DE102019213501A1 - Process for the production of isobutanol and / or 1-butanol - Google Patents

Abstract

The present invention relates to a method for the production of isobutanol and / or 1-butanol starting from synthesis gas comprising carbon monoxide and / or carbon dioxide and hydrogen, in which in a first step in a catalytic conversion of synthesis gas a first mixture is obtained comprising alcohols with at least two carbon atoms, alkanes and alkenes and, in at least one subsequent step, alcohols contained in this first mixture are converted into isobutanol and / or 1-butanol in a Guerbet reaction. The two-stage conversion according to the invention leads to the C4 alcohols in a more targeted manner than the direct catalytic conversion of synthesis gas. Isobutanol and 1-butanol have a high energy density and can advantageously be used as fuel additives.

Description

The present invention relates to a process for the production of isobutanol and / or 1-butanol starting from synthesis gas comprising carbon monoxide and / or carbon dioxide and hydrogen.

The Guerbet reaction is a long-known name reaction from the field of organic chemistry, which was first published in 1899 by the French chemist Marcel Guerbet. In the Guerbet reaction, primary or secondary alcohols are converted in the presence of catalysts to form longer-chain alcohols, also called Guerbet alcohols in this context.

The Guerbet reaction is a multistage reaction that involves the formation of several intermediate products. In a first reaction step, the alcohol is dehydrated to an aldehyde. In the following reaction step, the aldehyde reacts with another aldehyde in an aldol condensation to form a relatively long-chain unsaturated aldehyde, which is hydrogenated to the alcohol.

In the Guerbet reaction or the aldol reaction, both two identical aldehydes and carbonyl compounds with different organic radicals can react with one another. The reaction of carbonyl compounds with different organic radicals in the aldol reaction is also referred to as a crossed or mixed aldol reaction. If the two starting materials show a similar carbonyl activity in a crossed aldol reaction, a mixture of several different products can in principle arise. Crossed aldol reactions run particularly uniformly if one of the two carbonyl compounds used as starting material does not contain any α hydrogen atoms, e.g. formaldehyde or benzaldehyde. Such carbonyl compounds cannot form enolates and therefore cannot react with themselves in an aldol reaction.

State of the art

According to the fuel specification, higher alcohols such as ethanol, isopropanol, 1-butanol and isobutanol can be used as additives for fuels. The use of bioethanol as a fuel additive, e.g. in E5, E10, E85, is widespread and provides advantages, for example with regard to the octane number and the sustainability of the mixture. One of the disadvantages of using ethanol, however, is its low energy density. If it comes into contact with water, there is also the risk that the ethanol will be extracted from the fuel mixture. In contrast, 1-butanol and isobutanol have a higher energy density. Contact with water does not lead to a separation of the two alcohols from the fuel.

There are numerous homogeneous and heterogeneous catalysts for converting methanol and ethanol to synthesize isobutanol and 1-butanol (Aitchison et al, ACS Catal. 2016, 6, 7125-7132). Industrial processes for the synthesis of isobutanol and 1-butanol based on the Guerbet reaction, however, are not known.

From the DE 10 2010 024 099 A1 a process for the production of higher alcohols by catalytic conversion of ethanol is known, in which an activated carbon substrate is used as a catalyst, which has a metal doping. In this known process, temperatures between 350 ° C. and 425 ° C. and pressures in the range from 1 bar to about 20 bar are used. The catalysts used are, in particular, activated carbon substrates doped with alkali or alkaline earth metals and made basic by means of phosphate, with potassium being doped, for example. The process is suitable for the production of 1-butanol from ethanol.

In the EP 0335 092 A2 describes a process for the catalytic production of an alcohol mixture with increased isobutanol content, in which a synthesis gas comprising carbon monoxide and / or carbon dioxide and hydrogen is converted into the alcohol mixture in a single-stage synthesis via base-modified zirconium / zinc / manganese catalysts. The reaction takes place at temperatures in the range of about 700 K and a comparatively high pressure of 250 bar, with an isobutanol selectivity of between 27 and 44% by weight being achieved, depending on the catalyst. The isobutanol selectivity decreases with decreasing temperatures and the space-time yield of alcohols decreases with decreasing pressures.

In the EP 0 208 102 A2 also describes a process for the catalytic production of an alcohol mixture with an increased content of isobutanol from synthesis gas, in which a catalyst made of zirconium oxide or cerium oxide or palladium and an oxide or hydroxide of the alkali or alkaline earth metals is used. The reaction temperatures are from 300 ° C. to 450 ° C. and a high pressure of 250 bar is also used here. In this known process, a high proportion of methanol is formed, which is approximately 40 to 70% by weight and which is in some cases approximately twice as high as the proportion of the isobutanol sought as the preferred product.

The WO 2012/062338 A1 describes a process for the selective production of isopropanol, isobutanol and other C3 + alcohols from synthesis gas and methanol. In this process, synthesis gas is converted with the addition of methanol and a higher alcohol such as, for example, ethanol, in order to increase the selectivity to isobutanol. The two alcohols are added to the synthesis gas above the alcohol reactor. If only methanol is added to the synthesis gas, predominantly ethanol is formed in the product mixture. To obtain isobutanol, methanol and 1-propanol must be added. The catalyst used in this process is either copper on a carrier or copper in conjunction with zinc oxide and aluminum oxide, optionally with an alkali metal or a basic oxide of an alkaline earth metal as a promoter.

The U.S. 5,559,275 A describes a process for converting lower to higher alcohols, for example the production of isobutanol from methanol via the mechanism of an aldol condensation. Mixtures of metal oxide solutions are used as catalysts, for example zirconium oxynitrate, zinc nitrate and manganese nitrate, with potassium hydroxide being added as a base. It should be noted, however, that the first step in the condensation of methanol to ethanol is comparatively slow. The results are therefore unsatisfactory if only methanol is used as the starting material. A disadvantage of the process is also the formation of carbon dioxide, in some cases with high selectivities, as a further product. This document also mentions that the methanol can be obtained beforehand from synthesis gas, so that there is a two-stage synthesis of isobutanol from synthesis gas.

The object of the present invention is to provide an improved process for the production of isobutanol and / or 1-butanol in which the higher alcohols mentioned are produced in good yield.

Another concern of the present invention is to provide a method in which the complex first product mixture from a catalytic conversion of a synthesis gas, comprising alcohols and also hydrocarbons, can be converted into secondary products in a targeted and more effective manner in order to produce a high-quality product / high-quality products for to produce the fuel market and / or the chemical industry.

The aforementioned object is achieved by a method for producing isobutanol and / or 1-butanol of the type mentioned at the outset with the features of claim 1.

According to the invention it is provided that in a first step in a catalytic conversion of synthesis gas a first mixture is obtained, comprising at least one alcohol with at least two carbon atoms, with alcohols contained in this first mixture in a Guerbet reaction in at least one subsequent step Isobutanol and / or 1-butanol are implemented.

The first mixture obtained in the catalytic conversion of synthesis gas can contain, in particular, alkanes and alkenes as by-products.

In contrast to the prior art, the alcohols required for the consecutive Guerbet reaction are produced according to the invention by means of a catalytic conversion of synthesis gas to methanol and higher alcohols. These alcohols, such as in particular ethanol, methanol and optionally propanol, are found in a first product mixture after the synthesis gas conversion. The higher-value higher alcohols, such as in particular ethanol and propanol, do not have to be supplied from the outside as starting materials. In order to optimize the Guerbet reaction and to optimize the conversion of ethanol and propanol to isobutanol, it may be helpful to adjust the methanol concentration by supplying it from outside. In the process according to the invention, high quality higher alcohols are thus obtained in a two-stage synthesis from synthesis gas. It becomes clear here that the method according to the invention leads to a considerable simplification in the overall process of producing isobutanol (according to the exact chemical nomenclature 2-methyl-1-propanol) or 1-butanol.

Various process variants of the method according to the invention result from suitable steps for separating the groups of substances and processing the mixture of substances obtained in the first step in the catalytic conversion of synthesis gas.

The multi-stage synthesis of isobutanol and / or 1-butanol from synthesis gas is thus possible via the consecutive conversion of the alcohol mixture formed in the catalytic synthesis of alcohols. The consecutive reaction enables, in particular, the production of isobutanol. The value chain for the production of isobutanol from synthesis gas is as follows:

In a first step, synthesis gas is generated from a suitable feed stream and made available. This synthesis gas usually contains CO, H ₂ , optionally CO ₂ and optionally N ₂ . If necessary, this is followed by conditioning of the synthesis gas, which can include purification of the synthesis gas and setting of a ratio suitable for the subsequent reaction, in particular of the gases CO, CO ₂ and H ₂ . The synthesis gas conditioned in this way is used for the catalytic synthesis of higher alcohols. The term “higher alcohols” is understood here to mean that it contains at least one alcohol with at least two carbon atoms. For example, an alcohol mixture is produced which contains predominantly C2-C4 alcohols and also optionally methanol. For the catalytic synthesis of higher alcohols, specific catalysts are preferably used in the process according to the invention, the specification of which will be discussed in greater detail below.

In the synthesis of higher alcohols from synthesis gas (CO / H ₂ or CO ₂ / H ₂ mixture or CO / CO ₂ / H ₂ ) or from steel mill gases or from other industrial process gases, a mixture of various short-chain alcohols is usually produced such as methanol, ethanol, propanol and butanol. As a rule, the alcohols methanol and ethanol are obtained with a higher selectivity, whereas the longer-chain alcohols propanol and, in particular, butanols, which have good properties as fuel additives, are obtained with a lower yield. In particular, the often high proportion of methanol can be used as Fuel additive can be problematic. According to the DIN EN 228 fuel specification, a maximum of 3% by volume of methanol is permitted in petrol.

According to the invention, the product mixture obtained after this first synthesis step and containing the aforementioned higher alcohols is then subjected to a Guerbet reaction. In the process, in addition to isobutanol and / or 1-butanol and other alcohols, alkenes and alkanes are obtained as further valuable products, which are formed in the first step in the catalytic conversion of the synthesis gas in addition to the alcohols.

In the process according to the invention, the consecutive Guerbet reaction converts the alcohol mixture of short-chain alcohols such as methanol, ethanol, propanol obtained after the catalytic conversion of synthesis gas into isobutanol or 1-butanol and thus a high-quality fuel additive.

In the context of the present invention, catalysts and process variants for the catalytic synthesis of higher alcohols from synthesis gases were developed. Here, for example, synthesis gas can be converted, which is provided by cleaning and conditioning steel mill gases. However, the invention described below can expressly also be applied to other synthesis gas sources.

According to the present invention, the synthesis of higher alcohols from synthesis gas initially comprises the provision of the synthesis gas, the catalytic synthesis of the higher alcohols from this synthesis gas and, if appropriate, the purification or separation of the product mixture. The provision of the synthesis gas may also include the cleaning and conditioning of the synthesis gas in addition to the preparation of the synthesis gas. Both fossil fuels, such as natural gas, coal, but also _{gases rich in CO and CO 2,} for example from steel or cement works, and hydrogen can be used as feed for the provision of the synthesis gas. It is also possible to obtain the synthesis gas used from biomass. The hydrogen is preferably produced with a low CO ₂ footprint, for example by means of water electrolysis or methane pyrolysis. Hydrogen production is preferably operated with electricity that is produced using renewable energies.

A preferred development of the method according to the invention provides that the alkanes and alkenes are first separated from the alcohols from the first mixture of alcohols, alkenes and alkanes obtained after the catalytic conversion of synthesis gas and then the alcohols are converted in the Guerbet reaction.

Furthermore, butanols and optionally water are preferably separated off from the first mixture obtained after the catalytic conversion of synthesis gas and the Guerbet reaction is carried out with the remaining mixture of alcohols.

Thus, after the alkenes and alkanes have been separated off and after the water and optionally butanol have been separated off, the first mixture obtained and purified after the catalytic conversion of synthesis gas, with which the Guerbet reaction is carried out, essentially contains methanol, ethanol and propanol. Butanol and water can just as easily be separated from the product mixture only after the Guerbet reaction. The product mixture with which the Guerbet reaction is carried out then contains, after the alkenes and alkanes have been separated off, in addition to the alcohols with one to three carbon atoms mentioned, also 1-butanol and water.

The catalytic synthesis of the higher alcohols from synthesis gas can be carried out according to the invention, for example, at reaction temperatures from 200 ° C to 360 ° C, preferably at temperatures from 220 ° C to 340 ° C, more preferably at 240 ° C to 320 ° C, in particular at 260 ° C to 300 ° C, for example at about 280 ° C. In addition, this reaction can be carried out, for example, at a reaction pressure of 10 bar to 110 bar, in particular at 30 bar to 90 bar, preferably at 50 bar to 70 bar, for example at about 60 bar. The product mixture obtained from unconverted synthesis gas, alcohols, alkenes and alkanes can be heated to lower temperatures of, for example, 150 ° C or less, in particular to below 130 ° C, preferably to below 110 ° C or to even lower temperatures of less than 80 ° C, for example about 40 ° C to 20 ° C, especially cooled to about 30 ° C and separated into a gas and a liquid phase. The gas phase mainly contains the unconverted synthesis gas as well as any inert components (eg nitrogen) and the methane formed as a by-product. The gas phase is usually returned to the synthesis of the higher alcohols. Possibly is additional purification or conditioning of the gas phase, such as the conversion of the methane formed as a by-product into synthesis gas, is provided.

The liquid phase mainly contains the alcohols, alkenes and alkanes formed. By lowering the pressure, for example to less than 5 bar, in particular to about 1 bar, the alkenes and alkanes are evaporated and separated from the product mixture. In order to optimize the process economically and / or ecologically, it may be advantageous to convert the alkanes into synthesis gas, e.g. via partial oxidation, steam reforming or autothermal reforming and to return them to the process. If appropriate, the alkanes can also be dehydrogenated to the corresponding alkenes in order to increase the yield of alkenes. The alcohols remain in the liquid phase and, after the water formed as a coproduct has been separated off, are optionally converted as a product mixture to 1-butanol or isobutanol and, for example, marketed as a fuel additive or separated into the individual alcohols in a distillation and individually to 1-butanol or isobutanol implemented.

According to a further development of the invention, alkenes present in the mixture obtained after the alkenes and alkanes have been separated off can preferably be converted to alcohols by hydration or hydroformylation, which are then likewise subjected to the Guerbet reaction. The synthesis of isobutanol only describes the preparation of a high-quality fuel additive from the alcohol mixture, but not the utilization of the alkenes formed as by-products in the catalytic conversion of synthesis gas. The alkenes can be used by other useful subsequent reactions such as the integration of hydration and hydroformylation, which are thus integrated into the process concept of the catalytic synthesis of higher alcohols from synthesis gas. In this way it is possible to increase the oxygenate or alcohol yield of the first synthesis stage by converting the alkenes to further aldehydes or alcohols. The further alcohols or aldehydes formed by means of hydration and hydroformylation can then likewise be converted into isobutanol and / or 1-butanol in the Guerbet reaction. In the case of the reaction of isopropanol with methanol in the Guerbet reaction, which is also possible as an alternative within the scope of the present invention, 2-butanol is formed.

The alkenes and alkanes are preferably separated off from the alcohols prior to the Guerbet reaction at a lower temperature and pressure than the preceding catalytic synthesis of higher alcohols from synthesis gas, preferably at a temperature in the range from 20 ° C. to 40 ° C. and a pressure of less than 5 bar, particularly preferably at a pressure of less than 2 bar.

After this separation, for example one or more separation steps can be provided in which the alkanes are separated from the alkenes. Here, for example, the alkene / alkane mixture can first be separated into various fractions, in particular a C2 fraction (ethene / ethane), a C3 fraction (propene / propane) and a C4 fraction (butene / butane) and then divided into the separate fractions into an alkene and an alkane. However, the aforementioned conversion of the alkenes by hydration to alcohols or the aforementioned conversion of the alkenes by hydroformylation to aldehydes and / or alcohols leads to a simplification, since the resulting alcohols and / or aldehydes can be separated more easily from the alkanes due to their properties, than is the case with the direct separation of alkenes and alkanes, because the latter are chemically more similar. The alkenes can thus be converted into further products of value and the alkanes can be converted into further synthesis gas, for example by partial oxidation, autothermal reforming or steam reforming, and fed back into the process, i.e. they ultimately also serve to increase the yield of alcohols in the entire process.

Depending on the respective composition and concentration of the products formed after the catalytic conversion of the synthesis gas, the aforementioned process parameters can be varied in a suitable manner or supplemented by further separation steps within the scope of the method according to the invention.

The product mixture obtained after the Guerbet reaction is preferably purified from alcohols; in particular, the water is preferably separated off from the product mixture at this point in the process.

Furthermore, isobutanol and 1-butanol are preferably separated off from the product mixture obtained after the Guerbet reaction, for example by distillation, as well as optionally further alcohols obtained in the mixture, such as 2-butanol, 1-propanol or ethanol, in each case individually can be. The short-chain C1-C3 alcohols can optionally be returned to the Guerbet reaction and thus converted to C4 alcohols.

The above-described value chain according to the present process provides various principal advantages over the current state of the art in isobutanol synthesis from synthesis gas. In comparison to the processes mentioned at the outset, the catalytic conversion of the synthesis gas according to the invention is carried out at lower temperatures. There is no need to add ethanol from external sources when converting the synthesis gas. The selectivity of the two-stage overall process for isobutanol is increased compared to known processes.

A mixture of C4 alcohols (in particular 1-butanol and isobutanol), which is a high-quality fuel additive, is produced from the alcohol mixture obtained from the catalytic conversion of synthesis gas.

The consecutive conversion of the alcohols methanol, ethanol and propanol formed in the first reaction step in the catalytic synthesis of the higher alcohols enables the targeted production of isobutanol or 1-butanol. The synthesis of the high-quality fuel additives 1-butanol and isobutanol from synthesis gas (for example from steel mill gas) is achieved by coupling the synthesis of the higher alcohols with a downstream chemical plant for the Guerbet reaction. The Guerbet reaction is an aldol addition, aldol condensation or dimerization of alcohols, which leads to chain lengthening.

For the present invention, the reactions listed below of the alcohols formed from lower alcohols in the Guerbet reaction are particularly relevant: CH ₃ -CH ₂ -OH + CH ₃ -OH → CH ₃ -CH ₂ -CH ₂ -OH 1 (a) CH ₃ -CH ₂ -CH ₂ -OH + CH ₃ -OH → CH ₃ -CH (CH ₃ ) -CH ₂ -OH 1 (b) CH ₃ -CH ₂ -OH + CH ₃ -CH ₂ -OH → CH ₃ -CH ₂ -CH ₂ -CH ₂ -OH 2.

By reacting ethanol with methanol in a Guerbet reaction, 1-propanol is first formed (see reaction 1 (a), by reacting 1-propanol with methanol isobutanol is then formed (see reaction 1 (b). The one-step reaction is the same) of ethanol with methanol to isobutanol is described in the literature The dimerization of ethanol leads to the formation of 1-butanol (see above reaction 2).

In the method according to the invention, before the Guerbet reaction is carried out and after the catalytic conversion of the synthesis gas, at least one step is preferably carried out in which the first product mixture obtained during the conversion of the synthesis gas is separated into a gas phase and a liquid phase, the liquid phase is used for the subsequent Guerbet reaction and the separation is preferably carried out at a lower temperature and / or at lower pressure than the previous catalytic conversion of the synthesis gas. This separation step has the advantage that at this point in the process unconverted portions of the synthesis gas are separated from the reaction mixture and therefore no longer influence the subsequent reaction.

The liquid phase obtained in this separation step contains predominantly the alcohols, alkenes and alkanes formed. As a rule, after this gas / liquid separation, the alkenes and alkanes are separated off from the alcohols before the Guerbet reaction is then carried out with the alcohols. This separation of the alkenes and alkanes can take place in particular by lowering the pressure, for example to less than 5 bar, in particular to about 1 bar, the alkenes and alkanes being evaporated and thus separated from the product mixture.

Preferably, the gas phase obtained in the gas-liquid separation after the conversion of the synthesis gas is at least partially returned to the step of the catalytic conversion of the synthesis gas. As a result of this recirculation, a higher proportion of the synthesis gas can be made to react overall and thus the yield of alcohols can be increased.

After the hydrocarbons (alkenes and alkanes) have been separated off, a mixture of alcohols and, if appropriate, water is obtained. Butanols and optionally water formed during the catalytic conversion of the synthesis gas can optionally be separated off before the Guerbet reaction and that then remaining alcohol mixture of predominantly methanol, ethanol and propanol can then be converted into isobutanol and / or 1-butanol in a downstream Guerbet reaction.

The consecutive conversion of the alcohol mixture to isobutanol or 1-butanol is particularly suitable for methanol-rich alcohol mixtures, since the use of methanol as a fuel additive has disadvantages due, among other things, to a lower energy density, higher toxicity and low permitted admixture proportions (DIN EN 228) having. The compatibility of methanol with the fuel-carrying components of the engines has not yet been adequately investigated and is therefore currently the subject of major research projects. 1-butanol and isobutanol, on the other hand, are viewed as high-quality fuels even according to the current state of research. The Guerbet reaction converts methanol into a high-quality fuel.

According to a preferred variant of the method, it can optionally also be advantageous to first separate the alcohol mixture into the respective alcohols or into individual alcohol fractions with the same or different numbers of carbon atoms in order to individually adapt the composition of the starting materials for the subsequent Guerbet reaction and to be able to control the product composition of the Guerbet reaction.

In the WO 2015/086151 A1 describes a process by means of which synthesis gas can be provided by cleaning and conditioning various gas flows that arise in a steelworks. These gas flows can be collectively referred to by the term “steel mill gases”, which in particular includes blast furnace gas, converter gas and coke oven gas. For the first process stage described herein for the catalytic synthesis of alcohols having at least two carbon atoms from synthesis gas (also referred to herein as higher alcohols), synthesis gas from such sources is suitable, for example. In principle, however, any other suitable synthesis gas sources can also be used for the process according to the invention.

In the context of the present invention, an overall process was developed which enables isobutanol and / or 1-butanol to be produced with good yield starting from synthesis gas. The present application describes processes which, based on the product mixture obtained in the conversion of synthesis gas, comprising carbon monoxide and hydrogen or carbon dioxide and hydrogen or carbon monoxide, carbon dioxide and hydrogen, offer advantages in economic, technological and / or ecological terms compared to known processes , especially compared to a simple separation with subsequent individual marketing of the products / groups of substances. Particular attention was paid to optimizing the product separation in accordance with the synthesis steps. This concerns, among other things, the respective physical process conditions (pressure, temperature) as well as the setting of preferred or technologically tolerable educt ratios for the synthesis steps, taking into account, in particular, economic framework conditions.

Due to the large plant capacities, which are necessary, for example, for the utilization of significant quantities of steel mill gas, but also for other synthesis gas sources, processes are preferred that lead to products with sufficiently large (potential) markets. It is therefore particularly interesting to consider basic chemicals that can be used in the plastics or fuel sector, for example.

According to the above description, the process variant mentioned below is particularly preferred in the context of the present invention.

• - Herstellung höherer Alkohole (umfassend wenigstens einen Alkohol mit wenigstens zwei C-Atomen) durch katalytische Umsetzung von Synthesegas, vorzugsweise bei einer Temperatur von zwischen 200 °C und 360 °C und bei einem Druck von 10 bar bis 110 bar;
• - Trennung des erhaltenen ersten Produktgemisches in eine Gasphase und eine Flüssigphase;
• - gegebenenfalls Rückführung der abgetrennten Gasphase zur katalytischen Umsetzung des Synthesegases;
• - Abtrennung der Alkene und Alkane, die als Nebenprodukte anfallen von den erhaltenen Alkoholen, vorzugsweise bei einem niedrigeren Druck verglichen mit dem vorgenannten Trennschritt;
• - gegebenenfalls Auftrennung des von den Alkenen und Alkanen abgetrennten Alkoholgemisches in einzelne Verbindungen oder Verbindungsgruppen, insbesondere Ethanol, Propanole, Butanole und gegebenenfalls Methanol;
• - Umsetzung des Alkoholgemisches unter den Bedingungen einer Guerbet-Reaktion, wobei Isobutanol und/oder 1-Butanol erhalten wird;
• - gegebenenfalls Abtrennung von Wasser und Aufreinigung des nach der Guerbet-Reaktion erhaltenen Produktgemisches;
• - gegebenenfalls Trennung der in der Guerbet-Reaktion erhaltenen höheren Alkohole, insbesondere von Isobutanol und 1-Butanol.

In this preferred variant, the method preferably comprises the steps:

• - Production of higher alcohols (comprising at least one alcohol with at least two carbon atoms) by catalytic conversion of synthesis gas, preferably at a temperature of between 200 ° C and 360 ° C and at a pressure of 10 bar to 110 bar;
• - Separation of the first product mixture obtained into a gas phase and a liquid phase;
• - if necessary, recycling of the separated gas phase for the catalytic conversion of the synthesis gas;
• - Separation of the alkenes and alkanes which are obtained as by-products from the alcohols obtained, preferably at a lower pressure compared to the aforementioned separation step;
• - if appropriate, separation of the alcohol mixture separated from the alkenes and alkanes into individual compounds or groups of compounds, in particular ethanol, propanols, butanols and, if appropriate, methanol;
• - Implementation of the alcohol mixture under the conditions of a Guerbet reaction, isobutanol and / or 1-butanol is obtained;
• - If necessary, separation of water and purification of the product mixture obtained after the Guerbet reaction;
• - Optional separation of the higher alcohols obtained in the Guerbet reaction, in particular of isobutanol and 1-butanol.

As part of a further development of the present invention, specific cobalt-containing catalysts were developed which combine the properties of a methanol synthesis catalyst and a Fischer-Tropsch catalyst. In this way, the catalytic conversion of synthesis gas creates a product mixture which, in addition to methanol and the higher alcohols (especially ethanol, propanol and butanol), also contains high concentrations of hydrocarbons (especially C2 - C4 alkenes and C1 - C4 alkanes), water and CO ₂ .

A catalyst is used here; which comprises grains of non-graphitic carbon with cobalt nanoparticles dispersed therein, the cobalt nanoparticles having a mean diameter d _p in the range from 1 nm to 20 nm and the mean distance D between individual cobalt nanoparticles in the grains of non- graphitic carbon is in the range of 2 nm and 150 nm and ω, the combined total mass fraction of the metal in the grains of non-graphitic carbon, in the range of 30% by weight to 70% by weight of the total mass of the grains of non- graphitic carbon, where d _p , D and ω satisfy the following relationship: 4.5 dp / ω> D ≥ 0.25 dp / ω.

In the process according to the invention, it is particularly preferred to use a catalyst material which is doped with a metal selected from Mn, Cu or a mixture of these, the grains of non-graphitic carbon having a molar ratio of cobalt to doped metal in the range from 2 to 15 exhibit.

In experiments within the scope of the present invention it was found that the aforementioned grains of non-graphitic carbon with cobalt nanoparticles dispersed therein can be obtained from aqueous solutions of metallic precursors and organic carbon sources by combined spray-drying or freeze-drying of the aqueous solution and thermal treatment of the intermediate product obtained in this way at moderate temperatures.

Non-graphitic carbon can be identified by a person skilled in the art by TEM analysis (PW Albers, Neutron scattering study of the terminating protons in the basic structural units of non-graphitizing and graphitizing carbons, Carbon 109 (2016), 239 - 245, page 241 , figure 1c).

In comparison to the previous knowledge and also to the descriptions known from the literature, the abovementioned catalysts surprisingly have a significantly higher selectivity for alkenes than for alkanes (for example in the order of about 3: 1). As a result, in addition to the alcohols with the alkenes, the product mixture also contains other valuable products which, from an economic and ecological point of view, can advantageously be used materially and not energetically.

An important aspect in connection with an advantageous development of the invention is the separation of the products of value from the relatively complex product mixture at the reactor outlet. In addition to the products of value alcohols and alkenes, residual gases (depending on the feed gas: H ₂ , CO, CO ₂ , N ₂ ) and by-products (especially alkanes, CO ₂ and H ₂ O).

• 1 ein beispielhaftes Prozessschema betreffend eine beispielhafte Ausführungsvariante des erfindungsgemäßen Verfahrens.

The present invention is described in more detail below using an exemplary embodiment with reference to the accompanying drawings. It shows:

• 1 an exemplary process scheme relating to an exemplary embodiment variant of the method according to the invention.

In the following, the 1 Reference is made and an exemplary variant of the method according to the invention is explained in more detail on the basis of this schematic representation. From a feed stream 10 , for example from mill gas, is used in a device for generating synthesis gas 11 a synthesis gas 11 a generates comprehensive CO and H ₂ , optionally CO ₂ and N ₂ as an inert gas, which a reactor 12th is supplied, in which the synthesis of higher alcohols is carried out at a temperature of, for example, 280 ° C. and a pressure of 60 bar over a specific catalyst. The catalyst comprises grains of non-graphitic carbon with cobalt nanoparticles dispersed therein, the cobalt nanoparticles having an average diameter d _p in the range from 1 nm to 20 nm and the average distance D between individual cobalt nanoparticles in the grains from not graphitic carbon is in the range of 2 nm and 150 nm and ω, the combined total mass fraction of the metal in the grains of non-graphitic carbon, is in the range of 30% to 70% by weight of the total mass of the grains not graphitic carbon, where d _p , D and ω satisfy the following relationship: 4.5 dp / ω> D ≥ 0.25 dp / ω.

That in the reactor 12th The product mixture produced is via the line 13th a facility 14th supplied, in which, for example, at a pressure of 60 bar, which is thus about the same order of magnitude or lower than in the previous synthesis (for example 50 bar or less), and at a suitable temperature of for example about 30 ° C, a Separation into a gas phase and a liquid phase takes place. The gas phase is preferably via the line shown in dashed lines 15th in the synthesis of higher alcohols 12th returned. This recirculated gas phase can contain, for example, N ₂ and CH _{4 in addition to CO, H 2} and CO ₂ . The one in the facility 14th The separated liquid phase contains alcohols, alkenes and alkanes, predominantly with two to four carbon atoms each, and methanol. This product mixture of alcohols, alkenes and alkanes is over the line 16 a separator 17th fed, in which the alcohols are separated off from the alkenes and alkanes. The alkanes and alkenes leave the plant via the line 23 . The alcohols are over the pipe 18th a second reactor 19th supplied, in which the Guerbet reaction is carried out, in which isobutanol and / or 1-butanol are produced from the lower alcohols such as methanol and ethanol, optionally via 1-propanol as an intermediate or directly from 1-propanol. After the reaction, the product mixture can be passed through a line 20th the facility 21 are supplied, in which a purification takes place, in particular water is separated off and in which a separation into the individual higher C4 alcohols isobutanol and 1-butanol can take place. Water, isobutanol and 1-butanol leave the system via the lines 26th , 32 and 33 leave.

The separation into a gas phase and a liquid phase after the catalytic conversion of a synthesis gas stream can alternatively also be carried out by various other methods. If, for example, under the conditions of the process according to the invention, after the catalytic conversion of the synthesis gas, a product stream is present at a temperature of 280 ° C. and a pressure of 60 bar, this can first be increased in a turbine to a pressure of 5 to 20 bar, preferably to about 10 bar can be relaxed, whereby electrical energy is obtained, which can be used for the power requirements of the process.

The subsequent gas-liquid separation, which is used in particular to separate the inert gases (e.g. nitrogen) and unconverted components of the synthesis gas (hydrogen, carbon monoxide, carbon dioxide and methane), takes place, for example, by absorbing the product flow in a diesel oil (reference component Dodecane) or alternatively in an alkane or a hydrocarbon mixture with a comparatively low viscosity of, for example, less than 10 mPas at room temperature and preferably with a comparatively high boiling point of in particular more than 200 ° C. The water is not absorbed, but largely condenses as a second liquid phase.

The two liquid phases (organic phase and aqueous phase) can then be separated in a decanter, whereby the hydrocarbons hardly go into the aqueous phase, but some of the alcohols. For example, the alcohols can be distilled out of the water again as azeotropes by means of a first column. Alcohols and hydrocarbons are then desorbed from the diesel oil, which can be done in a column. After desorption, the diesel oil can be returned to the absorption process. In the case of smaller proportions of inert gas in the product stream of the catalytic conversion of synthesis gas, a condensation of the low-boiling components can alternatively also come into consideration.

The Guerbet reaction can at a temperature of, for example, about 120 ° C to 200 ° C, in particular at about 180 ° C with homogeneous catalysis on a ruthenium catalyst and with a Base can be carried out in an autoclave, with isobutanol being obtained almost exclusively when methanol is reacted with ethanol with high selectivity.

Alternatively, the Guerbet reaction can be carried out at a temperature of, for example, about 100 ° C. to 140 ° C., in particular at about 120 ° C., with homogeneous catalysis over an iridium catalyst and with a base in an autoclave, with the conversion of ethanol (Dimerization) is obtained with good selectivity of about 50% 1-butanol.

The one in the separator 17th separated alkenes and alkanes can optionally, which is according to the process scheme 1 is not shown, are separated from one another and then the alkenes can be converted to the corresponding alcohols by hydration or hydroformylation and then likewise in the reactor 19th be converted by Guerbet reaction to isobutanol and / or 1-butanol. The alkanes separated from the alkenes can in turn be introduced into a device for partial oxidation, in which they are at least partially converted back into synthesis gas by reaction with oxygen. This further synthesis gas (including in particular hydrogen and carbon monoxide) can, for example, the reactor 12th are supplied in which the catalytic conversion of the synthesis gas to alcohols takes place, so that the yield of alcohols is further increased.

Separation of alcohols and hydrocarbons

A separation of alcohols and hydrocarbons before the Guerbet reaction can take place, for example, by distillation in a second column, preferably at a high pressure of, for example, 10 bar to 40 bar, so that the C3 components still remain condensable in the presence of any residues of inert gas. This separation is preferably carried out in such a way that the hydrocarbons are practically completely removed from the alcohol fraction at the bottom, while lower alcohol contents (in particular methanol) in the hydrocarbons can be tolerated. If necessary, this process can be supported by a solubility-driven membrane.

Representation of the hydrocarbons

In a third distillation column, the hydrocarbons can be obtained at the top, for example at elevated pressure of, for example, 5 bar to 20 bar, while the remaining water and the alcohols dissolved therein are obtained and separated off in the bottom. This stream can be returned to the first distillation column to recover the alcohols. The condenser of the column can, for example, be a partial condenser. The outputs of the column are a gas phase made of hydrocarbons and inerts, a liquid phase made of hydrocarbons and an aqueous phase that can return to the column as reflux.

Dehydration of the alcohol fraction

The alcohol fraction can have a water content of, for example, about 10%. This water can be removed, for example, by means of a molecular sieve.

An alternative method for removing the water from the alcohol fraction is extractive distillation, for example with ethylene glycol, which, however, requires a further separation step, since the water is drawn into the sump from the ethylene glycol, while the alcohols methanol and ethanol are practically anhydrous overhead. About half of the propanol remains and the butanol remains entirely in the bottom and these C3-C4 alcohols must also be removed from the ethylene glycol via the top in a subsequent column.

The third alternative is pervaporation. Water passes selectively through a membrane and is withdrawn in vapor form as permeate. The energy consumption is even lower than with a molecular sieve.

Another alternative method would be an azeotropic distillation, e.g. with butane or pentane as a selective additive.

List of reference symbols

10

Feed stream

11

Synthesis gas

11a

Synthesis gas

12th

reactor

13th

management

14th

Separation facility

15th

management

16

management

17th

Separator

18th

management

19th

Guerbet reactor

20th

management

21

Device for purification and separation

23

management

26th

management

32

management

33

management

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• DE 102010024099 A1 [0007]
• EP 0335092 A2 [0008]
• EP 0208102 A2 [0009]
• WO 2012/062338 A1 [0010]
• US 5559275 A [0011]
• WO 2015/086151 A1 [0048]

Claims (17)

Process for the production of isobutanol and / or 1-butanol starting from synthesis gas comprising carbon monoxide and / or carbon dioxide and hydrogen, characterized in that in a first step in a catalytic conversion of synthesis gas a first mixture is obtained comprising at least one alcohol with at least two Carbon atoms and, in at least one subsequent step, alcohols contained in this first mixture are converted into isobutanol and / or 1-butanol in a Guerbet reaction. Procedure according to Claim 1 , characterized in that first the alkanes and alkenes are separated from the alcohols from a first mixture of alcohols, alkenes and alkanes obtained after the catalytic conversion of synthesis gas and then the alcohols are converted in the Guerbet reaction. Method according to one of the Claims 1 or 2 , characterized in that butanols and optionally water are separated from the first mixture obtained after the catalytic conversion of synthesis gas and the Guerbet reaction is carried out with the remaining mixture of alcohols. Procedure according to Claim 3 , characterized in that the first mixture obtained after the catalytic conversion of synthesis gas, with which the Guerbet reaction is carried out, essentially contains methanol, ethanol and propanol. Method according to one of the Claims 1 to 4th , characterized in that in the Guerbet reaction, methanol is reacted with ethanol to form 1-propanol, 1-propanol is reacted with methanol to form isobutanol and / or ethanol is reacted with methanol directly to form isobutanol and / or ethanol is dimerized to form 1-butanol . Method according to one of the Claims 1 to 5 , characterized in that the catalytic synthesis of the higher alcohols from synthesis gas is carried out at a reaction temperature in the range from 200 ° C to 360 ° C, preferably at temperatures from 220 ° C to 340 ° C, more preferably at 240 ° C to 320 ° C., in particular at 260 ° C. to 300 ° C. and at a reaction pressure of 10 bar to 110 bar, in particular at 30 bar to 90 bar, preferably at 50 bar to 70 bar. Method according to one of the Claims 2 to 6th , characterized in that alkenes contained in the mixture obtained after separation of the alkenes and alkanes are converted by hydration to alcohols or hydroformylation to alcohols and / or aldehydes, which are then likewise subjected to the Guerbet reaction or an aldol condensation. Method according to one of the Claims 1 to 7th , characterized in that the mixture of alcohols obtained after the catalytic conversion of synthesis gas in the first step, in particular after the separation of the alkenes and alkanes, is separated into individual alcohols or fractions of alcohols before the Guerbet reaction is carried out. Method according to one of the Claims 1 to 8th , characterized in that the product mixture obtained after the Guerbet reaction is purified from alcohols, in particular the water is separated from the product mixture. Method according to one of the Claims 1 to 9 , characterized in that isobutanol and 1-butanol are separated from the product mixture obtained after the Guerbet reaction. Method according to one of the Claims 2 to 10 , characterized in that the separation of the alkenes and alkanes from the alcohols takes place at a lower temperature and lower pressure than the previous catalytic synthesis of higher alcohols from synthesis gas, preferably at a temperature in the range from 20 ° C to 40 ° C and a pressure of less than 5 bar, particularly preferably at a pressure of less than 2 bar. Method according to one of the Claims 1 to 11 , characterized in that before the implementation of the Guerbet reaction and after the catalytic conversion of the synthesis gas at least one step is provided in which a separation of the first obtained during the conversion of the synthesis gas Product mixture takes place in a gas phase and a liquid phase, the liquid phase being used for the subsequent Guerbet reaction. Procedure according to Claim 12 , characterized in that the gas phase obtained in the separation is at least partially returned to the step of catalytic conversion of the synthesis gas. Method according to one of the Claims 12 or 13th , characterized in that after the catalytic conversion of the synthesis gas, the product mixture is processed which comprises at least the following steps: at least partial absorption of the alcohols and any alkenes and / or alkanes present in a high-boiling hydrocarbon or hydrocarbon mixture as the absorption medium; - Separation of the gases not absorbed in the absorption medium as a gas phase; - Separation of an aqueous phase from the organic phase of the absorption medium, preferably by decanting; - if necessary, distilling out the alcohols from the aqueous phase; - Desorption of the alcohols and any alkenes and / or alkanes present from the absorption medium. Procedure according to Claim 14 , characterized in that, prior to the Guerbet reaction, the separation of the alcohols from the alkenes and alkanes or the separation of the alcohols from the alkanes comprises at least the following steps: separation of the alcohols in at least one distillation column at an elevated pressure of preferably at least 10 bar; - Removal of the water from the alcohol fraction, preferably by means of a molecular sieve, by extractive distillation, by pervaporation or by azeotropic distillation. Method according to one of the Claims 1 to 15th , characterized in that a catalyst is used in the catalytic conversion of the synthesis gas which comprises grains of non-graphitic carbon with cobalt nanoparticles dispersed therein, the cobalt nanoparticles having an average diameter d _p in the range from 1 nm to 20 nm and the mean distance D between individual cobalt nanoparticles in the grains of non-graphitic carbon is in the range of 2 nm and 150 nm and ω, the combined total mass fraction of the metal in the grains of non-graphitic carbon, in the range of 30 wt % to 70% by weight of the total mass of the grains of non-graphitic carbon, where d _p , D and ω satisfy the following relationship: 4.5 dp / ω> D ≥ 0.25 dp / ω. Procedure according to Claim 16 , characterized in that the catalyst material is doped with a metal selected from Mn, Cu or a mixture of these, the grains of non-graphitic carbon having a molar ratio of cobalt to doped metal in the range from 2 to 15.

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