DE10139422A1 - Production of fatty acid esters from crude oils or fats by alkaline transesterification for use as bio-diesel fuel, comprises pretreatment with alkaline glycerol to remove free fatty acids and/or acid-alcohol mixture to remove slimes - Google Patents

Abstract

Production of fatty acid esters from crude oils or fats by alkaline transesterification with primary and/or secondary alcohols comprises pretreating the oil or fat by washing with an alkaline glycerol phase to remove free fatty acids and/or treatment with a mixture of primary alcohol and concentrated acid to remove insolubilized slimes. Production of fatty acid esters from crude oils or fats by alkaline transesterification with primary and/or secondary alcohols comprises pretreating the oil or fat by: (a) washing with an alkaline glycerol phase from the transesterification reaction to remove free fatty acids as soaps in the glycerol phase; and/or (b) treatment with 0.1-5 wt.% of a mixture of primary alcohol and concentrated acid and separation of insolubilized slimes.

Description

The invention relates to a method for pretreating crude oils and crude fats for a production of fatty acid esters by transesterification of oils and fats so-called bio-diesel.

The bio-diesel production is based on the base-catalyzed used in oleochemistry Transesterification reaction, in which glycerol fatty acid esters in the form of mono-, di- and tri-esters with an alkali hydroxide or an alkali alcoholate in the presence of slightly higher than stoichiometric amounts of primary alcohols (10% to 50% excess) at an elevated temperature of approx. 30 ° to 60 ° C almost completely below Cleavage and separation of glycerol to the fatty acid esters of the primary or secondary, short-chain (chain length from C1 to C4) alcohol react.

The content of free fatty acids in oils and fats interferes with the transesterification reaction considerably. On the one hand, more catalyst is required, on the other hand, the free ones form Fatty acids with the basic catalyst soaps that significantly increase the transesterification reaction hinder. The latter is probably due to the fact that the soaps are in turn with the unreacted tri-, di- and monoglycerides with the participation of the resulting Form glycerin gels that prevent the deposition of reaction glycerin and thus bring the transesterification reaction to a standstill and let it run incompletely.

To deal with the problem of free fatty acids, the direct transesterification of native oils carried out in several stages, with just as much catalyst in the first stage is added that the free fatty acids using catalyst completely convert to soaps and a slight excess of catalyst a partial transesterification with the separation of glycerin. This dissolve in this subset of glycerin formed soaps and can be largely separated with the glycerin. In the The following reaction stage is then added fresh catalyst, which is then no longer can be destroyed by free fatty acids.

Alternatively, one starts from deacidified oils. The latter is the norm. By both However, there are alternatives to losses in yield through the separated soaps or free ones Fatty acids.

The deacidification of oils and fats is usually done in a separate pre-treatment carried out, hot oil or fat (90 ° C) with hot sodium hydroxide solution for a short time is mixed and the soaps formed are separated off with the water phase. The so treated oils are washed with water to completely remove soaps and then vacuum dried. With this refining both the free ones go Fatty acids as well as small amounts of neutral oil are lost.

Another way is to get the free fatty acids at a very high temperature Distill off vacuum. The free fatty acids are used as a usable distillate won. However, this process requires that the oils be distilled from Phospholipids (phosphorus) are largely freed (residual phosphorus <5 ppm). she for this purpose, the most varied and complex pretreatments (degumming with water, acids or enzymes).

Raw press or solvent extraction oils and fats always contain mucilages that form difficult to destroy oil / water emulsions. These are essentially water-swellable mucilages, e.g. B. lecithin, and the non-water-swellable mucilage in Form of other phosphorus-containing compounds. This will make a clean one Phase separation z. B. prevented between glycerin and fatty acid ester formed. Furthermore, too washing the fatty acid ester generated to remove glycerol ester hindered with water by the emulsions.

Because phosphorus must not be present in the biodiesel anyway and the transesterification reaction In practice, residual phosphorus levels that are too high cannot be reliably eliminated alone preferably both "chemical" wet and "physical" dry deacidification an elaborate degumming upstream. With so-called degumming, the dissolved in the oil and therefore not separable by sedimentation Mucilage with water (water degumming) or acid or aqueous acid (acid Degumming) in hydrated, insoluble in oil and thus separable as a precipitate Mucus transferred. When they are separated, however, oil is always carried along and thus removed from a subsequent transesterification.

The invention has for its object to provide a pretreatment method with the oils and fats, the mucilages and / or noteworthy levels of free fatty acids included, inexpensive and yet effective for a subsequent transesterification can be pretreated.

This task becomes dependent on the loading of the starting oil with mucilages and free fatty acids and the goals of the user by the subject matter of claim 1 or 2 solved. Preferred further developments are characterized in the subclaims.

If the starting oil is an oil with a high content of free fatty acids, but little mucilage, as is the case with a cold-pressed oil, for example rapeseed oil, can occur so is the method of claim 1 with great advantage alone applicable.

After that, the free fatty acids from oils and fats are washed off with a basic glycerol phase removed from an alkaline catalyzed transesterification of an oil or fat is removed and is therefore incurred anyway and no additional costs caused. This is preferably transesterification, which directly affects the pretreatment according to the invention follows. The basic glycerin phase is an anhydrous, Residual alcohol (mostly residual methanol) containing soaps and alkaline residual catalyst Glycerol phase. This process represents a significant difference compared to the prior art simplified pretreatment to remove free fatty acids Residual alcohol content (residual methanol content) in the glycerin surprisingly enables despite the high Viscosity of the oil and glycerin a very quick neutralization and separation of the formed soaps. A complete separation of the washing glycerol phase z. B. means Polishing centrifuges are not required. It even turned out to be easier centrifugal separation z. B. in a separating decanter as microdroplets in the separated oil phase remaining 1 to 5 wt .-% of the original glycerol phase subsequent alkali-catalyzed transesterification with methanol (or another primary or secondary alcohol) even accelerate and parallel to the transesterification Suppress the progressive saponification of the oil.

The oil can be washed at room temperature, with a short contact Glycerol phase e.g. B. in a dynamic mixer and a direct separation of the phases in a downstream separator can take place. In the dynamic mixer they become Mixing liquids that are not soluble in each other by dividing them into small droplets intensely mixed together. According to a preferred variant, both Mixing and separation in an extraction decanter.

When washing the oil or fat, there is also an alkaline degumming, in which the phosphorus-containing oil substances are removed. Surprisingly occurs entraining neutral oil with the soap according to the usual saponification aqueous alkali when washing with alkaline glycerol according to the invention. This is of considerable advantage for a subsequent processing of the soaps to free Fatty acids.

When hot pressing oils, the yield of oil is known to be higher, however combined with the disadvantage that the mucilage content here is significantly higher than in cold pressed oil. In such a case, the pretreatment according to claim 2 is advantageous applicable.

According to the prior art, the oil is hot, e.g. B. with 75% to 85% phosphoric acid, added in an amount of about 0.05% by weight to 0.1% by weight, based on the oil, mixed intensively and then washed with aqueous alkali after a longer period of time.

According to the invention, degumming can be done very cold even at room temperature shortly with a comparable amount of phosphoric acid or sulfuric acid perform when the added acid is about the same amount of a short chain Alcohol, especially methanol is added. The short-chain alcohol is it is a commercially available anhydrous alcohol. The swelling or the Conditioning of the mucilage takes place in the homogenization of the mixture z. B. in one Mixer very quickly. Made from raw rapeseed oil pretreated in just 15 minutes an initial phosphorus content of 175 mg phosphorus per kg oil by alkaline catalyzed transesterification generated fatty acid methyl ester contains less than 1 mg phosphorus / kg oil, a value that is difficult to achieve according to the state of the art, even if from refined oil.

The mucilage can be separated by decanting or filtering. According to the invention, the mucilages are preferably separated off by centrifugation.

It is surprising that the slight addition of alcohol compared to Degumming, in which the separation of the mucilage by means of an acid only in The presence of water takes place, such a clear effect on the mucilage is achieved. So the mucilaginous substances with the alcohol additive according to the invention become very quickly converted into an oil-insoluble form by swelling and in this way made vulnerable. When the alcohol passes from the added acidic alcoholic Phase in the oil phase also get at least traces of the added acid with in there oil, these traces of acid apparently also precipitating the only acidic allow precipitable mucus.

According to the invention, concentrated acid is used which has no or correspondingly little Contains water. In the case of the preferred phosphoric acid used, 75% to 85% commercial acid worked. With sulfuric acid can also with 100% Acid to be worked. In principle, preferably less than 70% concentrated aqueous acid not used. A further dilution of the acid takes place only by the added alcohol instead.

The mixture of concentrated acid and the alcohol is based on what is used Oil or fat with 0.1 wt .-% to 5 wt .-%, preferably up to 2 wt .-% used. Depending on Quality of the oil or fat and the concentration of acidity is the weight ratio Acid to alcohol in this mixture to values between 2: 1 and 1: 5, preferably 1: 1 to 1: 2 set. With a preferred value of the mixture added, for example 1% by weight based on the oil or fat, the acid content is therefore between 0.66% by weight and 0.2% by weight.

The oil treated according to claim 2 can in turn at room temperature according to claim 1 be washed to also increase the free fatty acid content before the transesterification reduce.

The invention is explained in more detail below with reference to the drawings. Show it

Fig. 1 shows schematically an alkaline transesterification, for the pretreatment of the oil or fat according to the invention is applied and their alkaline glycerol from the transesterification in the inventive pretreatment can be inserted,

Fig. 2 shows schematically a neutralization and alkaline degumming of a crude oil by washing with alkaline glycerol according to claim 1 and

Fig. 3 shows schematically an acid degumming with subsequent washing with alkaline glycerol.

The invention is for crude oils (not refined, i.e. neither degummed nor deacidified) described, but is also applicable to raw, liquefied fats.

Referring to FIG. 1, the alkaline transesterification is carried out in two stages with methanol as an example of a preferred alcohol used, wherein after the first transesterification step with a separating decanter (solid wall bowl centrifuge) and the Methylester remaining mono- and diglycerides are separated from the alkaline glycerol. The separation into methyl ester and alkaline glycerol takes place after the second transesterification stage, e.g. B. in a separator with plate pack.

In Fig. 1 it is indicated that alkaline separated glycerol is removed centrifugally as a heavy phase from both the first and second transesterification stage. This discharged alkaline glycerol with residual contents of methanol and catalyst (e.g. 20% by weight of methanol and 15% by weight of KOH) is placed together with crude oil in an extraction decanter according to FIG. 2 (solid-bowl screw centrifuge with two inputs for the liquid crude oil phase and the viscous liquid alkaline glycerin phase). Mixing and separation takes place in the decanter in that, at the entry of the specifically heavier glycerol phase into the rotating decanter drum, there is intensive mixing with the specifically lighter oil phase, and likewise the separately supplied oil phase mixes intensively with the glycerin phase as it enters. After the intensive mixing of the two phases, the phases are separated in the centrifugal field. Neutral oil freed from free fatty acids is removed from the decanter, which is also at least partially degummed, as shown above. A heavy phase is a glycerine phase loaded with soaps.

To improve the washing effect, alcohol (methanol or another short-chain alcohol) are added.

With more heavily loaded with mucilage z. B. from a hot pressing, the oil is first mixed with dilute phosphoric acid and methanol (for example in a centrifugal mixer), then passed into a retention tank and washed with alkaline glycerol before being fed into a transesterification process according to claim 1. In Fig. 3, a separator (plate centrifuge) is alternatively used instead of a decanter.

The shown pretreatment of the oil with acid and alcohol Mucus separation can also be used to advantage in edible fats, because on the one hand the the amount of alcohol added is not a noticeable cost factor and the alcohol at others are completely removed anyway in the usual preparation process.

As already mentioned, the temperature in the treatment according to the invention can Contrary to the known hot processes, be low. Between 20 ° C. is preferred and 40 ° C-45 ° C, optionally worked up to 60 ° C.

example

A batch of about 60 kg of rapeseed crude oil (174 ppm phosphorus, acid number 2.5) was used in one Stirring vessel (80 l volume) submitted and in free fall with a performance of about 13 kg / h of oil with about 1.3 kg / h of alkaline glycerol from an alkaline transesterification over a Mixing stage (consisting of another mixing vessel with about 300 ml effective Volume) before the centrifuge inlet directly into a plate centrifuge (SA 1-01 Westfalia Separator AG, Oelde) and continuously separated. The acid number of the expiring Oil was determined by titration (in alcoholic solution with 0.1 N KOH) and was lying reproducible from zero.

A clear oil and an equally clear glycerin could be run out of the centrifuge become.

The neutral oil thus obtained was then alkaline in the usual way (with KOH) Addition of transesterified methanol. The phosphorus content of the methyl ester thus obtained was around 27 ppm.

A second batch of rapeseed crude oil (174 ppm phosphorus, acid number 2.5) of about 55 kg was in the template (80 l volume) with 275 g of a mixture of 160 g of 85% Mixed phosphoric acid and 115 g of anhydrous methanol and added for 15 minutes Room temperature (25-30 ° C) using a chemical centrifugal pump for intensive mixing circulated.

At first, the mixture became cloudy when pumping around, and then after about 5 minutes elucidate. After switching off the circulation pump and the agitator and during the Moving off the mixture, large dark brown flakes could be observed flocculated the oil.

The crude oil pretreated in this way was then in the smaller stirred vessel as above continuously mixed with about 10 wt .-% alkaline glycerol based on the oil and immediately afterwards in the disc centrifuge (SA 1-01, Westfalia Separator AG, Oelde) separated in neutral oil and glycerin.

The feed rate was also about 13 kg / h oil and about 1.3 kg glycerol / h.

The running off neutral oil was still slightly cloudy and was therefore replaced with a second one Disc centrifuge (TA 1-01, Westfalia Separator AG, Oelde) polished.

The resulting glycerin was visibly darker in color than in the previous batch with neutralization alone. A subsequent acidic cleavage of those dissolved in glycerin Soap only added the amount of fatty acids previously contained in the crude oil free fatty acids. For this purpose, the acid-releasable amounts of fatty acids in the glycerin determined and compared before and after washing. This ensured that at No neutral oil saponification had taken place above.

The degummed neutral oil thus obtained then became alkaline in the usual way (with KOH) transesterified addition of methanol below. The phosphorus content of the thus obtained Methyl ester was below 1 ppm.

For larger quantities, separating decanters in accordance with Figures worked. Incidentally, this is recommended when the crude oil is additionally strong is contaminated with solid impurities.

Claims (11)

1. A process for the pretreatment of crude oils and fats for a subsequent alkaline transesterification with primary and / or secondary alcohols, characterized in that the crude oil or fat loaded with free fatty acids and mucilages is washed with an alkaline glycerol phase which results from an alkaline transesterification reaction of the type mentioned, and that after the washing process the glycerol phase now loaded with soaps of the free fatty acids is separated as a heavy phase from the neutral oil freed from free fatty acids. 2. Process for pretreating raw oils and fats for a subsequent one alkaline transesterification with primary and / or secondary alcohols, characterized, that the raw oil or fat loaded with free fatty acids and mucilages with a Mixture is treated, which is based on the oil or fat with 0.1 wt .-% to 5 wt .-% is used and comprises a primary alcohol and concentrated acid, and that then those swollen by the treatment and no longer oil or fat soluble Mucilages are separated. 3. The method according to claim 1 and claim 2, characterized, that the crude oil or fat before washing with the alkaline glycerin with the Mixture of the primary alcohol and concentrated acid is treated, the Separation of the mucilage together with the separation of the soaps loaded glycerin. 4. The method according to claim 1, characterized, that the washing and separation are carried out in an extraction decanter. 5. The method according to claim 2, characterized, that the acid from the group phosphoric acid, sulfuric acid and p-toluenesulfonic acid is selected. 6. The method according to claim 1 and / or 2, characterized, that the glycerol loaded with soaps or the mucilages is separated off centrifugally become. 7. The method according to any one of claims 2, 3, 5 and 6, characterized, that the primary alcohol is selected from the group consisting of methanol, ethanol, propanol and Butanol. 8. The method according to claim 8, characterized, that the treatment in the mixture of alcohol and dilute acid in one Centrifugal mixer and then holding tank. 9. The method according to claim 2, characterized, that the acid has a concentration of at least 70% and that Weight ratio of acid to alcohol in the mixture depending on the acid concentration and the Quality of the oil or fat is set between 2: 1 and 1: 5. 10. Process for the preparation of fatty acid esters of primary and / or secondary alcohols from crude, unpurified free fatty acids and mucilaginous oils or fats or from waste oils in the food industry loaded with free fatty acids, characterized, that a pretreatment of the oil or fat is carried out according to claim 1 and / or 2, wherein the alkaline glycerol according to claim 1 from a subsequent transesterification step in the process is recycled, and optionally the mucilage through an upstream after treatment with the mixture of primary alcohol and concentrated acid Claim 3 can be removed from the oil or fat. 11. The method according to any one of claims 1 to 9, characterized, that the washing or treatment cold or in the preferred temperature range of about 20 ° C to 45 ° C.