A method for removing polyunsaturated hydrocarbons from a C4 hydrocarbon stream in the presence of thiols, disulfides, and C5 hydrocarbons.

Abstract

The present invention relates to a method for removing polyunsaturated hydrocarbons from a C4 hydrocarbon stream in the presence of mercaptans, disulfides and C5 hydrocarbons, and more particularly provides a two-step method for removing polyunsaturated hydrocarbons from a C4 hydrocarbon stream, wherein the C4 hydrocarbon stream contains, in addition to C4 hydrocarbons, C5 hydrocarbons and mercaptans and / or disulfides.

Description

[0001] The present invention relates to a two-stage process for removing polyunsaturated hydrocarbons from a C4 hydrocarbon stream which, in addition to C4 hydrocarbons, also contains C5 hydrocarbons and mercaptans and / or disulfides.

[0002] The C4 hydrocarbon stream containing olefins used in the petrochemical industry is usually a C4 hydrocarbon mixture from a catalytic cracker (FCC C4) or a steam cracker (cracking C4). Blends of C4 hydrocarbon mixtures (C4 fractions) from different sources can also be used in petrochemical processes. In addition to n-butene 1-butene, cis-2-butene and trans-2-butene, isobutene and homologous alkanes butane and isobutane, industrial C4 hydrocarbon mixtures such as the above-mentioned mixtures also contain polyunsaturated compounds, particularly 1,3-butadiene, but-3-ene-1-yne and 1,2-butadiene. Before the C4 hydrocarbon mixture can be used in processes such as oligomerization, or before each compound can be separated from the C4 mixture, it is usually necessary to remove polyunsaturated hydrocarbons.

[0003] The C4 hydrocarbon mixture from a steam cracker or catalytic cracker may contain a high proportion of polyunsaturated compounds, in particular a high proportion (40%+ by weight) of 1,3-butadiene. The treatment then initially begins with reducing the content of polyunsaturated compounds by, for example, extractive distillation to a value of less than or equal to 1% by weight, based on the total composition of the C4 hydrocarbon mixture. The resulting mixture, which contains only small residual amounts of butadiene, is also referred to as "raffinate I, from which isobutene can then be removed to produce raffinate II.

[0004] Further aftertreatment then usually comprises the further step for (almost) completely removing polyunsaturated hydrocarbons.In this respect, EP 2 590 913 A1 discloses the selective hydrogenation of polyunsaturated hydrocarbons still existing in the presence of hydrogen.In order to avoid unwanted side reactions and equipment state, required hydrogen must exist in the form of a uniform solution dissolved in the C4 feed mixture.Yet, in the C4 hydrocarbon mixture, there is an upper limit to the solubility of hydrogen, which imposes restrictions on the maximum content of polyunsaturated hydrocarbons allowed in the inflow of selective hydrogenation, or more precisely, imposes restrictions on the amount of polyunsaturated hydrocarbons that can be hydrogenated (selectively) by the maximum amount of soluble hydrogen.

[0005] In order to achieve (almost) complete conversion of polyunsaturated hydrocarbons, the C4 hydrocarbon mixture used must contain only the maximum amount of polyunsaturated hydrocarbons that can be hydrogenated with the maximum amount of soluble hydrogen. This is problematic for industrial processes, since the composition of the C4 hydrocarbon mixture used is subject to natural fluctuations that are difficult to absorb with such restrictions on the maximum amount of polyunsaturated hydrocarbons.

[0006] It is therefore an object of the present invention to provide a process which can respond more flexibly to fluctuations in the amount of polyunsaturated hydrocarbons and which makes it possible to remove potentially larger amounts of polyunsaturated hydrocarbons from C4 hydrocarbon streams.

[0007] The underlying object of the invention is achieved by a method according to claim 1. Preferred embodiments are specified in the dependent claims.

[0008] The method according to the invention is a two-step process for removing polyunsaturated hydrocarbons from an olefin-containing C4 hydrocarbon stream, which contains, in addition to C4 hydrocarbons, C5 hydrocarbons in a range between 0.01% by weight and 5% by weight and mercaptans and / or disulfides in a range between 0.01 ppm by weight and 200 ppm by weight. In the first step, at least some of the polyunsaturated hydrocarbons from the olefin-containing C4 hydrocarbon stream are hydrogenated and / or reacted with mercaptans and / or disulfides from the olefin-containing C4 hydrocarbon stream in a first reaction zone, which consists of one or more reactors connected in parallel and / or in series, wherein the first step is carried out using a first catalyst in the presence of hydrogen and the absence of carbon monoxide, and wherein no more than 80 mol% of the available polyunsaturated hydrocarbons from the C4 hydrocarbon stream are hydrogenated and / or reacted in the first step. In a preferred embodiment, some of the polyunsaturated hydrocarbons are hydrogenated, and some react with mercaptans and / or disulfides from the olefin-containing C4 hydrocarbon stream. Here too, a maximum amount of 80 mol % of polyunsaturated hydrocarbons to be reacted is not exceeded. Mercaptans are preferably removed from the olefin-containing C4 hydrocarbon stream to a level below the detection limit.

[0009] After the first step and before the second step, at least one removal of high boilers takes place, wherein in particular reaction products formed in the reaction of polyunsaturated hydrocarbons with mercaptans and / or disulfides and optionally at least some C5 hydrocarbons are removed from the C4 hydrocarbon stream.

[0010] In the second step of the process according to the invention, the unreacted polyunsaturated hydrocarbons in the olefin-containing C4 hydrocarbon stream in the first step are selectively hydrogenated in the presence of oxygen and carbon monoxide using a second catalyst in a second reaction zone consisting of one or more reactors connected in parallel and / or in series. The catalyst used in the first step and the catalyst used in the second step are different from each other.

[0011] The process according to the invention has the following advantages: in the first step, it is possible not only to hydrogenate at least some of the polyunsaturated hydrocarbons, in particular 1,3-butadiene and / or 1,2-butadiene and / or but-3-ene-1-yne, but also to react and then remove the mercaptans and / or disulfides, which are present in very small amounts in industrial C4 hydrocarbon mixtures and have to be removed due to their ability to damage the catalyst in the subsequent process. As a result, the maximum permissible amount of polyunsaturated hydrocarbons in the olefin-containing C4 hydrocarbon stream subjected to purification is almost twice as high as in the case of selective hydrogenation. The concentration of polyunsaturated hydrocarbons in industrial C4 hydrocarbon streams is subject to process-related fluctuations. These fluctuations in the concentration of polyunsaturated hydrocarbons in industrial C4 hydrocarbon streams can therefore be more easily absorbed by the process according to the invention.

[0012] The first step, i.e. the hydrogenation of the polyunsaturated hydrocarbons in the C4 hydrocarbon stream and / or the reaction of the polyunsaturated hydrocarbons with mercaptans and / or disulfides, takes place in the presence of hydrogen. In order to prevent side reactions, such as complete hydrogenation to alkanes or isomerization of double bonds in 1-olefins to internal olefins, the amount of hydrogen used in the first step should not be too high. The molar ratio of hydrogen to polyunsaturated hydrocarbons in the first step is preferably between 0.01 and 0.8, more preferably between 0.1 and 0.5. The hydrogen can be metered into the reaction zone separately from the incoming C4 hydrocarbon stream or it can be added to the incoming C4 hydrocarbon stream in advance; a homogeneous mixture of the C4 hydrocarbon stream and hydrogen must be present in the reactor.

[0013] Furthermore, the first step of the process according to the invention is carried out in the absence of carbon monoxide. This means that no carbon monoxide is added to the C4 carbon stream. However, there may be very small amounts of carbon monoxide potentially present as impurities in industrial hydrocarbon streams, since they cannot be removed without considerable effort.

[0014] In the first step of the method according to the invention, a heterogeneous catalyst containing at least two metals of the 10th group of the periodic table, preferably palladium and platinum, can be used as the first catalyst. As a result of calcination, the metals may be present in part in the form of their oxides. The metals are preferably present on a support material. The support material is selected from the group consisting of aluminum oxide, silica gel and activated carbon, wherein aluminum oxide is preferably used as a support material. In a particularly preferred embodiment, a shell catalyst is used as the first catalyst, which comprises aluminum oxide as a support material and palladium and platinum as metals, and wherein the catalyst has a palladium concentration of up to 2.0 wt %, more preferably up to 1.0 wt %, most preferably up to 0.5 wt %, and a platinum concentration of up to 1.0 wt %, preferably up to 0.5 wt %, more preferably up to 0.2 wt %. The concentration of palladium should be at least 2 times higher than platinum.

[0015] The first catalyst preferably has a 50-400 m 2 / g, more preferably 100-300m 2 / g, particularly preferably 200-300m 2 The specific surface area is 200 m / s, which can be determined by gas adsorption in accordance with DIN ISO 9277 (status: last updated 2014-01).

[0016] The inlet temperature of the olefin-containing C4 hydrocarbon stream entering the reactor of the first reaction zone in the first step is preferably in the range of 0-180° C., more preferably in the range of 60-150° C., particularly preferably in the range of 80-130° C. The pressure in the first step is preferably in the range of 2-50 bar, more preferably in the range of 6-40 bar, particularly preferably in the range of 10-30 bar.

[0017] The hydrogenation and / or reaction in the first step are preferably operated with a liquid phase method, which means that all components in the first reaction zone (that is, in at least one reactor) are present in the liquid phase or are introduced into the first reaction zone in liquid form. The suitable reactor for reacting in the first step is a fixed bed reactor or a tube bundle reactor. Preferably, hydrogen has been completely dissolved in the liquid phase. Obviously, then the temperature and pressure must be selected so that the hydrogen remains completely dissolved and does not produce a gas phase in the reaction zone upstream and in the reaction zone. Accordingly, hydrogen should be added to the C4 hydrocarbon stream containing olefins in a finely dispersed form and in an amount that makes the liquid phase homogeneous all the time in the reaction zone upstream and in the reaction zone. No carbon monoxide is added. The hydrogenation and / or reaction in the first step are also preferably carried out in only one reactor, i.e., the first reaction zone is preferably composed of only one reactor.

[0018] In the first step, after the hydrogenation of the polyunsaturated hydrocarbons and / or the reaction of the polyunsaturated hydrocarbons with mercaptans and / or disulfides, the reaction products can be removed as part of the removal of high boilers that occurs between the first and second steps. The removal is preferably carried out by distillation. High boilers present in the C4 hydrocarbon stream, such as C5 hydrocarbons, can be removed at least partially together with the reaction products. The high boilers (i.e. the reaction products and C5 hydrocarbons) are discharged via the bottom of the distillation column; the purified C4 hydrocarbon stream is discharged at the top of the distillation column and fed to the second step. Before carrying out the second step, further process steps can be carried out in which there are no interferences from polyunsaturated hydrocarbons, such as the synthesis of MTBE (isobutene can be removed by it) or the synthesis of TBA.

[0019] The distillation column preferably used for removing high boilers preferably has 40 to 150 theoretical plates, more preferably 40 to 100 theoretical plates, particularly preferably 50 to 80 theoretical plates. The reflux ratio can be between 0.5 and 5, particularly preferably between 1 and 2.5, depending on the available number of plates, the composition of the feed and the desired purity of the top product and bottom product. The reflux ratio is defined here as the reflux mass flow divided by the mass flow of the top product (distillate).

[0020] The distillation column for removing high boilers is preferably operated at a pressure of 1 to 20 bar (absolute), more preferably at a pressure of 5 to 12 bar (absolute). Depending on the available operating pressure, the condensation can be achieved against cooling brine, cooling water or air. The bottom product (i.e., high boilers) can be utilized thermally or used as starting material for other processes, for example in a synthesis gas plant.

[0021] After removal of high boilers, the C4 hydrocarbon mixture (which still contains polyunsaturated hydrocarbons) is fed to the second step of the process according to the invention, namely the selective hydrogenation. In the second step, hydrogen is likewise added, but this time not in a substoichiometric amount as in the first step, but at least equimolar to the molar amount of polyunsaturated hydrocarbons present in the inflow of the second step. The molar ratio of hydrogen to polyunsaturated hydrocarbons is in particular in the range from 2:1 to 1:1 (hydrogen to polyunsaturated hydrocarbons), preferably in the range from 1.5:1 to 1:1, more preferably in the range from 1.2:1 to 1:1. The hydrogen can be metered into the reactor of the second reaction zone separately from the incoming C4 hydrocarbon stream, or it can be added beforehand to the incoming C4 hydrocarbon stream.

[0022] In the second step, carbon monoxide is additionally added to the C4 hydrocarbon stream. The carbon monoxide content in the C4 hydrocarbon stream in the inflow to the second reaction zone is preferably from 0.05 to 20 ppm carbon monoxide, more preferably from 0.5 to 5 ppm, based in each case on the total amount of the C4 hydrocarbon stream. The carbon monoxide can be metered into the second reaction zone separately from the incoming C4 hydrocarbon stream or it can be added to the incoming C4 hydrocarbon stream in advance.

[0023] In the second step of the method according to the present invention, a heterogeneous catalyst containing a single metal of the 10th group of the periodic table (preferably palladium) can be used as the second catalyst. As a result of calcination, the metal can be partially present in the form of its oxide. Palladium is preferably present on a support material. The support material is selected from the group consisting of aluminum oxide, silica gel and activated carbon, wherein aluminum oxide is preferably used as a support material. In each case based on the total amount of the catalyst, the concentration of the metal in the second catalyst can be 0.01-3% by weight, preferably 0.1-1% by weight, more preferably 0.3-0.5% by weight. The second catalyst is different from the first catalyst according to the present invention.

[0024] The second catalyst preferably has a 50-400 m2 / g, more preferably 100-300m 2 / g, particularly preferably 200-300m 2 The specific surface area is 200 m / s, which can be determined by gas adsorption in accordance with DIN ISO 9277 (status: last updated 2014-01).

[0025] The inlet temperature of the C4 hydrocarbon stream in the inflow of the second reaction zone is generally in the range of 0 to 100° C., preferably in the range of 20 to 80° C., more preferably in the range of 30 to 60° C. The pressure is generally in the range of 2 to 50 bar, preferably in the range of 6 to 30 bar, more preferably in the range of 10 to 25 bar.

[0026] The selective hydrogenation in the second step is preferably operated in a liquid phase method, i.e., all components in the second reaction zone are present in the liquid phase or are introduced into the second reaction zone in liquid form. Suitable reactors for carrying out the selective hydrogenation are fixed bed reactors or tube bundle reactors. Preferably, hydrogen and carbon monoxide are fully dissolved in the liquid phase. Obviously, the temperature and pressure must be selected so that hydrogen and carbon monoxide remain fully dissolved and do not produce a gas phase upstream of the reaction zone and in the reaction zone.

[0027] The selective hydrogenation in the second step can be operated in a single stage, i.e. using a single reactor in the second reaction zone. The selective hydrogenation is preferably operated in more than one stage, i.e. using at least two reactors connected in parallel or in series in the second reaction zone, which means that the second reaction zone consists of at least two reactors connected in parallel or in series. The reactors are preferably connected in series in the second reaction zone. Hydrogen is fed together with the C4 hydrocarbon stream to each of the reactors connected in series in the second reaction zone, while carbon monoxide is added only to the first of the reactors connected in series in the second reaction zone, but not to the second or subsequent reactors.

[0028] In another embodiment of the method according to the invention, the second reaction zone is composed of at least three reactors. The first two reactors can be connected in parallel and are all connected in series to the third reactor. In the first two reactors connected in parallel, preferably hydrogen and carbon monoxide are metered in, and in the third reactor, only hydrogen is added.

[0029] Embodiment 1:

[0030] A C4 mixture liquefied at a pressure of 22 bar, consisting of 0.7% by weight of 1,3-butadiene, 19.9% ​​by weight of 1-butene, 38.0% by weight of 2-butene, 29.3% by weight of isobutene and 11.3% by weight of butane and 0.8% by weight of C5 hydrocarbons, was passed at 4 kg / h into a first reactor filled with 600 mL of a hydrogenation catalyst (0.5% by weight of Pd, 0.2% by weight of Pt supported on Al2O3) and heated to 90° C. The stream contained about 4 ppm by weight of dimethyl disulfide, about 3 ppm by weight of ethanethiol and about 0.5 ppm by weight of methyl mercaptan.

[0031] 9.3 Nl / h of an H2 stream were metered into the C4 mixture. About 73% of the butadiene present in the C4 mixture used reacted. The resulting composition of the outflow from the first reactor was 0.2% by weight of butadiene, 20.2% by weight of 1-butene, 38.2% by weight of 2-butene, 29.3% by weight of isobutene and 11.3% by weight of butanes, and also 0.8% by weight of C5 hydrocarbons. Mercaptans and disulfides were no longer detectable in the stream.

[0032] After removal of high boilers by MTBE synthesis and removal of most of the isobutene, the stream has the following composition: 0.3% by weight of butadiene, 28.6% by weight of 1-butene, 54.0% by weight of 2-butene, 1.1% by weight of isobutene and 16.0% by weight of n-butane. The stream is liquefied at a pressure of 12 bar and passed at 4 kg / h into a second reactor which is filled with 600 ml of hydrogenation catalyst (0.5% by weight of Pd supported on Al2O3) and heated at 40°C. 3.5 Nl / h of H2 stream are metered into the C4 mixture. 3 Nml / h of CO are also added. After passing through the second reactor, butadiene is no longer detectable in the stream.

Claims

1. A process for removing polyunsaturated hydrocarbons from an olefin-containing C4 hydrocarbon stream which, in addition to C4 hydrocarbons, contains C5 hydrocarbons in a range between 0.01% by weight and 5% by weight and mercaptans and / or disulfides in a range between 0.01% by weight and 200% by weight, wherein in a first step, at least some of the polyunsaturated hydrocarbons from the olefin-containing C4 hydrocarbon stream are hydrogenated and / or reacted with the mercaptans and / or disulfides from the olefin-containing C4 hydrocarbon stream in a first reaction zone, the first reaction zone consisting of one or more reactors connected in parallel and / or in series, wherein the first step is carried out using a first catalyst and in the presence of hydrogen and in the absence of carbon monoxide, and wherein not more than 80 mol % of the available polyunsaturated hydrocarbons from the C4 hydrocarbon stream are hydrogenated and / or reacted in the first step, In the second step, the polyunsaturated hydrocarbons in the olefin-containing C4 hydrocarbon stream that have not reacted in the first step are selectively hydrogenated in the second reaction zone in the presence of hydrogen and carbon monoxide using a second catalyst, the second reaction zone consisting of one or more reactors connected in parallel and / or in series, wherein at least one removal of high boilers occurs between said first step and said second step, and wherein the first and second catalysts are different from each other, wherein the first catalyst comprises alumina as a support material and palladium and platinum as metals, and wherein the first catalyst has a palladium concentration of up to 2.0 wt. %, and a platinum concentration of up to 1.0 wt. %, and wherein the palladium concentration is at least 2 times higher than the platinum concentration; wherein the molar ratio of hydrogen to polyunsaturated hydrocarbon in the first step is between 0.01 and 0.8; and The second catalyst contains a single metal of Group 10 of the periodic table.

2. The process according to claim 1, wherein the molar ratio of hydrogen to polyunsaturated hydrocarbon in the first step is between 0.1 and 0.

5.

3. The process according to claim 1 or 2, wherein the inlet temperature of the C4 hydrocarbon stream in the inflow of the first reaction zone consisting of one or more reactors connected in parallel and / or in series is between 0°C and 180°C.

4. The process according to claim 3, wherein the inlet temperature of the C4 hydrocarbon stream in the inflow of the first reaction zone consisting of one or more reactors connected in parallel and / or in series is between 60°C and 150°C.

5. The process according to claim 4, wherein the inlet temperature of the C4 hydrocarbon stream in the inflow of the first reaction zone consisting of one or more reactors connected in parallel and / or in series is between 80°C and 130°C.

6. The method according to claim 1 or 2, wherein the first step is performed only in liquid phase and the hydrogen present is already fully dissolved in the liquid phase.

7. The process according to claim 1 or 2, wherein in the second step, the content of carbon monoxide in the C4 hydrocarbon stream in the inflow of the second reaction zone consisting of one or more reactors connected in parallel and / or in series is 0.05-20 ppm based on the total amount of the hydrocarbon stream.

8. The method according to claim 1 or 2, wherein the single metal contained in the second catalyst is palladium.

9. The process according to claim 1 or 2, wherein the inlet temperature of the C4 hydrocarbon stream in the inflow of the second reaction zone consisting of one or more reactors connected in parallel and / or in series is between 0°C and 100°C.

10. The process according to claim 1 or 2, wherein the inlet temperature of the C4 hydrocarbon stream in the inflow of the second reaction zone consisting of one or more reactors connected in parallel and / or in series is between 20°C and 80°C.

11. The process according to claim 10, wherein the inlet temperature of the C4 hydrocarbon stream in the inflow of the second reaction zone consisting of one or more reactors connected in parallel and / or in series is between 30°C and 60°C.

12. The process according to claim 1 or 2, wherein the pressure in the second reaction zone consisting of one or more reactors connected in parallel and / or in series ranges between 2 and 50 bar.

13. The process according to claim 12, wherein the pressure in the second reaction zone consisting of one or more reactors connected in parallel and / or in series ranges between 6 and 30 bar.

14. The process according to claim 13, wherein the pressure in the second reaction zone consisting of one or more reactors connected in parallel and / or in series is in the range between 10 and 25 bar.

15. The method according to claim 1 or 2, wherein the second step is performed only in the liquid phase.

16. The process of claim 1 or 2, wherein the first reaction zone consists of a single reactor.

17. The process according to claim 1 or 2, wherein the second reaction zone consists of at least two reactors connected in parallel or in series.