Patent Application
20100266745
This application claims the priority of the French application FR0756716 which is incorporated herein in its entirety.
The present invention concerns a novel method for preparing fatty acid esters which can notably be used as biodiesel, prepared from oilseeds.
Biodiesel is a fuel obtained from vegetable oil or animal fat that is converted using a chemical process called transesterification, in order to obtain Vegetable Oil Methyl Esters (VOMEs) when using methanol or Vegetable Oil Ethyl Esters (VOEEs) when using ethanol. Biodiesel competes with vegetable oils used in the crude state and with petrodiesel i.e. conventional fossil diesel. Biodiesel can be used alone in engines or mixed with petrodiesel.
In prior art methods to obtain VOME's or VOEEs, either the crushed seeds are subjected directly to the transesterification reaction, or the oil is first extracted from the seeds, this oil is semi-refined and then the transesterification step is conducted on the neutral semi-refined oil. However, these prior art methods are not completely satisfactory. In the first case, at industrial level, the seeds must be finely crushed to obtain the best yield possible, but the phase separation step is all the more difficult the finer the crushing. In the second case, extraction of the oil and prior treatment make industrial application of the process complex and costly.
Other preparation methods have been described more recently, notably by Khalil et al (US2005/0011112) and Haas et al (US2006/0155138). These techniques, instead of seeds, use “flakes” obtained from hulled seeds. These flakes are abundantly manufactured in the agricultural industry but their use for the manufacture of biodiesel has several drawbacks: first the flakes are more fragile than the whole seeds, which leads to the formation of fine matter which has to be filtered so that the oil can be used as biodiesel; secondly the VOME and VOEE yields are not as high owing to the absence of the seed shells; finally the formation of these flakes requires costly packaging units.
The subject-matter of the present invention is a method to prepare fatty acid esters from oilseeds with excellent yield and which, at the same time, overcomes the disadvantages of the processes described in the prior art.
The first subject of the present invention is a method to prepare fatty acid esters which can be used as biodiesel, prepared from whole oilseeds, characterized in that it comprises the following successive steps:
By <<oilseeds>> is meant any plant seeds containing fat, preferably rich in triglycerides.
Therefore germ, pips, kernels, and nuts also come under this category. The oilseeds also contain proteins, fibres and minerals.
The seeds are preferably chosen from among plant seeds which can be cultivated. For example use may be of rapeseed, jatropha seed, groundnut, castor bean, sesame seed, sunflower seed, safflower seed, soybean, lupin seed, camelina seed, cotton seed. The preferred seeds are rapeseed, sunflower seed and jatropha seed. Further preferably the seeds are rapeseeds.
Additionally, it is also possible to use seeds chosen from among rapeseed, groundnut, castor bean, sesame, sunflower, safflower, soy, lupin, camelina, cotton.
In the method subject of the present invention, the seeds can be used with all or a large part of their husk. In the meaning of the present invention <<oilseeds>> designates the whole seed or the seed rid of part of its husk. For example, with regard to rapeseed, sunflower seed and jatropha seed, the seed is preferably used essentially whole i.e. with at last 80% of its husk. This forms an advantageous fibrous support which can avoid disintegration of the flattened seed when contacted with the alcohol medium during the transesterification step d).
However, if the husk is too voluminous compared with the fruit (for example macadamia nut, Brazil nut, andiroba nut, coconut, shea nut or cupuacu nut) it is preferable to rid the seed of part of its husk so as not to perturb the transesterification reaction. It may also be advantageous to conduct prior crushing of the seeds if they are of large size (e.g. for the macadamia, Brazil, andiroba nuts, coconut, shea or cupuacu nut).
According to step b) of the method subject of the present invention, the oilseeds are flattened. They are then generally in the form of a thin elongate sheet, flake or chip.
Before the flattening step, the seeds are preferably cleaned i.e. rid of their solid impurities such as stones, rags, sticks, metal particles, dust.
The thickness of the flattened seeds is preferably between 10 μm and 1 mm. According to one particularly preferred embodiment, the thickness of the flattened seeds lies between 0.1 and 0.3 mm, and further preferably the thickness of the flattened seeds is less than 0.2 mm notably for rapeseed.
Also, the size of the flattened seeds i.e. their length or width is preferably between 3 and 5 mm, notably for rapeseeds and other seeds of similar size, in which it is around 4 mm.
According to one particular embodiment the oilseeds can be preheated at a temperature of between 40° C. and 60° C., preferably 50° C. before carrying out the flattening step b) so as to increase their plasticity. However, the seeds are brought to this temperature just the time that is necessary to reach the desired plasticity. It is effectively preferable to avoid drying the seeds which causes their fractioning during the flattening. The seeds must not under any circumstance be baked or dried before they are flattened.
For this purpose, the oilseeds can preferably be heated at a temperature of between 50 and 55° C. for 5 to 60 min, preferably 30 minutes, before conducting the flattening step b), optionally under water vapour.
According to the present invention, flattening of the oil seeds is advantageously achieved using rollers which may be of any type, in particular smooth or fluted, preferably smooth. Their diameter may measure up to 80 cm. The distance between the rollers is preferably less than 0.2 mm, further preferably less than 0.1 mm.
The speed of the rollers is determined so as to avoid fractioning the seeds when they are being flattened. Preferably the diameter and speed of the rollers are identical to avoid phenomena of avulsion and hence fractioning of the seeds.
According to one particular embodiment, flattening of the oilseeds is achieved using smooth rollers preferably in a single pass.
The flattening step b) is an essential step in the method, since it allows a significantly higher yield to be obtained than without any flattening, i.e. a better transesterification yield and a better extraction yield of ethyl esters.
After the flattening step, the seeds must be dried as quickly as possible to stop enzymatic activity and thereby avoid degradation of their content matter. The drying step c) is therefore conducted immediately after the flattening step b) and no later than 24 hours after the flattening step b), preferably less than 2 hours after the flattening step b) and at best within one hour after flattening. Also, by means of the drying step, it is possible to store the flattened seeds before subjecting them to the transesterification step d). Drying of the flattened seeds is performed so as to obtain a water and volatile matter content of between 0.5 and 2.5%, preferably between 1.5% and 2%.
The water and volatile matter content of the dried seeds is assayed using the method NF V 03-909.
According to one particular embodiment, the drying step c) is performed at a temperature of between 50 and 100° C., preferably between 70° and 90° C.
After the drying step c), a transesterification step is conducted by contacting the flattened, dried seeds with an alcohol medium in the presence of a catalyst. The catalyst may be basic or acid, preferably basic.
The alcohol medium may comprise one or more alcohols chosen from among the C1-C6 alcohols such as methanol or ethanol, optionally in a mixture with one or more aliphatic hydrocarbons such as hexane. The alcohol medium is preferably ethanol containing a quantity of water of less than 5000 ppm, preferably 3000 ppm.
The basic catalyst is preferably anhydrous and homogeneous and can be chosen from among sodium hydroxide, potash, sodium or potassium carbonate or hydrogen carbonate, sodium or potassium carbonate, sodium or potassium methylate or ethanolate.
The acid catalyst may be sulphuric acid for example.
Before starting the transesterification step, it may be advantageous, under a discontinuous schedule, to place the flattened seeds previously in contact with the alcohol medium, so as to impregnate them with this alcohol medium and promote subsequent transesterification. Pre-impregnation can be conducted for a time of between 10 and 30 min., preferably 30 minutes, at a temperature of between 40 and 80° C., preferably 75° C. This step is to be omitted if the reaction takes place under a continuous schedule.
To optimize the yield of the transesterification reaction, the weight ratio of catalyst/flattened seeds is preferably between 0.5/100 and 2/100 and/or the weight ratio of alcohol/flattened seeds is preferably between 100/100 and 500/100.
If the method is conducted in discontinuous mode, the transesterification reaction is advantageously conducted at a temperature of between 45 and 55° C., preferably at around 50° C., for a time of 10 min to 2 hours, preferably between 20 and 40 min.
According to one particular embodiment, the contacting of the flattened seeds with the alcohol medium at the transesterification step d) is conducted under slow stirring or by sprinkling and percolation. It is preferably conducted by percolation of the alcohol medium containing the catalyst through the flattened seeds. In practice, percolation can be conducted by sprinkling a bed of flattened seeds, having a height of preferably around 80 cm.
After the transesterification step, the liquid and solid phases resulting from said transesterification are separated, preferably by draining. The liquid phase collected is high in fatty acid esters produced by the transesterification reaction.
It is preferably for the residual content of fat in the solid phase i.e. cake to be less than 1% by weight of the total dry matter.
To collect the remainder of the fatty acid esters present in the solid phase, it is possible to conduct the following additional steps:
The grouped liquid phases derived from step e) can be filtered, for example through a cloth having a pore size of between 10 to 50 μm, to remove all the fine particles.
The extraction step h) is preferably conducted by counter-current percolation with ethanol, with a weight ratio of alcohol/flattened seeds of between 100/100 and 200/100.
Also, the alcohol used at extraction step h) can be chosen from among the C1-C6 alcohols such as ethanol having a water content of less than 5000 ppm, preferably less than 3000 ppm.
The liquid phase derived from transesterification step e), optionally supplemented with the liquid phase derived from extraction step h), is then neutralized either using an acid if the reaction catalyst is basic, or with a base if the reaction catalyst is acid.
The acid is preferably chosen from among sulphuric acid, hydrochloric acid, phosphoric acid, citric acid or acetic acid.
The base may be sodium hydroxide for example.
The quantity of acid added to the liquid phase is determined so that the fatty acid content of the fatty acid ethyl esters remains less than 0.25% (equivalent to an acid number<0.5 mg KOH/g).
Neutralization of the liquid phase is performed in part so as not to increase the quantity of soaps therein.
According to one particular embodiment, the neutralization acid is added in a quantity leading to a pH close to 10, notably in a quantity of less than 0.04% of the total quantity of fatty acid esters present in said liquid phase.
After the neutralization step f), the alcohol is then removed from the liquid phase and the glycerine is separated from the fatty acid esters.
The alcohol is preferably removed by evaporation at a temperature of between 50 and 100° C. under a pressure of between 200 and 1000 mbars, preferably at around 80° C. under atmospheric pressure, until a residual alcohol content of less than 1%; is obtained.
The separation of the glycerine from the fatty acid esters is preferably carried out by centrifuging at a temperature of between 60 and 80° C. It may also be carried out by static decanting. The glycerine carries with it a large part of the impurities such as the catalyst, soaps, phosphoric derivatives or sodium sulphate.
The fatty acid esters are then advantageously washed with water, preferably at around 80° C. to fully remove the impurities, and then separated from the washing water notably by decanting or centrifuging, preferably at around 80° C., then dried preferably by evaporation at a temperature of between 90 and 100° C. under a pressure in the order of 200 mbars, until a residual water content of less than 500 ppm is obtained relative to the total dry matter. The fatty acid esters thus obtained can then be packaged under nitrogen after being cooled.
A second subject of the present invention is a method to prepare oilseed cakes intended for animal feed, using the solid phase derived from step e) or i) of the method to prepare fatty acid esters such as described previously, comprising the following steps:
The solid phase resulting from step 1) can also be supplemented with the washing waters described previously in the method to prepare fatty acid esters.
The solid phase derived from step e) or i) of said method to prepare fatty acid esters contains between 50 and 65% alcohol by weight. Removal of the alcohol from this solid phase can be achieved mechanically, notably by pressing or spinning, then thermally by entraining with water vapour until a residual water content of less than 500 ppm is obtained relative to the total dry matter.
The final oilseed cake obtained at step 2) can then be packaged in powder form or extruded.
The removed alcohol can be collected then dehydrated, for re-use in the method to prepare fatty acid esters.
The present invention and its advantages are illustrated by the following examples.
The abbreviations used in the examples are explained in the following table:
The objective of this first series of tests is to evidence the importance of the preheating step of the non-dried seed before it is flattened.
For this purpose, whole, non-dried rapeseed was obtained from agricultural farms in plastic bags and were treated by causing the oven preheating temperature to vary between 25, 35, 50 and 75° C. (temperature T) followed by conventional flattening and drying steps (90° C. for 12 hours). The flattened, dried seeds were finally contacted with anhydrous alcohol, which is passed by percolation through the bed of seeds and is collected downstream of the fixed bed, percolation taking place at a greater or lesser rate depending on the initial pre-treatment conditions of the seeds (preheating and flattening). During these tests, the quantity extracted fat and the percolation rate were measured.
More precisely, the operating mode comprises the following steps:
The results of these tests are grouped together in Table 1.
It is clearly apparent, in the light of the results in Table 1 that the best compromise between percolation rate and percentage of extracted fat is obtained at a seed preheating temperature of 50° C. As a matter of fact, at 50° C., all other conditions being equal, ethanol diffuses quicker in the flake with an oil extraction yield equivalent to that of the other seed preheating conditions. At industrial level, this allows high conversion rates to be achieved, since the extracted fat is rapidly converted into esters in the presence of a catalyst. On the basis of these results, the gain in productivity at this step, obtained by comparison with non-preheated seed (25° C.) can be estimated at +38% by calculation. Preheating of the seed at 70° C. before flattening does not bring any improvement in the productivity of the method since, for an almost equivalent extraction yield (around 30%) the percolation rate is very slightly reduced (versus preheating of the seeds at 50° C.).
At a temperature higher than 70° C. the seeds might dry before flattening, the consequence of which would be to make them harder, which would lead to the production of fine matter at the flattening step.
The preparation of flattened, dried seeds is a very important step in the method subject of the invention. It consists of:
Three series of rapeseed were prepared and examined:
Seeds prepared according to method 1,
Seeds prepared according to method 2,
Seeds prepared according to method 3.
According to method 1, flattening of the rapeseeds is achieved under the following conditions:
When the seeds are flattened in fresh form they are dried 48 h after flattening.
The flattened seeds were characterized by measuring the following parameters:
The conditions for these measurements and the operating conditions are grouped together in Tables 2a and 2b.
1The dry seeds were dried at a temperature of between 80 and 100° C.:
2Total fat content of rape seeds TH = 47% dry matter (DM)
3Direct extraction with hexane for 10 hours (8 + 2 h) (Soxlhet method)
4Characteristics of column used: L = 295 mm, dint = 39.3 mm, Sc = 1.21.10−3 m2, Sinter size = no0, Tap size = 4 mm, bed height = about 40 mm, Characteristics of ethanol used: Alcohol content = 96.2°, dam b = 0.807, dpercolation = 28330.6 L/h/m2; Operating conditions: hbed = 4 cm T = ambient, trep s = 10 min.
Flattening is conducted under the following conditions:
The total oil content of the seed is 50%. Calculation of crushing deficiency:
The flattened, non-dried seeds do not keep well. The acid number of the fat increases very significantly after 6 weeks storage (from 1 to 3.3 mg KOH/g). The finer the seeds are flattened, the greater the degradation of the fats. The content of extracted fats (with hexane) does not change with a roll spacing of 0.05 mm to 0.1 mm. It decreases on and after 0.2 mm and especially at 0.3 mm of spacing.
It is therefore absolutely necessary to dry the seeds after flattening. The roll spacing may range from 0.05 mm to 0.1 mm. Also, it appears that if the final oilseed cake is to have fat content of less than 2%, the thickness of the flattened seed must be less than 0.2 mm.
2.3.1) Objective
The fat of the flattened moist seeds may deteriorate through enzymatic hydrolysis during storage time. Its acid number is increased. The objective of the work conducted in this section is to determine the suitable conditions for storage of the flattened rape seeds.
The rape seeds were flattened and treated immediately on site.
2.3.2) Test Protocol
2.3.2.1) Flattening
The rape seeds (6-7% water) were flattened under the following conditions without being pre-heated:
2.3.2.2.) Drying
The flattened seeds are then dried in a Turbétuve drying oven either at 80° C. or at 90° C. to obtain a residual water content between 1 and 2%. The drying conditions are:
The dry seeds are packaged in sealed plastic bags and stored at room temperature. The quality of the seeds was monitored by measuring:
2.3.3.) Storage Results
Water intake by the flakes is very slow during storage. The other parameters for the quality of the fats show practically no change after 35 days' storage.
The flattened, non-dried seeds see the acidity of their oil rise very rapidly: for example, after one week acidity may reach a value of 17 mg KOH/g. This acidity is equivalent to 10% of the oil hydrolyzed into free fatty acids. The free fatty acids thus fabricated will have a negative impact on the reaction in a basic medium: they will be saponified (consumption of NaOH catalyst). Therefore the ester yield will be lower the greater the extent of hydrolysis. On the other hand, the seeds dried immediately after their fabrication have an oil acidity that is stable over time.
We conclude that the flattened, dried rapeseeds may be stored at least 35 days in a sealed plastic bag.
In the light of the experiments performed, it is preferable to proceed with the preparation operations for the seeds in the following order:
3.1) Influence of Alcohol Impregnation Temperature of the Conditioned Seed
The objective of this series of tests is to evidence the importance of the alcohol impregnation step of the previously flattened and dried seeds, and in particular its incidence on the extracting and reacting property of ethanol with respect to oily fat. For this purpose, we caused the temperature of alcohol impregnation to vary between 25, 50 and 75° C. (temperature T).
From an experimental viewpoint, the operating mode comprises the following key steps:
In this type of <<in planta>> method, since the medium consists of a liquid phase and a solid phase, the reaction is chiefly governed by the diffusion of alcohol in the seed. Alcohol plays the twofold role of solvent for the fats and of reagent. Therefore, the more the yield of extracted fat is promoted the higher the yield of target esters. Under reaction conditions in the presence of a catalyst, the extracted fat is rapidly converted to esters. Indeed, extraction of the fats from the seeds by alcohol is an essential factor of the method. The test results are given in Table 5.
It is clearly apparent, in the light of the results of Table 5, that the higher the alcohol impregnation temperature the higher the yield of fat extraction, hence its subsequent conversion into target esters.
This step can be used when operating in discontinuous mode to improve fat extraction and purity of the esters thus converted.
On the other hand, when operating in continuous mode, this step is not advisable since a precipitate has been observed at the head of the bed when the catalyst is added after an impregnation time of 30 min and even with an impregnation time of 5 min. This precipitate causes very rapid and very major decrease in percolation. At industrial level it cannot be contemplated to work with such low percolation rates as there is a risk of clogging the extractor.
Pre-impregnation has a positive effect on extraction (90-92%), on the other hand percolation rates are largely reduced when the catalyst is added. The flow rate then drops from 10 to 5 even to 1 m3/hm2 depending on pre-impregnation time.
The longer the pre-impregnation time, the greater the decrease in flow rate. This phenomenon can be accounted for as follows. In a neutral alcohol medium, sugars are soluble. The longer the extraction the more the quantity of soluble sugar increases. Sugars are no longer soluble in a basic medium on account of an aldol condensation reaction. A precipitate is then formed which concentrates at the head of the bed, and it is this precipitate which perturbs percolation.
Under discontinuous mode this reaction is also possible, with the difference that the precipitate thus formed is diluted in the entirety of the seeds and therefore has little impact on filtering.
3.2.) Reaction with EtONa as Catalyst
The objective of this series of tests is to validate the conditioning of the flattened, dried seeds before the reaction. We used EtONa as catalyst. The seeds were prepared according to method 2 described above:
drying at 60° C.,
flattening with two roll distances
storage in anhydrous ethanol
We reviewed the main operations of the method
1Determined as per standard V03-908
The final esters represent around 40% of the starting seeds. They have very high purity.
A roll spacing of 0.05 mm allows a greater quantity of esters to be produced than a distance of 0.1 mm. The yield of the transesterification reaction is therefore better with a roll spacing of 0.05 mm than with a spacing of 0.1 mm.
3.3) Optimisation of Reaction Conditions with NaOH as catalyst
As catalyst EtONa gives better performance than sodium hydroxide (NaOH). On the other hand, sodium hydroxide is much less costly than EtONa. The objective of this series of tests is therefore to define optimal reaction conditions using NaOH as catalyst (lowest consumption of catalyst and ethanol) for conversion of the triglycerides into ethyl esters.
The chief parameters examined are:
weight ratio <<Catalyst/Seed>> and effect of pre-impregnation,
weight ratio <<Ethanol/Seed>>,
water content of the ethanol,
thickness of flakes.
Operating Mode:
The reaction was carried out in a double-jacketed reactor with gentle stirring. The operating mode is as follows:
3.3.1) Influence of the Weight Ratio <<Catalyst/Seed>> and of Pre-Impregnation on the Reaction Under Discontinuous Operating Mode.
1Determined as per standard V03-908.
Under discontinuous mode, pre-impregnation is preferable for good fat extraction and conversion. The impregnation time of 30 min can be reduced to increase the productivity of the installation. Under discontinuous mode, the <<Catalyst/ethanol/seed>> ratio can be set at <<17.5 g/1500 g/1000 g>>. We note that the quality of the flattened seeds has a major influence on fat extraction. The test conditions F4, F5, F6 are the best.
1Determined as per standard V03-908
The <<Ethanol/Seeds>> ratio may lie between 1.3/1 under the stirred, discontinuous schedule of the reaction. For a continuous schedule and a fixed bed, this ratio must be adjusted.
The water content of the ethanol can be about 3000 ppm for the reaction.
3.4) Definition of Treatment Conditions for the Products after Reaction
3.4.1) Liquid-Solid Extraction after Reaction
Operating Mode:
Two tests were conducted under the same reaction conditions:
The oilseed cakes derived from the first filtration underwent 4 co-current extractions with ethanol having different water contents.
1Determined as per standard V03-908
The lower the water content of the ethanol, the better the seed-cake extraction. Absolute ethanol appears to be the best solvent for extraction with the flattened seeds.
3.4.2) Definition of the Treatment Conditions for the Liquid Phase
Operating Mode:
The liquid derived from transesterification was prepared under the following conditions:
The liquid phase (L0) was neutralized with a solution of sulphuric acid at different concentrations in 97% ethanol.
Table 11 shows that the esters obtained without neutralization have the lowest acid number. On the other hand, the quantity of collected esters is also the lowest. Partial neutralization allows more esters to be obtained. We can neutralize the liquid phase with a 10% sulphuric acid solution.
1Determined as per standard V03-908
Ethyl esters of rapeseed oil were produced from 20 kg of whole seeds. The implementation conditions for the method in discontinuous mode (closed reactor) are the following:
pre-heating temperature before flattening: 50° C.
flattening on roll flattener: roll spacing of 0.2 mm
drying temperature/time of the flattened seeds: 70° C./12 hours
residual moisture of the flattened seeds after drying: 1.9%
weight ratio alcohol/seeds/catalyst (NaOH): 160/100/1.7%
reaction phase temperature and time: 50° C./30 minutes
washing of seedcake with fresh ethanol: 3 times 100 g ethanol
Purification of ethyl esters:
The weight of the collected ethyl esters is 7600 g, i.e. an ethyl ester yield of 82%.
The esters thus prepared are analyzed on the basis of the chief criteria of European standard NF EN 14214 applicable to methyl esters intended for fuel applications. The results obtained show that the ethyl esters produced have high purity (>97%) free of contaminants and other sub-products below standard limits (total glycerol, water, ethanol, phosphorus, free fatty acids, mono- di- and triglycerides). They also have a ketane number well above standard specifications (>51), all these results confirming that these ethyl esters can be used as fuels.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0756716 | Jul 2007 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP08/59757 | 7/24/2008 | WO | 00 | 6/15/2010 |
