Metal-oxide-silica adsorbent for bleaching and refining oil

The invention provides a synthetic, calcined metal-oxide-silica adsorbent of which at least 40% of its surface area is contained in pores with radius of at least 2 nm. The invention further provides a process for refining oil, wherein the oil is treated with the adsorbent as a bleaching solid. The adsorbent can be regenerated by calcination without substantial loss of activity.

The present application relates to a process for refining oil by treatment 
of the oil with a bleaching solid and to a synthetic metal-oxide-silica 
adsorbent that can suitably be used as bleaching solid in such a process. 
The refining of oil by treatment with a bleaching solid is often referred 
to as bleaching. The purpose of the treatment is not only to remove 
coloured matter, such as carotenoids and chlorophylls, but also to remove 
other materials, for example residual phosphatides, soap, gums, metals and 
oxidation products. For example, it is thought that by bleaching edible 
oil, oxidation products can be removed, which are themselves tasteless but 
which would be converted into bad tasting products upon continued 
oxidation, and that thus taste deterioration can be avoided. ln the 
bleaching treatment, similarly thermally instable precursors of coloured 
substances can be removed and colour reversal in a subsequent heat 
treatment, for example a deodorization treatment, can thus be prevented. 
It has been common practice for decades to carry out the bleaching process 
with the use of natural or acid-activated bleaching earth or clay as the 
bleaching solid. Acid-activated clays generally have a higher bleaching 
capacity than natural clays. They can be prepared by subjecting clays 
consisting mainly of minerals belonging to the montmorillonite group to a 
treatment with sulphuric or hydrochloric acid. 
The clays that are used as bleaching earths generally contain substantial 
amounts of inactive minerals. The amount thereof may be as high as 30 or 
40%. This part of the clay does not significantly contribute to the 
refining of the oil. However, when after the treatment the bleaching clay 
is removed again, the inactive part of the clay does entrain oil and it, 
thereby, does add to the oil losses. 
Many attempts have been made to improve the bleaching process. One of the 
main cost-determining factors of the process is the loss of oil during the 
separation step. The cost of the bleaching adsorbent is often exceeded by 
that of the oil lost by retention in the adsorbent spent. This oil is 
difficult to recover and, after recovery, can be badly oxidized and is 
often of poor quality. Hence, the spent earth is often discarded without 
treatment. To reduce such losses it has been tried to increase the 
bleaching activity of the bleaching adsorbents to allow smaller quantities 
of adsorbent to be used. The need for highly active bleaching substances 
has become more urgent in recent years. lt has been recognized that for 
environmental reasons the amount of waste material to be discarded should 
be minimized. 
It has been proposed to employ instead of a natural clay (which may have 
been chemically activated e.g. by treatment with acid), synthetic 
adsorbent material as the bleaching solid. 
An advantage of employing synthetic material as the bleaching solid, 
thereby avoiding the use of natural products or products directly derived 
therefrom, is that the presence of inactive material can be prevented. 
Another advantage is that the purity of the bleaching solid can be 
controlled more easily and the presence of contaminants that cause 
unfavourable side reactions ca be avoided. 
In GB No. 1,349,409 it is proposed to use as the bleaching solid synthetic 
silicate adsorbent material, which has been prepared by reacting an 
acid-free aqueous salt solution that contains divalent and/or trivalent 
metal ions, with an aqueous solution of an alkali metal silicate at a 
temperature ranging from room temperature to the boiling point of the 
aqueous reaction medium at atmospheric pressure under conditions such that 
a silicate precipitate is obtained, neutralising and removing the alkaline 
material of the precipitate and subsequently drying the precipitate. The 
dried precipitate should have a calculated SiO.sub.2 content of 60-80 wt. 
%. The drying is preferably carried out at a temperature below 130.degree. 
C., usually at about 110.degree. C. According to the specification the 
adsorptive power of the precipitation products may be improved by means of 
an acid treatment. It is stated that the adsorption capacity of the 
products is mainly determined by the specific surface and the proportion 
of micropores. Typically the specfic surface is between 300 and 600 
m.sup.2 /g. The fraction of micropores, which are described as pores 
having a mean diameter of 0-80 nm or of 0-14 nm, should be large. 
It has now been found that, to obtain a good bleaching performance, a 
substantial part of the surface area of the synthetic metal-oxide-silica 
adsorbent should be provided by pores with radius of at least 2.0 nm; in 
particular by pores with radius of 2.0-4.0 nm. Pores having a radius less 
than 2.0 nm do not contribute substantially to the bleaching action. On 
the other hand, pores with a radius larger than 4.0 nm should be present 
to ascertain the accessibility of the smaller pores. For the bleaching 
function of the synthetic metal-oxide-silica to be optimal, the 
availability of a substantial specific surface area in pores with radius 
of 2.0 nm or more is crucial. A substantial part of this surface area 
should preferably be contained in pores with radius of 2.0-4.0 nm. 
In the metal-oxide-silica's according to GB No. 1,349,409 a substantial 
fraction of the pores has a radius of less than 2.0 nm. When determining 
the specific surface area contained in pores up to a certain size, e.g. by 
means of a nitrogen adsorption isotherm, for the products according to GB 
No. 1,349,409, and plotting the cumulative specific surface area, for 
example expressed as percentage of the total specific surface area, 
against the logarithm of the pore radius, generally a concave (i.e. a 
function of which the second derivative is not positive), increasing graph 
is obtained. In some cases the relationship between the cumulative surface 
area and the logarithm of the pore radius is close to linear, up to a 
cumulative surface area of e.g. 80 or 90% of the total surface area. In 
all cases the slope of the plot between pores with radius of 2.0 and 4.0 
nm is relatively small. 
It has now been found that good bleaching results can be obtained when 
using as the bleaching solid a metal- oxide-silica adsorbent having only a 
relatively small part of its surface area in pores with radius smaller 
than 2.0 nm but having a fairly large specific surface area in pores with 
radius of 2.0 nm or more, in particular in pores with radius of 2.0 to 4.0 
nm. In particular suitable results can be obtained when using a 
metal-oxide-silica adsorbent with an adequately large total specific 
surface area, having a pore size distribution such that the plot of the 
percentage cumulative surface area against the logarithm of the pore 
radius has a shape resembling an S-curve, with a relatively steep increase 
at pore radius above 2.0 nm and in particular between pore radius of 2.0 
and 4.0 nm, indicating that only a small part of the surface area is 
contained in very small pores and that a relatively large part of the 
surface area is provided by pores with radius of 2.0-4.0 nm. 
It has also been found to be beneficial for the bleaching results if the 
metal contained in the metal-oxide-silica consists for a substantial part 
of metal that can have an oxidation state higher than 2. 
It has further been found that, whereas the bleaching solids according to 
GB No. 1,349,409 are to be used only once, adequate bleaching results can 
be achieved with repeated use of calcined metal-oxide-silica having the 
above described properties. After the use of the calcined 
metal-oxide-silica adsorbent as the bleaching solid in an oil refining 
process the metal-oxide-silica adsorbent can be regenerated yielding a 
bleaching solid with adequate bleaching activity, by a repeated 
calcination. GB No. 1,349,409 teaches not to subject the 
metal-oxide-silica to temperatures higher than 130.degree. C. The 
regeneratability of the present bleaching solids allows the repeated use 
as bleaching solid which results in a substantial reduction of spent 
material. This not only substantially reduces the average costs of the 
bleaching process, but also the amount of spent bleaching solid to be 
discarded. Thus, the present invention provides a significant contribution 
to solving this environmental problem. 
According to a first aspect, the present invention provides a synthetic 
calcined metal-oxide-silica adsorbent of which at least 40% of its surface 
area is contained in pores with radius of at least 2.0 nm. Preferably, the 
metal-oxide-silica has at least 50%, more preferably at least 55% of its 
surface area contained in pores with radius of at least 2.0 nm. It is 
further preferred for the metal-oxide-silica to have a specific surface 
area in pores with radius of 2.0-4.0 nm of at least 90 m.sup.2 /g. 
Preferably, at least 50 mole % of the metal contained in the 
metal-oxide-silica is a metal that can have an oxidation state higher than 
2. The present metal-oxide-silica adsorbent is particularly suitable for 
use as the bleaching solid in a process for refining oil. 
Accordingly, the present invention provides in a second aspect, a process 
for refining oil by treatment of the oil with a bleaching solid wherein as 
the bleaching solid is used the above-described synthetic 
metal-oxide-silica adsorbent. 
The metal-oxide-silica adsorbent is especially suitable for the repeated 
use as the bleaching solid according to the present process. However, when 
using the metal-oxide-silica adsorbent for the first time in the present 
process, not in all instances need it be calcined, but then the surface 
properties of the regenerated material should be checked before employing 
it again as bleaching solid in a next run. 
The present metal-oxide-silica adsorbents can have a high bleaching 
activity. Consequently, satisfactory bleaching results can be obtained 
using only a small amount of bleaching solid. In this way the present 
invention not only contributes to solving the environmental problem by 
reducing the amount of spent material to be discarded, it also allows the 
oil losses to be reduced, thereby reducing the costs of the bleaching 
process. Alternatively, the present process can be used to improve the 
refining quality without causing an increase in oil loss or waste 
material. 
As described above, the surface area contained in pores below a certain 
size does not, we believe, contribute to the bleaching action of the 
metal-oxide-silica. It is therefore, especially preferred for the 
metal-oxide-silica to have at least 60% of its surface area contained in 
pores with radius of at least 2.0 nm. 
As referred to herein, the surface area of the metal-oxide-silica is 
determined according to conventional procedures, from nitrogen adsorption 
at liquid nitrogen temperature 77.degree. K). Because of the occurrence of 
pore interconnectivity, the adsorption isotherm is employed rather than 
the desorption data. The total specific surface area is calculated from 
the experimental gas adsorption data using the BET theory. In the 
determination of the surface area in relation to the pore size 
distribution the conventional assumption of cylindrical pores is made. An 
adequate description of the experimental procedure, the data processing 
and the theoretical basis is given by S. Lowell and J.E. Shields in Powder 
Surface Area and Porosity, second edition 1984, edited by B. Scarlett and 
published by Chapman and Hall, London, in the Powder Technology Series. 
The metal-oxide-silica preferably has a specific pore volume in pores with 
radius up to 2000 nm of at least 0.5 ml/g. We believe that adequate 
bleaching results can be obtained with metal-oxide-silica's having such a 
specific volume in pores of the indicated size, because relatively easy 
access is provided to the surface area in the smaller pores thereby 
allowing rapid adsorption to take place on that surface and thus, 
preventing substantial reduction in the rate of adsorption owing to 
diffusion limitation. 
The specific volume as referred to herein is determined using conventional 
methods by means of mercury porosimetry measurement, using the intrusion 
data. The specific volume in relation to the pore size distribution is 
obtained using again the cylindrical pore shape model. An adequate 
description of the relevant procedures is also given by Lowell and Shields 
in the publication cited above. 
Preferably 50-100 mole % of the metal contained in the metal-oxide-silica 
is a metal that can have an oxidation state higher than 2. The metal 
contained in the metal-oxide-silica need not actually be in the oxidation 
state higher than 2, but the metal should preferably be of the type that 
can occur in such higher oxidation state. Thus, for example, iron is 
suitable, whether it occurs in the metal-oxide-silica with oxidation state 
2 or 3. Alternatively, metal-oxide-silica in which the metal consists 
essentially entirely of e.g. zinc or calcium having only the oxidation 
state 2, is not preferred. 
The amount of metal that can have an oxidation state higher than 2, 
preferably is at least 70 mole % of the metal contained in the 
metal-oxide-silica. The balance of the metal contained in the 
metal-oxide-silica preferably consists essentially of alkaline earth 
metal, in particular of magnesium. 
The metal that can have an oxidation state higher than 2, preferably is 
metal that can occur in the oxidation state 3 and, preferably, it is metal 
having an atomic number in the range 13-40. Particularly preferred are 
aluminum, iron, zirconium, cobalt and manganese and mixtures of two or 
more thereof; aluminum being most preferred. 
The specific surface area of the metal-oxide-silica in pores with radius of 
2.0-4.0 nm is preferably 100-500 m.sup.2 /g, more preferably 110-400 
m.sup.2 /g. 
The specific pore volume in pores with radius up to 2000 nm is preferably 
0.7-5 ml/g, more preferably 1.5-4 ml/g. 
The metal-oxide-silica preferably is X-ray amorphous, by which is meant 
that it does not exhibit X-ray interferences, e.g. in a Debije-Scherrer 
diagram. The present metal-oxide-silica bleaching solid may contain some 
crystalline or microcrystalline material. However, we believe that such 
material does not contribute to the bleaching action and therefore its 
presence is not preferred. On the other hand, such (micro)crystalline 
material need not adversely affect the results of the refining process 
(apart from causing some increase in the oil losses). The presence in 
small amounts of such, essentially inert, crystalline or microcrystalline 
material in the metal-oxide-silica bleaching solid can, therefore, be 
tolerated. 
Alternatively, in the refining process the, preferably amorphous, 
metal-oxide-silica adsorbent to be used as the bleaching solid, may be 
used in admixture with other material, for example filter aid, to 
facilitate a subsequent filtration, or activated carbon, which other 
material may be crystalline. For example zeolites may be used in 
combination with the metal-oxide-silica bleaching solid. However, it is 
preferred that when using such mixtures, more than 50 wt.% thereof 
consists of metal-oxide-silica bleaching solid. More preferably the 
metal-oxide-silica is employed without such admixtures, because such 
admixtures cause an increase of oil loss to occur, owing to entrainment of 
oil in the filtration stage. 
Preferably, the total specific surface area of the metal-oxide-silica is at 
least 150 m.sup.2 /g, more preferably it is 200-600 m.sup.2 /g, a total 
specific surface area of 250-550 m.sup.2 /g being particularly preferred. 
It is further preferred for the specific pore volume of the 
metal-oxide-silica in pores with radius in the range of 100-2000 nm lo be 
at least 0.5 ml/g; more preferably it is 0.7-3 ml/g, a specific pore 
volume in such pores of 0.9-2 ml/g being especially preferred. 
To allow the metal-oxide-silica to have favourable filtration 
characteristics on the one hand and to allow the adsorption to take place 
rapidly on the other hand, it is preferred for the metal-oxide-silica to 
have a particle size, indicated as the volume weighted mean diameter, 
between 1 and 250 .mu.m. 
Preferably, the volume weighted mean diameter of the metal-oxide-silica 
particles is 5-100 .mu.m, more preferably it is 5-50.mu.m. The particle 
size distribution of the metal-oxide-silica can suitably be determined 
with, for example, an Elzone 80 XY.RTM. instrument. 
The metal content of the metal-oxide-silica calculated as mole fraction of 
the total metal plus silicon content, preferably is in the range of 0.04 
to 0.5, more preferably it is 0.1-0.3, a metal content expressed as mole 
fraction, between 0.13 and 0.23 being particularly preferred. 
The sodium content of the metal-oxide-silica preferably is as low as 
possible. Suitably it is less than 1 wt. %, a sodium content of less than 
0.5 wt. % being preferred. 
Although adequate bleaching results can be obtained in the present refining 
process with the use of uncalcined metal-oxide-silica bleaching solid, it 
is preferred to carry out the process with the use of the present calcined 
metal-oxide-silica adsorbent as the bleaching solid. The calcined 
metal-oxide-silica adsorbent that is employed may be freshly prepared or 
it may be material that has already been used as the bleaching solid in a 
previous refining process and that has been regenerated by calcination. 
The treatment as such of the oil with the bleaching solid in the present 
process, can be carried out in a conventional manner, choosing contact 
time, temperature and equipment to be used in dependence of the type and 
quality of oil to be refined. Suitably, the treatment of the oil with the 
bleaching solid in the present process comprises contacting the oil and 
the bleaching solid and maintaining the contact at elevated temperature. 
Preferably, the oil is held in contact with the bleaching solid at a 
temperature of at least 40.degree. C., more preferably at a temperature of 
50.degree.-200.degree. C. The amount of bleaching solid with which the 
treatment is carried out suitably is 0.05-10% calculated on the weight of 
the oil. Preferably 0.1-5% of bleaching solid, calculated on the weight of 
the oil to be treated, is employed. The contact time of oil and bleaching 
solid may be only one or two minutes, but usually a contact time between 
about 5 minutes and about 2 or 3 hours can adequately be employed. In most 
cases, adsorption on the bleaching solid will be completed well within 
about 20 or 30 minutes, depending inter alia on the temperature employed, 
but longer contact times do not normally adversely affect the quality of 
the oil obtained. After the oil and bleaching solid have been in contact 
for an adequate period of time at a suitable temperature, refined oil can 
be recovered from the admixture by removing the bleaching solid with 
adsorbed contaminants therefrom. This can be done in a conventional 
manner, for example by filtration. The refined oil can for example 
suitably be recovered by filtering the admixture of oil and bleaching 
solid using a plate and frame filter press. Alternatively, the bleaching 
solid with adhering contaminents can suitably be separated from the 
admixture to yield refined oil, e.g. by means of centrifugation. 
The present process is particularly suitable for refining fatty oil. 
Alternatively, other oils such as mineral oil can be used, but preferably 
the oil in the present process is fatty oil. "Fatty oil" means to include 
oils such as glyceride oil, e.g. palm oil, fish oil and non-edible tallow, 
as well as edible but indigestible or only partially digestible oils, e.g. 
waxes such as jojoba oil, drying oils such as tall oil and mixtures of 
oils. Preferably, the oil in the present process is glyceride oil in 
particular edible triglyceride oil. An advantage of the present process, 
especially when applied to refine glyceride oil, is that an improved 
removal of sulphur-containing compounds can be obtained, as compared with 
the removal of such substances when using conventional bleaching earths. 
Removal of sulphur-containing compounds is important, in particular to 
prevent poisoning of the catalyst to occur, if the refined oil is 
subsequently to be hydrogenated. 
When the oil to be refined is edible triglyceride oil, usually the use of 
about 0.3-2 wt. % bleaching solid, calculated on the weight of the oil, is 
adequate. The bleaching temperature is then preferably chosen between 
about 85.degree. C. and about 135.degree. C. For the refining of different 
oils, however, different conditions may be more appropriate. For example, 
for the bleaching of non-edible tallow preferably higher amounts of 
bleaching solid, e.g. about 4 wt. %, are used. 
The optimal choice of metal-oxide-silica to be employed, in particular 
regarding the metals contained therein, also depends on the oil to be 
refined. For example, for the refining of oils which are sensitive to 
oxidation, e.g. highly unsaturated edible triglyceride oils such as fish 
oil and soybean oil, preferably a bleaching solid is employed that does 
not contain a substantial amount of metal that may act as catalyst in the 
oxidation reaction such as iron and copper. For such oils, preferably a 
metal-oxide-silica is used in which the metal consists substantially 
completely of aluminum. 
The present process can suitably be carried out in the presence of other 
substances. For example, it can be beneficial to refine glyceride oil by 
the present process in the presence of added acid, e.g. citric acid or 
phosphoric acid. The acid can be admixed with the oil simultaneously with 
the bleaching solid. The acid and the bleaching solid can be admixed with 
the oil together, e.g. as a slurry, but preferably they are contacted with 
the oil separately. Alternatively, the acid can suitably be added before 
or after admixing the oil and the bleaching solid. 
The metal-oxide-silica can be prepared in several ways. It can, for 
example, suitably be prepared via coprecipitation of metal ions with 
silicate, followed by prolonged ageing, washing, drying and, preferably, 
calcination. A preferred process for the preparation of the synthetic 
metal-oxide-silica is by means of stepwise precipitation. ln this process 
first a silica hydrosol is prepared. Silica is caused to precipitate by 
admixing an aqueous silicate solution and acid under intensive mixing. 
Very small precipitate particles are formed. These particles are allowed 
to agglomerate to an aggregate structure. In the thus formed silica 
hydrogel metal ions are incorporated by addition of the metal ions in the 
form of a suitable salt solution. The product is then filtered, washed and 
dried, e.g. spray dried. If in the preparation sodium has been used, for 
example by using sodium silicate as starting material, then preferably the 
product is ion exchanged and filtered, washed again and dried. 
For example, for the preparation of alumina-silica the following process 
has been found to be very suitable. An aqueous solution of sodium silicate 
is contacted in a first stirred reactor with a sulphuric acid solution 
such that a pH of about 8-11, preferably 9.0-10.5 is obtained. The 
residence time in the first reactor is not critical. Suitably a residence 
time of about 5 seconds to 5 minutes is chosen. The admixture is then 
passed to a second reactor providing for a residence time of about 10 
minutes to 2 hours. The formed silica hydrogel is then passed to a third 
reactor. In this reactor, aqueous aluminum sulphate solution is admixed 
and sodium hydroxide is added to adjust the pH to about 4-6. The residence 
time in this reactor is about 10-30 minutes. Subsequently the product is 
filtered off. The temperature in the three reactors suitably is between 
about 20 and 80.degree. C and the process is preferably carried out at 
atmospheric pressure. The obtained filter cake is washed, preferably at 
least twice, with hot water. To effect ion exchange it is subsequently 
reslurried in, for example, a 10% ammonium carbonate solution, allowed a 
contact time of about 30 minutes or more, filtered and washed again with 
hot water. Subsequently, the product is dried, preferably by spray-drying. 
Preferably, the product is calcined by heating it. Adequately, it is heated 
for at least about 10 minutes at a temperature of at least about 
300.degree. C. Preferably, a temperature of about 400-1000.degree. C. is 
used, more preferably of 500-900.degree. C. When the calcination is 
carried out to regenerate metal-oxide-silica that has already been used as 
bleaching solid in an oil refining process, then preferably a temperature 
of at least about 550.degree. C., more preferably at east 600.degree. C. 
is employed. The optimal duration of the heat treatment depends on the 
temperature, at higher temperatures shorter times being sufficient. The 
desirable residence time further depends on the heat transfer and the 
atmosphere. For example, relatively short times can be sufficient when 
using a rotary calciner. When applying, for example, a tray oven at 
700.degree. C. usually a duration of 1/2-1 hour is adequate. The 
calcination preferably is carried out in equipment that allows gas 
circulation and removal of evaporation and combustion products. 
The calculated silicon dioxide content of the employed sodium silicate 
solution suitably is chosen between about 3 and about 10 wt. %. The 
concentration of the sulphuric acid solution used to control the pH in the 
first reactor, is not critical. Concentrations between about 1 and about 
6N can suitably be used. lnstead of sulphuric acid, nitric acid or another 
acid can adequately be used to control the pH in the first reaction stage. 
Similarly, instead of sodium hydroxide, another base can be employed to 
adjust the pH in the third reactor; for example ammonia can suitably be 
used. The concentration of base and of aluminum sulphate solutions 
employed are not critical. For example, a 4N sodium hydroxide and an 
aluminumsulphate solution having a calculated Al.sub.2 O.sub.3 content of 
5 wt. % can be employed. The process can be carried out batchwise or in a 
continuous manner.

EXAMPLE 1 
Alumina-silica was prepared using the general stepwise precipitation 
procedure described above. Starting from neutral waterglass (38-40 Be), a 
sodium silicate solution with a calculated silicon dioxide content of 5 
wt. % was prepared. The pH in the first reactor was adjusted to about 10.4 
using a 4N sulphuric acid solution. In the first and second reactor the 
temperature was 30.degree. C. and the residence times were 45 seconds and 
55 minutes respectively. In the third reactor aluminum sulphate solution 
with a calculated alumina content of 5 wt. % was introduced and the pH was 
adjusted to 4.5 using a 4N NaOH solution. The temperature in the third 
reactor was also 30.degree. C. and the residence time was 18 minutes. The 
product was then filtered off. The filter cake was reslurried with water 
of 75.degree. C., and filtered again. This washing step was repeated once 
more. The cake was then reslurried in a 10% ammonium carbonate solution. 
The dispersion was stirred for 1 hour at room temperature, and filtered. 
The cake was then washed again with hot water twice. It was then 
reslurried with water to give a dispersion comprising about 5-10% dry 
material and the dispersion was spray dried. The product was then calcined 
by heating it for 1 hour at 700.degree. C in an oven allowing air 
circulation. 
The alumina-silica obtained was analyzed. The aluminum content, expressed 
as mole fraction of the total metal plus silicon content was 0.14. The 
silicon dioxide content in the product was 80.5 wt. %. The sodium content 
of the silica-alumina was 0.3 wt. %. The total specific surface area was 
442 m.sup.2 /g. The cumulative surface area in pores up to a certain size, 
indicated as percentage of the total surface area is shown in FIG. 1. As 
can be seen from FIG. 1, about 30% of the surface area was contained in 
pores with radius smaller than 2.0 nm. Consequently, the alumina-silica 
had about 70% of its surface area outside such pores. About 70% of the 
surface area was provided by pores up to a radius of 4.0 nm. Accordingly 
about 40%, corresponding to a specific surface area of 177 m.sup.2 /g, was 
provided by pores with radius between 2.0 and 4.0 nm. In FIG. 2 the 
cumulative intrusion plotted against the pore radius, as determined by 
mercury porosimetry is shown. From this figure can be seen that the 
specific volume in pores with radius up to 2000 nm was about 1.8 ml/g and 
in pores with radius of 100-2000 nm it was about 1.0 ml/g. The product was 
X-ray amorphous. The volume weighted mean diameter of the particles was 
7.7 .mu.m. 
The alumina-silica was used to refine neutralized rapeseed oil. The alumina 
silica was admixed with the oil at 90.degree. C. After 20 minutes the 
admixture was filtered. The bleaching performance was evaluated by 
recording the absorption spectra before and after the treatment at 380-520 
nm and at 630-700 nm. The absorbance at 447 nm and at 667 nm were used as 
indicative for the presence of yellow (carotene) and green (pheophytin, 
chlorophyll) pigments, respectively. The oil treatment was carried out 
twice, once with 1.0% of bleaching solid and once with 0.5% of bleaching 
solid, calculated on the weight of the oil. 
The refining treatment with 1% solid removed 96% of the yellow pigments and 
93% of the green pigments. When using 0.5% solid the pigment removal was 
88 and 85% for the yellow and the green pigments, respectively. 
For comparison, the oil treatment was repeated using as bleaching solid 
Tonsil ACCFF.RTM., an acid-activated bleaching clay. The experiments were 
carried out in duplo, using two different batches of clay. The averaged 
results when using 1 wt. % clay on oil were 91 and 86% removal of yellow 
and green pigments, respectively. When using 0.5 wt. % clay, the removal 
was 70 and 52% of the yellow and green pigments, respectively. 
For comparison, alumina-silica was prepared according to example 9 of GB 
No. 1,349,409. The total specific surface area of the product obtained was 
203 m.sup.2 /g. The cumulative surface as percentage of the total surface 
area, plotted against the pore radius is shown in FIG. 3. The plot shows 
that almost 50% of the surface was contained in pores with radius smaller 
than 2.0 nm and that 29%, corresponding to a specific surface area of only 
about 60 m.sup.2 /g was provided by pores with radius between 2.0 and 4.0 
nm. 
The cumulative intrusion in dependence of the pore radius is shown in FIG. 
4. The specific pore volume in pores with radius up to 2000 nm was about 
0.8 ml/g and in pores with radius of 100-2000 nm was about 0.4 ml/g. With 
the use of this alumina silica as bleaching solid in the refining of the 
neutralized rapeseed oil, after 20 minutes at 90.degree. C, when using 1% 
alumina silica, calculated on the weight of the oil, the yellow and green 
pigment removal was only 28 and 17% respectively. 
EXAMPLE 2 
A series of bleaching processes was carried out wherein the contact time 
between the oil and the bleaching solid was varied. The processes were 
carried out at 90.degree. C., using neutralized rapeseed oil and alumina 
silica as described in Example 1. 1% of bleaching solid, calculated on the 
weight of the oil was employed. For comparison, the experiments were 
repeated using Tonsil ACCFF as bleaching solid. The results are shown in 
Table 1. 
The results show that with the present alumina silica not only a more 
complete pigment removal is obtained, but also that it is obtained more 
rapidly. 
TABLE 1 
______________________________________ 
pigment removal (%) 
contact time 
alumina silica 
Tonsil ACCFF 
(min.) yellow green yellow 
green 
______________________________________ 
1 85 83 42 32 
5 93 87 67 54 
10 94 89 78 59 
20 95 92 85 74 
40 96 93 90 85 
______________________________________ 
EXAMPLE 3 
Alumina-silica was prepared using a procedure similar to the one described 
in Example 1. The pH in the first two reactors was 10.1 and the residence 
times in the second and third reactor were 50 and 10 minutes respectively. 
The aluminum content of the resulting product was 18 mole % of the total 
metal plus silicon content. The product contained 75.3 wt.% silicon 
dioxide, calculated from the silicon content. The product contained 0.22 
wt. % sodium. The specific surface area contained in pores with radius 
between 2.0 and 4.0 nm was 186 m.sup.2 /g. 64% of the surface occurred 
outside pores with radius smaller than 2.0 nm. The total specific surface 
area was 423 m.sup.2 /g. The product was X-ray amorphous. 
This alumina-silica was used to refine neutralized rapeseed oil. After a 
contact time of 20 minutes at 90.degree. C., using only 0.5 wt. % 
bleaching solid on oil, 83% of the yellow pigments and 90% of the green 
pigments had been removed. 
EXAMPLE 4 
An aluminum-iron-oxide-silica was prepared as described in Example 3, but 
the sulphuric acid solution contained in addition some iron (II) sulphate. 
The aluminum and iron content of the resulting product, expressed as mole 
fraction of the total metal plus silicon content were 0.18 and 0.02, 
respectively. The specific surface area contained in pores with radius of 
2.0-4.0 nm was 124 m.sup.2 /g. 35% of the surface area was contained in 
pores with radius smaller than 2.0 nm. Consequently 65% of the surface 
area occurred outside such pores. The total specific surface area was 353 
m.sup.2 /g. The volume weighted mean diameter of the particles was 
12.6.mu.m. The product was X-ray amorphous. When using 0.5 wt. % of this 
aluminum-iron-oxide-silica to bleach neutralized rapeseed oil after 20 
minutes at 90.degree. C., 93% of the yellow pigments and 85% of the green 
pigments had been removed. 
EXAMPLE 5 
Alumina-silica was prepared using the procedure as described in Example 1, 
but ammonia was employed for pH control in the third reactor. In the first 
and second reactor the pH was about 9.5; in the third reactor it was kept 
at about pH=5. The material leaving the third reactor was filtered, the 
cake was reslurried in water and then spray dried. The resulting product 
was washed once with hot water, then ion exchanged with an ammonium 
sulphate solution and subsequently washed again with hot water. Then the 
product was reslurried with water once more, then flash dried, milled and 
finally calcined. 
The alumina-content of the resulting product, expressed as mole fraction of 
the metal plus silicon content was 0.15. The silicon dioxide content of 
the product was 78 wt. %. The product contained 0.02 wt. % sodium. The 
specific surface area in pores with radius of 2.0-4.0 nm was 240 m.sup.2 
/g. 75% of the surface area occurred outside pores with radius smaller 
than 2.0 nm. The total specific surface area was 440 m.sup.2 /g. The 
volume weighted mean diameter of the particles was 10.5 .mu.m. The product 
was X-ray amorphous. 
This alumina-silica was used to refine neutralized rapeseed oil by admixing 
1 wt. % of the bleaching solid with the oil at 90.degree. C. and 
maintaining the admixture for 20 minutes at that temperature before 
filtering it. From the refined oil, 95% of both the green and the yellow 
pigments had been removed by the treatment. 
EXAMPLE 6 
A series of alumina-silica's was prepared as described in Example 5, but 
the calcination temperature was varied. Calcination was carried out at 
700, 800 and 900.degree. C. The resulting products were used to bleach 
neutralized rapeseed oil using 0.5 wt. % of the bleaching solid. The 
bleaching time and temperature were 20 minutes and 90.degree. C., 
respectively. The bleached oil was subsequently deodorised. The colour of 
the oil before and after deodorisation, was measured using the Lovibond 
method. For comparison, the refining treatment was also carried out using 
0.8 wt. % of Tonsil ACCFF as bleaching solid. The results are shown in 
Table 2. In Table 2 also the results are shown that were obtained using 
only 0.4% of the alumina-silica that was calcined at 700.degree. C. (The 
Lovibond colours (using a 5 1/4" cell) of the neutralized rapeseed oil 
before the bleaching were 80, 8.0 and 3.5 for Yellow, Red and Blue, 
respectively.) 
TABLE 2 
______________________________________ 
Bleaching solid/ 
Amount Lovibond colours (51/4") 
Calcination temp 
bleaching Before deod. 
After deod. 
(.degree.C.) 
solid (wt. %) 
Y R B Y R B 
______________________________________ 
700 0.4 60 6.0 0 17 1.7 1.0 
700 0.5 51 5.1 0 16 1.6 0.6 
800 0.5 40 4.1 0 8 0.8 0.2 
900 0.5 47 4.7 0 12 1.2 0.4 
Tonsil ACCFF 
0.8 29 2.9 0 7 0.7 0.1 
______________________________________ 
Table 2 shows that the colour of the deodorised oil obtained after 
bleaching with only 0.5% of the product calcined at 800.degree. C. is 
essentially the same as that obtained with the use of 0.8 wt. % of the 
reference bleaching clay. 
The refined oils were analyzed for their contents of chlorophyll, carotene, 
iron, phosphorus and sulphur. The contents of chlorophyll, carotene and 
sulphur containing compounds were determined before and after 
deodorization. The contents of the other components do not change during 
deodorization and were only determined before the deodorization. For all 
samples the phosphorus content was less than 2 mg/kg oil. The results for 
the other components are shown in Table 3. 
TABLE 3* 
______________________________________ 
Amount 
Bleaching 
bleaching 
chloro- 
solid/calc. 
solid phyll carotene S 
temp (.degree.C.) 
(wt. %) nb.sup.+ 
nbd.sup.+ 
nb nbd Fe nb nbd 
______________________________________ 
700 0.4 3 3 3 0 .ltoreq.0.01 
11 7 
700 0.5 3 3 3 0 .ltoreq.0.01 
11 6 
800 0.5 &lt;1 &lt;1 1 0 .ltoreq.0.01 
11 4 
900 0.5 3 3 2 0 .ltoreq.0.01 
12 4 
ACCFF 0.8 &lt;1 &lt;1 0 0 0.04 12 7 
______________________________________ 
*The amount of each of the components is indicated in mg/kg oil 
.sup.+ nb indicates neutralized and bleached; nbd indicates neutralized, 
bleached and deodorized. 
The table shows that the synthetic bleaching solids are more effective in 
providing refined oil with low iron content (which is important for 
oxidative stability of the oil, because iron may catalyze undesirable 
oxidation reactions). Similarly, in the deodorized oil lower sulphur 
contents can be achieved, even when using less bleaching solid. 
Some of the refined oils (all before deodorisation) were further analyzed 
for their tocopherol contents. It is desirabe not to remove the 
tocopherols because they protect the oil against oxidation. The content of 
.delta. tocopherol was less than 30 mg/kg oil in all samples. The contents 
of .alpha.- and .gamma.-tocopherol were measured both via voltammetry and 
via HPLC. The average results of the analysis are shown in Table 4. 
TABLE 4 
______________________________________ 
Bleaching solid/ 
Amount 
Calcination 
of bleaching 
.alpha.-tocopherol 
.gamma.-tocopherol 
temp. (.degree.C.) 
solid (wt. %) 
(mg/kg) (mg/kg) 
______________________________________ 
700 0.5 380 530 
800 0.5 420 550 
900 0.5 380 510 
Tonsil ACCFF 
0.8 300 480 
______________________________________ 
EXAMPLE 7 
Alumina silica was prepared using a procedure essentially similar to the 
one described in Example 1. The product obtained was used to refine 
rapeseed oil as described in Example 6, using 0.5 wt. % of bleaching 
solid. 
The filter cake (containing spent bleaching solid, adsorbed contaminants 
and oil) that was obtained from the bleaching process was regenerated by 
calcining it again for 1 hour at 700.degree. C. After the calcination, the 
alumina-silica was white again and had the same appearance as before it 
had been used as bleaching solid. It was used again as the bleaching solid 
in a process to refine neutralized rapeseed oil, using substantially the 
same conditions as in the first run. The results were essentially the 
same. The filter cake obtained from this treatment was again calcinated at 
700.degree. C. and the regenerated material obtained, was used a third 
time as bleaching solid under the same conditions and with essentially the 
same results. 
EXAMPLE 8 
Alumina-silica was prepared as described in Example 5, but the calcination 
was carried out at 650.degree. C. This material was used as bleaching 
solid to refine neutralized rapeseed oil. 
After contacting the oil and the bleaching solid, using 0.6 wt. % bleaching 
solid, and maintaining the admixture for 20 minutes at 110.degree. C., 
followed by filtration, 80% of the chlorophyll contained in the starting 
oil, had been removed. To achieve the same results, using varying amounts 
of Tonsil ACCFF as the bleaching solid and keeping the other process 
conditions the same, 1.1% of the Tonsil ACCFF to be used. 
EXAMPLE 9 
Alumina-silica was prepared as described in Example 5. The volume weighted 
mean diameter of the product was 52 .mu.m. Batches of 60 kg each of 
neutralized palm oil were treated for 20 minutes at 90.degree. C. using 
either 0.50 or 0.75 wt. % bleaching solid. The filtration rate was 
measured and the Lovibond red and yellow colours were measured in a 5 1/4" 
cell. For comparison the experiments were repeated using Tonsil ACCFF as 
bleaching solid instead of the synthetic alumina-silica. The results are 
shown in Table 5. The samples were subsequently deodorized and stored. The 
taste stability of all samples was good. After 12 weeks the flavour of all 
samples was still acceptable. 
TABLE 5 
______________________________________ 
Bleaching solid 
Amount Lovibond (51/4") 
filtration rate 
Type (wt. %) Y R (l/m.sup.2 h) 
______________________________________ 
alumina- 0.50 23 2.3 2800 
silica 0.75 25 2.5 10000 
Tonsil 0.50 20 2.0 184 
ACCFF 0.75 21 2.1 421 
______________________________________ 
The table shows that with the synthetic alumina-silica much higher 
filtration rates can be achieved at essentially similar bleaching results. 
EXAMPLE 10 
A series of alumina silica's was prepared using the procedure described in 
Example 5, but using a higher amount of aluminum sulphate solution, 
resulting in an aluminum content expressed as mole fraction of the total 
aluminum and silicon content, of 0.20. The calcination time and 
temperature were varied. The average particle size of the products was 21 
.mu.m. Neutralized rapeseed oil was bleached at 90.degree. C., contact 
time 20 minutes, using 0.5 wt. % alumina silica as bleaching solid. The 
results are shown in Table 6. 
TABLE 6 
______________________________________ 
Calcination Colour removal 
time temp. Yellow Green 
(hour) (.degree.C.) (%) (%) 
______________________________________ 
1 650 58 54 
2 650 56 35 
3 650 58 54 
1 750 63 68 
2 750 63 68 
3 750 65 45 
1 850 68 71 
2 850 73 75 
3 850 61 45 
______________________________________ 
The table shows that at 750 and 850.degree. C. a calcination time as long 
as 3 hours has an adverse influence on the removal of green pigments. The 
bleaching performance of products calcined for 1 or 2 hours at 750.degree. 
C. or 850.degree. C. is better than of those calcined at 650.degree. C. 
The beaching process was repeated using a product calcined for 2 hours at 
850.degree. C. but having an average particle size of 38/.mu.m. 
The pigment removal was essentially the same as with the corresponding 
product with an average particle size 21 .mu.m. 
EXAMPLE 11 
Alumina-silica was prepared using the procedure described in Example 1, but 
the second reactor was bypassed. A somewhat higher amount of aluminum 
sulphate was employed resulting in an aluminum content, expressed as mole 
fraction of the total metal plus silicon content of 0.22. The silicon 
dioxide content of the product, calculated on the basis of the silicon 
content was 77 wt. %. The sodium content of the product was 0.4 wt. %. To 
test the bleaching properties of the product, it was used to bleach 
neutralized rapeseed oil for 20 minutes at 90.degree. C. When using 1 wt. 
% the removal of yellow and green pigments was 93 and 81%, respectively. 
When 0.5 wt. % was used the removal was 78 and 85% of the yellow and green 
pigments, respectively. 
The alumina-silica was then used for the decolourisation of non-edible 
tallow to be employed for soap-making. The absorbance at 400 nm was taken 
as a measure for the colour of the tallow. The treatment was carried out 
using 2, 4 or 8% bleaching solid and the contact time was varied. For 
comparison the experiment was repeated using 8 wt. % of Tonsil ACCFF as 
bleaching solid. The results are shown in Table 7. 
TABLE 7 
______________________________________ 
Pigment removal (%) 
Time synthetic alumina-silica 
Tonsil ACCFF 
(min.) 2% 4% 8% 8% 
______________________________________ 
1 43 60 81 53 
5 49 65 85 61 
12 54 -- -- 65 
20 55 68 -- -- 
30 -- -- 93 70 
40 57 -- -- -- 
60 -- -- 94 70 
______________________________________ 
The table shows that when using 8% of bleaching solid, much better colour 
removal is obtained with the synthetic alumina-silica than with the 
reference product. When using only 4% of the synthetic alumina silica, 
still slightly better results are obtained than with 8% of the reference 
product.