Magnesium Hydroxide in the Petroleum Industry F. T. GARDKER,University of Tulsa, Tulsa, Okla.,
ASD
E. C.
HIGGrns,
JR., Long Beach, Calif.
T
HE use of alkali in the
preferred in such cases. Several Passage of hydrocarbon mixtures containing petroleum i n d u s t r y is successive e x t r a c t i o n s w i t h phenols and hydrogen sulfide ocer granular principally confined to a small amount of suspension magnesium hydroxide results in the removal of will give effective r e m o v a l of the treatment of large volumes these impurities until the surface of the granules acid materials as will be shown of gas or liquid containing small is coated by a $film of reaction products. The subsequently. percentages of undesirable acid The ease of hydrolysis of magimpurities. The application of employment of magnesium hydroxide in the nesium salts of v o 1a t i l e weak a base in solid granular form, f o r m of a suspension makes possible ihe ready acids makes possible ready reover which the liquid or gas unremoval of high concentrations of hydrogen covery of the base f r o m s u c h dergoing treatment may p a s s , sulj?de f r o m hydrocarbon mixtures by a series salts. Boiling of salts ,of this offers the possibility of furnishof exlractions. Passage of liquid hydrocarbon type f o r a f e w m i n u t e s will ing a long operating cycle with result in expulsion of virtually a minimum of handling expense. mixtures which hace been treated with sulfur-ic all of t h e a c i d , l e a v i n g the The adaptability of magnesium acid over granular magnesium hydroxide results in a g n e s iuni hydroxide availhydroxide to such work has been in the neutralization of the mixture until the able, after cooling, for reaction studied. surfaces of the granules are coated by a &filmof with further weak acid. Mined as the mineral brucite, reaction products. Magnesium suljhydrale is Magnesium h y d r o x i d e has m a g n e s i u m h y d r o x i d e has been found to be a d a p t a b l e a h a r d n e s s of 2.5 on Moh’s readily hydrolyzed at the boiling point of the to four processes carried o u t scale. hlagnesium h y d r o x i d e suspended sojution, making possible the recovery in t h e petroleum i n d u s t r y : may also be prepared by hyof magnesium hydroxide f r o m the spent material. phenol removal, hydrogen suldroxylation of magnesium oxide, Basic magnesium mercapiides, soluble in gasofide removal, neutralization of prepared by calcination of magline, are believed to be formed when a gasoline acidified stocks, and conversion nesite. The oxide e m p l o y e d of mercaptans to disulfides, or for the purpose should contain containing mercaptans is passed through a “sweetening.” 90 to 95 per cent m a g n e s i u m column of dry magnesium hydroxide: elementary o x i d e , s h o w l e s s than 3 per sulfur reacts wilh these compounds, concerting cent ignition loss: contain less PHENOL REMOVAL ihem to disul$des. Magnesium hydroxide spent t h a n 2.5 p e r c e n t i n s o l u b l e in the sweetening process can be regenerated by The p r e s e n c e of p h e n o l > matter, and should not be “dead arid allied substances may be burnt,” since ready hydration boiling with water, boiling with sodium hyd e t e c t e d by m e a n s of ferric is d e s i r e d . T h e h y d r a t i o n droxide, washing twice with water, and drying. chloride ( 4 ) . Shaking of 300 cc. of g r a n u 1a r magnesium oxide of a c r a c k e d g a s o l i n e w i t h furnishes a nonfriable hydroxide 3 cc. of ferric chloride produced a pronounced change in niechanically satiqfactoiy as tower packing. Brucite is fou1id in commercial quantities af, Luning, color of the reagent. Another 300-cc. sample of this gasoSev., and Chewdah, K a s h . Seaton (5) has recently dis- line \vas h a k e n with two 3-cc. portions of a suspension of magnesium hydroxide in water (approximately 25 per cussed Pacific Coast magnesite deposits. The salts formed by the reaction of magnesium hydroxide cent by 1% eiqlit maqnesiuin hydroxide ground to pass 100with weak acids are subject to hydrolysis to a marked degree, mesh qcreen) and filtered to remove any trace of emulsified owing to the slight solubility of the base. I n employing a material Tile resulting material gave a negative phenol ton-er packed with magnesium hydroxide to remove weak test. A portion of the suspension v i t h which the gasoline had acids from liquid or gaseous petroleum products, the magnesium salts formed are deposited progressively on the sur- been agitated 11as acidified 11it11 hydrochloric acid and tested face of the base and thus the acids are removed as passage for phenols. -1pronounced color change with ferric chloride throupli the tower occurs, until, after contact with a large was observed. The balance of the suspension m-as boiled number of successive surfaces, the amount of free acid be- gently for a few minutes, cooled, acidified, and, when tested, comes small to the banishing point. Thus, even though gave a slight positive phenol test. the process of qalt formations is never complete, the removal A portion of the same gasoline r ~ a streated with granular of wcccssive increments of acids as salts insoluble in hydro- magnesium hydro.iide in a laboratory column. The column 90 cm., and concarlions re~ult.: in eventual neutralization of essentially all employed consisted of a glass tube, 1.2 free acid tained 125 grams of dry magnesium hydroxide. The gasoIf tlie concentration of the weak acids is appreciably large, line n-as introduced a t tlie bottom of the column a t the rate it is conceivable that the use of a d i d base may riot repre- of 5 cc. per minute under sufficient head to force it upward through the packing The efflux material v a s free from sent the moat economical mrtlioJ of application: that i;, the surface of the magnesium hydroxide n ill become coated phenols. I n no instance haT c plienols lieen detected in gasowith n film of reaction products so rapidly that the time line. m-lrich have been thus treated. The presence of other of u s e n d l be too short for effective plant operation. The undesiralile compounds in treated productq ha.; proved the use of magnesium hydroxide as a thin suspension is to be vitiation of the liaqe by snrface films of reaction products, >%
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E iF D U S T R I A L A N D E
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S G I N EER
I N G C H E hl I S T R Y
Vol. 24, No. 10
fide a t all levels, waa a l l o w e d t o stand overnight, after w h i c h the e f f l u x from t h e tower showed a slight but definite h y d r o g e n sulfide c o n t e n t . This finding is in accord with the exBnuctrc pectation that successive extraction by increments o c c u r E if sufficient time is allowed for equilibrium to be established a t each successive level of the packing. So little time wah a l l o w e d for reaction that the gasoline a t the 11p p e r m os t level contained substant i a l l y a l l of i t a FIGURE1. FLOWSHEETOF MAGXESIC'M HYDROXIDE SWEETENING USIT o r i g i n a1 hydrogen sulfide content. but phenol removal has always been substantially coni- Cpoii standing, equilibrium was ebtablished and the slight hydrogen sulfide content found was due t o the appreciable plete. hydrolysis of magnesium sulfhydrate [Mg(GH),]. Gasoline was again started through the apparatus a t a moderate rate. REMOVAL OF HYDROGHN SULFIDE ,\n efflux free from hydrogen sulfide was obtained after runTlie presence of hydrogen sulfide in liydrocarbon mixture> ning a few minutes, as was anticipated. Municipal natural gas was "loaded" with hydrogen sulfide may be followed readily with lead acetate. Work has been done with still gas, natural gas, gasoline, and crude oil, to by passage through a flask containing sodium sulfide on to determine the effectiveness of hydrogen sulfide removal from which dilute acid was slowly dropped. The gas, rich in hydrogen sulfide, n as then passed through a magnesium these materials by magnesium hydroxide. I n the presence of water a t atmospheric temperature the hydroxide column. A slight back pressure was maintained by bubbling the efflux gas through a few inches of water. following equilibrium ( 7 ) exists: The gas when bubbled through lead acetate (in place of the efflux water bubbler) gave no precipitate a t a fairly rapid 2H2S hlg(OH)z&h'lg(HS)2 2H2O (1) rate. Since hydrogen sulfide is feebly dissociated and magnesium Crude oil from tl:e Pecos field in West Texas, rich in hyhydroxide is very slightly soluble, the equilibrium should lie drogen sulfide, was passed through a column of magnesium appreciably to the left a t ordinary temperatures. At ele- hydroxide, resulting in tFe removal of the hydrogen wlfide vated temperatures in open containers the high vapor pres- from this material. sure of hydrogen sulfide from aqueous solutions should reOwing to the difficulty of maintaining a fixed percentage sult in ready shift of the equilibrium to the left, owing to loss of hydrogen sulfide in materials employed in prolonged laboratory runs, the qualitative laboratory findings were extended of hydrogen sulfide from the solution as rapidly as hydrolysis occurs. At atmospheric temperature, several successive ex- to a more exact basis in semiplant-scale apparatus. All tractions should be required to remove substantially all runs were made a t or near the maximum rate a t which comof the hydrogen sulfide from gaseous or liquid hydrocar- plete hydrogen sulfide removal was possible. In only one run was the magnesium hydroxide evhaurted for hydrogen bons. Gasoline rich in hydrogen sulfide was passed through a d f i d e removal a t the conclusion of the run. The resultq tower similar to that employed for phenol removal. When obtained are shown in Table I. An inspection of run 2 in Table I indicates that the length the rate was low, the efflux gasoline was substantially free of hydrogen sulfide. Upon accelerating the process greatly, of operation for removal of hydrogen sulfide from material< hydrogen sulfide was markedly present in the efflux. The extremely rich in this substance would probably be prohibitower, when filled with gasoline containing hydrogen sul- tively short in commercial oprntion before hvclrr~lv-is and
I
I
+
+
TABLEI. HYDROQEN SULFIDE RENOTALB Y DRY G R A S ~ L A R h l AGSESICM HYDROXIDES RWN
&flaTERIhL
Hi3 CONTENT
WEIGHT OF hIg(OH),
Grams/gal. .Mg./liter or cu. ft. Kg. 5.3 245 27.2 1 Still gasb 3 . 2 148 2 7.2 2 Still qasb 3 Gasolineo 7 .: < 8 0.53 4 Gasolincc S 0.53 (.a a Magnesium hydroxide exhausted at rate maintained when run ceased. liters at 1 atm. and 0' C.; or cubic feet at 1 atm. and b GBBvolumes: a Gasoline volumes in liters or gallons.
Lb. 60 60 16.5 16.5 60' F.
TIME
Hours 24 77 145 113
VOLUXET R E A T E D Lztsrs 4,750 44,453 2,017 3,085
RATEPER H O D R Lzters/metric Gal. or cu. Gal. or cu. f t . ton Wton 174 728 241 1632 2125 707 533 2240 14s 815 3720 373
October. 1932
I N D U S T R I l L .\>D
ENGISEERISG CHEMISTHY
rejuvenation of the surface of magnesium hydroxide granules would be necessary. Tlie application of magnesium hydroxide in a finely divided suspension in water appears to offer a more economical method of treatment for products heavily laden with hydrogen sulfide. In order to gain some information about the rate of extraction of hydrogen sulfide by magnesium hydroxide suspended in water, the following experiments were performed (a 5 per cent by weight suspension was employed throughout):
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in hydrogen sulfide content, but not completely free from it. The results obtained are included in Tahle 111. Tlie results obtained with magnesium hydroxide suspension show that this material is adaptable to rapid removal of large amounts of hydrogen sulfide from liquid and gaseous hydrocarbons, and further that regeneration of the base may readily be accomplished. The cost of heating the suspension to bring about hydrolysis should not be excessive if well-designed heat exchange equipment is employed in conjunction with continuous operation.
Gasoline hainples liere ''loaded" with h>drogen wlfide and were then hand-shaken intermittently with magnesium h\ -ACID ~ E U T R . 1 I ; I Z A T I O N droxide suspension for 30 minutes in each extraction. Thi. mixing was probably not as thorough as that obtained in a short Granular magnesium hydroxide is readily applicable for time with a well-de+qed mechanical mixer. The samples mere allowed to stand until 5eparation of the two layers wa- neutralizing acidified stocks. Many distillates require acid complete, before draining the water layer. In employing 10 treatment before the final stages of refinement. The stock per cent of the suspension by volume, no trouble with emulsions is desludged and washed with water immediately after the mas encountered. When employing 100 per cent of the suv acid treatment and then neutralized. Solid granular magpenqion, an emulsion persistent for some minutes wacl obtained The hydrogen sulfide content of samples was obtained by shaking nesium hydroxide is effectively used for this purpose. The an aliquot with three washings of 2 per cent sodium hydroxide. product of the reaction is magnesium sulfate (MgS04.7H20) poui inR the sodium hydroxide slowly, with stirring, into a vhich is readily soluble in water so that, upon revivification funnel immersed in a solution containing sufficient hydrochloric acid to neutralize the sodium hydroxide, to which a measured of the packed tower, this material is removed by washing, amount of standard iodine solution had been added. The leaving the surface of the magnesium hydroxide exposed excess iodine was then titrated with standard thiosulfate solu- again for neutralizing. tion. The results obtained are summarized in Table 11. Gas samples were enriched in hydrogen sulfide by passing MERCAPTAN ALTERATIOK natural gas a t constant rate through a flask containing sodium wlfide on to which acid of known normality was dropped at n I n tlie course of experimental work on hydrogen sulfide constant rate. The approximate hydrogen sulfide content of the gas could then be calculated. The validity of thi- method removal with granular magnesium hydroxide, it was observed \vas c h e c k e d by p a s s i n g a known v o l u m e of gas thus enriched through sodium hy-/ 4 " C o / / a r Sfeam 450.F droxide solution and analyzing as outlined above The calculated h y d r o g e n sulfide c o n t e n t mas 111 m g . per liter, whereas t h e a n a l y s i s MN showed a content of 115 mg. per liter. Rates of gas flow and hydrogen chloride addition were kept c o n s t a n t for SECT/ON A " 4 m i n u t e s , a f t e r which the gas was bubbled at a constant rate through t w o G e i s s l e r type p o t a s h b u l b s in series, each c o n t a i n i n g a p p r o x i mately 20 cc. of magnesium h y d r o x i d e suspension. The washed g a s w a s t e s t e d for hvdrogen sulfide c o n t e n t by hbbling through lead acetate. At the first indication of hyd r o g e n sulfide the r u n was c o n c l u d e d . A b l a n k was SKTION 6.5 run with Fater in place of the s u s p e n s i o n . The rates ohtained would o b v i o u s l y he greater if countercurrent movement of the suspension were e m p l o y e d . The results obtained are given in Table 111. The ease of hydrolysis of NO rf5 magnesium s u l f h y d r a t e at Pivet flue sheers to She// Tubes info flue sheers. % " R? with appror. the boiling point of the sus750 //e1' H o / e on /' Centem Supporfs a pension was studied quantiSO-Mesh Monr! M e h / Screen. tatively. Spent s u s p e n s i o n from gas extraction was employed. I t was boiled gently for 2 m i n u t e s and analyzed. The original spent, suspension -q contained 1.91 grams of hyNanqeJ drogen sulfide .per liter, and, after hydrolysis, 0.357 gram per l i t e r o r a d e c r e a s e of 81.2 per cent. T h e h y d r o lyzed s u s p e n s i o n was used in hydrogen sulfide extraction -S€tT/ONAL EL EVA 72ON from gas. As a n t i c i o a t e d . t h e r e P u l t i n g g a s &is low FIGURE 2. DETAILOF DRYIXGEQUIPMEST
El IBi
--
fi,llo\vtxl by tlioruirgli drying. Tile rtwlt,iiig iiiwtcrial did not behave as well as before treatniixit. An aiialysis 01 tlie l>ascrwealctl the presence of appruximatcly 2 per enit s i l k wild a trace of nonvolatile acid materials. If either or both of t.lresc rnatcrials wcre present on the siirface of the mag:iesimn liyilroxide, they should be removed by boiling ivitli s , d i i i n i hydroxide. Roiling of the spent imgnesium hydroxide with 2 pcr ecnt sodium hydroxide, followed by washing wit11 \r:it(v t i l i d drying, furnishes a product a.s active as wlieit tirst i ~ m ~ ~ l o y incsmecteniug. d Experinieiits haye indicated that a~ialugousrasukr can be 'I'lw iilctititimhlii rd n i i i y i i w i i m i sirltide iih ii p ~ . o i I i i ,sf ~ t ubtaind ivlien using mqpesiurn oxide as a hasc, instead of i l i c rcaciiuii /VAS iiiit brcn iiiiidi,. If magn~:simri sulfide iu magncsiurn hydroxide, in tlx sweetening process. Tliis jlFeSeIit i1S 8, pl'lduct
