Process and apparatus for producing propylene and hydrogen from propane

Abstract

A process for producing propylene and hydrogen from propane, the process comprising the steps of: a) reacting a mixture comprising propane and bromine to produce a first reaction mixture comprising bromopropane and hydrogen bromide, b) subjecting the first reaction mixture obtained in step a) to at least one separation step to obtain a bromopropane-rich composition and to obtain a hydrogen bromide-rich composition, c) subjecting the bromopropane-rich composition obtained in step b) to a catalytic reaction to produce a second reaction mixture containing propylene and hydrogen bromide, d) subjecting the second reaction mixture obtained in step c) to at least one separation step to obtain a hydrogen bromide-rich composition and to obtain propylene, and e) subjecting the hydrogen bromide-rich composition obtained in step b) and / or the hydrogen bromide-rich composition obtained in step d) to electrolysis to obtain hydrogen and a bromine-containing composition, wherein preferably at least a portion of the bromine-containing composition is recycled back to step a).

Description

[0001] The present invention relates to a method and apparatus for preparing propylene and hydrogen from propane.

[0002] Propane is a common product in refineries or natural gas processing plants. Currently, propane is value-added for its calorific value or used as a starting material for the production of propylene. In the current energy transition period, many refineries are looking for options to increase petrochemical production based on propane feedstock. However, the amount of propane available from a single refinery is relatively limited, and it is not economically justifiable to invest in dedicated propylene production via direct propane dehydrogenation. Therefore, in most cases, propane is usually converted into a mixture containing approximately 28% fuel gas in a steam cracker, the combustion of which results in significant carbon dioxide emissions. The fuel gas yield obtained by converting propane in a steam cracker is much higher than the fuel gas yield obtained from ethane feedstock (i.e., approximately 8% fuel gas) or from naphtha feedstock (i.e., approximately 12% to 15%). In view of this, propane is very inefficient and a polluting feedstock for steam crackers. Therefore, new technologies are needed to increase the value of propane feedstock.

[0003] In recent years, new bio-sourced propanes have emerged, providing opportunities for producing bio-propylene. However, there is a need for an efficient propane-to-propylene technology that is economically attractive even on a small to medium scale. Currently, there are several known biomass-to-energy conversion methods in which bio-propane is produced as a co-product, wherein a wide variety of biomass feedstocks can be used in these methods. These methods range from hydrotreating vegetable oils to produce hydrotreated vegetable oil (HVO) biodiesel to producing synthetic fuels through gasification and synthesis. Currently, the main production route for bio-propane is as a co-product of HVO biodiesel, with the method yield ranging from 5 to 8%. Due to the large amount of HVO biodiesel produced, significant amounts of bio-propane can be obtained. There are also a few new methods that produce bio-propane as the main target product. These include using specialized microorganisms to ferment organic waste to produce bio-propane (rather than biomethane), and directly synthesizing propane from the synthesis gas produced by gasification of woody biomass.

[0004] Propylene is a valuable raw material for chemical synthesis and is in fact one of the two most important starting materials in the petrochemical industry (together with ethylene). For example, propylene is the starting material for the preparation of polypropylene, which is one of the most widely used polymers because it is odorless, skin-friendly, physiologically harmless and has excellent mechanical properties. For example, polypropylene is used for packaging, films, textiles, lids, medical products, mattress covers and many other products. In addition, propylene is used to prepare other important chemicals, such as propylene glycol, acrylonitrile, acrylic acid and propylene oxide.

[0005] Hydrogen is also an important compound, particularly important as an ecologically sustainable energy source, as it produces only water when used as an energy source in fuel cells or burned with oxygen. Furthermore, hydrogen is an important raw material for fertilizer production and in the refining of mineral oils, and is used as a coolant in power plants and for many other purposes. Due to its ecologically sustainable nature, global demand for hydrogen and hydrogen-derived fuels is expected to increase significantly in the coming years, particularly as hydrogen is expected to play a key role in mitigating global warming.

[0006] Hydrogen is typically produced by the electrolysis of water, such as by alkaline electrolysis, proton exchange membrane electrolysis, or solid oxide electrolysis. Different electrolysis technologies have different operating ranges and different efficiencies. Although solid oxide electrolysis, for example, is a high-temperature solution that generally provides relatively high efficiency, the technology has serious disadvantages, such as having a limited lifespan and requiring relatively high capital expenditures, combined with generally low technological maturity. Alkaline electrolysis does not allow power to be adjusted over a fairly wide range, and is furthermore subject to unfavorable low current densities, which in turn increases capital expenditures. In contrast, proton exchange membrane electrolysis can generally operate at higher current densities, which reduces capital expenditures. In addition, proton exchange membrane electrolysis is much more flexible than other water electrolysis technologies (particularly alkaline electrolysis). In view of this, proton exchange membrane electrolysis is generally advantageous for water electrolysis to produce green hydrogen. However, water electrolysis requires a large amount of energy. Therefore, alternative electrolysis pathways for producing hydrogen would be desirable.

[0007] Accordingly, propylene is currently produced primarily in steam crackers and refineries, and several specialized technologies are known. The production of such petrochemicals is associated with significant carbon dioxide emissions, creating a need for new low-carbon technologies to improve this situation. More specifically, propylene is typically produced by direct catalytic dehydrogenation of propane to propylene, which is carried out at relatively high temperatures of 550 to 680°C and relatively low pressures (typically below atmospheric pressure). However, if non-renewable fuels (such as coal) that form large amounts of carbon dioxide during combustion are used to generate the energy required to maintain the required high reaction temperatures, these propane-based direct catalytic dehydrogenation methods—particularly due to the required high reaction temperatures—are energy-intensive and ecologically harmful. The predominantly used direct dehydrogenation methods utilize circulating catalysts or multiple reactors that cycle in a production-purge-regeneration-purge sequence. This requirement stems from propane-propylene equilibrium constraints, which are mitigated by high-temperature and / or low-pressure operation. Overall, these propane-based direct catalytic dehydrogenation methods suffer from high capital expenditures, high operating costs, and the production of large amounts of carbon dioxide. These types of processes are economical only for large scale (e.g., propylene production capacities above 500 kt / y), if at all. In contrast, conventional propane dehydrogenation is not suitable for upgrading petrochemical production in refineries where the availability of large quantities of propane must be guaranteed for very long periods of time.

[0008] Other methods for preparing propylene are known, such as methods based on chemical looping. For example, methods for preparing propylene are known in which bromopropane reacts with copper oxide to form propylene, copper bromide and water, and then copper oxide is regenerated by reacting copper bromide with oxygen to form bromine and copper oxide. However, this method is very energy-consuming. Before bromine is recovered from hydrogen bromide by oxidizing hydrogen bromide to bromine and water, a method in which the bromopropane obtained is dehydrobrominated to propylene and hydrogen bromide with bromine is also known. However, this method requires separation of bromine from water, which is very energy-consuming and makes such methods characterized by high operating costs.

[0009] In summary, known methods for producing propylene suffer from at least one of the following disadvantages, and most suffer from two or more of the following: high operating costs, production of large amounts of carbon dioxide, and the need for high capital expenditures. Furthermore, none of these methods allow for the exclusive electrochemical production of valuable hydrogen. However, electrochemical production of hydrogen would also allow for the utilization of renewable electricity. Furthermore, known methods for producing hydrogen are energy-intensive and do not allow for the production of propylene.

[0010] In view of this, it was an object of the present invention to provide a process for preparing propylene and hydrogen, wherein the process can be operated on an industrial scale, has a relatively low energy requirement, is eco-friendly and, in particular, does not produce large amounts of carbon dioxide and does not require high capital expenditures.

[0011] According to the present invention, this object is solved by providing a process for producing propylene and hydrogen from propane, comprising the following steps:

[0012] a) reacting a mixture comprising propane and bromine to produce a first reaction mixture comprising bromopropane and hydrogen bromide,

[0013] b) subjecting the first reaction mixture obtained in step a) to at least one separation step in order to obtain a composition enriched in bromopropane and in order to obtain a composition enriched in hydrogen bromide,

[0014] c) catalytically reacting the bromopropane-rich composition obtained in step b) to produce a second reaction mixture containing propene and hydrogen bromide,

[0015] d) subjecting the second reaction mixture obtained in step c) to at least one separation step to obtain a composition enriched in hydrogen bromide and to obtain propene, and

[0016] e) subjecting the composition enriched in hydrogen bromide obtained in step b) and / or the composition enriched in hydrogen bromide obtained in step d) to electrolysis to obtain hydrogen and a bromine-containing composition.

[0017] Thus, hydrogen and propylene can be produced in an eco-friendly manner, with relatively low operating costs and relatively low capital expenditures. Furthermore, the method according to the present invention is characterized by a high propylene yield. Since the method according to the present invention is not based on the direct conversion of propane to propylene, this method—in contrast to known methods for the direct catalytic dehydrogenation of propane to propylene—is not limited by the propane-propylene equilibrium and therefore does not require reactions at relatively high temperatures. In contrast, the dehydrobromination reaction in step c) can be carried out at relatively low reaction temperatures. This not only reduces operating costs but also increases propylene yields and reliably avoids the disadvantages of coking caused by high temperatures. Furthermore, since the reaction in step c) is carried out catalytically, energy-intensive chemical looping, as used in some prior art methods, can be avoided. Furthermore, the regeneration of bromine from hydrogen bromide by electrolysis in step e) contributes positively to the low operating costs and low capital expenditures of the method according to the present invention, as it does not require the energy-intensive separation of water and hydrogen bromide from a mixture containing them. Furthermore, the electrolytic method also allows the production of pure hydrogen. In summary, the process according to the invention produces both propylene and hydrogen, can be operated on an industrial scale, has a rather low energy requirement, is eco-friendly and, in particular, does not produce large amounts of carbon dioxide and does not require high capital expenditures.

[0018] In step a), a mixture comprising propane and bromine is reacted to produce a first reaction mixture containing bromopropane and hydrogen bromide. Good results are particularly achieved when the mixture comprising propane and bromine used in step a) contains 10 to 90 volume % and preferably 50 to 80 volume % propane and 10 to 50 volume % and preferably 20 to 45 volume % bromine. Furthermore, it is preferred that the mixture contain less than 0.5 volume % of unsaturated compounds, particularly propylene, unsaturated hydrocarbon compounds, and unsaturated brominated hydrocarbon compounds. This allows for limiting the polybrominated compounds in the first reaction mixture and allows for easy separation of unreacted propane from the reaction mixture and for propane recycling to be fed to the mixture of bromination reaction a).

[0019] About the source of propane contained in the mixture reacted in step a), there is no particular limitation according to the method of the present invention. For example, pure propane can be used and mixed with bromine to obtain the mixture used in step a). However, a crude composition comprising propane as one of the multiple components can also be used. Suitable examples are therefore natural gas, refinery gas and petroleum gas. Therefore, a mixture can be reacted in step a), the mixture containing a gas selected from natural gas, refinery gas and petroleum gas, biopropane prepared in a biodiesel plant, biopropane synthesized by glycerol, biopropane prepared as biogas by fermentation of organic waste, biopropane directly synthesized by synthesis gas produced by gasification of woody biomass or other renewable sources, and two or more of the above-mentioned gases in any combination, and the mixture further contains bromine. The mixture can optionally further contain purified propane, and in fact preferably contains purified propane, which is separated from the first reaction mixture and recycled to the mixture reacted in step a).

[0020] The propane feedstock typically contains a significant amount of propylene. Furthermore, in some embodiments of the present invention, a small amount of propylene is also formed during the reaction in step a) and is thus contained in the first reaction mixture, which, as further described below, can be recycled to step a) along with the purified propane composition. In such cases, it is preferred that the propane feedstock or the mixture reacted in step a) be subjected to at least one purification step before being added to the mixture reacted in step a) to selectively remove propylene from the propane feedstock or the mixture reacted in step a), respectively. The method according to the present invention is not particularly limited in terms of the method for purifying the propane-rich composition. For example, currently commercially available methods, namely distillation and catalytic hydrogenation, can be used. Distillation is a viable technique for removing propylene from propane, but due to the very low relative volatility of the two species, both capital and energy costs are high. Catalytic hydrogenation is simple and straightforward, but also has high capital costs, and the cost / availability of the required continuous hydrogen production can also be problematic. Alternative methods are based on absorption / stripping based on aqueous silver nitrate and pressure swing adsorption (PSA) based on zeolite molecular sieves, preferably silver-containing molecular sieves, i.e., AgX zeolites. Membranes can also be used, i.e., in a single-stage separation, to achieve propylene-propane separation results equivalent to those obtained with distillation involving multiple stages, using simple, compact, and robust equipment. Chemoselective adsorbents provide an even higher degree of separation in a single stage, although more complex equipment is required. An interesting alternative is the selective oxidation of propylene to carbon monoxide over a silver-containing catalyst. If the propylene concentration in the composition to be purified is very high, such as 10% by weight or more, only distillation or direct hydrogenation is preferred. If the propylene concentration in the composition to be purified is in the mid-range of 2 to 8% by weight, membranes and physical adsorption are promising options. If the propylene concentration in the composition to be purified is relatively low, i.e., less than 2% by weight, chemical absorption and adsorption are the most preferred separation techniques. If the propylene concentration in the composition to be purified is less than 2% by weight, distillation and membranes are uneconomical, and if the propylene concentration in the composition to be purified is 0.1% by weight or less, only chemical absorption, adsorption, or hydrogenation is preferred. The principle of absorptive separation is based on contacting a propane-propylene mixture with a liquid containing, for example, silver(I) ions. Propylene binds to silver, while propane does not. Thus, propane loading is limited to its physical solubility, while propylene loading can approach a 0.3:1 molar ratio to silver loading. The liquid is then depressurized or heated to break the propylene-silver bonds and recover relatively pure propylene. In its simplest embodiment, the system looks and operates very similar to an amine absorber / stripper for acid gas removal. In turn, the principle of propane / propylene separation by PSA adsorption can be based on, for example, 13X zeolite. Alternatively, the Petrofin process can be used, which utilizes 4A zeolite and a process specifically tailored for "kinetic" propylene / propane separations.Kinetic separation is possible when two competing species adsorb approximately equally at equilibrium, but one species adsorbs "faster" than the other due to a higher diffusion rate in the pores. This is the case in the Petrofin process, where propylene indeed diffuses into the pores faster than propane, making it possible to selectively remove propylene by keeping the PSA cycle time too short to allow true equilibrium to be reached.

[0021] The present invention is not particularly limited as to the ratio of propane to bromine in the mixture used in step a). Good results are particularly achieved when the molar ratio of propane to bromine in the reaction mixture used in step a) is from 10:1 to 1:1 and preferably from 3:1 to 2:1.

[0022] The reaction in step a) can be carried out in the presence of a catalyst. However, in order to save costs, a further development of the concept of the invention proposes to induce the reaction in step a) only thermally and to react the mixture in step a) without a catalyst.

[0023] To thermally induce the reaction in step a), the mixture is preferably reacted in step a) at a temperature of 200 to less than 420° C., more preferably 230 to 410° C., even more preferably 240 to 400° C., and most preferably 240 to 300° C. In addition to being sufficiently high to thermally induce the reaction in step a), the aforementioned temperature is also sufficiently low to minimize the formation of undesirable unsaturated compounds (such as propylene and allyl bromide) and undesirable coke formation in step a). This is advantageous because allyl bromide has a boiling temperature very close to that of propane bromide and is therefore extremely difficult to separate from it, for example, by distillation. In addition, allyl bromide may deactivate the dehydrobromination catalyst used in step d). Avoiding propylene formation is advantageous because otherwise the unreacted propane contained in the first reaction mixture cannot be effectively separated from the first reaction mixture and recycled to step a) at low operating costs.

[0024] Preferably, the mixture is reacted in step a) under elevated pressure, more preferably at a pressure of at least 400 kPa, even more preferably at a pressure of at least 1 MPa and most preferably at a pressure of 1 to 4 MPa. Elevated pressure leads to high conversions per time unit and advantageously avoids or at least minimizes the formation of unsaturated products (such as allyl bromide or propene) in the reaction mixture.

[0025] According to another particularly preferred embodiment of the present invention, in step a), the residence time of mixture is at least 10 seconds and more preferably 20 seconds to 2 minutes. In this respect, residence time refers to the time period between the mixture entering the reactor (carrying out the reaction in the reactor) and the first reaction mixture leaving the reactor. A residence time of at least 210 seconds ensures that all or at least substantially all bromine is consumed. This is important because if the reaction mixture contains a certain amount of highly reactive bromine, it will be necessary to use a container made of more expensive materials in the downstream of the reactor so that they tolerate bromine.

[0026] The reaction in step a) can be carried out in any reactor type, such as an isothermal reactor or an adiabatic reactor. For example, the mixture is reacted in step a) in an adiabatic reactor, preferably with an outlet temperature of less than 450° C., more preferably at most 420° C. and even more preferably at most 400° C.

[0027] In practice, not all of the bromine and / or propane will react to form bromopropane during the reaction in step a), but polybromopropanes will also be formed, and small amounts of bromine and propane will remain in the reaction mixture as unreacted educts. Therefore, the first reaction mixture obtained in step a) will, in practice, further contain one or more polybromopropanes, unreacted propane, and optionally at least trace amounts of unreacted bromine. A polybromopropane is any brominated propane having two or more bromine residues per molecule, i.e., any dibromopropane, tribromopropane, or higher brominated propane.

[0028] In step b) of the process according to the present invention, the first reaction mixture obtained in step a) is subjected to at least one separation step to obtain a bromopropane-enriched composition and a hydrogen bromide-enriched composition. A bromopropane-enriched composition is any composition having a higher bromopropane concentration after the separation step in step b) than the first reaction mixture. Similarly, a hydrogen bromide-enriched composition is any composition having a higher hydrogen bromide concentration after the separation step b) than the first reaction mixture. Preferably, the bromopropane-enriched composition has a bromopropane concentration of at least 10% by weight, and more preferably at least 50% by weight.

[0029] Preferably, step b) comprises at least one and preferably two distillation steps for separating the bromopropanes from the first reaction mixture in order to obtain said bromopropane-enriched composition.

[0030] In addition, preferably step b) comprises at least one absorption step, which is used to separate hydrogen bromide from the first reaction mixture to obtain a composition rich in hydrogen bromide. When water or an aqueous composition is used as an absorbent in at least one absorption step, particularly good results are obtained. For example, the absorbent can be an aqueous composition containing at least 80% by weight and preferably at least 95% by weight of water and one or more compounds such as hydrogen bromide to make up to 100% by weight. Particularly preferably, the aqueous composition used as the absorbent contains hydrogen bromide, such as hydrogen bromide recovered from the spent absorbent, which is preferably used in the loop, i.e., recovered after the absorption step.

[0031] Furthermore, it is preferred that the hydrogen bromide-rich composition has a hydrogen bromide concentration of at least 30% by weight, and more preferably at least 40% by weight, and an absorbent content of at most 60% by weight, and more preferably at most 48% by weight. If the absorbent is water, in practice the hydrogen bromide-rich composition is an aqueous solution containing hydrogen bromide.

[0032] According to a particularly preferred embodiment of the present invention, step b) comprises a distillation step for distilling the first reaction mixture to obtain a composition rich in bromopropanes and polybromopropanes as a bottom composition and a tower overhead composition containing hydrogen bromide, unreacted propane and unreacted bromine. The tower overhead composition obtained in the distillation step is then preferably subjected to an absorption step with water or an aqueous composition to obtain a purified propane composition (or a propane-rich composition, respectively) and a hydrogen bromide-rich composition, the hydrogen bromide-rich composition being a mixture comprising hydrogen bromide, water and optionally trace amounts of bromine. The purified propane composition can then be dried to remove traces of water still contained therein. The purified propane composition obtained preferably contains at least 80% by weight and more preferably at least 95% by weight of propane and less than 500 ppm and more preferably less than 100 ppm of water and other impurities. At least a portion of the purified propane composition, such as at least 80% by volume and preferably all of the purified propane composition, is recycled to the mixture used in step a). Recycling the purified propane composition to step a) means that the purified propane composition is mixed with a starting composition containing propane (such as natural gas) and bromine to form the mixture that is reacted in step a).

[0033] It is further preferred in this embodiment that the bottoms composition obtained in the distillation step is subjected to a (further) distillation step to obtain a bromopropane-rich composition as an overhead composition and a polybromopropane-rich composition as a bottoms composition. Particularly preferably, the bromopropane-rich composition subjected to the dehydrobromination reaction in step c) contains less than 2% by weight and most preferably less than 0.5% by weight of polybromopropanes.

[0034] The dehydrobromination reaction in step c) is endothermic and is therefore preferably carried out at elevated temperature. Good results are particularly achieved when the bromopropane-rich composition obtained in step b) is reacted in step c) at a temperature of 250 to 450° C. For example, in step c), the weight hourly space velocity of bromopropane in the bromopropane-rich composition is from 0.1 to 20 l / h, and the partial pressure of bromopropane is less than 500 kPa, and more preferably less than 200 kPa.

[0035] The dehydrobromination reaction of step c) can be carried out in one reactor or in multiple reactors arranged in series with interstage reheating. The reactor or (if two or more reactors are used) each reactor can be a fixed bed, multi-tubular reactor, moving bed reactor or fluidized bed reactor. For example, the dehydrobromination reaction of step c) can be carried out in a series of adiabatic fixed bed reactors with interstage reheating. The fixed bed reactor can also be a radial reactor or a spherical reactor.

[0036] According to the present invention, the dehydrobromination reaction of step c) is carried out as a catalytic reaction. Good results are particularly achieved when the bromopropane-rich composition obtained in step b) is reacted in step c) in the presence of a catalyst selected from the group consisting of alumina, silica, silica-alumina, zeolites with a Si / Al ratio greater than 25, titanium oxide, zirconium oxide, and any combination of two or more of the aforementioned materials.

[0037] Particularly preferably, the catalyst may additionally contain 0.1 to 10% by weight of at least one transition metal selected from the group consisting of iron, cobalt, molybdenum, nickel, tungsten, copper, silver, manganese, and any combination of two or more of the aforementioned metals. The metal-containing catalyst may additionally be doped with an element selected from the group consisting of boron, phosphorus, platinum, palladium, and any combination of two or more of the aforementioned elements.

[0038] It is particularly preferred if the alumina is gamma-alumina of high purity. Alumina with a purity of 99.99% or more can be synthesized, for example, by the alkoxide route. The alkoxide route is a well-established large-scale production technology based on the hydrolysis of aluminum alkoxides. In this process, the alcohol of the aluminum alkoxide is recycled back to the synthesis. Alumina is produced as a co-product with a synthetic linear alcohol (Ziegler process) or directly from aluminum metal (dedicated route). The Ziegler route for the synthesis of alumina involves the oligomerization of ethylene using triethylaluminum and subsequent oxidation. Triethylaluminum can be produced by reacting aluminum, ethylene and hydrogen. In this production process, two-thirds of the triethylaluminum produced is recycled back to the reactor and only one-third is used to produce the alcohol. The recycling step is used to produce triethylaluminum with higher yields and shorter times. Triethylaluminum reacts with ethylene to form trialkylaluminum of higher molecular weight. The number of ethylene equivalents, n, is equal to the total number of monomer units grown on the initial ethylene chain, where n=x+y+z, where x, y and z are the number of ethylene units per chain. The trialkylaluminum is oxidized with air to form an aluminum alkoxide, which is ultimately hydrolyzed to aluminum hydroxide and the desired alcohol.

[0039] Al+3C2H4+1.5H2→Al(C2H5)3

[0040] Al(C2H5)3+nethylene→Al((CH2CH2) n CH2CH3)3

[0041] Al((CH2CH2) n CH2CH3)3+O2→Al(O(CH2CH2) n CH2CH3)3

[0042] Al(O(CH2CH2) n CH2CH3)3→Al(OH)3+CH3CH2(CH2C2) m OH

[0043] Optionally, the catalyst contains 0.1 to 5 wt% of magnesium, calcium, cerium or lanthanum. For example, the catalyst can be made of magnesium-doped alumina, calcium-doped alumina, cerium-doped alumina, or lanthanum-doped alumina.

[0044] The catalyst may contain 3.8 to (Angstroms) pore size of the medium-pore zeolite having a Si / Al ratio greater than 25. Most preferably, the catalyst is composed of a zeolite having a pore size of 4.5 to The catalyst is made from a medium-pore zeolite having a pore size of 1000 nm and a Si / Al ratio of greater than 150. The zeolite may have been subjected to steam treatment, ion exchange or modification with phosphorus before use as a catalyst.

[0045] In a further development of the inventive concept, it is proposed to react the bromopropane-rich composition obtained in step b) in the presence of hydrogen in step c). The presence of hydrogen improves catalyst stability and also prevents rebromination of the produced propene. Good results are particularly achieved when the molar ratio of bromopropane to hydrogen in the mixture reacted in step c) is from 10:1 to 1:10 and more preferably from 5:1 to 1:5.

[0046] Alternatively, the dehydrobromination reaction of step c) can be carried out in the absence of hydrogen, but hydrogen is added to the second reaction mixture obtained in step c) after termination of the reaction.

[0047] In yet another preferred embodiment of the present invention, a heat carrier is added to the reactor in which the reaction of step c) is carried out to make the reaction more isothermal. Suitable examples of heat carriers are nitrogen, argon, C 5-12 Alkanes, water, hydrogen bromide solution and hydrogen bromide gas.

[0048] In a further development of the concept of the invention, it is proposed to recirculate part of the second reaction mixture as heat carrier into step c).

[0049] According to the present invention, in step d), the second reaction mixture obtained in step c) is subjected to at least one separation step to obtain a composition enriched in hydrogen bromide and to obtain propylene. Similarly, a composition enriched in hydrogen bromide is any composition having a higher hydrogen bromide concentration than the second reaction mixture after separation step d). Preferably, the propylene contains less than 1,000 ppm and more preferably less than 50 ppm of impurities.

[0050] According to a particularly preferred embodiment of the present invention, step d) comprises at least one and preferably two purification steps, which are most preferably distillation steps, for separating propene from the second reaction mixture to obtain propene.

[0051] Furthermore, it is preferred that step d) include at least one absorption step for separating hydrogen bromide from the second reaction mixture to obtain a composition rich in hydrogen bromide. Good results are particularly achieved when water or an aqueous composition is used as the absorbent in at least one of the absorption steps. As in step b), the absorbent may contain at least 80% by weight and preferably at least 95% by weight of water and one or more compounds, such as hydrogen bromide, to a total of 100% by weight. It is particularly preferred that the aqueous composition used as the absorbent contain hydrogen bromide, such as hydrogen bromide recovered from the spent absorbent, which is preferably used in the loop, i.e., recovered after the absorption step.

[0052] Furthermore, it is preferred that the hydrogen bromide-rich composition has a hydrogen bromide concentration of at least 30 wt. %, and more preferably at least 40 wt. %, and an absorbent content of at most 60 wt. %, and more preferably at most 48 wt. %. Likewise, if the absorbent is water, the hydrogen bromide-rich composition is, in effect, an aqueous solution containing hydrogen bromide.

[0053] According to a particularly preferred embodiment of the present invention, step d) comprises a distillation step for distilling the second reaction mixture to obtain a polybrominated propane-rich composition as a bottoms composition and an overhead composition comprising propene, hydrogen bromide, and optionally hydrogen. The overhead composition obtained in the distillation step is then subjected to an absorption step, preferably with water or an aqueous composition, to obtain propene or a composition comprising propene and hydrogen, and to obtain a composition enriched in hydrogen bromide, which is a mixture comprising water and hydrogen bromide. If a composition comprising propene and hydrogen is obtained, the hydrogen is then preferably separated from the composition, for example by pressure swing adsorption, to obtain (pure) propene.

[0054] It is further preferred in this embodiment that the bottoms composition obtained in the distillation step is subjected to a (further) distillation step to obtain C as overhead composition. 4-5 A hydrocarbon composition and a polybrominated propane-rich composition as a bottoms composition.

[0055] According to the present invention, in step e), the hydrogen bromide-rich composition obtained in step b) and / or the hydrogen bromide-rich composition obtained in step d) is subjected to electrolysis to obtain hydrogen and a bromine-containing composition. Preferably, in step e), the hydrogen bromide-rich composition obtained in step b) and the hydrogen bromide-rich composition obtained in step d) are subjected to electrolysis.

[0056] Furthermore, it is preferred to recycle at least a portion, and more preferably all, of the bromine-containing composition obtained in the electrolysis back to step a).

[0057] In a further development of the concept of the invention, it is proposed to carry out the electrolysis in step e) by using an electrolysis cell comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode, wherein an electric field can be applied between the anode and the cathode, the composition enriched in hydrogen bromide obtained in step b) and / or (and preferably together with) the composition enriched in hydrogen bromide obtained in step d) being fed to the anode, optionally a second composition comprising hydrogen bromide and water being fed to the cathode, and the electrolysis cell being operated so as to produce hydrogen at the cathode, wherein a bromine-containing composition is produced at the anode.

[0058] As explained in further detail below, the electrolysis in step e) is preferably carried out by using an electrolysis cell comprising a membrane made of a fluoropolymer having a glass transition temperature of at least 110°C.

[0059] Furthermore, it is preferred that the electrolysis is carried out in step e) by operating the electrolysis cell at an operating temperature of at least 70°C, wherein the operating temperature is below the boiling point of the optional second composition fed to the cathode, and preferably at an operating temperature of 70 to 122°C.

[0060] Furthermore, it is preferred that the electrolysis is carried out in step e) by operating the electrolysis cell at an operating pressure which increases from the anode to the cathode.

[0061] The anode and cathode typically comprise a conductive material, in particular a metal, a coated metal, carbon cloth, graphite felt, a carbon fiber composite, a carbon-loaded polymer or graphite, and are preferably made of a carbon fiber composite or a coated metal. The membrane can be a sheet or layer that can be used in a standard electrolyzer, preferably as a proton exchange membrane. Therefore, preferably, protons can migrate through such membranes.

[0062] As described above, electrolysis is preferably carried out with a liquid (i.e., aqueous) composition rich in hydrogen bromide obtained in the absorption step carried out in step b) and / or step d). However, alternatively but less preferably, if before electrolysis, separation and removal of absorbent are performed from hydrogen bromide, or if separation of hydrogen bromide is achieved by a separation technique different from absorption in step b) and / or step d), the gaseous composition rich in hydrogen bromide can be used for the electrolysis in step e). In the aqueous composition containing hydrogen bromide, hydrogen bromide is dissolved in water, wherein the hydrogen bromide dissolved in water will generally dissociate in water so that the composition will include ionic species, especially protons, hydronium ions, and bromine cations. At the anode of the feed hydrogen bromide, protons are produced during electrolysis, and the protons subsequently migrate to the cathode through the membrane. According to the present invention, the aqueous composition rich in hydrogen bromide can also be fed to the cathode. This allows electrolyzers to be operated at lower operating voltages, which reduces operating costs. In addition, this allows operating the electrolyzer at a higher temperature, which reduces the cooling and / or heating requirements of the electrolyzer, which also reduces operating costs. In addition, this allows operating the electrolyzer at a higher current density, which reduces the capital expenditure of the electrolyzer. In addition, this can reduce the concentration gradient across the membrane, and thus reduce or even alleviate the undesirable transfer of hydrogen bromide and / or bromine and / or bromine cations through the membrane from anode to cathode. In addition, the presence of hydrogen bromide on the cathode side can allow hydrogen bromide to pass through the membrane from the cathode to the anode side. This improves system efficiency and allows avoiding any disturbance during the electrolysis. Without wishing to be bound by theory, it is assumed that in this embodiment, there is actually hydrogen bromide in the opposite direction to cross, i.e. from cathode to anode. The reverse crossing of this type of hydrogen bromide is considered to be one of the reasons that can improve the electrolysis efficiency of this embodiment. In this embodiment, it is preferred that the hydrogen bromide concentration of the composition fed to the cathode is at least 0.5 mol / kg, more preferably at least 1 mol / kg, even more preferably at least 2 mol / kg, even more preferably at least 3 mol / kg, further preferably at least 4 mol / kg, even further preferably at least 5 mol / kg and most preferably at least 6 mol / kg, wherein mol / kg refers to the number of moles of hydrogen bromide per kilogram of the corresponding composition.

[0063] Regardless of whether the hydrogen bromide composition is directed to the cathode of the electrolysis cell, it is preferred that during the electrolysis in step e) the operating voltage U is from greater than 0 mV to 1,900 mV and preferably from greater than 0 mV to 1,700 mV. op Operating the electrolyzer at such an operating voltage improves the selectivity of the reaction to hydrogen bromide electrolysis and thereby reduces the operating costs of the electrolysis.

[0064] In a further development of the inventive concept, the electrolysis in step e) is preferably carried out by operating the electrolysis cell at an operating temperature of 70° C. to 122° C. Operating the electrolysis cell at such an operating temperature can reduce cooling and / or heating requirements. Such higher temperatures increase the proton conductivity of the membrane comprising the fluoropolymer, which allows the electrolysis cell to be operated at higher current densities and / or lower voltages. Higher current densities help keep capital expenditures low. It is therefore particularly preferred to maintain an operating temperature of greater than 70° C., more preferably greater than 90° C., and most preferably greater than 100° C.

[0065] It is further preferred that the electrolyzer is operated at an operating pressure during the electrolysis in step e), and the operating pressure is increased from the anode to the cathode. In other words, there is a pressure gradient increased from the anode to the cathode, wherein the corresponding pressures at the anode and cathode have the same reference point, that is, both are absolute pressures, or both are gauge pressures relative to the atmosphere around the electrolyzer. In such cases, electrolysis typically occurs in the gas phase, i.e., by feeding a gaseous stream to the anode and cathode. In such cases, the pressure at the cathode is higher than the pressure at the anode, preferably at least 0.01 MPa (i.e., the difference between the pressure at the cathode and the pressure at the anode is 0.01 MPa or more), more preferably at least 0.02 MPa, more preferably at least 0.05 MPa, and most preferably at least 0.1 MPa. For example, when the absolute pressure at the anode is 0.1 MPa, the absolute pressure at the cathode is 0.11 to 0.3 MPa, more preferably 0.12 to 0.25 MPa, more preferably 0.15 to 0.2 MPa, and most preferably 0.2 MPa. However, an optional pressure at the cathode is also contemplated, which is 1 MPa, 2 MPa, 3 MPa, 4 MPa or even 5 MPa higher than the pressure at the anode. Using such a gradually increasing pressure or pressure gradient, a reduced operating voltage of the electrolyzer can be achieved, which can reduce operating costs. In addition, the pressure gradient can allow hydrogen to be obtained at a higher pressure on the cathode side, making it possible to subsequently eliminate the need for compression or require less compression to densify the hydrogen obtained. In addition, operation under differential pressure improves operating parameters.

[0066] According to another preferred embodiment of the present invention, the membrane used for the electrolysis of step e) is a fluoropolymer membrane. When the fluoropolymer membrane has a glass transition temperature of at least 110°C, preferably at least 120°C and more preferably at least 125°C, good results are particularly obtained. Preferably, the fluoropolymer membrane (in a dry state) is composed of a fluoropolymer, and more preferably is composed of a chemically stable form of the fluoropolymer. As used herein, a fluoropolymer is a fluorocarbon-based polymer with multiple carbon-fluorine bonds. Such fluoropolymers generally do not contain silicon atoms. Such fluoropolymers may further contain no chlorine, bromine and / or iodine atoms. As used herein, the glass transition temperature of the fluoropolymer membrane is determined according to DIN EN ISO 11357-2:2020-08 (half-step height method). Therefore, as used herein, the glass transition temperature of the fluoropolymer membrane is determined by differential scanning calorimetry (DSC) measurement, more specifically by the curve obtained by such DSC measurement. The glass transition temperature of the fluoropolymer membrane is determined on a sample of the fluoropolymer membrane, more specifically on a sample of the fluoropolymer membrane in the fully hydrated state. According to the present invention, a fluoropolymer membrane in a fully hydrated state is a fluoropolymer membrane that does not absorb any further (deionized) water (deionized H2O, as described in the ASTM D5127-13 (2018) standard) at a temperature of 80°C after 24 hours, which is therefore a fully hydrated fluoropolymer membrane or a fluoropolymer membrane saturated with water. Therefore, the water absorption of the fluoropolymer membrane has reached its maximum value. A fully hydrated fluoropolymer membrane is obtained by immersing the fluoropolymer membrane in deionized water, which will result in an increase in the weight of the fluoropolymer membrane that can be measured by a balance. When the weight no longer increases over time, the fluoropolymer membrane is in a fully hydrated state. A fluoropolymer membrane in a fully hydrated state is typically obtained by immersing the fluoropolymer membrane in deionized water having a temperature of 80°C for 24 hours. As used herein, the glass transition temperature refers to the lowest glass transition temperature of the fluoropolymer. It is known that certain polymers or films made of a plurality of polymers, respectively, e.g. Membranes of this type may have several glass transition temperatures, in particular two glass transition temperatures. The first glass transition temperature is due to the mobility of the main chain in the polymer matrix, while the second glass transition temperature is due to side chain effects, in particular effects associated with strong interactions of functional groups in such side chains (such as sulfonic acid groups). Once the first glass transition temperature is reached, the membrane undergoes irreversible changes and, in particular, can no longer be used in electrolysis processes. Therefore, in the context of the present invention, if a material, in particular a membrane or a membrane sample, exhibits multiple glass transition temperatures, only the lowest glass transition temperature is relevant to the definition of glass transition temperature provided herein.

[0067] Fluoropolymer membranes having a glass transition temperature of at least 110°C allow electrolysis to be performed at higher temperatures and / or higher pressures. This is because the fluoropolymer membrane is more resilient. Without wishing to be bound by theory, it is hypothesized that the resiliency to hydrogen bromide at higher temperatures and higher pressures, as well as to hydrogen and bromine after electrolysis, is provided by the fluoropolymer membrane having a glass transition temperature of at least 110°C. Furthermore, higher temperatures, in particular, can reduce the electrical resistance of the fluoropolymer membrane, which can allow for higher proton conductivity. Higher proton conductivity enables higher current densities to be achieved at lower operating voltages. Higher current densities help keep capital expenditures low, while lower operating voltages lead to lower operating costs.

[0068] Preferably, the fluoropolymer of the membrane comprises -(CF2-CF2)- repeating units. Such -(CF2-CF2)- repeating units increase the elasticity of the fluoropolymer membrane. The increased elasticity allows hydrogen bromide electrolysis to be carried out at higher temperatures and higher pressures, which allows operation at higher current densities and / or lower voltages, thereby making the electrolysis more economical. Furthermore, it is preferred that the fluoropolymer of the membrane does not contain structural entities of the formula -O-CF2-CF(CF3)-O-. Such structural entities are found in the membranes marketed under the trade name In commercially available films, however, this may result in a less rigid film that is therefore more susceptible to degradation at higher temperatures and higher pressures.

[0069] Preferably, the fluoropolymer membrane, and more specifically the fluoropolymer contained in and preferably constituting the membrane, comprises -CF3 chain ends. Such -CF3 chain ends can increase the elasticity of the fluoropolymer membrane. Increased elasticity can allow HBr electrolysis to be performed at higher temperatures and higher pressures, and can allow operation at higher current densities and / or lower voltages, thereby making the process according to the present invention more economical.

[0070] According to a particularly preferred embodiment of the present invention, the fluoropolymer of the membrane is a sulfonated fluoropolymer. As used herein, sulfonation means that the fluoropolymer of the fluoropolymer membrane carries -SO3H groups. Such -SO3H groups increase the proton conductivity of the fluoropolymer membrane, which allows electrolysis to be operated at higher current densities and / or lower voltages, thereby making electrolysis more economical. It is particularly preferred that the sulfonated fluoropolymer contains -O-(CF2) n -SO3H group, wherein n is an integer selected from 1, 2, 3, 4 and 5, preferably 2. Such -O-(CF2) nThe -SO3H group contributes to achieving an improved proton conductivity of the fluoropolymer membrane while increasing the elasticity of the fluoropolymer membrane. A favorable balance between these effects is particularly achieved when n is selected from 1 to 5 and especially when n is 2. Without wishing to be bound by theory, it is assumed that -O-(CF2) n The relatively short chain length of the -SO3H groups increases the glass transition temperature of the fluoropolymer membrane, making it more resilient at higher temperatures. Therefore, the sulfonated fluoropolymer membrane is particularly advantageous from the perspective of hydrogen bromide electrolysis at higher temperatures and / or higher pressures, and therefore at higher current densities and / or lower voltages. Consequently, the sulfonated fluoropolymer membrane makes electrolysis particularly economical.

[0071] The sulfonated fluoropolymer membrane preferably comprises a hydrolyzed copolymer of F2C=CF2 and CF2=CF-O-(CF2)2-SO2F. Such a hydrolyzed copolymer can result in improved proton conductivity and / or increased elasticity of the fluoropolymer membrane. Therefore, the sulfonated fluoropolymer membrane is particularly advantageous from the perspective of hydrogen bromide electrolysis at higher temperatures and / or higher pressures, and therefore at higher current densities and / or lower voltages. Consequently, the sulfonated fluoropolymer membrane makes electrolysis particularly economical.

[0072] It is further preferred that the fluoropolymer membrane has an acid capacity of at least 0.9 meq / g, more preferably 0.95 to 1.5 meq / g and most preferably 1.0 to 1.2 meq / g. As used herein, meq / g refers to milliequivalents / gram, wherein the equivalent is mol-H (i.e., the mole number of H-acidic sites), preferably mol-SO h (i.e., the mole number of H-groups). The acid capacity represents the sum of the active sites or functional groups responsible for the proton exchange of the fluoropolymer membrane. This type of acid capacity can improve proton conductivity, and can cause the hydrogen bromide conversion rate to improve in the electrolysis thus. The hydrogen bromide conversion rate improved reduces the need for separation and possible recycling of unconverted hydrogen, which can help to maintain low capital expenditure.

[0073] It is further preferred that the fluoropolymer membrane (in the dry state) has a thickness of 25 to 350 μm, more preferably 40 to 150 μm, even more preferably 45 to 130 μm, and most preferably 45 to 55 μm. Such thicknesses achieve a good balance between sufficient flexibility on the one hand and low capital expenditure on the other. At lower thicknesses, there is a risk of undesirable crossover of hydrogen / bromine through the fluoropolymer membrane, and at higher thicknesses, an undesirable reduction in proton conductivity may result.

[0074] In a further development of the concept of the invention, it is proposed that the fluoropolymer film (in the dry state) has a viscosity of at least 1.70 g / cm 3, more preferably at least 1.80 g / cm 3 , even more preferably 1.80 to 2.00 g / cm 3 and most preferably 1.90 to 1.95 g / cm 3 The density of the fluoropolymer film can be measured on its sample according to ASTM D79220. It is further preferred that the fluoropolymer film (in a dry state) has a tensile modulus of 100 to 500 MPa, more preferably 150 to 400 MPa, even more preferably 200 to 300 MPa and most preferably 260 to 280 MPa. The tensile modulus of the fluoropolymer film can be measured on its sample according to ASTM D63814. In addition, it is preferred that the fluoropolymer film (in a dry state) has a tensile stress at break in the machine direction (MD) according to ASTM D882-18 of 10 to 70 MPa, more preferably 20 to 60 MPa, even more preferably 30 to 50 MPa and most preferably 35 to 45 MPa. Furthermore, it is preferred that the fluoropolymer film (in a dry state) has a tensile stress at break in the transverse direction (CD) according to ASTM D882-18 of 5 to 60 MPa, more preferably 10 to 50 MPa, even more preferably 20 to 40 MPa, and most preferably 25 to 35 MPa. Furthermore, it is preferred that the fluoropolymer film (in a dry state) has an elongation at break in the machine direction (MD) according to ASTM D882-18 of 100 to 200%, more preferably 120 to 180%, even more preferably 140 to 160%, and most preferably 145 to 155%. Similarly, it is preferred that the fluoropolymer film (in a dry state) has an elongation at break in the transverse direction (CD) according to ASTM D882-18 of 100 to 350%, more preferably 120 to 300%, even more preferably 150 to 250%, and most preferably 190 to 210%. The above properties enhance the elasticity of the fluoropolymer film. The increased flexibility allows the hydrogen bromide electrolysis to be performed at higher temperatures and higher pressures, which can allow operation at higher current densities and / or lower voltages, thereby making the electrolysis of step e) more economical.

[0075] The bromine-containing composition obtained during the electrolysis in step e) may contain water and may contain more or less unconverted hydrogen bromide. Therefore, in a further development of the inventive concept, it is proposed to purify the bromine-containing composition obtained during the electrolysis in step e), and then preferably recycle at least a portion thereof back to step a). Preferably, the purification comprises a distillation step. During the distillation, a mixture of hydrogen bromide and water is obtained as a bottoms composition, and purified bromine is obtained as an overhead composition. Although the purified bromine can be further purified, for example by subjecting it to a drying step to further reduce its water content, the mixture of water and hydrogen bromide obtained as the bottoms composition of the distillation can be used as an absorbent in the absorption step, before preferably recycling at least a portion, and more preferably all, of the thus purified bromine back to step a). Optionally, before using the bottoms composition as an absorbent, residual traces of bromine may be removed from the bottoms composition, wherein the removal of residual traces of bromine may be carried out by treating the bottoms composition with an oxidizable compound, such as a compound selected from the group consisting of hydrogen, a composition containing carbon monoxide, ammonia, hydrogen sulfide, sulfur dioxide, and any combination of two or more of the foregoing compounds. For example, a mixture of hydrogen bromide and water obtained as a distilled bottoms composition and subsequently optionally dried contains 50 to 99% by weight of water and 1 to 50% by weight of hydrogen bromide.

[0076] The hydrogen produced during the electrolysis in step e) can be withdrawn completely from the process as product, or a portion of the produced hydrogen can be recycled to the dehydrobromination reaction carried out in step c).

[0077] As described above, step b) and step d) may comprise the production of a polybrominated propane-rich composition. Preferably, the polybrominated propane-rich composition is subjected to thermal oxidation in a thermal oxidizer in order to burn or oxidize, respectively, the polybrominated propanes contained in the polybrominated propane-rich composition, thereby recovering the bromine. The bromine thus recovered is preferably introduced together with the hydrogen-rich composition and subjected to the electrolysis of step e). More specifically, the polybrominated propane-rich composition or a portion thereof is contacted with oxygen at an elevated temperature of greater than 700° C., during which the polybrominated propanes are converted into a gaseous mixture comprising carbon dioxide, hydrogen bromide and bromine. The resulting gas stream is then preferably subjected to an absorption step using an aqueous hydrogen bromide solution in order to separate the hydrogen bromide and bromine from the remainder of the gaseous products. The liquid stream obtained, containing the recovered hydrogen bromide and bromine, is then preferably fed to the electrolysis.

[0078] Alternatively, the composition rich in polybrominated propanes can be reacted to bromopropanes in a thermal manner or in the presence of a catalyst. For example, the catalyst can comprise a metal selected from a transition metal (such as molybdenum, cobalt, iron, nickel, copper or silver) and a noble metal (such as platinum, ruthenium or palladium), wherein the metal is supported on a carrier, such as a carrier made of aluminum oxide, silicon oxide, titanium oxide, cerium oxide or carbon. Particularly preferably, the metal is platinum, palladium or a mixture of platinum and palladium. In a further development of this embodiment, the reaction of the composition rich in polybrominated propanes to bromopropanes is preferably carried out in the presence of hydrogen. When the molar ratio of polybrominated propanes to hydrogen is 10:1 to 1:10, more preferably 5:1 to 1:5, even more preferably 2:1 to 1:2 and most preferably about 1:1, particularly good results are obtained.

[0079] According to another alternative embodiment, the polybrominated propane-rich composition is fully hydrogenated to propane and / or higher alkanes in the presence of hydrogen and a suitable catalyst.

[0080] According to another embodiment, the polybrominated propanes-rich composition or a portion thereof is subjected to a hydrotreatment step over a platinum-containing catalyst at a temperature of at least 300° C., a pressure of at least 2 barg and a hydrogen / feed molar ratio of at least 1, so as to produce a mixture of propane, propene and bromopropane products from the polybrominated propanes-rich composition. The resulting mixture can be further sent to a separation step b), such as to the second column used in separation step b), as further preferably described above.

[0081] According to another aspect, the present invention relates to a plant for producing propylene and hydrogen from propane, comprising:

[0082] a) a (bromination) reactor for reacting a mixture comprising propane and bromine to produce a first reaction mixture comprising bromopropane and hydrogen bromide, wherein the reactor comprises an inlet line for the mixture and an outlet line for the first reaction mixture,

[0083] b) a first separation unit comprising an inlet line for the first reaction mixture, an outlet line for a composition enriched in bromopropane and an outlet line for a composition enriched in hydrogen bromide, connected to the outlet line for the first reaction mixture of reactor a),

[0084] c) a (dehydrobromination) reactor for catalytically reacting the bromopropane-rich composition to produce a second reaction mixture containing propene and hydrogen bromide, wherein the reactor comprises an inlet line for the bromopropane-rich composition connected to the outlet line for the bromopropane-rich composition of the separation unit b), and an outlet line for the second reaction mixture,

[0085] d) a second separation unit comprising an inlet line for the second reaction mixture connected to the outlet line for the second reaction mixture of reactor c), an outlet line for propene and an outlet line for a composition enriched in hydrogen bromide, and

[0086] e) an electrolysis cell comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode, and an inlet line for a composition comprising hydrogen bromide, an outlet line for hydrogen and an outlet line for a composition comprising bromine, wherein the inlet line of the electrolysis cell is connected to the outlet line of the first separation unit for a composition rich in hydrogen bromide and / or to the outlet line of the second separation unit for a composition rich in hydrogen bromide.

[0087] Preferably, the outlet line of the electrolysis cell e) for the bromine-containing composition is connected to the inlet line of the reactor a).

[0088] The outlet line for the bromine-containing composition of electrolysis cell e) can be connected directly to the inlet line of reactor a) or indirectly, i.e. to another device or unit (e.g. a purification unit) arranged between the bromine-containing composition of electrolysis cell e) and the inlet line of reactor a).

[0089] In a further development of the concept of the invention, it is proposed that the first separation unit comprises at least one distillation column and / or at least one absorption column. More preferably, the first separation unit comprises at least one distillation column and at least one absorption column, and even more preferably, the first separation unit comprises two distillation columns and one absorption column.

[0090] According to a particularly preferred embodiment of the present invention, the first separation unit comprises:

[0091] a first distillation column comprising an inlet line connected to the outlet line of reactor a) for the first reaction mixture, an overhead outlet line and a bottoms outlet line,

[0092] an absorption column comprising an inlet line connected to the overhead outlet line of the first distillation column, an inlet line for an absorbent, an outlet line for a composition rich in hydrogen bromide and an outlet line for a purified propane composition, and

[0093] a second distillation column comprising an inlet line connected to the bottom outlet line of the first distillation column, an overhead outlet line for a composition rich in bromopropane, and a bottom outlet line.

[0094] According to another particularly preferred embodiment of the present invention, the reactor c) further comprises an inlet line for hydrogen. Alternatively, the apparatus comprises a line for hydrogen which leads to the inlet line for the bromopropane-rich composition of the reactor a).

[0095] Furthermore, it is preferred that the outlet line for the purified propane composition is connected directly or indirectly to the inlet line of the bromination reactor a).

[0096] Similar to the first separation unit, the second separation unit preferably comprises at least one distillation column and / or at least one absorption column. More preferably, the second separation unit comprises at least one distillation column and at least one absorption column, and even more preferably, the second separation unit comprises two distillation columns and one absorption column.

[0097] Good results are particularly achieved when the second separation unit comprises the following components:

[0098] a first distillation column comprising an inlet line connected to the outlet line of reactor c) for the second reaction mixture, an overhead outlet line and a bottoms outlet line,

[0099] an absorption column comprising an inlet line connected to the overhead outlet line of the second distillation column, an inlet line for an absorbent, an outlet line for a composition rich in hydrogen bromide and an outlet line for propylene or for a composition comprising propylene and hydrogen, and

[0100] - a second distillation column comprising an inlet line connected to the bottom outlet line of the first distillation column, an overhead outlet line, and a bottom outlet line.

[0101] Furthermore, it is preferred that the second separation unit additionally comprises a separation device comprising an inlet line connected to the outlet line of the absorption column for the composition comprising propylene and hydrogen, an outlet line for hydrogen and an outlet line for propylene, wherein the separation device is preferably a pressure swing adsorption column.

[0102] In a further development of the concept of the present invention, it is proposed that the apparatus further comprises an oxidation unit and an absorption column. While the oxidation unit comprises an inlet line for air, an inlet line connected to the bottom outlet line of the second distillation column of the first separation unit and to the bottom outlet line of the second distillation column of the second separation unit, and an outlet line, the absorption column comprises an inlet line connected to the outlet line of the oxidation unit, an outlet line for a composition rich in hydrogen bromide of the absorption column of the first separation unit and to the outlet line for a composition rich in hydrogen bromide of the absorption column of the second separation unit, an outlet line for air, and an outlet line for a composition rich in hydrogen bromide connected to the inlet line for a composition containing hydrogen bromide of the electrolysis cell e).

[0103] Preferably, the apparatus further comprises a purification unit for obtaining purified bromine from the bromine-containing composition obtained in electrolysis cell e). Good results are particularly achieved when the purification unit comprises a distillation column comprising an inlet line connected to the outlet line for the bromine-containing composition of electrolysis cell e), an overhead outlet line, and a bottoms outlet line. It is further preferred that the purification unit further comprises a dryer comprising an inlet line connected to the overhead outlet line of the distillation column and an outlet line for purified bromine connected to the inlet line of reactor a).

[0104] Specific embodiments according to the present invention will be described below by way of examples with reference to the accompanying drawings.

[0105] Figure 1 is a schematic diagram of an apparatus for producing propylene and hydrogen from propane according to one embodiment of the present invention.

[0106] Figure 2 The results of Example 3 are shown.

[0107] Figure 3 The results of Example 4 are shown.

[0108] Figure 4 The results of Comparative Example 1 are shown.

[0109] Figure 1 The device 10 shown comprises:

[0110] i) a bromination reactor 12 for reacting a mixture comprising propane and bromine to produce a first reaction mixture comprising bromopropane and hydrogen bromide,

[0111] ii) a first separation unit 14 for separating a bromopropane-rich composition, a propane-rich composition, a polybrominated propane-rich composition, and a hydrogen bromide-rich composition from the first reaction mixture,

[0112] iii) a dehydrobromination reactor 16 for catalytically reacting the bromopropane-rich composition obtained in the first separation unit 14 to obtain a second reaction mixture containing propene and hydrogen bromide,

[0113] iv) a second separation unit 18 for separating propylene, a polybrominated propane-rich composition, and a hydrogen bromide-rich composition from the second reaction mixture,

[0114] v) a thermal oxidizer 20 for oxidizing the polybrominated propane-rich composition obtained in the first and second separation units,

[0115] vi) an absorption column 22 for contacting the composition rich in hydrogen bromide obtained in the first and second separation units with the oxidation product obtained in the thermal oxidizer 20,

[0116] vii) an electrolysis cell 24 for producing hydrogen and a bromine-containing composition from the hydrogen bromide-rich composition treated in the absorption column 22, and

[0117] viii) a purification unit 26 for obtaining pure bromine from the bromine-containing composition obtained in the electrolysis cell 24 .

[0118] More specifically, the bromination reactor 12 comprises an inlet line 28 for a mixture comprising propane and bromine and an outlet line 30 for a first reaction mixture. The inlet line 28 is connected to a feed line 32 for a propane-containing gas (e.g., natural gas), a recycle line 34 for propane, and a recycle line 36 for bromine, wherein a heat exchanger 38 is arranged so that the first reaction mixture withdrawn from the bromination reactor 12 via the outlet line 30 preheats the propane-containing gas introduced through the feed line 32. The outlet line 30 passes through another heat exchanger 40 before it is introduced into the first separation unit 14. Viewed from upstream to downstream of the first separation unit 14, the first separation unit 14 comprises a first distillation column 42, an absorption column 44, and a second distillation column 46. The first distillation column 42 includes an inlet line 48 connected to the outlet line 30 for the first reaction mixture of the bromination reactor 12, an overhead outlet line 50, and a bottom outlet line 52, while the absorption column 44 includes an inlet line 54 connected to the overhead outlet line 50 of the first distillation column 42, an inlet line 56 for the absorbent, an outlet line 58 for a composition rich in hydrogen bromide, and an outlet line for a purified propane composition 60. The outlet line for the purified propane composition 60 is introduced into the recycle line 34 for propane via a compressor 62. In turn, the second distillation column 46 includes an inlet line 64 connected to the bottom outlet line 52 of the first distillation column 42, an overhead outlet line 66 for a composition rich in bromopropanes, and a bottom outlet line 68 for a composition rich in polybrominated propanes.

[0119] Dehydrobromination reactor 16 for catalytically reacting the bromopropane-rich composition to produce a second reaction mixture containing propylene and hydrogen bromide comprises an inlet line 70 for the bromopropane-rich composition connected to overhead outlet line 66 for the bromopropane-rich composition of second distillation column 46 of first separation unit 14 via heat exchanger 72, and an outlet line 74 for the second reaction mixture directed to second separation unit 18 via heat exchanger 72 and compressor 76. Viewed from upstream to downstream of second separation unit 18, second separation unit 18 comprises a first distillation column 80, an absorption column 82, and a second distillation column 84. The first distillation column 80 comprises an inlet line 78 for the second reaction mixture of the bromination reactor 12 connected to the outlet line 74 of the dehydrobromination reactor 16, an overhead outlet line 86, and a bottoms outlet line 88, while the absorption column 82 comprises an inlet line 90 connected to the overhead outlet line 86 of the first distillation column 80, an inlet line 92 for the absorbent, an outlet line 94 for a composition rich in hydrogen bromide, and an outlet line 96 for (purified) propylene. The outlet line 96 for (purified) propylene leads to a pressure swing adsorption column 98 comprising an outlet line 100 for propylene and an outlet line 102 for hydrogen, said outlet line 102 branching into a take-off line 104 for hydrogen and a recycle line 106 leading back to the inlet line 70 for the second reaction mixture of the dehydrobromination reactor 16. Furthermore, the second distillation column 84 of the second separation unit 18 comprises an inlet line 108 connected to the bottom outlet line 88 of the first distillation column 80, a 4-5 An overhead outlet line 110 for the hydrocarbon composition, a bottoms outlet line 112 for a composition rich in polybrominated propanes, and a recycle line 114 for the composition rich in polybrominated propanes that leads to the overhead outlet line 66 of the second distillation column 44 of the first separation unit 14 .

[0120] The oxidation unit 20 includes an inlet line 116 for air, an inlet line 118 connected to the bottom outlet line 68 of the second distillation column 46 of the first separation unit 14 and to the bottom outlet line 112 of the second distillation column 84 of the second separation unit 18, and an outlet line 120. Furthermore, the absorption column 22 includes an inlet line connected to the outlet line 120 of the oxidation unit 20, an inlet line 122 for a composition rich in hydrogen bromide connected to the outlet line 58 for a composition rich in hydrogen bromide of the absorption column 44 of the first separation unit 14 and to the outlet line 94 for a composition rich in hydrogen bromide of the absorption column 82 of the second separation unit 18, an outlet line 124 for air, and an outlet line 126 for a composition rich in hydrogen bromide connected to the inlet line for a composition containing hydrogen bromide of the electrolysis cell 24. Electrolyzer 24 comprises an outlet line 128 for the bromine-containing composition, an outlet line 130 for hydrogen connected to compressor 132, a recycle line 134 leading to recycle line 106, and a hydrogen removal line 136. Finally, purification unit 26 comprises a distillation column 138 comprising an inlet line connected to outlet line 128 for the bromine-containing composition of electrolyzer 24, a bottoms outlet line for a mixture of water and hydrogen bromide, a recycle line 140, and an overhead outlet line 142 for hydrogen. The bottom outlet line and recycle line 140 of the purification unit 26 lead to the absorbent inlet lines 56, 92 of the second distillation columns 44, 82 of the first and second separation units 14, 18, while the overhead outlet line 142 leads to a condenser 144 and from there to a container 146, from which a return line 148 leads back to the distillation column 138, and an outlet line 150 leads to a dryer column 152. The dryer column 152 comprises a bottom outlet line for bromine connected to the recycle line 36 and an overhead outlet 156 that leads back to the overhead outlet line 142 of the distillation column 138.

[0121] During operation of the apparatus 10, a mixture comprising propane and bromine is introduced via line 28 into the bromination reactor 12, where the propane reacts with bromine to form bromopropane and hydrogen bromide. Furthermore, the (first) reaction mixture comprises unreacted propane, unreacted bromine, and by-products such as polybrominated propanes. Subsequently, the (first) reaction mixture is introduced via lines 30 and 48 into the first distillation column 42 of the first separation unit, where the reaction mixture is separated into a bottoms composition comprising primarily bromopropane and a small amount of polybrominated propanes, and an overhead composition comprising primarily hydrogen bromide, unreacted propane, and unreacted bromine. The overhead composition is fed to an absorption column 44 via lines 50, 54 and contacted there with an absorbent, which is an aqueous solution containing a small amount of hydrogen bromide that is recycled to the absorption column 44 via lines 140, 56, to obtain a purified propane composition that is recycled to the mixture used in step a) via lines 60, 34 and compressor 62, and a composition rich in hydrogen bromide is withdrawn from the absorption column 44 via line 58. The bottoms composition of the first distillation column 42 of the first separation unit 14, which contains mainly bromopropane and a small amount of polybrominated propanes, is introduced into the second distillation column 46 via lines 52, 64, where polybrominated propanes are separated from bromopropanes as a bottoms composition. Simultaneously with the withdrawal of a polybrominated propane composition from the second distillation column 46 via line 68, a bromopropane composition rich in propane is withdrawn from the second distillation column 46 via line 66. Subsequently, the bromopropane-rich composition is dehydrobrominated in the presence of hydrogen in the dehydrobromination reactor 16 to obtain a second reaction mixture containing propylene, hydrogen bromide, hydrogen, and polybrominated propanes. The second reaction mixture is then separated in the second separation unit 18 into pure propylene withdrawn via line 100, pure hydrogen withdrawn via line 102 and partially recycled to the dehydrobromination reactor 16 via lines 102, 106, and 70, a polybrominated propane-rich composition withdrawn via line 112, and a hydrogen bromide-rich composition withdrawn via line 94. The two polybrominated propane-rich compositions withdrawn from the first and second separation units via lines 68 and 112 are oxidized primarily to bromine in the thermal oxidizer 20, which are then contacted together with the two hydrogen bromide-rich compositions withdrawn from the first and second separation units via lines 58 and 94 in the absorption tower 22, from which the hydrogen bromide-rich composition (which is actually an aqueous solution containing hydrogen bromide) is withdrawn via line 126 and introduced into the electrolysis cell 24. Electrolyzer 24 produces hydrogen from the composition at the cathode and bromine from the composition at the anode. While hydrogen is withdrawn from electrolyzer 24 via line 130 and partially recycled to dehydrobromination reactor 16 via lines 134, 106, 70, a bromine-containing composition (which is an aqueous solution containing bromine and hydrogen bromide) is withdrawn from electrolyzer 24 via line 128.Subsequently, the bromine-containing composition is separated in a distillation column 138 into an aqueous solution containing hydrogen bromide, which is withdrawn via line 140 and recycled as absorbent to the absorption columns 44, 82 of the first and second separation units 14, 18 via lines 56, 92, and a composition rich in bromine. The latter is withdrawn from the distillation column 138 via line 142 and dehydrated in a distillation column 152 to obtain pure bromine, which is introduced via lines 154, 36 into the mixture introduced via line 28 into the bromination reactor 12. Example

[0122] Example 1

[0123] (Bromination Test - Effect of Pressure on Bromine Conversion)

[0124] A mixture of propane and bromine in a molar ratio of 2.4:1 was reacted at a reaction temperature of 250° C. at different pressures as summarized in Table 1 below, and the residence time necessary to achieve complete conversion of bromine was measured. The results are also shown in Table 1 below.

[0125] Table 1

[0126] run Pressure (bar) Residence time required to achieve complete bromine conversion (seconds) 1 1 120 2 2 90 3 4 57 4 6 46 5 8 40 6 10 36 7 13 32 8 15 32

[0127] The results show that the pressure during the bromination reaction has an impact on the bromine conversion and the selectivity of the reaction for polybrominated compounds and unsaturated compounds (such as propylene and allyl bromide). Due to the longer residence time required for complete conversion of bromine, unsaturated compounds can be produced thermally at low partial pressures below 4 bar. The (unsaturated) propylene produced significantly complicates the recycling of propane and should be avoided. In general, higher residence times lead to higher concentrations of polybrominated compounds and unsaturated compounds.

[0128] Example 2

[0129] (Bromination Test - Effect of Propane to Bromine Ratio)

[0130] Different mixtures of propane and bromine having the compositions and flow rates summarized in Table 2 below were reacted in an adiabatic tubular reactor, and the inlet and outlet temperatures are summarized in Table 2 below. The pressure inside the reactor was 13 bar.

[0131] Table 2

[0132]

[0133] The results show that the higher the molar ratio of propane to bromine, the lower the propane conversion but the higher the selectivity to bromopropane.

[0134] Example 3

[0135] (Catalytic Test: Dehydrobromination of Bromopropane)

[0136] 2 grams has 180m 2 Gamma-alumina having a specific surface area of ​​1000 g, a sodium compound content of less than 100 ppm and a silica content of less than 100 ppm was treated with an iron (III) nitrate solution for incipient wetness to obtain approximately 5% by weight of iron on the catalyst. The material was dried at 100° C. for 24 hours and subjected to calcination at 550° C. for 5 hours in an air stream (temperature increase = 5° C. and holding time = 5 hours). The obtained material was granulated and subsequently crushed and sieved to a 35 to 45 mesh fraction. 2 grams of the obtained fraction of the catalyst containing 5% by weight of Fe on alumina was loaded into a fixed-bed tubular quartz reactor with an inner diameter of 10 mm. The dead volume above the catalyst in the reactor was filled with spherical quartz beads. The loaded catalyst was heated to 450° C. at atmospheric pressure in a 3 Nl / h N2 flow, followed by stopping the nitrogen flow and switching to 3 Nl / h hydrogen for 1 hour. Subsequently, the reactor was cooled from 450° C. to the reaction temperature in a hydrogen flow, the H 2 flow was increased to 48.6 ml / min, and gaseous bromopropane (16 g / h) was fed into the reactor.

[0137] At a temperature of 300°C, WHSV (2-bromopropane) -8h -1 The conversion and selectivity to propylene in the catalytic dehydrobromination of 2-bromopropane over the catalyst prepared above (i.e., catalyst performance) were measured for 50 hours at a molar ratio of H2 / 2-bromopropane of 1:1 and 2:1. Subsequently, the temperature was raised to 350°C, and performance was measured for an additional 25 hours. The hydrogen flow was then replaced with the same N2 flow, and the test was continued for an additional 25 hours, keeping the remaining parameters the same.

[0138] The results are shown in Figure 2 The abscissa shows the run time in hours, and the ordinate shows the % conversion (circular data points) and % selectivity (square data points).

[0139] The results showed a nearly complete and stable conversion of bromopropane and a very high selectivity to propylene of greater than 99%.

[0140] Example 4

[0141] (Catalytic Test: Dehydrobromination of Bromopropane)

[0142] 2 grams has 180m 2 / g of specific surface area, a sodium compound content of less than 100 ppm and a silica content of less than 100 ppm were treated with an incipient wetness impregnation solution of cobalt nitrate to obtain approximately 5 wt% cobalt on the catalyst. The material was dried at 100°C for 24 hours and subjected to calcination at 550°C in an air stream for 5 hours (temperature increase = 5°C and holding time = 5 hours). The obtained material was granulated and subsequently crushed and sieved to a 35 to 45 mesh fraction. 2 grams of the obtained fraction of the catalyst containing 5 wt% Co on alumina were loaded into a fixed bed tubular quartz reactor with an inner diameter of 10 mm. The dead volume above the catalyst in the reactor was filled with spherical quartz beads. The loaded catalyst was heated to 450°C at atmospheric pressure in a 3 Nl / h N2 flow, followed by stopping the nitrogen flow and switching to 3 Nl / h hydrogen for 1 hour. Subsequently, the reactor was cooled from 450° C. to the reaction temperature in a hydrogen flow, the H 2 flow was increased to 48.6 ml / min, and gaseous bromopropane (16 g / h) was fed into the reactor.

[0143] At 350°C, WHSV (2-bromopropane) -8h -1 The conversion and selectivity to propylene in the catalytic dehydrobromination of 2-bromopropane over the catalyst prepared above were measured (catalyst performance) at a molar ratio of H2 / 2-bromopropane of 1 for about 200 hours.

[0144] The results are shown in Figure 3 The abscissa shows the run time in hours, and the ordinate shows the % conversion (circular data points) and % selectivity (square data points).

[0145] The results showed a nearly complete and stable conversion of bromopropane and a very high selectivity to propylene of greater than 99%.

[0146] Comparative Example 1

[0147] (Blank test without catalyst: Dehydrobromination of bromopropane)

[0148] The same reactor as in Example 4 was filled with spherical silica beads (the same inert material used in the catalytic tests). The reactor loaded with silica beads was heated to 450° C. at atmospheric pressure in a 3 Nl / h N2 flow, followed by stopping the nitrogen flow and switching to 3 Nl / h hydrogen for 1 hour. Subsequently, the reactor was cooled from 450° C. to the reaction temperature in a hydrogen flow, the hydrogen flow was increased to 48.6 ml / min, and gaseous bromopropane (16 g / h) was fed into the reactor.

[0149] The conversion and selectivity to propylene in the catalytic dehydrobromination of 2-bromopropane over the catalyst prepared above were measured at a temperature of 350° C. and a molar ratio of H 2 / 2-bromopropane of 1 (catalyst performance).

[0150] The results are shown in Figure 5. The abscissa shows the run time in hours, and the ordinate shows the % conversion (circular data points) and % selectivity (square data points).

[0151] The results clearly show very low conversion and much lower selectivity. Therefore, the hot gas phase reaction is not significant. This shows that the process requires a catalyst.

[0152] Reference Signs List

[0153] 10 Equipment

[0154] 12 Bromination Reactor

[0155] 14. First separation unit

[0156] 16 Dehydrobromination Reactor

[0157] 18 Second separation unit

[0158] 20 Thermal Oxidizer

[0159] 22 Absorption Tower

[0160] 24 electrolytic cells

[0161] 26 purification units

[0162] 28 Inlet line for the first reaction mixture of the bromination reactor

[0163] 30 Reactor outlet pipeline

[0164] 32 for feed lines containing propane gas

[0165] 34 Recirculation line for propane

[0166] 36 Recycle line for bromine

[0167] 38 Heat Exchanger

[0168] 40 heat exchanger

[0169] 42 The first distillation column of the first separation unit

[0170] 44 Absorption tower of the first separation unit

[0171] 46 The second distillation column of the first separation unit

[0172] 48 inlet pipeline of the first distillation column of the first separation unit

[0173] 50 overhead distillate outlet pipeline of the first distillation tower

[0174] 52 Bottom outlet pipeline of the first distillation tower

[0175] 54 Inlet pipeline of absorption tower

[0176] 56 Inlet line for absorbent

[0177] 58 outlet line for a composition rich in hydrogen bromide

[0178] 60 Export line for purified propane composition

[0179] 62 compressor

[0180] 64 Inlet pipeline of the second distillation column

[0181] 66 The top distillate outlet pipeline of the second distillation tower

[0182] 68 Bottom outlet pipeline of the second distillation tower

[0183] 70 Inlet line for the second reaction mixture of the dehydrobromination reactor

[0184] 72 heat exchanger

[0185] 74 outlet line for the second reaction mixture

[0186] 76 compressor

[0187] 78 Inlet pipeline of the first distillation column of the second separation unit

[0188] 80 The first distillation column of the second separation unit

[0189] 82 Absorption tower of the second separation unit

[0190] 84 The second distillation column of the second separation unit

[0191] 86 overhead distillate outlet pipeline of the first distillation tower

[0192] 88 Bottom outlet pipeline of the first distillation tower

[0193] 90 Inlet pipeline of absorption tower

[0194] 92 Inlet line for absorbent

[0195] 94 outlet line for a composition rich in hydrogen bromide

[0196] 96 Export line for purified propylene

[0197] 98 Pressure Swing Adsorption Tower

[0198] 100 Export line for propylene

[0199] 102 Export pipeline for hydrogen

[0200] 104 Take-out line for hydrogen

[0201] 106 Recirculation line for hydrogen

[0202] 108 inlet pipeline of the second distillation column of the second separation unit

[0203] 110 for C 4-5 Overhead distillate outlet line for hydrocarbon composition

[0204] 112 The bottom outlet pipeline of the second distillation tower of the second separation unit

[0205] 114 Recycle line for polybrominated propane-rich composition

[0206] 116 Inlet line for air

[0207] 118 Inlet line for polybrominated propane-rich composition

[0208] 120 thermal oxidizer outlet pipeline

[0209] 122 Inlet line for a composition rich in hydrogen bromide

[0210] 124 outlet line for air

[0211] 126 outlet line for a composition rich in hydrogen bromide

[0212] 128 Export pipeline for bromine-containing composition

[0213] 130 Export pipeline for hydrogen

[0214] 132 compressor

[0215] 134 Recirculation line for hydrogen

[0216] 136 Hydrogen removal line

[0217] 138 Distillation column of purification unit

[0218] 140 bottom outlet pipeline for mixture of water and hydrogen bromide

[0219] 142 Overhead distillate outlet line for hydrogen

[0220] 144 Condenser

[0221] 146 Container

[0222] 148 return line

[0223] 150 Container outlet line

[0224] 152 Dryer Tower

[0225] 154 Bottom outlet of dryer tower

[0226] 156 Dryer tower overhead distillate outlet

Claims

1. A process for producing propylene and hydrogen from propane, comprising the steps of: a) reacting a mixture comprising propane and bromine to produce a first reaction mixture comprising bromopropane and hydrogen bromide, b) subjecting said first reaction mixture obtained in step a) to at least one separation step in order to obtain a composition enriched in bromopropane and in order to obtain a composition enriched in hydrogen bromide, c) catalytically reacting the bromopropane-rich composition obtained in step b) to produce a second reaction mixture containing propylene and hydrogen bromide, d) subjecting the second reaction mixture obtained in step c) to at least one separation step in order to obtain a composition enriched in hydrogen bromide and to obtain propene, and e) subjecting said composition rich in hydrogen bromide obtained in step b) and / or said composition rich in hydrogen bromide obtained in step d) to electrolysis to obtain hydrogen and a bromine-containing composition.

2. The process according to claim 1 , wherein the mixture comprising propane and bromine used in step a) contains 10 to 90% by volume and preferably 50 to 80% by volume of propane and 10 to 50% by volume and preferably 20 to 45% by volume of bromine, wherein the molar ratio of propane to bromine in the reacted mixture used in step a) is from 10:1 to 1:1 and preferably from 3:1 to 2:

1.

3. The process according to claim 1 or 2, wherein the mixture is reacted in step a) at a temperature of 200 to less than 420°C, preferably 230 to 410°C, more preferably 240 to 400°C and most preferably 240 to 300°C, wherein the mixture is reacted in step a) at a pressure of at least 400 kPa, preferably at least 1 MPa and most preferably 1 to 4 MPa, and wherein the residence time of the mixture in step a) is at least 10 seconds and preferably 20 seconds to 2 minutes.

4. The process according to claim 1 , wherein step b) comprises at least one, and preferably two, distillation steps for separating bromopropane from the first reaction mixture to obtain the bromopropane-enriched composition, and wherein step b) comprises at least one absorption step for separating hydrogen bromide from the first reaction mixture to obtain the hydrogen bromide-enriched composition.

5. The process according to claim 1 , wherein the bromopropane-rich composition obtained in step b) is reacted in step c) at a temperature of 250 to 450° C. in the presence of a catalyst selected from the group consisting of alumina, silica, silica-alumina, zeolites with a Si / Al ratio higher than 25, titanium oxide, zirconium oxide and any combination of two or more of the foregoing materials.

6. The process according to any one of the preceding claims, wherein the bromopropane-rich composition obtained in step b) is reacted in step c) in the presence of hydrogen, wherein the molar ratio of bromopropane to hydrogen is preferably from 10:1 to 1:10 and more preferably from 5:1 to 1:

5.

7. The process according to any one of the preceding claims, wherein step d) comprises at least one and preferably two purification steps, preferably distillation steps, for separating propene from the second reaction mixture to obtain propene, and wherein step d) comprises at least one absorption step for separating hydrogen bromide from the second reaction mixture to obtain a composition enriched in hydrogen bromide.

8. The process according to any one of the preceding claims, wherein in step e) the composition enriched in hydrogen bromide obtained in step b) and the composition enriched in hydrogen bromide obtained in step d) are subjected to electrolysis.

9. The process according to claim 1 , wherein the electrolysis in step e) is carried out by using an electrolysis cell comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode, wherein the composition rich in hydrogen bromide is fed to the anode, optionally a second composition comprising hydrogen bromide and water is fed to the cathode, and the electrolysis cell is operated so as to produce hydrogen at the cathode, wherein a bromine-containing composition is produced at the anode.

10. The process according to any of the preceding claims, wherein the electrolysis in step e) is carried out by using an electrolysis cell comprising a membrane made of a fluoropolymer membrane having a glass transition temperature of at least 110°C, wherein the electrolysis in step e) is carried out by operating the electrolysis cell at an operating temperature of at least 70°C, wherein the operating temperature is below the boiling point of the optional second composition fed to the cathode, and preferably at an operating temperature of 70°C to 122°C, and wherein the electrolysis in step e) is preferably carried out by operating the electrolysis cell at an operating pressure that increases from the anode to the cathode.

11. The process according to claim 1, wherein at least a portion, and preferably all, of the bromine-containing composition obtained during the electrolysis of step e) is recycled back to step a).

12. An apparatus for producing propylene and hydrogen from propane, comprising: a) a reactor for reacting a mixture comprising propane and bromine to produce a first reaction mixture comprising bromopropane and hydrogen bromide, wherein the reactor comprises an inlet line for the mixture and an outlet line for the first reaction mixture, b) a first separation unit comprising an inlet line for the first reaction mixture, an outlet line for a composition enriched in bromopropane and an outlet line for a composition enriched in hydrogen bromide, connected to the outlet line for the first reaction mixture of the reactor a), c) a reactor for catalytically reacting the bromopropane-rich composition to produce a second reaction mixture containing propene and hydrogen bromide, wherein the reactor comprises an inlet line for the bromopropane-rich composition connected to the outlet line for the bromopropane-rich composition of the separation unit b), and an outlet line for the second reaction mixture, d) a second separation unit comprising an inlet line for the second reaction mixture connected to the outlet line for the second reaction mixture of the reactor c), an outlet line for propene and an outlet line for a composition enriched in hydrogen bromide, and e) an electrolysis cell comprising an anode, a cathode and a membrane sandwiched between the anode and the cathode, and an inlet line for a composition comprising hydrogen bromide, an outlet line for hydrogen and an outlet line for a composition comprising bromine, wherein the inlet line of the electrolysis cell is connected to the outlet line of the first separation unit for a composition rich in hydrogen bromide and / or to the outlet line of the second separation unit for a composition rich in hydrogen bromide.

13. The apparatus of claim 12, wherein the first separation unit comprises: a first distillation column comprising an inlet line connected to the outlet line of the reactor a) for the first reaction mixture, an overhead outlet line and a bottoms outlet line, an absorption column comprising an inlet line connected to the overhead outlet line of the first distillation column, an inlet line for an absorbent, an outlet line for a composition rich in hydrogen bromide and an outlet line for a purified propane composition, and a second distillation column comprising an inlet line connected to the bottom outlet line of the first distillation column, an overhead outlet line for a composition rich in bromopropane, and a bottom outlet line.

14. The apparatus according to claim 12 or 13, wherein the second separation unit comprises: a first distillation column comprising an inlet line connected to the outlet line of the reactor c) for the second reaction mixture, an overhead outlet line and a bottoms outlet line, an absorption column comprising an inlet line connected to the outlet line of the overhead product of said first distillation column, an inlet line for an absorbent, an outlet line for a composition rich in hydrogen bromide and an outlet line for propylene or for a composition comprising propylene and hydrogen, and - a second distillation column comprising an inlet line connected to the bottom outlet line of the first distillation column, an overhead outlet line and a bottom outlet line.

15. The apparatus according to any one of claims 12 to 14, further comprising a purification unit, wherein the purification unit comprises a distillation column comprising an inlet line connected to the outlet line for the bromine-containing composition of the electrolysis cell e), an overhead outlet line, and a bottoms outlet line, wherein the purification unit further comprises a dryer comprising an inlet line connected to the overhead outlet line of the distillation column and an outlet line for purified bromine connected to the inlet line of the reactor a).

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