DE102010053290A1 - Method and apparatus for producing hydrogen from glycerin - Google Patents

Abstract

The invention relates to a method and a device for generating hydrogen, in which an insert (1) containing glycerol and salts is processed into an intermediate product (4), from which a pyrolysis gas (6) is obtained by pyrolysis (P), which is subsequently described in a hydrogen product (7) is implemented. The pyrolysis gas (6) is fed to a membrane reformer (M) as an insert, from which hydrogen (7) is withdrawn in product purity.

Description

The invention relates to a process for the production of hydrogen, wherein a glycerol and salt-containing feed is treated to form an intermediate from which a pyrolysis gas is obtained by pyrolysis and subsequently converted into a hydrogen product.

Furthermore, the invention relates to a device for carrying out the method according to the invention.

In the following, pyrolysis is to be understood as meaning the thermal decomposition of organic material in the optional presence of water but excluding a further gasification agent (eg air, O ₂ , CO ₂ ), as described in the specialist publication Pyrolysis of Waste ( KJ Thomé-Kozmiensky, EF-Verlag 1985, p. 4ff ) is defined.

In the effort to reduce the carbon dioxide input into the earth's atmosphere, or at least not to increase it further and as alternatives to dwindling reserves of oil and natural gas, in the future more and more energy sources will be produced from renewable raw materials. Biodiesel plays an outstanding role here and is already added to the diesel fuel available at German filling stations today in a concentration of up to five percent.

Biodiesel is a standardized fuel, which is mainly derived from rapeseed oil, but also from other vegetable oils and fats. Vegetable oils and fats are composed of triglycerides, d. H. Fatty acids, each of which is bound to three glycerol. This structure has the consequence that vegetable oils and fats are viscous to solid at normal ambient temperatures, ie have a much higher viscosity than the fuels for which a commercial diesel engine is designed. Vegetable oils and fats behave differently during the injection process, and the combustion also runs less cleanly. These disadvantages can also be compensated only imperfectly by motor interventions - such as the preheating of the vegetable oil.

Biodiesel is made from vegetable oils and fats by replacing glycerine with methanol. Its viscosity corresponds to that of commercial diesel fuel, which is why it can be easily burned in unmodified diesel engines.

The separated from the vegetable oils and fats in the biodiesel production glycerol is not recovered in pure form, but falls as part of mixtures containing glycerol in addition to larger amounts of impurities. Such a substance mixture is, for example, so-called crude glycerol which has a glycerol content of 80-85%, but also contains even larger amounts of water and salts, residues from the production process (eg solvents and catalyst residues) and other organic components which are commonly used as MONG (Material Organic Non Glycerol). According to the prior art, the crude glycerol is purified in elaborate process steps by vacuum distillation, deodorization and filtration to the extent that it meets the strict requirements of the European Pharmacopeia (European Pharmacopeion), with a purity of at least 99.5% as a pharmaceutical glycerol to the pharmaceutical industry to be delivered. At present, all of the amount of glycerol accumulated in biodiesel production can be recovered in this way. With the foreseeable expansion of biodiesel production, however, this will become more and more difficult in the future, so that there is a need to search for other ways of using crude glycerine.

In order to economically utilize crude glycerine, several patent applications of the Applicant ( DE 10 2007 022 962 . DE 10 2007 060 166 ) Discloses methods and devices of the generic type. For the preparation of the crude glycerol, a separation of undesired substances from the crude glycerol preceding the pyrolysis, for example by thermal drying or vacuum distillation, is proposed here. Furthermore, the DE 10 2007 045 360 the Applicant to take a process in which a pyrolysis is performed so that residues formed in a use of crude glycerol can be continuously withdrawn.

To produce a hydrogen product from the crude glycerol, beat DE 10 2007 022 962 and DE 10 2007 060 166 suggest that the pyrolysis gas generated in the pyrolysis is reacted by steam reforming. Steam reforming is a process that has been known for many years, in which, in particular, short-chain hydrocarbons, such as, for example, methane or naphtha, are reacted together with water vapor with catalytic support in a reaction space to give carbon oxides and hydrogen. The temperature in the reaction space is typically between 800 and 950 ° C, while the pressure is 15 to 40 bar. Essentially, in steam reforming, a reforming and a shift reaction proceed according to the following reaction equations: C _n H _m + _n H ₂ O ⇔ n CO + (m / 2 + 2n) H ₂ (1) CO + H ₂ O⇔CO ₂ + H ₂ (2)

Usually, the reaction space is arranged in a heatable reactor tube, which of outside, the energy required for the overall strongly endothermic reforming process is supplied. At one end, the educts (carbonaceous feed and steam) are introduced into the reactor tube, while at the other end of a product gas containing hydrogen and carbon monoxide is withdrawn. If the recovery of a hydrogen product is the actual goal of the process, then a water gas shift follows, in which carbon monoxide is converted with water to hydrogen and carbon dioxide. The hydrogen product must then be separated from the gas mixture generated in the water gas shift, for example by pressure swing adsorption.

The object of the present invention is to provide a method of the generic type and a device for carrying it out, which make it possible to produce hydrogen, in particular from incurred in the production of biodiesel, glycerol by-products with less effort than is possible in the prior art ,

The stated object is achieved according to the method according to the invention in that the pyrolysis gas is fed to a membrane reformer as an insert, is withdrawn from the hydrogen in product purity.

A membrane reformer is to be understood as meaning an apparatus which comprises a reaction space in which a catalyst suitable for carrying out a steam reforming is arranged and which is delimited by a membrane which is selectively hydrogen-permeable at least in sections. Hydrogen formed in the steam reforming can be continuously withdrawn from the reaction space via the membrane with high purity and be continued as a hydrogen product without a further purification step. The removal of the hydrogen from the reaction space is connected to the product side with a shift in equilibrium of the reactions (1) and (2) taking place there. Compared to a conventional steam reformer thereby increases the hydrogen yield while reducing carbon monoxide formation. The patent applications EP0167101 and WO2010000375 enter as membrane reactors designed as membrane reformers containing the selectively hydrogen-permeable membrane in the form of one or more tubes whose axes are arranged parallel to the reactor axis. Preferably, such a membrane reformer designed as a tubular reactor is used to carry out the process according to the invention.

By removing the hydrogen from the reaction space and the resulting shift of the reaction equilibrium, the steam reforming can be carried out at comparatively low temperatures between 450 and 800 ° C. In order to prevent the selectively hydrogen-permeable portions of the partition, which are preferably made of palladium or a palladium alloy, such as a palladium-gold alloy or a palladium-silver alloy, are damaged by overheating, it is proposed that the hydrogen-permeable partition at temperatures between 450 and 700 ° C is operated.

The driving force in removing the hydrogen is the hydrogen partial pressure difference prevailing between the reaction space and the hydrogen withdrawal side (permeate side) of the selectively hydrogen-permeable membrane. The higher this pressure difference, the greater the hydrogen flow across the membrane. Preferred embodiments of the method according to the invention provide that the steam reforming is carried out at a pressure between 5 and 50 bar (a), preferably between 10 and 30 bar (a), the hydrogen pressure on the permeate side being between 1 and 10 bar ( a), but preferably between 1.5 and 5 bar (a) is set.

As has been shown by experiments, from glycerol and salts containing inserts, such as from crude glycerol, especially salts, which may be harmful in subsequent steps, can be easily and inexpensively separated by thin film evaporation, especially when the thin film evaporation is carried out under vacuum conditions. On the other hand, other components, in particular water and certain MONG constituents, which do not necessarily affect the subsequent process steps, can partly enter the vaporization product (vapors) and thus be converted, for example, into a subsequent pyrolysis device. By choosing suitable temperature and pressure conditions, the distribution of the components between vapors and bottom product can be adjusted specifically. Organic components, which are pyrolyzed together with glycerol, can thus also be utilized for hydrogen production. In the conventional purification for the production of pharmaglycerol, however, corresponding components are separated with energy expenditure and may need to be disposed of at not inconsiderable expense.

In the context of the present application, the evaporation residue containing the salts can be discharged as a highly viscous, volume-reduced liquid from the bottom of the evaporator. The passing water can without much additional energy input in the Pyrolysis subsequent steam reforming process are used. In this case, advantageously, a targeted control of the evaporation conditions can be carried out, so that the desired water content is already adjustable in the treatment step.

Through the use of thin-film evaporation, a purification of the crude glycerol is made possible by the reliable, inexpensive and inexpensive targeted only the undesirable for a downstream thermal process components are removed.

The thin-film evaporation itself is known. The evaporation takes place in a thin-film evaporator out of a thin liquid film. For this purpose, the substance mixture to be separated is distributed via a rotating distributor system from above on the circumference of a cylindrical evaporator and flows downwards on its inner surface. A wiper system ensures an even distribution on the inner surface and for a permanent mixing of the downflowing material.

The evaporator is usually double-walled. For uniform heating of the evaporator surface, a heat transfer medium (eg thermal oil or steam) is passed through the double jacket. Depending on the temperature of the liquid and the operating pressure in the evaporator, the more volatile substances evaporate from the liquid film running downwards. The vapors are conducted upwards in countercurrent to the liquid film.

The operating pressure in thin-film evaporators is generally at an absolute pressure of 1 mbar to 1 bar, ie in the vacuum range up to atmospheric pressure. On the one hand, the thin-film evaporation makes it possible to significantly reduce the evaporation temperatures in comparison to other evaporation processes. On the other hand, the residence time of the mixture fed to the evaporation temperature is very short and is often considerably less than one minute. Due to the low residence time, higher evaporation temperatures can be used without fear of undesirable thermal decomposition processes.

It has been found that in the thin film evaporation of crude glycerol, in contrast to the commonly used temperatures of about 160 ° C with particular advantage a temperature of 170 to 240 ° C, advantageously a temperature of more than 200 ° C, in particular from 200 to 240 ° C, preferably from 200 to 220 ° C can be used without the glycerol shows decomposition processes. The higher evaporation temperatures are also accompanied by a higher evaporation pressure, which can be achieved simply and cost-effectively by means of simplified vacuum devices. Particularly advantageous in this context, an absolute pressure of 10 to 80 mbar has been found.

As a particular advantage of the thin-film evaporation has been shown that by the targeted use of the specified higher evaporation temperatures or pressures a so-called. Wasserflash (ie sudden evaporation of water at pressure drop and formation of aerosols or water droplets) can be avoided. This is the main cause of the formation of saline aerosols that can pass into the distillate, safely eliminated.

For a further purification, in particular for the removal of salts, the evaporation product, ie the vapors generated by the thin-film evaporation, can be purified by at least one washing device, for example a vapor scrubber. Even at high salt loads, a safer process can be achieved without the risk of catalyst damage or corrosion, since the salt transfer is minimized.

In addition to the thin-film evaporation, other techniques are also suitable for the preparation of a glycerol and salts containing use. For example, the use of a vacuum distillation can be subjected, wherein water is distilled off at relatively low temperatures. It makes sense to place a vacuum distillation upstream of the thin-film evaporation in order to relieve it. The invention therefore provides that the use is processed by thin-film evaporation and / or vacuum distillation and / or scrubbing and / or thermal drying and / or filtering via activated carbon or membrane and / or chromatography and / or ion exchange and / or ion exclusion.

In test series it has been shown that the pyrolysis of a correspondingly prepared intermediate to obtain gaseous pyrolysis products at a temperature of 600 to 900 ° C and an absolute pressure of 5 to 40 bar can be made meaningful. The pyrolysis product contains essentially carbon monoxide, methane, hydrogen and carbon dioxide. The pyrolysis conditions mentioned can be optimized by adjusting the temperature, pressure and water content and the type of heat input and thus the residence times so that the formation of solid and liquid products is largely avoided.

Conveniently, the water or water vapor content of the used from the glycerol use-containing intermediate product by adding or removing water or Water vapor adjusted to a value that allows the implementation of a subsequent pyrolysis without soot formation and at the same time minimal energy use. As mentioned, the water or water vapor content can already be preset by adjusting the water content of the insert by predrying or by selecting the evaporation conditions. Another embodiment of the method according to the invention provides that the water required for the pyrolysis in more than one step, before and / or supplied at a suitable point during the pyrolysis step. If the pyrolysis is carried out in several successive steps, the water supply is usefully carried out before each pyrolysis step.

If the intermediate product is supplied to the pyrolysis in liquid form, water is preferably introduced in the form of water vapor, the steam being injected into the intermediate product or the intermediate product into the water vapor. Part of the energy required for the subsequent pyrolysis is already introduced with the steam, which leads to a reduced heating effort in the pyrolysis reactor and to a reduction in the apparatus required for the pyrolysis reactor.

The energy consumption of the process according to the invention is influenced inter alia by the amount of water to be heated in the membrane reformer. The larger this amount of water, the higher the energy requirement. In order to optimize the energy requirement of the process according to the invention, therefore, the use fed to the membrane reformer expediently has only a minimum water content whose size is determined by the subsequent process steps. The minimum water content results from the requirement that soot formation in the membrane reformer is completely suppressed and, at the same time, sufficient water is present for the shift reaction taking place in parallel to the reforming reaction. The water or steam content of the feed supplied to the membrane reformer is therefore expediently adjusted to the minimum water content by addition or removal of water or steam.

Furthermore, the invention relates to a device for generating hydrogen with a treatment device in which a glycerol and pesticide-containing insert can be processed to form an intermediate, a pyrolysis for converting the intermediate into a pyrolysis gas and a device in which a hydrogen product are obtained from the pyrolysis gas can.

According to the invention, the stated object is achieved in that it comprises a membrane reformer to which the pyrolysis gas can be supplied as starting material and can be stripped off from the hydrogen with product purity.

Preferably, the membrane reformer is designed as a tubular reactor containing an at least partially selectively hydrogen-permeable membrane in the form of one or more tubes whose axes are arranged parallel to the reactor axis.

In practice, palladium or palladium alloy membranes have proven suitable for use in membrane reformers. Conveniently, therefore, the selectively hydrogen-permeable portions of the membrane of palladium or a palladium alloy, such as a palladium-gold alloy or a palladium-silver alloy.

At least one catalyst material selected from nickel, platinum, palladium, iron, rhodium, ruthenium and / or iridium may be arranged in the reaction space of the membrane reformer. Advantageously, the catalyst material is a material which is also suitable for the catalytically assisted steam reforming of naphtha or methane.

A preferred embodiment of the device according to the invention provides that the treatment device has a thin-film evaporator with the aid of which the use containing glycerol and salts can be processed. In addition, however, the treatment device may also comprise a vacuum distillation device and / or a laundry and / or a thermal drying device and / or a filter device with activated carbon or membrane and / or a chromatography device and / or an ion exchanger and / or ion exclusion device.

The invention enables hydrogen production from a glycerol-containing insert with a considerably lower cost compared to the prior art. The decisive factor here is that it is possible to dispense with a water gas shift reactor and with a downstream purification stage. In addition, a membrane reformer is operable at much lower temperatures than a conventional steam reformer, and therefore can be made of less high grade materials. In addition, reduced by the lower temperature level of the heating energy demand and heat losses.

In the following, the invention is based on a in the 1 schematically illustrated embodiment.

In the only one 1 is a running according to a particularly preferred embodiment of the invention process shown.

Via wire 1 For example, a glycerol, water and salts containing use, for example, crude glycerol from the production of biodiesel, a processing device A and fed there into a vacuum distillation device V, in which a majority of the water contained 3 is distilled off. The remaining, enriched in the glycerin content stream 2 is continued in the thin-film evaporator D and here by thin-film evaporation in an intermediate containing most of the glycerol 4 and a residue 5 decomposed, which is, for example, a saline solution. The residue 5 , which is withdrawn continuously or intermittently from the bottom of the thin film evaporator D, can be further treated, for example, by granulation or washing for better landfillability and / or utilization.

The intermediate 4 is now by pyrolysis P to a pyrolysis gas 6 reacted, which contains substantially carbon monoxide, methane, hydrogen and carbon dioxide, and which is subsequently fed to the membrane reformer M as starting material. As a further educt, water or steam can be fed to the membrane reformer M. The educt or the educts are reformed or shifted in the membrane reformer M with catalytic support, hydrogen and carbon dioxide being produced as products in particular. By means of a selectively hydrogen-permeable membrane arranged in the membrane reformer M, hydrogen of high purity can be obtained as permeate, which can be used as hydrogen product 7 is continued. The remaining residual gas, which mainly consists of carbon dioxide, is sent via line 8th withdrawn and burned, for example, to recover heat for distillation and / or pyrolysis and / or reforming, or discharged into the atmosphere.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007022962 [0008, 0009]
• DE 102007060166 [0008, 0009]
• DE 102007045360 [0008]
• EP 0167101 [0013]
• WO 2010000375 [0013]

Cited non-patent literature

• KJ Thomé-Kozmiensky, EF-Verlag 1985, p. 4ff [0003]

Claims (10)

A process for the production of hydrogen, wherein a glycerol and salt-containing feed is processed to an intermediate product, from which a pyrolysis gas is obtained by pyrolysis, which is subsequently converted into a hydrogen product, characterized in that the pyrolysis gas is fed to a membrane reformer as an insert from the hydrogen is removed in product purity. A method according to claim 1, characterized in that the arranged in the membrane reformer partition is operated at a temperature between 450 and 700 ° C. Method according to one of claims 1 or 2, characterized in that the running in the membrane reformer steam reforming at a pressure between 5 and 50 bar (a), preferably between 10 and 30 bar (a) is operated. Method according to one of claims 1 to 3, characterized in that the glycerol and salts containing use by thin film evaporation and / or vacuum and / or washing and / or thermal drying and / or filtering on activated carbon or membrane and / or chromatography and / or ion exchange and / or ion exclusion is processed. Method according to one of claims 1 to 4, characterized in that the pyrolysis is carried out at a temperature between 600 and 900 ° C and a pressure between 5 and 40 bar (a). Device for producing hydrogen with a treatment device in which a glycerol-containing salt and use can be processed to an intermediate, a pyrolysis for converting the intermediate into a pyrolysis gas and a device in which a hydrogen product can be obtained from the pyrolysis, characterized in that it comprises a membrane reformer to which the pyrolysis gas can be supplied as starting material and can be taken off from the hydrogen with product purity. Apparatus according to claim 6, characterized in that the membrane reformer is designed as a tubular reactor containing a selectively hydrogen-permeable membrane in the form of one or more tubes whose axes are arranged parallel to the reactor axis. Device according to one of claims 6 or 7, characterized in that the membrane reformer contains a selectively hydrogen-permeable membrane consisting of palladium or a palladium alloy, such as a palladium-gold alloy or a palladium-silver alloy. Device according to one of claims 6 to 8, characterized in that a selected from nickel, platinum, palladium, iron, rhodium, ruthenium and / or iridium catalyst material is arranged in the reaction space of the membrane reformer. Device according to one of claims 6 to 9, characterized in that the processing device comprises a thin film evaporator and / or a vacuum distillation device and / or a laundry and / or a thermal drying device and / or a filter device with activated carbon or membrane and / or a chromatography device and / or an ion exchanger and / or ion exclusion device.

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