Note: Descriptions are shown in the official language in which they were submitted.
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CONTINUOUS COUNTER-CURRENT BIO-DIESEL REFINING METHOD
BACKGROUND
With the ever-increasing demand for petroleum-based fuels, combined with the
decrease
in proven reserves of petroleum, and the current concern over the
environmental impacts
of using petroleum-based fuels, there has been a growing interest in the use
of atternative
sources of energy. It had been previously discovered that traditional diesel
engines are
able to use plant-based oils as fuel. As triglycerides can be obtained from
plant and
animal sources, there has thus been great interest in the production of fuel
from biological
rather than mineral resources.
While plant-based oils can be used in principle, a number of factors make them
less
desirable as fuels than petroleum base diesel. For ezample, plant oils are of
higher
viscosity and density than diesel making it difficult to form a combustible
aerosol within
the engine's combustion chamber. Plant oils also have a lower cetane number (a
measure
of ignitability) and thus are less potent as fuels when compared to
traditional petroleum-
derived diesel products. In addition, the use of high levels of unmodified
triglycerides
has been shown to result in undesirable deposits in the engine combustion
chamber
However, it has been discovered that methyl or ethyl esters derived from
triglycerides
solve many of the problems associated with unrefined plant oils, and can be
used as a
effective and practical substitute for petroleum-based diesel fuels. These
methyl ester
derivatives are collectively termed "biodiesel fuels" and are characterized by
relatively
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low emissions. Biodiesel fuels are also essentially sulfur-free. Sulfur is a
problem in
diesel applications as it witt convert to sutfuric acid, an environtnental
contaminant as
well as a corrosive substance in the engine itself.
One of the present disadvantages of using biodiesel is cost, made relatively
expensive as
compared to petroleum-based fuels due to the cost of raw materials as wetl as
the cost of
refining. Thus, methods of producing biodiesel that reduce the ultimate cost,
increase the
likelihood that biodiesel will become a viable alternative to traditional
diesel fuels, and
are thus desirable.
The production of biodiesel can be accomplished by treating triglycerides
obtained from
plant or animal sources, or waste oils and the like with sodium or potassium
hydroxide
and methanol (which produces rnethoxide), which result in a
transesterification of the
triglycerides in oils to methyl or ethyl esters and glycerol. These esters are
useful as
fuels, while glycerol is also desirable as a product and has application in
the manufacture
of pharmacsutical and in the food and beverage industries.
The conversion reaction is difficult due to the relative immiscibility of oil,
triglycerides
and methanol. When reacted in a batch process, the esterification reaction
occurs
relatively slowly until such time as some mono- and di-glycerides are formed,
after which
the reaction more rapidly proceeds to completion. While agitation is sometimes
used to
increase the rate of the reaction, high rates of agitation can be problematic
due to
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emulsification as a result of the unavoidable preseace of water and fine3y
divided
glycerol droplets.
Thus, to drive the reaction to completion, it is often the case that extra
methanoi and
catalyst are used, and the crude ester reacted a second time with fresh
methoxide in order
to obtain an ester product of higher purity. While these methods generally
work, they are
expensive and wasteful of reagents, unless methanol recovery systems are
included,
which in turn add to the cost and complexity of the production system.
Typical prior art methods perform the conversion and separation steps using a
batch
method. A reactor taak is filled with triglyceride and a compound that drives
the
transesterification of the triglyceride (e.g. methoxide). Mixing is used to
ensure complete
interaction of the reactants.
Once the reaction is complete, the products will typically be transferred to a
settling tank,
where the glycerol and methyl ester separate based on their d'rfferential
density. Glycerol
being of a higher density than the esters settles to the bottom of tho
settling tank, while
the esters rise to the top. After a sufficient time, the glycerol is drained
from the settling
tanlc The ester is subsequently drained following tlie removal of the
glycerol. Typically
each product fraction is withdrawn from the reactor through appropriately
located outlet
ports (Normally a single bottom discharge point).
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The primary drawback in this method is that large tanks are required, and
reaction rates
are generally slow. In addition, the reactor tank and settling tanks have to
be repeatedly
filled and emptied, increasing the time and effort and thus the cost of
producing biodiesel.
Discrete methods of production also necessitate a significant downtime when
reactors are
5 not producing the desired fuel product. Batch methods also increase the
chance of batch-
to-batch variability in product quality, making production of a consistent and
reliable
product more difficult.
Thus, it would be desirable in the field of biodiesel production to have a
system that
operates in a continuous flow arrangement with relativeiy rapid reaction rates
to improve
the throughput of the biodiesel production process.
Prior art methods of continuous flow production of methyl esters from
triglyceride have
been described. U.S. Patent Application 2006/0069274 (Dias de Morales e Silva
et al.)
discloses a method of continual production of inethyl esters from biological
oils.
Cotumns of calcium and magnesium oxide catalyst in the form of "stones"' are
provided.
Oil passing over the "stones" is converted to methyl ester and glycerol. While
the
method provides for the continual production of methyl ester it does not teach
a method
for the continual separation of the products of the reaction.
Likewise, U.S_ Patent Application 2005/0081435 (Lastella) discloses a method
of
continual production of methyl ester from triglyceride. However, the
separation of
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products and reactants occurs in a separate "settler" tank and so the method
is a
discontinuous, batch-type one.
Thus, there is a need to provide an efficient method of converting
triglyceride to methyl
ester (biodiesel), and separating the biodiesel from the glycerol produced in
the reaction
in a continuous flow manner.
SIJNINIABY
In one embodiment the invention provides a method and apparatus adapted for
the
production of biodiesel fuel in a continuous flow manrter. The reactor is
preferably a
single vertical column with a cone-shaped bottom. Reagents such as potassium
methoxide and oil feedstock comprising triglyceride are continuously added in
correct
proportions and at a predetermined point in the reactor, such that complete
conversion of
feedstock to methyl ester and glycerol is obtained.
Mixing of the reactants and feodstock, optimization of the reaction conditions
and
separation of the products are achieved by a countercurrerit mechanism. Methyl
ester
rises to the top of the reactor column, while glycerol sinks to the bottom. By
providing a
predetermined input flow, essentially pure glycerol and methyl ester
(biodiesel) are
extracted from the reactor column in a continuous manner.
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In another embodiment, an additional reactor is used such that the crude
methyl ester
produced in a first stage reactor becomes a feedstock in a second stage
reactor, with the
glycero3imethoxide being recycled and used as the reagent for the first stage
reactor. One
advantage of a multi-reactor system is that the installation requires lower
headroom and
provides easier control visibility_ Another advantage to the multi-stage
reactor is that
later stages provide for extraction of higher purity methyl ester than would
be normally
produced in a single reactor system.
The invention furtber provides a collector means to trap excess unreacted
methoxide to
permit the recycling of methoxide back to the reactor.
The invention includes a means for regulating flow of reactants into the
reactor, and for
removing products produced by the transesterification reaction. The invention
may also
include means for gentle agitation of reactants in order to enhance the rate
of the
transesterification of the triglyceride.
In addition, there will be apparatus and controls for regulating temperature
such that
optimum conditions for the reaction can be provided. For example, it is
typical to
perform the transesterification reaction at a temperature between 60-70 C, and
in
particular at about 65 C.
Thus, in contrast to prior art batch methods of biodiesel production, the
present invention
provides for the continual conversion of triglyceride to methyl ester and
glycerol and the
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separation of these two products. The invention fisrther provides that
synthesis and
separation can be achieved using smaller vcssels than are typica4ly used when
employing
prior art methods of producing biodiesel.
DESCRIPTION OF FIGiTRES
While the invention is claimed in the concluding portions hereof, preferred
embodiments
are provided in the accompanying detailed description which may be best
understood in
conjunction with the accompanying diagrams where like parts in each of the
several
diagrams are labeled with lilce numbers, and where:
Fig. 1 is a diagram representing a single reactor continuous flow biodiesel
production system; and
Fig. 2 is a diagram representing a multiple reactor continuous flow biodiesel
production system.
DETAILED DESCRIPTION
The detailed description below is intended as a description of presently
preferred
embodiments of the invention. It is not intended to represent the only way in
which to
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practice the invention, and thus is not intended to be limiting to either the
scope or spirit
of the invention as claiined. It wiSt be underst9od by those skilled in the
art that
equivalent fimctions and products may be accomplished by variations in the
described
embodiments. Such variation will be readily apparent to one skilled in the art
of
biodiesel production and are intended to fall within the scope of the present
invention.
In one embodiment, shown in Fi& 1, the invention comprises a single reactor
system 10
for the continuous conversion of triglyoerides to methyl esters and glycerol
using
methoxide and triglycerides as the reactants. The invention further provides a
means for
the continuous separation of inethyl esters and glycerol, the products of the
conversion
reaction, and their eontinuai withdrawal from the reactor vessel as these
products are
produced.
The two primary reactants are triglycerides and methoxide. Triglycerides are
typically
obtained from oilseed, animal sources, or from waste oils used in cooking and
the like.
The use of used oils from sources such as restaurant may require various pre-
treatment
before the material is suitable for use as an oil feedstock in the present
invention, but
such treatments and methods are well known in the prior art.lfie choice of
oils feedstock
is not considered to be limiting of the invention, and one skilled in the art
will readily
recognize that a variety of triglyceride sources are useful without departing
from the
spirit of the invention.
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Methoxide is required for the conversion reaction. It can be obtained
commercially and
mixed with methanol, or synthesized on site from methanol and sodium (or
potassium)
hydroxide. In the present invention, methoxide will be provided from a
methoxide
supply means. Conveniently, a methoxide tank 20 containing sufficient
methoxide to
5 supply the reactor or reactors for a desired period of time is provided.
The oil feedstock has a density of about 0.91 on average, while the methoxide
has a
density of about 0.8. The products of the reaction, glycerol and methyl esters
have
significantly different densities (1.26 and 0.86 respectively) and thus will
naturally tend
10 to separate. Thus, as triglyceride is converted to methyl ester and
glycerol, the methyl
ester will tend to rise to the top of the reactor column while glycerol well
tend to sink to
the bottom, generating a countercurrent within the reactor as the reaction
proceeds.
Both the conversion reaction and separation take advantage of the
countercurrent
mechanism established by virtue of the differential density of the
triglyceride feedstock
and products of the triglyceride conversion process. Under ideal conditions,
the
countercurrent mechanism provides that the most depleted methoxide comes into
contact
with fresh oil, and fresh methoxide comes into contact with the most reacted
oil. As
methoxide has a relatively low density compared to the other reactants, it is
added in a
lower region of the reactor column, and in two or more separate stages, via at
least one
methoxide inlet port 22.
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Triglyceride from plant or animal oil sources is introduced from an oil
feedstock supply
12 into a vertically oriented reactor chamber 15 to a first stage reaction
zone 30.
Conveniently, the oil feedstock is fed into the reactor chamber through an oil
inlet 32. A
circulating pump 34 provides the force to draw oil from the oil feedstock
supply and
move it into the reactor chamber. Preferably the oil inlet is located toward
the bottom of
the reactor chamber. In other embodiments the oil inlet may also serve as an
inlet for the
introduction of other materials into the reactor chamber. The reactor chamber
may
further comprise an upper methoxide inlet 36, through which fresh methoxide
may be
introduced into the reactor.
In one embodiment the rate at which oil and methoxide are added to the reactor
is
regulated by at least two metering pump 38A and 3SB. Introducing materials
into the
reactor chamber can also be readily accomplished using pumping means suitable
for each
particular component, with the rate of flow controlled by flowmeters and flow
control
valves. Alternatively, gravity feed methods could also be used, for example in
smaller
scale operations where high throughput is not required.
For optimal reaction control, the flow of reactants into the reactor, and
withdrawal of
products from the reactor will be best achieved through the use of metering
pumps,
flowmeters and flow control valves. Control systems can conveniently be used
to
monitor reaction conditions and thus restrict the input of reactants to a
desired rate in
order to maximize throughput and purity of the products.
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The desired rate will depend on a number of factors including the actual rate
of the
conversion reaction, volume and geometry of the reactor chamber, other
attachments to
the reactor, and the desired degree of pnrity of the glycerol and methyl ester
produced.
One skilled in the art will appreciate that by adding the reactants in the
correct
proportion, and to an optimal location in the reactor chamber, the reaction
will approach
stoichiometric conversion wherein alt input materials are substantially
converted to
products.
The location of the arcthoxide inlet, through which the methoxide is
introduced into the
reactor, can be varied in order to optimize the geometry of the triglyceride
conversion
reaction. While the best position is high in the column to contact the most
reaeted ester
with the fresh reagent, a lower position will give a higher density
glycerollmethoxide
byproduct in the secand stage reaction zone 31, which will separate easier
from the
methyl ester. The most desirable situation is where essentially ati the
triglyceride is
converted to methyl ester and glycerol, and the products of the conversion
reaction can be
collected essentially free of unreacted triglyceride and methoxide. Thus, the
methoxide
inlet will reside somewhere near the midpoint of the reactor chamber, with the
precise
location being readily determined by one skilled in the art.
As introduced above, the basic mechanism of the invention is the mixing of
triglyceride
and methoxide, and the separation of the products of the conversion reaction
by a
countercurrent mechanism. The reactor chamber thus comprises four functional
zones.
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These first and second reactions zones, 30 and 31 respectively, a glycerol-
settling zone
50 and a methyl ester separation zone 51.
Oil feedstock is introduced in the lower portion of the reactor chamber. The
feedstock is
mixed with a small amount of recovered methoxide from a methoxide collector
60, as
well as partially reacted methyl ester from the top of the glyceroi-settling
zone 50. The
circulating pump discharges through near, or slightly below, the midpoint of
the reactor
chamber. Here the mix of fresh triglyceride and pataally reacted material
comes in
contact with a mix of methoxide and glycerol as it settles down the column
from the
second stage reaction zone as descn'bed below. In the countercurrent system an
advantage is provided in that the reaction is fast as it occurs continuously,
thus avoiding
the delayed reaction observed when using batch systems.
Methoxide is introduced into the reactor between the first and second stage
reaction
zones. This provides sufficient contact with the most reacted material present
in the
second stage reaction zone, thus completing the conversion reaction. The
methoxide rises
through the second stage reaction zone, coming in contact with the relatively
pure ester as
it rises through the column from the first stage reaction and thus further
converting
remaining triglyceride to yield a relatively pure ester. The glycerol formed
by the reaction
will mix with the excess methoxide and settle in the column providing the bulk
of the
fresh reagent to the first stage reaction zone.
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Unreacted methoxide, which is lower in density than the unreacted oil and the
glycerol
produced by the conversion reaction, will rise in the reactor chamber where it
can be
collected by a methoxide collector 641ocated in the upper portion of the
reactor chamber.
In one embodiment the methoxide collector is an inverted cone. The methoxide
collected
can then be returned to the reactor for reuse, via a connection to the
recirculation pump
circuit that draws material from near the top of the reactor chamber and
reintroduces it
into the bottom of the reactor chamber.
A heating means may also be provided in order to maintain the contents of the
r=tor
chamber at a desired temperature. Typically, the conversion of trigfyceride to
methyl
ester is most effective at a temperature in the range of 60-70 C, and in
particular at about
65 C. Thus, in another embodiment heat exchangers 70 are provided to heat the
oil and
reactants to the desired temperature. A variety of heat exchange tecbniques
area
available and one skilled in the art would readily appreciate the best
particular form of
heat exchange system that would be most advantageous for use in the reactor
chamber of
the present invention.
As the conversion reaction progresses, relatevely lighter methyl ester will
rise ttnaugh the
reactor, while denser glycerol will settle to the bottom of the reactor. The
tnovement of
the two products of the conversion reaction will therefore provide at least
some of the
impetus to develop the countercurrent flow present in the reactor chamber.
Other means
of enhancing mixing of reactants, such as agitators 80 and the like, couf d be
incfuded in
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the reactor chamber to improve the efficiency of the conversion reaction and
to enhance
the countercurrent flow.
Providing agitation means will also serve to facilitate the conversion
reaction by
5 providing increased contact surface area for the oil and metboxide to react
with each
other. In one embodiment agitators comprise perforated plates mounted on a
vertically
oriented shaft are either rotated or nioved up and down to provide mild
agitatian.
Agitator plates might aJso serve to enhance the removal of the more dense
glycerol by
providing a surface upon which glycerol will coalesce into larger droplets,
improving the
10 rate of settling of glycerol in the reactor.
As products are removed, the reactor contents will b$ replenished witb
triglyceride and
methoxide as described earlier. Conveniently, methyl ester will overflow from
a methyl
ester outlet port 90 located at or near the top of the reactor as it is
produced, while
15 glycerol is removed from a glycerol outlet port 91 at or near the bottom of
the reactor. In
this way, a continuous flow system is established that both converts
triglyceride to methyl
ester and glycerol, as well as provides for the separation of these two
products in a single
reaction vessel.
In practice a small amount of oil and other reactants might be expected to
settle along
with the glycerol collected. Removal of contaminants of the glycerol, which
will include
methyl ester and methoxide may be removed by a variety of means including, but
not
limited to density centrifugation or by transfer of the glycerol to a separate
settling tank.
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Lighter density components may be returned if desired to the reactor chamber.
Alternatively increasing the height or diameter of the reactor chamber might
also be used
to provide more effective separation of the glycerol and methyl ester
products.
Advantages provided by variations to reactor chamber geometry will be apparent
to those
skilled in the art of density separation_
In another embodiment, shown in Fig. 2, the invention comprises a multi-
reactor system
100 comprising two or more reactors to improve both the output and efficiency
of the
conversion reaction, as well as to increase the purity of the methyl ester and
glycerol
products obtained. In a multiple reactor system, oil is added only to a first
reactor 101
and methoxide are continuously added to each to a second 102, or fmal, stage
reactor
chamber via adjustable metering pumps or by supply pumps regulated by
flowmeters or
flow control valves.
Oil is added to the intake of the circulating pump 34 of the first reactor 101
along with
glycerol and methoxide collected from the bottom portion of the second reactor
102. The
conversion reaction will thus occur in the pump, the circulation leg 35, and
fmally in the
reactor chamber.
Crude methyl ester produced in the first reactor chamber 101 is collected from
the top of
the first reactor chamber 101 and is passed to the input of a second line pump
36 and to
the second reactor 102. As with the first reactor 101 and recirculation pump
both
circulate materiai from the upper portion to the bottom portion of the second
reactor 102,
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which will include unreacted oil and methoxide as well as methyl ester and
glycerol. In
addition, unreacted od and the crude methyl ester obtained from the fust
reactor 101 will
be fed into the bottom of the second reactor 102 via the recirculation pump.
One advantage provided by using multiple reactors is that the conversion
reaction may be
more effectively carried out than if a single reactor chamber 102 were used.
While the
glycerol/methoxide collected from the second stage 102 will have to be
carefully
controlled with no interruptions in flow, since it provides the reagent to the
fiust stage
reactor 101, the net result will be that in the second 102 and subsequent
reactors (if more
than reactor chambers are used in-line), the addition of methyl ester from
previous
reactors in the process stream will result in the production of progressively
higher purity
methyl ester than would be obtained with a single reactor. As before, the
products
methyl ester and glycerol will be collected from the top of the second stage
reactor 102
(or fmal stage reactor, if more than two) with the glycerol withdrawn from the
bottom of
the first stage reactor 101, the second stage reactor 102 and subsequent
reactors.
The present invention provides a further advantage in that it is adaptable for
use in
conjunction with an oilseed processing plant. Oil suitable for use in a
biodiesel
production process can be produced from seeds using techniques well known in
the prior
art. For example, oil is extracted by caushing seeds at 60 C. Crude oil is
then filtered to
remove pulp, gum and fine particulates. Oil is then transferred to a holding
tank large
enough to provide a continuons supply of oil to the reactor system.
Preferably, the oil
will be pre-heated to 60-70 C in the holding tanks so that the oil is at an
optimum
CA 02561797 2006-10-02
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temperature for the conversion reaction to proceed once the oil is introduced
into the
reactor chamber.
Combining the oil production and biodiesel production provides several
advantages. The
biodieset produced by the plant could be used to drive diesel equipment used
in the
cultivation and harvesting of oilseed. For exampie, one acre of palm trees is
capable of
producing 650 gallons of oil feedstock, while algal sources may produce up to
10,000
gaiSons of oil feedstock per acre. Excess Iriodiesel could be mwketed
providing
profitability to the production setup.
Thus is provided a method and apparatus for the continuous production of
biodiesel that
solves many of the problems and limitation inherent in prior art methods of
biodiesel
production.
While specifc embodiments of the invention have been described, the foregoing
is
considered as illustrative of the principles of the inventian. Further, since
numerous
changes and unodif'ications will readily occur to t3iose skilled in the art,
it is not desired to
limit the invention to the exact construction and operation shown and
described.
Accordingly, all such suitable changes or ru,odiCications in structure or
operation that may
be resorted to are intended to fall within the scope of the claimed invention.
