WO2009098301A1

WO2009098301A1 - Treatment of residues containing salt and glycerol

Info

Publication number: WO2009098301A1
Application number: PCT/EP2009/051393
Authority: WO
Inventors: Alfred Westfechtel; Thomas Kapala; Hans-Juergen Strunk; Reinhard Schulz; Jens Vier
Original assignee: Cognis Oleochemicals Gmbh
Priority date: 2008-02-07
Filing date: 2009-02-06
Publication date: 2009-08-13
Also published as: DE102008008319A1; DE102008008319B4

Abstract

The present invention relates to a process for preparing a composition containing salt and glycerol that comprises the following process steps: i) providing a raw glycerol phase, containing ia) 10% to 99% by weight of glycerol, ib) 0.1% to 30% by weight of water, ic) 0.1% to 15% by weight salts, and id) 0.1% to 15% by weight of impurities other than glycerol, water and salts, the sum of components ia) to id) being 100% by weight; ii) distilling the raw glycerol phase to give a pure glycerol phase and a bottom product containing salt and glycerol; iii) contacting the bottom product containing salt and glycerol with water and an acid which has a pKa of not more than 5.0, based in each case on the total weight of the bottom product containing salt and glycerol, to give a composition containing salt and glycerol. The present invention also relates to the composition containing salt and glycerol that is obtainable by this process, to a process for preparing a gas containing methane, to the gas containing methane that is obtainable by this process, to a process for preparing fatty acid alcohol esters, to the use of a composition containing salt and glycerol, and to the use of a combination of water and an acid.

Description

Treatment of salt and glycerine-containing residues

The present invention relates to a process for producing a salt and glycerol-containing composition, the acid and glycerin-containing composition obtainable by this process, a process for producing a methane-containing gas, the methane-containing gas obtainable by this process, a process for the preparation of fatty acid alkyl esters, the use of a salt and glycerol-containing composition and the use of a combination of water and an acid or a derivative thereof.

Glycerol is used today among other things as a moisturizer in cosmetics, as antifreeze, as a lubricant and as a plasticizer and is therefore used, inter alia, in the production of plastics, microchips, dyes and toothpaste. Glycerol is also used as a food additive. Furthermore, glycerol can be used as starting material for the preparation of other chemically interesting monomers. Thus, for example, glycerol can be converted by dehydration to acrolein, which can then be converted by catalytic oxidation into acrylic acid.

Starting material for glycerol, which is used for the purposes described above, is usually so-called "raw glycerol", which is usually obtained in the lipid cleavage or in the fatty transesterification, such as in the production of biodiesel.

In lipolysis, natural oils and fats are hydrolyzed with water under pressures of up to 100 bar and temperatures between 100 and 250 ^° C. This gives a light phase containing the fatty acids and a heavy phase consisting essentially of glycerol and water, also referred to as "glycerol water." The resulting glycerol water is then concentrated by evaporation to give about 75 to 85% by weight. % of crude glycerol containing concentrated. Such a method is described, for example, in WO-A-87/002378. In addition to the high-pressure cleavage of triglycerides described above, the so-called alkali process or the carbonate process are known in which the triglycerides are cleaved under normal pressure but in the presence of basic catalysts (sodium hydroxide solution or sodium carbonate). Here, too, an aqueous glycerol phase and a soap phase separating from this aqueous glycerol phase are formed.

For fat transesterification, such as in biodiesel production, vegetable oil is mixed with about 10% methanol and various reagents (especially potassium hydroxide or sodium hydroxide and more rarely alcoholates). At normal pressure and temperatures around 60 ^° C., the fatty acid groups in the triglycerides of the vegetable oil are esterified with the methanol (transesterification). The resulting glycerol and the fatty acid methyl esters form two immiscible phases, so that the glycerol can be easily separated from the fatty acid methyl ester phase.

For the areas of use mentioned above, however, the purity of the crude glycerol obtained in this way is insufficient, so that further purification steps are necessary. Often, this further purification is carried out by thermal separation processes, in particular by distillation. In this case, however, large amounts of salt-containing bottoms are obtained, which may still contain considerable amounts of glycerol, the salts in particular on the catalysts used for lipid cleavage or transesterification, on the reagents used for neutralization of the reaction mixtures or salts, which already can be contained in the used for fat cleavage or transesterification vegetable or animal fats or oils. For example, the reaction mixture obtained in the transesterification in the presence of potassium hydroxide, sodium hydroxide, potassium alcoholate or sodium alcoholate in biodiesel production is frequently neutralized with hydrochloric acid, so that the Crude glycerin considerable amounts of sodium or potassium chloride are included.

From an economic point of view, it is disadvantageous to discard these saline bottoms because they still contain considerable amounts of glycerin. It is therefore desirable to continue to utilize these saline residues, for example as biomass in a biogas plant. The use of these residues in one

Biogas plant for the production of methane failed so far however at the high

Viscosity of the residues or because they were already solid at room temperature. The attempt to use these solutions at a higher temperature to the biogas

To feed process, fails due to the temperature sensitivity of the

Biogas production used microorganisms.

The object of the present invention was to overcome the disadvantages resulting from the state of the art in connection with the use of saline residues, which are produced in the distillation of crude glycerol, in biogas plants.

In particular, the present invention was based on the object of specifying a method by means of which such salt-containing residues can be pretreated in the most advantageous and cost-effective manner in such a way that they can be used without problems as biomass in a biogas plant. The operator of a biogas plant should be able to convert the salt and glycerol-containing compositions provided as biomass into a state by the addition of the lowest possible amounts of additive, which makes possible a problem-free use of these compositions in biogas production.

A contribution to the solution of the abovementioned objects is made by a process for the preparation of a salt and glycerol-containing composition, comprising the process steps: i) providing a crude glycerol phase, including

ia) 40 to 99 wt .-%, particularly preferably 50 to 95 wt .-% and most preferably 60 to 90 wt .-% glycerol, ib) 0.1 to 30 wt .-%, particularly preferably 1 to 25 wt %) and most preferably 5 to 20% by weight of water, ic) 0.1 to 15% by weight, more preferably 1 to 12.5% by weight and most preferably 2 to 10% by weight Salts, and id) from 0.1 to 15% by weight, more preferably from 0.5 to 12.5% by weight, and most preferably from 1 to 10% by weight of glycerol, water and salts of various impurities,

wherein the sum of components ia) to id) is 100% by weight;

ii) distilling the crude glycerol phase to obtain a pure glycerol phase and a bottoms and glycerol-containing bottoms product;

iii) bringing into contact the salt and glycerol-containing bottom product with water, preferably with 1 to 50 wt .-%, particularly preferably 2.5 to

40% by weight and most preferably 5 to 15% by weight of water and with an acid having a pKa of at most 5.0, more preferably at most 4.5, even more preferably at most 4.0 and most preferably at most 3.5, or a derivative thereof, preferably at 0.1 to 10 wt .-%, particularly preferably 0.5 to 5 wt .-% and most preferably 1 to 3 wt .-% of such an acid or such a derivative thereof, in each case based on the total weight of the salt and glycerol-containing bottom product, wherein a salt and glycerol-containing composition is obtained.

- A - In the first step of the process according to the invention for producing a salt and glycerol-containing composition, a crude glycerol phase is provided, this crude glycerol phase being obtained, for example, in the context of a triglyceride transesterification or in the context of a triglyceride transesterification, for example in the case of biodiesel. manufacture, may have been obtained.

According to a first particular embodiment of the process according to the invention for preparing a salt and glycerol-containing composition, the crude glycerol provided in process step i) is obtained in a process which comprises the following process steps:

(αl) cleavage of mono-, di- or triglycerides with water to give an aqueous glycerol phase and a fatty acid phase;

(cc2) Work-up of the aqueous glycerol phase to give crude glycerol.

In the context of the present invention, mono-, di- or triglycerides are generally compounds of the general formula (I)

CH ₂ (θ ₂ CR ¹ ) -CH (θ ₂ CR ² ) -CH ₂ (θ ₂ CR ³ )

in which the radicals R ¹ , R ² and R ³ independently of one another denote a hydrogen atom or an alkyl radical having 5 to 23 carbon atoms, which may be saturated or unsaturated, straight-chain or branched, where in the case of a monoglyceride two of the radicals R ¹ , R ² or R ³ , in the case of a diglyceride of one of the radicals R ¹ , R ² or R ³ and in the case of a triglyceride none of the radicals R ¹ , R ² or R ^{3 represent} a hydrogen atom.

The mono-, di- or triglycerides can be present in pure form (that is to say as pure mono-, di- or triglyceride) or else in the form of mixtures of at least two of these glycerides. Furthermore, the mono-, di- or triglycerides or the mixture of at least two of these glycerides of natural or synthetic origin, wherein a use of glycerides of natural origin is particularly preferred.

In connection with the first particular embodiment of the process according to the invention for preparing a salt and glycerol-containing composition, the mono-, di- or triglycerides are preferably used in the form of plant or animal substances which contain these mono-, di- or triglycerides. Vegetable or animal fats or vegetable or animal oils are particularly suitable here. Specific examples of substances which comprise mono-, di- or triglycerides are, for example, vegetable oils such as rapeseed oil, peanut oil, olive oil, nut oil, corn oil, linseed oil, hemp oil, grapeseed oil, cottonseed oil, babassu oil, jojoba oil, sunflower oil, soybean oil, Coconut oil, palm oil, palm kernel oil, sesame oil or castor oil or animal oils or fats, such as tallow, lard, chicken fat, bone fat, milk fat or fish oil, such as sperm whale oil, dolphin oil, whale oil, seal oil, sardine oil, herring oil or cod liver oil, the use of animal fats, in particular the use of tallow is particularly preferred.

The cleavage of the mono-, di- or triglycerides or the mixture of at least two thereof in process step (αl) can be carried out by any method known to those skilled in the art, with the aid of mono-, di- or triglycerides in the presence of water in fatty acids and glycerol can be split. Particularly suitable here is the process of high-pressure cleavage, in which in a first step (αl) the mono-, di- or triglycerides are hydrolyzed with water under pressures of from 10 to 100 bar and temperatures between 100 and 250 ^° C. However, it is also conceivable in principle to cleave by means of basic catalysts, such as by means of the alkali or carbonate process.

In process step (α2), the aqueous glycerol phase obtained in process step (αl) is purified to give crude glycerol. For this purpose, next the water-insoluble fatty acids which form the upper phase of the reaction mixture, separated from the aqueous glycerol phase (lower phase). At least part of the water is then separated off from the obtained aqueous glycerol phase, for example by distillation or simple evaporation, to give crude glycerol.

In connection with this first particular embodiment of the process according to the invention for preparing a salt and glycerol-containing composition, it is further preferred that the crude glycerol phase

ia) 70 to 98 wt .-%, particularly preferably 80 to 95 wt .-% and most preferably 85 to 90 wt .-% glycerol, ib) 1 to 15 wt .-%, particularly preferably 2 to 10 wt. % and most preferably 3 to 8% by weight of water, ic) 0.1 to 5% by weight, more preferably 0.5 to 2.5% by weight and most preferably 1 to 2% by weight Salts, and id) 0.1 to 10 wt .-%, particularly preferably 0.5 to 7.5 wt .-% and most preferably 1 to 5 wt .-% of glycerol, water and salts different impurities,

wherein the sum of components ia) to id) is 100% by weight.

The impurities other than glycerol, water and salts are, in particular, so-called "MONG" (Matter of Organic Non Glycerol), which in particular comprises mono-, di- or triglycerides, fatty acids and condensation products of glycerol, such as di- or tri-glycerol Triglycerin.

Furthermore, in connection with this first particular embodiment of the process according to the invention for the preparation of a salt and glycerol-containing composition, it is preferred that this be carried out in process step ii) Distillation of the above-described crude glycerol phase obtained bottom product

iia) 10 to 90 wt .-%, particularly preferably 25 to 85 wt .-% and most preferably 35 to 80 wt .-% glycerol, üb) 0 to 1 wt .-%, particularly preferably 0.001 to 0.5 wt % and most preferably 0.01 to 0.1% by weight of water, iic) 5 to 20% by weight, more preferably 6 to 15% by weight and most preferably 7 to 10% by weight. Salts, and iid) 5 to 75% by weight, more preferably 8 to 65% by weight and most preferably 12.5 to 60% by weight of glycerine, water and salts of various impurities,

wherein the sum of the components iia) to iid) is 100% by weight.

It should be noted that the precise composition of the bottoms product described above depends critically on the pressure and temperature conditions in the distillation of the crude glycerol, the type of distillation apparatus used and in particular also on the quality of the crude glycerol used.

According to a second particular embodiment of the process according to the invention for producing a salt and glycerol-containing composition, the crude glycerol provided in process step i) is obtained in a process which comprises the following process steps:

(β1) transesterification of mono-, di- or triglycerides with alcohol, preferably with methanol or ethanol, most preferably with methanol, to form a glycerol phase and a fatty acid alkyl ester phase;

(β2) separation of the glycerol phase from the fatty acid alkyl ester phase; (ß3) workup of the glycerol phase to give crude glycerol.

The process defined by process steps (β1) to (β3) corresponds to the customary process for the production of crude glycerol as a by-product in the production of biodiesel.

In this second particular embodiment of the process according to the invention for preparing a salt and glycerol-containing composition, it is also possible in principle to use all mono-, di- or triglycerides which have already been mentioned in the context of the first particular embodiment of the process according to the invention for preparing a salt and Glycerol-containing composition have been mentioned as preferred mono-, di- or triglycerides. However, particularly preferred in connection with the second particular embodiment of the process according to the invention is the use of vegetable oils, in particular the use of vegetable oils selected from the group consisting of rapeseed oil or rapeseed oil, peanut oil, olive oil, nut oil, corn oil, linseed oil, hemp oil, grapeseed oil , Cottonseed oil, babassu oil, jojoba oil, sunflower oil, soybean oil, coconut oil, palm oil, palm kernel oil, sesame oil and castor oil.

In connection with this second particular embodiment of the process according to the invention for the preparation of a salt and glycerol-containing composition, it is further preferred that pure triglycerides or compositions which, in addition to triglycerides, also contain mono- and / or diglycerides are used which have an acid number below 4. The acid number (SZ) is known to the amount of potassium hydroxide in mg, which is required for the neutralization of 1 g of the sample to be tested (determined according to the method known to those skilled in the DIN 53402). The acid number is preferably below 2 and in particular below 1. Triglycerides or compositions which, in addition to triglycerides, also contain mono- and / or diglycerides which do not have the desired acid number, can be subjected to a pretreatment by means of which the acid number is correspondingly reduced. The person skilled in the art can resort to all the methods familiar to him. Examples of such methods include, but are not limited to:

Refining of raw natural oil;

Pre-esterification of the crude natural oil using an acidic catalyst;

Pretreatment of the raw, natural oil with the help of enzymatic procedures.

The triglycerides or the compositions which, in addition to triglycerides, also contain mono- and / or diglycerides, are preferably used in degummed form. This can be done in different ways, for example by enzymatic catalysis. It should be noted at this point that the degumming of an oil and the reduction of the acid number (SZ) of an oil are two different methods serving different purposes. The degumming provides for the removal of mucilages, e.g. Phospholipids whose presence can cause adverse process behavior. The reduction in the SZ causes the amount of free fatty acids present in the oil to be reduced physically (e.g., by washing) or chemically (e.g., by reaction with an alcohol).

The production of biodiesel from vegetable or animal fats or oils is known from the prior art. Examples of processes for the production of biodiesel include, in particular, the processes described in DE-A-103 20 203 and DE-A-10 2006 028 560. In process step (β1), first the transesterification of the mono-, di- or triglycerides with alcohol takes place, preferably with methanol or ethanol, most preferably with methanol, to form a glycerol phase and a fatty acid ester phase. For transesterification, preference is given to using basic catalysts, in particular inorganic and organic bases, more preferably metal hydroxides, oxides, carbonates or alkoxides, with the use of sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium carbonate and potassium carbonate being very particularly preferred. In addition to these basic catalysts, the phase transfer catalysts described in DE-A-10 2006 028 560 can in principle also be used. The reaction time is preferably chosen in the range of 1 to 60 minutes, with reaction rates of at least 98%, preferably at least 99%, generally being aimed for. The degree of conversion of the reaction refers to the proportion of glycerides (= sum of mono-, di- or triglycerides) still present after the end or termination of the reaction, based on the initial content of these components in the oil or fat used.

During the transesterification, a fatty acid alkyl ester and a glycerol phase are formed, which can be easily separated from one another by known process steps, such as decanting, according to process step (β2).

The glycerol phase obtained in this way is further worked up in process step (β3). This workup usually comprises the following process steps:

(β3_l) at least partial removal of unreacted alcohol (both here and in step (ß3_4) possible);

(ß3_2) Cleavage of the catalyst from biodiesel production; (ß3_3) cleavage of the soaps, at least partial separation of the fatty acids and other remaining organic products in the glycerol and subsequent neutralization;

(β3_4) separation of unreacted alcohol;

(ß3_5) concentration of glycerol to give crude glycerol, this concentration is preferably carried out by evaporation.

In connection with this second particular embodiment of the process according to the invention for preparing a salt and glycerol-containing composition, it is further preferred that the crude glycerol phase

ia) 70 to 97% by weight, particularly preferably 75 to 95% by weight and most preferably 80 to 85% by weight of glycerol, ib) 1 to 15% by weight, particularly preferably 2 to 10% by weight. % and most preferably 3 to 8 wt .-% water, ic) 1 to 10 wt .-%, particularly preferably 2 to 9 wt .-% and most preferably 3 to 8 wt .-% salts, and id) 0 From 1 to 20% by weight, more preferably from 0.5 to 15% by weight, and most preferably from 1 to 10% by weight of glycerin, water and salts of various impurities,

wherein the sum of components ia) to id) is 100% by weight. In contrast to the component id) of the crude glycerol from the cleavage of mono-, di- and triglycerides, the component id) of the crude glycerol from the transesterification also contains residues of unreacted alcohol.

Furthermore, in connection with this second particular embodiment of the process according to the invention for producing a salt and glycerol-containing composition, it is preferred that this be carried out in process step ii) Distillation of the above-described crude glycerol phase obtained bottom product

iia) 10 to 59 wt .-%, particularly preferably 25 to 50 wt .-% and most preferably 35 to 40 wt .-% glycerol, üb) 0 to 1 wt .-%, particularly preferably 0.001 to 0.5 wt % and most preferably 0.01 to 0.1% by weight of water, iic) 40 to 70% by weight, more preferably 45 to 65% by weight and most preferably 50 to 60% by weight Salts, and iid) 1 to 30% by weight, more preferably 5 to 25% by weight and most preferably 10 to 20% by weight of glycerine, water and salts of various impurities,

wherein the sum of the components iia) to iid) is 100% by weight.

In accordance with process step iii) of the process according to the invention for producing a salt and glycerol-containing composition, the bottoms product containing the salt and glycerol is brought into contact with water. If the composition containing the salt and glycerol is a composition which has been obtained as bottom product according to the first particular embodiment of the process according to the invention (bottom product from the distillation of crude glycerol which consists of the cleavage of mono-, di-, or triglycerides), so it is particularly preferred that the salt and glycerol-containing bottom product in process step ii) with 6 to 14 wt .-%, particularly preferably 8 to 12 wt .-% water, each based on the total weight the salt and glycerol-containing bottoms product is brought into contact. If the salt- and glycerol-containing composition is a composition which has been obtained as bottom product according to the second particular embodiment of the process according to the invention (bottom product from the distillation of crude glycerol which has been produced in the production of biodiesel) it is particularly preferred that the salt and glycerol-containing Bottom product in process step ii) with at least 10 wt .-%, particularly preferably at least 20 wt .-%, more preferably at least 50 wt .-% and most preferably at least 100 wt .-% water, each based on the total weight of the salt - And glycerol-containing bottoms product is brought into contact.

Furthermore, in process step iii) of the process according to the invention for the preparation of a salt and glycerol-containing composition, the salt and glycerol-containing bottom product is admixed with from 0.1 to 10% by weight, more preferably from 0.5 to 5% by weight. and most preferably from 1 to 3% by weight of the acid having a pKa of at most 5, more preferably at most 4.5, even more preferably at most 4.0, and most preferably at most 3.5, or Derivatives thereof, in each case based on the total weight of the salt and glycerol-containing bottom product, brought into contact.

Suitable acids having the abovementioned pKa values are both organic and inorganic acids, with organic acids being particularly preferred.

For example, HCl, H ₂ SO ₄ or else H 3 PO ₄ can be used as the inorganic acid, while organic acids are known as organic acids, but especially mono-, di- or tricarboxylic acids preferably having 2 to 10 carbon atoms or hydroxycarboxylic acids, in particular hydroxymonocarboxylic acids. Hydroxydicarbonsäuren or Hydroxytricar- bonsäuren preferably having 2 to 10 carbon atoms, are used. Derivatives of a carboxylic acid or a hydroxycarboxylic acid in the context of the present invention in such a case would in particular comprise salts of carboxylic acids or hydroxycarboxylic acids, such as sodium or potassium salt, as well as all compounds which, on contact with water, comprise a carboxylic acid or a hydroxycarboxylic acid form. The term "derivative of a carboxylic acid" or "derivative of a hydroxycarboxylic acid" are therefore in particular dere also carboxylic acid or Hydroxycarbonsäureanhydride and Carbonsäurebzw. Hydroxycarboxylic acid chlorides includes.

Organic acids which are particularly preferred according to the invention are selected from the group consisting of acetic acid, lactic acid, propionic acid, 3-hydroxypropionic acid, butyric acid, 3-hydroxybutyric acid, 3-hydroxyisobutyric acid, oxalic acid, succinic acid, malonic acid, methylmalonic acid, fumaric acid, maleic acid, maleic anhydride, glutaric acid, adipic acid , Pimelic acid, suberic acid, azelaic acid, sebacic acid, tartaric acid, malic acid and citric acid, with citric acid being particularly preferred as the organic acid.

According to a preferred embodiment, as inorganic acids, those having a single central atom are selected, for example hydrochloric acid, sulfuric acid, nitrating acid or phosphoric acid, or a combination of two or more thereof. This embodiment excludes the use of heteropolyacids and isopolyacids.

It is inventively preferred that bringing into contact the salt and glycerol-containing bottom product with the water and the acid or the derivative thereof by simply mixing the salt and glycerol-containing bottom product with the water and the acid or the derivative thereof , wherein it can prove to be advantageous in particular to use for this purpose an aqueous solution which includes water and the acid or the derivative thereof.

If the salt-rich or glycerol-containing bottom product used is the particularly salt-rich bottoms product which is obtained in the distillation of crude glycerol obtained in the production of biodiesel (see the above-described second particular embodiment of the process according to the invention for the preparation of a salt and glycerol -containing composition), so this bottom product is at room or ambient temperature, due to the high salt content, often as a solid. Here it may prove to be advantageous to make the bringing into contact of the bottom product with the water and the acid so that the solid bottom product with preheated to a temperature in a range of 30 to 80 ⁰ C, particularly preferably 35 to 55 ° C. Water or with a preheated to a temperature in a range of 30 to 80 ⁰ C, more preferably 35 to 55 ° C aqueous solution containing the acid or the derivative thereof is brought into contact, so as to convert the bottom product into a liquid form. The bringing into contact in this case, for example, by the fact that the solid bottom product is placed on a substrate, for example on the ground, and then rinsed along the surface of the substrate, the preheated water or the preheated aqueous solution. In this way, the solid bottom product is gradually transferred from below into a liquid state. However, it is also conceivable that solid bottom product first to comminute, in which it is processed, for example, in a mill to a powder, and then bring the comminuted bottom product with the water or the aqueous solution in contact.

A contribution to the solution of the abovementioned objects is also made by a salt and glycerol-containing composition obtainable by the above-described process for the preparation of a salt and glycerol-containing composition.

A contribution to the solution of the abovementioned objects is also made by a process for the production of a methane-containing gas, preferably of biogas, by fermentative degradation of an organic phase, comprising the process steps:

I) providing a salt and glycerin-containing composition by the above-described process for the preparation of a salt and glycerol-containing composition; II) optionally mixing this salt and glycerol-containing composition with further organic material;

III) anaerobic fermentation of glycerol in the salt and glycerol-containing composition or in the mixture of the salt and glycerol-containing

Composition and the other organic material to form a methane-containing gas, preferably with the formation of biogas.

According to process step I) of the process according to the invention for the production of biogas, a salt and glycerol-containing composition is first prepared by the process described above for producing a salt and glycerol-containing composition, this preparation preferably being carried out according to the first invention described above or second particular embodiment of the inventive method for producing a SaIz- and glycerol-containing composition can take place.

In process step II) of the process according to the invention for the production of biogas, this salt and glycerol-containing composition can then optionally be mixed with further organic material. In this case, therefore, the salt and glycerol-containing composition is used only as an organic additive component in biogas production. In particular, activated sludge from sewage treatment plants, livestock waste products such as manure or manure, plant material such as straw, grass, hay, beets, corn and whole plant silage (GPS) such as green rye, residues of food production such as slaughterhouse effluents are used as further organic material , Brewery lamb, wastewater from dairies and sugar factories and other residues of biotechnological production plants as well as domestic waste. The proportion of salt and glycerin-containing composition in the total amount of the organic material used in the biogas production is preferably in a range of 0.01 to 40% by weight, particularly preferably 0.1 to 20 wt .-% and most preferably 1 to 5% by weight. It should be noted that in the case of salt and glycerol-containing compositions with a particularly high salt content, the amount used in the biogas production must be chosen so that does not set too high for the microorganisms in the biogas reactor salt concentration.

In process step III) of the process according to the invention for the production of biogas, the glycerol is anaerobically fermented in the salt and glycerol-containing composition or in the mixture of the salt and glycerol-containing composition and the further organic material to form a methane-containing gas.

For this purpose, it may prove advantageous to subject the biomass used in the biogas production of their fermentation initially preheating outside the fermenter. The preheating of the products to be fermented in this respect to the necessary fermentation temperature omits the otherwise usually to be accepted temperature fluctuations within the fermenter and the associated slowing down of the fermentation process and the reduction of the yield of biogas. When the salt or glycerine-containing composition used is a composition obtained by contacting the salt and glycerol-containing bottom product from the crude glycerol distillation with preheated water or with a preheated aqueous solution containing the acid or the derivative thereof Depending on the proportion of this salt- and glycerol-containing composition in the total amount of biomass used, further preheating may be dispensed with, if appropriate.

The production of biogas from the above-described organic material can be carried out in bioreactors known to the person skilled in the art and under the conditions known to the person skilled in the art. As an example of suitable biogas reactors and process guides, reference is made to DE-A-10 2005 030 980, DE-A-10 2004 009587, DE-C-32 39 304 DE-C-32 49 717. A contribution to the solution of the abovementioned objects is also provided by a methane-containing gas which can be obtained by the process described above.

A further contribution to the solution of the abovementioned objects is also provided by a process for the preparation of fatty acid alkyl esters, comprising the process steps:

(γl) providing a composition comprising mono-, di- or triglycerides;

(γ2) transesterification of the mono-, di- or triglycerides with alcohol to form a glycerol phase and a fatty acid alkyl ester phase;

(γ3) separation of the glycerol phase from the fatty acid alkyl ester phase;

(γ4) work-up of the glycerol phase to give crude glycerol;

(γ5) working up the crude glycerol to obtain a salt and glycerol-containing composition by the inventive method for producing a salt and glycerol-containing composition.

Process steps (γ1) to (γ4) have already been described in connection with the second particular embodiment of the process according to the invention for preparing a salt and glycerol-containing composition (see the process steps (β1) to (β2) described above).

According to a particular embodiment of the process according to the invention for the preparation of fatty acid alkyl esters, the process described in (γ5) fermented to form a methane-containing gas, as described above in connection with the inventive method for producing a methane-containing gas.

Also, the use of a salt and glycerol-containing composition, obtainable by the method described above for producing a SaIz- and glycerol-containing composition, in particular obtainable by the first or second particular embodiment of this method, as biomass for the production of biogas makes a contribution to solve the problems mentioned above.

A further contribution to achieving the abovementioned objects is also provided by the use of a combination of water and an acid which has a pKa of at most 5.0, more preferably at most 4.5, even more preferably at most 4.0, and most preferably has at most 3.5, or a derivative thereof for the treatment of residues containing salt and glycerol, wherein as acids and as derivatives thereof are those compounds which are already mentioned in the beginning in connection with the inventive method for producing a salt and glycerol -containing composition as preferred acids and derivatives thereof, wherein the use of citric acid is particularly preferred here as well.

The invention will now be explained in more detail by way of non-limiting examples.

EXAMPLE 1

Two different samples of the residue from the distillation of crude glycerol, obtained by fission of animal fats, are in terms of their glycerol, MONG and ash content (this corresponds substantially to the Salinity). The viscosity of the residue was also determined at 80 ^° C. The results are shown in Table 1 below:

Table 1

nb = not determinable.

These samples were mixed with 10 or 11 wt .-% water and then the viscosity was again determined at 80 ⁰ C. In a further experiment, in addition to water in the abovementioned amounts, the samples were also admixed with 1.3 or 1.0% by weight of citric acid in accordance with the method according to the invention. Also in the compositions thus obtained, the viscosity at 80 ⁰ C was determined. The results are shown in Table 2 below.

Table 2

The experiment shows that by the combined addition of water and acids, the viscosity drops significantly, in particular, the addition of citric acid shows a clear and surprising effect. In fact, it was not to be expected for the person skilled in the art that the viscosity could be significantly reduced by adding citric acid and water to such salt and glycerol-containing compositions in comparison to adding pure water.

By using acids with small amounts of water thus an effective reduction of the viscosity of the residue can be made possible. moreover The addition of citric acid leads to a pH buffering, which protects the microorganisms against fluctuations in the pH when adding the substrate and thus allows a stable biogas process.

EXAMPLE 2

Two different samples of the residue from the distillation of crude glycerol obtained by transesterification of vegetable oils have been analyzed for their glycerol, MONG and ash content (this essentially corresponds to the salt content). The viscosity of the residue was also determined at 80 ^° C. The results are shown in Table 1 below:

Table 1

nb = not determinable; > 100.00 mPas.

Each 10 parts of these samples were mixed with one part 1 of a mixture of 30 wt .-% citric acid and 70 wt .-% glycerol at a temperature of about 150 ⁰ C, and mixed with a stirrer. After cooling to about 95 ⁰ C, a water content of 10 wt .-%, and adjusted with citric acid, a pH in a range of 5 to 6. The viscosity of the samples treated in this way was determined at 50 ^° C. The results are shown in Table 2 below. Table 2

The experiment shows that by the combined addition of glycerol and acids strongly saline residues from the Glycerindestillation can be converted into a pumpable mixture. Through the use of a 70/30 mixture of glycerol and citric acid, it is possible to treat residues at temperatures of more than 100 ⁰ C and make pumpable, which could be made non-pumpable when treated with an aqueous citric acid solution below 100 ⁰ C. ,

Claims

claims

1. A process for preparing a salt and glycerin-containing composition, comprising the process steps: i) providing a crude glycerol phase, comprising ia) 40 to 99% by weight of glycerol, ib) 0.1 to 30 Wt .-% water, ic) 0.1 bisl5 wt .-% salts, and id) 0.1 to 15 wt .-% of glycerol, water and salts different impurities, wherein the sum of the components ia) to id) 100 Wt .-% is; ii) distilling the crude glycerol phase to obtain a pure glycerol phase and a bottoms and glycerol-containing bottoms product; iii) contacting the salt and glycerol-containing bottoms product with 1 to 50% by weight of water and 0.1 to 10% by weight of an acid having a pK _s of not more than 5.0, respectively based on the total weight of the salt and glycerin-containing

Bottom product, wherein a salt and glycerol-containing composition is obtained.

2. The process according to claim 1, wherein the crude glycerol has been obtained in a process comprising the following process steps:

(αl) cleavage of mono-, di- or triglycerides with water to give an aqueous glycerol phase and a fatty acid phase; (cc2) Working up of the aqueous glycerol phase to obtain crude glycerol.

3. The method of claim 2, wherein the crude glycerol phase ia) 70 to 98% by weight of glycerol, ib) 1 to 15% by weight of water, ic) 0.1 to 5% by weight of salts, and also id) 0.1 to 10% by weight of glycerol, Water and salts of various impurities, wherein the sum of the components ia) to id) is 100 wt .-%.

4. The process according to claim 2 or 3, wherein the bottoms product obtained in process step ii) comprises 10 to 90% by weight glycerol, from 0 to 1% by weight water, from 5 to 20% by weight salts , and iid) 5 to 75 wt .-% of glycerol, water and salts different

Impurities, wherein the sum of components iia) to iid) is 100% by weight.

5. The method according to any one of claims 2 to 4, wherein the salt and glycerol-containing bottom product in process step ii) with 6 to 14 wt .-% water, based on the total weight of the salt and glycerol-containing

Sumpfproduktes, is brought into contact.

6. The method of claim 1, wherein the crude glycerol has been obtained in a process comprising the following steps: ßl) transesterification of mono-, di- or triglycerides with alcohol

Formation of a glycerol phase and a fatty acid alkyl ester phase; (β2) separation of the glycerol phase from the fatty acid alkyl ester phase; (ß3) work up the glycerol phase to obtain crude glycerol.

7. The process according to claim 6, wherein the crude glycerol phase comprises ia) 70 to 97% by weight of glycerol, ib) 1 to 15% by weight of water, ic) 1 to 10% by weight of salts, and also id) 0.1 to 20% by weight of glycerol, water and salts

Impurities, wherein the sum of the components ia) to id) is 100 wt .-%;

8. The method of claim 7, wherein the bottom product obtained in step ii) iia) 10 to 59 wt -.% Glycerol, üb) 0 to 1 wt .-% water, iic) 40 to 70 wt .-% salts, and iid) 1 to 30% by weight of glycerol, water and salts contain various impurities, the sum of the components iia) to iid) being 100% by weight,

9. The method according to any one of claims 6 to 8, wherein the salt and glycerol-containing bottom product in process step ii) with at least 10 wt .-% water, based on the total weight of the salt and glycerol-containing bottom product, in Contact is brought.

10. The method according to any one of the preceding claims, wherein the salt and glycerol-containing bottom product in process step ii) with 0.5 to 5 wt .-% of the acid, based on the total weight of the salt and glycerol-containing bottom product, in Contact is brought.

The process of any one of the preceding claims, wherein the acid is a carboxylic acid or hydroxycarboxylic acid having 2 to 10 carbon atoms.

The method of any one of the preceding claims, wherein the acid is citric acid.

13. The process of any one of the preceding claims, wherein contacting the salt and glycerol-containing bottoms product with the water and the acid is accomplished by mixing the salt and glycerine-containing bottoms product with the water and the acid.

14. The process of any one of the preceding claims, wherein contacting the salt and glycerol-containing bottoms product with the water and the acid is accomplished by mixing the salt and glycerol-containing bottoms product with an aqueous solution comprising water and the acid.

15. A salt and glycerin-containing composition obtainable by a process according to any one of claims 1 to 14.

16. A process for producing a methane-containing gas by fermentative degradation of an organic phase, comprising the steps of:

I) providing a salt and glycerin-containing composition by a method according to any one of claims 1 to 14;

II) optionally mixing this salt and glycerol-containing composition with further organic material; III) anaerobic digestion of the glycerol in the salt and glycerine-containing composition or in the mixture of the salt and glycerol-containing composition and the further organic material to form a methane-containing gas.

17. A methane-containing gas obtainable by a process according to claim 16.

18. A process for the preparation of fatty acid alkyl esters, comprising the process steps:

(γl) providing a composition comprising mono-, di- or triglycerides;

(γ2) transesterification of mono-, di- or triglycerides with alcohol

Formation of a glycerol phase and a fatty acid alkyl ester phase; (γ3) separation of the glycerol phase from the fatty acid alkyl ester phase; (γ4) work-up of the glycerol phase to give crude glycerol; (γ5) Working up the crude glycerol to obtain a salt and glycerin-containing composition by a method according to any one of claims 1 to 14.

19. The process of claim 18 wherein the salt and glycerin-containing composition obtained in step (γ5) is anaerobically submerged

Forming a methane-containing gas is fermented.

20. Use of a salt and glycerin-containing composition, obtainable by a process according to any one of claims 1 to 14, as a biomass for the production of a methane-containing gas.

21. Use of a combination of water and an acid which has a pKa value of at most 5.0, for the treatment of salt and glycerol-containing residues.

Use according to claim 21, wherein the acid is citric acid.