Recovery of Inorganic Ash from Petroleum Oils Radiochemical Evaluation L. 0. MOHGAN AND S. E. TURNER The University of Texas, .lustin, Tex.
I
X THE operation of fluid catalytic cracking processes it is dreirable to have reasonably accurate information concerning the amounts of inorganic or nietallo-organic contaminants in the feed storks. Contamination may be present in the crude oils, or may he accumulated in the processing or storage of the oils or oil fractions. The accuracy of t,he deterniinat,ion of the metallic elements depends upon the efficiency with n-hich the elements may be recovered from the oil. The most convenient and widely used method of recovery is t,he standard ashing procedure of the American Society for Testing Materials (1). The procedure is subject, to three possible major sources of error: loss of ashforming constituents by volatilization during comhust,ion, loss of :iyh by mechanical entrainment of ash particles during combustion, and loss by volat,ilization during ignition. It has been found ( 2 ) that ignition of the ash wit>ha blast burner (ca. 900' C.) results in significant loss of some volatile ash components, mch as sodium chloride. The loss may be reduced to practical insignificance by ignition in an electric furnace a t 550' C., if the ignition period is less than 24 hours. I n the same work a number of synthetic blends were analyzed and found to yield results which suggested that losses attributable t,o volatilization and entrainment during oomhustion w r e not highly significant. The majority of blends investigated contained large amounts of contaminat,ion to increase the precision of the chemical analysis and may not have revealed possible losses a t low concentrations. Very little is known of the compound form of the metallic ashforming constituents in petroleum oils and it is possible that the addit,ives did not, adequately represent, the true s i t u a h r i with respect, t,o the native or accumulated contamination. It was decided to repeat and extend the last experiments, using radioactive tracer techniques, in the hope that the greater sensitivity and discrimination of the method would contribute to a better understanding of the problem. The use of radioactive tracers should permit the analysis and determination of smaller amount.3 of ash and reduce errors caused by accidenhl csperimental contamination. Iron, sodium, and calcium were chosen to represent, the elenients commonly occurring as cont,aniinants. The elements were added in the form of inorganic compounds, d to provide a range of compound naphthenates, ~ n salirylatrs types.
ishing techniques in coininon use for the determination of inorganic ash components in petroleum oils may lead to Folatilization and combustion losses, therehj contributing to analytical error. This stud? was carried out in an attempt to evaluate the s i p nificanceof the possible errors. Radiochemicaltechniques were used to trace the metallic constituent* of contaminants added to scleral tjpical oils through the standard comhustion and ignition processes. Essentiallj complete recoFerj of the iron, calcium, and sodium tracers ohtained when they w-ere added to the oils as naphthenates, salicjlates, and inorganic salts, if conihustion was carefully controlled andignitionwascarried otrtat less than 550" C. Traces of water and other sources of surface turbulence during combustion led to losses. It was concluded that properlj controlled combustions and ignitions j ield ash samples representing quantitatile recoterj- of metallic contaminants from petroleum oils, if the additiies used are considered to be tjpical of those normall? occurring as wntaminants.
idciuin 45 (half-life 180 clay? cdciuni carbonate; iron 55: 59 (half-life ca. 4 years, 46.3 d , :is metal. Stork solutions of solving the samples in xater the tracers were prepared by (sodium carbonate) or hgdrochloric acid (iron and cdciunl carbonate). Individual compounds were prepared by evaporation of aliquots of the stock solutions and solution in the appropriate acids. Naphthenates and salicylates were retained in xylene solution; inorganic salt,s were dried and used as finely ground solids. Samples were blended by addition of aliquots of the xylene solutions, or by t,rituration of t,he solid materials in the basis oil. A11 chemicals used were of reagent grade, except the naphthenic acid mixture, which was commercial grade. Oil samples were burned in porcelain crucibles having total volumes of approximately 20 nil. Samples smaller than 15 ml. were blended in the crucibles: larger samples were blended in flasks and added to the crucililrs as needed. In the latter cares, the flasks \yere washed with sylenr, which was then burned with the main samples. Comhustion was carried out by heating the oils t80the fire point and then allowing them t o burn until solid carbonaceous residues were obtained. The residues were then ignited t o constant weight in an electric furnace a t 550 C. Experiments in which entrained ash was to be recovered \yere rarried out in a closed glass chamber. Effluent gases, smoke, and possible entrained ash were passed through a compact, lox-ash filter to remove solid particles. Incoming air was filtered to remove the majority of dust particles. Upon completion of combustion, collected carbon and entrained ash were removed and ignited in porcelain crucibles. The activity of ashed samples TWS det'ermined by counting the crucibles after ignition. I n each sequence, the residual activity was compared to control samples prepared from the stock solutions in such a way as to duplicate the condition of the test samples. The crucibles were counted a t 0.5% geometry to minimize differences in distrihution of active material in the crucibles. Any ash remaining on the upper walls of the crucibles was scraped to the bottom before counting. A Radiation Counter Laboratories pressure-seal, mica, window (2.5 mg. per sq. em.) counter tube was used in th(8 activity measurements.
MATERIALS AND METHODS
Petroleum oils and residua used as bases for the synt'hetic blends in this investigation were supplied by the Humble Oil and Refining Co. Sample A. Deasphalted residuum produced experimentally by deasphalting a bottoms fraction from distillation of coastal crude oil. Total ash content, 0.0012 weight - yo(standard method) pi incipally nickel. Sample B. Residuum comprising the bottoms fraction obtainrd bv distillation of mid-continent crude oil and containing a considerable amount of asphalt. Total ash content, O.Og90 weight 7c,mostly sodium chloride and calcium salts. Sample C. Process gas oil, which had been in storage in a metal container for several months. Ash content, increased gradually during this period. Incremental ash was mostly iron oxide. Total ash content, 0.0028 weight %. The radioactive tracers used were obtained from the Isotopes Division, Cnitetl States .4toniic Energy Commission. Sodium 2.1 (half-life 14.8 hours) \vas ~ ~ ~ ( ~ r as i v rsodium d carbonate;
In all experiments, the total mass of ash was limited, so that loss of counting efficiency attributable to self-absorption in t'he
978
V O L U M E 2 3 , NO. 7, J U L Y 1 9 5 1 Table I.
979
Comparison of Counting -Methods
Crucible Method ______
Aliquot hlethod-Counts/min. 7r 1 . 2 8 X 10' 86 85 1 . 1 0 x 10; 92 94 1 . 2 1 x 10 91 89 1 . 1 7 X 10: 93 93 1 . 1 9 x 10 3 . 4 5 x 10' 102 101 3 . 5 0 x 10' 105 103 3.54 x 104 x e r c c o i t n r t d a t a geometry slightly lower t h a n ~
Sample Standard A Test -41 Test A2 Test .4:1 Test A4 Standard H' Test B1 Tent I32
Counts/min. 795 fi77 _..
730 717 740 1576 1610 1655 'I I n ceriw E, crucibles O..5nL,
Cr
Table 11. Conipoutids of Sodium Weight % (as X5.C Oii Gidrh--Forind ( n i r a II ,
>odium naphrhrridtr Sample A
Sample H Snmple C Sodium chloridr Sample R Sample C Sodium carbonate Sample C Sodirirn sulfa t 1, Sample C
0.0017 0.0063 0.0315 0.0945 0 0062 0,0294 0 0038 0,0058
0 001.; 0 0058 0 0313 0 0966 0 0002 0 0288 0 0038 0 0058
0.0059 0.00:3'3
0,0038
0.0038 0.0058
0,0038 0.0055
0.0038
0.0038
0.0059
samples \vas mininiized. .\ stniidard cieviatioii uf' 1.7yo\\-as valculated from the range of error in replicate samples. .I series of' iron samples which had been measured by counting thr samples in the crucibles was checkcd by stimpling the dissolved ash arid counting the dried aliquots a t 10% geometry. The sample aliquots mere mounted on glass inicroscope slide cover glasses and dried uiider an infrared lamp. The two methods yielded comparable results in ter.m.: of 1 ) i w v i i t : i gr of the stand:ii,d raniples ('r:llJll* 1).
observed. Oils containing constituents of widely divergent boiling points may show marked surface t'urbulence unless combust,ion is rigorously controlled. In the combustion of some samples, particularly those with high fire points, crawling of the oil over the edge of the crucible was observed. When the displaced oil was checked with a Geiger counter, no activity could be detected. Crawling of the oil across the flame boundary would thus appear to have heen a process of distillat,ion in which compounds of the metallic elements played 110 significant part. Losses observed in turbulent combustion may then be attributed to the entrainment of ash f i i i ~ m c din the combustion of drops or filaments above the surface of thc. hurning oil. The controlled air supply in closed system cwmhistioris contributed to smoother burning and, therefore, to tiwrrtised loss. Thr thrrnitil r;tabilit,yof the compounds st,udied was probably riot s o great :is that expected for some of the more highly organizrd c h e h t e compounds. Thus, some portion of native cont:iniiiiants m:iy he lost, by volatilizatioii during the combustion step. In principle, it should be possible to irradiate characteristic petroleuni oils wit.h thermal neutrons in order to synthesize tlit. r;tdioni:tive species in t,heir native compound form. In the :it)sc.iicr of appreciable activated decomposition, the resulta would he representative of the true stat,e of affairs. I t is proh:ilJle that drc.oiiiposit,ion would be extensive for such compounds :ind that exchange of the active products wit.h inactive, undissociated species would be small. I t is planned to invefitigate this mode of approach in later experiments. It is concluded t,hat,, if t,he additives used in this study a d e quately represrnt, t,he condit,ion of normally occurring metallic contaminants, losses attributable to volatilization and entrainment' of ash component,s are not of great significance in properly c.onduc,t,ed analyses.
Table IV.
Compounds of Calcium
Calcium naphthenate I{ ESC LTS
Sample A Sample C
I h t n obtained in the experiments re given in Tahlw 11 10 I\-. 1,istctl values for \\eight pvr rent found usually repi,ereiit tluplivatti rraiilts; a fea- were ohtained iii quadruplicatr. In genrral, rec30vrry of the added tracer activities was satisfactory. although dcviiition? of possilllr signific*:iiic,r\ v c w o1)rervrd with IO\\. (*oncfiiilrations of wdiuni a ~ i diwii ii:ilhthei~atesin nils X : i r i d (', respc~c~tively.Comparable drviations \\ere not observed iri curresponding experiments carried out in the closed system (Tahle T). It is probable that losses observed in the open combustion,* represent experimental error arising from improper combustioil of the oil samples. Exploratory experiments indicated that high rates of combustion and thr presence of traces of Mater in the oils c ~ a u ~ ead considerable aniouiit of surface turbulence during comhiiPtinn and iii tlirse cases high and variahle lnwes were
___
..
.
_
_
Iron naphthenate Sample A Sample C
Iron salicylate Sample C Iron oxide Sample C
~
0 0077 0 0023
0 0 0 0 0
0073 0077 0154 0237 0382
0 0062 0 0023
0 0 0 0 0 0 0
0076 0020 0072 0071 0145 0232 0357
0.0061 0 0028
Weight % (as CaCOa) .4dded Found (mean) 0.0015 0.0022 0,0077
0.0013 0,0023 0.0077
Table V. Closed System Combustions Weight 7c (as XasCOa or FezOa) Compound rodium naphthenate Iron naphthenatr
/'
Sample
Added
Entrained
.I
0 0058 0 0019 0 0362
x 10-5 N o t detectable" Kot detectablea Not detectable"
6C
0 0990
Limit of (ietertion was approximately 10-s neight
1.5
56.
hCKNOWLEDG\I EVT
This investigation was supported by a grant from the Humble Oil and Refining Co., Houston, Teu. The authors gratefully ackiionledge the cooperation of members of the technical staff of the technical and research divisions of the company, particularly that of J. 1 2 . Powers, r h w e comments and suggestions were e~peciallvhrlpful. LITERATURE CITED
(1) .2m. Yoc. Testing Materials, Philadelphia, "A.S.T.M. Stand-
ards on Petroleum Products and Lubricants," Designation D 482-46. 1947.
( 2 ) Humhle Oil and Refining Co., Refining Department. Technical aiid Research Divisions, Baytown, Tex., private conimiinica-
tion. RECE1vF:n November 2 5 , 1950. Presented before the Division of Petroleum Chemistry, Symposium on the Use of Isotopes in Petroleum Chemistry, a t SOCIETY. Chicago. Ill. t h e 118th l l r e t i n n of the AMERICAS CHEMICAI,
