CA2561797A1 - Continuous counter-current bio-diesel refining method - Google Patents

Abstract

The present invention provides a continuous flow method of producing methyl esters and glycerin from triglycerides. Reaction of methoxide with triglycerides produces glycerin and methyl esters, the methyl esters useful as a biodiesel fuel. The present invention takes advantage of the differences in density of triglycerides, glycerol and methyl esters while providing a method of dealing with the unfavorable density of methoxide to achieve reaction separation of the desired products by a countercurrent mechanism.
Reactants are injected into a central zone in a biodiesel reactor. Lighter methyl esters rise to the top of the reactor, while higher density glycerol settles to the bottom of the reactor.
Ports at the top and bottom facilitate continuous collection of products. The reactor is continually charged with fresh reactant as products are removed, such that a continuous flow system producing biodiesel is provided.

Description

2 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

3 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

4 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).

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

6 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.

7 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

8 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

9 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.

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.

11 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.

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.

13 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.

14 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 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.

16 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,

17 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

18 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.

Claims