HYDROGENATION OF FATS OSCAR H. WURSTER Wurster & Sanger, Inc., Chicago, Ill. YDROGENATION has opened up new uses for many to which i t is to be put or the form in which i t is to be fats and oils. Vegetable oils, such as cottonseed, soymarketed. bean, and peanut, are partially hydrogenated to a suitable consistency for shortening, margarine, and other Hydrogen edible purposes. These oils are also completely hardened to The hydrogen is usually obtained by the steam-iron process stearin for subsequent mixing with low-melting-point oils to or the electrolytic decomposition of water. An important make compounds suitable for shortening and other products. source of hydrogen i s the electrolytic alkali and chlorine inLarge quantities of fish and whale oils are hydrogenated for dustry. I n some localities hydrogen can be purchased in both edible and industrial uses. Hydrogenation destroys cylinders a t a cost permitting its use for hydrogenation. The permanently the characteristic objectionable taste and odor use of cracked ammonia has been developed and found pracof marine animal and fish oils so that they can be used in tical under some conditions. making shortenings and also soap. Lard is slightly hydroAll commercially produced hydrogen contains imp.irities genated to improve its consistency and keeping qualities. which may be divided into four groups in accordance with Tallow is hardened for industrial uses. Substantial quantities their behavior in hydrogenation : of fatty acids are also hydrogenated. Fats and oils as they occur in nature consist of mixtures of 1. Gases which have no effect on the catalyst or the oil. Their glycerides of various saturated and unsaturated fatty acids effect is merely to dilute the hydrogen-typical example, nitrogen. 2. Gases which, under the influence of the catalyst, undergo and also of mixed glycerides. I n the process of hydrogenachemical reactions and thereby use some of the catalyst for such tion, hydrogen is added to the unsaturated constituents of reactions-typical example, carbon monoxide. the mixture to produce more highly or completely saturated 3. Gases which react chemically n-ith the catalyst and kill itglycerides. The purpose is to produce fats of higher melting typical example, hydrogen sulfide. 4. Gases or vapors which can react chemically with the oilpoints which are less readily oxidized, and in some cases to typical example, steam remove objectionable tastes and odors. The reaction between the oil and the hydrogen proceeds only in the presence of a Gas made by the electrolytic processes will contain only catalyst, and in commercial practice nickel is used almost oxygen and nitrogen as impurities and will run from 99.5 to exclusively. 99.8 per cent hydrogen. An analysis of such a gas is as Temperature, pressure, kind and amount of catalyst, infollows: tensity of the mixing, kind and quality of the oil, and purity Hydrogen 99.75% of the hydrogen affect the velocity of the reaction and its Nitrogen 0.20 Oxygen 0.05 selectivity. When the hydrogenation is carried on to a low 100.00 iodine number for hard fat, the essential consideration is the time required; in the production of partially hardGas made by the steamened oils for edible puriron process will contain poses, the manner of carrycarbon d i o x i d e , c a r b o n ing out the hydrogenation monoxide, and nitrogen as so as to obtain selectively impurities, and should conthe desired constituents tain 98 to 99.5 per cent in the fat, to give i t the hydrogen and not over 0.1 p r o p e r characteristics, per cent carbon monoxide. becomes of prime imporThere must be no sulfur tance. dioxide, hydrogen sulfide, The h y d r o g e n a t i on or carbon disulfide in the plant consists of (a) hygas. Sulfur compounds drogen generating, hanand carbon monoxide act dling, and storage equipas catalyst poisons. Inert ment, (b) catalyst making equipment, (c) oil regases such as carbon difining and bleaching equipoxide and nitrogen act as ment for preparing the diluents and decrease the oils for hydrogenation, r e a c t i o n v e l o c i t y . An (d) the h y d r o g e n a t i n g analysis of hydrogen made equipment proper, consistby the steam-iron process TO TANK CARS ing essentially of a conis as follows: vertor or hydrogenator, and (e) such equipment as is necessary for the Hydrogen 99.1% C a r b o n dioxide 0.2 subsequent treatment C a r b o n monoxide 0.1 CON74 /N&K?S Nitrogen 0.6 of the hardened fat, dep e n d i n g u p o n the use FLOW SHEETOF HYDROGENATION PLANT 100.0
H
1193
1194
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 32, NO. 9
ELECTROLYT HIYCDROGEN IAKD OXYGEN GENERATORS WITH COMPRESSORS
The amount of gas consumed will depend on the oil being hardened and the degree of hardness desired (the reduction in iodine number), the purity of the hydrogen, and the tightness of the equipment.
Hydrogen Consumption in Commercial Fat Hardening The theoretical amount of gas necessary for the complete saturation of any given f a t is calculated from its iodine value by applying the stoichiometric ratio between iodine and hydrogen. The amount of gas necessary is the hydrogen equivalent of the iodine absorbed. The weight of 1000 cubic feet of hydrogen a t 760 mm. pressure is 5.6 pounds a t 0" C. (32" F.) and 5.23 pounds a t 20" C. (68" F.). On this basis 1 pound of oil absorbs 0.015 cubic foot of hydrogen per 1 point reduction in iodine value, or 30 cubic feet of hydrogen per ton (2000 pounds) of oil. I n practice the actual amount of hydrogen required is always more than the theoretical, owing to leakage, venting, etc. With a high quality of electrolytic hydrogen, the actual gas consumption is usually from 105 to 110 per cent of the theoretical, and with less pure hydrogen, as from the steamiron process, the actual consumption may run up t o 120 per cent of the theoretical.
Preparation of the Catalyst Two methods are in general use for the preparation of catalyst; the older is by dry reduction and the more recent one is the wet reduction process. Wet reduction is carried out by suspending nickel formate or carbonate in oil in a heated vessel; dry reduction, starting with nickel carbonate or oxide, takes place in a rotating tube furnace. There are a number of special catalysts, each with its own method of preparation. The wet reduction of nickel formate in oil is simple and most satisfactory. This method requires little supervision and technical control, and therefore meets satisfactorily the average plant operating condition. The catalyst is extremely active, has a minimum susceptibility to poisons, and is highly selective. The hazard which exists in dry reduction of passing hydrogen through a furnace heated by an open flame is eliminated. The temperature required for wet reduction is considerably lower than that for dry reduction. The ac-
curacy of automatic temperature and time control obtained in wet reduction produces a uniformity in the catalyst which results in uniformity of product in hydrogenation.
Wet Reduction of Nickel Formate The reducer is a vessel provided with electrical heating and an agitator. To prepare catalyst, the reducer is charged with oil of the same kind as that to be hydrogenated, and 25 to 100 per cent of finely divided nickel formate is stirred in thoroughly. The heat is turned on and reduction proceeds smoothly under automatic temperature control. The reduction of a charge consisting of 4 parts oil and 1part nickel formate is common practice. The final oil-nickel mixture will then contain approximately 7 per cent nickel. The catalyst is usually used a t the plant where produced, and therefore the dilution with oil and the consequent bulk are not objectionable. Catalyst is prepared as required, and the handling of the catalyst-oil mixture is entirely by pump. If a more concentrated catalyst is desired-for example, when it is to be shipped to other plants-nickel formate u p to the weight of the oil, or slightly more, may be added. With equal weights of oil and nickel formate, the final oil-nickel mixture will contain approximately 23 per cent nickel. The reduction is carried out a t atmospheric pressure. The temperature of the mixture rises steadily until it reaches about 365' F. (185" C.). When the temperature reaches 302" F. (150" C.) the initial reaction usually begins, and a t this point or sooner the introduction of hydrogen gas is started. Only a small amount of hydrogen need be introduced, since its function is chiefly to facilitate the removal of the gaseous reaction products. The reduction is thermal and not dependent on the reducing action of the hydrogen. The coincident hardening of the oil carrier during reduction is, however, advantageous if the catalyst is to be shipped as the hard fat protects the catalyst. The reaction becomes active a t 374" F. (190" C.) with the evolution of steam from the water of crystallization. The temperature holds steady for about 30 minutes until the moisture is driven off and then rises rapidly to 464" F. (240" (3.). The breaking-down temperature of nickel formate is from 338" to 464' F. (170" to 240" C.). It is necessary to hold the charge a t 464" F., or a few degrees higher, for a half to one hour to complete the reaction.
SEPTEMBER, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
1195
batch is spent. Under this method each succeeding oil charge requires more time for hardening to a definite titer, until finally the time required makes the use of the catalyst uneconomical, and it is discarded. For uniformity in operation, the following method has been found satisfactory: The catalyst is allowed to accumulate to the capacity of the filtering equipment. This quantity is then held practically constant by discarding a fraction after each run and adding an equivalent fresh portion of catalyst for the next run. The quantity of catalyst required mill depend on the kind of oil and the degree to which it is refined, but will usually be from 0.05 to 0.1 per cent nickel on the weight of the oil.
Preparation of Fats and Oils
FIGURE1. TEMPERATURE RECORDOF THE REDUCTION OF h7;ICKEL FORMATE I N O I L AT A M A X I M U M T E M P E R A T U R E O F 464' F.
The reduction of nickel formate is as follows: Ni(HOOC)*.2H20 184.77
=
Ni
58.69
+
2C02 88.02
+
H2
2.02
+ 36.04 2H20
For each pound of nickel formate 5.5 cubic feet of carbon dioxide and hydrogen and 3.9 cubic feet of steam are given off, or a total volume of approximately 9.4 cubic feet of gases to be rented. About one hour is usually required to bring the reducer charge up to 360" F. (182" C.), a half hour to one hour to drive off moisture and gases a t 360" to 374" F. (182" to 190" C.), a half hour to raise to 464' F., and another half to one hour to complete the reduction, or a total time of 3 to 4 hours. A factor in the rapidity of reduction of nickel salts appears to be their age, freshly precipitated salt reducing more readily at low temperature. Figure 1 shows a temperature record of the reduction of a typical charge of nickel formate in oil. When the charge in the reducer is finished, it may be pumped directly to the convertor or held in the reducer until required. If the oil-catalyst mixture is to be cast into blocks, the charge is cooled until a temperature of 212' F. (100" C.) is reached, when it can be withdrawn into pans. Since the nickel particles are coated with hard fat, they are not subject t o the oxidizing action of air, and catalyst so prepared may be kept indefinitely without injury. The hot catalyst-oil mixture may also be run directly to a chilling and flaking roll. The flaked catalyst gives a uniform product with definite nickel content and is convenient to handle, pack, and use when the catalyst must be shipped. As with the catalyst cast into blocks, the flaked catalyst may be held indefinitely without deterioration.
The nature and condition of the oil or fat have an important bearing upon the subsequent hardening operation. The purity of the oil or fat has considerable influence on catalyst consumption. The phosphatide content of cottonseed oil, the sulfur content of soybean oil, the amount of soap in refined coconut oil, all have either a direct poisoning or inhibiting action on the catalyst. In general, the following substances should be largely removed from fats prior to hardening in order to decrease catalyst consumption : soaps ; oxidized fats ; gelatin and gelatin decomposition products usually met with in animal fats; colloidal suspensions of albuminous matter, proteins, etc.; phosphatides; organic and inorganic sulfur compound ; organic and inorganic chlorine compounds; water; high free fatty acids. Caustic refining or treatment with monosodium phosphate coagulates and removes most of these objectionable compounds, and further treatment with fuller's earth, vegetable carbon, activated earths, and filter aids assist in purifying the
Methods of Csing the Catalyst There are two methods of handling catalyst, either of which will give satisfactory results. Some technologists prefer to start with a small quantity of catalyst and make small additions to each succeeding charge of oil. I n the second method of operation a larger quantity of catalyst is used in the initial batch and re-used without addition of fresh nickel until the
REDUCER AND CONTROL P.4XEL FOR M A K I N G WET REDUCED CAT.4LYST FROM N I C K E L FORMATE Automatic control results in uniform catalyst production.
CATALYST
INDUSTRIAL AND ENGINEERING CHEMISTRY
1196
VOL. 32, NO. 9
catalyst to the action of the hydrogen. The gas circulating pump, when used, takes the hydrogen from the top of the convertor and pumps i t through the perforated pipe in the bottom of the convertor. The hydrogen then passes up through the body of the oil and catalyst mixture in fine streams and causes further agitation. With dilute, impure hydrogen, such increased circulating of the gas is desirable. Internal mechanical agitators are of various types. A propeller agitator may be mounted on a horizontal shaft near the bottom of the convertor. One advantage of this design is that the shaft stuffing box is below the liquid level. Turbine agitators mounted on a vertical shaft give effective agitation. There are, then, three methods of agitation to bring the oil, the catalyst, and the hydrogen into intimate contact: circulation and spraying of the oil and catalyst, circulation of the hydrogen, and mechanical agitation. The handling of the convertor involves the following steps: charging and heating the oil; introducing, regulating, and circulating the gas; circulating and cooling the oil; testing for completion of hardening; venting; separating the catalyst from the hardened fat.
I
d I
WITH INSIDE HEATING AND 2. HYDROGEKATOR COOLING COIL, OIL AND CATALYST CIRCULATING PUMP, GAS CIRCULATING PUMP,AND PROPELLER-TYPE MEFIGURE
CHANICAL
AGITATOR
fat. I n general, oils which are to be hydrogenated for edible products are fully refined before hardening. Such oils require a minimum of catalyst. Oils high in free fatty acids and intended for industrial uses are usually given special treatments, since caustic refining would entail too high a refining loss to be economical. Such partially refined oils require more catalyst.
Operation of the Convertor The requirement in the hydrogenation of oil is to bring the hydrogen gas, the liquid oil, and the solid catalyst-namely, three phases-into intimate admixture under proper and controlled conditions of temperature and pressure. Convertors are designed so that they can be operated to fulfill these necessary conditions most effectively. Convertors are provided with a pump which circulates the oil and catalyst from the bottom back into the top. The hydrogen is injected into the bottom of the convertors in such a manner as to give thorough distribution in the oil. When the quality of the hydrogen is such that inert gases accumulate in the convertor and dilute the hydrogen as with steam-iron hydrogen, a gas circulating pump is also used. With electrolytic hydrogen of a high degree of purity, a gas circulating pump is not required. Convertors are also provided with internal mechanical agitation. Two methods of heating and cooling are used-one with heating-cooling coils inside the convertor and the other with an external heat exchanger. Hydrogenators with different arrangements and combinations for circulating and mixing the oil, catalyst and gas, and with internal and external heating and cooling, are shown in Figures 2, 3, and 4. The oil circulating pump takes the oil and catalyst from the bottom of the convertor and pumps it back through the spray nozzles in the top. The fine, mistlike spray of oil mixed with catalyst passes through the gas space in the top of the convertor, exposing a maximum surface of oil mixed with
Charging and Heating the Oil The catalyst is pumped directly from the reducer or mixing tank to the convertor. The oil is pumped to the convertor from a storage or measuring tank. Some of the oil charge may be run to the catalyst mixing tank to dilute the catalyst cake from the filter press for transfer to the convertor. At this point a filter aid can be added. After the convertor has been charged with oil and catalyst, circulation is started and steam is turned on the heating coil or heat exchanger. The oil and catalyst are withdrawn from the bottom of the convertor and sprayed into the top through the spray nozzles. Vacuum is pulled on the convertor to dry the oil and remove air and moisture before running in t h e hydrogen. When a vacuum of about 25 inches has been reached and the oil heated to about 212" F., the vacuum equipment is shut off and hydrogen is run in.
Introduction and Regulation of Hydrogen When hydrogen is used from cylinders, they are connected to the cylinder manifold and are ready for use before starting to heat the oil. Gas pressures in the cylinders average about 2000 pounds per square inch, and the pressure regulating valve
FIGURE 3. HYDROGENATOR WITH ExTERNAL HEATEXCHANGER A N D OIL AND CATALYST CIRCULATING PUMP
SEPTEMBER, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
1197
XYORO
C
OIL C/RCULA?/NG
FIGURE 4. HYDROGESATOR W I T H I S T E R N A L HE.4TINGi A S D C O O L I N G C O I L , OIL AND CATALYST CIRCUL.4TING P C M P , AND TURBINE-TYPE M E C H A N I C A L AGITATOR
is usually set a t 30 to 60 pounds per square inch and feeds the line to the convertor a t that pressure. When hydrogen is supplied from a generating plant operated in conjunction with the hydrogenation plant, the gas is usually compressed to 300 pounds per square inch and stored in pressure tanks holding from 10,000 to 30,000 cubic feet of gas each. The hydrogen is drawn directly from these tanks through a reducing valve set a t 30 to 60 pounds per square inch to the convertor.
Circulating and Cooling the Oil Hydrogenation is an exothermic reaction. Xhen the hydrogen is turned in, the temperature is around 250" to 275" F. (121" to 135" C.). Steam is turned off the convertor coil or heat exchanger, and the hydrogen is fed as rapidly as the oil will absorb it. The rise in temperature of the oil indicates that hardening is progressing. If uncontrolled, the temperature during active hardening might rise to a point where the oil would be darkened. Cooling coils are provided t o give a means of regulating the temperature by circulating cold water. On most oils the best results from the standpoint of color, rate of hardening, and gas consumption are obtained a t temperatures between 350" and 375" F. (177" and 191" C.) although finishing temperatures as high as 425" F. (218" C.) are necessary on refractory oils or when catalyst activity becomes low. Some refined oils can be completely hardened within normal hardening time without using temperatures in excess of 340" F. (171" C.). The control of the temperature, pressure, and velocity of the reaction for the selective HYDROGESATOR WITH SUPPORThydrogenation of the several ING SKIRT ASD WORKISGPLATglycerides constituting the fat FORM (above), AND CONVERTORS so as to obtain a product with WITH EXTERNAL HEAT ExCHANGERS AND CIRCULATING the desired chemical and physiPUMPS cal properties is extremely im-
1198
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 32, NO. 9
HYDROGENATIOK PLANT
portant in some operations, as in the production of shortening and other food fats. Briefly, this problem resolves itself to a proper control of the operating conditions-catalyst, hydrogen, temperature, and pressure-so as to obtain as high an olein content as possible by converting the less saturated esters to olein, and without the formation of the esters of completely saturated acids and iso-oleic acids. I n so far as the preferential hydrogenation of the less saturated esters t o olein and avoidance of the formation of stearin and other completely saturated esters and of hard iso-olein are dependent upon temperature, the best temperature is approximately 350" F. Convertor pressures of 20 to 40 pounds per square inch are best for high selectivity. By such suitable control, partially hydrogenated fats are produced having a lardlike consistency and wide plastic range, with an iodine value around 65 and a melting point of 95" to 97" F. (35" to 36" C.). When hydrogenating fats such as fish oil, whale oil, and tallow to a low iodine number, the question of selectivity is usually of negligible importance, since the same end product is reached regardless of the composition of the intermediate products. For this purpose convertor temperatures up to 425" to 450" F. (218" to 232" C.) are used with pressures of 60 to 75 pounds per square inch. However, in partially hardening fish and whale oil for soap making, the question of selectivity is also important from the standpoint of the lathering qualities of the soap made from it.
Testing for Completion of Hardening During the operation the rate of gas absorption decreases as the oil becomes saturated. Samples are drawn to determine the progress of the hydrogenation. When oils are to be completely hardened, the control requirements are simplified since it is necessary only to know how the absorption is progressing and when saturation to the required point is reached. When
producing partially hydrogenated fats, the desired degree of saturation and hardness must be controlled accurately, and tests must be made rapidly. Various simple melting and solidifying point tests have been worked out for approximate plant control purposes. The quickest and most accurate determination, however, is the refractive index, which can be determined in a few minutes. It is convenient for plant control to prepare curves for the oils to be hardened which show the iodine number, titer, or melting point corresponding to the refractive index. The iodine number of oils varies uniformly with the index of refraction during hydrogenation. For each kind of oil a curve can be made from which the iodine number can be read immediately and with a close degree of accuracy on determining the refractive index. The curves for the various oils will be different since the chemical compositions of the oils are not the same and the iodine numbers corresponding to a given refractive index are different. Determinations on the same kind of oil will vary only to the extent that different samples of the oil vary slightly in composition. The titer and melting point of each kind of oil also vary uniformly with the refractive index during hydrogenation, provided the process is carried out each time under uniform conditions. Under different conditions of hardening, resulting in varying degrees of selectivity, different samples of the same oil hardened to the same refractive index and iodine number may have a wide range of titers and melting points. This is important when a high degree of selectivity is desired, as for edible fats, and has been referred to above.
Venting With impure or moist hydrogen the reaction may slow down due to the accumulation of inert gases in the convertor. It is then desirable during the run to pull a vacuum on the con-
SEPTEMBER, 1940 vertor as was done a t the s t a r t of t h e o p e r a t i o n . With electrolytic hydrogen, dried by compressing to 300 pounds per square inch pressure in storage tanks, this venting during the run is usually unnecessary. The presence of gases other t h a n h y d r o g e n i n the upper convertor space is undesirable primarily because they retard the absorption of hydrogen and, if p r e s e n t i n sufficient quantity, prevent the further flow of hydrogen to the convertor. But there are also other objections: oxygen oxidizes the oil and catalyst, carbon monoxide poisons the catalyst, and steam reacts with the oil.
INDUSTRIAL AND ENGINEERING CHEMISTRY
_. ~
1199
~
HYDROGESATION P L ~ NSHOWISG T REDUCER, MIXINGTASK,FILTER PRESS,AND CONVERTOR
Separation of Catalyst from Hardened Fat When the tests show that the desired hardness has been reached, the hydrogen supply is shut off and the hard fat charge is cooled preliminary to filtration. Water is turned into the internal cooling coil or to the external heat exchanger, and the oil is cooled to such a temperature that on filtration i t will leave the filter press a t a temperature low enough not to darken; this temperature is 120" to 160" F. (49" to 71" C.), depending on the oil. The clear oil is run to the finished oil-receiving tank. The filter press cake is dropped into the catalyst mixing tank and
held there for mixing with the next batch of oil. The catalyst is used over and over, either alone or with slight addition of fresh catalyst, until i t is no longer sufficiently active to harden a charge of oil within the normal hardening period. The handling of the hardened fat depends upon the oil and the use for which it is intended. Completely hardened oils are usually employed for technical purposes without deodorizing. Such oils may be pumped directly to tank cars, or flaked or molded into cakes for packing in bags. Partially hardened oil for edible purposes is deodorized and is then further processed to shortening or other products.
CATALYSTS FROM ALLOYS Nickel Catalysts
A
MURRAY RANEY, Gilman Paint and Varnish Company, Chattanooga, Tenn.
LARGE portion of the literature relating to hydro-
genations is devoted to the preparation of catalysts. Because nickel is so generally adaptable, there is more reference to the preparation and use of nickel catalysts than to all others combined. Fraser published a comprehensive abstract of the literature relating to the subject (6). Any critical discussion of the many proposed and practiced methods for producing nickel catalyst should be approached with tolerance. Consideration of these methods does lead to the conviction that nickel is not only a versatile catalyst, but that its catalytic properties may be developed in many ways. Whether this means that nickel may be prepared in the same form by many different methods or that it is a good catalyst in many different forms is probably not known a t present.
Comparison of Catalysts There are recognizable differences in good nickel catalysts prepared by different methods for the same reaction, but these
differences do not fix the value of the catalysts. While the catalytic property may be associated with one or more of them, i t is not determined by specific gravity, state of division, magnetic or pyrophoric properties, or any other measurable characteristic of the metal. The probability that nickel or any other substance will catalyze a given reaction is based on the great amount of work that has been done in many fields, rather than on any correlated, calculable properties of either the catalyzing substance or the reacting elements or compounds. The catalytic value of a substance is determined by trial; if it does its work, it is good. The statement that nickel, cobalt, chromium, iron, copper, and other metals are catalysts is true or false, depending entirely on the form in which the metals are used. Because nickel prepared in a certain way may not be a satisfactory catalyst for a given reaction does not show that nickel is not a catalyst for the reaction. Such a conclusion should be modified by a description of the method used in preparing the catalyst and, as has been said ( I ) , of the operator's state of mind.
