A process for producing olefins

Abstract

The invention relates to a process for producing olefins, comprising: (a) converting an oxygenate into at least one olefin in an oxygenate-to-olefin reactor (9), thereby obtaining an olefin containing crude reaction product; (b) cooling the crude reaction product in a first cooling stage (11), thereby obtaining a cooled gaseous crude reaction product; (c) condensing the cooled gaseous crude reaction product at least partly in a second cooling stage (25), thereby obtaining a condensed crude reaction product; (d) neutralizing the condensed crude reaction product to obtain a neutralized crude reaction product; (e) working up the neutralized crude reaction product, wherein heat released from the crude reaction mixture in the first cooling stage (11) is used for producing steam (19, 23) and / or for heating material streams in the process for producing olefins and wherein heat released from the cooled crude reaction mixture in the second cooling (25) stage is used as a heat source in a heat pump for producing steam (29).

Description

[0001] A process for producing olefins

[0002] Specification

[0003] The invention relates to a process for producing olefins, comprising:

[0004] (a) converting an oxygenate into at least one olefin in an oxygenate-to-olefin reactor, thereby obtaining an olefin containing crude reaction product;

[0005] (b) cooling the crude reaction product in a first cooling stage, thereby obtaining a cooled gaseous crude reaction product;

[0006] (c) condensing the cooled gaseous crude reaction product at least partly in a second cooling stage, thereby obtaining a condensed crude reaction product;

[0007] (d) neutralizing the condensed crude reaction product to obtain a neutralized crude reaction product;

[0008] (e) working up the neutralized crude reaction product.

[0009] Presently, olefins either are produced by steam cracking of a petroleum feedstock or by converting oxygenates, particularly alkanols, to olefins. Generally, methanol is used as an oxygenate for producing olefins.

[0010] For converting oxygenates to olefins, an oxygenate containing feed stock is fed into an oxygen- ate-to-olefin reactor, in which the oxygenate is converted into an olefin and water in the presence of a catalyst. As the reaction is highly exothermic and the reaction product is typically obtained at high temperatures, it is necessary to cool the obtained crude reaction product containing olefins and water.

[0011] The heat stored in the crude reaction product for example may be used for producing steam as described for example in US-A 2004 / 0152936. Here, cooling of the crude reaction product is carried out in four steps, wherein in two steps high pressure steam and medium pressure steam are produced by evaporating water, which is used as cooling medium for cooling the crude reaction product. In a further cooling step, the crude reaction product is cooled by using the feed stream as cooling medium, thereby heating the feed stream.

[0012] Further processes for using the heat stored in the crude reaction products from oxygenate-to- olefin processes are described for example in CN-A 105399592, CN-A 103557597 and CN-U 204963233. In the processes described in CN-A 103557597 and CN-U 204963233 a part of the heat further is used for heating and vaporizing methanol which is used as oxygenate. A methanol-to-olefins process, in which the crude reaction stream obtained in the reaction is used for preheating and vaporizing the methanol is described in CN-A 109020772.

[0013] In all known processes, the cooled reaction product still is gaseous after having passed all cooling stages, in which the heat stored in the reaction product is used for producing steam or for preheating and vaporizing the oxygenate. For further cooling and condensing the water that is formed as a by-product in the reaction, the cooled gaseous crude reaction product is fed into a quench device, in which a part of the gaseous crude reaction product is condensed by direct contact with a quench medium.

[0014] After cooling and at least partially condensing the crude reaction product, water and high boiling by-products are removed. Subsequently, the thus obtained reaction product is further worked- up for separating different olefins produced by the reaction.

[0015] By carrying out the last cooling step, in which at least the high boiling components condense, by quenching, it is not possible to use the heat dissipated in this cooling step.

[0016] As generally carboxylic acids are formed as by-products, it is further necessary to neutralize the crude reaction product, which also may be carried out in the quench device. To reduce corrosion, it is known from US-B 7,495,141 to inject one or more neutralization agents into various target regions in the process that are susceptible to the formation of localized condensation having a pH less than 7.0.

[0017] It is an object of the present invention to provide a process with an improved heat recovery, in which also the heat released by condensing at least a part of the crude reaction product can be used.

[0018] This object is achieved by a process for producing olefins, comprising:

[0019] (a) converting an oxygenate into at least one olefin in an oxygenate-to-olefin reactor, thereby obtaining an olefin containing crude reaction product;

[0020] (b) cooling the crude reaction product in a first cooling stage, thereby obtaining a cooled gaseous crude reaction product;

[0021] (c) condensing the cooled gaseous crude reaction product at least partly in a second cooling stage, thereby obtaining a condensed crude reaction product;

[0022] (d) neutralizing the condensed crude reaction product to obtain a neutralized crude reaction product;

[0023] (e) working up the neutralized crude reaction product, wherein heat released from the crude reaction mixture in the first cooling stage is used for producing steam and / or for heating material streams in the process for producing olefins and wherein heat released from the cooled crude reaction mixture in the second cooling stage is used as a heat source in a heat pump for producing steam.

[0024] For producing olefins from oxygenates, one or more oxygenates are fed into a suitable oxygen- ate-to-olefin reactor and converted into olefins in the presence of a catalyst.

[0025] Oxygenates that can be used for the production of olefins for example are aliphatic-containing compounds that may contain hetero-atoms, like alcohols, amines, carbonyl compounds, such as aldehydes, ketones and carboxylic acids, ethers, halides, mercaptans, sulfides and mixtures thereof. The aliphatic moiety of the aliphatic-containing compound may be branched or unbranched and typically comprises 1 to 40 carbon atoms, preferably 1 to 20 carbon atoms, more preferred 1 to 10 carbon atoms and particularly 1 to 6 carbon atoms.

[0026] Suitable aliphatic-containing compounds for example are alcohols like methanol or ethanol, al- kyl-mercaptans like methyl mercaptan and ethyl mercaptan, alkyl-sulfides liked methyl sulfide, alkyl-amines like methyl amine, alkyl-ethers like dimethyl ether, diethyl ether or methylethyl ether, alkyl-halides like methyl chloride or ethyl chloride, alkyl ketones like dimethyl ketone, formaldehydes, and various acids like acetic acid.

[0027] It is possible to feed one or more oxygenates into the oxygenate-to-olefin reactor, however, preferably, one oxygenate is fed into the oxygenate-to-olefin reactor. Preferably, an oxygenate containing at least one oxygen atom is used. Particularly preferably, the oxygenate is an alcohol, more preferred an aliphatic alcohol and most preferred a Ci- to Ce-alkanoL

[0028] The oxygenate particularly is selected from methanol, ethanol, n-propanol, isopropanol, methylethyl ether, dimethyl ether, diethyl ether, di-isopropyl ether, formaldehyde, dimethyl carbonate, dimethyl ketone, acetic acid, methyl acetate, ethyl acetate, methyl formate, ethyl formate and mixtures thereof.

[0029] Particularly preferably, the oxygenate is selected from one or more of methanol, ethanol, dimethyl ether, diethyl ether, or a combination thereof, more preferred the oxygenate is selected from methanol and dimethyl ether, and most preferred, the oxygenate is methanol.

[0030] Besides the oxygenate, a non-reactive species may be fed into the oxygenate-to-olefin reactor for diluting the oxygenate. Non-reactive species that may be used are inert to the oxygenate and to a catalyst used in the oxygenate-to-olefin reactor. Suitable non-reactive species for example are noble gases like helium or argon, essentially non-reactive species like nitrogen, carbon monoxide, carbon dioxide, water, alkanes such as methane, ethane, and propane, essentially non-reactive aromatic compounds, and mixtures thereof. Particularly, the essentially non- reactive species is water or nitrogen, most preferably water. The water may be used either in liquid or in vapor form. The oxygenate and the non-reactive species may be mixed before being fed into the oxygenate- to-olefin reactor. Further, it is possible to feed the oxygenate and the non-reactive species separately into the reactor. If a catalyst is used which flows through the oxygenate-to-olefin reactor, the catalyst may be mixed with the non-reactive species and the mixture of catalyst and non- reactive species may be fed into the oxygenate-to-olefin reactor.

[0031] Generally, the oxygenate and / or the non-reactive species, particularly the oxygenate and the non-reactive species are preheated before being fed into the oxygenate-to-olefin reactor. If the oxygenate and the non-reactive species are mixed before being fed into the oxygenate-to-olefin reactor, it is further preferred to preheat the mixture of oxygenate and non-reactive species.

[0032] The temperature to which the oxygenate and / or the non-reactive species are heated is such, that the temperature at the reactor entry is in a range from 100 to 700 °C, more preferred in a range from 150 to 600 °C and particularly in a range from 200 to 550 °C.

[0033] In the oxygenate-to-olefin reactor, a reaction takes place in which the oxygenate is converted into at least one olefin.

[0034] Olefins produced by the conversion of the oxygenate usually are olefins comprising 2 to 40 carbon atoms, preferably the olefins comprise 2 to 10 carbon atoms, more preferred 2 to 8 carbon atoms, and particularly 2 to 3 carbon atoms.

[0035] The reaction generally is carried out at a temperature in a range from 200 to 800 °C, more preferred in a range from 300 to 600 °C and particularly in a range from 350 to 550 °C and a pressure in a range from 10 kPa to 10 MPa, preferably in a range from 50 kPa to 1 MPa and particularly in a range from 100 kPa to 0.5 MPa.

[0036] The reaction usually is carried out in the presence of a catalyst. The catalyst may be provided as a fluidized bed, a fixed bed, a moving bed or in the form of particles being fed into a flow reactor and, flow through the reactor, being separated from the crude reaction product after leaving the reactor and then recycled into the reactor. The reactor might comprise a single stage or multiple stages. Suitable catalysts to be used for the oxygenate-to-olefin reaction may be for example molecular sieve catalysts or catalyst compositions. Catalysts and reactor types to be used for the oxygenate-to-olefin reaction are well-known to the skilled person and described for example in US-A 2004 / 0152936.

[0037] For example, typically in fixed bed processes, if the oxygenate is methanol, the methanol is mixed with water and preheated. The preheated stream is fed into a first reaction stage, in which a part of the methanol is converted into dimethyl ether. The thus obtained stream containing methanol, steam and dimethyl ether is mixed with a recycled stream containing hydrocarbons and steam and is then fed into a second reaction stage. Before being fed into the second reaction stage, the mixed streams may be heated to reaction temperature, however, this is not necessary, because the reaction in the second reaction stage is highly exothermal and the reaction heat can be used for heating the stream containing methanol, the stream containing steam and dimethyl ether and / or the stream containing hydrocarbons and steam. The temperature of the stream fed into the second reaction stage preferably is in a range from 100 to 700 °C, more preferred in a range from 150 to 600 °C and particularly in a range from 200 to 550 °C.

[0038] As coking of the catalyst cannot be avoided, it generally is necessary to regenerate the catalyst. If a continuous fluidized bed reactor is used, the catalyst is fed into the reactor at an inlet point, moves through the reactor and is withdrawn at an exit point. After being withdrawn from the reactor, the catalyst can be regenerated and then recycled into the reactor. If a fixed bed reactor is used or a fluidized bed reactor with a stationary catalyst, the reaction must be interrupted for regeneration of the catalyst.

[0039] During regeneration, a regeneration medium is brought into contact with the catalyst. The regeneration medium contains oxygen that can react with the carbon of the coke, so that the coke is burned off the catalyst. Suitable regeneration media are for example oxygen, O3, SO3, N2O, NO, NO2, N2O5, air, air diluted with nitrogen or carbon dioxide, oxygen and water, and mixtures thereof. For burning the coke from the coked catalyst, regeneration is carried out at a temperature in a range from 200 to 1200 °C, more preferred in a range from 300 to 1000 °C and particularly in a range from 550 to 750 °C.

[0040] To terminate the reaction and to avoid polymerization of the olefin, and to separate the components contained in the crude reaction product, the crude reaction product is cooled.

[0041] In the first cooling stage, the crude reaction product is cooled to a temperature above condensation temperature, so that the cooled crude reaction product remains gaseous. To avoid condensation of components, the crude reaction product is cooled to a temperature in a range from 40 to 350 °C, more preferred to a temperature in a range from 90 to 300 °C and particularly to a temperature in a range from 120 to 280 °C.

[0042] The first cooling stage may be carried out in one step, however, it is preferred to carry out the first cooling stage in at least a first cooling step and a second cooling step. If the first cooling stage is carried out in more than one cooling step, each cooling step is operated in such a way that the crude reaction product is cooled by at least 10 °C, preferably by 40 to 500 °C, more preferred by 60 to 300°C and particularly by 80 to 250 °C.

[0043] To use the heat released from the crude reaction product by cooling, it is preferred that heat released in the first cooling step is used for producing steam. The steam may be low pressure steam, medium pressure steam or high pressure steam, preferably medium pressure steam or high pressure steam and particularly high pressure steam. The steam may either be produced directly by evaporating and optionally superheating water in a heat exchanger, in which the first cooling step is carried out. Alternatively, a cooling medium may be used for cooling the crude reaction product in the first cooling step and the cooling medium subsequently is used for pro- ducing the steam, for example as a heat source in a heat pump. However, preferably, for producing steam water is used as a cooling medium in the first cooling step and the water evaporates by absorbing heat from the crude reaction product.

[0044] For producing high pressure steam in the first cooling step, the water to be evaporated either directly by heat transfer from the crude reaction product or, indirectly, in a heat exchanger of a heat pump by heat transfer from a cooling medium which was used for cooling the crude reaction product, has a pressure in a range from 1 to 200 bar(abs), more preferred a pressure in a range from 10 to 150 bar(abs) and particularly a pressure in a range from 15 to 130 bar(abs).

[0045] The water may either be evaporated in the first cooling stage at a pressure below the pressure of the steam or at the pressure of the steam to be produced. If the water has a pressure below the pressure of the steam, the steam obtained by evaporation of the water is compressed in at least one compressor to the desired pressure. The pressure of the steam preferably corresponds to the pressure of the water, which is evaporated by absorbing the heat dissipated from the crude reaction product in the first cooling step. Preferably, if high pressure steam is produced, the water has a pressure in a range from 1 to 200 bar(abs), more preferred a pressure in a range from 10 to 150 bar(abs) and particularly a pressure in a range from 15 to 130 bar(abs).

[0046] In the first cooling step, the crude reaction product preferably is cooled to a temperature in a range from 200 to 550 °C, more preferred in a range from 220 to 500 °C and particularly to a temperature in a range from 230 to 470 °C. The steam produced by heat exchanger in the first cooling step preferably has a temperature in a range from 200 to 550 °C, more preferred to a temperature in a range from 220 to 500 °C and particularly to a temperature in a range from 230 to 470 °C.

[0047] The heat released in the second cooling step may be used for producing low pressure steam, medium pressure steam or high pressure steam. For producing steam, the crude reaction product is cooled by a cooling medium and the heated cooling medium then is used as a heat source in a heat pump for producing the steam.

[0048] For producing steam, preferably medium pressure steam, in the second cooling step, the water to be evaporated indirectly in a heat exchanger of a heat pump by heat transfer from a cooling medium which was used for cooling the crude reaction product, has a pressure in a range from 1 to 70 bar(abs), more preferred a pressure in a range from 5 to 60 bar(abs) and particularly a pressure in a range from 10 to 50 bar(abs).

[0049] The water may either be evaporated in the second cooling stage at a pressure below the pressure of the medium pressure steam or at the pressure of the medium pressure steam. If the water has a pressure below the pressure of the medium pressure steam, the steam obtained by evaporation of the water is compressed in at least one compressor to the desired pressure. The pressure of the medium pressure steam preferably corresponds to the pressure of the water which is evaporated by absorbing the heat released from the crude reaction product in the second cooling step. In the second cooling step, the crude reaction product preferably is cooled to a temperature in a range from 40 to 350 °C, more preferred in a range from 90 to 300 °C and particularly to a temperature in a range from 120 to 280 °C. The steam, preferably the low pressure steam or the medium pressure steam, particularly the medium pressure steam, produced by using the released heat of the second cooling step as heat source in the heat pump preferably has a temperature in a range from 100 to 450 °C, more preferred to a temperature in a range from 130 to 400 °C and particularly to a temperature in a range from 150 to 360 °C.

[0050] If it is intended to produce a larger amount of high pressure steam, it is possible, to compress at least a part of the medium pressure steam in at least one compressor to the pressure of the high pressure steam to obtain high pressure steam. For setting the temperature of the high pressure steam obtained by compression of the medium pressure steam, it is possible to inject water into the steam downstream of at least compressor, preferably downstream of each compressor.

[0051] If the first cooling stage is carried out in more than two cooling steps, it is possible to provide additional cooling steps upstream the first cooling step, between the first cooling step and the second cooling step and / or downstream the second cooling step.

[0052] An additional cooling step upstream the first cooling stage can be operated for example with the high pressure steam obtained in the first cooling stage as a cooling medium. In this case, the high pressure steam is superheated by heat transfer from the crude reaction product.

[0053] An additional cooling step between the first and the second cooling steps can be used for example for superheating the medium pressure steam obtained in the second cooling step by using the medium pressure steam of the second cooling step as a cooling medium and superheating the medium pressure steam by heat transfer from the crude reaction product. Alternatively, a cooling step between the first and the second cooling steps also may be used for producing steam. If the steam produced in the additional cooling step between the first and second cooling steps has a pressure below the predefined pressure of the high pressure steam, it is possible to compress the steam in at least a compressor to the pressure of the high pressure steam. If the pressure corresponds to the pressure of medium pressure steam, at least a part of the steam obtained in the additional cooling step may be mixed with the steam obtained in the second cooling step and / or at least a part of the steam may be compressed in at least one compressor to obtain high pressure steam.

[0054] If an additional cooling step is provided downstream the second cooling step, it is possible to use this cooling step for producing steam, which, in case the pressure is below the pressure of medium pressure steam or high pressure steam, can be compressed in at least one compressor to obtain the required pressure of medium pressure steam or high pressure steam or in which low pressure steam is produced. Further, any of the additional cooling steps can be used for preheating the feed streams into the oxygenate-to-olefin reactor. Using the additional cooling step downstream of the second cooling step for preheating the feed streams into the oxygenate- to-olefin reactor is described for example in US-A 2004 / 0152936.

[0055] Besides being used for producing steam, the heat released from the crude reaction product in the first cooling stage may also be used for heating any material stream in the process for producing olefins, for example a bottom stream of a distillation apparatus in a work-up section of the crude reaction product or feed streams fed into the oxygenate-to-olefin reactor. For heating the bottom stream of a distillation apparatus, the bottom stream of the distillation apparatus is heated by absorbing heat from the crude reaction product and then is recycled into the distillation apparatus.

[0056] If the first cooling stage is carried out in at least two cooling steps, the material stream may be heated by heat transfer from the crude reaction product in any of the cooling steps.

[0057] In the second cooling stage, the gaseous crude reaction product obtained in the first cooling stage is further cooled. By cooling in the second cooling stage, at least a part of the gaseous crude reaction product condenses, thereby obtaining the condensed crude reaction product.

[0058] According to the invention, the heat released by cooling the gaseous crude reaction product in the second cooling stage is used as a heat source in a heat pump for producing steam, preferably low pressure or medium pressure steam.

[0059] Besides producing steam, it additionally may be possible to use heat released by cooling the gaseous crude reaction product in the second cooling stage for heating material streams, for example feed streams fed into the oxygenate-to-olefin reactor, or streams to be heated in a workup section of the process following the cooling. A stream to be heated in a work-up section of the process particularly is at least one bottom stream of a distillation apparatus, wherein the at least one bottom stream is heated by absorbing heat from the condensing crude reaction product and recycled into the distillation apparatus.

[0060] As at least a part of the crude reaction stream is condensed in the second cooling stage, the second cooling stage preferably is carried out in a condenser. The condenser may be any type of condenser known to a skilled person. Suitable condensers for example are plate heat exchanger, double pipe heat exchanger or tube-and-shell heat exchangers.

[0061] The crude reaction product usually comprises different components with different boiling temperatures. Therefore, during condensation, components having a higher condensation temperature start to condense firstly. Due to the different boiling temperatures, it is possible to separate the crude reaction product at least partly in the second cooling stage. For this purpose, it is for example possible to operate the second cooling stage in at least two cooling steps, cooling the crude reaction product in each cooling step to a defined temperature at which specified components condense from the crude reaction product and to separate the liquid phase from the gas phase before feeding the remaining gaseous part of the crude reaction product into the follow- ing cooling step. As, however, in each cooling step several components may condense, by separation of the liquid phase a mixture of different components is obtained, which may be further worked-up to separate the different components contained in each liquid phase. This is particularly preferred for the liquid phase containing the olefins, which must be worked-up by a separation process to obtain the different olefins as pure product.

[0062] During cooling several phases may form. These typically contain acids, for example organic acids, particularly organic acids with 1 to 6 carbon atoms, and inorganic acids, particularly carbonic acid which is formed by dissolution of carbon dioxide in water. For this reason, it is necessary to neutralize the crude reaction product. Generally, neutralization is carried out by a caustic quench. In the caustic quench, a caustic, particularly an aqueous caustic solution is mixed with the crude reaction product. Suitable caustics that can be used for example are ammines, ammonia or hydroxides of ammonium or potassium.

[0063] If the oxygenate is methanol, it is preferred to cool and condensate the crude reaction product to the extent possible at the desired temperature and pressure and not to remove components from the crude reaction product during condensation. After neutralization and / or workup of the crude reaction product, a part of the crude reaction product may be recycled into the oxygenate- to-olefin reactor. Preferably, the recycled part of the crude reaction product is mixed with the methanol, dimethyl ether and steam containing stream leaving the first reaction stage.

[0064] If the gaseous crude reaction product obtained in (c) is only partly condensed, besides the condensed crude reaction product a gaseous phase is obtained. This gaseous phase may also contain acidic components so that it is preferred also to neutralize the gaseous phase. Independently of being neutralized or not, the gaseous phase may be worked-up, for example by distillation.

[0065] Since acids have the disadvantage that they may cause corrosion, particularly the apparatuses in which the crude reaction product condenses may be subject to corrosion. As corroded equipment may cause further negative effects on material or persons, timely replacement is necessary. Negative effects that may be induced by corroded material, for example corroded heat exchangers may be for example a risk for explosions, if a pressurized fluid, for example high pressure steam, flows through the apparatus, or hazardous or poisonous components may leak through holes formed by corrosion and may contaminate the environment, deplete natural resources, or may have negative effects on the health of people, particularly if poisonous components escape from a corroded apparatus. Further, even if no harmful escape, a corroded apparatus may have a visually unpleasant appearance that may create the impression of an operation with unsafe equipment. For this reason, presently equipment coming into contact with corrosive media needs to be replaced at regular intervals. Further, to increase the lifetime, apparatuses may be oversized to take possible corrosion into account, for example by using thicker material, which, on the other hand, may result in a loss of efficiency. Additionally, also corrosion may result in a loss of efficiency, for example due to reduced heat conductivity in heat exchangers. Leakages formed by corrosion may result in a loss of product, either by the product leaking from the apparatus or by contamination of the product. As damages of apparatuses or replacement of apparatuses or preventive maintenance further require shutdown of the respective equipment, corrosion may also result in a reduced yield.

[0066] For this reason, to increase the lifetime of apparatus, particularly of the condenser, pipes and the flash apparatus, it is preferred that the respective apparatus are made of a corrosion resistant material or have corrosion resistant surfaces. Particularly preferably, the condenser is a corrosion resistant heat exchanger.

[0067] Corrosion resistant heat exchangers may be heat exchangers made of a corrosion resistant material or heat exchangers being provided with a non-corrosive coating.

[0068] Suitable corrosion resistant materials for example are highly alloyed metals, particularly highly alloyed iron like stainless steel, carbon based materials like graphite or silicon carbide. Further, particularly in heat exchangers through which fluids with different corrosive properties flow, bimetallic tubes may be used which are made of two different materials, one more corrosive on the side being in contact with the less corrosive fluid, for example water and / or steam, and one less corrosive material on the side being in contact with the corrosive fluid, particularly the crude reaction product containing acidic components. Such bimetallic tubes usually are produced by co-extrusion.

[0069] Besides bimetallic tubes for providing different surfaces, it is also possible to provide surfaces that come into contact with the corrosive fluid with a corrosion resistant coating or corrosion resistant film. Such coatings may be for example metallic coatings that can be applied for example by hot dipping, electroplating, spraying, cementation or diffusion. The method used for applying the coating depends on the required corrosion resistance and the anticipated lifetime. Corrosion resistant coatings further may be organic coatings like paints, resins, lacquers, varnishes and plastic linings, or inorganic non-metal coatings like hydraulic cements, ceramics, carbon, silicates, and class. Further suitable inorganic coatings are such that change the natural characteristics of the oxide film, with a low corrosion resistance, into a different protective film or metallic oxide with a higher corrosion resistance in the specific operational environment. Such coatings may be obtained for example by anodising, nitriding, and phosphatising. Suitable methods for corrosion prevention are described for example by Willem Faes et aL, “Corrosion and corrosion prevention in heat exchangers”, Corrosion Reviews 2019 (https: / / doi.Org / 10.1515 / corrrev-2018-0054).

[0070] To prevent abrasion of the corrosion resistant surfaces by catalyst fines, a solids removal step may be included between the first and the second cooling stages. This solids removal step may contain any of typical unit operations used for solids removal such as filters, cyclones, electrostatic solids removal, etc. However, due to the pressure range in this part of the process, electrostatic solids removal is particularly preferred. Cyclones usually are included in state-of-the-art fluidized bed processes but do not remove all entrained solids. If the process comprises a quench step, residual solids generally are removed from the raw product stream by the quench. The heat of condensation may be used for producing steam, preferably low pressure steam. In this case, it is preferred to use water as a cooling medium in the condenser and to evaporate the water by absorbing heat from the cooled gaseous crude reaction product. However, also in this case, it may be preferred that the condenser is connected to a heat pump for producing steam, preferably for producing low pressure steam.

[0071] The heat pump for producing steam may be an open loop heat pump or a closed loop heat pump. If the heat pump is a closed loop heat pump, a cooling medium is used as working medium of the heat pump for producing steam. In this case the cooling medium is heated by heat transfer from the crude reaction product, compressed and fed into a heat exchanger for evaporating water. In the heat exchanger for evaporating water, the water is evaporated by heat transfer from the compressed cooling medium which thereby is cooled and, generally, at least partly condensed. Subsequently, the cooling medium is expanded and then recycled into the heat exchanger for condensing the crude reaction product.

[0072] If the heat pump is an open loop heat pump, water is used for cooling and at least partially condensing the crude reaction product. By heat transfer from the crude reaction product, the water at least partially evaporates. If only a part of the water evaporates, the liquid phase and the gaseous phase are separated, the liquid phase preferably is recycled into the condenser and the gaseous phase is compressed to obtain the steam, preferably low pressure steam. This may be carried out for example in a steam drum, preferably in a low-pressure steam drum. In case the water evaporates completely, the whole water stream is compressed to obtain the steam, preferably the low pressure steam.

[0073] Alternatively, it is also possible to heat the water in the condenser by heat transfer from the crude reaction stream but not to evaporate the water at least partly. In this case, after being heated the water is expanded so that a part of the water evaporates due to expansion. Subsequently, the evaporated part may be compressed to obtain steam at a defined pressure level, preferably low pressure steam, and the liquid phase is returned into the condenser. Expanding and evaporating at least a part of the heated water stream may be carried out for example in a flash apparatus, for example a flash tank. Generally, the liquid phase and the gas phase are separated in the flash tank and can be withdrawn separately.

[0074] If water is used for cooling and at least partly condensing the crude reaction product, it is preferred that the water evaporates at a pressure between 0.01 and 20 bar(abs), more preferred between 0.05 and 17bar(abs) and particularly between 0.1 and 15 bar(abs). By heat transfer from the crude reaction product, the water is heated to a temperature in a range from 20 to 300 °C, more preferred to a temperature in a range from 35 to 270 °C and particularly to a temperature in a range from 45 to 250 °C.

[0075] In the context of the present invention, “high pressure steam” means steam having a pressure in a range from 40 to 150 bar(abs) and a temperature in a range from 250 to 450 °C, “medium pressure steam” means steam having a pressure in a range from 10 to 40 bar(abs) and a temperature in a range 180 to 250 °C and “low pressure steam” means steam having a pressure in a range from 1 to 10 bar(abs) and a temperature in a range from 100 to 200 °C.

[0076] Independently of heating material streams or producing low pressure steam, connecting the condenser to a heat pump particularly is preferred, if the heat of condensation of the crude reaction product is not sufficient for heating the material stream and / or evaporate the water.

[0077] To further improve the use of the heat of the crude reaction product, it is possible to operate the second cooling stage in at least two cooling steps.

[0078] In this case, in a first cooling step of the second cooling stage, it is preferred to use water as a cooling medium for cooling and at least partly condensing the crude reaction product, wherein the water at least partly evaporates by heat transfer from the crude reaction product. The at least partial evaporation of the water may be carried out either in an open loop heat pump or, preferably, by evaporating water in the condenser, wherein the pressure of the water corresponds the pressure of the steam produced, preferably of the low pressure steam, so that by the partial evaporation directly steam at a defined pressure level, preferably low pressure steam, is generated. In this case, it is particularly preferred that the condenser is part of a steam drum in which the steam, preferably the low-pressure steam is generated.

[0079] In a second cooling step, the heat released by cooling and condensing the crude reaction product is used in a heat pump. In this case, it is particularly preferred that the heat pump is a closed loop heat pump with a cooling medium as working fluid of the heat pump. By the second cooling step of the second cooling stage additional heat at comparatively low temperatures of the crude reaction product can be used. Generally, the crude reaction product entering the second cooling step of the second cooling stage has a temperature between 40 and 140 °C, preferably between 50 and 100 °C and most preferred between 60 and 80°C, and can be cooled by heat transfer to the cooling medium to a temperature between 10 and 120 °C, preferably between 20 and 80 °C and most preferably between 30 and 60°C.

[0080] Depending on the temperature of the condensed crude reaction product, it may be necessary to continue cooling of the crude reaction product after the second cooling stage. In this case, a third cooling stage is carried out, in which the crude reaction product is cooled in a direct quench. The quenching liquid may be water. However, it is preferred to use a caustic aqueous solution for simultaneously neutralizing the crude reaction product. The caustic aqueous solution preferably is the same as described above. The third cooling stage particularly is carried out, if in the second cooling step steam is generated in the second cooling stage without the use of a heat pump. However, even if a heat pump is used, the third cooling step may be necessary.

[0081] Independent of cooling is carried out in two or three cooling stages, the crude reaction product preferably is cooled to a temperature between 10 and 190°C, more preferred to a temperature between 20 and 100 °C and particularly to a temperature between 30 and 90 °C. After cooling and neutralizing, the crude reaction product is worked-up. By working-up, by-products, inert components and reactants that have not reacted are removed from the crude reaction product to obtain olefins. Working-up generally is carried out by distillation and phase separation and is well known to the skilled person. As usually different olefins are produced, by work- ing-up also the different olefins are separated to obtain pure olefins.

[0082] Embodiments of the invention are shown in the figures and explained in more detail in the description below.

[0083] In the figures:

[0084] Figure 1 shows schematically an oxygenate-to-olefin process in a first embodiment;

[0085] Figure 2 shows schematically an oxygenate-to-olefin process in a second embodiment,

[0086] Figure 3 shows the cumulated heat recovery as a function of the cooling temperature.

[0087] A process for producing olefins by conversion of oxygenates is shown in figure 1 in a first embodiment.

[0088] For producing olefins, an oxygenate 1 , for example methanol, can be mixed with a stream 3 that can contain hydrocarbons, preferred aliphatic hydrocarbons of 1 to 40 carbon atoms, more preferred 1 to 10 carbon atoms and particularly 1 to 6 carbon atoms, and / or water to obtain a feed stream 5. The feed stream 5 is preheated in a first heat exchanger 7. The preheated feed stream then is fed into an oxygenate-to-olefin reactor 9, in which the oxygenate is converted into at least one olefin, thereby obtaining an olefin containing crude reaction product.

[0089] The oxygenate-to-olefin reactor may be of any type suitable for converting oxygenates into olefins. Suitable reactors for example are fluidized bed reactors, moving bed reactors or fixed bed reactors, wherein the fluidized bed, moving bed or fixed bed comprises a catalyst. Moreover, the reaction can be carried out in more than one reactor.

[0090] The crude reaction product obtained in the oxygenate-to-olefin reactor 9 leaves the oxygenate- to-olefin reactor 9 with a temperature in a range between 350 and 550 °C and is fed into a first cooling stage 11. In the embodiment shown here, the first cooling stage 11 comprises a first cooling step 13 and a second cooling step 15.

[0091] In the first cooling step, the crude reaction mixture is cooled to a temperature in a range from 230 to 470 °C by heat transfer to a water stream 17. The water stream is evaporated and, preferably, superheated to obtain steam, preferably high pressure steam 19. For this purpose, it is preferred that the water being fed into the first cooling step 13 has a pressure in a range from 15 to 130 bar(abs). The crude reaction product leaving the first cooling step 13 generally has a temperature in a range from 200 to 470 °C and is fed into the second cooling step 15, in which the crude reaction product is cooled to a temperature above condensation temperature, generally to a temperature in a range from 120 to 280 °C. In the second cooling step, the heat of the crude reaction mixture is used for producing steam, preferably for producing medium pressure steam. For this purpose, a water stream 21 is used for cooling the crude reaction stream. By heat transfer from the crude reaction stream, the water is evaporated and, preferably, superheated to a temperature in a range from 180 to 360 °C. The water stream preferably has a pressure in a range from 10 to 50 bar(abs), which preferably corresponds to the pressure of the medium pressure steam 23 generated by cooling the crude reaction stream in the second cooling step 15.

[0092] After leaving the second cooling step 15, the gaseous crude reaction product is fed into a second cooling stage 25, in which the gaseous crude reaction product condensates at least partly. The heat released by cooling and at least partly condensing the crude reaction product may be used for producing low pressure steam. For this purpose, a water stream 27 is fed into the second cooling stage 25 and at least partly evaporated by heat transfer from the crude reaction stream. To produce steam, preferably low pressure steam, it is for example possible to use a steam drum in the second cooling stage, wherein the water is partly evaporated and separated into a gas phase and a liquid phase. If the condenser for at least partly condensing the crude reaction stream and the steam drum are separate apparatuses, the liquid phase is recycled into the condenser to be evaporated. The gas phase may be used as saturated steam or may be compressed in at least one compressor to obtain superheated steam having a pressure above the pressure of the water being at least partly evaporated in the condenser.

[0093] Preferably, the water being fed into the second cooling stage 25 evaporates at a pressure in a range from 0.1 to 15 bar(abs). If a steam drum is used, the pressure generally corresponds to the pressure of the generated steam or may be below the required pressure of the steam. In this case, evaporation is carried out at a lower pressure and the steam subsequently is compressed to the required pressure.

[0094] However, alternatively, it is also possible to feed water having a pressure above the evaporation pressure into the second cooling stage 25. In this case, the water is heated in the condenser and subsequently expanded. By expansion at least a part of the water evaporates. The evaporated part may be compressed to obtain low pressure steam 29, which is withdrawn from the second cooling stage 25. The low pressure steam produced in the second cooling stage 25 preferably has a pressure in a range from 1 to 15 bar(abs) and a temperature in a range from 100 to 260 °C.

[0095] In the embodiment shown in figure 1 , a first part 31 of the low pressure steam is used as heating medium in the first heat exchanger 7 to preheat the feed stream 5.

[0096] Besides or additionally to generate steam, preferably to generate low pressure steam, by heat transfer from the crude reaction product to water, it is also possible to use the crude reaction stream as a heat source of a heat pump. In this case, the crude reaction product is cooled by a cooling medium in the condenser, the cooling medium thereby evaporates and, subsequently, the evaporated cooling medium is compressed. By compression, the cooling medium is heated and the compressed and heated cooling medium is cooled by heat transfer to for example a water stream or any process stream. The cooling medium then is expanded and returned into the condenser, so that the cooling medium flows in a closed loop. The water, which is heated by heat transfer from the cooling medium may only be heated and subsequently partially evaporated by expansion or may be at least partly evaporated by heat transfer from the cooling medium. The generation of the steam, preferably of the low pressure steam then corresponds to the generation of low pressure steam as described above for the alternative, in which the water is heated by heat transfer from the crude reaction product in the condenser.

[0097] Particularly preferably, the second cooling stage 25 comprises two steps. A first step, in which the crude reaction product is cooled to a temperature in a range from 60 to 250 °C and a second step, in which cooling is continued to a temperature in a range from 30 to 60 °C. In the first step, it is preferred to use a steam drum for producing low pressure steam and in the second step, it is preferred to use a heat pump for generating low pressure steam.

[0098] As the crude reaction product generally contains acidic components, which are corrosive, particularly after being condensed, the condenser used for at least partly condensing the crude reaction product, is a corrosion resistant heat exchanger.

[0099] To neutralize the crude reaction product, after being cooled and at least partly condensed, the crude reaction product is fed into a neutralization step 33. In the neutralization step 33, the crude reaction product is mixed with a caustic solution 35, preferably an aqueous caustic solution. The caustic solution 35 reacts with the acidic components in the crude reaction product, so that the crude reaction product is neutralized. If the temperature of the crude reaction product still is above a required temperature, generally a temperature below 50 °C, the neutralization step 33 is combined with a third cooling stage, in which the crude reaction product is cooled to the required temperature by quenching. In this case, cooling and neutralizing may be carried out separately, for example first cooling in a water quench and then neutralizing by mixing the cooled reaction stream with the caustic solution 35. However, preferably, an aqueous caustic solution is used as quench medium so that cooling and neutralizing the crude reaction product take place simultaneously.

[0100] To obtain purified olefins, the condensed and neutralized crude reaction product is fed into a work-up section 37. In the work-up section 37, non-reacted reactants, water and by-products are separated from the olefins and, preferably, the olefins are separated into pure olefins and withdrawn from the work-up section 37 as product streams 39.

[0101] Besides the olefins, by working-up the crude product stream, also an aqueous product stream 41 is obtained. The aqueous product stream generally comprises water, olefins, non-reacted methanol and further organic components. An optional and preferred recycling stream 43 containing water and optionally hydrocarbons, particularly non-reacted reactants and olefins may be recycled into the reactor 9. For this purpose, the recycling stream 43 preferably is mixed with the oxygenate upstream the first heat exchanger 7 so that the oxygenate, the stream 3 that can contain hydrocarbons and the recycling stream 43 are combined and form the feed stream 5 that is heated in the first heat exchanger 7 and then fed into the reactor 9.

[0102] A part of the high pressure steam 19 and / or a part of the medium pressure steam 23 and / or a part of the low pressure steam 29 may be used as energy source in the work-up section 37, for example for heating distillation processes. Which kind of steam is used in the work-up section 37 depends on the processes carried out and the energy demand.

[0103] Besides using the part 31 of the low pressure steam for heating the feed stream 5, it is also possible to use a part of the high pressure steam 19 or of the medium pressure steam 23 for preheating the feed stream 5.

[0104] High pressure steam 19, medium pressure steam 23 and low pressure steam 29 not being used in the process for producing olefins may be fed into respective steam grids or may be used directly in other processes.

[0105] Figure 2 shows a process for producing olefins in a second embodiment.

[0106] In difference to the embodiment shown in figure 1 , in the process in figure 2, the feed stream 5 is preheated in the second step 15 of the first cooling stage 11 and either medium pressure steam or high-pressure steam can be produced in the first step 13 of the first cooling stage 11 . For this purpose, the feed stream 5 is used as cooling medium in the heat exchanger of the second cooling step 15. After being preheated in the second step 15 of the first cooling stage 11 , the feed stream 5 is fed into the oxygenate-to-olefin reactor 9. Additionally, a solids removal step 16 may be included between the first and the second cooling stage. The solids removal step 16 removes any solids that typically are removed in a quench step of state-of-the-art processes. Here, the solids removal step 16 is necessary to protect any anti-corrosion layer in the second cooling step 25.

[0107] Besides only generating low pressure steam in the second cooling stage 25 as shown in figures 1 and 2, it is also possible to carry out the second cooling stage 25 in at least two cooling steps and to preheat the feed stream 5 in one cooling step and to produce low pressure steam 29 in a second cooling step. In this scenario the preheating of the feed stream 5 in the first cooling stage 11 can be omitted.

[0108] The low pressure steam 29 generated in the second cooling stage 25 can also be compressed further to produce medium pressure steam. Figure 3 shows the cumulated heat recovery during cooling, if also the heat can be used that is released in the second cooling stage by condensation of the crude reaction product. The x-axis 100 shows the cooling temperature and the y-axis 101 the cumulated heat recovery.

[0109] For determining the graph, the heat dissipated from a crude reaction product containing 60 wt- % steam, 17 wt-% ethylene, 17 wt-% propylene and 6 wt-% butylene having a temperature of 500 °C and a pressure of 0.20 MPa and 0.25 MPa, respectively, was calculated. As can be seen, during cooling of the gaseous crude reaction stream to a temperature of 120 °C only about 30 % of the heat that is available to be recovered in an interval from 500 to 10 °C can be recovered. During condensation and cooling of the crude reaction product from 120 to 60 °C, additional 60 % of the heat that is available to be recovered in an interval from 500 to 10 °C can be recovered and during condensation and cooling from 60 to 10 °C, the remaining heat can be recovered. In the graph, curve 103 shows the cumulated heat recovery of the crude reaction product having a pressure of 0.20 MPa and curve 105 shows the cumulated heat recovery of the crude reaction product having a pressure of 0.25 MPa.

[0110] In contrast to known processes, which only use the heat of cooling the gaseous crude reaction product and in which a quench is used for cooling from a temperature at which condensation starts, additional 65 % of heat can be recovered and used for example for heat integration or for producing steam.

[0111] Further, to avoid to decrease the level of vacuum for evaporating the water in the condenser, for example if a steam drum is used or if the water completely evaporates in the condenser, it is advantageous to increase the pressure of the crude reaction stream, because an increased pressure of the crude reaction stream allows for a larger heat recovery, if it is cooled to a defined temperature.

[0112] As can be seen here, only slightly shifting the reactor operation pressure allows for severely more heat to be recovered at high temperatures, particularly at temperatures above 100 °C. Further, the higher reactor operation pressure also allows for steam generation at higher temperatures which results in lower energy demand and costs of a heat pump for generating steam.

Claims

Claims1 . A process for producing olefins, comprising:(a) converting an oxygenate into at least one olefin in an oxygenate-to-olefin reactor (9), thereby obtaining an olefin containing crude reaction product;(b) cooling the crude reaction product in a first cooling stage (11), thereby obtaining a cooled gaseous crude reaction product;(c) condensing the cooled gaseous crude reaction product at least partly in a second cooling stage (25), thereby obtaining a condensed crude reaction product;(d) neutralizing the condensed crude reaction product to obtain a neutralized crude reaction product;(e) working up the neutralized crude reaction product, wherein heat released from the crude reaction mixture in the first cooling stage (11) is used for producing steam (19, 23) and / or for heating material streams in the process for producing olefins and wherein heat released from the cooled crude reaction mixture in the second cooling (25) stage is used as a heat source in a heat pump for producing steam (29).

2. The process according to claim 1 , wherein the first cooling stage (11) is carried out in at least a first cooling step (13) and a second cooling step (15).

3. The process according to claim 2, wherein heat released in the first cooling step (13) is used for producing steam (19).

4. The process according to claim 3, wherein the steam (19) produced from the heat released in the first cooling step (13) is high pressure steam.

5. The process according to claim 3 or 4, wherein for producing high pressure steam (19) water (17) is used as a cooling medium in the first cooling step (13) and the water evaporates by absorbing heat from the crude reaction product.

6. The process according to any of claims 1 to 5, wherein the steam (23) produced from the heat released in the second cooling step (15) is medium pressure steam (23).

7. The process according to any of claims 2 to 6, wherein in the first cooling step (13) and / or in the second cooling step (15) a heat exchanger is used for cooling the crude reaction product and the heat exchanger is connected to a heat pump.

8. The process according to any of claims 1 to 7, wherein the second cooling stage (25) is carried out in a condenser.

9. The process according to claim 8, wherein the condenser is a corrosion resistant heat exchanger.

10. The process according to claim 8 or 9, wherein for producing steam (29), water is used as a cooling medium in the condenser and the water evaporates by absorbing heat from the cooled gaseous crude reaction product.11 . The process according to any of claims 8 to 10, wherein the condenser is connected to a heat pump for producing steam or heating material streams in the process.

12. The process according to any of claims 1 to 11 wherein the material streams in the process for producing olefins are feed streams and / or at least one bottom stream of a distillation apparatus, wherein the at least one bottom stream is heated by absorbing heat from the crude reaction product and / or the condensed crude reaction product and recycled into the distillation apparatus.

13. The process according to any of claims 1 to 12, wherein a solids removal step (16) is included between the first cooling stage (11 ) and the second cooling stage (25).

14. The process according to claim 13, wherein the solids removal step (16) comprises an electrostatic solids removal.

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