CA2087300A1 - Antioxidant compositions and methods of inhibiting polymerization in diolefin containing feedstocks - Google Patents

Abstract

ABSTRACT

Methods and compositions are provided for inhibiting the formation of polymers in diolefin containing hydrocarbon feed-stocks during their processing. The compositions comprise a phenylenediamine compound and a dithiocarbamate compound.

Description

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ANTIOXIDANT COMPOSITIONS AND METHODS FOR INHIBITING
POLYMERIZATION IN DIOLEFIN CONTAINING FEEDSTOCKS

FIELD OF THE INVENTION

The present invention pertains to antioxidant com-positions and methods for inhibiting the polymerization of diolefin containing feedstocks during their processing. The mekhods comprise adding an effective amount of the composition of a phenylenediamine compound and a dithiocarbamate compound.

BACKGROUND OF THE INVENTION

Fouling can be defined as the accumulation of unwanted matter on heat transfer surfaces. This deposition can be very costly in refinery and petrochemical plants since it increases fuel usage, results in interrupted operations and production losses and increases maintenance costs.

Deposits are found in a variety of equipment: preheat exchangers, overhead condensers, furnaces, heat exchangers, fractionating towers, reboilers, compressors and reactor beds.

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Tllese deposlts are complex but they can be broadly charaeter~2ed as organ~c and ~nor~an1c. Thsy con~lst o~ tal ~xldes and sulftdQs, soluble organlc metals, organlc polynl~rs, cok~, salt and varlous other partleulate mattcr. Ch~mlcal ant~o~ n~s h~v~ b~n dev~lop~d 5 that effect1vely combat foul~ng.

Th~ chan~1cal composltton of or~an1c ~oul~nts 1s rar~ly ldontlf1ed compl~t~ly. Organ1c foulln~ ls ~aus~d by ~nsoluble polymeri wh~ch somet1mes are degraded to coke. The polymers are usually formed by react~ons of unsaturated hydracarbons, although any hydrocarbon can polymer~ze. Generally, Qlsfins tend to polymer~ze more read~ly than aromat~cs, which ln turn pclymertze more read11y than paraff~ns. trac~ or~an~c ~at~r~ls cont~tn1n~
hetero ~toms such as n1trogen, oxygen and sul~ur a~so contr1bute to polymerl~at~on, often through a condensation mechan~sm.

In refiner~es, depos1ts usua~ly contatn both organ1c and lnorganlc compounds. Thls makes the ~dent~f~cat~on of the exact cause oF foul~ng extremely d~fficult. Even 1f 1t were poss~ble to prec~sely ~dentlfy every s1ngle depos~t constltuent~ th~s would not guarantee uncoverlng the.cause of the problem. Assumpt~ons are often erroneously made that ~f a depos~t ~s predom~nantly a certa~n compound, th~n th~t compound ls the cause of the foullng. In real~ty, oftentlmes a m~nor const1tuent 1n the depos~t could be acting as a blnder, a catalyst, or in some other role that tnfluences actual deposit formation.

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The final for~ of the deposit as vi~wQd by analyt1c~1 ch~ml~ts m~y not ~lways tndlcat~ 1t3 orlglr or cause, B~fQr~
open1ng~, equlpmant 1~ st~m~d, ~terwash~d, or Dth~rw1se r~d1~d for lnspectlon. During th1s preparat10n, foulln~ Matter can be ehanged both phys1cally and ehem1cally. ~or example~ water-so~uble salts can be washed away or certa~n deposlt constl~uents oxld1zed to another form.

In petrochemical plants, foul1ng matter ~s often organic 1n nature. Foul1ng can be severe when monom~rs convert to polymers b~for~ they l~av~ the plant. ~hl~ ls most 11kely to happen 1n streams hl~h 1n ~thyl~n~, propylons, butad10ne, ~tyr~n~
and other unsaturates. Probable locat-lons for sueh reaet10ns lnc?ude unlts where the unsaturates are ba1ng handled or pur~f~ed, ur 1n streams wh1ch contaln these reactlve mater~als only as cont~m1nants.

Even through some petrochem~c~7 foul~ng problems seem s1milar, subtle differences ln feedstock, process1ng schemes, process1ng equipment and type of contam1nants can lead to var1at10ns tn foul~ng severlty. For Qxample, ethy1eno plant depropanl2Qr rebo11ers exp~r1ence foul1ng that appears to be pr1marily polybutad~ene 1n nature. The sever~ty of the problem var1es slgn1f~cantly from plant to plant, however. Th~ average rebo11er run length may vary from one to two weeks up to four to s~x months (w1thout ohemical treatment).

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Although lt is usually ~mpract~cal to ~dent~y the fou71ng proble~ by analyt1ca7 tachniques alone, thls lnformat~sn comblned w1th knowledge of th~ process, proce~sing condlt~ns and thc factors known to contribute to foul1n~, ~re all essent1al to understand~ng the pr~b?em.

` There are many ways to reduce foullng both mechan~cally ~nd ch~mlcally. Cha~lc~l ~dd1t~v~s oft~n o~f~r an ~f~ctlve ant~-fouling means; howev~r, process~ng changes, ~echan~6al mod~ftcatlons equ1pment and other methods ava~lable to the plant should not be overlooked.

Antifoulant chem~cals are formulated from s~ver~l ~aterl~ls: soms prevent foulants from form~ng, others prevent foulants from deposltlng on heat transfer equ~pm~nt. Mater~als that prevent depaslt format~on 1nclude ant10xtdants, mstal coord~nators and corroslon ~nhlb~tors. Compounds that prevent depos1tlon are surfactants whlch act as detcr~ents or d1sp~rsants.
D~fferent comb1nat~ons of these properties are blended together to maximlze results for each d~fferent appl kat10n. These "poly-funct~onal" ant~foulants are generally more versatlle and e~fective s~nce they can be des~gned to combat var~ous types of foullng that can be present ln any 91ven system.

Condensatiun inhibitors include mater~als that ~nterfere with ac~d/base react~ons, and others that react w~th hetero atom compounds such as carbonyls and pyrroles. These ~nh1b~tors `
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prevent growth o~ thà hydrocarbon molecul~s and ~hus hslp to lnh1blt ~oullny.

Research 1nd~cates that even Yery small amounts ~f ~xygen can cause or ac~e1~rat~ p~ly~Qr12~tlon. A~eord7n~1y~ ~ntlox1dant type anttfoulants have been developed to prevent oxygen ~n1t~ated foul1ng. Antloxldants act as chaln-stoppers by forming ~nert molecules wlth the ox~d~zed free rad~cal hydrocarbons, ~n accordance wlth the follnw~ng react~on:

~hain Termination ~00~+ Ant~oxldant ~ ROOH ~ Antlox~dant tH) Surface mod~fiers Dr detergents change m~tal s~rface character1stics to preY~nt foulan~ from depo~e~n~. D~sp0rsants or stabtllz~rs prevent ~nsoluble polymers, coke and other partlcu-late matter from agglo~erat~ng 1ntD large part~cles wh~ch can settle out of the process stream and adhere to the metal surfaces of process equipment. They also modify the part1cle sur~ace so that polymer~zat~on cannot read11y take place.

Ant~foulants a~e des~gned to prevent ~qulpment surfaces from fou11ng. ~hey are not des1gned to clean up exlstlng foulants.
Therefore, an ant~foulant should be started ~mmedlately after equ~pment ts cleaned. It 1s usual7y advantageous to pretreat the system at double the recommended dosage for two or three weeks to reduce the in~tial high rate of foul~ng ~mmed~ately after startup.

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The lncreased prof~t possible w~th the use of ant~foulants ~arles from appl~cat10n to appllcAtlon. It c~n ~nc1udo ~n tncr~as~ ln production, fuel s~v~ngs, ~alntenanc~ s~vings and other sav~ngs from greater operating eff~c~ency.

There are many areas in the hydrocarbon processtng ~ndustry wh~re anti~oulants have been used extenslvely; th~ main area~ of treatment are d~scussed below.

In a rsflnery, the crude unit has been the focus of attent~on b~causo of lncreassd fu~l costs. Antlfoulants havs been I0 successfully appl~ed at the exchang~rs; downstr~m and up~tr~m o~
the Jc~alter, on the product s~de of the preheat train, on both sides of the desalter ~akeup water exchanger and at the sour water strtpper.

~ Hydrodesulfuri~atlon units o~ all types experience preheat 15 ~oullng prob1~s. A~ong thos~ that hava baen successfully trQat~d are reform~r pretreaters proc2ss1ng both stralght run and coker naphtha, desulfurlz2rs processing catalyt~cally cracked and coker gas oil, and dlstillate hydro-treaters. In one case, fouling of a Un~f~ner stripper column was solved by apply~ng a corrosion 20 lnhib~tor upstream of the problem source.

Unsaturated and saturated gas plants (ref1nery vapor recovery unlts) experience ~ouling ~n the variQus fractionat10n columns, rebo~lers and compressors. In some casesj 3 corros~on ~.

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control prugram combined with an antifoulant program gave the best results. In other cases, an application of antifQulants a10ne was enough to solve the problem.

Cat cracker preheat exchanger foul~ng, both at the vacuum column and at the cat cracker ltself, has ~lso been corrected by the use of antifoulants.

The two most prevalent areas for fouling problems in petro-chemical plants are at the ethylene and styrene plants. In an ethylene plant, the furnace gas compressors, the various fraction-ating columns and reboilers are subject to fouling. Polyfunctionalantifoulants, for the most part, have provided good results in these areas. Fouling can also be a problem at the butadiene extraction area. Both antioxidants and polyfunctional antifoulants have been used with good results.

In the different design butadiene plants, absorption oil fouling and d;stillation column and reboiler fouling have been corrected with various types of antifoulants.

Chlorinated hydrocarbon plants, such as VCM, EDC and perchloroethane and trichloroethane have all experienced various types of fouling problems. The metal coordinating/antioxidant-type antifoulants give excellent service in these areas.

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SUMMARY OF THE INYENTION

The present invention pertains to methods and compositions for inhibiting polymerization in hydrocarbon feedstocks during their processing. The compositions provide for adding a combination of a phenylenediamine compound and a dithiocarbamate compound to the feedstock. This invention is particularly effective in hydrocarbons with a high diolefin content.

DESCRIPTION OF THE RELATED ART

U.S. 4,466,905l Butler et al., teaches a process for inhibiting the polymerization of a vinyl aromatic compound.
2,6-Dinitro-p-cresol and a phenylenediamine compound are employed in the presence of oxygen.

U.S. 4,720,566, Martin, teaches methods and compositions for inhibiting acrylonitrile polymerization in a quench column of a system producing acrylonitrile. The composition comprises a hydroxylamine compound and a phenylenediamine compound.

U.S. 4,775,458, Forester, teaches a multifunctional process antifoulant method utilizing a polyalkenylthiophosphonic a~id and at least one of the following: antioxidant compound, corrosion inhibiting compound and a metal deactivator. A
phenylenediamine compound can be used as the antioxidant compound.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, methods and compositions are provided for inhibiting the polymerization of diolefins in diolefin containing hydrocarbon feedstocks during their processing comprising adding to said feedstocks an effective amount of a combination of a phenylenediamine compound and a dithiocarbamate compound.

The feedstocks treated by the present invention are composed of ethane, propane, butanes, light naphtha, heavy naphtha, gas oil, and mixtures thereof. There are also present diolefin compounds such as butadiene and isoprene which their polymerization ;s sought to be inhibited by the present invention.

The phenylenediamine component of the inhibitor mixtures of this invention include phenylenediamine and derivatives thereof having at least one N-H group. It is thought that o-phenylene-diamine or derivatives thereof having at least one N-H group are 3 ~ ~

suitable in accordance with the instant invention. Howeven, the preferred phenylenediamine is p-phenylenediamine having the formula \ A
N ~ N

whereln R1, R2~ ~3, and R4 ~r~ th~ ~m~ or d~ r~nt ~n~
. ~r~ hydrogen~ ~lkyl, 3ryl, alk~ryl, aralkyl groups w~h the prov1s~ th~t at least one ~ ~ , R2, R3, or R4 1s hydrogen, more preferably the alkyl, aryl, alkaryl, and aralkyl groups have one to about twenty carbon atoms.
The alkyl, aryl~ alkaryl, and aralkyl groups may be stra~ght or branched-chaln groups. Exemplary p-phenylene-dlamlnes ~nclude p-phenylenedlamine where1n Rl, ~2, R3, and R4 are hydnogen; N-phenyl-N'-alkyl-p-phenylened~amines such as, N-phenyl-N'-methyl-p-phenylenedlam~ne, N-ph~nyl-N'-ethyl-p-phenylened~am~neO
N~ph~nyl-N'-propyl-p-phenylenedlamlne, N-phenyl-N'-lsopropyl-p-phenylened~am~ne, N-phenyl-N'-n-butyl-p-phenylenedlam~ne, N-phenyl-~'-1sobutyl-p-phenylened~am~ne, N-phenyl-N'-sec-butyl-p-phenylened~amlne, o ~

N-phenyl-N'-~ert-butyl-p-phenylened~amlne, N-phenyl-NI-n-pentyl-p-pheny1enedlamlne~
N~phenyl-N'-n-h~xyl-p-phenylenedl~mlne, N-phenyl-N'~ methylhexyl)~p phenylened1am~ne, N-pheny~-~N' il,3-d1methylbutyl)-p-phenylenedlamlne, N-phenyl-N'-11,4-dlmethylpentyl)-p-phenylenedlamlne;
N-phenyl N'~N'-d~alkyl-p-phenylened~a~nes, such as N-phenyl-N',N'-dlmethyl-p-phenylened~amlne~
N-phenyl-N'7N'-dle~hyl-p-phenylened1amlne, N-phenyl-N',N'-d~-n-butyl-p-phenylgned~am~ne J
N-phenyl-N'~N'-d~-sec-butyl~p-phenylened~amlne, N-phenyl-N'-m~thyl-N'-eth~l-p-phenylonedl~mlne;
N,N-dlalkyl-p-phenylened~am1nes such as N,N-dlmethyl-p-phenylened~am~ne and N,N'-dlethyl-p-phenylened~am1ne;
N,N'-d~alkyl-p-phenylenedlamlnes such as .N,N'-dl-1sopropyl-p-phenylenedlam~ne;
~,N'-dlaryl-p-phenylenedlamlnes such as N,N'-d~pheny~-p-phenylened~amlne;
2~ N,N~N'-tr1alkyl-p-phenylened~am~nes such as N,N,N'-trlmethyl-p-phenylened1amlne, N ,N ,N ' -trl ethyl -p-phenylenedlam1ne. Prefer~bly, the p-phenylened1am1ne 15 selected fro~ the group cons1stlln~
of N-ph~nyl-N'-I1-3~dlml~thylbutyl)~p-ph2nylened1~mlne and N-phenyl-N'-~1,3-dlmethylpentyl)-p-phenylenedlamlne.

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The preferred dithiocarbamate compound is 3,5-di-t-butyl-4-hydroxybenzyl N,N-d;-n-butyldithiocarbamate (EIDC). The compounds of the present invention generally ha~e the formula OH
115 ~n6 ~H2 C=S
/ N \

wherein R5 6 are hydrogen or an alkyl group havlng from 1 to 8 carbon atoms and R7 8 are the same or different and are. an alkyl group hav;ny from 1 to 8 carbon atoms.

The preparation of this molecule is detailed in Neftechimia, 26, (1986) 563-570, N.S. Peresl~gina et al. and Neftechima 28 ~1988) 813-822, N.S. Pereslegina et al., both articles being wholly incorporated herein by reference. This procedure is outllned below.

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In a 250-ml 2-necked, round-bottomed flask equipped with a magnetlc stirrer, a condenser, and a thermome~er was placed 20.6 g (0.10 mole~ of 2,6-di-t-butylphenol, 3.0 9 (0.10 mole) of paraformaldehyde, 12.9 g (0.10 mole) of di-n-butylamine, and 50 ml of xylene. This m;xture was heated at 110C for 3 1/4 hours.
The temperature was then increased to 1~1C and a Dean Stark trap was inserted. After about 30 minutes, about 1.7 ml of water and 15 ml of xylene were removed. The mlxture was then cooled to 54C and 6.0 ml ~about 7.6 ~, 0.10 mole) of carbon disulfide was a~ded over 30 seconds. The temperature increased to 61C and then the mixture was heated at 7&C for 2 hours. 70.7g of a brown solution resulted which, assuming lO0 percent reaction, was calculated to be about 60% active carbamate.

2 ~ 3 The total amount of combined treatment used in the present invention is that amount wh;ch is sufficient to effect inhibition of polymerization and will, of course, vary according to the conditions under which the hydrocarbon is being processed. At higher processing temperatures, larger amounts of the polymerization inhibiting treatment are generally required.

Preferably, the total amount of the combined treatment is ~rom ab~ut 5 part per million to about 1000 parts per million parts combined treatment based on the weight of the hydrocarbon.

The weight ratios of phenylenediamine compound to dithio-carbamate compound are preferably in the range of about 0.05:1 to about 20:1. Most preferably, the weight ratio is about 0.25:1 to about 4:1.

The combined polymerization inhibition treatment can be added to the hydrocarbon charge by any conventional method. The components can be added separately or as a combination containing both components. It is clearly preferred to add as a single composition containing both the phenylenediamine compound and the dithiocarbamate compound.

Accordingly, it is therefore possible to produce a more effective polymerization inhibition treatment than that obtainable by the use of either individual ingredient alone when measured at comparable treatment levels. Because of the enhanced polymeri-zation inhibiting activity of the combination, the concentration .

of each of the ingredients may be lowered and the total quantity of the polymerization inhibitor required for an effective treat-ment at elevated temperatures may be reduced.

The composition may be added to the hydrocarbon as either a dispersion or as a solution using a suitable liquid carrier dispersing medium or solvent which is compatible with the hydrocarbon being processed. Preferably, a solution is provided and the solvent is a non-polar organic solvent such as xylene (a commercial ~ixture of o, m and p isomers) or heaYy aromatic naphtha (~AN).

The surfaces of the processing equipment are primarily composed of ferrous metal. Iron, as well as iron alloys such as low and high carbon steel, and nickel-chromium-iron alloys are customarily used for the production of hydrocarbon processing equipment such as furnaces, transmission lines, reactors, heat exchangers, separation columns, fractionators, and the like.

The data set forth below were developed and demonstrate the unexpected results occasioned by use of the invent;on. The following examples are included as being illustrations of the invention and should not be construed as limiting the scope thereof.

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EXAMPLES

In the ASTM D-525-88 test, a sample is oxidized in a bomb initially filled at 15 to 25C with oxygen at 100 psi and heated at a temperature between 98 and 102C. Pressure is read and the time of the break point is recorded. This is the observed induction period, and the induction period at 100C can be calculated. A long induction period is indicative of good stability. The testing results are reported in Table I.

TABLE I

RROA BDC Induction Time Induction Time (Dosaqe in PDm) Found in Minutes Avq.Calculated 126 . 124 - 4Z8 - - - - 242 61 1~9 - 282 - - - - ~61 Calculated = [ppm RROA X (396-37)/250 [ppm RDC X (85-37)/250] + 37 RROA = [N-phenyl-N'-(1,4-dimethylpentyl)-P-phenylenediamine BDC = 3,5-di -t-butyl-4-hydroxybenzyl N,N-di-n-butyldithiocarbamate These results indicate the enhanced activity of the combination over that of the individual components alone.

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While this invention has been described with respect to particular embod;ments thereof, it is apparent that numerous other fQrms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention S generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.

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Claims (17)

1. An antioxidant composition comprising a phenylenediamine compound and a dithiocarbamate compound.

2. The composition as claimed in claim 1 wherein said phenylenediamine compound has the formula wherein R1, R2, R3 and R4 are the same or different and are hydrogen, alkyl, aryl, alkaryl or aralkyl groups with the proviso that at least one of R1, R2, R3 and R4 is hydrogen, wherein the alkyl, aryl, alkaryl and aralkyl groups have one to about 20 carbon atoms.

3. The composition as claimed in claim 2 wherein said phenylenediamine is N-phenyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine.

4. The composition as claimed in claim 1 wherein said dithiocarbamate compound has the formula wherein R5 6 are hydrogen or an alkyl group having from 1 to 8 carbon atoms and R7,8 are the same or different and are an alkyl group having from 1 to 8 carbon atoms.

5. The composition as claimed in claim 4 wherein said dithiocarbamate compound is 3,5-di-t-butyl-4-hydroxybenzyl N,N-di-n-butyidithiocarbamate.

6. A method for inhibiting the polymerization of diolefin containing feedstocks during their processing comprising adding an effective amount for the purpose of a combination of a phenylenediamine compound and a dithiocarbamate compound.

7. The method as claimed in claim 6 wherein said phenylenediamine compound has the formula wherein R1, R2, R3 and R4 are the same or different and are hydrogen, alkyl, aryl, alkaryl or aralkyl groups with the proviso that at least one of R1, R2, R3 and R4 is hydrogen, wherein the alkyl, aryl, alkaryl and aralkyl groups have one to about 20 carbon atoms.

8. The method as claimed in claim 6 wherein said phenylenediamine is N-phenyl-N'-(1,4-dimethylpentyl)-p-phenylenediamine.

9. The method as claimed in claim 6 wherein said dithiocarbamate compound has the formula wherein R5, 6 are hydrogen or an alkyl group having from 1 to 8 carbon atoms and R7 8 are the same or different and are an alkyl group having from 1 to 8 carbon atoms.

10. The method as claimed in claim 9 wherein said dithiocarbamate compound is 3,5-di-t-butyl-4-hydroxybenzyl N,N-di-n-butyldithiocarbamate.

11. The method as claimed in claim 6 wherein said combination is added to said feedstocks in an amount from about 5 parts to about 1000 parts per million parts feedstock.

12. The method as claimed in claim 6 wherein said combination is contained in a carrier solvent.

13. The method as claimed in claim 12 wherein said carrier solvent is a non-polar organic solvent.

14. The method as claimed in claim 13 wherein said non-polar organic solvent is xylene.

15. The method as claimed in claim 13 wherein said non-polar organic solvent is heavy aromatic naphtha.

16. The method as claimed in claim 6 wherein said feedstocks contain ethane, propane, butanes, light naphtha, heavy naphtha or gas oil or mixtures thereof.

17. The method as claimed in claim 6 wherein said diolefin compound is butadiene or isoprene.