Method and system for producing one or more olefins and one or more carboxylic acids

Abstract

The invention relates to a method for producing one or more olefins and one or more carboxylic acids, in which one or more paraffins is or are subjected to an oxidative dehydrogenation. For the oxidative dehydrogenation, a reactor (10) having a plurality of reaction zones (11, 12, 13) is used, a gas mixture comprising the one or more paraffins is successively passed through the reaction zones (11, 12, 13), and at least two of the reaction zones (11, 12, 13) are subject to varying temperature influences. The invention also relates to a corresponding system (100).

Claims

1. Method for producing one or more olefins and one or more carboxylic acids, in which one or more paraffins is or are subjected to an oxidative dehydrogenation, characterized in that a reactor (10) having a plurality of reaction zones (11, 12, 13) is used for the oxidative dehydrogenation, that a gas mixture comprising the one or more paraffins is successively passed through the reaction zones (11, 12, 13) and that at least two of the plurality of reaction zones (11, 12, 13) have a catalyst of the same type of catalyst and/or are subjected to varying temperature influences.

2. Method according to claim 1, wherein in a second of the reaction zones (13) through which the gas mixture is passed after it has previously been passed through a first one of the reaction zones (11, 12), it is formed with a higher catalyst loading and/or with a higher catalyst activity per space unit than the first reaction zone (11, 12).

3. Method according to claim 1, wherein a minimum and a maximum reaction temperature are predetermined and in which the temperature is influenced in the reaction zones (11, 12, 13) in such a way that the maximum reaction temperature is not exceeded in any of the reaction zones (11, 12, 13) at any given position and the minimum reaction temperature is not undershot.

4. Method according to claim 3, wherein a reactor (10) is used which comprises a number of at least partially parallel reaction tubes (10c), wherein the predetermined position lies on the central axis of at least one of the plurality of reaction tubes (10c).

5. Method according to claim 1, which is carried out in such a way that the maximum reaction temperature is not exceeded in at least 30% of each of the reaction zones (11, 12, 13) and the minimum reaction temperature is not undershot.

6. Method according to claim 5, which is carried out in such a way that in the second reaction zone (13), the maximum reaction temperature does not exceed a higher percentage and the minimum reaction temperature is not undershot to a greater extent than in the first reaction zone (11, 12).

7. Method according to claim 1, wherein the reactor (10) has at least one further reaction zone (11) through which the gas mixture is passed before it is passed through the first reaction zone (12) and the second reaction zone (13).

8. Method according to claim 7, wherein the catalyst bed (13a) of the second reaction zone (13) is formed with a higher catalyst loading and/or catalyst activity per space unit than the catalyst bed (11a) of the further reaction zone (11, 12).

9. Method according to claim 1, wherein catalyst beds (11a, 12a, 13a) of the reaction zones (11, 12, 13) each have a proportion of active catalyst of at least 0.1% by weight.

10. Method according to claim 1, wherein the reaction zones (11, 12, 13) are temperature-controlled by means of one or more temperature control agent flows (105, 106).

11. Method according to claim 10, wherein a cooling system is provided with a plurality of temperature control agent flows (105, 106), wherein at least one of the plurality of temperature control agent flows (105, 106) is used for cooling only one or only one part of the reaction zones (11, 12, 13).

12. Method according to claim 1, wherein a process gas containing water is removed from the reactor (10) and wherein the method comprises adjusting a water partial pressure in the process gas removed from the reactor (10) to a value in a range between 0.5 and 5 bar (abs.).

13. Method according to claim 1, wherein the number of carbon atoms of the olefin, the carboxylic acid and the paraffin is two.

14. System (100) for producing one or more olefins and one or more carboxylic acids, which is designed to subject one or more paraffins having the number of carbon atoms to an oxidative dehydrogenation, characterized in that the system (100) for the oxidative dehydrogenation has a reactor (10) comprising a plurality of reaction zones (11, 12, 13), that means are provided that are designed to pass a gas mixture with the one or more paraffins successively through the reaction zones (11, 12, 13), that at least two of the plurality of reaction zones (11, 12, 13) have a catalyst of the same type of catalyst and/or that means are provided that are designed to subject the at least two reaction zones (11, 12, 13) to varying temperature influences.

15. System (100) according to claim 14, comprising means designed to remove a process gas containing water from the reactor (10) and to set a water partial pressure in the process gas removed from the reactor (10) to a value in a range between 0.5 and 5 bar (abs.), in particular between 0.7 and 3 bar (abs.), depending on a predetermined product ratio of acetic acid to ethylene.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0074] FIG. 1 illustrates a system for producing ethylene and acetic acid with a reactor according to an embodiment of the invention.

[0075] FIG. 2 illustrates selectivities to ethylene and acetic acid.

[0076] FIG. 3 shows product molar flow ratios in relation to ethylene and acetic acid to illustrate the background of the invention.

[0077] FIG. 4 shows product molar flow ratios in relation to ethylene and acetic acid to illustrate the background of the invention.

[0078] FIG. 5 illustrates a method that can be used in the context of an embodiment of the present invention.

[0079] FIG. 6 illustrates product selectivities within the context of a non-inventive method.

[0080] FIG. 7 illustrates product selectivities within the context of a non-inventive method and within the context of a method according to an embodiment of the invention.

[0081] FIG. 8 illustrates reactor temperature curves within the context of a non-inventive method and within the context of a method according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0082] In the following figures, elements functionally or structurally corresponding to one another are indicated by identical reference symbols and are not explained repeatedly for the sake of clarity. If system parts are described below, the explanations relating to these also apply analogously to the method steps implemented by means of these system parts and vice versa.

[0083] FIG. 1 illustrates a system for producing olefins in accordance with an embodiment of the invention in the form of a highly simplified system diagram and is designated generally by 100. The system 100 is only indicated schematically here. Although a system 100 for the ODH of ethane (ODH-E) is described below, as mentioned, the present invention is also suitable for use in the ODH of higher hydrocarbons. In this case, the following explanations apply accordingly.

[0084] The system 100 has a reactor 10 to which, in the example shown, an ethane-containing gas mixture obtained in any way required is fed in the form of a material flow 101. The material flow 101 can be taken, for example, from a rectification unit not shown, which separates higher hydrocarbons from an initial mixture. The material flow 101 may also be preheated and otherwise prepared, for example. The material flow 101 may already contain oxygen and optionally a diluent such as water vapor, but corresponding media may also be added to the reactor upstream or in the reactor 10 as representatively illustrated herein in the form of material flows 102 and 103.

[0085] The reactor 10 has a plurality of reaction tubes 10c arranged in parallel (marked only in part), which run through a plurality of reaction zones 11, 12, 13 which are three in number in the example shown, and which are surrounded by a jacket region 10d. In the reaction tubes 10c, a catalyst bed 11a, 12a, 13a is provided in each case in the corresponding reaction zones (only illustrated on one reaction tube 10c). A gas mixture containing ethane and oxygen and optionally a diluent is passed in succession through the reaction zones 11, 12, 13 in the form of the material flow 101 or the combined material streams 101 to 103. An inert zone 14 is connected upstream of the reaction zones 11, 12, 13. The reaction zones 11, 12 13 are arranged between an inlet opening 10a and an outlet opening 10b of the reactor 10, wherein one of the reaction zones, here the reaction zone 13, which is arranged closer to the outlet opening 10b than another of the reaction zones, here one of the reaction zones 11 and 12, is referred to as a “second” reaction zone and one of the other reaction zones 11, 12 is referred to as a “first” reaction zone. The catalyst bed 13a of the second reaction zone 13, through which the gas mixture is passed after it has previously been passed through the first reaction zone 11, 12, is in particular formed with a higher catalyst loading and/or catalyst activity per space unit than the catalyst bed 11a, 12a of the first reaction zone 11, 12. This leads to the advantages which are also explained again with reference to FIGS. 7 and 8. Alternatively or additionally, a zonally different temperature control can also take place.

[0086] A process gas flows out of the reactor 10 in the form of a process gas flow 104 containing ethylene formed in the reactor 10 through the ODH of a portion of the ethane in the reaction feed flow. Further, the process gas contains acetic acid that has also been formed from ethane during the ODH in the reactor 10, water, carbon monoxide, carbon dioxide, unconverted oxygen, as well as the diluent or diluents and other compounds, if these have been added or have previously formed in the reactor 10. The reaction tubes 10c are temperature controlled by means of a temperature control agent flow 105, 106 which is passed through the jacket region. As not illustrated here, in particular a plurality of temperature control medium circuits can be provided which temperature control or cool the reaction tubes 10c in sections.

[0087] It goes without saying that the system 100 can have one, but also a plurality of reactors 10, which are operated in parallel, for example, as illustrated. In the latter case, corresponding reaction feeds, which may be of identical or different composition, are respectively supplied to these reactors 10 and corresponding process gas flows 104 are formed in each case. The latter can, for example, be combined and supplied together as process gas to subsequent method steps or system parts.

[0088] A water partial pressure can be identified downstream of the reactor 10. This can be adjusted, for example, by adding water or steam to the gas mixture of the material flow 101 or in the form of the material flows 102 or 103. Further influencing, in particular fine adjustment, can be effected by adjusting the temperature in the reactor 100.

[0089] Subsequent method steps or system components are not illustrated. The process gas can be brought into contact therein with washing water or a suitable aqueous solution, as a result of which the process gas can in particular be cooled and acetic acid can be washed out of the process gas. The process gas, which is at least largely freed of acetic acid, can be further processed and subjected to separation of ethylene. Ethane contained in the process gas may be recycled into the reactor 10.

[0090] FIG. 2 illustrates selectivities to ethylene and acetic acid obtained in a corresponding process in a diagram, in which water partial pressures in bar (abs.) in a process gas flowing out of a reactor are plotted on the abscissa against selectivity values shown as a percentage on the ordinate. The selectivity values shown for the individual products are calculated from the ratio of the respective product molar flow relative to the molar amount of ethane, which is converted per unit of time in the reactor.

[0091] The data shown relate to two series of tests with different flow rates, thus to different space velocities and different temperatures. In both series of experiments, no ethylene was added at the reactor inlet. As expected, at higher flow rates, lower conversions occur (approx. 19% as opposed to approximately 40%), but the product selectivities and thus the product molar flow ratio (corresponding here to the ratio of the two selectivities) are virtually identical at the same water partial pressures at the reactor outlet. This shows that the process control in the aforementioned region can be based to a considerable degree on the water partial pressure at the outlet.

[0092] The values obtained at the higher flow rates and lower conversion rates are illustrated for ethylene with filled (black) squares and for acetic acid with filled (black) triangles, while the values obtained at the lower flow rates and higher conversion rates are correspondingly illustrated for ethylene with unfilled (white) squares and for acetic acid with unfilled (white) triangles.

[0093] The ratio of the product quantities as a function of the water partial pressure at the reactor outlet is again illustrated in FIG. 3. Here, the water partial pressures in bar (abs.) on the abscissa are plotted against the product molar flow ratio of acetic acid to ethylene (corresponding here to the ratio of the values shown in FIG. 2 to each other). Here, the product molar flow ratios for the higher flow rates and lower conversion rates are illustrated with filled (black) squares and for the lower flow rates and higher conversion rates with unfilled (white) squares. The partially clearly linear course of the product mix is evident above all for the economically relevant operation at higher conversions.

[0094] This simplified behavior of the reaction system can be explained by two effects, which could be proven experimentally, but which are explicitly indicated here as being non-binding: On the one hand, the oxidation of ethylene formed is facilitated at elevated water partial pressures, wherein the selectivity for the formation of acetic acid increases. At the same time, desorption of the acetic acid formed from the catalyst surface is facilitated by increased water partial pressures, as a result of which less acetic acid of the subsequent oxidation of acetic acid to carbon monoxide and carbon dioxide likewise occurring on the catalyst is available. This results in the shift of the overall selectivity toward acetic acid, with virtually constant selectivity to carbon monoxide and carbon dioxide.

[0095] The determining influence of the water partial pressure at the outlet on the product ratio between acetic acid and ethylene can be demonstrated by further measurements, partly using different dilution media and widely varying experimental conditions. Reference is made to FIG. 4, which shows corresponding product molar flow ratios of acetic acid to ethylene. The illustration corresponds to that of FIG. 3.

[0096] FIG. 5 illustrates a corresponding method in the form of a schematic flow diagram, generally designated 200. In each case, 211 to 214 denotes partial objectives to be achieved, with 221 to 224 denoting the settings or specifications specifically to be implemented for this purpose.

[0097] The desired product distribution of acetic acid to ethylene is given in step 211. Based on this, a target value for the water partial pressure at the reactor outlet is established in step 221. On the basis of a total product quantity predetermined in step 212 and associated recycling quantities, a flow rate and thus the conversion in the reactor (see in particular FIGS. 2 and 3) is established in step 222.

[0098] In step 213, a correspondingly defined operating point is approached, for which purpose a water content in the reaction feed flow is adjusted in step 223. The fine tuning of the operating point, step 214, is performed by adjusting the reactor temperature in step 224. The water partial pressure at the reactor outlet is observed in each case.

[0099] FIG. 6 illustrates the results of three selected experiments 52, 56 and 71 performed within the context of an extensive series of experiments using a pilot reactor. In turn, a strong correlation of the product ratio of ethylene to acetic acid to the water partial pressure at the outlet of the reactor was observed within the context of the entire experimental series. This applies to different conversions and different process conditions, i.e. changed compositions, current quantities, pressures and temperatures.

[0100] Experiments 52 and 71 were carried out at the same space velocities of 0.9 kg of ethane/(kg of catalyst×h); in experiment 56, on the other hand, this was 1.4 kg of ethane/(kg of catalyst×h). The water partial pressures at the reactor inlet were 0.56 bar for experiment 52, 0.58 bar for experiment 56 and 0.46 bar for experiment 71. In other words, in experiments 52 and 56, nearly identical water partial pressures were used at the reactor inlet and, in experiment 71, the water partial pressure at the reactor inlet clearly decreased. The water partial pressures at the reactor outlet were 1.28 bar for experiment 52, 0.99 bar for experiment 56 and 1.00 bar for experiment 71. In other words, almost identical water partial pressures were therefore observed at the reactor outlet in experiments 56 and 71, and in experiment 52, the water partial pressure at the reactor outlet deviated significantly. The different water partial pressures at the reactor outlet between experiments 52 and 56 resulted from the different space velocities at substantially equal water partial pressures at the reactor inlet.

[0101] The experimental conditions for experiments 52, 56 and 71 are summarized again in the table below. The salt temperature here represents the temperature of a molten salt which was used for cooling the reactor and therefore forms a reference for the reactor temperature:

TABLE-US-00001 Experiment no. 52 56 71 Reactor inlet pressure 3.81 3.67 3.10 [bar (abs.)] Space velocity [kg of ethane/ 0.9 1.4 0.9 (kg of catalyst × h)] Water/ethane [mol/mol] 0.26 Oxygen/ethane [mol/mol] 0.35 0.31 0.33 Salt temperature [° C.] 302 316 311 Water partial pressure reactor 0.56 0.58 0.46 inlet [bar (abs.)] Water partial pressure reactor 1.28 0.99 1.00 outlet [bar (abs.)]

[0102] In experiment 52, a feed with 56.7 mole percent ethane, 19.6 mole percent oxygen, 14.8 mole percent water and 8.9 mole percent nitrogen, in experiment 56, a feed with 60.2 mole percent ethane, 18.4 mole percent oxygen, 15.8 mole percent water and 5.7 mole percent nitrogen, and in experiment 71, a feed with 57.3 mole percent ethane, 18.8 mole percent oxygen, 14.9 mole percent water and 9.0 mole percent nitrogen were used.

[0103] FIG. 6 illustrates values for selectivity (S) for ethylene (C2H4), acetic acid (AcOH), carbon monoxide (CO), carbon dioxide (CO2) and residual compounds (residue not visible due to low values) for the three experiments 52, 56 and 71. Here, the ordinate shows the values with regard to the selectivities. The ethane conversion varied by no more than 5% in the three experiments 52, 56 and 71

[0104] It can clearly be seen that in experiments 56 and 71, similar product ratios are observed at similar water partial pressures at the outlet, with different water partial pressures at the inlet. The product molar flow ratio of acetic acid to ethylene (corresponding here to the ratio of the corresponding selectivities) is in each case around 0.14 in experiments 56 and 71. In experiments 52 and 56, on the other hand, similar water partial pressures are present, but due to the changed space velocities, significantly different water partial pressures are present at the outlet. Despite similar water partial pressures at the inlet, clearly different product ratios also result for the test points 52 and 56. The product molar flow ratio of acetic acid to ethylene is around 0.17 for experiment 52 and is thus far higher than the above-mentioned value for experiment 56.

[0105] In the context of the present invention, a shift in the value product selectivity to more ethylene can be achieved overall despite increased conversion rates compared to the operation of a single-layer catalyst bed or a reactor having only one corresponding reaction zone. This is achieved at the same vapor dilution rates in the reaction feed. Provisions for controlling the development of the catalyst activity over time by adjusting a water partial pressure in the reaction feed or the gas mixture flowing out of a corresponding reactor retain their validity even when a multilayer bed is used.

[0106] The characteristic selectivity curves shown can thus be shifted parallel to more ethylene when an adequately designed, multilayer catalyst bed or a reactor having a plurality of corresponding reaction zones is used. The adaptation possibilities during operation on the basis of the control of the water partial pressure at the reactor outlet is thus maintained.

[0107] The limitations in the further economic optimization of the process described when using a single-layer bed can thus be overcome by using a process control with multilayer beds and targeted temperature control. The economic viability and the marketability of the ODH-E technology are thus noticeably improved.

[0108] FIG. 7 shows, comparable to FIG. 6, values for selectivity (S) for ethylene (C2H4), acetic acid (AcOH), carbon monoxide (CO), carbon dioxide (CO2) and residual compounds (residue, not visible due to low values), although for case A of a conventional single-layer catalyst bed reactor, and for case B of a multilayer catalyst bed, in this case for a three reaction zone reactor, having increasing catalyst activities or catalyst contents per space unit. The ordinate here also shows the values with regard to the selectivities. Identical compositions of the reaction feed and identical mass streams were used in each case.

[0109] In both cases A and B, no appreciable increase in the conversion could be achieved by a further increase in temperature without an increased risk of a thermal throughput or a significantly increased formation of carbon oxides occurring. When using a three-layer bed or three corresponding reaction zones, however, a minimum temperature higher by 15 K can be set in the respective catalyst zones, as a result of which, in case B, a significant increase in conversion and ethylene selectivity can be achieved compared to case A. The associated value product losses toward carbon oxides are low.

[0110] In 100% of all three reaction zones or their catalyst beds, process temperatures on the central axis of at least 318.5° C. were maintained. In 100% of the last two reaction zones in the direction of the reactor outlet (case B), even process temperatures on the central axis of at least 327° C. are maintained. In comparison, the minimum temperature in the entire single-layer bed (case A) is 303.5° C., and is 310° C. at the end of the catalyst bed.

[0111] In FIG. 8, corresponding temperature curves are again illustrated by a reactor 10 for the cases also denoted here by A and B, wherein a reactor length in mm is indicated on the abscissa and a temperature is shown in ° C. on the ordinate. The reaction zones, also designated 11, 12 and 13 here, are present only in case B. In case A, instead of the three reaction zones designated 11, 12 and 13, only one reaction zone is present. In both cases, an inert zone 14 is present upstream of the reaction zone or reaction zones. Also illustrated are coolant (liquid salt) temperatures denoted A and B′.