GB2466493A - Process for the production and treatment of biodiesel with improved cold soak test results - Google Patents

Abstract

A process for the production of fatty acid monovalent C1-05 alkyl esters comprising the steps of:a) a multi-stage, alkali-catalyzed transesterification of fatty acid glycerides with monovalent C1-C5 alkyl alcohols providing a fatty acid ester stream and a plurality of alcohol streams comprising glycerol;b) removing more than 80% of said alkyl alcohol from said fatty acid ester stream by evaporation providing an alkyl alcohol evaporate and a residue;c) washing said residue with water to deactivate said alkali catalyst and remove some residual C1-C5 alkyl alcohol from said fatty acid ester stream; andd) subjecting said fatty acid ester stream to a thermal treatment thereby providing fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of less than 200 s.

Description

PROCESS FOR THE PRODUCTION AND TREATMENT OF BIODIESEL

WITH IMPROVED COLD SOAK TEST RESULTS

FIELD OF THE INVENTION

The invention relates to the production and treatment of lower alkyl esters of fatty acids that are suitable for inclusion into biodiesel and exhibit improved cold-soak test results.

BACKGROUND OF THE INVENTION

Fatty acid esters such as fatty acid methyl esters (FAME) have been produced on an industrial scale for more than half a century. Prior to the 1940s, most soap was produced by the traditional process of boiling oils and fats with caustic soda or potash. The glycerol liberated by this process was left in the soap and provided some moisturising benefit. The high demand for glycerol for the production of explosives during the Second World War led to ways being sought to isolate by-product glycerol and this resulted in the methanolysis of oils and fats yielding by-product glycerol and subsequent saponification of the FAME to form soaps.

Since these FAME were intermediate products for soap production, their 20 specifications were oriented towards this end-use. Subsequently, FAME also - * came to be used in the oleochemical industry as intermediates in the production of fatty alcohols and again, their specifications were concerned with this particular application.

* * **** * More recently, political decisions have led to FAME becoming a preferred *. 25 or even mandatory fuel ingredient for diesel engines: biodiesel. In fact the 1.

introduction of FAME as a fuel may well have been facilitated by the very existence of processes to produce these FAME. Accordingly, their scale of production has increased considerably, the range of raw materials used for their production has broadened and there has also been an application-oriented evolution in the quality criteria these FAME have to meet. Raw materials used for biodiesel production now include materials such as trap grease, low quality tallow and used frying fats in addition to the triglyceride oils used traditionally for soap production.

A large variety of transesterification processes has been disclosed but despite this variety, they have the same target and have aspects in common.

They all include the reaction of a lower monovalent alcohol with triglyceride oil.

This leads to two phases: a fatty phase comprising fatty acid esters, partial glycerides and part of the excess of monovalent alcohol and an alcohol phase comprising glycerol and the remainder of the monovalent alcohol, which alcohol phase may also contain some soaps. A further common aspect is therefore the separation of these phases. In addition to the compounds mentioned, the phases will also contain reaction products of the alkaline catalyst and their inactivation/removal is another common aspect. Finally, the product streams need to be purified and the excess of monovalent alcohol needs to be recovered in such purity that it can be recycled into the transesterification process, which is a further common aspect.

The processes that have been disclosed for the synthesis of FAME differ in the sequence in which these common aspects are performed. US 2,353,633 discioses a process in which a fatty glyceride is contacted with an alcohol in the presence of an alkaline alcoholysis catalyst for a relatively short time, with the * mixture optionally being kept at room temperature or optionally being heated "s during a few minutes' interval to obtain rapid alcoholysis. The process further I...

comprises increasing the temperature to vaporize unreacted alcohol, but preferably only to a temperature insufficient for substantial reversal of the reaction in the absence of the alcohol, the unreacted alcohol thus being removed in a single distillation and in substantially anhydrous conditions. The *S* S.. process then (after removal of the alcohol) further comprises acidification of the *. *.

: * . 25 residue, preferably with a mineral acid, and is thereafter allowed to settle, whereupon glycerine separates out as a fluid lower layer substantially free of fatty acids and is withdrawn, and the upper layer containing alkyl esters, and in some cases incompletely reacted glycerides, is also removed for further processing. Evaporating the alcohol before the catalyst is inactivated and while the glycerol is still present may cause the alcoholysis reaction to reverse with formation of partial glycerides and may lead to partial glyceride contents, which are sufficently high to render the product unacceptable for use as a raw material in the production of biodiesel.

US 4,371,470 discloses another sequence for manufacturing a high quality lower alkyl ester of a fatty acid by alcoholysis of a fatty acid glyceride comprising the steps of: (a) esterifying the fatty acid glyceride by a first alcoholysis reaction with a lower alcohol in the presence of an alkali catalyst to form a first crude esterification product and glycerine, (b) separating the glycerine from the first crude esterification product, (c) esterifying the first crude esterification product by a second alcoholysis reaction with the lower alcohol in the presence of an alkali catalyst to form a second esterification product containing the unreacted lower alcohol and glycerine as dissolved or dispersed therein, (d) admixing the second crude esterification product with water in an amount from 30% to 150% by weight based on the amount of the lower alcohol contained in the second crude esterification product, (e) subjecting the second crude esterification product admixed with water to phase separation into the aqueous layer and layer of the lower alkyl ester of fatty acid, (f) stripping the lower alkyl ester of fatty acid of the water and unreacted lower alcohol contained therein, (g) admixing the thus stripped lower alkyl ester of fatty acid with from I to 10% by weight of an adsorbent to effect decolorization, and (h) removing the adsorbent from the thus decolorized lower alkyl ester of fatty acid.

This sequence entails a two-stage transesterification with methanol followed by ..s.' 20 catalyst inactivation by the addition of water, whereupon the mixture is separated into an aqueous layer that also contains glycerol and methanol and a layer of the lower alkyl ester of fatty acids containing some residual methanol which is then removed together with any water present by stripping. This *:::: sequence avoids the reaction reversing but it has the disadvantage that the r*' 25 methanol has to be recovered from wet substrates which involves rectification.

DE 42 38 195A discloses a process for the discontinuous manufacture of rapeseed oil methyl ester, suitable for use as a fuel in combustion engines, using yet another sequence in which the rapeseed oil is reacted with methanol in the presence of an alkaline catalyst at normal pressure and elevated temperature to give the methyl ester and glycerol, this being followed by separation of the glycerol, deactivation of the catalyst and distillative removal of any excess of methanol; characterized in that the esterification is effected at 50- 75°C and with 1.3-1.8 times the stoichiometrically required amount of methanol in two sequential transesterification steps; the first of which being performed with 60-80% of the total methanol and catalyst amount and reacting 80-95% of the rapeseed oil to rapeseed oil methyl ester and the second of which being performed after separation off of the glycerine by-product produced in the first step with the remaining 20-40% of the methanol and catalyst amount and substantially reacting the remaining rapeseed oil to rapeseed oil methyl ester, so that a degree of transesterification of 96-99% is realized and the conversion of the remaining rapeseed oil is effected, so as to give a total conversion of 96- 99. After each of the two alkali-catalyzed transesterification stages, the reaction mixture is separated into two phases. Consequently, two glycerol phases and one FAME phase are collected. According to the process schema given in Figure 2 of DE 4238195A, the purification of the rapeseed oil methyl ester is performed after transesterification and separation off of the glycerol by addition of citric acid to deactivate the residual excess alkaline catalyst and then distillative removal of the excess methanol present.

US 5,434,279 on the other hand, discloses a process for preparing fatty acid esters and mixtures of fatty acid esters of short-chain monohydric alcohols having from 1 to 5 carbon atoms or short-chain diols having from 2 to 5 carbon *:*::* atoms, which are monoalkylated by alkyl radicals having from I to 3 carbon *. 20 atoms, by transesterification of fatty acid glycerides with the alcohols or *.*.

monoalkylated diols in the presence of a basic catalyst, in a plurality of steps, *..: wherein a) the trans-esterification is carried out in the presence of from 0.5% to 5.0%, referred to the mass of the fatty acid glyceride used, of a basic catalyst, in an excess of the short-chain alcohol or monoalkylated diol of from 1.1 to 3.0 mol per mol of glycerine-bound fatty acid, optionally in the presence of from 0.5% to : * 10% water, referred to the mass of the fatty acid glyceride used; b)the glycerine phase obtained by settling and separation after transesterification has been done in the first step is added either entirely or in part, but at least up to an amount of one-tenth, after the transesterification of the second step or of a further step, to this step while stirring, and C) after renewed settling and separation of the heavy glycerine phase and after removal of excess short-chain alcohol or monoalkylated diol, an optionally diluted organic or inorganic acid is added while stirring, and after phase separation has been done the fatty acid ester phase is removed and optionally filtered: In this process a two-stage alkali-catalyzed transesterification is followed by the removal of the excess of short chain alcohol and completed by the neutralisation of the catalyst by the addition of an acid such as an aqueous solution of citric acid, and removal of the fatty acid ester phase. Example I of this US 5,434,279 discloses that the non-transesterified fatty acid glycerides present in the FAME amounted to 0.9%.

Industrial plants also exist in which the transesterification reaction mixture is first subjected to a limited flash desolventisation. This has the advantage that the methanol thus obtained can be recycled without requiring further rectification treatment and of limiting the risk of the reaction reversing. After the flash desolventisation, the catalyst is deactivated with water and the phases are allowed to separate.

The above processes have in common that the purity of the resulting FAME varies, whereas the use of FAME as a fuel ingredient in diesel engines has shown the necessity of improving the quality and in particular the purity of FAME.

Prior to legislative action to prevent substandard products reaching the market, biodiesel had been known to precipitate material out of solution when exposed to cold temperatures, which could lead to extensive diesel engine damage. The latest testing requirement for biodiesel fuel testing is the cold soak filtration test (CST). This procedure was added in October 2008 to the American Standard and Testing Methods as ASTM 6217 Annex Al Biodiesel Cold Soak Filtration Standard. The CST measures the time needed for a preconditioned s..., biodiesel sample to pass through a calibrated filter. A sample fails the test if the S...

filtration time exceeds 300 seconds for a summer grade or 200 seconds for a winter grade. The CST can be used to assess levels of minor filter plugging components in biodiesel and biodiesel blends.

US 2007/0175091A discloses a method for removing impurities from biodiesel, comprising: converting a feedstock into biodiesel having a temperature exceeding 98°C; cooling the biodiesel to a temperature range sufficient to form particulates of impurities; and filtering the cooled biodiesel to remove the particulates. Optionally this filtering step includes multiple stages process, the first filtering step preferably including the addition of an adsorbent, such as diatomaceous earth, silica, sand and mixtures thereof, to the biodiesel.

Furthermore, US 2007-0151146A discloses a process for reducing the filter blocking tendency of biodiesel, comprising: placing the biodiesel in contact with a solid or liquid, the solid or liquid comprising a compound capable of reducing the filter blocking tendency of biodiesel. These processes represent an additional process step and thus augment the cost of biodiesel production.

Moreover, these processes generate polluted effluent(s) which have to be disposed of, which is an additional cost.

WO 2008/130974A discloses a process for producing a biodiesel, comprising: reacting a feedstock oil, alcohol and catalyst to form a mixture of biodiesel reaction product and by-products; quenching the reaction by adding a catalyst kill agent; decanting the mixture to separate biodiesel reaction product from by-products, the by-products comprising glycerine and excess alcohol; distilling the biodiesel reaction product in a distillation column to separate biodiesel from the biodiesel reaction product, recover tocopherols, and remove sterol glucosides from the biodiesel; and adding a biodiesel stabilizer to the biodiesel. Such a distillation process would require considerable capital investment to implement and would incur operating costs typical of those related to the use of a distillation column. * . * ***

OBJECT AND ADVANTAGES OF THE INVENTION

*. It is an object of the invention to provide a process for the production and S..... . * * the treatment of monovalent C1-C5 alkyl esters of fatty acids having improved cold soak test results that can be advantageously included into biodiesel. S...

SUMMARY OF THE INVENTION

This great variety in process step sequences involved in the production and the purification listed above illustrates and even demonstrates that there is no clear teaching for a preferred route. However, one of the sequences listed above has surprisingly been found to offer advantages provided some additional measures are taken. These advantages are concerned with the particulate contamination of the FAME and meeting specifications such as ASTM D6751 and the specific cold soak filtration test according to ASTM D 6217, which is concerned with the fuel filter blocking potential of the FAME to be used as biodiesel.

It has surprisingly been found that fatty acid monovalent C1-C5 esters suitable for incorporation into biodiesel and having cold soak filtration test times according to ASTM D 6217 of less than 200 s, preferably less than 150 s and particularly preferably less than 110 scan be produced in a process comprising the steps of: a) a multi-stage, alkali-catalyzed transesterification of fatty acid glycerides with monovalent C1-C5 alkyl alcohols providing a fatty acid ester stream and a plurality of alcohol streams comprising glycerol; b) removing more than 80% of the unreacted monovalent C1-C5 alkyl alcohols from said fatty acid ester stream by evaporation thereby providing, an alkyl alcohol evaporate and a residue; C) washing said residue with water to deactivate the alkali catalyst and remove residual monovalent C1-C5 alkyl alcohols from the fatty acid ester stream; d) subjecting said washed fatty acid ester stream to a thermal treatment.

Aspects of the present invention are realized by a process for the purification of fatty acid monovalent C1-C5 alkyl esters comprising residual monovalent C1-C5 alkyl alcohol comprising the steps of: :.:: 20 e) providing a fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s; b) removing said residual alkyl alcohol from said fatty acid monovalent C,-C5 alkyl esters by evaporation providing a monovalent alkyl alcohol evaporate and a residue; S...

c) washing said residue with water; : * d) subjecting said washed residue to a thermal treatment thereby providing fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of less than 200 s.

Aspects of the present invention are also realized by a process for the purification of fatty acid monovalent C1-C5 alkyl esters comprising residual monovalent C1-C5 alkyl alcohol comprising the steps of: e) providing a fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 5; c) washing said fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s with water; d) subjecting said washed fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s to a thermal treatment thereby providing fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of less than 200 s.

Aspects of the present invention are also realized by a process for the purification of fatty acid monovalent C1-C5 alkyl esters comprising residual monovalent C1-C5 alkyl alcohol comprising the steps of: e) providing a fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s; d) subjecting said fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s to a thermal treatment thereby providing fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of less than 200 s.

Aspects of the present invention are also realized by fatty acid monovalent Cl -C5 alkyl esters obtained by any one of the above-mentioned processes.

Further embodiments of the present invention are disclosed in the detailed

description. * S 5S5.

DETAILED DESCRIPTION OF THE INVENTION ** . * S S * **

The present invention will be described with respect to particular embodiments, but the invention is not limited thereto but only by the claims. ****

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may.

Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes **I.

grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the * following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are set forth.

However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure

an understanding of this description.

The following terms are provided solely to aid in the understanding of the invention.

DEFINITIONS

The "Biodiesel Cold Soak Filtration Standard" is specified in ASTM 6217 Annex Al and the cold soak filter test consists of chilling the sample for a specified time and then allowing it to warm to room temperature prior to vacuum filtering in a modified ASTM D 6217 "Particulate Contamination in Middle Distillate Fuels by Laboratory Filtration" procedure through a single 0.7 tm glass fiber filter. In this test the cold soak treatment and filtration are carried out on 300 ml samples. The sample is stored at 4.4 degrees Celsius (40 degrees Fahrenheit) for 16 � 0.5 hour (cold soak"), then allowed to warm up to 20-22°C (68-72°F). After briefly swirling to disperse any precipitates which had settled to the bottom of the container the sample is then filtered within 1 hour of the $ sample using a modified ASTM D 6217 vacuum (71.1 to 84.7 kPa) filtration procedure. *S*$

The term fatty acid triglyceride, as used in disclosing the present invention, means glycerol in which all three hydroxyl groups are esterified with fatty acids.

The term fatty acid diglyceride, as used in disclosing the present invention, means glycerol in which two of the three hydroxyl groups are esterified with fatty acids.

The term fatty acid monoglyceride, as used in disclosing the present invention, means glycerol in which only one of the three hydroxyl groups is esterified with fatty acids. i1

The term evaporation, as used in disclosing the present invention, means any process in which a liquid is vaporized including, but not limited to, flashing and distillation.

The term evaporate, as used in disclosing the present invention, means the liquid vaporized in an evaporation process as above-defined.

PROCESS

When fatty acid glycerides, which from now on will be referred to as triglycerides, are mixed with monovalent C1-C5 alkyl alcohols, a two-phase system results in which some of the alkyl alcohol is dissolved in the fatty phase and very little triglyceride is dissolved in the alkyl alcohol phase. Among monovalent C1-C5 alkyl alcohols, methanol is the least soluble in triglycerides so the transesterification process will be described using methanol as an example.

If this methanol contains an alkali interesterification catalyst, such as but not limited to sodium methanolate, some of this catalyst will also be present in the fatty phase and thus catalyze the formation of fatty acid methyl esters (FAME).

In the early stages of the transesterification reaction, FAME formation will be accompanied by the formation of partial glycerides (fatty acid diglycerides and fatty acid monoglycerides) and they increase the solubility of methanoJ in a..

the fatty phase. Consequently, the methanol will gradually dissolve in the fatty phase so that the methanol phase will gradually disappear. This causes the catalyst to migrate to the fatty phase as a result of which the rate of transesterification increases. In due course, the partial glycerides that were formed from the triglycerides will also be transesterified so that ultimately * glycerol will be formed. As long as the concentration of the partial glycerides is sufficiently high, these partial glycerides can act as entrainer and keep the glycerol in solution but at a certain stage in the reaction, the glycerol solubility in the reaction mixture will have decreased to such an extent that the glycerol starts to form a separate phase in which part of the MeOH will dissolve.

Accordingly, the catalytic activity also concentrates in this phase and this causes the reaction in the fatty phase to slow down.

There is as yet no agreement with respect to the relative importance of the catalytically active species acting during the transesterification reaction, but it is clear that several species are involved. These species are in equilibrium with each other and the positions of these equilibria depend on the concentrations of the reaction partners involved. The species concerned may well be the methanolate anion, the glycerolate anion and the enolate anion which is formed by the abstraction of an a-hydrogen from a fatty acid moiety. So in the early stages of the transesterification reaction when there are still two phases, the methanolate anion will predominate in the alcoholic phase and the enolate anion will be the main catalytically active intermediate in the fatty phase. As and when more partial lycerides are formed, the glycerolate anion will gain in importance and when a separate glycerol phase emerges, this will attract most of the alkalinity in the form of the glycerolate anion; since the glycerol phase also contains some methanol, some methanolate anions will also be present in the glycerol phase. The alkalinity left in the fatty phase as enolate anions may be only 10% of the total alkalinity. Consequently, the transesterification reaction slows down considerably as soon as a separate glycerol phase has been formed.

In order to increase the reaction rate, it is common practice to remove this separate glycerol phase and add further methanol containing additional catalyst.

This methanol will dissolve in the fatty phase still containing partial glycerides and the additional catalyst will ensure further transesterification. This will of course lead to the formation of glycerol that will form a separate phase which phase also has a great affinity for the alkalinity. However, this phase will be 25 much smaller than during the first stage of the transesterification reaction and consequently, the fraction of the alkalinity moving into the glycerol phase will be much smaller than before. Accordingly, transesterification in the fatty phase will * proceed but at a much reduced rate because the concentration of the remaining partial glycerides is also quite a bit lower.

It is economically unfavorable to continue the last stage of the transesterification to near completion in view of the degree to which the process slows down as it nears completion. However, it has been surprisingly found that allowing it to proceed to near completion, i.e. to a residual monoglyceride content below 0.8% by weight and preferably below 0.4% by weight of the fatty matter present in the fatty phase or even lower, has the totally unexpected advantage that the resulting FAME exhibits much improved Cold Soak Test (CST) results. Furthermore, these unexpectedly favorable CST results appear to be even more favorable the lower the methanol content in the residue in step b) of the process and prior to water washing in step c). Furthermore, unexpectedly favorable CST results also result from intensive thermal treatment of the washed fatty phase from step c) leading to a reduction in the residual water content in the dried FAME lowered to at most 0.05% by weight and preferably below 0.02% by weight.

An alternative embodiment, according to the present invention is a process for the production of fatty acid monovalent C1-C5 alkyl esters comprising the steps of: a) a multi-stage, alkali-catalyzed transesterification of fatty acid glycerides with monovalent C1-C5 alkyl alcohols providing a fatty acid ester stream and a plurality of alcohol streams comprising glycerol; b) removing said alkyl alcohol from said fatty acid ester stream by evaporation providing an alkyl alcohol evaporate and a residue; c) washing said residue with water to deactivate said alkali catalyst and remove some residual C1-C5 alkyl alcohol from said fatty acid ester stream; and f) drying said washed residue until its residual water content has fallen below 0.05% by weight, preferably by stripping with an inert gas or by thermal *...

treatment.

In a particular embodiment of the process, according to the present 25 invention, the final transesterification stage in step a) is continued until the fatty acid monoglyceride content of the fatty ester stream has fallen below 0.8% by weight, preferably below 0.4% by weight.

* In another embodiment of the process, according to the present invention, the final thermal treatment in step d) is continued until the water content of the fatty ester stream has fallen below 0.05% by weight, preferably below 0.02% by weight.

The oil or fat used in the process, according to the present invention, is not critical but this process is most beneficial for raw materials that are prone to lead to FAME with poor CST results such as but not limited to soya bean oil and palm oil. To limit catalyst usage and avoid phase separation problems, the raw material preferably has a free fatty acid (FFA) content below 0.1%. If the FFA exceeds this value, the raw material is preferably neutralised by methods known in the art, but the process according to the invention is in no way limited to oils or fat with FFA contents below 0.1%.

The transesterification step a) of the process, according to the present invention, must be carried out in two or more stages, whereby each stage includes mixing a fatty stream with monovalent C1-C5 alkyl alcohol comprising an alkali transesterification catalyst followed by phase separation. The total amount of monovalent C1-C5 alkyl alcohol used in the process, according to the present, invention must exceed the mo'ar equivalent of the fatty acid moieties present in the raw material. Good results have been obtained when the molar ratio of the alcohol to the fatty acid moieties was in the range of 1.5 to 2.5 but the process according to the present invention is not limited to this range.

The alkali catalyst to be used in the process according to the invention is not critical. It can be an alkali hydroxide or alkanolate, such as but not limited to sodium or potassium hydroxide, methanolate or ethanolate. When sodium methanolate is used, the total amount of catalyst need not exceed 5 kg per tonne of oil or fat being transesterified. A higher catalyst requirement is an *1*** indication that the fatty raw material contains too much FFA or other :.:: contaminants which react with the catalyst (e.g. water) and that problems such Is..

as excessive foam andlor poor phase separation step(s) will arise.

During the first stage of the transesterification process, according to the :: 25 present invention, mixing is continued until a single phase has been formed.

The reaction mixture is then allowed to settle by gravity, after which the two ::: phases are separated by decantation or centrifugal separator; decantation * being preferred for cost reasons and because the separation process is hardly critical. The alcohol phase, comprising glycerol, methanol, catalytically active intermediates and possibly soaps, resulting from the first stage of the transesterification process, may be fed to a treatment section to recover its main constituents but it can also be used to pie-treat the oil or fat to be processed in step a). This has the advantages that the transesterification can already start due to the presence of residual catalyst and methanol in this alcohol phase and that at least some of the free fatty acids present in said oil or fat are neutralised before they are mixed with the monovalent C1-C5 alkyl alcohol comprising the transesterification catalyst. The neutralisation of the free fatty acids converts them into soaps that dissolve in the glycerol layer and thus remove them from the fatty phase. Their removal reduces the amount of catalyst required for the transesterification reaction in step a). If some methanol is present in the glycerol phase and its alkalinity exceeds the free fatty acids present in said oil or fat, the pre-treatment may even lead to some transesterification. This increases the partial glyceride concentration and thus the solubility of methanol. Consequently, the induction period of the transesterification reaction when the reaction is slow because of the low methanol concentration is virtually eliminated so that a smaller reactor suffices.

Because the fatty material has already been partially transesterified, a smaller excess of methanol will suffice which saves on distillation costs and catalyst consumption.

For the last stage of the transesterification of step a) of the process, according to the present invention, a larger reactor, or rather a larger settler, is required to enable the reaction to be continued until the monoacyl glycerol content of the fatty ester stream has fallen below 0.8% by weight and preferably below 0.4% by weight. The stream fed to the settler consists of two phases: a fatty phase comprising FAME, small amounts of partial glycerides, and S...

methanol and an alcoholic phase comprising glycerol and methanol. Both phases also contain catalytically active intermediates. Accordingly, the fatty phase will continue to transesterify as a result of which the monoglyceride content will continue to fall. Indeed, the transesterification equilibrium is displaced in favour of the FAME due to the removal of one of the reaction * products, the glycerol, which migrates towards the alcoholic phase. However, this continued conversion of the monoglycerides into FAME is slow because of the low concentration of methanol, monoglycerides and catalytically active intermediates present in the fatty phase. Paradoxically, this mechanism will also lead to a fatty phase containing less glycerol. Indeed, although converting monoglycerides into FAME liberates glycerol at the same time, this glycerol will form a separate phase because the fatty phase is already saturated with respect to glycerol and the lowering of the monoglyceride content of the fatty phase will decrease the solubility of the glycerol in this phase. Therefore, the time provided for settling not only causes the reaction to continue, but also leads to a lower glycerol content in the fatty phase. This period of time should therefore be on average at least 0.5 hours, preferably 1 to 2 hours. Even if definitive conclusions cannot be drawn, it is believed that the particularly low concentration of rnonoglycerides and glycerol resulting from this characteristic step of the process, according to the present invention, may contribute to the improvement of the CST results. Indeed, it is believed that glycerol and monoglycerides, being polar compounds, are more attracted to and adsorbed onto the filter used for the CST than FAME molecules and may therefore aggravate the clogging of the filter not only by themselves but also by attracting solid particulates such as sterol glucosides or oxidised substances, both of which are polar materials.

Phase separation after the last stage of the transesterification process, according to the present, invention may be realized by decanting or centrifuging. Since, subsequently, methanol will be evaporated from the fatty phase while the transesterification catalyst is still present and active, there is a preference for using a centrifuge for phase separation, as this will ensure the absence of free glycerol in the fatty phase and thus minimize the reversion of the transesterification reaction. However, good results have also been obtained when the phases were separated by decantation.

The fatty phase obtained during this phase separation will contain less :: 25 than 0.8% by weight of partial glycerides based on its fatty matter and up to 5% by weight or even more of the monovalent C1-C5 alkyl alcohol. The latter is then evaporated from the FAME phase in step b) of the process, according to the : * present invention, leaving a low residual alcohol content without the transesterification reaction reversing and causing partial glycerides to be formed. In step c) more than 80% of the alcohol present is required to be evaporated, according to the present invention, as a result of which the residual alcohol content of the (evaporation) residue is reduced to below 2% by weight, preferably below 1% by weight and particularly preferably below 0.5% by weight. The alcohol evaporate thus obtained is anhydrous and can be used as such in the transesterification process, according to the present invention.

The glycerol streams resulting from this process can be combined and their constituents can be recuperated according to methods known to those skilled in the art. If any soaps are present, their fatty acid moieties can be recuperated as free fatty acids by acidulation. Subsequently, these FFA can be esterified and thus increase the fatty acid ester yield. The methanol can be recuperated and recycled in the transesterification process and the glycerol can be purified to various degrees for outside sales.

The fatty acid monovalent C1-C5 alkyl ester residue resulting from step b) of the process, according to the present invention, is subsequently washed with water in step c). This causes the catalyst to be deactivated and catalyst residues such as alkali hydroxides are removed with the washing water. The washing water can be acidified, e.g. with citric acid, if so desired and the washing can be carried out in more than one stage in co-or counter-current mode. The water will also remove some of the residual monovalent alcohol present in the residue, but the extent of this removal will be limited by the partition coefficient of the alcohol between the water and the fatty acid C1-C5 alkyl ester phase and the proportion of water washing used. This washing step may also remove polar molecules or substances such as sterol glucosides, monoglycerides and oxidised materials. The efficiency of the washing step for the removal of sterol glucosides appears to be improved when the * ..

concentration of the residual methanol in the evaporation residue from step b) is reduced to below 2% by weight, preferably below 1% by weight and particularly :" 25 preferably below 0.5% by weight. Indeed, although our invention is not limited to this particular theoretical justification, it is believed that any methanol still present in the fatty phase may contribute to less efficient water washing due to * the fact that the higher the content of methanol in the fatty phase, the higher its polarity will be and therefore the higher will be its tendency to retain polar contaminants such as sterol glucosides, monoacyl glycerol and oxidised materials.

Finally, the fatty ester stream resulting from step c) of the process according to the invention is thermally treated in step d) by exposing it to high temperature and optionally to reduced pressure and afterwards, optionally incorporating one or more antioxidants and/or one or more metal deactivators to yield a product that is ready to be used as biodiesel and which exhibits remarkably improved CST results.

It has been found that a thermal treatment reducing the water content to below 0.02% is preferred. Depending on the water content present in the fatty acid ester stream originating from step c), this can be achieved by a thermal treatment of at least 5 minutes duration at 150°C to 180°C (but preferably at a temperature below the flash point of FAME for safety reasons) under autogenous pressure or at reduced pressure, by evaporating water during the thermal treatment or by flashing after the thermal treatment. In order to avoid FAME evaporation during the flashing it may be preferred to allow the thermally treated fatty stream to cool to temperatures between 100 and 150°C before exposing it to a reduced pressure.

Indeed, although our invention is not limited to this particular explanation, it is believed, that during the washing step c) part of the water is in fact dispersed in the fatty phase and forms an emulsion of very small water droplets in the fatty phase. This type of water is referred to as dispersed water in contrast to the dissolved water. It is believed that a part of this dispersed water is retained on the filter during the CST. As a result, the filter used in the CST is partially clogged by water. Due to the presence of this water, the filter is more polar and may further attract polar contaminants present in the sample. Of * *.* course both mechanisms increase the CST filtration time.

These two examples demonstrate the influence of the water concentration ": 25 of a Biodiesel sample, and most particularly the influence of the dispersed water on the CST result. Indeed, although our invention is not limited to this theoretical explanation, it is believed that dispersed water may behave as * particles, some of which are separated by the filter during the CST thereby clogging it. Treatments applied during step d) can also involve microwave electromagnetic radiations. In this case thermal energy is concentrated towards the micro-droplets of the dispersed water. Consequently, it is possible to induce the boiling and the removal of water from the fatty acid ester stream from step c) in a more economical way than when using conventional heating equipment.

Thermal treatments applied during step d) may also involve ultrasonic acoustic wave. Ultrasonic acoustic wave can enhance the boiling and the removal of water from the fatty acid ester stream originating from step c) in a more economical way than when using conventional heating equipments.

Treatments applied during step d) can also involve stripping by vapors for

example water.

The use of microwave electromagnetic radiations, ultrasonic acoustic wave or a stripping medium in step d) can be the unique or a complementary means of treating the fatty phase or a part of the fatty phase originating from step C).

The treatment of step d) involving microwave electromagnetic radiation or the ultrasonic acoustic wave can be performed under autogenous pressure or at reduced pressure. In order to avoid FAME evaporation during the flashing it may be preferred to allow the treated fatty stream to cool to a temperature between 100 and 150°C before exposing the fatty stream to reduced pressure.

The duration of the treatments during step d) should be limited in time in order to avoid excessive energy consumption and in order to limit potential degradation and/or oxidation of the fatty phase being treated. It has been found that thermal treatments of 5 minutes are effective to improve the CST results but the process according to the invention is not limited to this particular duration. The duration of the thermal treatment will depend, for example, on the :::::: concentration of water in the fatty acid ester stream from step c), on the temperature selected for the thermal treatment, the presence of optional microwave radiation and/or ultrasonic acoustic wave and the pressure applied to the fatty acid ester stream during or after the thermal treatment. The duration of the heat treatment will be adapted, depending upon the selected thermal s..

treatment conditions, to yield a fatty acid ester phase with a water content below : * the set target, for example 0.02% by weight.

Optionally, mechanical agitation can be provided during step d) in order to homogenise the treated fatty acid ester stream during step d). Mechanical agitation can be provided by static mixer or rotating agitators and the like.

Antioxidants and/or metal deactivators or their blends may be used such as for example Ethanox 4760E, Ethanox 4733 such as marketed by Albemarle Europe SPRL, Parc Scientifique de LLN, Rue du Bosquet 9, B-i 348 Louvain-la-Neuve Sud, Belgium. It may also be advisable already to include antioxidant and/or metal deactivator or their blends in the fatty acid ester stream from step c) in order to minimize any degradation of the fatty phase during the thermal treatment in step d). Additionally, the thermal treatment of step d) ensures an efficient homogenisation and dissolution of these additives and therefore may render redundant a downstream blending step. If needed, additional antioxidant and/or metal deactivator or their blends can be incorporated in the treated FAME.

Since the CST results of a particular FAME sample are determined by the sum of the different contaminants present in said FAME sample, in the multi-step process, according to the present invention, improved CST results require that each of the steps aimed at removing a particular type of contaminant has to be successful. However, our invention is not limited to the sequential and complete execution of steps a) to d). Indeed, the cause(s) leading to the failure to pass the CST of a given FAME sample can be multiple of course but could also due to a single contamination such for example solely excessive sterol glucosides contamination or for example solely excessive water content. The individual execution of one step of our process, for example step d) to remove the excessive concentration of water in FAME falls within the scope of the invention. Indeed, refined FAME passing originally the CST may fail this test after having been stored for prolonged time. This failure can be due for example to water condensation occurring on the walls of the tank containing the FAME.

In that case, the individual execution of step d) will remove the water contained in the contaminated FAME and lead to dry and optionally stabilised FAME passing the CST. Such individual treatment falls within the scope of our invention. Similarly, batches of FAME failing the CST and containing for * example excessive concentration of methanol, sterol glucosides and water can be advantageously treated by step b), c) and d) as described in this disclosure to yield purified, dried and optionally stabilised FAME passing the CST. Such a sequence also falls within the scope of the invention.

The following examples are provided only for the purpose of illustration of the invention and should not be understood as limiting the invention in any aspect.

EXAMPLES

Experiments were performed on biodiesel samples produced from palm, rapeseed and soybean oil respectively designated POME, RSME and SBME.

These samples were subjected to various thermal treatments including exposure to microwave, ultrasonic and reduced pressure. For comparative purposes, the effect of filtration, clarification and distillation were also investigated.

Example 1

CST filtration time and other characteristics of various untreated samples have been determined according to the recommendation of the Biodiesel norm EN 14214.

Example I shows the influence of the vegetal oil used to produce the biodiesel on the value of the CST filtration results. If no treatment is applied to the biodiesel presented in table 1, only one sample of the four passes the CST

specification (SBM2). *... * * ****

Table 1:

Sample POME RSME SBME1 SBME2 failed, Failed, failed, passed, filtration time (\ * / >3600 675 1008 210s Free glycerol, [%, m/mJ** 0.009 0.001 0.015 0.011 Monoglyceride content, MG [%, 0.60 0.43 0.51 0.64 Diglyceride content, DG [%, mlm]** 0.10 0.12 0.11 0.19 Triglyceride content, TG [%, m/m]** 0.03 0.04 0.02 0.08 Acid value, AV [ mg KOH/g]* 0.34 0.15 0.32 0.29 Soaps [mg/kg] N.D. N.D. N.D. ND.

H20 [mg/kg]## 210 330 560 260 Free steryl glucosides [mg/kg] 118 12 13 11 Total contamination [mg/kgj# 183 2 24 N.A.

Elements [mg/kg] _________ _________ _________ _________ Na 1.1 0.7 1.5 0.8 K 0.5 0.1 0.4 0.2 Ca 0.4 0.1 0.2 0.2 Mg 0.1 <0.1 <0.1 <0.1 P 0.6 0.2 0.4 0.4 *EN 14104 **EN14105# EN12662## EN1S012937

Example 2

The glycerol content of the SBME 2 sample, the only one passing the CST filtration time specification, was increased by adding a certain amount of pure and GC grade glycerol (water free). The samples were then homogenized using a high shear mixer at 16000 RPM for 1 mm. The resulting glycerol content of biodiesel was determined with gas chromatography according to the norm EN14105. The moisture content of the same SBME 2 sample was increased by storing the sample several days in an open beaker placed in moisture saturated air at ambient temperature. Water content was determined by Karl-Fischer titration. POME was distilled in a lab-deodorizer at 180°C, 3 mbar and 0.5-1% steam injection for 30-60 minutes. Droplets of water were added to the distilled POME. The sample was then homogenized with an Ultraturax at 16000 RPM for I mm. After this operation the sample was perfectly clear and transparent. The sample was then conditioned in a 4.4°C (40°F) bath for a 16-hour (� 10 minutes) "cold soak", then allowed to warm up to 20-22°C (68-72°F) over a period of 2.5 hours (� 15 minutes) prior to the * * Table 2 gives the results obtained for the sample containing additional quantities of glycerol and water in SBME 2 and additional quantities of water in **** * S distilled POME. The addition of only 30 ppm of glycerol to SBME 2 already had ** a detrimental effect on CST filtration time. Water has also detrimental effect on CST filtration time. This is particularly demonstrated in the case of water added to distilled POME. The water content of distilled POME is very low (105 ppm) and the CST filtration time is very good because the distillation process efficiently eliminates most contaminants. However, it has most surprisingly been observed that if 300 ppm of water is mixed to the very same distilled FAME using a high shear mixer during one minute, the sample fails the CST with a very much increased time. The result obtained in example 2 demonstrates that water is attracted by the filter used in the CST procedure and increase dramatically the CST result. Indeed, the water concentration of the sample before CST is 415 ppm but after the CST the water concentration of the filtrate has been reduced to 271 ppm.

Table 2:

Sample SBME 2 SBME 2 SBME 2 SBME 2 Distilled Distilled + GC + GC + water POME POME grade grade absorbed + 300 ppm glycerol glycerol from air water mixed _______ _______ _______ _______ ________ ________ with_HSM CST passed, failed, failed, failed, passed, failed, filtration 210 422 670 410 88 2260 time [s] __________ _________ _________ ___________ ___________ ______________ glycerol 0.011 0.014 0.018 0.011 na na [%, rn/rn] ______ ______ ______ _______ _______ _________ H20 260 260 260 623 105 415 [mg/kg] _________ _________ _________ ___________ ___________ ______________ H20 after na na na na na 271

CST

filtration [mg/kg] _________ _________ _________ __________ __________ _____________ Example 2 shows that the CST filtration time is strongly affected by presence of minor quantities of polar compounds in biodiesel, such as glycerol *:*::* 10 and water. * ***

EXAMPLE 3

** The effect of the post-treatments on the CST was studied on RSME and SBME1. The processes were simulated on a laboratory scale in the following ways: i) Cold filtration: a sample was prepared by adding 0.05% Filtracel EFC-250-C (Rettenmaier) as body feed and allowing the sample to equilibrate at 5 °C above its cloud point (+3°C for RSME and +5°C for SBME1) for 12 h under gentle agitation (120 rpm). Then the sample was vacuum filtered in a Buchner flask over Whatman I filter paper.

ii) Clarification: centrifugation at 5500 rpm for 15 mm at 20°C and decantation of the supernatant.

iii) Distillation: 500-1000 ml biodiesel was distilled in a laboratory deodorizer at 18000,3 mbar and 0.5-1% steam injection during 30-60 minutes.

iv) Thermal treatment: in different trials one of the following treatments were applied using a rotary evaporator: A) Thermal treatment A consists of applying vacuum of 50 mbar and heating the sample from 60°C to 150°C during 6 mm by submerging the flask in a pre-heated bath of thermal oil; allowing an isothermal period at 150-155°C for 4 mm; releasing vacuum and cooling the sample from 150°C to 60°C by submerging the flask into a bath of cold water.

B) Thermal treatment B consists of applying vacuum of 200 mbar and following the procedure as described above.

C) Thermal treatment C consists of applying vacuum of 50 mbar, heating a sample 105°C by submerging the flask into a pre-heated bath of thermal oil; allowing an isothermal period at 105°C for 20 mm; releasing vacuum and cooling the sample to 60°C by submerging the flask into a bath of cold water.

Table 3

Treatment CST filtration time CST filtration time CST filtration time __________________ for RSME (s) for SBME 1 (s) for POME (s) Untreated Sample 675 1008 > 3600 Cold Filtration 86 88 102 Clarification 569 80 > 3600 Distillation 72 na 88 Thermal Treatment A 139 na na * * Thermal Treatment B na 161 na

SI I

Example 3 shows the effect of different post-treatments on the CST * 20 filtration time i.e. cold filtration, clarification, distillation, and different thermal treatments. Thermal treatment A, in particular, reduced the CST filtration time of S.., the RSME sample from 675 s to 139 s and thermal treatment B reduced the CST filtration time of the SBME1 sample from 1008 s to 161 s.

Example 4

A sample of SBME1 (300 ml) was conditioned in a 4.4°C (40° F) bath for a 16-hour (� 10 minutes) "cold soak", then allowed to warm up to 20-22°C (68- 72°F) over a period of 2.5 hours (� 15 minutes) prior to the CST-filtration according the official CST procedure.. Just before the CST-filtration, the sample was placed in an ultrasonic bath at 17°C for 20 mm. During the treatment, the temperature of the water increased to 20°C. The sample was filtered immediately after the ultrasound treatment and the filtration time was 90 s. If no ultrasonic treatment was applied, the CST filtration time was 210 sec.

A sample of SBME1 (300 ml)) was treated in a microwave oven for I mm.

The temperature of the sample was increased from 20°C to 55°C. Then CST filtration time was determined according to the standard procedure to be 149 s.

If no microwave treatment was applied the CST filtration time was 210 sec.

Example 4 illustrates that CST filtration time can be surprisingly improved by thermal treatment using different techniques. A possible non-binding explanation for this effect is that very fine droplets of water/other polar compounds that might form in FAME are physically broken down 1) by application of ultrasound to biodiesel just before the CST-filtration, or 2) by application of microwave treatment to biodiesel before its cold soak.

Example 5

A sample of RSME was treated according to thermal treatment B process using the procedure described for EXAMPLE 3 and stored at 18°C for 72 h. After three days of storage the CST filtration time was determined according to the standard procedure. to be 90 s. This result is similar to that obtained for another RSME sample, which was subjected to the CST immediately after it was treated according to the thermal treatment B process (139 s).

": 25 Example 5 shows that biodiesel post-treated with CSPT process maintains its ability to pass the CST during at least 3 days of storage. S... ** S. * S I

S

Claims (13)

1. CLAIMS1) A process for the production of fatty acid monovalent C1-C5 alkyl esters comprising the steps of: a) a multi-stage, alkali-catalyzed transesterification of fatty acid glycerides with monovalent C1-C5 alkyl alcohols providing a fatty acid ester stream and a plurality of alcohol streams comprising glycerol; b) removing more than 80% of said alkyl alcohol from said fatty acid ester stream by evaporation providing an alkyl alcohol evaporate and a residue; c) washing said residue with water to deactivate said alkali catalyst and remove some residual C1-C5 alkyl alcohol from said fatty acid ester stream; d) subjecting said fatty acid ester stream to a thermal treatment thereby providing fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of less than 200 s.
2. 2) The process according to claim 1, wherein the final transesterification stage in step a) is continued until the fatty acid monoglyceride content of said fatty ester stream has fallen below 0.8% by weight.
3. 3) The process according to claim 1, wherein the final transesterification stage in step a) is continued until the fatty acid monoglyceride content of said fatty ester stream has fallen below 0.4% by weight. * **
4. 4) The process according to claim 1, wherein the final thermal treatment step d) is continued until the water content of said fatty ester stream has fallen below 0.05% by weight. **$S * *
5. 5) The process according to claim 1, wherein the final thermal treatment step d) is continued until the water content of said fatty ester stream has fallen below 0.02% by weight.
6. 6) The process according to claim 1, wherein the alcohol stream containing glycerol resulting from any stage of the alkali-catalyzed transesterification in step a) is used for pretreating said fatty acid glycerides.
7. 7) The process according to any one of the preceding claims in which said residue resulting from step b) comprises less than 2% by weight of said monovalent alcohol.
8. 8) The process according to any one of the preceding claims in which said residue resulting from step b) comprises less than 1% by weight of said monovalent alcohol.
9. 9) The process according to any one of the preceding claims in which said residue resulting from step b) comprises less than 0.5% by weight of said monovalent alcohol.
10. 10) The process according to any one of the preceding claims in which the monovalent alcohol evaporate is recycled to the transesterification step a) without further rectification.
11. 11) A process for the purification of fatty acid monovalent C,-C5 alkyl esters comprising residual monovalent C1-C5 alkyl alcohol comprising the steps of: e) providing a fatty acid monovalent Ci-C5 alkyl esters with a cold soak *.* filtration test time according to ASTM D 6217 of at least 200 s; b) removing said residual alkyl alcohol from said fatty acid monovalent C1-C5 alkyl esters by evaporation providing a monovalent alkyl alcohol 4..*.evaporate and a residue; 25 C) washing said residue with water; *11S ri':. d) subjecting said washed residue to a thermal treatment thereby providing fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of less than 200 s.
12. 12) A process for the purification of fatty acid monovalent C1-C5 alkyl esters comprising residual monovalent C1-C5 alkyl alcohol comprising the steps of: e) providing a fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s; C) washing said fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s with water; d) subjecting said washed fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s to a thermal treatment thereby providing fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of less than s.
13. 13) A process for the purification of fatty acid monovalent C1-C5 alkyl esters comprising residual monovalent C1-C5 alkyl alcohol comprising the steps of: e) providing a fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s; d) subjecting said fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM 0 6217 of at least 200 s to a thermal treatment thereby providing fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of less than 200 s... 20 14) The process according to any one of claims 11 to 13, wherein the final **,*** thermal treatment step d) is continued until the water content of said washed residue has fallen below 0.05% by weight.**....0 15) The process according to any one of claims 11 to 13, wherein the final . 25 thermal treatment step d) is continued until the water content of said washed *SOS residue has fallen below 0.02% by weight.16) The process according to any one of the preceding claims in which said thermal treatment comprises maintaining said fatty ester stream according to claims 1 to 10, said washed residue according to claims 11, said washed fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s according to claim 12 or said fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM 0 6217 of at least 200 s according to claim 13 within a temperature range between 100°C and 180°C.17) The process according to any one of claims ito 16 in which said thermal treatment comprises subjecting to microwave radiation.18) The process according to one of claims I to 16 in which said thermal treatment comprises subjecting to ultrasonic acoustic waves.19) The process according to any one of the preceding claims in which said thermal treatment is performed under autogenous pressure.20) The process according to any one of claims I to 18 in which said thermal treatment is performed under reduced pressure.21) The process according to claim 20 in which said fatty ester stream according to claims 1 to 10, said washed residue according to claim 11, said washed fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test *:::* 20 time according to ASTM D 6217 of at least 200 s according to claim 12 or said fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s according to claim 13 is maintained at reduced pressure after reducing the temperature below 150°C. * *22) The process according to any one of the proceeding claims in which antioxidant and/or metal deactivator is/are blended in said fatty ester stream according to claims 1 to 10, said washed residue according to claim 11, said washed fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s according to claim 12 or said fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s according to claim 13 prior to step d).23) The process according to any one of the proceeding claims in which antioxidant and/or metal deactivator is/are blended in said fatty ester stream according to claims 1 to 10, said washed residue according to claim 11, said washed fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s according to claim 12 or said fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s according to claim 13 after step d).24) The process according to any preceding claims in which antioxidant and/or metal deactivator is/are blended in said fatty ester stream according to claims 1 to 10, said washed residue according to claim 11, said washed fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s according to claim 12 or said fatty acid monovalent C1-C5 alkyl esters with a cold soak filtration test time according to ASTM D 6217 of at least 200 s according to claim 13 prior to and after step d).25) Fatty acid monovalent C1-C5 alkyl esters obtained by any one of the processes according to claims I to 24. * ** e* * S. * S *5*S *. S o * * * S.SIS.. 55 * I S... * . S... IS 0. * a.I