GB2230020A

GB2230020A - Hydrogenation method

Info

Publication number: GB2230020A
Application number: GB8901872A
Authority: GB
Inventors: Godefriedus Carolus Mari Colen; Duijn Gerrit Van; Johannes Christian Ma Keltjens
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 1989-01-27
Filing date: 1989-01-27
Publication date: 1990-10-10
Also published as: GB8901872D0

Abstract

A method for the hydrogenation of unsaturated oil comprises reacting said oil with hydrogen in the presence of a suitable catalyst, wherein during at least the latter part of the hydrogenation reaction the concentration of hydrogen dissolved in the reaction mixture is used to control said hydrogenation reaction, and a control system for this method which comprises: (a) means for sensing the hydrogen pressure above the reaction mixture and providing a signal representative thereof; (b) means for measuring the flow of hydrogen to the reaction mixture and providing a signal representative thereof; and (c) computing means responsive to said signals for determining suitable adjustment of the dissolved-hydrogen concentration.

Description

HYDROGENATION METHOD The invention relates to a method for the hydrogenation of unsaturated fatty oils, in particular glyceride oils, which comprises reacting said fatty oil with hydrogen in the presence of a suitable catalyst.

Hydrogenation of glyceride oils is primarily carried out to improve the stability of the oil and to increase its solid fat content at certain temperatures, for example in the range of 5 30etc. Because of the reduced level of unsaturation, hydrogenated oil is less prone to oxidative deterioration, which, for example in the case of edible oil, improves the taste keepability. For many applications of glyceride oils, for example for the preparation of edible products such as margarine, it is necessary for the oil to have, depending on the temperature, a certain solid fat content. If, for a certain application, the solid fat content of an oil is too low, hydrogenation may be used to increase the solid fat content.

The solid fat content of an oil at a temperature of tiC can be conveniently characterized by means of the Nt-value, the percentage by weight of solid fat at temperature t as determined by means of NMR, as described in F.S.A. 80(5) (1978), 180-186.

Generally, the hydrogenation reaction is carried out at elevated temperature in the presence of a catalyst. The reaction is controlled using the temperature of the reaction mixture and the hydrogen pressure in the head space of the reaction vessel.

Such control may be manual or automatic.

The suitability of a hydrogenated oil for its intended purpose is primarily determined by its iodine value (IV), which, for a given type of oil, determines its taste keepability to a large extent as well as its solid fat content as a function of temperature. Accordingly, the specifications a hydrogenated oil required for an intended application can suitably be expressed in terms of a maximum IV and an Nt profile within specified limits.

Generally, the reproducibility of hydrogenation reactions of glyceride oils is not very good. If a hydrogenation of a given type of oil, for example soybean oil from the USA, or Norwegian or Japanese fish oil, is repeated a number of times, using the same type and amount of catalyst each time, applying the same temperature and hydrogenation pressure, using the same equipment, stirring speed etc. and allowing the reaction to proceed for the same period of time, hydrogenated oils may be obtained showing rather large variations in IV and Nt profile.

Even if the reaction times are adjusted such that the IVs of the resulting products are constant, still substantial variations in the Nt profiles may occur. Consequently, the hydrogenated oil may fail to meet the requirements regarding IV and Nt profile for the intended application.

This lack of reproducibility is possibly caused by small variations in the starting oil, for example in the presence of minor ingredients that may act as catalyst poison and thereby affect the activity and specificity of the catalyst. Small differences may further occur between different batches of catalyst. Generally, hydrogenation catalysts are used in a number of hydrogenation reactions before being discarded. Differences in age, and thus differences in catalyst properties introduced in previous reactions, further contribute to the lack of reproducibility of hydrogenation reactions.

A further problem is how to determine the end point of the hydrogenation reaction. In Bailey's Industrial Oil and Fat Products, 3rd Edition, Interscience Publishers (1964), Chapter 17, in particular pa ges -'877-881, there are described a number of ways to determine when to stop the reaction. For example, the solid fat index, congeal point, cloud point or refractive index may be used to determine the end point. However, these determinations may be lengthy and/or may fail to give an accurate indication of whether the desired extent of hydrogenation has been achieved.While the test sample is being measured, the hydrogenation reaction may be interrupted, which makes the final phase of the reaction cumbersome, or the reaction may be allowed to proceed, which implies the risk that while the sample is being measured, the hydrogenation proceeds too far. According to Bailey's Industrial Oil and Fat Products cited above, the lack of reproducibility of the hydrogenation reaction is such that the reaction cannot be controlled by means of the quantity of hydrogen absorbed but that, instead, it is necessary to control it according to the physical characteristics of the oils being hydrogenated, using, for example, methods as mentioned above.

We have now found that the reproducibility of the hydrogenation result in terms of the characteristics of the hydrogenated oil can be substantially improved, when for a given type of oil, hydrogenation temperature profile, and type and amount of catalyst the concentration of the hydrogen dissolved in the reaction mixture is used to control the hydrogenation reaction instead of, for example, the hydrogen pressure in the head space of the reaction vessel.

Accordingly, in a first aspect of the present invention there is provided a method for the hydrogenation of unsaturated fatty oils which comprises reacting said fatty oil with hydrogen in the presence of a suitable catalyst, wherein during at least the latter part of the hydrogenation reaction the concentration of hydrogen dissolved in the reaction mixture is used to control said hydrogenation reaction.

The dissolved hydrogen concentration is controlled by adjusting it to a level which generally and preferably is a function of time, i.e. the level to which the dissolved hydrogen concentration is adjusted is a function of the progression of the hydrogenation reaction, which is not constant over time.

In practice, it has been found very convenient to use the IV of the unsaturated oil as a measure of the various characteristics that may change as the reaction proceeds. The IV can be obtained from the IV of the starting oil and the change in IV since the beginning of the reaction. For a given type of starting oil, it is often sufficient only to take the change in IV during the reaction into account, provided that the variation in IV of the starting oils used is not substantial. Under such circumstances, the change in IV during the reaction is directly related to the IV of the oil and can be used as a parameter with respect to which characteristics, changing as the reaction proceeds, can be expressed.

The IV of the starting oil can be measured in a conventional manner, for example via titration. The change in IV as the reaction proceeds can be estimated by monitoring the hydrogen consumption, for example with the use of a hydrogen flow meter.

The level to which the hydrogen concentration is adjusted in accordance with the method of the present invention, is'suitably selected from a database containing the data relevant to the starting oil concerned and the hydrogenation result desired.

Accordingly, the method of the invention preferably comprises the steps of: (a) representing a relationship between the Nt-profile of the oil after the hydrogenation reaction, and the iodine-value of the oil and the dissolved-hydrogen concentration during the hydrogenation reaction; (b) determining said iodine-value and said dissolved-hydrogen concentration during the hydrogenation reaction; and (c) controlling the dissolved-hydrogen concentration on the basis of said relationship to obtain said Nt-profile.

According to a preferred procedure, a database is built up empirically by monitoring for a given type of oil, type and amount of catalyst and temperature profile during a hydrogenation, the dissolved hydrogen concentration and including said information in the database, together with information of the resulting hydrogenated oil, in particular its IV and Nt profile. Such a first hydrogenation reaction is carried out without controlling the dissolved hydrogen concentration, and can, for example, be controlled by manual adjustment of the hydrogen pressure in the head space of the reaction vessel. In subsequent reactions of the same type, the recorded dissolved hydrogen concentration from the earlier reaction can be used as selected level to which the dissolved hydrogen concentration is adjusted.Simultaneously, the actual dissolved hydrogen concentration during the reaction can be monitored, for example as function of the IV of the oil, and included in the database together with the other relevant process parameters and characteristics of starting oil and product. In this way, a database can be built up without the need to carry out many extra experiments only for the purpose of creating the database.

Depending on the particular process conditions employed a wide variety of relationships between dissolved hydrogen concentration, the IV of the oil, and the IV and N-profile of the resulting hydrogenated oil can be obtained. On the basis af these empirical relationships the hydrogenation of an oil can be guided to substantially similar, or if so desired, quite different hydrogenation results in different runs, simply by adjusting the dissolved hydrogen concentration to similar or different dissolved hydrogen concentration / IV paths.

When an oil is to be converted into a hydrogenated oil with certain specifications in view of an intended use, the database can be used to select the most appropriate process conditions to convert an oil such as the starting oil into a hydrogenated oil with the desired characteristics, and, in particular, to select an appropriate level of dissolved hydrogen concentration, conveniently and preferably stored in the database as a Cb (dissolved hydrogen concentration) versus IV curve, to which the dissolved hydrogen concentration is to be adjusted during the reaction to get the desired end product.

The dissolved hydrogen concentration can be suitably adjusted by controlling the hydrogen supply, in particular by controlling the hydrogen pressure in e.g. the head space of the reaction vessel. If the dissolved hydrogen concentration at a certain stage of the reaction (for example expressed as a Cb (IV) value) differs from the selected level at that stage, the pressure can be changed so as to reduce the difference between the actual and the selected Cb values. The comparison between actual and selected Cb values and the subsequent adjustment of the actual Cb value can be carried out substantially continuously (i.e. intermittently with a high frequency), or allowing some longer period of time between two subsequent comparisons.The adjustment of Cb to the selected level during the reaction allows some deviation of the actual Cb from the selected level, but preferably it is ensured that such differences remain small to achieve optimal reproducibility.

Preferably, the rate of hydrogen consumption is monitored during the reaction. This can be suitably done by means of a hydrogen flow meter measuring, continuously or intermfttently, the flow of hydrogen to the reaction mixture. From the rate of hydrogen consumption the change in IV during the reaction can be calculated and from this, provided the IV of the starting oil has been determined, the IV value of the oil can be calculated.

The dissolved hydrogen concentration Cb is governed, on the one hand, by the dissolution of supplied hydrogen gas in the oil and, on the other hand, by the consumption of hydrogen by the reaction. During the reaction preferably both the rate of hydrogen consumption (R) and the hydrogen pressure (p) are monitored. The dissolved hydrogen concentration Cb can then be adequately estimated by means of the formula : R Cb - m(T).p - K wherein m(T) is Henry's law constant and K is an equipment constant. The equipment constant K can be suitably determined by means of some test hydrogenations.

According to a preferred embodiment of the present process the selected level which the dissolved hydrogen concentration Cb is adjusted to, is replaced by another selected level, which Cb is subsequently adjusted to, if the difference between Cb and the selected level exceeds a set value. Such value can be set in dependence of practical considerations. For example, if Cb is adjusted by varying the hydrogen pressure, limits may be set between which the hydrogen pressure must be kept. An upper limit may be set on the basis of safety considerations in view of the equipment used. A lower limit can, for example, be set in view of considerations of length of reaction time.Thus, if the difference between Cb and the selected level gets such that a hydrogen pressure outside the set range would be required to adjust Cb to the selected level, the selected Cb level profile is replaced by a different selected Cb profile, closer to the instant actual Cb but still leading to substantially similar end product specifications, the Cb adjustment now being possible with a hydrogen pressure within the set limits.

The dissolved hydrogen concentration need not be controlled during the entire process, but preferably it is controlled during at least the latter part of the reaction. More preferably, Cb is cotntrolled-during the major part of the reaction, or even the entire reaction, the most appropriate level to which Cb is to be adjusted being selected in the very early stage of the reaction.

As catalyst, any hydrogenation catalyst can be used. For example, the commonly used nickel-on-carrier catalysts are suitable. Usually the reaction is carried out at a temperature between about 90etc and about 200C, in particular between about 1000C and 1800 C. The temperature can be kept constant during the reaction but also a non-constant temperature profile may be applied. For example, a two-step temperature profile may be chosen, the first part of the reaction being carried out at 150'C and the second part at 1800C, the temperature change being effected once a certain IV has been reached. The reaction can be carried out in conventional equipment, for example batchwise in a closed vessel provided with stirring means.

In general, the reaction will be terminated when the IV of the oil has reached a selected value. Preferably, the selected end value of IV is chosen in dependence of the selected level profile of the dissolved hydrogen concentration. The Nt curve of a hydrogenated oil having a certain IV value in general depends on the selected curve to which Cb has been adjusted during the reaction, and accordingly, the Nt curve of the resulting product will be closer to the desired Nt curve if this dependence on the selected level is taken into account.

As described hereinbefore the IV of the oil is preferably determined by means of the rate of hydrogen consumption. The present process allows this very convenient way of determining the end point without large variations occurring in e.g. the Ntprofile of the resulting oil. Such variations would occur in conventional hydrogenations if the hydrogen consumption were used to determine the end point of the reaction. With the present process, the reproducibility of the reaction is such that products with only small variations in the Nt curve are obtained.

In a preferred embodiment of the present invention the following procedure is used. For the particular hydrogenation equipment used a database is built up containing information of a large number of hydrogenations. For each reaction, the data of the starting oil (type, IV, etc) as well as the IV and the Nt- profile of the resulting hydrogenated oil are recorded. In addition, for each hydrogenation reaction the following process parameters are recorded: type and amount of catalyst, and during the reaction, the IV of the oil, the temperature, the hydrogen pressure and the dissolved hydrogen concentration. Data of a number of hydrogenations carried out with the same starting oil, type and amount of catalyst and temperature profile but with different Cb versus IV curves are included.

If then a certain type of starting oil is to be converted into a hydrogenated oil with certain specifications regarding IV and solid fat content, the IV of the starting oil is determined and process conditions are selected from the database via which the starting oil can be converted into the desired end product (the "reference reaction"). If several sets of process conditions are suitable, the selection can be made by the operator or by means of a computer programme, taking economical considerations, such as the cost of catalyst, etc., into account.

When the optimal process conditions have been selected, the oil is introduced in the reaction vessel. Catalyst of a type and in an amount as used in the "reference reaction" selected from the database is admixed with the oil. Hydrogen gas is introduced into the vessel, the pressure being chosen in the same way as in the reference reaction and heat is supplied to raise the temperature of the oil. The temperature, pressure and hydrogen consumption are monitored. The-strt of the reaction is indicated by the hydrogen consumption. The IV and Cb are calculated, as described above, intermittently, for example every 10 seconds.

The temperature and pressure are kept, as a function of the IV, at the same level as in the reference reaction. When the reaction has proceeded to some, preferably small, extent, for example when a set reduction of the IV has been achieved or a temperature set point has been reached , the pressure is no longer kept at the above indicated level but is, instead, varied to adjust the Cb, as a function of the IV, to the same level as in the reference reaction. When the IV has been reduced to the desired extent, the reaction is stopped by blocking the hydrogen flow. The reaction mixture is then cooled down, the catalyst is removed, for example by filtration, and the resulting hydrogenated oil is further processed in conventional manner.

,~ + If during the process, in order to adjust the Cb to the selected level, a hydrogen pressure outside set levels would have to be applied, from the database a different reference reaction relating to the same type of oil, the same type and amount of catalyst and the same temperature and IV profiles is selected involving a Cb value at the instant IV of the oil closer to the actual Cb value. During the remainder of the reaction, the Cb as function of the IV is adjusted to the Cb (IV) curve of the newly selected reference reaction. The selected end point IV is adjusted accordingly to obtain a hydrogenated oil with characteristics as close to the desired characteristics as possible.

Several of the above-mentioned aspects are illustrated in figure 1. The figure shows, for a given type of oil, hydrogenated with a given type and amount of catalyst and a given temperature profile, a number of typical Cb vs IV curves.

During the initial stage the reaction rate is high causing a rapid decrease in Cb. When the reaction slows down, Cb increases again. Curves 1, 2 and 3 correspond to different hydrogen pressures (once the IV has been reduced to IV'), the pressure being higher for curve 1.

The hatched area indicates the area within which the hydrogenated oil meets a chosen set of requirements - a maximum IV (in Fig. 1: IV - 85) to ensure taste keepability; - Nt values within certain limits; - a minimum value for Cb (determined by economical considerations to avoid too long a reaction time, corresponding to the minimum acceptable level set for the hydrogen pressure).

The asterisk in the hatched area indicates, when using curve 2 as selected level to adjust Cb to, the optimal IV to end the reaction in order to obtain a product meeting the specifications.

The hydrogenation can be carried out by first applying the same hydrogen pressure as used to obtain curves 1-3, until the IV has been reduced to IV', and then changing over to controlling the Cb in dependence on IV, by varying the pressure such that the actual Cb is adjusted to the Cb of curve 2. The dotted line illustrates how the actual Cb may vary during the process. If somehow the difference between the actual Cb and curve 2 would become so large that a pressure outside the set limits would be required to adjust the Cb, another Cb (IV), between curves 1 and 3, is chosen from the database. As is clear from figure 1, the optimal end point IV to obtain a product meeting the specifications, would be different from the optimal end point IV for curve 2.

According to a further aspect the present invention provides an control system for the hydrogenation method in accordance with the present invention which comprises: (a) means for sensing the hydrogen pressure above the reaction mixture and providing a signal representative thereof; (b) means for measuring the flow of hydrogen to the reaction mixture and providing a signal representative thereof; and (c) computing means responsive to said signals for determining suitable adjustment of the dissolved-hydrogen concentration.

System wherein said computing means is responsive to said hydrogen-flow signal for determining the hydrogen consumption.

System wherein said computing means is responsive to said hydrogen-flow signal for determining the iodine value of the oil.

System wherein said computing means determines the adjustment of the hydrogen pressure corresponding to said determined adjustment of the dissolved-hydrogen concentration.

System wherein said computing means is connected to a hydrogenpressure control means.

System wherein said hydrogen-pressure control means is responsive to the output signal of said computing means representative of said determined adjustment of the hydrogen pressure.

System wherein said computing means is software controlled.

Claims

1. Method for the hydrogenation of unsaturated oil which comprises reacting said oil with hydrogen in the presence of a suitable catalyst, characterised in that during at least the latter part of the hydrogenation reaction the concentration of hydrogen dissolved in the reaction mixture is used to control said hydrogenation reaction.

2. Method according to claim 1 wherein during the hydrogenation reaction said dissolved hydrogen concentration is adjusted as a function of the iodine-value of the oil.

3. Method according to claim 2 wherein the hydrogen consumption is used to determine said iodine value.

4. Method according to claim 3 wherein the rate of hydrogen consumption is used to determine said hydrogen consumption.

5. Method according to any one of the preceding claims wherein the iodine value of the oil is used as a stop condition for the hydrogenation reaction.

6. Method according to any one of the preceding claims comprising the steps of: (a) representing a relationship between the Nt-profile of the oil after the hydrogenation reaction1 and the iodine-value of the oil and the dissolved-hydrogen concentration during the hydrogenation reaction; (b) determining said iodine-value and said dissolved-hydrogen concentration during the hydrogenation reaction; and (c) controlling the dissolved-hydrogen concentration on the basis of said relationship to obtain said Nt-profile-.

7. Method according to claim 6 wherein said relationship is determined empirically.

8. Method according to any one of the preceding claims wherein the rate of hydrogen consumption is used to determine said dissolved-hydrogen concentration.

9. Method according to claim 8 wherein said dissolved-hydrogen concentration is determined from said rate of hydrogen consumption according to the equation: Cb - m . p - / k wherein Cb is the dissolved-hydrogen concentration, m is Henry's law constant, p is the hydrogen pressure above the reaction mixture, r is the rate of hydrogen consumption and k is an equipment constant.

10. Method according to claim 9 wherein said hydrogen pressure is used to control said dissolved-hydrogen concentration.

11. Method according to claim 10 wherein said control is substantially continuous.

12. Method according to claim 10 or 11 wherein the measurement and control of said hydrogen pressure is computer-controlled.

13. Control system for the method in accordance with any one of the preceding claims which comprises: (a) means for sensing the hydrogen pressure above the reaction mixture and providing a signal representative thereof; (b) means for measuring the flow of hydrogen to the reaction mixture and providing a signal representative thereof; and (c) computing means responsive to said signals for determining suitable adjustment of the dissolved-hydrogen concentration.

14. System according to claim 13 wherein said computing means is responsive to said hydrogen-flow signal for determining the hydrogen consumption.

15. System according to claim 14 wherein said computing means is responsive to said hydrogen-flow signal for determining the iodine value of the oil.

16. System according to any one of the preceding claims 13 to 15 wherein said computing means determines the adjustment of the hydrogen pressure corresponding to said determined adjustment of the dissolved-hydrogen concentration.

17. System according to claim 16 wherein said computing means is connected to a hydrogen-pressure control means.

18. System according to claim 17 wherein said hydrogen-pressure control means is responsive to the output signal of said computing means representative of said determined adjustment of the hydrogen pressure.

19. System according to any one of the preceding claims 13 to 18 wherein said computing means is software controlled.