US2186425A - Process for removing naphthenic acids from hydrocarbon oils - Google Patents

Description

Patented Jan. 9, 1940 I umfrsn STATES a18 2 ..:ff V

PROCESS FOR. REMOVINGv NAPHTHENIG ACIDSFROM H-XDROCARBON OILS Franz Rudolf 'Moser, Amsterdam, "Netherlands, assignor toShell Development Company, San Francisco, Calif; a corporation of Delaware No Drawing. Application December .24," 1937, Serial No. 181,702. In the Netherlands Janu- This invention relates to the removal of naph-' thenic acids from hydrocarbon oils. by catalytic destruction of the latter at elevated temperatures,- and in particular deals with the'removal 5 of naphthenic acids from mineral lubricating oil distillates.

Hydrocarbon oils often contain considerable,

amounts of acidic components, whichduring the processing of the oils, particularly at elevated 10 temperatures, maycausesevere corrosion of. the

treating equipment. Thus corrosion difllculties have been experienced, for instance, when dis- 'tilling, with or without steam, relatively high f boiling oils such asgas oil, Diesel fuel oils, lubri-' eating oils, etc., containing free naphthenic acids particularly if their acid numbers are high, for

instance above..2. In order to overcome, this difliculty variousmeans have been employed, all of which, however, have certain disadvantages. For instance it has'been attempted'to subject the oils to selective, crackingat temperatures between about 315 to 400 C. in the-liquid phase'without a catalyst, wherebyitwas hoped the naphthenic acids would be decomposed to neutral compounds and CO2, while the hydrocarbon oils remained substantially uncracked. It was foundthat under these conditions some decomposition oi naphthenic acids takes place, but it is slow and incomplete. Moreover, the corrosion during. this treatment may be severe and may persist insubsequent treatments. I Another method consisted of' passing vapors of mineral oilcontaining naphthenic acids over alkaline earth metal, oxide at temperatures of about 200 C. to produc'ealkaline earth naph'. thenates, and heating subsequently the naphthenates so produced to about-400 C. to remove therefrom ketones and 00:, thereby restoring the V alkali earth oxide. 40 has the disadvantage that it requiresfrequent changes of temperatures of the reacting masses, which reduce the available operating time, make. operating of the process on a large scale diiil--- cult; and raise operating expenses; i

Other methods of removing naphthenic acids comprise distilling. oils containing naphthenic 1 acid for instance overcaustic soda under conditions to retain the naphthenic acidsiin the alka:

line-reacting residue in the form ofa so-called soda asphalt, which, however, is atroublesome material of little use.

It is the purpose of this invention to providea. continuous fmethod, whereby naphth'enic acids contained in m neral oil can be eliminated quick-l ly and substantially, completely, without produc- This intermittent process ing an. undesirable residue and without materially decomposing or otherwise damaging the hydro carbons with which the acids are associated; I- have discovered; that 'naphthenic acids can be eliminated quickly and substantially com-V 5' pletely in, a single step operation'from mineral oilscontaining them by conducting the oil, preferablyin the vapor phase, at an elevated temperature, preferably above 250 to. 300C if desired in the presenceof steam andunder conditions 10 substantially to avoid cracking of the hydrocarbons, over a catalystpromoting thedestructlon of'thelcarboxylic'group' orthe conversion of thecarboxylic group into 2. non-acidic group.

The reaction by whichthenaphthenic acids 7 areeliminated isone of decomposition, free CO: and neutral compounds, presumably ketones and/or hydrocarbons being formed.

The, catalysts suitable for the above purpose are known as c'atalysts for ketonic decomposition I0 or for decarboxylization, .videe. g.: Sebatierz 'Die Katalyse' in der vorganischen ,Chemie, l927, 'pagef253 et seq.

Ipatiefl': Catalytic Reactions atHigh Pressure and Temperatures, 1936, page12l et'seq,

manganese, chromium, uranium, cadmium and zinc, are also effective to some extent. Of these,

t b nates of lithium and the a k n a:

metals, and particularly of the gro metals having combining weights below sodium, i, e. lithium, magnesium and calcium, are particu- 'la'rly. .eifective.

Mixtures of several catalysts may "be used. 45 often to considerable advantage. For instance mixtures consisting predominantly of an .alkali earth carbonate and a small amount of lithium,

carbonate prove to be very active. Thus a calcium carbonate catalyst containing 1% lithium 5o carbonate may be almostas'effective asj lithium carbonate alone. Catalysts which have'an acid character andespecially those which; contain a substantial amount of freemineral acid cannot 'be used for'the process according to'the inven technischen so i tion; for the rest such catalysts are not known to be catalysts for ketonic decomposition.

The method of preparing the catalyst has ususize 3040 A. S. T. M. sieve), is a suitable catalyst for the purpose described. Lithium carbonate and earth alkaline carbonates may be obtained from solutions of soluble salts by precipitation; or by calcining or igniting their. bicarbonates, or car'- boxylic acid salts which upon heating will decompose to form carbonates, in particular formates, acetates, oxalates and higher fatty acid salts, and naphthenates. Carbonates obtained by pyrogenetic decomposition of organic salts are usually more efiicient than the precipitated forms. Furthermore'the degree and temperature of the heat treatment normally has a considerable influence. Thus between three calcium carbontes produced by calcining the acetate in a closed furnace at 450 C., by igniting the acetate in contact with air in a crucible until gray and by igniting until completely white respectively, the relative efficiencies as measured by the length of the life of each under a given set of conditions'were l-: 4 6, the higher figures indicating longer life. Analysis showed that all three catalysts consisted essentially of calcium carbonate, containing only small amounts of calcium oxide and the only difference between the three catalysts apparently being in the surface structures.

Certain active metal carbonatestend to decompose materially under the conditions of my treatment to the oxides or basic carbonates and CO2, particularly if steam is present as is usually the case when treating relatively heavy lubricating oil distillates. If desired; CO2 may be added to the hydrocarbon vapors in such an amount that the partial pressure of the CO2 inthe vapor phaseis equal to or higher than equilibrium CO: pressure of the metal carbonate. In this way the decomposition of the carbonates into oxides or basic carbonates may be prevented, although in general the said decomposition does not influence the working of the catalyst. The lithium, magnesium and calcium carbonates have a sufficiently low CO2 pressure under the treating conditions, so that ordinarily no CO2 need be added to the vapors, even in the presence of substantial amounts of steam, the partial pressure of CO2 in the vapors due to the decomposition of the naphthenic acids usually being sufficient to prevent a material decomposition of these carbonates.

Active catalysts may be used alone or deposited on inert solid carriers, such as coke, tile, majolica, asbestos, graphite, porcelain, etc.. and if desired, in combination with a variety of activators.

Suitable contact temperatures range from about 300 C. to temperatures of incipient cracking or slightly above. i. e. about 475 C. Incipient cracking temperatures and rates of cracking at a given cracking temperature vary somewhat with the boiling range and the nature of the oil, as shown by Geniesse and Reuter in Industrial Engineering Chemistry 24 1932), page 219 et seq. "Exposure of the oil to temperatures above incipient cracking temperatures should be 'so limited to avoid substantial cracking. In general treating temperatures should not exceed about 475 C. and are preferably below about 450 C.

The limited time available when treating at temperatures above incipient cracking is, however, more than sufficient to eliminate the largest portion of naphthenic acids contained in hydrocarbon oils. For instance, whereas at 450 C. it requires between 3 to 4 seconds to crack a oil to the extent of 1%, a contact time of second is usually sufilcient at temperatures from 400 C. to 450 C, to remove 95% or more of the naphthenic acids in contact with an active carbonate catalyst. Since a longer time of contact results in a more'complete removal, I may extend this time to several seconds, where this can be done without danger of cracking or otherwise adversely affecting the oil. j

The following examples further illustrate my process: v

' A lubricating oil distillate containing naphthenic acids and having an acid number of 2, produced by distillation of Venezuelan crude oil, was

passed in the vapor'phase at a pressure of H33 millimeters Hg and in the presence of steam over a catalyst consisting of granulated lithium car-' bonatej About volumes liquid oil were thus contacted with 1 volume of catalyst per hour. The calculated time of contact was second.

The treated oil vapors were condensed and small amounts of liberated gaseous COz -were separated from the liquid. The catalyst remained active until about 5 mols of "naphthenic acids per mol. of carbonate had been decomposed.

tate, had relatively long life, which compared favorably with those of lithium carbonate. 'Ho 7 ever, under the conditions of the above experiments magnesium carbonate reduced the acid numberof the oil to about .3 only, and 'alonger time of contact was necessary in order further.

to reduce the naphthenic acid content.

Calcium carbonate, particularly when obtained by ignition of calcium acetate under conditions to produce a pure white substance, analyzing as substantially pure calcium carbonate containing but small amounts of CaO, proved to bevery'efiicient, and had an active life comparing favorably with .those of many forms of lithium carbonates. Also mixtures of calcined and precipitated calcium carbonates were very efiective though perhaps somewhat inferior to pure cal-- cined calcium carbonate.

Addition of 1 1% lithium carbonate to a relatively poor calcium carbonate, which was obtained by calcining calcium acetate at 450 C. in a closed furnace, and which had an active life of or less of the pure white carbonate described above,extended the life of the former 6 to 8 times. Moreover, its effectiveness was raised, so that without changing the conditions of the treatment the acid valve of the treated oil was reduced from .45 to .15 due to the addition of the lithium carbonate.

An unrefined Venezuelan lubricating oil distillate containing about 2% sulphur, with an acid I over 10 cm? (:83 g. of a lithium carbonatemasses we throu h A. S.--T. sieve'40. 1 After heating to400 space-of this catalyst wasdeterminedby filling a a -pycnometer with catalyst and weighing it.

' use pastries-tram by weight of steam at 400; 'C. in the vapor phase catalyst. t c

The catalyst hadbeen obtained by compressing I technical lithium carbonateto pills and reducing them to such (a size of grain that they pass M. sieve '30 and 'not through C. the hollow subsequently evacuating, "introducingwater and 3 weighing once more. 7

taken up, calculated from the increase in weight, 7

The amount of cm. water was looked upon as hollow space and'amounted The average molecularweight ofthe oil as 370.80 g. (=100 cm?) oil passed through per hour.

From these figures it 'can-be calculated that the oil vapor remained in the catalyst for about The progress of thedesulfurization and the de-' acidification is illustrated by the following table:

1: a m 33 l? an on roug 8 inhours 4 40 mo atus witl gut catalyst) Acldflgun aoo 0.0a coo "0.00 T 1.80 Bulphurcontent. 2.19% 1.93% 1.o2% 2.06% 2.08

The acid figure or the oil has therefof, dropped from 2 to'0'.06,"this drop beingmaintained for 100 hours or use, whilst the'sulphur content remains practically unchanged] I claim as my invention: i

1. In the process of removing naphthenic acids 1 iromhydrocarbon oils containing same, the steps comprising contacting said oil in a heated vaporous condition at a temperature between 300 and 4'15? C. with lithium carbonate for a time sufficient to decompose amajor portion or the naphthenic acids, thereby liberating CO2, but in-; sufllcient substantially to crack the oil.

2. In the process of removing naphthenic acids from hydrocarbon oils'containing same, the steps comprising,

liberating CO2, but insufficient substantially to crack the oil. 0

3, In the process of removing naphthenic acids disdaine c iiromhydrocarbonoils. containing samathe steps crack the, oil.

comprising contacting said oilinaheated vaporous condition at a-itemperature between 300and 475 C. with a calcium catalyst comprising'white calcium carbonate obtained'by igniting calcium ace- -tate, for a time sufficient to decompose a major portion of the naphthenic acids, thereby liberat-i ing CO2, but insuflicient substantially to crack the oil. Y

, 4. In the-process-of removing naphthenic acids ,fromoa hydrocarbon oil containing same, the I steps comprising contacting saidoil in a,.heatfed vaporous condition at a temperature between '300" and 475 C. with an amount substantially less than the equivalent of said naphthenic acids of a metal carbonate which is substantially stable under the conditions of the treatment, for a time I sufficient to decompose a major portion of the naphthenic acids, thereby liberating, gaseous CO2, but insufficient substantially to crack'the' oil. 5. In the process of removing naphthenic acids I from hydrocarbon oils containing the same, the steps comprising contacting saidoil in a heated vaporous condition at a temperature between 300 and 475 C. with an amount substantially less than'the equivalent of saidnaphthenic acids of ,a catalyst-whose active component consists essentiallyiof the carbonate of an alkaline earth metaLior a time sum'cient to decompose a major portion of the naphthenic acids, thereby liberating gaseous CO2, but insuflicient substantially to 6. In the process a irom hydrocarbon oils containing the same, the steps comprisingcontacting said oil in a heated vaporous condition at a temperature between 300 and 475 C.

of removing naphthenic acids lyst whose active; component, consists essentially oia carbon t of an'alkali earth metahior a time sufficient to decompose a-maior portion of the naphthenic acids, thereby liberating CO2, but insufficient substantially toj-crack the oil, said carbonate having been produced by igniting a salt of one of said metals and afcarboxylic acid, which salt upon heating is converted to the carbonate. r

, '7 In the process oi! removing naphthenic acids from hydrocarbon oils containing the same, the. steps comprising contacting saidoil in a heated vaporous condition at a temperature between 300 and 475 C.with'a catalyst the active com-- ponent of which consists essentially of an amount of calcium carbonate substantially less than the equivalent of said naphthenic acids, tor a time 'sufiicient to decompose a major portionof the naphtheriic'acids, thereby liberating but insuflicient substantially to crack the oil.

gaseous C02, 1 u