I N D U S T R I A L A N D E,VGINEERING C H E M I S T R Y
868
Vol. 19, No. 8
Chemical Processes for Re-refining and Decolorizing Dry-Cleaners’ Solvent by Continuous Automatic Methods’ By Alan E. Flowers, Ford H. McRerty, and Melvin A. Dietrich THED E LAVAL S E P A R A T OCOXPANY, R POUGHKEEPSIE, Ii. Y.
T
1-The solvent should not affect the strength, flexibility, HE dry-cleaning industry is a large consuiner of petrofiber. leum products whose problems appear to have received smoothness~Or luster Of the little attention from petroleum technologists. This 2-The not the dyestuffs used. 3-The solvent should not be injurious to plant workers. industry now does a gross business of about $150,000,000,2 4-The solvent should have a high initial boiling point to and consumes about 100!OoO!Ooo liters (30,000,000 gallons) minimize evaporation losses and particularly the fire hazard. of petroleum annually in the cleaning operation.’ On the 5-The solvent should have a reasonably low end point to average 0.5 kg. of “solvent” is consumed for each kilogram facilitate the removal of the last traces of solvent in drying. &--The solvent should be free from colored Or ~ ~ d o r o ucons of goods cleaned. There are approximately four thousand dry-cleaning establishments in this country, rangillg in size stituents and from suspended solids or moisture which might be retained by the goods. from the large “wholesalers,” who clean 1,500,000 kg. or The first three of these requirements are apparently filled 1,000,000 or more “suit-equivalents” per year, to the small “retailer” cleaning only i by any of the properly refew thousand k i l o g r a m s fined petroleum distillates.6 Dry-cleaners are large consumers of light petroleum annually. Although these solvents can distillates. During use in the cleaning operation these hardly be called non-poiDefinitions solvents become contaminated by dirt and moisture, and sonous,6they probably have become dark in color and odoriferous. The economical as little effect on the human D r y - c l e a n i n g consists reclamation is a difficult technical problem. Purificasystem as any available nonessentially in washing textion processes now in use include steam distillation and aqueous solvent. tiles in a s u i t a b l e nonprocesses utilizing caustic solutions and activated carThe requirements of high a q u e o u s “solvent.” Sobons and earths. A new process is described herein for initial point and low end called “wholesale” cleaners use in conjunction with continuous centrifugal solvent point are not met by ordio b t a i n t h e i r work chiefly clarification which permits simultaneously continuous nary motor gasoline, which from tailors and others who decolorizing by means of concentrated sulfuric acid and is the solvent in most gendo not have their own drya neutralizing treatment. Data are presented on the eral use a t the present time. cleaning equipment. The chemical and economic aspects of the new process in An effort is being made by “retailer” deals directly with comparison with the others. the Sational Association of the individual customer. In Dvers and Cleaners to 1310order to render the results mote the use of the so-called stated in this mblication ,~ reduces evaporation losses and more easily understood, the “suit-equivalent,” equivalent to Stoddard type ~ o l v e n twhich 1.5 kg. (3.3 lbs.) of textiles to be cleaned is a convenient unit, fire hazard without sacrificing ease of drying. This type of this being about the average weight of a man’s three-piece suit. solvent has a flash point (Cleveland open cup) between 40.6” The articles submitted for dry-cleaning range from gloves to and 43” C.. (105” and 110” F.) and users of solvent having a carpets, and it is not customary to weigh the goods cleaned. flash point above 100’ F. (37.8’ C.) are a t present exempted from compliance with the New York State Labor DepartThe Process of Dry-cleaning ment Code.8 The difference betwecn this type of solvent and the usual winter grade of motor gasoline is clearly shown by In the process of dry-cleaning which is almost universally the distillation curves (Figure 1) for the two solvents before used in this country, the goods are washed with gasoline in a laundry type masher. Most of the excess solvent is then and after the \\-eathering which occurs during use in a drycleaning system. “extracted” by centrifugal force, and finally the last portion The evaporation loss when using the Stoddard type of of the solvent, amounting to about 20 per cent of the dry solvent is so much lower than when motor gasoline is used weight of the goods, is evaporated by the use of air at about for cleaning that this alone more than compensates for the 80” C. (180” F.) in a drying tumbler. hlany cleaners add slightly higher price charged for the Stoddard type of solyent. some type of dry-cleaners’ soap4to the solvent in the washer. Others add ammonia, mixtures of dry-cleaners’ soap and Solvent Contamination ammonia, or even water. Data on the use of dry-cleaners’ The removal of dirt, moisture, and color from the solvent soap are presented in Table I. and the elimination of any odor which might be retained by the goods are the dry-cleaners’ most difficult problems. UnSolvent Characteristics Required til the advent of continuous centrifugal solvent clarification Petroleum hydrocarbons used for dry-cleaning qhould con- it was considered satisfactory to wash in contaminated solform to the following general requirements: vent, relying on rinsing a t least the light-colored goodr in cleaners’ solvent to prevent discoloration. The modern cleaner 1 Presented before the Division of Petroleum Chemistry a t the 73rd Meeting of t h e American Chemical Society, Richmond, Va., April 11 t o 16,
1927.
6
Goldman, H u b b a r d , and Schoffstall, Bur Standards, T e c h Papev 322
(1926) 2
Tull, Cleaners Dyers Reu., 10, S o . 9, p. 37 (February, 1927).
4
Matthews, Color Trade J . , 16, 79 (1924).
* N a g . Cleaner D y e r , 17, 84 (August, 19261.
e Engler-Hofer, “ D a s Erdol,” Vol. I, p. 786 11913). 7 Stoddard Can Colorzrt Terlzle Processor 5, 180 (1925) 8 State of S e w York Dept Labor, Industrial Code Bull 29
(1926).
INDCSTRIAL A X D ENGIXEERI;YG CHEMISTRY
August, 1927
demands that the solvent in tlie washer be dry. fairly clean, light-colored, arid free from objectioiiable odor a t all times; and further that the solvent condition a t the end of the washing 1:eriod be such that no riming is needed. The dirt picked up by cleaners' solvent is, of course, derived entirely from the goods cleaned. On the average, 100 kg. (65 suit-equivalents) of goods yield 1.6 kg. of dry solid dirt. The goods also contain considerable amounts of da,rkcolored substances which dissolve in the cleansing solvent. The extent of such contamination is shown by the following test, which indicated that 100 kg. (65 suit-equivalents) of average goods contained about 1.8 kg. of high-boiling substances soluble in the cleansing fluid: Eighty kilograms of clothing were washed in about 300 liters of Stoddard type solvent. The initial color of the solvent was 10. Kofe-In this paper, solvent colors are given in terms of t h e free iodine concentration (milligrams per liter) in a n aqueous iodine-potas5ium iodide solution of equal color appearance. T h e solutions used contained t w o p a r t s of potassium iodide f o r each p a r t of iodine. Such solutions fade on standing. even in sealed tubes, and must h e prepared t h e same d a y t h e y are used.
of a Stoddard type dry-cleaners' qolvent by the method of Egloff and Alorrellg are g h e n in Table 11. T a b l e 11- A n a l y s e s of S t o d d a r d S o l v e n t a n d M o t o r G a s o l i n e n (Figures In per cent) STODDARD MOTORG i s 0 ~ 1 h . E HYDROCARBOY SOL? ENT (1) (2) Unsaturates 0 5 6 5 i o i 3 7 2 4 4 Aromatics 4 7 28 7 22 4 Saphthenes Paraffins 87 5 57 6 66 2 Gasoline samples were purchased from local dealers a n d were n o t redistilled before analyzing.
Removal of Solvent Contamination The removal of suspended solids and moisture from used cleaners' solvent is iiot particularly difficult. The centrifugal clarifier does this cheaply and effectkely. dggloineration by mixing with alkali solutions followed by gravity qettlinp is another time-tried procedure, which, however, 240 I
Volume heavy ends cc. Neutralization value, mg. K O H p e r gram (A. S. T. X )
10
0.7
SOLVEST USED 30 50 100
OK
OK
...
OK OK OK
. .
OK OK OK OK
OK OK OK OK
1
1
I
1
I
1
::I
2
w
t.
100
Used Stoddard-Type Solvent x New Stoddard-TypeSolvcnt
P
80
0
Used Motor Gasolins fi-om
Experimental c1cdniqj Plant o New Motor Gasoline Fall of 1926 n Used Motor Gasoline fi-om
20
Wholosale Cleaner- Boston
'0
IO
20
30
40
50
60
70
90
80
100
PERCENT DISTILLED Figure 1-Distillation
Curves f o r Yew a n d Used D r y - c l e a n i n g Solvents
iieceysitates the prorision of cettling tanks holding twenty to fifty times the amount of solrent actually used in the wadier, if serious accumulation of dirt in the cleansing fluid is to 1)e avoided. Filtration is used to some extent in Europe. hut because of the slimy nature of the solid, t o be renioved and the necessity of minimizing solvent loss, this method would seem to be less desirable than either of the others. Tlie of C l o t h a f t e r W a s h i n g and D r y i n g
+ 0.1% DIRT
AND
0.1';
U'ATZR
SDLVEST
-+ 0.1%
IIIRT, 0.lrL SOAP
WATER, A K D 0 . 4 '
;
O F N E W A N D U S E D STODDARD S O L V E N T
Spots, wrinkles, and discoloration Spots, wrinkles, a n d discoloration Spots, wrinkles, and discoloration U'rinkles a n d discoloration
, . .
S E R I E S II--MIXfURI?S
n'ater-white (new-) 20 60 1 on
il3
+
OK OK OK
I
I6O
T a b l e I - L a b o r a t o r y W a s h i n g T e s t s on W h i t e Silk G o o d s - C o n d i t i o n F I L T L R C D D R YSOLDRY YSST t SOLVEXT 0.1'6 DIRT AND 0.470 SOLVSNT SOLVEKT 0.1'; DIRT SOAP S E R I E S I-MIXTURES
lvater-white (new)
8
6.6
The preseiice of small aiiiomit? of suspended ro!ids or even of "dirt'! in the cleaiiiing fluid is iiot necessarily objectiouable. Tlie te,st data presented in Table I show that even fine white silks may safely be washed in solvent containing appreciable amounts of dirt: if no free nioisture is present. If, however. tlie solvent contains as little as 0.1 Fer cent (by rolunie) of free vater a large part of the dirt and iiioiRture is picked u p by the goods rausing spots a i d geiierzil discoloraation. The importance of guarding against the presence of free moisture in tlie clesnsing solvent, which may contain a trace of dirt,,, cannot be too strongly emphasized. Tests made in this laboratoryiritlicate that the largeamouiits of unsaturated hydrocarbons contained in preseiit-day motor gasoline may be responsible for some of the color and odor formed when this solvent is used. Tlie varnishlike odor which such a solT-ent may develop is particularly objectionable. ,since it R i retained by the goods after drying. This cannot be completely eliminated by distillation or by treatment with :llkaline solutions, activated carbon, or coinbinations of these. 130th color and odor, howel.-er, can be removed by suitable treatment with concentrated sulfuric acid.
C O L O R O F STODDARD
I
I
200
AFTER ~VASHING GOODS 16
GOODS
I
220
Dirt (1.5 kg. dry basis) was removed from the solvent by continuous circulation through a centrifugal clarifier. At the end of the washing operation the color of the dirt-free solvent was 100. One-liter quantities of this solvent before and after use were steam-distilled a t 100' C. The heavy ends left in the flask had the following characteristics: BEFORE XUrixxc
869
Streaks, wrinkles, and clisroloration Streaks, wrinkles, a n d discoloration Wrinkles a n d discoloration Wrinkles and discoloration
OF N E W A N D A C I D - T R B A T E D U S E D STODDARD S O L V E N T S
F a i n t discoloration and wrinkles F a i n t discoloration a n d wrinkles Trace of discoloration a n d wrinkles Trace of discoloration a n d wrinkles
The ne\T Stodclard type solvent is practically free from unsaturated compounds, and does not appear to develop appreciable amounts of either color or odor spontaneously, even when exposed to air iii the presence of alkalieq The results of an examinaticni of a 1926-27 winter motor gaqoline and
Streaks, \winkles, and discoloration Streaks, wrinkles, and di5coloration Streaks, wrinkles;, and discoloration Slight wrinkles a n d discoloration
Hele-Shaw "edge filter" ha< h e n recominended'n for this service. THISJ O U R U 4 I , , 18, 354 (1026) Hlnckley, ind
chemlsr February, 1 9 2 i
67
44, lliT
13125),
Anon I n d u s f r l a l
INDUSTRIAL A N D ENGINEERING CHEMISTRY
870
x Used Motor Gasoline from Exparimontal Cleaning Plant Wholesale Cleaner-Boston
0
20
40
60
80
I
100
PERCENT OP SOLVENT DISTILLEDOVER Figure 2-Steam
Distillation of Dry-cleaning Solvents
The problem of the removal of color and odor is much more complex than is that of the removal of suspended dirt and moisture. White cotton or silk goods cleaned in solvent of a color of 60 or more may show a slight yellow discoloration after drying (Table I). To avoid the possibility of such discoloration, a solvent color of less than 50 should be maintained for washing such goods. Although pure white goods represents only a small portion of the work handled by the average cleaner, the practice of using very dark colored solvent, even for dark goods, is rapidly becoming obsolete. This is probably due in part t o the fact that dark-colored solvent (at least if this mas originally motor gasoline) is likely t o have a varnish-like odor, which is very difficult to remove from the goods in the drying operation. Distillation is perhaps the most obyious means for purifying contaminated solvent, and has found wide application in this field. Batch distillation by the use of open steam appears to be the accepted procedure, probably because of the rather high finishing temperature which makes the use of steam in coils impractical, and because of the necessity of minimizing fire hazard and odor in the distillate. Laboratory tests (Figure 2 ) indicate that steam distillation under average dry-cleaning plant condition4 will cost at least 5 t o 10 mills per liter for steam. cooling water, and solvent loss, depending on the type of solvent in uqe and the degree of contamination. Distillation cannot eliminate volatile substances, nor does it remove the varnish-like odor commonly found in used motor gasoline, and the distilled solvent may also contain substances which cauw it to cling tenaciously to traces of moisture after separation.
VOl. 19, No. 8
missible and is apparently unavoidable. For this type of work steam distillation has so far been able to compete with proposed chemical processes for color and odor removal, particularly because of the simplicity of the process and apparatus involved. I n the modern cleaning plant the accumulation of large amounts of color, etc., in the solvent is no longer tolerated. While the cleaner who relies on the batch method of contamination removal may continue to use the cleansing fluid until its color has reached 250 or more, the cleaner who operates a continuous system for the removal of solvent contamination uses a solvent whose color varies only between the limits of about 20 to 60. The continuous removal of solvent contamination has numerous advantages from the point of view of the dry-cleaner, as well as from that of his customers, and the use of continuous clarifying and decolorizing systems of one type or another for handling cleaners’ solvent is rapidly becoming well-nigh universal in this country. The problem of continuous removal of color and odor from cleaners’ solvent is fundamentally different from that of batch removal of such contamination. The system for continuous removal of color and odor receives solvent from the washer a t a color of 60 or less and removes part or all of this color content before returning the solvent to the washer. It must therefore handle many times the volume of solvent that would be handled by a batch system washing the same quantities of goods. Under these conditions the cost of processing a liter of solvent must be very low indeed, and should preferably vary with the amount of contamination removed from the solvent during its flow through the processing system. Steam distillation, a t least with the type of equipment now used by dry-cleaners for distilling batches of dirty solvent, is far too costly for use as a continuous decolorizing process, It is also seriously handicapped by the fact that just as much steam and cooling water are required for distilling a liter of water-white solvent as for reclaiming a liter of solvent of color 500.
SOLVENT COLOR Figure 3-Laboratory Tests on Batch Decolorizing of Used Dry-cleaning Solvents
Batch vs. Continuous Contamination Removal
Chemical Processes for Solvent Decolorizing
Until the present decade batch treatment of solvent to eliminate accumulated contamination x+-asthe accepted practice. Under these conditions the contaminating substances are contained in a relatively small volume of solvent, and a fairly high unit cost for reclaiming the solvent may be per-
Certain chemical processes conform more or less to the above requirements for a satisfactory treatment for the removal of low color concentrations from large volumes of solvent. The first such process t o come into general use consisted in washing the dirty solvent with a caustic soda
August, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
solution and then with water. It was soon found, however, that this process did not prevent the slow accumulation of color and odor. I n 1924 work instituted a t the Bureau of Standards by the National Association of Dyers and Cleaners” demonstrated that used cleaners’ solvent could be reclaimed by the use of certain types of activated carbon in conjunction with aqueous alkaline solutions. Although this process was originally proposed for treating batches of contaminated solvent, i t was soon found that the process could readily be applied in the continuous systems, which had preriously used caustic solutions alone. 11
Hubbard, Bur T i a n d a v d s , Tech Pa$er 280 (lq25).
871
The activated carbon process for removing solvent contamination is essentially suitable for operation on the continuous system, rather than on the batch system, in that the cost of completely decolorizing a liter of badly contaminated solvent is quite high (comparable with the cost of steam distillation), while the cost of removing more or less completely a small amount of color from a large volume of solvent is low. (Figures 3 and 4) Laboratory tests indicate that the activated carbon process will not completely remove the varnish-like odor from used solvent, and there is some evidence that gradual accumulation will occur in continuous systems using this process in conjunction with motor gasoline. Xumerous attempts have been made to utilize fuller’&earth and the newer activated earths for decolorizing used solvents, and equipment for this purpose is on the market. Laboratory tests (Figures 3 and 4), as well as actual cleaning-plant trials, indicate that the relatively large quantity of such decolorizing agents required and the considerable losses of solvent that are involved, together with the necessity for proper control of moisture content, more than compensate for the simplicity of equipment and process involved. The regeneration of exhausted earths, as practiced in the petroleum industry, does not appear to be feasible under the conditions of the dry-cleaning plant. Continuous Decolorizing in Conjunction with Continuous Centrifugal Clarification
SOLVENT Loss
LITERS PER 1000 LITERS OF USED SOLVENT TREATED Figure 4-Laboratory Tests o n Batch Decolorizing of Used Dry-cleaning Solvents
Ever since the introduction of the centrifugal clarifier for the continuous removal of suspended dirt and moisture from cleaners’ solvent, attention has been given the question of selecting or developing suitable processes and equipment for removing color and odor from the clarified solvent. Three years ago it was definitely recognized that such a color-removing process must be of the continuous type; also t h a t under the conditions met in the average cleaning establishment the decolorizing equipment need only handle a fraction of the solvent stream passed through the centrifugal 260 240
I
,
I
I
I
I
I
1
I 50
1 60
I
I
70
80
220
200 IEO 160 140
I20 100
80 60
o Motor Gasoline
PERCENT OF COLORORIGINALLYPRESENT I
REMOVEDBY ACIDTREATMENT
Figure &Effect
of Acid Strength a n d Temperature on Decolorizing Used Dry-cleaning Solvents
0
10
I 20
I 30
I 40
90
100
PERCENT DISTILLED Figure 6-Effect of 93 a n d 98 Per Cent Sulfuric Acid o n Distillation Curves of Motor Gasoline and Stoddard Type Solvent
m;ida f i x dr:Awiug frcsli i:linrgw of clmnicals irito tiic resljectivc tsnks by cstablisliirig a partin1 VBCU~IIIi n tlreiri by means [if a sindl mciiuin piimp.
Tlrc dr>r-oleaiier is intercstiid primarily i i i the solvent color which ciiii he riiniiitaiiiod wlieii washing dotlies at. a given rate. Sirico the wirric ilonc i n the cxpcriinental eieaililig plant represeiitcd miy about Sf3500 grow iricoiiie per year (at $1.00 per kilograin of gtr)ds domed), it affords only B little infor-
tlio disk-stack ( 7 ) , w1iii:h providoi about 2.2 siplare nicters ling ar(!:i in wliicli tlic lietivim coinponetit is requircil to fnll a In:isiriiuiri of i r1111i. bcfme it strikes is disk surface, o i i lid duwn \vIii~!li it flow tii drop fiii:tlly back pnae (3). 'l'lie solvent stream, nii%-i:&rryi i 0.05 per cent by r o l i i i n r i of acid tar (or about 0.15 per ccnt of iicutnilieing soliitiun), flows iipwarrls pixst thc pcripliery of the disks and finally out tlirougli (8). Application to Decolorizing of Dry-Cleaners' Solvent
TIic re-refining of used cleaners' solveiil. by IIIIXIIS of SUIfiiric ailid is, of course, o d y practical fur a solvent frriiii which suspended dirt and moisture liive already been reinoval. Furthermore, siiice the neutralized light-colored sdvi:nt may entrain a h u t 0.15 per cent of aqueous sdiitioti, it cannot lie adniittcd tu tlie msher uiitil this 1 ~ biien s rmiiovrd. Tu meet time coiiditiuiis a circulating system, sliowii scliematically in Figure 9, is us A p1iutugr:iph of a dry-cleaning plant ili wliich such a em lias been iiisttrllod is shown iii Figurc 10. The presetit units for decoioriaiiig iised cleaitcrs' sol\oiit by means of coiieentrated sulfuric acid are designed t,o rcceive continuously from the ccritrifugtil clarifier iised solvent of a color of iiot. more t,lian 100, at, a r:itttc of 500 lit,ers per hour, a i d to deliver to the centrifugd clarifier, and tlirougli this to tile nashcr, this stream of solvent decolorized to lxdween 0 i ~ n d20 color, dcpending upon the coiiditioii of the acid cbargc. When rcc,civiirg solvents at, an averagc cdor of about 40 and retiiriiing it at, a.ri average of alxiiit 10, the riecoloriziiig operation costs titiout 0.5 mill pcr litcr, as sliowi by data from eight, nionths' cxpcrimcntrti plant operation, during which t i m e 5000 kp. of clnt,Iiing, lilankr!t~s, rugs, et ai t h e l ~ a i l d i n01~tanker Beets, iitiliration of nations! iiIr"1lOi. etc.
The Dcpartmcnt has information that Russian intcrcsts arc pcnctrating European oil markets with products of their newly developed oil fields. Paralleling this movement is ail apparent American overproduction which makes shipment or surplus to foreign purchasers desirable iiom the producers' viewpoint. Recent reports to thc Department of Commerce stated t h a t a hill to form a French petroleum monopoly has been presentcd. I n Italy state subsidies are granted oil operators. Poland is reported considering reviving its cartel, while Rumania has alrcady nationalized the oil industry. A report on Spanish petroleum importation in 1928, h?"d
