Note: Descriptions are shown in the official language in which they were submitted.
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PRODUCTION OF HIGH GRADE AND HIGH CONCENTRATION OF
FREE FATTY ACIDS FROM RESIDUAL OILS, FATS AND GREASES
FIELD OF THE INVENTION
The present invention relates to the production of free fatty acids from
residual oils, fats and greases. More precisely, the present invention relates
to a process for the production of unsaturated and saturated free fatty acids
from residual oils, fats and greases.
BACKGROUND OF THE INVENTION
Most commercial unsaturated acids (i.e. oleic acid) are derived from animal
tallow (by- product of the meat industry), tall oil (by-product of paper
mills)
or natural vegetable oils.
Fat splitting processes are well known in the art. The most common
methods are:
1 ) Twichell process;
2) Batch autoclave process;
3) Continuous process; and
4) Enzymatic process.
In Twichell process, the fat is hydrolyzed at a temperature of
100°C to
105°C and at atmospheric pressure for 12 to 48 hours. Alkyl-aryl acid
or
cycloaliphatic sulfonic acid with sulfuric acid (0.75 - 1.25% w/w) are used
as catalysts. Yields of 85% - 95% are obtained. The main inconvenients of
this process are the catalyst handling, long reaction time, tendency to form
dark-colored acid and high labor cost.
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In the batch autoclave operations, the fat is hydrolyzed in the presence or
absence of a catalyst. Live steam is injected continuously at the bottom
while venting a small amount to maintain the desired agitation and
operating pressure. After settling and formation of an aqueous and a fatty
acids phase, the fatty acids phase is treated with mineral acid to separate
the soap formed. The fatty acids phase is further washed with water to
remove traces of the mineral acid. Under catalytic conditions (i.e. zinc,
calcium or magnesium oxides) the fatty acids phase is reacted for a period
of 5 to 10 hours at 150°C - 175°C. A high yield of about 85% -
95% is
obtained. Without catalyst the fatty acids phase is reacted for a period of 2
to 4 hours at a high temperature (240°C) to give similar yields. The
principal
inconvenient of this process is the catalyst handling, and high labor cost.
In continuous operations also known as the Colgate - Emery process, a
single-stage countercurrent high pressure splitting is carried out for fat
hydrolysis. The fat is introduced by means of a sparge ring from the bottom
of the splitting tower while water is introduced by the top. The crude fat
passes as a coherent phase from the bottom to the top, while heavier
splitting water travels downward as a dispersed phase through the mixture
of fat and fatty acids. The high temperatures involved (250°C -
260°C)
associated to high pressures (725 psi) assures degrees of splitting up to
98% in only 2 to 3 hours. The principal inconvenient of this process is the
high cost associated with the equipment and the restriction to relative clean
starting materials.
In enzymatic operations, the lipase from Candida rugosa, Aspergillus niger,
and Rhizopus arrhizus had been studied at temperatures of 26°C to
46°C
for periods of 48 to 72 hours. Even though 98% of splitting is claimed there
is no commercial process available until now. The principal inconvenient of
this process is that because enzymes work very well over a specific
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substrate under specific conditions, when the starting material is composed
of more than one product, the reaction is less selective. Long reaction times
and great volumes required to satisfy the optimal concentration are also
current problems involved in this kind of procedure.
Fractionation of free fatty acids is commonly performed by distillation of
tall
oil. Tall oil is recovered in most paper mills by acidulation of the soap
skimming from black liquor. Crude tall oil (CTO) consists of a mixture of
fatty acids (40% - 45%), resin acid (40% - 45%) and various neutral
components (i.e. hydrocarbons, wax alcohols, sterols, esters and residues).
About 40% to 50% of the fatty acids contained in tall oil are oleic acid,
while
another 35% to 45% are linoleic acid. Higher quality of tall oil fatty acids,
TOFA, (less than 2% of resins acid) can be obtained by distillation through
two columns: a rosin column and a fatty acids column.
Oleic acid is probably the most important unsaturated fatty acids (UFA)
because many applications have been developed for its use in different
fields (i.e. cosmetics, chemicals, lubricants, textiles, etc.). Separation of
oleic acid form tall oil distillates requires additional refining steps. Best
known-process for fractionation of fatty acids by crystallization from solvent
is the "Emersol" process, developed by Emery Industries Inc. in 1934.
Different American patents used different solvents (methanol: 2,421,157;
acetone: 2,450,235 and methyl formate: 3,755,389) to separate saturated
fatty acids from unsaturated fatty acids. The process was optimized by
addition of crystallizing promoters (neutral fats, tallow, and glycerol tri-
stearate). One more refined promoter is described in Australian patent AU-
28434/92. It is the reaction product of: 1) a polyhydric alcohol (i.e.
glycerol,
pentaerythritol, trimethylol pentane, etc.), 2) a dicarboxylic acid (i.e.
adipic,
oxalic, succinic, azelaic, glutaric and tartaric) and 3) a fatty acids.
All these process require explosion proof installations and low temperature
refrigeration systems.
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Other methods for producing oleic acid involve separation over molecular
sieves (US 4,529,551 and US 4,529,551); lithium soap separation (US
4,097,507), urea complexation (US 2,838,480 and US 4,601,856) and
complexation with dienophiles (US 5,194,640). All these process have the
inconvenient of a high cost operation associated to the use of chemicals
required.
Dry fractionation technology was originally developed for treatment of
animal fat (i.e. beef tallow) in the 60's. Since this time, many improvements
were performed in response to the ever-increasing demand of the industry
for new products with very specific requirements. Two main sources are
now the target of this technology: 1 ) vegetable oils such as palm oil,
soybean oil, sunflower oil, rapeseed oil, groundnuts oil, cottonseed oil and
palm kernel oil and 2) animal fats such as beef tallow, milk fat, lard and
fish
oil.
These fats and oils are mainly composed of triglycerides, diglycerides and
monoglycerides (i.e. a broad range of melting points) constituting a large
number of intersoluble glycerides that are very difficult to separate by dry
fractionation (i.e. solvent free crystallization). The separation of a liquid
fraction (i.e. olefin, used in food oil) and a solid fraction (i.e. stearin,
used in
shortening and margarine) can be achieved through dry fractionation.
In the present invention, dry fractionation was used to separate purified free
fatty acid obtained by splitting the residual oils and greases recuperated
from industrial and commercial operations (i.e. trap greases, yellow greases
and brown greases).
The free fatty acids obtained from these starting materials are mainly
constituted by unsaturated fatty acids, such as mainly oleic acid, linoleic
acid, linolenic acid and saturated fatty acids such as palmitic acid and
stearic acid. The range of melting points for these limited number of
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products, in comparison with all the possible combinations presented by
glycerides, was' shown to be wide enough to perform a highly selective
separation.
SUMMARY OF THE INVENTION
5 An object of the present invention is to provide a process for the
production
of free fatty acids that uses residual oils, fats and greases as the starting
material.
Another object of the present invention is to provide an inexpensive and
simple way to produce high grade and high concentration of free fatty acids.
A further object of the invention is to overcome most of the drawbacks
mentioned hereinabove.
More precisely, the objects of the present invention are provided by a
process for producing unsaturated and saturated free fatty acids, the
process comprising the steps of:
a) selecting a starting material from the group consisting of trap oils
and greases, yellow greases and brown greases,
b) pre-treating the oils and/or greases selected in step a) in order to
separate the oils and/or greases, from residual solids and water
and obtain a mixture consisting principally of saturated and
unsaturated free fatty acids,
c) bleaching the mixture of free fatty acids obtained in step b) in
order to obtain a suitable coloration thereof,
d) fractionating the bleached mixture of free fatty acids obtained in
step c) in two fractions: saturated and unsaturated fatty acids,
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e) purifying the unsaturated fatty acids obtained from step d), and
f) purifying the saturated fatty acids obtained from step d).
The process of the present invention has the advantage of using
inexpensive starting material thereby reducing the cost all the while
allowing the recycling of the starting material that is normally eliminated
through costly treatments thereof.
The process of the present invention also has the advantage of giving the
option of eliminating a hydrolysis step in the production of the free fatty
acids, thereby simplifying the process for the production of fatty acids and
reducing the production cost of same.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a graphical representation of the differential scanning
calorimetry of free fatty acids of trap oils and greases used in the process
of
the present invention.
Figure 2 is a graphical representation showing the cooling curve of the free
fatty acids produced by the process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
According to a preferred embodiment of the present invention, the process
can be achieved in the following sequential step: 1) selecting a starting
material from the group consisting of: trap oils, greases and fats; 2) pre-
treating the selected oils, fats and greases in order to separate residual
solids and water therefrom so to obtain a mixture consisting principally of
saturated and unsaturated free fatty acids; 3) fat splitting of the pretreated
mixture by hydrolysis or saponification 4) bleaching the hydrolysed or
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saponified free fatty acids; 5) fractionating the bleached free fatty acids so
to obtain an unsaturated and a saturated fraction of fatty acids; 6) purifying
the unsaturated fraction of fatty acids; and 7) purifying the saturated
fraction
of free fatty acids.
In step 1 ), the starting material is selected from the group consisting of:
residual oils, fats and greases. This step is crucial and constitutes the gist
of the present invention. The residual oils, fats and greases are post-
consumers and/or by-products of industrial and commercial operations.
Three principal sources are trap oils and greases, yellow greases and
brown greases.
Trap oils and greases are collected in the traps installed on the sewage
water outlet of restaurants and food industries. These traps allow the
collection of the oils and greases carried over with the wastewater of
washing operations, before they reach the municipal sewage network.
These greases are collected by dedicated trucks and sent to pre-treatment
plants.
Yellow and brown greases are residual oils and greases from cooking
operations. They are mainly collected in restaurants and food industries.
Yellow greases have a low concentration of free fatty acids (acid value of
about 5 to 15 mg KOH / g) as a result of its short and limited contact with
water (i.e. moisture of food). As in the case of trap oils and greases used in
frying process (i.e. high temperature in presence of air) principal alteration
lead to oxidized monomers, dimers, oligomers, volatile compounds, cyclic
monomers and non-polar compounds.
Trap oils and greases are mainly constituted of a mixture of oils and
greases (3 to 10%), water (90 to 95%) and residual solids (1 to 5%). At
room temperature, trap oils and greases form a non-homogeneous and
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unstable emulsion. They have a strong odor characteristic of acetic and/or
butyric fermentation (i.e. fermentation of olives before oil extraction).
In step 2), once the starting material is selected, it undergoes a pre-
treatment step for eliminating the water and residual solid present in the
raw material. Different known methods may be used for eliminating water
and residual solids. Such known methods may include hot filtration, in order
to separate the suspended solids, and a hot decantation, in order to
separate oils and greases from water. Decantation can be done in a batch
mode in heated decanting tanks or in a continuous mode in a three phase
dynamic separator where oils and greases are recovered in the upper
phase (i.e. floating phase), the solids being decanted at the bottom of the
separator and the water been extracted in the middle of the separator. Any
temperature between 50°C and 100°C could be used for decanting,
but
preferably the temperature should range between 60°C and 80°C.
The recovered oily phase is a mixture of free fatty acids, tri, di, and
monoglycerides, trimers and dimer acids, oxidized monomers,
unsaponifiables and other colored long chain oxidized products. A typical
composition of pre-treated trap oil is: 98% oil, 2% residual solids and traces
of water. The oil is mainly constituted by free fatty acids (acid value of
about
130 to 160 mg KOH /g) coming from the natural enzymatic hydrolysis,
which occurs during the lying time of the oils and greases in traps. A typical
composition of pretreated trap oils and greases is presented in Table
N°1.
In step 3), the mixture principally comprising unsaturated and saturated free
fatty acid obtained from the pre-treatment step may undergo fat splitting in
order to complete the hydrolysis of the non-hydrolysed compounds (i.e. tri-,
di- and monoglycerides). Fat splitting can be achieved by hydrolysis at high
temperature and pressure. Typical temperature ranges from 150°C to
260°C, and more preferably from 200°C to 240°C. Typical
pressure ranges
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from 75 psi to 500 psi and more preferably from 150 psi to 450 psi. The
reaction time can vary between 1 to 6 hours and more preferably between 2
to 4 hours. Metal oxide catalysts, such as zinc, calcium, and magnesium
could favor the reaction at a concentration by weight of 1 % to 5% and more
preferably 2% to 4%. A typical composition of free fatty acids (FFA)
obtained by hydrolysis is presented in Table N°1. Typical color values
are
shown in Table N°2.
Fat splitting could also be achieved by saponification under controlled
temperature and pressure conditions. Suitable temperature or pressure
conditions for saponification are about 100°C to 150°C and about
20 to 50
psi respectively. After saponification, the mixture is cooled to about
85°C to
95°C. Neutralization is carried out with a mineral acid selected from
the
group consisting of H2S04, H3P04, HCI and the like, at a pH of about 5 to 7.
Separation of the aqueous phase leads to the oily phase containing free
fatty acids (FFA).
In step 4), the so-obtained mixture of unsaturated and saturated free fatty
acids is bleached in order to give a suitable coloration thereof. Various
known bleaching procedures namely adsorption, treatment with hydrogen
peroxide (H202) or various distillation techniques may be used.
Bleaching by adsorption is carried out with one adsorbent or a combination
of adsorbents of the group consisting of: silica gel, crystalline silica,
bentonite, Fuller's earth, diatomaceous earth and activated carbon.
Bleaching could be performed in a batch or continuous mode by percolation
in different columns. This step may further be carried out at a temperature
varying from 100°C to 150°C and more preferably from
115°C to 130°C.
The time reaction may vary from 15 minutes to 1 hour and more preferably
from 30 minutes to 45 minutes.
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When the bleaching step is carried out by adsorption, inert atmosphere is
strongly recommended. Under batch mode it could be successfully
achieved under vacuum and in continuous mode it can be achieved under
nitrogen atmosphere. A typical composition for bleached free fatty acids
5 (FFA) obtained under batch conditions is presented in Table N°1.
Typical
color values are shown in Table N°2.
Bleaching by treatment with a hydrogen peroxide solution (H202 at 35%
w/w) may be achieved at a temperature of 80°C for one hour.
Concentration by weight of the peroxide solution could be at 1 %, 10% or
10 30% but more preferably at 10%.
Bleaching by distillation techniques such as the ones selected from the
group consisting of falling film evaporation, wiped film evaporation,
fractional distillation and molecular distillation may also be carried out.
One particular method for bleaching (known as "short path") is based in the
separation of the colorful products by molecular distillation. Industrially
this
application could be done by a vacuum thin-film distillation process, which
permits distillation at very reduced pressure (i.e. between 0.1 mm Hg - 5
mm Hg) and at a temperature ranging between 150° - 200°C.
The equipment used for the molecular distillation comprises essentially a
vertical which one double jacketed cylinder with an internal condenser and
a rotating roller wiper system. Free fatty acids (FFA) are heated until
complete homogenization. They are then continuously fed onto the rotating
distributor and thrown by centrifugal force on a heated wall. They are
further uniformly distributed by wiping elements while flowing downwards.
The internal condenser and film of the product to be evaporated (i.e. 1 mm
thick) are so close that condensation is almost instantaneous. The very
short residence time (i.e. about 1 minute) avoid degradation reactions and
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limit the risk of fouling in the internal wall of the cylinder. The absence of
oxygen (i.e. high vacuum) also contributes to prevent most common
degradations associated to air oxidation.
In another preferred embodiment, the bleaching of the free fatty acids is
carried out by molecular distillation. The main interest of this bleaching
technique is to furnish a high quality material that could be directly
fractionated without the fat splitting operation. Table N°1 shows the
composition of trap oils and greases pretreated and distilled by molecular
distillation. It is evident that the quality is as good as, if not better,
than
those bleached free fatty acids (FFA) obtained by other techniques such as
clay and hydrogen peroxide.
Thus the fat splitting step 3) is eliminated when the mixture are bleached by
molecular distillation.
In this case the process is reduced to the following steps:
a) Pre-treatment of the trap oil and greases.
b) Molecular distillation of the pre-treated trap oils and greases.
c) Fractionation of the resulting distillate in two fractions: saturated and
unsaturated.
d) Purification of unsaturated fatty acids (UFA).
e) Purification of saturated fatty acids (SFA).
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Table N°2: Typical color for different products obtained at different
stages of
the process.
Pretreated Free FattyBleached Free
Fat Free Fatt
Acids
Oils & GreasesAcids Fatt UnsaturatedSaturated
Acids
Molecular (FFA) Clay H202 (UFA)* (SFA)*
Dist.**
Color FAC
(AOCS CC 13a-43) > 45 < 7 < 11 < 11 < 1
B
Yellow 1"
Lovibond 25 Out of 10 50 21 3
(AOCS CC 13b-45) range
Red 1" Lovibond
(AOCS CC 13b-45)3 Out of 3.2 6 4.8 1
range
*
Fractionated after clay bleaching.
**
Measured in the 5'/d' Lovibond's scale.
*** After hydrolysis (without any molecular distillation treatment).
In step 5), fractionation of bleached free fatty acids or pretreated and
molecular distilled trap oils and greases could be achieved by different
methods:
a) By quenching the bleached free fatty acids oils in a solvent at low
temperatures. Solvent could be one selected from the group consisting
of hexane, acetone, isopropyl alcohol and ethanol. The reaction
temperature may range from -5°C to - 20°C. Unsaturated fatty
acids
(UFA) are dissolved in the solvent while saturated fatty acids (SFA)
precipitates under these conditions. Filtration could be easily achieved
by a filter press, a Sparkler filter, a centrifuge or similar equipment.
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b) By crystallization of saturated fatty acids (SFA) using a detergent that
coats the crystals, then increasing their specific weight. Filtration could
be achieved by previously described equipment.
c) By dry fractionation, based on differences between melting points of
saturated (SFA) and unsaturated (UFA) free fatty acids. The principal
advantages of this technology are that there is no solvent required and
the temperature range is warmer than previous cases (i.e. over zero
degrees). Differential Scanning Calorimetry (DSC) was used in order to
determine the best cooling profile. Figure N°1 shows the spectra for
free
fatty acids obtained after splitting of trap oils and greases.
Crystallization is carried out by a detailed program of cooling (i.e.
precision
of 0.1°C). Details of this program are shown in Figure N°2:
Bleached Free
Fatty Acids cooling curve.
It is important to note that unsaturated fatty acids (UFA) and saturated fatty
acids (SFA) are mutual contaminants. Poor filtration lets important
quantities of UFA in SFA reducing the yield of UFA and decreasing the
purity of SFA. This problem could be successfully overcome by using a filter
press under pressure. Pressure is generated by squeezing the membrane,
which wraps the filter cloth. A refrigerated liquid or gas could generate the
pressure in order to keep the right temperature of crystallization. Pressures
could vary from 10 bars to 30 bars.
In step 6), unsaturated free fatty acids (UFA) are finally purified by another
treatment of bleaching in similar conditions then that of free fatty acids
(FFA).
In step 7), saturated free fatty acids (SFA) cake's is melted and send to be
distillated. Any distillation procedure (i.e. falling film evaporation, wiped
film
evaporation, fractional distillation and molecular distillation) could be
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successfully achieved to separate stearic acid from palmitic acid due to the
difference in their vapor pressures at high temperature (Table N°4 and
Table N°5).
5 Table N°4: Vapor Pressures of Palmitic and Stearic Acids.
Vapor Pressure
(mm Hg)
Temperature (C) Palmitic Stearic
200 6.15 2.60
230 22.53 10.56
260 67.01 41.15
Table N°5: Boiling Points of Palmitic and Stearic Acids.
Boiling
Point
(C)
Vapor Pressure 1 2 4 8 16 32 64
(mm Hg)
PalmiticAcid 165,9 178,0 191,2 205,7 221,5 239,1 258,6
Stearic Acid 182,5 195,0 208,6 223,6 240,0 285,3 278,6
Although the present invention has been explained hereinabove by way of
a preferred embodiment thereof, it should be pointed out that any
modifications to this preferred embodiment within the scope of the present
invention is not deemed to alter or change the nature and scope of the
present invention.
