REDUCTION trole Arranned on Flow Sheet
A Staff-IndustryCollaborative Report MERRITT L. KASTENS Associate Editor
c,
.
H. PEDDICORD
in collaboration with
INCE the discovery of the reaction by Bouveault and Blanc L (20 26) in 1903, the reduction of esters with metallic sodium in the presence of a reducing alcohol to form sodium =Its of high molecular weight alcohols has been a claasio laboratory technique (1, 2, 21, M ,89, 51, 38, 36, 46, 6366). However, the reaction requires an excess of sodium and quantities of absolute ethyl alcohol, both relatively expensive, and reported modifications of this original procedure (2f,22,24,SO, 86) have indicated little or no improvement in percentaxe yield. It is still necessary to w e ~. large excesses of sodium which are subsequently neutralieed and
..
Procter &
Gamble Company, C i m i n m t i , Ohio
soveral investigators discovered the proeoss independently within a period of a tew yeam (4, 6, 28, 80,61, 69. 71, 79). Tlie first commercial plant WBS installed at the Deutsche Hydrierwerke, A-G, Berlin-Charlottenhurg in 1928 (271. This and other German plants supplied the United States market until 1933 when E. I. du Pont de Nemours & Company, h e . , commenced operations at Deepwater, N. J. (60,68). SODIUM REDUCTION PROCESS
Du
. ,.-~
108% (4~1.
The development of commercial production of fatty alcohols has been intimately connected with the introduction of synthetic detergents. Early synthetic detergents, dating back to 1834, were sulfuric acid derivatives of vegetable oils. However. in 1925 a sulfuric acid ester of butyhicinoleic ester was introduced as a wetting agent and shortly thereafter I. G. Farbenindustrie developed Igepon A, a sulfonated fatty acid ester, and Igepon T. a fatty acid amide of methyltaurine. Studies made in the development and Utib5atiOn of these products led to a better understanding of the mechanism and chemistry of their detergent action. Bertsch (IS), realizing that the carboxyl group inhibited detergent action, suggested modifying it to the hydroxyl configuration. This discovery led to the introduction of the fatty alcohol sulfate detergents and indirectly initiated the commercial demand for fatty alcohols.
plant. Du
reduction process as a commercial operation because it permits the production of unsaturated alcohols. The high pressure hydrogenation procedure used in Germany usually attacks the ethylenic bonds before the ester group is reduced resulting in the formation of almost completely saturated alcohols (49). Sodium reduction seldom affects unsaturatian although certain conjugated system are reduced to the extent of destroying the conjugation (30,789 74). During the last decsde the Du Pont process has heen perfected to give almost quantitative yields of alcohols baaed on the sodium used (88, 40-44, 73, 74). In this procedure the concentration of reducing alcohol is kept at a minimum by adding it only as fast as it is consumed by the reaction. Reducing alcohols have been chosen so that any sodium eater intermediatea formed are d e composed rapidly and direct reaction between the sodium and the reducine alcohol is neelieible. It is rewrted ( ..La.671.thatsecondary, tertiary, or high aliphatic primary alcohols are suitable and waste little sodium through hydrogen-forming side reactions. However, primary alcohols tend to react too easily with sodium and the tertiary alcohols do not carry the reaction to completion with sufficient speed. Secondary alcohols, therefore, are most satisfactory. The particular secondary alcohol to be used is determined largely by such factom as cost and availability, ease of recovery, and the solubility of the intermediate products I
HIGH PRESSURE PROCESS
Ahnoatat thesametimethisnew demandbecameapparent, higb pressure catalytic processes for the production of these alcohols were perfected in Europe (47,80,70, 78) and the United States (8. 6 4 . T h e hydrogenation processes used, variously, copper chromite (a, nickel or copper carbonates (471, and copper and chromium oxides (3) for catalysts. P m u r e s reported ranged from 100 to 220 atmospheres a t temperatures between 200" and 300" C. No one man is credited with the development of the high presaure reduetion process. I t is generally assumed that
was firat attracted to the sodium
I I
.
(%, 43, 74).
The Du Pont plant is small, producing only a few tone of product alcohol per day for the company's Duponol D production. 418
I N D U S T R I A.L A N D E N G I N E E R I N G C H E M IS T R Y
March 1949
Procter & Gamble Plant No. 1. I n 1933 Procter & Gamble began the commercial manufacture of Dreft,, a detergent based on a sodium salt of sulfated fatty alcohols. Pilot plant work on Dreft was done with fatty alcohol sulfates imported from Germany; these were made from alcohols produced in high pressure hydrogenators. By the time commercial operations were begun, fatty alcohols from Du Pont's high pressure reduction units in this country were available. Shortly after the start of World War 11, the War Production Board allocated Du Pont's entire output of higher alcohols to war uses. Faced with this situation and knowing the serious disadvantages of the high pressure process (49),Procter & Gamble engineers considered producing their own alcohols by the sodium reduction process. After discussions with D u Pont, Procter & Gamble obtained a license (59, '73) for the process and, within 10 days of the inception of the idea, the first plant to be constructed a t Ivorydale, Ohio, was designed. In 45 days it was built. The first alcohol was produced in June of 1942. This remarkable performance was possible largely because the sodium reduction reaction can be performed in ordinary carbon steel vessels. As practiced a t Ivorydale, using methyl amyl alcohol as a reducing alcohol to reduce triglyceride esters present in coconut oil a simplified equation for the process can be written as: o R-A-0-CH O
H
H CHI
I
H
+ 12K;a 4. GlIC--b-OH
R-b-CrCH
+ 3R-C-ONa
HC -0Na
CHI
-+ Hb-ONa + GHeC,--b-ONa H L N a
R - L HL (REDUCING:
(TRIQLYCERIDE)
ALCOHOL)
@ODIUM SALT OF PRODUCT ALCOHOL)
Actually the reaction is believed (16-18, b$, 16,34, 48, 68, 69, 80, 81) to proceed in five steps going through a ketal configuration; the existence of a ketal configuration has never been proved but this seems to afford the most logical explanation of the mechanism. The hydrolysis of the sodium salts may be expressed:
H
H + 3Hz0 +3RC-OH + 3NaOH H H C3H6(ONa)3+ 3H20 +CBH~(OH)B + 3NaOH
3R-C-ONa
(Glycerol) 6H9C4-
lH3+ -ONa
H
6H20
-+6H&-
r
H-OH
+ 6NaOH
(Regenerated Reducing Alcohol) Hydrogen is generated by the reaction of the product and reducing alcohols with sodium and by other side reactions including the acetoacetic ester condensation. If any water is present, in the reactants, additional hydrogen is formed by the reaction: H20
+ Na +NaOH + 1/2Ha
Control of t'his latter side reaction is tho primary problem in int~intainingt,he production efficiency of these units. The first Procter & Gamble plant, which is still in limited opei,:Lt ion, mas built primarily of tanks, pipes, and vessels pirated ('1.0111 o(liei unils nnd divisions within the company. I n spite of i l s Iiasty construction, the plant operated without serious trouble r i w i i i (Itc l i i w it8 W ~ L R tirst put on stream. It turned out a comI I I ~ ~ I I ~ I : I I ~clu:uiOity Ic of fatty alcohols throughout the war. It \Y:I< P I I V I I :I. sii(mss i i i 'fmt, t.liat as soon as it got into production I l i t ' \\:ir l ' t x ) ( l i i t \ l i o i i l3oard allocated its entire production to est ( iiil (tioii(1ci v i ?(.titj iiiniiuf:tct~uring) activities. \\'liile l'ixwlcr & Gaiuble did not have fatty alcohols for their owii IISC (Itiimiiig (,lit W:II~ years they did acquire much valuable exl ) c i , i ( % i i ( a c ~ ~ l i i c \l Yi ~ Si n c o i ~ p i ~ted : i into the design of plant No. 2. *(si
439
Procter & Gamble Plant No. 2. The second Procter & Gamble Ivorydale plant, with which this report is particularly concerned, was begun early in 1946 and produced its first alcohol in January 1947. Essentially the new plant is a shinier, smoother version of the war built installation. The biggest improvement has been in the handling of the metallic sodium. The original installation used 12-pound pigs of the metal which were hand-fed into an agitated sodium melter containing xylene held a t a temperature near its boiling point. The resultant slurry then was pumped into the reactor. The newer unit provides for the handling of all sodium in a liquid state from tank cars at a special unloading dock, and substantial changes in control and instrumentation have been made. During the construction of the new plant a fundamental change was made in the process reactants. In the original process methylcyclohexanol was used as the reducing alcohol and xylene as the reaction solvent. However, subsequent investigations indicated that percentage yield and malcing could be improved by reducing with methyl amyl alcohol in the presence of toluene. The change to this system was made in 1946 and plant No. 2 was designed to use these solvents. DESCRIPTION O F PROCESS
The sodium reduction reaction as employed at this plant requires, as raw materials, sodium and fatty esters in the form o$ hydrogenated coconut oil. The sodium is obtained from Du Pont's electrolytic plant a t Niagara Falls, N. Y., and from the Ethyl Corporation. As delivered it is almost pure sodium contaminated only by traces of calcium. The coconut oil used is obtained from Pro'cter & Gamble's edible oil division. Its fatty ester distribution is: Ce, trace; CS,8.7%; CIO,5.7%; (312, 50.3%; CIC, 17.4%; CIS, 7.070; C ~ S10.970. , Over-all composition is approximately: 99.0'% triglycerides; 0.75% unsaponifiables; 0.25% fatty acids. It is particularly desirable to hold the fatty acid content t o the lowest possible percentage since this portion reacts with the sodium to form anhydrous soap. Sodium consumed in such a side reaction represents an economic loss to the process. The coconut oil is passed through a two-stage vacuum dryer to reduce the moisture content to the lowest practical level. The first stage, evacuated by two steam ejectors in series, operates at 28.5 mm. pressure. The second stage reduces the pressure to 5 mm. by means of a third steam ejector backed by the first stage system. The ejectors operate on 150-pound steam and have an individual capacity of 25 pounds of air per hour. The oil going into the dryers is heated by internal, G-fin, steam heat exchangers. Temperature is measured only at the oil outlet from the second stage where a controller indicator automatically adjusts the heating steam to maintain an exit temperature of 270' * 5' F. This dryer system reduces the moisture content of the oil to 0.0301,. The dried oil is held in a 12,000-gallon storage tank until it is taken off into the reaction mix scale tank. Process water for the unit is obtained from a central unit where city water is treated with lime and soda ash, coagulated with alum, and filtered. No deionizing treatment is used. Reduction. The reduction step of the process is a batch operation carried out in a mechanically agitated reactor fitted with a reflux condenser and blanketed with nitrogen. Molten sodium (2000 pounds) is weighed out for each batch and dropped into the reactor which already contains 2000 pounds of toluene. The toluene acts as a solvent for the reaction mass and a dispersing medium for the sodium. Since the molten sodium is at a temperature above the boiling point of toluene a reflux cycle starts a t this point so that the reactor temperature is maintained at the boiling point of toluene. When the sodium is in the reactor, coconut oil-solvent solution is fed from the mix feed tank to the reactor at a rate controlled so that only a slight excess of unreacted ester is present in the re-
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Figure 1.
Process Flow Sheet
V d . 41, No. 3
I N D U S T R I A L A N D E N G :NE E R I N 0 C H E M I S T R Y
March 1949,
8cdium atream Fmm tank car Fmm soale tank
240 240
* 10 * 10
270 - 6 150 150
1w 981 220
220 235 495 520
aao
800
820
580
880 290
275
actor at any time. The coconut oil-solvent solution is prepared in a scale tank where the theoretical quantity of the oil based on ita saponification numher is added to a solvent mix composed of equal parts of toluene and methyl amyl alcohol containing an equivalent amount of reducing alcohol as oslculated from the hydroxyl value. The reduction liberates about 125 kg.-cal. per ester equivalent; this cannot be removed etiectively through the sides of the reactor, hence it is m o v e d by refluxing the toluene. Vapor from the reactor paases through a toluene gage tank fitted with a ningle bubble cap tray and is condensed in a falling film condenser. AE the condensed toluene returns to the gage tank over the bubble tray. it is reheated to the boiling point by the rising vapor p b . The boiling toluene then can be reintrcdud into the reactor without danger of chilling +e reaction mixture. A water trap in the toluene line between the condense? and the gage tank trapsout any water in the cycle and provides immediate evidenm of any possible water leakage in the condenser before the water c ~ enter n the reactor. When the entira batch of reaction mix has been added,, an amount of toluene equal to the initial reactor charge (2ooo pounds) is kept from returning to the reactor by olasiog tbs lower tank. Afterthereactor batah hasbeendmpped, valve on the & ~ F B this toluene will be readmitted to the reactor to begin the next cycle. Only toluene is removed at this point so that a hydmxylfree diapereing medium is available to receive the d u m for the next batch. If a solvent mix containing reducing alcohol were used, the hydmgen-producing dum-hydroxyl reaction would take p h More the reduction reaction waa begun. Hydrolysis. The mixture in the reactor is dropped into a mechanically agitated quench tenk containing 17,000 pound^ of water where hydrolysis occm. The quench tank, like the reactor, is fitted with a water cooled reflux condenser. When the entire reactor batch has been dropped, agitation in the quench tank is stopped and the mixture separates into three layers.
TAB- 11. MAT~BIAISBALANCE (Calcuhted for E%
of theoretical yield)
441
The top @rsolvent layer comprises the'product alcobol and the regenerated reducing alcohol. The middle and smallest layer is a dark, soap-stabhed emulsion of the solvent and aqueous layera. T h e aqueous layer in the quench tank contains the glycerol and the caustic formed in the hydrolysis. The layers are separated by settling and the caustic snd emuldon layers are withdrawn from the bbttom of the tank. W h e n the emulaion-solveut interface is reached, suction is shifted to a standpipe for the solvent pumpoIT. This procedure reduces the amount of caustic pumped to the solvent stills where the weter and the caustic would interfere with tbe distillation. Pump wntrols are located next to a hmk box so that the operator can cootrol the cute visually. The dark color of the middle emulsion layer makes the divisions between the layers readily discernable. The solvent layer is pumped directly to the still feed tank. The emulsion layer is pumped off to a settling tank where the emulsion gradually breaks down and the respective water and solvent layera can be drawn off. A small portion of the emulsion containing about 0.03% of the total solvent is stable. After the emulsion layer has been reduced to a minimum in the settling tank,thia portion is acidulated with sulfuric acid to recover the solvents and fatty alcohols. The reeultant oil layer is returned t,a the quencb tank snd the aqueous layer or "seat" is discarded. The aqueous Layer from the quench tank is pumped into a continuous settling tauk to recover entrained solvent. The solution enters the settling tank through a basket made of 0.25-inch steel having 510 1-inch boles. This baaket ~ I V ~toB M u s e the incoming stream and prevent turbulence. 9olvent overflows from the top of the tank and lye solution is taken off from the bottom. The interface level is kept constant 88 shown in Figure 2. The bottom layer containing sodium hydroxide equivalent. to 15% NarO is pumped to the soap' kettles wbere the sodium bydroxide is utilized in the saponification reaction and the glycerol is recovered along with that produced in the soap making proceas. Distillation. One of the major improvements of thenewProcter&
'
tions hae been the introduction of continuous d b tillation of product alcohols from other Organic components. A t the original Du Pout and F'rocter & Figure 2. Lye Ssttliw T a d Gambleplantsthe reduction batches were distilledindiv i d d y in pot stills. At Pmcter & Gmble'e No.2 plant, crude alcohol product now is fed from a still feed tank into a continuous atmaspheric distilling column where water and solvent mix are re moved from the crude alcohol. The column is equipped with 30 bubblecap trays and is b a t e d by circulation of ita pot liquor through Dowtherm hest exchangers. A mixture of solvents (47 to 55% reconstituted reducing alcohol and the remainder toluene) is removed from the column at the 28th tray and returned to the eelvent mix storage tanka. Tbe separation is not di5cult since the lowest reduced alcobol p m n t boils at 310' F. and methyl amyl alcohol and toluene boil at 267" and 230' F., respectively. The overhead from the column is condensed and passed through two successive gravity separators where water is removed before the solvent is returned to the top of the column an d u x . Re turning the entire overhead gives a reflux-to-product ratio of about 1.5to 1. The crude alcohol bottom from the still are tgken to a second
442
INDUSTRIAL AND ENGINEERING CHEMISTRY
colwnn, operating a t a reduced pressure of from 10 to 15 mm. This column is similar in design to the stripping column but operates at higher temperatures. It has 15 trays and is heated by Dowtherm heat exchangers, as is the stripping still. However, because of' the greater temperatures required the circulating lines from thc still pot to the heat exchangers are induction heated to maintain the temperature of the circulating bottoms during transfer. The overhead from the still is passed through a condenser cooled with boiling water. The high temperature condenser is used to prevent overcooling the reflux and chilling the column. Reflux is taken from the product line and returned to the still head a t a reflux-to-product ratio of about 1 t o 5 .
Quench Tank Pump-Off Control Station Look box permits observation of layer interfaces
Bottorns from the still consist of the uonvolatile pl'oducts of side reactions in the reduction and hydrolysis, as well as the inert hydrocarbons of t'he original oil and a small amount of fatty alcohol which does not distill over. The side reaction products are believed to include high molecular weight ethers formed by t,he bimolecular dehydration of fatt,y alcohols, olefins formed by the monomolecular dehydration of the alcohols, and polymerization products probably in the form of double alcohols and long chain hydrocarbons. An appreciable amount of anhydrous soap is present also; this is formed by t)he saponificat,ion of free fatty acids in the original fat and the saponification, in the quench tank, of any unreacted fat. This soap causes the bottoms to solidify below 400 ' F. Consequently the still bott'oms must be taken off in induction-heated lines and quenched in water to dissolve the soap. When the quenched bottoms are allowed to settle, the oil and water phases separate. The resultant oil layer, containing everything but the soap, is liquid a t ordinary temperatures. At present it i s burned under the power boilers. Thc soap layer is acidulated t o release the fatty acids, which are subsequently purified and used in soap making operations. The overhead product from the alcohoI still is a mixture of C6 to ClS alcohols in approximately the same proportions as were present in the original coconut oil. Although there is obviously some decomposition of the original ester chains during the reduction and hydrolysis, this degradation is apparently not preferential and affects molecules of all sizes equally. The mixture of alcohols obtained from the still a t Ivorydale is subsequently sulfated to form the sodium alkyl sulfate type of synthetic detergent. Although the complete mixture often is sulfated, for certain products the alcohols may be fractionated into two or three cuts.
Vel. 41, No. 3
OPERATING COKDITIONS
The primary danger in the reduction of esters with metallic sodium is the accidental admixture of sodium with water. Accidental introduction of unreacted sodium into water is prevented by an elaborate svstem of safety devices. However, the reactor charges are based on theoretical proportions and like most OPganic reactions, the reduction does not go to completion. Thc completeness of reduction is affected by variations in scaling, lack of perfect agitation, and the probability of the last bit of sodium finding and reducing the last bit of oil. The unreacted sodium in the reactor is dropped into the water in the uench tank a t the end of the normal reaction time, When t%e quant>ity of unreacted sodium is small, it reacts with the water to form sodium hydroxide with little disturbance; the heat of the reaction is carried off by the refluxing solvent. However, if the sodium residue is large, what the operators call a hot batch, the water-sodium reaction is violent and appreciable heat is liberated. Such a condition is remedied quickly by cutting the flow of reaction mix from the reactor to the quench to a rate a t which the hydrolysis of the reaction product progresses quietly. On every batch the flow from the reactor to the quench is controlled to keep the exit, gas temperature from the reflux condenser below 100" F. to assure that the heat generated by the quenching reaction is being oompleteIy absorbed by the reflux system. Gelling, a serious casualty which may occur in eit,her the reactor or the quench, has been avoided in the full scale operations a t Ivorydale. It will occur in the quench tank only if water is introduced into the reactor mix instead of the mix into the water. This possibility is eliminated by the automatic interlock system. The most likely place for a batch "setup" is in the reactor. Here it may be caused by alloffing the temperature of t,he reactor to drop below the boiling point of toluene, or by adding the solvent mix a t too great a rate so that toluene is lost through the reflux condenser. Gels formed in pilot units have proved difficult to remove; the material is completely firm and agitators merely cut a hole through its centxr. I n production equipment, gelling is prevented by adjusting the addition rate and providing the reactor vessels w-ith external heating coils. Side reactions for this process result in the gcneration of hydrogen. K drogen generated in t,he reactor is believed to be mostly due to txc reaction of sodium with the moisture contained in the solvents and oil feed. Hydrogen from t'he quench tank is believed to come entirely from t,he reaction between the unreacted sodium and the quench water. All molecular hydrogen produced is lost, to the process. It has been proved that such gas is not absorbed by the reaction mixture (4%). Shutdown. The sodium reduct,ion plant runs on a 24-hour day for a &day week. This is 'possible because a t the end of each reactor cycle the reactor and the quench tank are emptied of liquids and automatically filled with nitrogen. By closing all valvcs thcy can bc left without further attention. To shut down the still, the feed is cut off and the Dowtherm heating furnaces allowed to cool. For repairs which require opening the system to the air, the routine shutdown procedure is observed, and then the system is boiled out with solvent mix, drained, and st'eamed out. After reassembly the unit is once more st'eamed out, boiled out' with t,he solvent, and it is ready to resume operations. After a routine week-end shutdown the plant can be started up in about 4 hours. After a take-down the plant can be back on the line in a maximum of 6 hours. Before start>ingup, the rcactm, thc toluene gage tank, and the alcohol still are preheated. CHEiMICAL CONTROL
Chemical control of the process begins with analysis of the raw materials. Calcium is the only common contaminanb in coniinercial sodium. Because the solubility of calcium in molten sodium is low (echnology is economical only for the production of saturated alcohols, The only major commercial market for fatty alcohols a t present is in the manufacture of synt,hetic detergents. However, the esterification of higher alcohols pith phthalic or maleic anhydride to form plasticizers may afford a new market, for these solvents in the future. Because of its extreme flexibility (both raw materials and products) the reduct,ion by sodium process will be able to take advantage of this OP any other new market for high molecular weight alcohols which may develop with new technological advances. However, a serious competitor in the manufacture of custonimade alcohols may be the recently exploited Oxo process, which treats olefins with carbon monoxide and hydrogen under high pressure in the presence of catalyst to produce an alcohol mixture. Several plants are already built or are being built to use this process to produce alcohols up to nonyl. The Oxo process might prove adaptable to the production of still higher alcohols for sulfonation or others used yet to be discovered if the market becomes sufficiently attractive. It has the advantage of using relatively cheap petroleum distilla,te and natural gas as raw materials. In contrast,, the market price of fatty alcohols madc by either of’ the two older processes is intimately dependent on the price of coconut oil which has fluctuated widely from time to time. During the past decade the record high for the oil was ten times the lowest figure. The going prices of sodium hydroxidc and glyceride, both important by-products of reduction by sodiun, also have a critical effect on the over-all economics of the process. However, the reduciion by sodium process is the subject of widespread research study as evidenced by the impressive nuinber of reports which have appeared in the technical literature (57) during the past 2 years. Of unusual interest is a report of improved yields of up t,o 95% of oleyl alcohol by a modification of the present procedure (IS). A U. S.patent (75) claims a process in which sodium amalgam is used as the reducing agent while a Belgian patent (76) recommends a return to Bouveault and Blanc’s ahsolute drohol B H n reducing alcohol. RIHLIOC,KAPIIY
( 1 ) Adam, N. I
