EP2200959A2 - Method for producing 1,2-propandiol by hydrogenating glycerine in at least three successive reactors - Google Patents

Abstract

The invention relates to a method for producing 1,2-propandiol, wherein a flow containing glycerine, in particular a flow produced on an industrial scale during the production of biodiesel, is subjected to hydrogenation in an at least three-step reactor cascade.

Description

 Process for the preparation of 1, 2-propanediol by hydrogenation of glycerol in at least three reactors connected in series

description

The present invention relates to a process for the preparation of 1,2-propanediol in which a glycerol-containing stream, in particular a stream obtained industrially in the production of biodiesel, is subjected to hydrogenation in an at least three-stage reactor cascade.

Dwindling oil supplies and rising fuel prices are generating growing interest in replacing petroleum-based fuels with low-cost and environmentally friendly alternatives. Processes for the production of fuels from biogenic fat- or oil-containing starting mixtures and, for example, used oils and animal fats obtained in restraurants have been known for a long time, with predominantly rapeseed oil being used as starting material in the production of biogenic fuels in Central Europe. Biogenic oils and fats themselves are less suitable as motor fuel, since they must first be cleaned by most complex procedures. These include the removal of lecithins, carbohydrates and proteins, the removal of the so-called oil sludge and the removal of the free fatty acids contained in larger quantities in rapeseed oil, for example. However, vegetable oils processed in this way deviate from the technical properties of conventional diesel fuels in several ways. Thus, they usually have a higher density than diesel fuel, the cetane number of rapeseed oil is lower than that of diesel fuel and the viscosity is many times higher than that of diesel fuel. This leads to an unacceptable deterioration of the fuel properties, such as uneven running behavior of the engine, significantly increased noise emission and due to the higher viscosity to a worse atomization and combustion in the combustion chamber. The use of pure vegetable oils therefore leads to coking in conventional engines, associated with increased particle emission. To solve these problems, it is known to convert the triglycerides (fatty acid esters of glycerol) contained in the biogenic oil and fat starting mixtures into fatty acid monoalkyl esters, in particular methyl or ethyl esters. These esters, also referred to as "biodiesel", can generally be used without major retrofits in diesel engines, with the output of unburned hydrocarbons and soot particles in many cases even being able to be reduced in comparison to normal diesel fuel. In the transesterification of triglycerides for biodiesel production is also glycerol (= 10%), which for reasons of economy as well as the sustainability of a recovery should be supplied. There is therefore a need for effective and economical processes that also make it possible to utilize the glycerol obtained in the production of biodiesel. These processes should in particular also be suitable for the utilization of further commercially available glycerol streams.

No. 2,360,844 describes a process for producing soaps in which a crude glyceride is transesterified with C 1 -C 4 -alkanols and the glycerol released is separated off from the monoalkyl esters. The utilization of the resulting glycerol is not described.

US 5,354,878 describes a process for the preparation of lower alkyl esters of higher fatty acids having a low residual glycerol content by transesterification of fatty acid triglycerides and the use of these esters as diesel fuel.

DE 102 43 700 A1 describes a pressureless process for the preparation of alkyl esters of higher fatty acids, in particular biodiesel, from fatty acid triglyceride starting mixtures containing free fatty acids with a combination of acid esterification and basic transesterification. The glycerol obtained during the transesterification is used in part as an entraining agent in the esterification of the free fatty acids.

It is known to convert higher alcohols by catalytic hydrogenation into lower alcohols. Thus, DE-PS-524 101 describes such a method in which u. a. Glycerol undergoes a gas phase hydrogenation in the presence of a hydrogenation catalyst with hydrogen in substantial excess. Specifically, for the hydrogenation of glycerol with Cr activated copper or cobalt catalysts are used.

DE-PS-541 362 describes a process for the hydrogenation of Polyoxyverbindun- gene, such as. As glycerol, in the presence of catalysts at elevated temperatures above 150 ⁰ C and under elevated pressure. Specifically, the hydrogenation of glycerin with a nickel catalyst at a temperature of 200 to 240 ⁰ C and a hydrogen pressure of 100 atm is described.

R. Connor and H. Adkins describe in J. Am. Chem. Soc. 54, 1932, p. 4678-4690, the hydrogenolysis of oxygen-containing organic compounds, including 98% glycerol, to 1, 2-propanediol in the presence of a copper-chromium-barium oxide catalyst. C. Montassier et al. describe in Bulletin de Ia Societe Chimique de France 1989, no. 2, p. 148-155 studies of the reaction mechanism of the catalytic hydrogenation of polyols in the presence of various metallic catalysts such. Of glycerol in the presence of Raney copper.

J. Chaminand et al. describe in Green Chem. 6, 2004, pp 359-361 the hydrogenation of aqueous glycerol solutions at 180 ⁰ C and 80 bar hydrogen pressure in the presence of supported metal catalysts based on Cu, Pd and Rh.

DE 43 02 464 A1 describes a process for the preparation of 1, 2-propanediol by hydrogenation of glycerol in the presence of a heterogeneous catalyst at pressures of 20 to 300 bar, in particular at 100 to 250 bar and temperatures of 150 ⁰ C to 320 ⁰ C. in which glycerol is passed in vapor or liquid form over a catalyst bed. Catalysts mentioned include, inter alia, Cu chromite, Cu zinc oxide, Cu aluminum oxide and Cu silicon dioxide. The use of glycerol-containing streams from the biodiesel production and measures for the pretreatment of such streams before their use for hydrogenation are not described in this document.

EP 0 523 015 describes a process for the catalytic hydrogenation of glycerol for the preparation of 1, 2-propanediol and 1, 2-ethanediol in the presence of a Cu / Zn

Catalyst at a temperature of at least 200 ⁰ C. In this method, the glycerol is used as an aqueous solution having a glycerol content of 20 to 60 wt .-%, the maximum glycerol content in the embodiments is 40 wt .-%.

WO 2005/095536 describes a low-pressure process for the conversion of glycerol into propylene glycol, in which a glycerol-containing stream having a water content of at most 50 wt .-% at a temperature in the range of 150 to 250 ⁰ C and a pressure in the range of 1 up to 25 bar undergoes catalytic hydrogenation.

MA Dasari et al. describe in Appl. Catalysis A: General 281, 2005, pages 225-231 describes a process for the low pressure hydrogenation of glycerol to propylene glycol at a temperature of 200 ^° C. and a hydrogen pressure of 200 psi (13.79 bar) in the presence of a nickel, palladium, platinum , Copper or copper-chromite catalyst. Different reaction parameters were tested, including the water content of the glycerol used. Although the conversion increased with decreasing water content, the highest selectivity was achieved in this low-pressure process at a water content of 20 wt .-%. No. 5,616,817 describes a process for the preparation of 1,2-propanediol by catalytic hydrogenation of glycerol at elevated temperature and elevated pressure, in which glycerol having a water content of at most 20% by weight in the presence of a catalyst containing 40 to Contains 70 wt .-% cobalt, optionally manganese and / or molybdenum and a low content of copper from 10 to 20 wt .-%, reacted. The temperature is in a range of about 180 to 270 ⁰ C and the pressure in a range of 100 to 700 bar, preferably 200 to 325 bar.

The unpublished PCT / EP2007 / 051983 describes a process for the preparation of 1, 2-propanediol, which comprises a glycerol-containing stream of hydrogenation in the presence of a copper-containing, heterogeneous catalyst at a temperature of 100 to 320 ⁰ C and a pressure of 100 to 325 bar.

The present invention is based on the object to provide an improved process for the preparation of 1, 2-propanediol available. Thus, the known methods are still in need of improvement in terms of the most complete hydrogenation of glycerol with good selectivity with respect to the desired 1, 2-propanediol. In addition, many processes known from the prior art require relatively large amounts of catalyst or have too low a space-time yield. The process according to the invention should also be suitable, in particular, for the further processing of large-scale glycerol streams, as obtained in the transesterification of fatty acid triglycerides for the preparation of alkyl esters of higher fatty acids.

The invention therefore provides a process for the preparation of 1, 2-propanediol, in which

a) provides a glycerol-containing stream, and

b) subjecting the glycerol-containing stream to a continuous hydrogenation in at least three hydrogenation reactors connected in series in the presence of a copper-containing, heterogeneous catalyst.

The hydrogenation product obtained in step b) may optionally be subjected to at least one work-up step (step c)).

According to the invention, the hydrogenation is carried out continuously in n hydrogenation reactors connected in series (in series), where n is an integer of at least 3. Suitable values for n are 3, 4, 5, 6, 7, 8, 9 and 10. Preferably, n is 3 to 6 and especially 3.

The reactors used for the hydrogenation in step b) can independently of one another have one or more reaction zones within the reactor. The reactors may be the same or different reactors. These can be z. B. each have the same or different mixing characteristics and / or be subdivided by internals one or more times.

Suitable pressure-resistant reactors for the hydrogenation are known to the person skilled in the art. These include the commonly used reactors for gas-liquid reactions, such as. B. tube reactors, tube bundle reactors, gas circulation reactors, bubble columns, loop apparatus, stirred tank (which can also be designed as stirred tank cascades), air-lift reactors, etc.

The process according to the invention using heterogeneous catalysts can be carried out in fixed bed or suspension mode. The fixed bed mode can be z. B. in sump or in trickle run. The catalysts are preferably used as shaped bodies, as described in the fol lowing, z. In the form of pressed cylinders, tablets, pastilles, carriage wheels, rings, stars or extrudates, such as solid strands, poly-lobar strands, hollow strands, honeycomb bodies, etc.

In the suspension mode, heterogeneous catalysts are also used. The heterogeneous catalysts are usually used in a finely divided state and are finely suspended in the reaction medium before.

Suitable heterogeneous catalysts and processes for their preparation are described in more detail below.

In the hydrogenation on a fixed bed, a reactor is used, in the interior of which a fixed bed is arranged, through which the reaction medium flows. The fixed bed can be formed from a single or multiple beds. Each bed may have one or more zones, wherein at least one of the zones contains a material active as a hydrogenation catalyst. Each zone can have one or more different catalytically active materials and / or one or more different inert materials. Different zones may each have the same or different compositions. It is also possible to provide several catalytically active zones, for example are separated by inert beds. The individual zones may also have different catalytic activity. For this purpose, various catalytically active materials can be used and / or at least one of the zones an inert material can be added. The reaction medium which flows through the bed contains according to the invention at least one liquid phase. The reaction medium may also contain a gaseous phase in addition.

As reactors in the hydrogenation in suspension are in particular loop apparatuses, such as jet loops or propeller loops, stirred tank, which can also be configured as Rührkesselkaskaden, bubble columns or air-lift reactors are used.

Preferably, the continuous hydrogenation in step b) takes place in at least three fixed bed reactors connected in series (in series). The reactors are preferably operated in direct current. The feeding of the feed streams can be done both from above and from below.

In the hydrogenation, the glycerol and the resulting 1, 2-propanediol are preferably in the liquid phase.

The temperature in the hydrogenation in step b) is generally about 150 to 250 ^° C., in particular 160 to 230 ^° C., in all reactors.

If desired, in the case of a hydrogenation apparatus comprising n reactors, at least two of the reactors (ie, 2 to n of the reactors) may have a different temperature from each other. In a specific embodiment, each downstream reactor is operated at a higher temperature than the previous reactor. In addition, each of the reactors may have two or more different temperature reaction zones. Thus, for example, in a second reaction zone another, preferably a higher, temperature than in the first reaction zone or in each subsequent reaction zone a higher temperature than in a preceding reaction zone can be set, for. B. to achieve the fullest possible conversion in the hydrogenation. In a hydrogenation of three reactors z. B. the first reactor about 170 to 178 ⁰ C, the second at about 179 to 183 ⁰ C and the third at about 184 to 190 ⁰ C operated.

The reaction pressure in step b) is preferably in all reactors generally about 30 to 300 bar, more preferably 60 to 250 bar, in particular 140 to 250 bar. If desired, in the case of a hydrogenation apparatus comprising n reactors, at least two of the reactors (ie, 2 to n of the reactors) may have a different pressure from each other. In a specific embodiment, each downstream reactor is operated at a higher pressure than the previous reactor.

The feeding of the hydrogen required for the hydrogenation can be carried out in the first and optionally additionally in at least one other Rector. Preferably, the feed of hydrogen takes place only in the first reactor. The amount of hydrogen fed to the reactors results from the amount of hydrogen consumed in the hydrogenation reaction and the amount of hydrogen optionally discharged with the exhaust gas. The molar ratio of hydrogen to glycerol is preferably 1: 1 to 500: 1, especially 1, 1: 1 to 100: 1. Preferably, the hydrogen is used in a stoichiometric excess of about 2 to 25 mol%, more preferably 5 to 15 mol%. %, based on glycerol used.

The catalyst loading in continuous operation is preferably 0.05 to 1, particularly preferably 0.1 to 0.5 kg, in particular 0.1 to 0.3 kg of glycerol to be hydrogenated per kg (catalyst) per h.

The setting of the reacted in the respective reactor glycerol content can, for. B. on the reactor volume and / or the residence time in the reactor. The conversion in the first reactor, based on the glycerol contained in the glycerol-containing stream, is preferably at least 60%, more preferably at least 70%. The total glycerol in step b), based on that in the glycerol-containing

Current contained glycerol is preferably at least 97%, more preferably at least 98%, in particular at least 99%.

For removing the heat of reaction arising during the exothermic hydrogenation, one or more of the reactors may be provided with at least one cooling device. In a specific embodiment, at least the first reactor is provided with a cooling device. The heat of reaction can be removed by cooling an external recycle stream or by internal cooling in at least one of the reactors. For internal cooling, it is possible to use the customary devices, generally hollow-body modules, such as field tubes, tube coils, heat exchanger plates, etc. Alternatively, the reaction can also be carried out in a cooled tube bundle reactor. The hydrogenation in step b) is preferably carried out in n hydrogenation reactors connected in series, n being an integer of at least three, and at least one reactor having an external circulation stream from the reaction zone (external recycle stream, liquid recycle, loop). driving style). Preferably, n stands for three.

The hydrogenation in step b) preferably takes place in n hydrogenation reactors connected in series, where n is preferably three, and the first to (n-1). Reactor has a guided in an external circuit current from the reaction zone.

The hydrogenation in step b) preferably takes place in n hydrogenation reactors connected in series, n preferably being three, and the reaction being carried out adiabatically in the nth reactor (the last reactor through which the reaction mixture to be hydrogenated is flowed).

The hydrogenation in step b) preferably takes place in n hydrogenation reactors connected in series, where n is preferably three, and the n. Reactor is operated in a straight pass.

If the hydrogenated reaction mixture in one of the reactors downstream of the first reactor (ie the second to nth reactor) has only small amounts of hydrogenatable glycerol, then the heat of reaction which occurs during the reaction is insufficient to maintain the desired temperature in the reactor. It may also be necessary to heat the reactor (or individual reaction zones of the second reactor). This can be done analogously to the previously described removal of the heat of reaction by heating an external circulation stream or by internal heating. In a suitable embodiment, the heat of reaction from at least one of the previous reactors can be used to control the temperature of a reactor.

Furthermore, the heat of reaction removed from the reaction mixture can be used to heat the feed streams of the reactors. This can z. B. the Glycerinzulaufstrom in the first reactor at least partially mixed with an external recycle stream of this reactor and the combined streams are then fed into the first reactor. Furthermore, when m = 2 to n reactors, the feed stream from the (m-1) -th reactor in the mth reactor can be mixed with a recycle stream from the mth reactor and the combined streams then into the mth reactor be guided. Furthermore, the Glycerinzulaufstrom and / or another feed stream can be heated by means of a heat exchanger, which is operated with withdrawn Hydrierwärme. In a special embodiment of the process, a reactor cascade of n reactors connected in series is used, the reaction being carried out adiabatically in the nth (nth) reactor. This term is understood in the context of the present invention in the technical and not in the physicochemical sense. Thus, the reaction mixture as it flows through the second reactor generally undergoes a temperature increase due to the exothermic hydrogenation reaction. Adiabatic reaction is understood to mean a procedure in which the amount of heat liberated during the hydrogenation is taken up by the reaction mixture in the reactor and no cooling by cooling devices is used. Thus, the reaction heat is removed with the reaction mixture from the second reactor, except for a residual portion which is discharged by natural heat conduction and heat radiation from the reactor to the environment. Preferably, the nth reactor is operated in a straight pass.

For the hydrogenation in step b), preference is given to using a three-stage reactor cascade, the first and the second hydrogenation reactor having a stream flowing out of the reaction zone in an external circuit. In a specific embodiment of the process, a reactor cascade of three reactors connected in series is used, the reaction being carried out adiabatically in the third reactor.

In one embodiment, additional mixing can take place in at least one of the reactors used. Additional mixing is particularly advantageous if the hydrogenation takes place at high residence times of the reaction mixture. For mixing z. B. the currents introduced into the reactors are used by introducing them via suitable mixing devices, such as nozzles, in the respective reactors. For the purpose of mixing, it is also possible to use streams in an external circuit from the respective reactor.

To complete the hydrogenation of the first to (n-1) th reactor is taken from a discharge, which still contains hydrogenatable glycerol and fed into the respective downstream hydrogenation reactor. In a specific embodiment, the discharge is separated into a first and a second partial flow, the first partial flow being recirculated to the reactor from which it was withdrawn and the second partial flow being supplied to the downstream reactor. The discharge may contain dissolved or gaseous portions of hydrogen. In a specific embodiment, the discharge from the first to (n-1) th reactor is a phase separation vessel fed, separated into a liquid and a gaseous phase, the liquid phase separated into the first and the second partial stream and the gas phase at least partially fed separately to the subsequent reactor. In an alternative embodiment, the discharge from the first to (n-1) th reactor is fed to a phase separation vessel and separated into a first liquid hydrogen-depleted substream and a second hydrogen-enriched substream. The first part-stream is then fed back into the reactor as a cycle stream, to which it has been taken off and the second part-stream is fed to the subsequent reactor (as a glycerol- and hydrogen-containing feed). In a further alternative embodiment, the feed of the second to nth reactor with hydrogen is not carried out via a hydrogen-containing feed taken from the upstream reactor, but with fresh hydrogen via a separate feed line.

Preferred is an embodiment of the method step b), in which one

b1) feeds a glycerol-containing feed and hydrogen into the first reactor of a reaction system, which consists of n-1 reactors with a current conducted in an external circuit and an n-th downstream reactor, and in the presence of a copper-containing, converts heterogeneous catalyst to a partial conversion,

b2) takes a discharge from each of the first to (n-1) th reactor, which contains hydrogen, glycerol and 1, 2-propanediol,

b3) separates the discharge into a first liquid hydrogen-depleted substream and a second hydrogen-enriched substream,

b4) the first partial flow after removal of part of the heat contained in the

Returns the reactor from which it was taken,

b5) feeds the second partial stream into the respective subsequent reactor and further reacted in the presence of a copper-containing, heterogeneous catalyst.

The process variant described above is particularly advantageous for controlling the reaction temperature and the heat transfer between the reaction medium, limiting apparatus walls and environment. Another way to control the heat balance is to control the inlet temperature of the glycerol-containing feed. Thus, a lower temperature of the incoming feed usually leads to an improved removal of the heat of hydrogenation. When easing the Catalyst activity, the inlet temperature can be set higher to achieve a higher reaction rate and thus to compensate for the decreasing catalyst activity. Advantageously, as a rule, the service life of the catalyst used can be extended.

The first partial stream is generally recycled chemically unchanged into the reaction system. If desired, the temperature and / or pressure may be adjusted to the desired values prior to recycling. The feed of the first partial stream into the reactor from which it was taken off can take place together with the glycerol-containing feed or separately therefrom. The ratio by weight of first partial stream (recycle stream) fed into a reactor to glycerol-containing feed (feed stream) is preferably in the range from 1: 1 to 50: 1, more preferably from 2: 1 to 30: 1.

In a special embodiment, heat is also withdrawn from the second partial stream before it enters the subsequent reactor. For this purpose, a conventional heat exchanger can be used, which makes it possible to use the amount of heat recovered elsewhere in the process again.

FIG. 1 shows the schematic representation of a three-stage reactor cascade suitable for carrying out the hydrogenation process, wherein, for reasons of clarity, the reproduction of such details is omitted which are not relevant for the explanation of the invention. The plant comprises three hydrogenation reactors (1), (1 1) and (19). The hydrogenation reactors (1) and (11) are designed as circulation reactors and the hydrogenation reactor (19) as an adiabatic flow tube reactor. Hydrogen gas is introduced under pressure into the reactor (1) via the pipeline (2), and a glycerol-containing stream is introduced into the reactor (1) via the pipeline (3). Via the pipe (4) and the pump (7), a discharge from the reactor (1) is removed, fed to the phase separation vessel (5) and separated into a liquid phase and a gaseous phase. The liquid phase obtained in the phase separation vessel (5) is separated into a first and a second substream. The first partial stream (6) is cooled in the heat exchanger (8) and mixed as a circulating stream with the feed stream (3) and fed back to the reactor (1). The second partial stream (9) is fed to the second reactor (11). The gas phase obtained in the phase separation vessel (5) is fed as stream (10) to the second reactor (11) separately. Via the pipe (4a) and the pump (14), a discharge from the reactor (11) is removed, fed to the phase separation vessel (12) and separated into a liquid phase and a gaseous phase. The liquid phase obtained in the phase separation vessel (12) is separated into a first and a second substream. The first partial flow (13) becomes cooled in the heat exchanger (15) and mixed as a circulating stream with the feed stream (9) and fed to the reactor (1 1) again. The second partial stream (16) is cooled in the heat exchanger (18) and fed to the third reactor (19). The gas phase obtained in the phase separation vessel (12) is fed separately as stream (17) to the second reactor (19). As shown, the phase separation vessels (5) and (12) can be made separately or, alternatively, integrated into the reactors (1) and / or (11). The hydrogenation product leaves the reactor (19) via the pipeline (20).

FIG. 2 shows the schematic representation of an alternative embodiment of a three-stage reactor cascade suitable for carrying out the hydrogenation process. The plant comprises three hydrogenation reactors (1), (10) and (17). The hydrogenation reactors (1) and (10) are designed as circulation reactors and the hydrogenation reactor (17) as an adiabatic flow tube reactor. Hydrogen gas is introduced into the reactor (1) via the pipeline (2) under pressure, and a glycerol-containing stream is introduced into the reactor (1) via the pipeline (3). Via the pipe (4) and the pump (7), a discharge from the reactor (1) is removed and fed to the phase separation vessel (5). The liquid phase obtained in the phase separation vessel (5) is cooled in the heat exchanger (8) and mixed as a circulating stream with the feed stream (3) and returned to the reactor (1). In the phase separation vessel (5), a further stream (9) is separated, which contains gaseous and liquid components and fed via a separate line to the reactor (10). Via the pipe (4a) and the pump (13), a discharge from the reactor (10) is removed and fed to the phase separation vessel (11). The liquid phase obtained in the phase separation vessel (11) is cooled in the heat exchanger (14) and mixed as a circulating stream with the feed stream (9) and returned to the reactor (10). In the phase separation vessel (1 1), another stream (15) is separated, the gaseous and liquid fractions containing and fed via a separate line to the reactor (17). The hydrogenation product leaves the reactor (17) via the pipe (18).

In principle, all glycerol-containing streams are suitable for use in the process according to the invention, including those from industrially practiced processes and with the resulting purity grades. These include in particular glycerol-containing streams from the processing of oil and / or fatty starting materials, eg. Preferably, the glycerol-containing stream provided in step a) is a glycerol-containing stream obtained in the production of alkyl esters of higher fatty acids by transesterification of fatty acid triglycerides, such as, in particular in the production of "biodiesel" is obtained. This embodiment of the method according to the invention will be described in more detail below. The glycerol-containing stream used in step a) preferably has a water content of at most 30% by weight, preferably of at most 20% by weight. Particularly preferred is a water content corresponding to the glycerol monohydrate (water content 16.3 wt .-%) or less. In a specific embodiment, a glycerol-containing stream is used, which is essentially anhydrous. By "substantially anhydrous" in the context of the present invention, a water content of at most 3 wt .-%, particularly preferably at most 1 wt .-% understood. The use of glycerol-containing streams having a water content in the range of up to 30% by weight, in particular up to 20% by weight, makes it possible to produce 1,2-propanediol in high yields and with high selectivity in the temperature and pressure range used for the hydrogenation , The hydrogenation of glycerol-containing streams which are not substantially anhydrous and in particular streams which have a higher water content than the glycerol monohydrate is also possible with high yields and selectivities, but less economical due to the reduced space-time yield. Nevertheless, a water content in the range of 3 to 30 wt .-% may be advantageous for the rheological properties during the hydrogenation. A specific embodiment of the process according to the invention therefore relates to the use of glycerol-containing streams having a water content in the range from 3 to 30% by weight, preferably from 5 to 20% by weight, for reducing the viscosity in the hydrogenation.

The glycerol-containing streams may, instead of or in addition to water, comprise at least one further, preferably glycerol-miscible (and thus as a rule also water-miscible) organic solvent. The glycerol-containing streams provided in step a) preferably have a total solvent content of at most 20% by weight, more preferably at most 15% by weight, in particular at most 10% by weight and especially at most 5% by weight. If solvent mixtures are used which contain water and at least one glycerol or water-miscible organic solvent, then the proportion of the organic

Solvent preferably at most 50 wt .-%, more preferably at most 20 wt .-%, based on the total weight of the solvent. Suitable glycerine-miscible organic solvents are C 1 -C 4 -alkanols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, polyols and mono- and dialkyl ethers thereof, cyclic ethers, such as dioxane and tetrahydrofuran, etc Suitable solvents are also aromatic hydrocarbons, such as benzene, toluene or the xylenes. Preferred organic solvents are C 1 -C 4 -alkanols, in particular methanol and / or ethanol, and mixtures thereof with water. However, the glycerol-containing streams used in step a) preferably have no organic solvents. The glycerol-containing streams provided in step a) may be subjected to at least one work-up step. This includes z. B. at least one cleaning step to remove unwanted components. This also includes a reduction in the content of water and / or, if present, organic solvents.

Depending on their origin, the glycerol-containing streams may still contain inorganic salts as an undesired component. These can be removed from the crude glycerol according to the work-up procedures described below. In particular, thermal workup is suitable for this purpose (eg using a Sambay evaporator).

Depending on their origin, the glycerol-containing streams may also contain catalyst poisons, i. H. Components which interfere with hydrogenation by deactivating the hydrogenation catalyst included. These include z. For example, nitrogen-containing compounds such as amines, and sulfur-containing compounds such as sulfuric acid, hydrogen sulfide, thio alcohols, thioethers, z. Dimethylsulfide and dimethyl disulfide, carbonyl sulfide, amino acids, e.g. B. sulfur and additional nitrogen-containing amino acids, fatty acids and their salt, etc. The catalyst poisons continue to include halogen compounds, traces of common extraction agents, eg. As acetonitrile or N-methylpyrrolidone, etc. and optionally organic phosphorus and arsenic compounds. A catalyst poison frequently contained in glycerol-containing streams from oil and fat refinement is sulfuric acid, which is used as catalyst in the esterification or transesterification.

For working up the glycerol-containing streams in step a), for. As a thermal workup, preferably a distillation, adsorption, ion exchange, a membrane separation process, crystallization, extraction or a combination of two or more of these methods are used. Membrane separation processes using membranes of defined pore sizes are particularly suitable for reducing the water content and / or for salt removal. Crystallization is also understood to mean the partial freezing of the glycerol-containing streams on cooled surfaces. Thus, impurities can be removed that accumulate in the solid phase.

In a first embodiment, the glycerol-containing stream in step a) is subjected to a distillation to reduce the water content and / or to remove components which impair the catalytic hydrogenation. This can basically be in accordance with customary distillation methods known to the person skilled in the art. Suitable apparatus for distillative workup include distillation columns, such as tray columns, which may be equipped with bells, sieve plates, sieve trays, packings, random packings, valves, side draws, etc. Evaporators, such as thin-film evaporators, falling-film evaporators, forced-circulation evaporators, Sambay

Evaporator, etc. and combinations thereof. The removal of sulfuric acid is already possible by a simple distillation, in particular a short path distillation.

Suitable separation methods are described in the following documents: Sattler, Klaus: Thermal Separation Methods, 3rd Edition, Wiley VCH, 2001; Schlünder E.U., Thurner F .: Distillation, Absorption, Extraction, Springer Verlag, 1995; Mersmann, Alfons: Thermal Process Engineering, Springer Verlag, 1980; Grassmann P., Widmer F .: Introduction to Thermal Process Engineering, de Gruyter, 1997; White S., Militzer K. -E., Grammer K .: Thermal Process Engineering, Dt. Verlag für Grundstoffindustrie, Leipzig, Stuttgart, 1993. Reference is made to these documents.

In a further embodiment, the glycerol-containing stream in step a) is subjected to a reduction in the content of sulfur-containing compounds, especially sulfur-containing aromatic compounds, a catalytic desulfurization, optionally in the presence of hydrogen. Suitable desulfurizing agents include a metal component, which metal is preferably selected from metals of Groups 6, 7, 8, 9, 10, 11 and 12 of the Periodic Table. Preferably, the metals are selected from Mo, Ni, Cu, Ag, Zn, and combinations thereof. Suitable further components of the desulfurization agents are dopants. The metal component may be used in oxidic form, reduced form or a mixture containing oxidized and reduced components. The active component of the desulfurizing agent (metal component (s) and optional dopant (s)) may be applied to a support. Suitable carriers are in principle the adsorbents and catalyst carriers mentioned below. Preferably, the support material is selected from activated charcoal, graphite, carbon black, Al 2 O 3, Si 2 O, TiO 2, ZrO 2, SiC, silicate, zeolites, clays (eg bentonites) and combinations thereof. The application of at least one metal component and optionally further components to a carrier material can be carried out by known methods, for. By (Co) precipitation or impregnation. The desulfurization can be used as a molded body, z. In the form of pressed cylinders, tablets, pastilles, wagon wheels, rings, stars or extrudates, such as solid strands, poly-lobar strands, hollow strands and honeycomb bodies or other geometric bodies. Unsupported desulfurizing agents may be removed by conventional methods. be formed, z. By extruding, tableting, etc. The shape of supported desulfurizing agent is determined by the shape of the carrier.

For catalytic desulfurization, it is preferable to use a desulfurizing agent containing copper and zinc in an atomic ratio of 1: 0.3 to 1:10, preferably 1: 0.5 to 1: 3, more preferably 1: 0.7 to 1: 1 , 5, contains. Preference is given to using a desulphurising agent which comprises 35 to 45% by weight of copper oxide, 35 to 45% by weight of zinc oxide and 10 to 30% by weight of aluminum oxide. In a specific embodiment, the desulfurizing agent is a component capable of being used as a hydrogenation catalyst in step b). In this regard, reference is made to the following disclosure for hydrogenation catalysts of the aforementioned composition and methods for their preparation.

In one embodiment of this process variant, the glycerol-containing streams are brought into contact with the desulfurizing agent in at least one desulfurization zone and then hydrogenated in at least one reaction zone.

It will be understood by those skilled in the art that the specific design and arrangement of the desulfurization and reaction zone (s) may be in any known manner. It is possible to arrange the desulfurization and reaction zone (s) spatially separated, i. H. structurally separate from one another by means of the apparatus configuration or also to be realized in one or more common desulfurization / hydrogenation zone (s).

The copper-zinc desulfurizing agent may, for. B. obtained by a conventional precipitation or co-precipitation and used in oxidized as well as in reduced form.

In a particular embodiment, the copper-zinc desulfurizing agent contains at least copper, zinc and aluminum, wherein the copper: zinc: aluminum atomic ratio ranges from 1: 0.3: 0.05 to 1: 10: 2, preferably 1: 0.6: 0.3 to 1: 3: 1 and especially 1: 0.7: 0.5 to 1: 1, 5: 0.9.

For conversion to the reduced form, it is possible to subject the desulfurizing agent to a hydrogen reduction. This is carried out at about 150 to 350 ⁰ C, preferably at about 150 to 250 ⁰ C, in the presence of hydrogen, wherein the hydrogen by an inert gas such. As nitrogen, argon, methane, in particular nitrogen, is diluted, so that the hydrogen content is 10 vol .-% or less, preferably 6 vol .-% or less, in particular 0.5 to 4 vol .-%, is. That so obtained copper-zinc desulfurizing agent ("reduced form") can be used in this form in the desulfurization.

In one embodiment, the desulfurization of the glycerol-containing stream is carried out on the copper-zinc desulfurizing agent in oxidized form without the addition of hydrogen.

In a further embodiment, the desulfurization of the glycerol-containing stream is carried out on the copper-zinc desulfurizing agent in oxidized form in the presence of hydrogen.

In a further embodiment, the desulfurization of the glycerol-containing stream is carried out on the copper-zinc desulfurizing agent in reduced form without the addition of hydrogen.

In another embodiment, the desulfurization of the glycerol-containing stream on the copper-zinc desulfurizing agent is carried out in reduced form in the presence of hydrogen.

Usually, the desulfurization is in a temperature range of 40 to

200 ⁰ C, especially at 50 to 180 ⁰ C, in particular at 60 to 160 ⁰ C, preferably at 70 to 120 ⁰ C, at a pressure of 1 to 40 bar, especially at 1 to 32 bar, preferably at 1, 5 bis 5 bar, in particular at 2.0 to 4.5 bar performed. The desulfurization can in the presence of inert gases such. As nitrogen, argon or methane, are performed. In general, however, the desulfurization is carried out without the addition of inert gases.

Usually, if desired, hydrogen is used here with a purity of ≥99.8% by volume, in particular of ≥99.9% by volume, preferably of ≥99.95% by volume. These degrees of purity apply analogously to the hydrogen which is used in the optionally carried out activations of the catalysts.

Usually, the weight ratio of glycerol-containing stream to hydrogen is in the range of 40,000: 1 to 1,000: 1, especially in the range of 38,000: 1 to 5,000: 1, in particular in the range of 37,000: 1 to 15,000: 1, preferably in the range of 36,000: 1 to 25,000: 1, especially in the range of 35,000: 1 to 30,000: 1. The thus desulfurized glycerol-containing stream generally has a content of sulfur-containing impurities, especially of aromatic sulfur compounds, of at most 70 ppb, preferably of at most 50 ppb, and the total sulfur content is in total <200 ppb, preferably <150 ppb, in particular <100 ppb.

The desulfurizing agents described above also make it possible to reduce or remove chlorine, arsenic and / or phosphorus or corresponding chlorine-, arsenic- and / or phosphorus-containing compounds from the aromatic hydrocarbon or the mixture of aromatic hydrocarbons.

In another embodiment, the glycerol-containing stream is contacted with at least one adsorbent in step a) to remove components which interfere with the catalytic hydrogenation.

The adsorbents preferably have a specific surface area, determined by BET, in the range from 10 to 2000 m ² / g, more preferably in the range from 10 to 1500 m ² / g, in particular in the range from 10 to 400 m ² / g, especially in Range from 60 to 250 m ² / g.

Suitable adsorbents are z. B. active aluminas. Their preparation takes place for. B. starting from aluminum hydroxide, which is obtainable by conventional precipitation of aluminum salt solutions. Active aluminas suitable for the process according to the invention are also obtainable starting from aluminum hydroxide gels. For the preparation of such gels z. Example, precipitated aluminum hydroxide after conventional work-up steps, such as filtering, washing and drying, activated and then optionally ground or agglomerated. If desired, the resulting alumina may then be subjected to a shaping process, such as extrusion, granulation, tabletting, etc. Suitable adsorbents are preferably the Selexsorb ™ grades from Alcoa.

Suitable adsorbents are also alumina-containing solids. These include z. As the so-called clays, which also have aluminum oxides as the main component.

Further suitable adsorbents are aluminum phosphates.

Further suitable adsorbents are silicas, the z. B. by dehydration and activation of silica gels are available. Another method for preparing silica is the flame hydrolysis of silicon tetrachloride, wherein by suitable variations of the reaction parameters, such. As the stoichiometric composition of the educt mixture and the temperature, the desired surface properties of the resulting silica can be varied within wide ranges.

Further suitable adsorbents are diatomaceous earth, which also have silicas as their main constituent. This includes z. As the diatomaceous earth obtained from silica sediments.

Further suitable adsorbents are titanium dioxides and zirconium dioxides, as z. In Römpp, Chemie-Lexikon, 9th edition (paperback), Vol. 6, p. 4629f. and pp. 5156f. and the literature cited therein. This is hereby fully incorporated by reference.

Further suitable adsorbents are phosphates, in particular condensed phosphates, such as. As melting or annealing phosphates, which have a large active surface area. Suitable phosphates are, for. In Römpp, Chemie-Lexikon, 9th edition (paperback), Vol. 4, p. 3376f. and the literature cited therein. This is hereby fully incorporated by reference.

Further suitable adsorbents are carbonaceous adsorbents, preferably activated carbon. Activated carbon is generally understood to mean carbon with a porous structure and a high internal surface area. For the production of activated carbon are plant, animal and / or mineral carbonaceous raw materials, eg. B. with dehydrating agents such as zinc chloride or phosphoric acid, heated or charred by dry distillation and then activated by oxidation. This can be z. B. treat the charred material at elevated temperatures of about 700 to 1000 ⁰ C with water vapor, carbon dioxide and / or mixtures thereof.

It is also possible to use ion exchangers and / or adsorber resins.

The adsorbents are preferably selected from titanium dioxides, zirconium dioxides, silicium dioxides, diatomaceous earth, aluminas, alumina-containing solids, aluminum phosphates, natural and synthetic aluminosilicates, phosphates, carbonaceous adsorbents and mixtures thereof.

The adsorbents generally have a specific surface area, determined by BET, in the range of about 10 to 2000 m ² / g, in particular in the range of 10 to 1500 m ² / g and especially in the range of 20 to 600 m ² / g , For the adsorptive removal of undesired components, in particular components which impair the catalytic hydrogenation, the glycerol-containing stream is brought into contact with at least one adsorption agent in step a) in an adsorption zone.

In a specific embodiment, an adsorbent is used which contains at least one component which is also capable of being used as hydrogenation catalyst in step b). The hydrogenation catalysts described in more detail below are hereby incorporated by reference in their entirety. Combinations of two or more than two adsorbents are also suitable for use as adsorbents. In this case, both exclusively as hydrogenation catalysts capable components, not suitable as hydrogenation adsorbents and combinations thereof are used exclusively.

In a preferred embodiment, the same component is used as adsorbent and as hydrogenation catalyst. If appropriate, one additionally uses one or more further conventional adsorbents other than the hydrogenation catalyst, as described above.

In one embodiment of the method, the glycerol-containing streams are brought into contact with the adsorbent in at least one adsorption zone and then hydrogenated in at least one reaction zone.

It will be understood by those skilled in the art that the specific configuration and arrangement of the adsorption and reaction zone (s) may be in any known manner. It is preferable to arrange the adsorption and reaction zone (s) spatially separated from each other, that is, to separate the adsorption and reaction zones (n). H. structurally separated from each other by the apparatus design.

If one uses different adsorbents, z. B. a first adsorption zone in a first reactor, which contains a first adsorbent, and separately, so separated by equipment, z. B. in a second reactor, a second adsorption zone containing a second adsorbent. Here, the first and / or the second adsorbent may contain at least one component capable of being used as a hydrogenation catalyst.

In another embodiment, a conventional adsorbent is combined with an adsorbent capable of hydrogenation in a single embodiment Adsorption zone, z. B. in layered form, mixed in the form of a random distribution or in the form of a gradient bed. The use in mixed form optionally allows better control of the temperature. In the case of a gradient bed, linear and non-linear gradients can be used. It may be advantageous in this case to carry out the distribution within the bed such that the glycerol-containing stream to be hydrogenated is first brought into contact with the conventional adsorbent before it is brought into contact with the adsorbent capable of hydrogenation.

Advantageously, at least two adsorption zones will be arranged so that the glycerol-containing stream to be hydrogenated in the first adsorption zone is contacted with a conventional adsorbent and contacted in the second adsorption zone with an adsorbent containing at least one component capable of use as a hydrogenation catalyst becomes.

The glycerol-containing streams provided in step a) of the process according to the invention are preferably derived from the production of biodiesel. In the context of the present invention, "biodiesel" is understood as meaning a mixture of fatty acid monoalkyl esters which can be obtained from biogenic oil and / or fat-containing starting mixtures and used as fuel in diesel engines.

In principle, all available biogenic oil and / or fat-containing starting mixtures are suitable for providing the glycerol-containing stream. Oils and fats are generally solid, semi-solid or liquid fatty acid triglycerides, especially from vegetable and animal sources, which consist essentially of glycerol esters of higher fatty acids chemically. Suitable higher fatty acids are saturated or mono- or polyunsaturated fatty acids having preferably 8 to 40, particularly preferably 12 to 30 carbon atoms. These include z. N-nonanoic acid, n-decanoic acid, n-undecanoic acid, n-tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, melissinic acid, palmitoleic acid, oleic acid, linoleic acid, linolenic acid, stearic acid, Elaostearic acid, etc.

Vegetable fats and oils are essentially based on straight-chain fatty acids, whereas animal fats and oils may also contain odd-carbon fatty acids in free or triglyceride-bound form. The unsaturated fatty acids found in vegetable fats and oils are in the cis form, while animal fatty acids are often transconfigured. To provide the glycerol-containing stream in step a), it is possible in principle to use used or unused, unpurified or purified vegetable, animal or industrial oils or fats or mixtures thereof. These parts of other ingredients, eg. As free fatty acids. The proportion of free fatty acids is generally 0% to 50%, z. B. 0.1 to 20%, of the starting mixture used for the transesterification of the fatty acid triglycerides. If desired, free fatty acids can be removed before or after the transesterification of the fatty acid triglycerides. Salts of these fatty acids (e.g., the alkali salts) may be previously purified by acidification with a strong acid, e.g. As HCl, are transferred to the free acid. The separation of the free fatty acids succeeds z. B. by centrifugation. Preferably, the free fatty acids contained in the starting mixture are also converted into the alkyl esters. This can be done before, during or after the transesterification of the fatty acid triglycerides.

To provide the glycerol-containing stream in step a) suitable used fats and oils are fat and / or oil-containing components, which after their extraction from corresponding biogenic starting materials for other purposes, eg. As for technical purposes or purposes of food production, have been used and which are chemically modified or unmodified as a result of this use or additional ingredients that are particularly related to this use may have. If desired, these may be at least partially removed by transesterification prior to use to provide the glycerol-containing stream. For the provision of the glycerol-containing stream in step a) suitable unused fats and oils are fat or oil-containing components which, after their recovery from the corresponding vegetable or animal starting materials have not yet been put to any other purpose and which therefore have only ingredients derived from the starting materials or related to the extraction from the starting materials. From these starting materials, too, ingredients other than fatty acid triglycerides (and optionally free fatty acids) may, if desired, be at least partially removed by transesterification prior to use to provide the glycerol-containing stream.

For purification and / or enrichment, the unused or used fats or oils may be subjected to the removal of undesired ingredients such as lecithins, carbohydrates, proteins, oil sludge, water, etc.

Vegetable oils and fats are those which are predominantly derived from vegetable raw materials such as seeds, roots, leaves or other suitable plants. parts of the origin. Animal fats or oils are predominantly derived from animal feedstocks such as animal organs, tissues or other body parts or body fluids such as milk. Technical oils and fats are those obtained in particular from animal or vegetable raw materials and processed for technical purposes. The used or unused, unrefined or purified oils and / or fats used according to the invention are in particular selected from the group consisting of soapstock, brown grease, yellow grease, technical tallow, technical lard, frying oils, animal fat, edible tallow, vegetable crude oils, animal crude oils or greases or mixtures thereof.

"Soapstock" is understood to mean a by-product obtained in the processing of vegetable oils, in particular a by-product of edible oil refineries based on soybean, rapeseed or sunflower oil. Soapstock has a content of free fatty acids of about 50% to 80%.

By "Brown Grease" is meant an animal fat-containing waste product having a content of free fatty acids of more than 15% to 40%. "Yellow Grease" contains about 5% to 15% free fatty acids.

"Technical tallow" and "technical lard" are animal fats that are manufactured for technical purposes and obtained by the dry or wet-melt process, for example, from slaughterhouse waste. Technical Tallow are evaluated and traded according to their acid number, the content of free fatty acids depending on the origin z. B. between 1 and 20 wt .-%, such as in the range of 1 to 15 wt .-% is. However, the content of free fatty acids may be more than 20 wt .-%.

The "animal fats" include in particular in the recovery of poultry, beef, pork, fish and marine mammal bodies sloping fatty products, such as solar stearin, a solid residue that remains after pressing lard oil from lard.

The provision of the glycerol-containing stream in step a) is preferably carried out from vegetable crude oils as starting material. This can be based on unrefined vegetable crude oils, ie of liquid or solid compositions consisting of vegetable raw materials such. B. obtained by pressing, where they have not undergone treatment other than settling in common time periods and centrifuging or filtering, in which for the separation of the oil of solid components only mechanical forces such as gravity, centrifugal force or pressure are used. Such unrefined vegetable crude oils may also be obtained by extraction of vegetable oils, if their properties are not or only slightly different from the corresponding obtained by pressing vegetable oils. The proportion of free fatty acids in unrefined vegetable fats and oils is different and is z. B. at about 0 to 20%, such as. B. 0.1 to 15%.

Of course, the vegetable oils may be subjected to one or more workup steps prior to their use for transesterification, as described in more detail below. Thus, purified vegetable oils, for example, raffinates or semi-refined, of the abovementioned vegetable oils can also be used as starting materials.

Preferably, to provide the glycerol-containing stream in step a) a vegetable oil or fat is used, which is preferably selected from rapeseed oil, palm oil, rapeseed oil, soybean oil, sunflower oil, corn oil, cottonseed oil, palm kernel and coconut fat and mixtures thereof. Particular preference is given to using rapeseed oil or a rapeseed oil-containing mixture.

Suitable for providing the glycerol-containing stream in step a) is also animal oil or fat, which is preferably selected from milk fat, wool fat, beef tallow, lard, fish oils, fish oil, etc., and mixtures thereof. These animal fats or oils can also be subjected to one or more processing steps before they are used for transesterification, as described in more detail below.

Preferably, the provision of the glycerol-containing stream in step a) comprises the following steps:

a1) provision of a biogenic fat and / or oil-containing starting mixture,

a2) transesterifying the fatty acid triglycerides present in the starting mixture with at least one C 1 -C 9 -monoalcohol and optionally esterifying the free fatty acids contained in the starting mixture to form an esterification mixture, a3) separating the esterification mixture to obtain at least one fraction enriched in biodiesel and at least one fraction enriched in the esterification of released glycerol,

a4) optionally purifying the glycerol-enriched fraction.

Step a1)

The provision of the biogenic fat and / or oil-containing starting mixture in step a1) comprises in a preferred embodiment at least one purification step. For purification, the fat and / or oil-containing starting mixture at least one commonly used cleaning method for fats and oils, such as clarification, filtration, treatment with bleaching earths or treatment with acids or alkali to remove interfering impurities such as proteins, phosphatides and mucilage and a combination of at least be subjected to two of these purification steps.

Step a2)

For transesterification of the fatty acid triglycerides is preferably at least one

Ci-Cg monoalcohol, in particular at least one Ci-C4 monoalcohol used. Preference is given to the use of methanol or ethanol.

The transesterification of the fatty acid triglycerides can be catalyzed acidic or preferably catalytically. Suitable acids are, for example, mineral acids such as HCl, H ₂ SO ₄ or H ₃ PO ₄ .

Preferably, at least one base is used as the catalyst. This is preferably selected from among alkali hydroxides, such as NaOH and KOH, alkaline earth hydroxides, such as Ca (OH) ₂ , alkali metal and alkaline earth d-Ce alkoxaten, such as NaOCH ₃ , KOCH ₃ ,

Na (OCH ₂ CH ₂ ) and Ca (OCH ₂ CH ₂ ) ₂ and mixtures thereof. Particularly preferably, very particularly preferably used NaOH, KOH or NaOCH _3, NaOCH _third

The amount of base used is usually in the range from 0.1 to 10% by weight, in particular from 0.2 to 5% by weight, based on the amount of fatty acid triglycerides used.

The base is preferably used in the form of an aqueous or alcoholic, particularly preferably alcoholic, solution. Advantageously, one uses as Lö- For the base, the solvent already used for the alcoholysis of the triglycerides. Preferably, a NaOCH3 solution in methanol is used for transesterification.

The transesterification is preferably carried out at a temperature of about 20 to 150 ⁰ C, in particular 30 to 95 ⁰ C.

The transesterification takes place in customary, known to those skilled devices. After a suitable execution, the transesterification takes place continuously. The transesterification preferably takes place in at least one column, the resulting transesterification mixture being simultaneously subjected to a separation. In this case, a higher-boiling phase is generally obtained, which is enriched in the basic catalyst, unreacted monoalcohol and the glycerol formed in the transesterification and obtains a lower-boiling phase which is enriched in the transesterification product. If the transesterification product does not contain transesterified triglycerides, these can likewise be separated off and subjected to renewed transesterification in the first or a further transesterification stage.

Subsequently, the last transesterification mixture is transferred to a drying plant, again removing residual amounts of water. After drying in the drying device, the desired end product is biodiesel in purified form and can be used directly as a fuel.

If the fat and / or oil-containing starting mixture used to provide the glycerol-containing stream in step a) contains free fatty acids, these may preferably be subjected to esterification for conversion into biodiesel-suitable esters.

The free fatty acids are preferably transesterified with the same d-Cg monoalcohol used to transesterify the fatty acid triglycerides. The esterification of free fatty acids can take place before, during or after the transesterification of the fatty acid triglycerides. In a preferred embodiment, the esterification of free fatty acids takes place before the transesterification of the fatty acid triglycerides.

The esterification of the free fatty acids can be basic or preferably acid catalysed. Suitable acids are the aforementioned mineral acids, such as HCl, H 2 SO 4 or H 3 PO 4, p-toluenesulfonic acid, etc. The esterification is preferably carried out at a temperature of about 20 to 95 ⁰ C, in particular 40 to 80 ⁰ C. The esterification takes place in customary, known to those skilled devices. These include stirred tank and / or columns, which are optionally connected to cascades. Preferably, the esterification of the free fatty acids takes place in at least one esterification unit designed as a column, the resulting esterification mixture being simultaneously subjected to a separation. In a suitable embodiment, the esterification is carried out in the presence of an entraining agent to facilitate the separation.

Step a3)

During or after the transesterification and / or esterification, the esterification mixture is subjected to separation to obtain at least one fraction enriched in d-Cg monoalkyl esters and at least one fraction enriched in glycerol released in the transesterification. The separation is preferably carried out by distillation according to customary methods known to the person skilled in the art. Suitable distillation apparatuses are those mentioned above.

Step a4)

The glycerol-enriched fraction obtained after separating the esterification mixture in step a3) may optionally be subjected to at least one work-up step. These include, for example, the removal of undesired components, such as salts, as well as components which impair the catalytic hydrogenation or the separation of water and, if present, organic solvent. Full reference is made to the previous comments on these work-up steps.

The catalysts used in the process according to the invention may be unsupported catalysts or supported catalysts. They can be used in the form of uniformly composed catalysts, impregnated catalysts, coated catalysts and precipitation catalysts.

In principle, a plurality of copper-containing catalysts are suitable, which additionally at least one further element of the I., II., III., IV or V. main group, the I., II., IV., V., VI., VII VIII. Subgroup and the lanthanides may contain (IUPAC: groups 1 to 15 and the lanthanides), in particular Ca, Mg, Al, La, Ti, Zr, Cr, Mo, W, Mn, Ni, Co, Zn and combinations thereof. A specific embodiment of catalysts which are particularly advantageously suitable for use in the process according to the invention are skeletal or metal sponge catalysts, which are referred to as "Raney catalysts". These include especially Raney copper and copper-containing metal alloys in the form of a Raney catalyst. Preference is given to Raney catalysts whose metal component consists of at least 95%, in particular at least 99%, of copper. Methods for the preparation of Raney catalysts are known in the art and z. In DE-A-43 35 360, DE-A-43 45 265, DE-A-44 46 907 and EP-A-842 699. Raney copper can be prepared in a manner known per se by treating copper-aluminum alloys with alkali metal hydroxides. A suitable for use in the process according to the invention Raney catalyst is z. B. obtainable by preparing a mixture of at least one copper-containing catalyst alloy and at least one binder, wherein the catalyst alloy comprises copper and optionally at least one further catalytically active catalyst metal and a leachable alloy component, optionally with the addition of humectants and / or additives such as shaping aids, lubricants , Plasticizers and / or pore formers, homogenizing this mixture and shaping to the desired shaped body, calcining the shaped body and activating the catalyst precursor thus obtained by partial or complete leaching of the leachable alloy component and optionally final washing of the finished catalyst.

A further specific embodiment of catalysts which are particularly advantageous for use in the process according to the invention are catalysts which contain copper in oxidic form and optionally additionally in elemental form. The hydrogenation catalyst used in step b) then preferably contains at least 23 wt .-%, more preferably at least 35 wt .-%, copper in oxidic and / or elemental form, based on the total weight of the catalyst.

A frequently used process for the preparation of such catalysts is the impregnation of support materials with solutions of the catalyst components, which are then converted by thermal treatment, decomposition or reduction in the catalytically active state.

Another suitable method for the preparation of catalysts comprises the precipitation of a catalyst component or the co-precipitation of two or more than two catalyst components. Thus, for the preparation of a shaped catalyst body, a copper compound, optionally at least one further Metal compound and / or an additive can be precipitated and then subjected to drying, quenching and shaping. The precipitation can be carried out in the presence of a carrier material. Suitable starting materials for the precipitation are metal salts and metal complexes. In principle, all known Cu (I) and / or Cu (II) salts which are soluble in the solvents used for application to the support can be used as copper compounds for the precipitation. These include z. As nitrates, carbonates, acetates, oxalates or ammonium complexes. In a preferred embodiment, copper nitrate is used. The catalytic active component of the catalyst, apart from a copper compound, further elements as additives, for. As metals, non-metals and their compounds. These are preferably metals of groups 4 to 15 and the lanthanides. Particularly preferred metals are La, Ti, Zr, Cu, Mo, W, Mn, Re, Co, Ni, Cu, Ag, Au, Zn, Sn, Pb, As, Sb and Bi. Preferably, an aqueous medium is used for the precipitation ,

Suitable aqueous media are substances or mixtures which are liquid under the process conditions and which contain at least 10% by weight, particularly preferably at least 30% by weight, in particular at least 50% by weight, of water. The portion other than water is preferably selected from inorganic or organic compounds which are at least partially soluble in water or at least partially miscible with water. For example, the compounds other than water are selected from organic solvents, such as C 1 -C 20 -alkanols, in particular methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, penthanols and hexanols, C 8 -cycloalkyl ethers, such as tetrahydrofurans, pyrans, dioxanes and trioxanes, C 1 -C 12 -dialkyl ethers, such as dimethyl ether, dibutyl ether and methyl butyl ether. The aqueous medium preferably contains less than 40% by weight, more preferably less than 30% by weight and in particular less than 20% by weight of organic solvents. In a preferred embodiment of the process according to the invention, the aqueous medium is substantially free of organic solvents.

The precipitation may be carried out by known methods, e.g. B. cooling a saturated solution, adding a precipitant, etc. induced. Suitable precipitants are for. As acids, bases, reducing agents, etc.

The precipitate may be induced by adding an acid or a base to the aqueous medium containing the copper compound and optionally further compounds. Suitable acids are mineral acids such as HCl, H2SO4 and H3PO4. The base is preferably selected from metal oxides, metal hydroxides, in particular in particular alkali metal hydroxides, such as sodium hydroxide and potassium hydroxide, metal carbonates, in particular alkali metal and alkaline earth metal carbonates, such as lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate and calcium carbonate, nitrogen bases, in particular ammonia and primary, secondary and tertiary amines.

Examples of suitable reducing agents are carboxylic acids, such as formic acid, citric acid, lactic acid, tartaric acid and especially salts of carboxylic acids, preferably the alkali metal, alkaline earth metal, ammonium and C 1 -C 10 -alkylammonium salts, phosphorous or hypophosphorous acid, the salts of phosphorous or hypophosphorous acid, in particular the alkali metal or alkaline earth metal salts, C 1 -C 10 -alkanols, such as methanol, ethanol and isopropanol, sugars, such as aldoses and ketoses in the form of monosaccharides, disaccharides and oligosaccharides, in particular glucose, fructose and lactose, aldehydes, such as For aldehyde, boron-hydrogen compounds, such as borohydrides, boranes, metal borohydrates and borane complexes, such as diborane, sodium borohydride and aminoboranes, in particular trimethylaminoborane, hydrazine and alkylhydrazines, such as methylhydrazine, hydrogen dithionites and dithionites, especially sodium and potassium hydrogendithionite, sodium, Potassium and zinc dithionites, hydrogen sulfides and S ulfides, in particular sodium and potassium hydrogen sulfides, sodium-potassium and calcium sulfides, hydroxylamine and urea, and mixtures thereof.

For the hydrogenation z. As catalysts containing on a support of silica nickel and copper, among other metals as active ingredients. Such catalysts are z. B. in DE-A 26 28 987 described. The active material of these catalysts contains specifically 40 to 80 wt .-% nickel, 10 to 50 wt .-% copper and 2 to 10 wt .-% manganese.

EP-A-0 434 062 describes hydrogenation catalysts obtainable by reduction of a precursor of oxides of copper, aluminum and at least one other metal selected from magnesium, zinc, titanium, zirconium, tin, nickel and cobalt.

Also suitable are the hydrogenation catalysts described in DE 102 18 849, which contain 0.1 to 10% by weight of chromium, calculated as Cr ₂ O ₃ , 0.1 to 10% by weight of calcium, calculated as CaO _x and 5 to 20 wt .-% copper, calculated as CuO, deposited on a silica support material and in each case based on the total weight of the calcined catalyst included. Copper-zirconium oxide catalysts are known from DE-A-40 21 230, the ratio of copper atoms to zirconium atoms, expressed as a weight ratio, being 1: 9 to 9: 1.

DE-A-4 028 295 describes copper-manganese hydrogenation catalysts.

EP-A-552463 describes in a first embodiment hydrogenation catalysts, wherein the oxidic form substantially corresponds to the composition Cu _a AlbZr _c MndOχ, wherein the following relationships apply: a>0;b>0; c ≥ 0; d>0;a> b / 2; b> a / 4; a>c;a>d; and x denotes the number of oxygen ions required to maintain electroneutrality per formula unit. According to a further embodiment, the catalyst according to the invention contains a smaller proportion of aluminum oxide. The catalyst according to this embodiment essentially corresponds to the composition Cu _a AlbZr _c MndOχ, the following relationships apply: a>0; a / 40 <b <a / 4; c>0;d>0;a>c; 0.5d <a <0.95d and x denotes the number of oxygen ions required to maintain electroneutrality per formula unit.

WO 2006/005505 describes shaped catalyst bodies which are particularly suitable for use in the process according to the invention. These can be produced by a process in which

(i) an oxide material comprising copper oxide, alumina and at least one of the oxides of lanthanum, tungsten, molybdenum, titanium or zirconium, wherein the oxides of lanthanum and / or tungsten are to be preferred, is provided,

(ii) powdered metallic copper, copper flakes, powdered cement or mixtures thereof or a mixture thereof with graphite may be added to the oxidic material, and

(iii) the mixture resulting from (ii) to a catalyst tablet or a catalyst extrudate with a diameter d and / or a height h <6.0 mm, catalyst balls with a diameter d <6.0 mm or catalyst honeycomb body with a Cell diameter rz <6.0 mm is deformed.

Of the oxides of lanthanum, tungsten, molybdenum, titanium or zirconium, lanthanum oxide is preferred. The composition of the oxide material is generally such that the proportion of copper oxide is in the range of 40 to 90 wt .-%, the proportion of oxides of lanthanum, tungsten, molybdenum, titanium or zirconium in the range of 0 to 50 wt .-% and the proportion of aluminum oxide in the range up to 50 wt .-%, each based on the total weight the sum of the abovementioned oxidic constituents, wherein these three oxides together represent at least 80% by weight of the oxidic material after calcination, whereby cement is not attributed to the oxidic material in the above sense.

In a preferred embodiment, the oxide material comprises

(a) copper oxide in a proportion in the range of 50 <x <80 wt .-%, preferably 55 <x ≤ 75 wt .-%,

(b) alumina having a content in the range of 15 <y <35 wt%, preferably 20 <y ≤ 30 wt%, and

(C) at least one of the oxides of lanthanum, tungsten, molybdenum, titanium or zirconium, preferably of lanthanum and / or tungsten, with a content in the range of 2 <z <20 wt .-%, preferably 3 <z <15 wt. -%

in each case based on the total weight of the oxidic material after calcination, where: 80 <x + y + z <100, especially 95 <x + y + z <100.

Preferred catalysts include the following metals in oxidic form, reduced form (elemental form) or a combination thereof. Metals that are stable in more than one oxidation state can be used completely in one of the oxidation states or in different oxidation states:

Cu

Cu ₁ Ti Cu, Zr

Cu, Mn

Cu ₁ Al

Cu, Ni, Mn

Cu, Al, at least one other metal selected from La, W, Mo, Mn, Zn, Ti, Zr, Sn, Ni, Co

Cu, Zn, Zr

Cu, Cr, Ca

Cu, Cr, C

Cu, Al, Mn, optionally Zr Particularly preferred catalysts include the following metals:

Cu Cu, Ti Cu ₁ Al Cu, Al, La Cu, Al, Zn Cu, Zn, Zr Cu ₁ Al ₁ Mn Cu, Cr, C

As an inert support material for the catalysts of the invention, virtually all support materials of the prior art, as they are advantageously used in the preparation of supported catalysts, for example SiC "2 (quartz), porcelain, magnesium oxide, tin dioxide, silicon carbide, TiO 2 (rutile, anatase) Al2O3 (alumina), aluminum silicate, steatite (magnesium silicate), zirconium silicate, cerium silicate or mixtures of these support materials are preferred support materials are aluminum oxide and silicon dioxide. pyrogenic silicas or wet-chemically prepared silicas, such as silica gels, aerogels or precipitated silicas, are used for catalyst preparation (for the preparation of the various SiO 2 starting materials see: W. Buchner, R. Schliebs, G. Winter, KH Buchel: Industrial Inorganic Chemistry, 2nd ed., Pp. 532-533, VCH Verlagsgesellschaft, Weinheim 1986).

The catalysts can be used as shaped bodies, for. B. in the form of spheres, rings, cylinders, cubes, cuboids or other geometric bodies. Unsupported catalysts can be formed by conventional methods, e.g. By extruding, tableting, etc. The shape of supported catalysts is determined by the shape of the support. Alternatively, the support may be subjected to a molding process before or after application of the catalytically active component (s). The catalysts may, for. B. in the form of pressed cylinders, tablets, pastilles, carriage wheels, rings, stars or extrudates, such as solid strands, polylobären strands, hollow strands and honeycomb bodies or other geometric bodies are used.

The catalyst particles generally have an average of the (largest) diameter of 0.5 to 20 mm, preferably 1 to 10 mm. These include z. Eg cat lysatoren in the form of tablets, z. B. with a diameter of 1 to 7 mm, preferably 2 to 6 mm, and a height of 3 to 5 mm, rings with z. B. 4 to 7 mm, preferably 5 to 7 mm, outer diameter, 2 to 5 mm in height and 2 to 3 mm hole diameter, or strands of different lengths of a diameter of z. B. 1, 0 to 5 mm. Such forms can in a known per se manner

Tabletting, extrusion or extrusion can be obtained. For this purpose, the catalyst composition customary auxiliaries, for. For example, lubricants such as graphite, polyethylene oxide, celluloses or fatty acids (such as stearic acid), and / or molding aids and reinforcing agents, such as fibers of glass, asbestos or silicon carbide, are added.

A specific embodiment of supported catalysts are shell catalysts. Shell catalysts are also particularly suitable for the process according to the invention. Shelled catalysts comprise a cup-shaped catalytic mass applied to a carrier. They can be in the form of spheres, rings, cylinders, cubes, cuboids or other geometric bodies. Regardless of the nature and composition of the catalytically active material, the provision of coated catalyst particles can in principle be accomplished by contacting the support with a liquid binder and the catalytically active composition, thereby applying a layer of the composition to the support, and then optionally the binder partially removed. In this case, to provide the catalyst particles, the catalytically active material is already applied in its finished catalytically active form, for example as a calcined mixed oxide. Suitable processes for the preparation of coated catalysts are, for. For example, in DE-A-29 09 671 and in EP-A-714 700 described. According to the latter method, the support is first moistened with the liquid binder, then adhered to the surface of the moistened support body by contacting with dry, finely divided, active catalyst mass a layer of active catalyst mass and then optionally partially removed the liquid binder. In a specific embodiment, the steps of wetting the carrier, contacting the catalyst mass and removing the liquid binder are repeated one or more times until the desired layer thickness of the coated catalyst is reached.

Another specific embodiment of supported catalysts are catalysts prepared by impregnation. For this purpose, the catalytically active catalyst components or precursor compounds thereof can be applied to the support material. In general, for impregnating the support material aqueous salt solutions of the components, for. As aqueous solutions of their halides, sulfates, nitrates, etc. applied. The copper component may, for. Example, in the form of an aqueous solution of their amine complex salts, for example as [Cu (NH ₄ ) ₄ ] SO ₄ - or as [Cu (NH3) 4] (NO3) 2 solution, optionally in the presence of sodium carbonate, onto the support material. Of course, other copper amine complexes than those exemplified may be used with equal success for catalyst preparation.

The impregnation of the support material with the precursor compounds of the catalytically active components can in principle be carried out in one or more stages. The impregnation can be carried out in conventional impregnating devices, e.g. Impregnated drums. After drying and / or calcination, the finished catalyst is then obtained. The drying of the impregnated catalyst form body can continuously or batchwise, for. B. in band or Hordenöfen done. The drying can be carried out at atmospheric pressure or reduced pressure. Furthermore, the drying in a gas stream, for. As an air stream or a stream of nitrogen, take place. Depending on the applied pressure, the drying is generally carried out at temperatures of 50 to 200 ⁰ C, preferably 80 to 150 ⁰ C. The calcination of the optionally previously dried catalyst is generally carried out at temperatures of 200 to 800 ⁰ C, preferably 500 to 700 ⁰ C. The calcination, like the drying, continuously or batchwise, z. B. in band or Hordenöfen performed. The calcination may be carried out at atmospheric or reduced pressure and / or in a gas stream, e.g. B. in an air or a hydrogen stream. Pre-treatment with hydrogen or hydrogen-containing gases generally under conditions which correspond to the hydrogenation conditions serves to pre-reduce / activate the hydrogenation catalyst. However, the catalyst can also be reduced in situ under the conditions predetermined during the hydrogenation, preferably under pressure (for example at a hydrogen pressure of about 100 to 325 bar).

The hydrogenation discharge consists essentially of 1,2-propanediol. Other ingredients include methanol, ethanol, n-propanol, isopropanol, 1, 3-propanediol, glycerol, ethylene glycol and water. The hydrogenation discharge can then be worked up by customary methods known to the person skilled in the art. For example, thermal processes, preferably distillative processes, adsorption, ion exchange, membrane separation processes, crystallization, extraction or a combination of two or more of these processes are suitable for this purpose. Preferably, the hydrogenation is worked up by distillation. Suitable for this purpose are customary distillation processes known to the person skilled in the art. Suitable apparatus for the work-up by distillation comprise distillation columns, such as tray columns, which may be provided with bells, sieve plates, sieve trays, packings, internals, valves, side draws, etc. Particularly suitable are dividing wall columns which are equipped with side drawers, return ments, etc. may be provided. For distillation, a combination of two or more than two distillation columns can be used. Also suitable are evaporators, such as thin film evaporators, falling film evaporators, Sambay evaporators, etc., and combinations thereof. Glycerol still present in the hydrogenation effluent can, if appropriate after distillative separation, be recycled to the hydrogenation stage.

The invention will be further illustrated by the following non-limiting examples.

Examples

example 1

FIG. 2 shows the schematic representation of the three-stage reactor cascade used for carrying out the hydrogenation process according to Example 1, wherein for the sake of clarity, the reproduction of such details is omitted, which are not relevant for the explanation of the invention. In all three reactors, the catalyst is an oxidic material comprising CuOo, 6-o, 85 (AbOs) O, 1-0.34 (La2θ3) o, oi-o, 2 and which, based on the total weight of the oxide Materials, up to 20% may contain adjuvants. The reactor (1) contains 100 ml, the reactor (10) 75 ml and the reactor (17) 70 ml of catalyst. The catalyst is reduced in the hydrogen stream before the hydrogenation reaction. As feed stream (3), pure glycerin is mixed with water in a mass ratio of glycerol to water of 9: 1. The reaction parameters are shown in Table 1.

Table 1

K. B. = catalyst loading

RÜFÜ = liquid return (circulation) The analysis of the starting material glycerol and the reaction output is carried out by gas chromatography (data in GC area%).

Device: HP5890-2 with sample sampler

Range: 2

Column: 30 m ZB5; Film thickness 0.2 mm

Sample volume: 0.2 μl

Carrier gas: helium

Flow rate: 100 ml / min

Injector temperature: 290 ⁰ C

Detector: FID

Detector temperature: 300 ⁰ C temperature program: 150-280 ⁰ C with 15 ° C / min; Total running time 10 min

Table 2: Analysis of the Pharmaglycerin

Table 3: GC analysis of the reactor discharges

Claims

claims

1. A process for the preparation of 1, 2-propanediol, in which

a) provides a glycerol-containing stream, and

b) subjecting the glycerol-containing stream of a continuous hydrogenation in at least three hydrogenation reactors connected in series in the presence of a copper-containing, heterogeneous catalyst.

2. The method of claim 1, wherein the hydrogenation in step b) takes place in three hydrogenation reactors connected in series.

3. The method according to any one of the preceding claims, wherein the hydrogenation is carried out in all hydrogenation reactors at a temperature in the range of 150 to 250 ⁰ C.

4. The method according to any one of the preceding claims, wherein the hydrogenation in all hydrogenation reactors at a pressure in the range of 30 to 300 bar, preferably in the range of 60 to 250 bar occurs.

5. The method according to any one of the preceding claims, wherein the Gesamtglyce- rinumsatz in step b), based on the glycerol contained in the glycerol flow, at least 97%, preferably at least 98%, in particular at least 99%.

6. The method according to any one of the preceding claims, wherein the hydrogenation in

Step b) at least three successive fixed bed reactors are used.

7. The method according to any one of the preceding claims, wherein the hydrogenation in

Step b) takes place in n hydrogenation reactors connected in series, where n is an integer of at least three, and wherein at least one reactor has a stream in the external reaction zone from the reaction zone.

8. The method according to any one of the preceding claims, wherein the hydrogenation in

Step b) takes place in n successive hydrogenation reactors, where n is for is an integer of at least three, and the 1st to (n-1). Reactor has a guided in an external circuit current from the reaction zone.

9. The method according to any one of the preceding claims, wherein the hydrogenation in step b) takes place in n successive hydrogenation reactors, wherein n is an integer of at least three, and wherein the reaction in the n. Reactor is performed adiabatically.

10. The method according to any one of the preceding claims, wherein the hydrogenation in step b) takes place in n successive hydrogenation reactors, wherein n is an integer of at least three, and wherein the n. Reactor is operated in a straight pass.

1 1. The method according to any one of the preceding claims, wherein the feed of hydrogen takes place only in the first reactor.

12. The method according to any one of the preceding claims, wherein in process step b)

b1) in the first reactor of an n-stage reaction system, which consists of n-1 reactors with a current conducted in an external circuit and a nth downstream operated in straight-through reactor, a glycerol-containing feed and hydrogen and feeds in the presence of a copper-containing , heterogeneous catalyst converts to a TeN conversion,

b2) takes a discharge from each of the first to (n-1) th reactor, which contains hydrogen, glycerol and 1, 2-propanediol,

b3) separates the discharge into a first liquid hydrogen-depleted substream and a second hydrogen-enriched substream,

b4) returns the first substream after removal of a portion of the heat contained in the reactor from which it was taken,

b5) feeds the second partial stream into the respective subsequent reactor and further reacted in the presence of a copper-containing, heterogeneous catalyst.

13. The method according to any one of the preceding claims, in which one provides in step a) in the production of alkyl esters of higher fatty acids by transesterification of fatty acid triglycerides resulting glycerol-containing stream.

14. The method according to any one of claims 1 to 13, wherein the glycerol-containing stream has a water content of at most 30 wt .-%, preferably of at most 20 wt .-%, having.

15. The method according to any one of claims 1 to 13, wherein the glycerol-containing stream is substantially anhydrous.

16. The method according to any one of the preceding claims, wherein in step a) the glycerol-containing stream is subjected to a work-up by at least one processing method which is selected under thermal work-up,

Adsorption, ion exchange, membrane separation, crystallization, extraction or a combination of two or more of these methods.

17. The method according to any one of the preceding claims, wherein in step a) the glycerol-containing stream of a distillation for reducing the water content and / or for removing components which impair the catalytic hydrogenation subject.

18. The method according to any one of the preceding claims, wherein in step a) the glycerol-containing stream for reducing the content of sulfur-containing

Compounds, especially sulfur-containing aromatic compounds, a catalytic desulfurization, optionally in the presence of hydrogen, subjected.

A process according to any one of the preceding claims, wherein in step a) the glycerol-containing stream is contacted with at least one adsorbent to remove components which interfere with the catalytic hydrogenation.

20. The method of claim 19, wherein the adsorbent contains at least one component capable of use as a hydrogenation catalyst in step b).

21. The method according to any one of the preceding claims, wherein the provision of the glycerol-containing stream in step a) comprises the following steps: a1) provision of a biogenic fat and / or oil-containing starting mixture,

a2) transesterifying the fatty acid triglycerides present in the starting mixture with at least one C 1 -C 9 -monoalcohol and optionally esterifying the free fatty acids contained in the starting mixture to form an esterification mixture,

a3) separating the esterification mixture to obtain at least one fraction enriched in C 1 -C 4 -alkyl monoesters and at least one fraction enriched in glycerol released during the transesterification,

a4) optionally purifying the glycerol-enriched fraction.