MXPA01000652A - Process for the preparation of styrene and propylene oxide - Google Patents

Abstract

Process for the joint preparation of styrene and propylene oxide comprising the steps of:(a) reacting ethene and benzene to form ethylbenzene;(b) reacting ethylbenzene with oxygen or air to form ethylbenzene hydroperoxide;(c) reacting at least part of the ethylbenzene hydroperoxide obtained with propene in the presence of an epoxidation catalyst to form propylene oxide and 1-phenyl ethanol, and (d) dehydrating at least part of the 1-phenyl ethanol obtained into styrene in the presence of a suitable dehydration catalyst, wherein the ethene used in step (a) and the propene used in step (c) are at least partly provided by a fluid catalytic cracking unit.

Description

PROCESS FOR THE PREPARATION OF STYRENE AND OXID OF OWNER Description of the Invention The present invention relates to a process for the joint preparation of styrene and propylene oxide. Such a process is known in the art and is commonly referred to as the styrene monomer / propylene oxide (SM / OP) process. In general, an SM / OP process comprises the steps of: (a) reacting ethene and benzene to form ethylbenzene, (b) reacting ethylbenzene with oxygen or air to form ethylbenzene hydroperoxide, (c) reacting at least part of the ethylbenzene hydroperoxide obtained with propene in the presence of an epoxidation catalyst, to form propylene oxide and 1-phenyl ethanol, and (d) dehydrate at least part of the 1-phenyl ethanol obtained in styrene in the presence of a suitable dehydration catalyst . The above SM / PO process is well known in the art. In step (a) ethylbenzene is formed by the alkylation of benzene in an ethylbenzene unit. The Ref: 126614 Benzene can be derived, for example, from a platinum reformer unit, while ethene can be derived from a catalytic steam thermofraction. The alkylation reaction could be carried out in various ways known in the art. This reaction can be carried out for example as a reaction in gas phase or liquid phase using a catalyst based on aluminum chloride catalyst. Solid phosphoric acid catalysts or solid acid catalysts based on alumina activated with boron trifluoride are also used in certain processes of alkylation of benzene to produce ethylbenzene. An additional suitable process is the process known as the Mobil / Badger process. In this process, a synthetic zeolite catalyst, ZSM-5, is used. In this process the reaction is typically carried out at high temperatures (usually 380-420 ° C) and moderate pressure. The preparation of ethylbenzene from ethene and benzene with a zeolite catalyst is described in US-4, 107, 224. Step (a) of the process can be carried out independently of steps (b) to (d) of the process , ie in a different place. However, it is preferred that the production of ethylbenzene equals the production of styrene in step (d), so that the unit of Ethylbenzene is an integrated part of the SM / PO process or is located in the vicinity of an SM / PO plant. An SM / PO plant with an integrated ethylbenzene unit is generally preferred. In the oxidation step (b) the liquid phase oxidation of ethylbenzene in ethylbenzene hydroperoxide is presented at a temperature of 100-160 ° C, suitably 130-150 ° C, and at a pressure of 1-4 bar, suitably 2- 3 bar Oxidation is typically carried out with air as the oxidizing gas, but oxygen could also be applied. The main by-product formed in this step is acetophenone, which could be hydrogenated in the SM / PO process in 1-phenylethanol, used in step (d) to produce styrene. In the epoxidation step (c) the ethylbenzene hydroperoxide is reacted with propene to produce propylene oxide and 1-phenyl ethanol or substituted 1-phenyl ethanol. In such an epoxidation step, a homogeneous catalyst or a heterogeneous catalyst can be applied. Molybdenum compounds are frequently applied as homogeneous catalysts, while titanium-based catalysts on a silica support are often used as heterogeneous catalysts. The conditions under which epoxidation is carried out are known in the art and include typically temperatures of 75 to 150 ° C, and pressures of up to 80 bar, with the reaction medium being in the liquid phase. The effluent from the epoxidation step is usually first subjected to a separation treatment to remove the formed propylene oxide, after the waste stream, which contains 1-phenyl ethanol, is suitably subjected to one or more separation treatments., inter alia to remove ethylbenzene for reuse at an earlier stage of the process. The optionally obtained stream containing 1-phenyl ethanol is then subjected to the dehydration treatment in step (d). The dehydration of 1-phenyl ethanol in styrene is also known in the art. It can be carried out in both gas phase and liquid phase. Suitable dehydration catalysts include, for example, acidic materials such as alumina, alkali alumina, aluminum silicates and synthetic H-type zeolites. Dehydration conditions are also well known and usually include reaction temperatures of 100-210 ° C for in-phase dehydration. liquid and 210-320 ° C, typically 280-3 ° C, for gas phase dehydration. The pressures are usually in the range of 0.1 to 10 bar. In principle any dehydration process can be applied in step (d). In a commercial SM / PO process, the propene used in step (c) can be supplied either from an external source or it can be made in the same SM / PO site, usually in a steam catalytic thermofraction unit ( also commonly referred to as an ethene plant). The last option is the preferred option and it is applied more frequently. An SM / PO process comprising the steps of (a) to (d) as described above requires equal amounts of ethene and propene as feed. Because of this, SM / PO plants are typically located in the vicinity of an ethene plant, which produces both the ethene and propene required. Therefore, if a new SM / PO plant is to be designed and built, this plant is usually located near an existing ethene plant that has an overcapacity of ethene and propene, or an ethene plant should be included in the the design to ensure the necessary supply of ethene and propene. This is not a very advantageous situation from a logistical and economic perspective, since it limits the selection of a site to build an SM / PO plant and links the economy to that of an ethene plant. Therefore, it would be beneficial if the ethene and propene could be supplied from an alternative source without having the aforementioned drawbacks.

Within the context of the present invention it has been found that integrating an SM / PO process with a fluid catalytic thermofraction unit (FCC) could overcome the economic and logistic restrictions already mentioned.

Therefore, the present invention relates to a process for the joint preparation of styrene and propylene oxide comprising the steps (a), (b), (c) and (d) as described above, wherein the ethene used in step (a) and propene used in step (c) are provided at least partially by an FCC unit. A typical FCC unit within the context of the present invention comprises a reactor section and a preparation section. In the section of the reactor real catalytic thermofraction is carried out, after which in the preparation section the effluent of the catalytic thermofraction is separated into different products. The reactor section typically comprises a reactor, a catalyst regenerator and a separator. The temperature in the FCC reactor of the fluid catalytic heat fractionation unit is typically less than 550 ° C, and it is preferably within the range of 500 to 525 ° C. The effluent from the reactor section is then conducted to the preparation section. Suitably, such preparation section begins with a main fractionator where the catalytic thermofracting effluent of the reactor section is introduced. The upper fraction of this main fractionator contains the low-boiling components, which are mainly hydrocarbons from Cl to C4. In addition, gases such as hydrogen sulfide, carbonyl sulphide, hydrogen and nitrogen are present in small amounts. This upper fraction is typically compressed and sent to an absorption / rectification column. Here the so-called exit gas - which mainly comprises Cl and C2 components and some components of hydrogen, nitrogen and sulfur - is removed and sent, via a unit to remove the sulfur components (typically one unit of amine), to the fuel gas system. The recovered material C3 / C4 is suitably sent to a debutanizer, a depropanizer and optionally a propane / propene separator, where the separation is effected in a stream of C4, a propane stream and a propene stream. All the treatments that begin with the separation in the main fractionator are part of the preparation section. As indicated above, the exit gas containing the Cl and C2 components of an FCC unit would normally be sent to the fuel gas system. Nevertheless, within the structure of the present invention this exit gas is used as the source of ethene to be used in the ethylbenzene unit. Similarly, the propene used in the epoxidation step (c) is derived from the propene / propane separator. However, an FCC unit does not produce ethene and propene in the desired ratio of 1: 1. It is possible within the structure of the present invention to use the propene and ethene produced in the FCC unit together with the ethene and / or propene coming from other sources, preferably located in the vicinity of the SM / PO plant, if the production of ethene and / or propene from the FCC unit is not sufficient to satisfy the ethene and / or propene demand of the SM / PO process. As stated above, the ethene used in step (a) is suitably derived from the outlet gas of the fluid catalytic thermofraction unit containing the components Cl and C2. However, it is preferred that the exit gas, after having passed through an amine unit, it is subjected successively to an absorption / desorption treatment to remove hydrogen, nitrogen and methane, and to a treatment to remove or hydrogenate acetylene before the resulting stream containing ethane and ethene is sent to a unit of ethylbenzene production. It has been found particularly advantageous for the purpose of the present invention that in the ethylbenzene production unit, the stream containing ethane and ethene is contacted with benzene in the presence of a zeolite catalyst, suitably a catalyst based on ZSM-5. , and that the ethylbenzene and the remaining ethane are subsequently recovered. If the ethene produced in the reactor section of the FCC unit is not sufficient to fully meet the ethene demand of the SM / PO process, it has been found very useful to produce the remaining part of ethene needed in one or more thermo-fractionation furnaces. catalytic, which are supplied with ethane and propane is optionally produced in the reactor section of the fluid catalytic thermofraction unit. In this way, the C2 and C3 products produced in the FCC process are optimally used to create the ethene supply for the ethylbenzene unit. The ethane produced in the FCC unit could be fed directly to the catalytic thermofraction furnace (s). However, it is preferred to send the ethane as a stream of ethane / ethene to the ethylbenzene production unit, where the ethene is reacted with benzene in ethylbenzene. The remaining ethane is recovered from the ethylbenzene production unit and then fed to the catalytic thermal cracking furnace (s). If the ethane in the FCC unit does not produce just enough additional ethene for the catalytic thermofraction furnace (s) to supply the necessary ethene, ethane could be added from an external source. If the FCC process produces insufficient propene to meet the propene demand of the SM / PO process, the feed of the catalytic thermofraction furnace (s) could also contain propane recovered from the fluid catalytic thermofraction unit, optionally supplemented with external propane or even butane. It will be understood that external ethane and / or propane are needed, if required by the ethene and / or propene demand of the SM / PO process. To optimize the use of the preparation section of the FCC unit and therefore increase the overall efficiency of the process, it is preferred that the effluent from the catalytic thermofraction furnace (s), the effluent containing ethene and optionally propene, be prepared in the preparation section of the fluid catalytic thermofraction unit together with the effluent of the section of the reactor of the fluid catalytic thermofraction unit. The effluent from the catalytic thermofraction furnace (s) typically contains hydrogen, methane, unconverted ethane and heavier components, in addition to a high amount of ethene. If propane is also introduced into the furnace (s), the effluent also contains propene as well as unconverted propane and heavier components. In this way, the effluent from the furnace is mixed with the catalytic thermofraction effluent from the reactor section of the FCC unit before entering the main fractionator. In this way, the effective separation of propene and ethene is effected and any pollutant and methane formed in the catalytic thermofraction furnaces are removed in the preparation section. It will be understood that the integration of an FCC unit with an SM / PO process, according to the present invention, is particularly effective in a situation where an SM / PO plant is to be built simultaneously with an FCC plant in the same site, as this allows an optimally integrated global design. Alternatively, it can also be effective, although normally less than in the previous situation, to build a SM / PO plant in a site where an FCC plant is already present. The invention is further illustrated by Figures 1 and 2. Figure 1 shows the general concept that highlights the present invention. Figure 2 schematically shows a particularly preferred form of integrating an FCC unit and an ethylbenzene unit for the purpose of the present invention. In Figure 1, the FCC feed (e.g., heavy distillates) enters the reactor section 2 of the FCC. The effluent from reactor 3 is subsequently prepared in preparation section 4, resulting in a stream of ethene 5 and a stream of propene 7. The ethene stream 5 is introduced into the ethylbenzene unit 9, optionally with additional ethene 6 from an external source, together with the benzene stream 17. The stream that contains ethylbenzene 10 is then conducted to oxidation unit 11, where ethylbenzene is oxidized to ethylbenzene hydroperoxide (EBHP), using air or oxygen 18 as the oxidizing gas. The EBHP formed leaves the oxidation unit 11 as the stream 12 and is fed to the epoxidation unit 13, where it is reacted with the propene of the propene stream 7 and optionally with propene 8 from an external source to form propylene oxide 19 and 1-phenylethanol 14. The stream of 1-phenylethanol 14 is converted to dehydration unit 15 in styrene 16 and water 20. In figure 2 the effluent 2 from the reactor section of FCC 1 is passed to the main fractionator 3 The upper fraction 4, recovered from the main fractionator 3, is fed into the absorption / rectification column 5, where it is separated in a gas stream of outlet 7 and a current of C3 / C4 6. The outlet stream 7 is sent via an amine unit 8 (to remove the sulfur components), absorption / desorption unit 10 (to remove hydrogen, nitrogen and methane to prevent the accumulation of these components in the process), and acetylene removal unit or of h hydrogen to the ethylbenzene unit 15. The effluent from the amine unit 8 is essentially free of sulfur components, while the stream 12 leaving the absorption / desorption unit 10 is free of nitrogen, NOx, hydrogen and methane , which they all combine in stream 11. Stream 14 leaving the acetylene or hydrogen removal unit 13 contains mainly ethane and ethene and is sent to the ethylbenzene unit 15, where it is converted to ethylbenzene, which exits as the stream. which is to be sent to the oxidation unit of the SM / PO process (not shown). The stream of C3 / C4 6 is sent to the debutanizer 20, in which an upper butane / C3 fraction is recovered 21. This upper fraction 21 is fed to the depropanizer 22, where it is separated in stream of butane 23 and a stream of C3 24, which consists mainly of propane and propene. Other components present in minor amounts are methylacetylene and propadiene (MA / PD) formed in the catalytic thermofraction furnace (s) 18 and sulfur components. Therefore, the C3 current 24 is passed through an amine unit 25, after which the desulfurized stream 26 is passed through a MA / PD removal unit or hydrogenation unit 27, producing a propane stream. / propene 28. This propane / propene stream 28 is separated into a propene stream 30 and a propane stream 31 in the propane / propene separator 29. The propene stream 31 can be sent directly to the epoxidation unit of the process SM / PO (not shown). The Propane stream 31, optionally supplemented with additional propane 32, is combined with the ethane-containing effluent 17 of the ethylbenzene unit 15. This effluent 17 could be supplemented with external ethane 33. The combined stream is subsequently passed to the furnace (s) of catalytic thermofraction 18 where the catalytic thermocracking of ethene and propene is presented. The catalytic thermofraction effluent 19 containing ethene / propene is then combined with effluent 2 from the FCC reactor section, thus making optimum use of the final section of the FCC already available or to be installed. The ethene of the catalytic thermofracting effluent 19 eventually ends up in the ethene / ethane stream 14, while the propene ends in the propene stream 30. The invention is further illustrated by the following example without limiting the scope of the invention to this mode particular.

Example The integration between an FCC unit and an SM / PO plant, as illustrated in Figure 2, is carried out using an FCC unit 1 having a feed conversion capacity of 6000 tonnes per day.

Three conventional catalytic thermofraction furnaces are used. 18. The integrated process is designed to operate a large scale SM / PO plant that requires an equal amount (12.5 tons / hour) of ethene and propene. In table I the amounts of hydrogenNitrogen, methane, acetylene, ethane, ethene, propane and propene in various numbered process streams as indicated in Figure 2 are given in tons / hour (t / h). As can be seen in Table I, the integrated part of the FCC process and the SM / PO process produces the required amount of ethene (12.5 t / h: stream 14), while at the same time producing more than enough propene (13.80 t / h: stream 30) to supply the epoxidation section of the SM / PO plant (not shown in Figure 2) with the required amount of propene. Thus, it can be seen that the integration between an FCC unit and an SM / PO plant in accordance with the present invention is very possible without the need for a complete catalytic steam thermofraction unit to supply the required ethene and propene.

TABLE I. Current compositions It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (9)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. Process for the joint preparation of styrene and propylene oxide, characterized in that it comprises the steps of: (a) reacting ethene and benzene to form ethylbenzene, (b) reacting ethylbenzene with oxygen or air to form ethylbenzene hydroperoxide, (c) reacting at least part of the ethylbenzene hydroperoxide obtained with propene in the presence of an epoxidation catalyst, to form propylene oxide and 1-phenyl ethanol, and (d) dehydrating at least part of the 1-phenyl ethanol obtained in styrene in the presence of a suitable dehydration catalyst, wherein the ethene used in step (a) and the propene used in step (c) are at least partially provided by a fluid catalytic thermofracting unit.

2. Process according to claim 1, characterized in that the ethene used in step (a) is derived from the outlet gas of the fluid catalytic thermofraction unit containing the components Cl and C2.

3. Process according to claim 2, characterized in that the exit gas after having passed through an amine unit, is subjected successively to an absorption / desorption treatment to remove hydrogen, nitrogen and methane, and to a treatment for remove acetylene before the resulting stream containing ethane and ethene is sent to an ethylbenzene production unit. Process according to claim 3, characterized in that in the ethylbenzene production unit the stream containing ethane and ethene is contacted with benzene in the presence of a zeolite catalyst and the ethylbenzene and the remaining ethane are recovered. Process according to any of claims 1-4, characterized in that a part of the ethene used in step (a) is produced in the reactor section of the fluid catalytic thermofraction unit and the other part of the ethene The necessary one is produced in one or more catalytic thermofraction furnaces, which are fed with ethane and propane is optionally produced in the reactor section of the fluid catalytic thermofraction unit. 6. Process according to claim 4 and 5, characterized in that the ethane is first sent as a stream of ethane / ethene to the ethylbenzene production unit, after which it is fed to the catalytic thermofraction furnace (s) as the recovered ethane from the ethylbenzene production unit. Process according to claim 5 or 6, characterized in that the feed to the catalytic thermofraction furnace (s) also contains propane recovered from the catalytic fluid thermocracking unit, optionally supplemented with external ethane and / or propane. 8. Process according to any of claims 5-7, characterized in that the effluent from the catalytic thermofraction furnace (s), this effluent contains ethene and optionally propene, is prepared in the preparation section of the fluid catalytic thermal fractionation unit. with him Effluent from the reactor section of the fluid catalytic thermofraction unit. 9. Process according to any of the preceding claims, characterized in that the temperature of the reactor in the reactor section of the catalytic fluid fractionation unit is less than 550 ° C, preferably within the range of 500 to 525 ° C.