12).

The results of the treatment with Compositions Y and Z
were and have been quite unexpectedly excellent with run lengths extended from 4-6 weeks to over 40 weeks with no exchanger cleanings necessary as a result of slurry foulings. Refinery personnel have been quite pleased with the results of the evaluation and are currently purchasing the combination treatment.

Case History No. 2 ., ~!FCC slurry fouling at another Texas refinery caused significant losses in exchanger heat transfer efficiency. Heat exchange losses in two key exchanger bundles were 0.55 BTU/hr./ft2/
F. Because of the prior experience as described in the foregoing ,15 Case History No. 1, the slurry was characterized and it was decided to again treat the system with a combination of Composition Y and Z. In this instance Composition Y was fed at 150 ppm to the slurry ,!

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with 100 ~p~ of Composition Z Performance of the treatment was considered satisfactory by refinery personnel since the U-Coefficient decline was reduced to 0.14 BTU/hr/ft2/F. It was believed that most of the decline in heat transfer efficiency was ;5 related to fouling on the untreated side of the exchanger. The -molar ratio of Product I~ III for combination treatment was 16:1:12.

It is apparent from the foregoing that the three component system ~ and Y or (I, II, and III) was quite superior in performance over Compositions X or Y (the use and sale of both of which occurred more than one year from the filing date of this application).

The characterization of the slurries used for the laboratory testing and the case studies appear hereinafter.

While the compositions representing the inventive treatment were fed independently for a while, a composition containin~ the three ingredients was also fed.
.
~, ` PETROLEUM ANALYSIS REPORT
`~ Description: Laboratory Hot Wire Test :1 FCC Sl urry Filterable solids, ptb 49.7 Bromine No. 31.5 Ash, wt YD 0.03 API gravity, 60F 7.2 V~scosity, SFS @ 122 F 77.4 ~ 25 Conradson carbon, wt qO 4.73 -i Asphaltenes, wt 70 0.02 ' Sulfur, wt qO 0.68 - Carbonyls, % < 0.01 i ~,~
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1 32q 1 64 , Metals, ppm Aluminum 14.4 Calcium 0.9 Chromium < 0.1 Copper 0.2 Iron 40 Lead < 0-1 Magnesium 0.2 Manqanese 0.1 Nickel 0.1 Po~assium 0.7 Sodium 3.9 ` Tin 0.3 Vanadium < 0.1 Zinc 1.1 ., .PETROLEUM ANALYSIS ~EPORT
i Description: Case History No. 1 ; FCC Slurry Fllterable solids, ptb 384.3 ~:~ 20 Bromine No. 15.5 . Conradson carbon, wt ~ 10.0 Basic nitrogen, ppm < 10 Asphaltenes, wt % 1.93 . Mercaptan sulfur, ppm 40 i 25 Carbonyls, ~ 0.085 Metals, ppm Aluminum< 0.10 Calcium 7.44 . Chromium 0.30 Copper 0.95 . Iron 43 Lead 0.29 -; Magnesium 2.18 . Man~anese 0.23 Y. 2S Nickel 1.0 ;i Potassium 1.2 ~ Sodium 14.8 , ,, .
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Case History No. l (Cont'd) Tin <0.10 Yanadium 0.43 - Zinc 1.8 PETROLEUM ANALYSIS REPORT
Description: Case History No. 2 FCC Slurry Filterable solids, ptb 1,929.2 Bromine No. 73.1 ln Conradson carbon, wt % 18.31 Asphaltenes, wt % 5.08 Metals, ppm Aluminum 413 Calcium lO.O
lS Chromium 0.5 Copper 0.6 ; Iron 29 Lead l.l . Magnesium 3.1 20 Manganese 0.2 Nickel 6.8 Potassium l.9 . Sodium 9.5 Tin 0.4 1 25 Vanadium 4.7 Zinc 3.5 While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present inventlon.

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Claims (12)

1. A method of controlling the formation and deposition of fouling materials in a slurry comprising high molecular weight hydrocarbons containing residual FCC catalyst, which slurry is derived from the fluidized catalytic cracking of petroleum and is at an elevated temperature, said method comprising adding to said slurry in an amount effective for the purpose an effective combination of the following:

Product I: Mannich-type products formed via reaction of the reactants (A), (B), and (C); wherein (A) is an alkyl substituted phenol of the structure FORMULA (A) wherein R and R1 are the same or different and are independently selected from alkyl, aryl, alkaryl, or aralkyl of from about 1 to 20 carbon atoms, x is 0 or 1; wherein (B) is a polyamine of the structure FORMULA (B) wherein z is a positive integer, R2 and R3 may be the same or different and are independently selected from H, alkyl, aryl, aralkyl, or alkaryl having from 1 to 20 carbon atoms, y may be 0 or 1; and wherein (C) is an aldehyde of the structure wherein R4 is selected from hydrogen and alkyl having from 1 to 6 carbon atoms;

Product II: a polyalkenylthiophosphonic compound; and Product III: a reaction product of an alkyl succinic acid or anhydride with a polyamine having the formula:

wherein n is an integer between 2 and 10, and m is an integer between 1 and 10.

2. A method according to claim 1 wherein Product I is the reaction product of p-nonylphenol, ethylenediamine and formaldehyde.

3. A method according to claim 2 wherein Product II is the pentaerythritol ester of polyisobutenylthiophosphonic acid.

4. A method according to claim 3 wherein the Product III
is a reaction product of succinic acid or anhydride and triethylenetetramine.

5. A method according to claims 1, 2, 3, or 4 where the molar ratio of Product I to Product II to Product III is from about

6:1:12 to 40:12:1.

6. A method according to claim 5 wherein the slurry is being used in a heat exchange capacity.

7. An antifoulant composition comprising a combination of Product I: a Mannich-type product formed by the reaction of the reactants (A), (B), and (C); wherein (A) is an alkyl substituted phenol of the structure FORMULA (A) wherein R and R1 are the same or different and are independently selected from alkyl, aryl, alkaryl, or aralkyl of from about 1 to 20 carbon atoms, x is 0 or 1; wherein (B) is a polyamine of the structure FORMULA (B) wherein z is a positive integer, R2 and R3 may be the same or different and are independently selected from H, alkyl, aryl, aralkyl, or alkaryl having from 1 to 20 carbon atoms, y may be 0 or 1; and wherein (C) is an aldehyde of the structure wherein R4 is selected from hydrogen and alkyl having from 1 to 6 carbon atoms;

Product II: a polyalkenylthiophosphonic compound, and Product III: a reaction product of a alkylsuccinic acid or anhydride with a polyamine having the formula wherein n is an integer between 2 and 10, and m is an integer between 1 and 10.

8. A composition according to claim 7 wherein Product I
is the reaction product of p-nonylphenol, ethylenediamine and formaldehyde

9. A composition according to claim 8 wherein Product II
is the pentaerythritol ester of polyisobutenylthiophosphonic acid.

10. A composition according to claim 9 wherein Product II
is a reaction product of succinic acid or anhydride and triethylenetetramine.

11. A composition according to claims 7, 8, 9, or 10 wherein the molar ratio of Product I to Product II to Product III is from about 6:1:12 to 40:12:1.

12. A composition according to claim 11 wherein Products I, II and III are dissolved in an organic solvent.