Method for preparing triacetone amine

Abstract

A process for preparing triacetone amine (TAA) comprises (i) reacting acetone and ammonia to yield a reaction product comprising TAA, acetone, mesityl oxide and TMDP; (ii) directing the reaction product to an acetone separation tower to obtain an unreacted acetone stream; and a first bottoms stream; (iii) directing the first bottoms stream to an azeotrope separation tower to obtain an azeotrope distillate stream containing aqueous azeotropes of mesityl oxide and TMDP; and a second bottoms stream; (iv) directing the second bottoms stream to a middle-boiler separation tower to obtain a middle-boiler stream; and a third bottoms stream; (v) directing the third bottoms stream to a finishing tower to obtain pure TAA as a distillate stream; (vi) subjecting the azeotrope distillate stream to phase separation to obtain an organic phase and an aqueous phase; directing the organic phase to a TMDP separation tower to obtain a recyclables distillate stream containing mesityl oxide, and a bottoms stream containing TMDP; and (vii) recycling the unreacted acetone stream, the middle-boiler stream and the recyclables distillate stream at least partially to step (i); and discarding the TMDP bottoms stream.

Description

[0001] Method for Preparing Triacetone Amine

[0002] Triacetone amine (2,2,6,6-tetramethyl-4-piperidinone; hereinafter "TAA") is an important chemical intermediate which is used for the synthesis of numerous derivative products, for example hindered amine light stabilizers (HALS), and nitroxyl radicals that are employed, e.g., as polymerization moderators.

[0003] TAA is produced by the reaction of acetone with ammonia. Known methods for the preparation of TAA include homogeneously catalyzed methods or heterogeneously catalyzed methods.

[0004] Catalysts used in homogeneously-catalyzed reactions include calcium chloride (e.g., in Chemical Industries 2003, 89, 559-564; Zeitschrift fur Naturforschung 1976, 328-337 and 338-345), ammonium chloride (e.g., in JP 2003-206277 A; JP 2001-31651 A; JPH4-154762 A) and hydrazine derivatives (e.g., in JPS54-88275 A, J PS54-112873 A).

[0005] Heterogeneous catalysts have been described, for example in DE 28 07 172 A1 and CN 103224465 A.

[0006] US 10,807,954 discloses a method for preparing triacetone amine while recycling byproducts. The method involves treating the crude product from the triacetone amine preparation with water, which allegedly leads to an increased content of compounds which react readily with ammonia.

[0007] TAA is generally prepared in a matrix in which acetone is present in a large excess and serves both as a reactant and solvent. The reaction is an equilibrium reaction and hence inherently incomplete. Therefore, at the end of the reaction a crude product is obtained which, aside from TAA, contains unreacted acetone, unreacted ammonia, and water formed by the condensation reaction. In addition, further secondary components are present, e.g., acyclic condensation products (e.g., diacetone alcohol, diacetone amine, mesityl oxide, phorone, etc.), cyclic condensation products (e.g., acetonin, 2, 2,4,6- tetramethyl-2,3-dihydropyridine (hereinafter "TMDP")) or higher molecular weight condensation products ("high boilers").

[0008] Some acyclic addition and condensation products (e.g., diacetone alcohol (4-hydroxy-4- methylpentan-2-one), diacetone amine (4-amino-4-methylpentan-2-one), mesityl oxide (4-methylpent-3-en-2-one), phorone, etc.) can be reacted with ammonia to give TAA. Hence they may be used as a partial replacement of acetone. Recycling of the acetone condensation products within the process has been suggested in DE 28 07 172 AT Unreacted acetone is predominantly isolated during downstream distillation steps. The described by-products are difficult to remove from excess acetone and the desired product TAA. The known processes suffer from limited separation efficiency. This is, in part, due to the close proximity of the boiling points of some of the by-products. The situation is aggravated by formation of closely boiling azeotropic mixtures. The following table shows the order of the boiling points (at 1 bar) of the predominant by-products and their azeotropes along with selected boiling points.

[0009] The most problematic by-product in the synthesis of TAA is TMDP. It has a high thermal stability and, unlike the other by-products of TAA synthesis, cannot be reused as starting material in the synthesis of TAA. In this sense, TMDP is an organosynthetic dead end. Recycling of TMDP into the TAA synthesis adds to the energy consumption of the process or, worse, may lead to undesirable side reactions that reduce the yield of TAA.

[0010] In addition, TMDP complicates the distillative purification of the TAA from the resulting reaction mixture. TMDP tends to be ubiquitous in the distillation train and significant amounts are found in the isolated TAA. This difficulty arises from the fact that TMDP forms both azeotropes with water and acetone condensation products such as DAAM and DAA. These azeotropes have intermingling boiling points resulting in TMDP being "smeared", that is, having a broad boiling range. In distillative purification, many distillation stages are therefore necessary to recover TAA and unreacted starting material such as acetone or other by-products such as mesityl oxide essentially free of TMDP. This in turn requires a complex distillation apparatus, such as a column with a large number of theoretical plates.

[0011] Thus, an object of the present invention is to overcome the abovementioned drawbacks and to provide an improved process for producing purified TAA.

[0012] Another object of the present invention is to provide an improved process for producing TAA with lower amounts of by-products; preferably a lower amount of TMDP.

[0013] Yet another object of the present invention is to provide an improved process for producing triacetone amine with an efficient re-utilization of the by-products obtained in the TAA synthesis.

[0014] The invention relates to a process for preparing triacetone amine, the process comprising

[0015] (i) reacting acetone and ammonia in the presence of a catalyst to yield a reaction product comprising TAA, acetone, mesityl oxide and TMDP;

[0016] (ii) directing the reaction product to an acetone separation tower to obtain an unreacted acetone stream; and a first bottoms stream;

[0017] (iii) directing the first bottoms stream to an azeotrope separation tower to obtain an azeotrope distillate stream containing aqueous azeotropes of mesityl oxide and TMDP; and a second bottoms stream;

[0018] (iv) directing the second bottoms stream to a middle-boiler separation tower to obtain a middle-boiler stream; and a third bottoms stream;

[0019] (v) directing the third bottoms stream to a finishing tower to obtain pure TAA as a distillate stream, and a bottoms stream containing high-boilers;

[0020] (vi) subjecting the azeotrope distillate stream to phase separation to obtain an organic phase and an aqueous phase; directing the organic phase to a TMDP separation tower to obtain a recyclables distillate stream containing mesityl oxide, and a bottoms stream containing TMDP; and

[0021] (vii) recycling the unreacted acetone stream, the middle-boiler stream and the recyclables distillate stream at least partially to step (i); and discarding the TMDP bottoms stream. Reacting Acetone and Ammonia in the Presence of a Catalyst

[0022] Step (i) of the inventive method is carried out in the presence of a catalyst. The catalyst is not especially limited and all catalysts customary for this type of reaction are suitable as catalyst. The catalyst can be homogeneous or heterogeneous, but is preferably heterogeneous.

[0023] All homogeneous catalysts described in the related art for this type of reaction are suitable as homogeneous catalyst, e.g., Bronsted acids, salts of Bronsted acids or Lewis acids.

[0024] The term "Bronsted acids" in the context of the invention includes mineral acids, carboxylic acids, organic sulfur-oxygen or organic phosphorus-oxygen acids. As the mineral acid, there can be mentioned hydrohalogen acids e.g., hydrochloric, hydrobromic or hydroiodic acid, nitric acid, sulfuric acid and phosphoric acid.

[0025] As the carboxylic acid, there can be mentioned monobasic, dibasic and tribasic aliphatic and aromatic carboxylic acids. For instance, there can be employed saturated and unsaturated monobasic aliphatic acids having preferably from 1 to 18 carbon atoms, such as formic acid, acetic acid, propionic acid, butyric acid, lauric acid, palmitic acid, stearic acid, acrylic acid and methacrylic acid, halogen-containing carboxylic acids such as chloroacetic, dichloroacetic or trichloroacetic acid and trifluoroacetic acid, saturated and unsaturated dibasic aliphatic carboxylic acids having preferably from 2 to 12 carbon atoms such as malonic acid, succinic acid, adipic acid, sebacic acid, tartaric acid, malic acid, fumaric acid, maleic acid, tribasic aliphatic carboxylic acids such as citric acid, monobasic optionally substituted aromatic carboxylic acids such as benzoic acid, toluic acid and naphthoic acid, dibasic aromatic carboxylic acids such as phthalic acid and terephthalic acid, and tribasic aromatic carboxylic acids such as trimellitic acid.

[0026] As organic sulfur-oxygen acids, there may be mentioned alkylsulfuric acids, such as methylsulfuric acid, sulfinic acids, such as benzenesulfinic acids, but especially sulfonic acids. As the sulfonic acid, there can be mentioned aliphatic and optionally substituted aromatic sulfonic acids such as methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid and naphthalene-1,5-disulfonic acid.

[0027] As organic phosphorus-oxygen acids, there may be mentioned aliphatic or aromatic phosphonic or phosphinic acids, such as methyl-, benzyl- or phenylphosphonic acid or dimethyl- or diethyl-phosphonic acid or diethyl- or benzenephosphinic acid. Lewis acids include salts of Lewis-acidic alkali metals or alkaline earth metals (e.g., CaCI2, MgCI2, LiCI).

[0028] Further there may be used as catalysts a salt of a Bronsted acid with ammonia or a nitrogen-containing organic base. Salts of ammonia and strong Bronsted acids, e.g., hydrochloric acid, sulfuric acid, nitric acid, carboxylic acids or sulfonic, are especially useful. A preferred homogeneous catalyst is ammonium nitrate. Ammonium nitrate has the advantage of being cheap, non-toxic, halide-free and hence less corrosive.

[0029] Where a homogeneous catalyst is used, the catalyst is generally destroyed after the reaction by adding quantitative aqueous alkali to the reaction mixture. The biphasic mixture is phase-separated and the essentially anhydrous organic phase constitutes the reaction product.

[0030] Preferably, a heterogeneous catalyst is used as catalyst. These are solid acidic catalysts which are practically insoluble in the reaction medium. The catalyst may be inorganic or organic and has active acid groups, preferably sulfonic ester groups or phosphoric ester groups.

[0031] The catalyst is preferably selected from aluminium hydrosilicates of bentonite and / or montmorillonite type, inorganic ion exchangers based on aluminium silicate of zeolite type, mordenite type, erionite type or else diatomaceous earth treated with phosphoric acid.

[0032] Further, ion exchange resins may be used as catalyst, such as styrene-divinylbenzene copolymers, which have protic acid groups, especially alkylsulfonic ester groups, sulfonic ester groups, phosphoric ester groups, especially sulfonic ester groups.

[0033] Useful ion exchange resins include a polystyrene or styrene-divinylbenzene copolymer having -SO3functional groups, commercially available as Amberlyst® 15, Amberlite® 200, Lewatit® SP 120 or Lewatit® K2621.

[0034] Useful ion exchange resins include protic acids, especially sulfonic acid in polymeric form which can be perfluorinated (described in DE 10 2010 062 804 A1, US 4,831,146). This may for example be a sulfonated tetrafluoroethylene or a solid supported perfluorinated sulfonic acid in polymeric form with silicon dioxide as carrier material. Such catalysts are, inter alia, available under the trade names Nation®, Aciplex® F, Femion®, Neosepta®, and Fumion® F. A preferred catalyst is Nation® SAC-13. Nation® SAC-13 is porous silicon dioxide particles onto which Nation® has been adsorbed in a charge of approximately 13 wt %; poly(2-acrylamido-2-methyl-1-propanesulfonic acid), sold as PolyAMPS® by Lubrizol.

[0035] The ratio of the reactants in step (i) of the inventive method can be selected within broad ranges; acetone is especially used in excess relative to ammonia. Preferably, the molar ratio of acetone to ammonia used is 3:1 to 20:1, with a ratio of 6:1 to 10:1 being preferred and a ratio of 7:1 being particularly preferred.

[0036] The amount of catalyst is not particularly restricted and can be determined by those skilled in the art.

[0037] In the preferred embodiment in which a heterogeneous catalyst is used, the latter can be used as a fixed bed.

[0038] The feed can be passed once through the fixed bed reactor ("in a single pass") or recirculated through the fixed bed reactor so, that the level of TAA production is increased with every pass through the fixed bed reactor for a desired amount of passes to reach a desired level. The recirculation can be carried out in a traditional tube reactor with a recirculation loop or in loop reactors (e.g., Buss Loop Reactors) and varieties of reactors, based on the principles of this reactor type, where the fixed bed catalyst is placed in the reaction zone of the reactor.

[0039] In an embodiment, the acetone and ammonia are reacted in presence of a catalyst at a pressure in the range of from 1 bar to 10 bar and at a temperature in the range of from 40 °C to 90 °C for a time period in the range of from 0.5 to 20 hours.

[0040] In an embodiment, the reaction product obtained in step (i) comprises an acetone content in the range of from 30 to 80 wt.-%, preferably 40 to 70 wt.-%, based on the total weight of the reaction product.

[0041] In an embodiment, the reaction product obtained in step (i) comprises water in the range of from 1 to 20 wt.-%, preferably 5 to 8 wt.-%, based on the total weight of the reaction product.

[0042] Acetone Separation Tower

[0043] The reaction product comprises TAA, acetone, mesityl oxide and TMDP. In addition, it may comprise isomesityl oxide, diacetone amine, diacetone alcohol and other compounds formed as by-products during the process. The reaction product may comprise water of reaction but does not necessarily contain water.

[0044] The primary reaction product is directed to an acetone separation tower to obtain an unreacted acetone stream; and a first bottoms stream. Removal of the majority of the unreacted acetone from the primary reaction product is a critical feature of the invention, as it allows the formation of aqueous heteroazeotropes of mesityl oxide and TMDP that can be separated in a subsequent step.

[0045] In a preferred embodiment, the acetone separation tower is operated at a pressure of 0.8 to 1.5 bara. Herein, the term "bara" is understood to mean the absolute pressure in bar. All operational pressures of separation towers given herein are column head pressures. In a preferred embodiment, the acetone separation tower is operated at a pressure ranging of from 0.8 to 1.3 bara, preferably 0.9 to 1.2 bara, more preferred about 1 bara.

[0046] The bottom temperature of the acetone separation tower is preferably in the range of 80 to 120 °C. In a preferred embodiment, the acetone separation tower is operated at a bottom temperature ranging of from 85 to 115 °C, preferably 90 to 110 °C, more preferred about 100 °C.

[0047] The acetone separation tower preferably has from 1 to 25 theoretical plates, more preferably from 5 to 20 theoretical plates. In particular, the stripping section of the acetone separation tower preferably has 7 to 18 theoretical plates. The rectifying section of the acetone separation tower preferably has 9 to 15 theoretical plates.

[0048] Besides unreacted acetone, water contained in the reaction product fed to the acetone separation tower may be partially removed via the unreacted acetone stream.

[0049] In an embodiment, the first bottoms stream contains 2 wt.-% of acetone or less, for example 0.01 to 2 wt.-%, based on the total weight of the first bottoms stream.

[0050] In an embodiment, the water content in the first bottoms stream is in the range of from 0.5 to 25 wt.-%, such as 0.5 to 20 wt.-% or 0.5 to 15 wt.-% for example 0.5 to 10 wt.-% based on the total weight of the first bottoms stream.

[0051] Azeotrope Separation Tower

[0052] The first bottoms stream is directed to an azeotrope separation tower to obtain an azeotrope distillate stream containing aqueous azeotropes of mesityl oxide and TMDP; and a second bottoms stream. More particularly, the azeotrope distillate stream comprises a heteroazeotrope of water and mesityl oxide and a heteroazeotrope of water and TMDP.

[0053] In addition to aqueous azeotropes of mesityl oxide and TMDP, the azeotrope distillate stream may contain aqueous azeotropes of isomesityl oxide, diacetone amine, and diacetone alcohol formed as by-products during the process.

[0054] In a preferred embodiment, the azeotrope separation tower is operated at a pressure of 0.2 to 0.5 bara. In a preferred embodiment, the azeotrope separation tower is operated at a pressure ranging of from 0.3 bar to 0.4 bara, preferably about 0.35 bara.

[0055] The bottom temperature of the azeotrope separation tower is preferably in the range of 105 to 155 °C. In a preferred embodiment, the azeotrope separation tower is operated a bottom temperature ranging of from 115 to 145 °C, preferably about 135 °C.

[0056] The azeotrope separation tower preferably has from 1 to 25 theoretical plates, more preferably from 5 to 20 theoretical plates. In particular, the stripping section of the azeotrope separation tower preferably has 7 to 18 theoretical plates. The rectifying section of the azeotrope separation tower preferably has 9 to 15 theoretical plates.

[0057] The first bottoms stream preferably comprises 20 to 70 wt.-% of TAA, more preferably 35 to 55 wt.-%.

[0058] The azeotrope distillate stream is typically withdrawn at the top of the azeotrope separation tower in gaseous form and condensed to obtain a liquid two-phase stream. The two-phase stream is preferably allowed to phase-separate in a separating vessel to obtain an aqueous phase and an organic phase. The organic phase is preferably partially returned to the top of the azeotrope separation tower as a reflux stream. Another part of the organic phase is directed to the TMDP separation tower.

[0059] Preferably, in the azeotrope separation tower a sufficient amount of water is available to permit formation of aqueous azeotropes of essentially the total amount of mesityl oxide and TMDP contained in the first bottoms stream fed to the azeotrope separation tower. This may be accomplished by a sufficient amount of water being contained in the first bottoms stream. Alternatively, water may be purposively added to the azeotrope separation tower. In an embodiment, part or all of the aqueous phase obtained in step (vi) is recycled to the azeotrope separation tower. Recycle of the aqueous phase obtained in step (vi) is preferred over the addition of extraneous water. Since the aqueous phase from the phase separation is saturated with organic phase, its recycle to the azeotrope separation tower does not extract organic valuables.

[0060] The location of addition of aqueous phase into the azeotrope separation tower is not critical and the aqueous phase may added at one or multiple points. The aqueous phase may be added as a reflux to the top of the azeotrope separation tower, as an admixture to the first bottoms stream fed into the azeotrope separation tower or as a separate stream fed into the azeotrope separation tower at about the same height as the first bottoms stream.

[0061] Generally, the aqueous phase not recycled to the azeotrope separation tower is discarded from the process.

[0062] Middle-Boiler Separation Tower

[0063] The second bottoms stream is directed to a middle-boiler separation tower to obtain a middle-boiler stream; and a third bottoms stream. The middle-boiler stream is typically withdrawn at the top of the middle-boiler separation tower.

[0064] The term "middle-boilers" is understood to refer to organic compounds having a boiling point lower than that of TAA, hence a boiling point of lower than about 203.7 °C, at atmospheric pressure, but equal to or higher than about 100 °C. The most common middle-boilers are water, iso-mesityl oxide, mesityl oxide, diacetone amine, diacetone alcohol, diacetone amine and TMDP formed as by-products during the process.

[0065] In a preferred embodiment, the middle-boiler separation tower is operated at a pressure of 0.05 to 0.07 bara. The bottom temperature of the middle-boiler separation tower is preferably in the range of 105 to 145 °C.

[0066] In a more preferred embodiment, the middle-boiler separation tower is operated at a pressure of about 0.06 bara and a bottom temperature of about 125 °C.

[0067] The middle-boiler separation tower preferably has from 1 to 25 theoretical plates, more preferably from 5 to 20 theoretical plates. In particular, the stripping section of the middleboiler separation tower preferably has 7 to 18 theoretical plates. The rectifying section of the middle-boiler separation tower preferably has 9 to 15 theoretical plates. Finishing Tower

[0068] The third bottoms stream is directed to a finishing tower to obtain pure TAA as a distillate stream, and a bottoms stream containing high-boilers.

[0069] The term "high-boilers" is understood to refer to organic compounds having a boiling point higher than that of TAA, i.e., higher than about 203.7 °C, at atmospheric pressure. High-boilers are compounds whose structure has not been fully elucidated formed as byproducts during the process.

[0070] In a preferred embodiment, the finishing tower is operated at a pressure of 0.004 to 0.008 bara. The head temperature of the finishing tower is preferably in the range of 60 to 80 °C.

[0071] In a more preferred embodiment, the finishing tower is operated at a pressure of about 0.006 bara and a head temperature of about 70 °C.

[0072] The finishing tower preferably has from 1 to 30 theoretical plates, more preferably from 5 to 25 theoretical plates. In particular, the stripping section of the finishing tower preferably has 7 to 23 theoretical plates. The rectifying section of the finishing tower preferably has 9 to 20 theoretical plates.

[0073] The distillate stream preferably comprises 99.0 to 100.0 wt.-% of TAA, more preferably 99.5 to 99.9 wt.-%.

[0074] TMDP Separation Tower

[0075] The azeotrope stream obtained from the azeotrope separation tower is subjected to phase separation to obtain an organic phase and an aqueous phase. The organic phase is directed to the TMDP separation tower to obtain a recyclables distillate stream containing mesityl oxide, and a bottoms stream containing TMDP.

[0076] Under the anhydrous conditions in the TMDP separation tower, an efficient separation of TMDP and recyclables, in particular mesityl oxide, is achieved. The recyclables distillate stream contains mesityl oxide and other acetone condensation products. It has a reduced content of TMDP, relative to the azeotrope stream obtained from the azeotrope separation tower. In an embodiment, the TMDP separation tower is operated at a pressure in the range of from 0.1 to 0.5 bara and at a bottom temperature in the range of from 90 °C to 130 °C. In a preferred embodiment, the TMDP separation tower is operated at a bottom temperature in the range of from 100 to 120 °C, preferably about 110 °C.

[0077] In a preferred embodiment, the TMDP separation tower is operated at a pressure in the range of from 0.05 to 0.4 bara, preferably 0.10 to 0.3 bara, more preferred about 0.2 bara.

[0078] The towers and columns used in the inventive process and plant may be conventional distillation columns. Suitable types of distillation columns include packed columns, such as columns with random packing or structured packing, plate columns (i.e., tray columns), and mixed columns comprising both packings and trays.

[0079] Suitable plate columns may comprise internals over which the liquid phase flows. Suitable internals include sieve trays, bubble cap trays, valve trays, tunnel trays and Thormann® trays, in particular bubble cap trays, valve trays tunnel trays and Thormann® trays.

[0080] Random packed columns may be filled with a variety of shaped bodies. Heat and mass transfer are improved by enlarging the surface area by means of shaped bodies, which usually have a size in the range of 25 to 80 mm. Suitable shaped bodies include Raschig rings (hollow cylinders), Lessing rings, Pall rings, Hiflow rings and Intalox saddles. The packing materials may be provided in the column in a regular or irregular manner (as bulk material, i.e., loosely filled). Suitable materials include glass, ceramics, metal and plastics.

[0081] Structured packings are an advancement of regular packings and have a regularly shaped structure. This allows for the reduction of gas flow pressure loss. Suitable types of structured packings include fabric and metal sheet packings.

[0082] The term "top" or "head" of the column refers to a region free of internals located above the topmost tray or above the topmost layer of packing. It is generally formed by a domed base (head, e.g., Klbpper head or Korbbogen head), which forms the terminating element of the distillation column.

[0083] The term "bottom" or "sump" of the column refers to a region free of internals located below the lowest tray or lowest layer of packing.

[0084] The inventive process may be carried out continuously or batchwise. Preferably, the inventive process is carried out continuously. The presently claimed invention offers one or more of the following advantages:

[0085] 1. The process of the present invention helps to produce purified TAA with a reduced amount of by-products, especially TMDP. This is achieved by distillative work-up process involving heteroazeotropic distillation that allows to remove a certain amount of TMDP during the purification by using a heteroazeotropic distillation of water, mesityl oxide, and TMDP.

[0086] 2. The process of the present invention also helps to produce TAA with the efficient re-utilization of the by-products obtained in the TAA synthesis.

[0087] 3. The process of the present invention for producing TAA does not require the use of an expensive distillation apparatus having a high number of theoretical plates and does not require the use of (an) additional de-watering step(s) during extraction. Thus, the process of the present invention is simple and economic.

[0088] The invention is further illustrated by the appended figure and the examples that follow.

[0089] Fig. 1 schematically depicts a process for preparing TAA according to the invention.

[0090] According to Fig. 1, acetone and ammonia are reacted in fixed bed reactor 1 in the presence of a heterogeneous catalyst. The reactor comprises an external recirculation loop consisting of line 2 and recirculation pump 3. Ammonia is supplied via line 4; acetone is supplied from buffer tank 5 to which fresh acetone is supplied via line 6.

[0091] A reaction product comprising TAA, acetone, mesityl oxide and 2,2,4,6-tetramethyl-2,3- dihydropyridine (TMDP) is withdrawn via line 8 and directed to acetone separation tower 9.

[0092] An unreacted acetone stream 10 is withdrawn at the top of acetone separation tower 9, and a first bottoms stream 11 is withdrawn at the bottom of acetone separation tower 9; The unreacted acetone stream 10 is directed to buffer tank 5.

[0093] The first bottoms stream is directed to azeotrope separation tower 12 to obtain an azeotrope distillate stream 13 containing aqueous azeotropes of mesityl oxide and TMDP; and a second bottoms stream 14. Azeotrope distillate stream 13 is subjected to phase separation in separator 15 to obtain an upper organic phase and a lower aqueous phase. The organic phase is directed via line 16 to TMDP separation tower 15 to obtain a recyclables distillate stream 19 containing mesityl oxide, and a bottoms stream 20 containing TMDP. The recyclables distillate stream 19 is directed to buffer tank 5. Bottoms stream 20 is discarded from the process. The aqueous phase from separator 15 is withdrawn via line 17 and may be recycled to azeotrope separation tower 12 and / or discarded.

[0094] The second bottoms stream 14 is directed to middle-boiler separation tower 21 to obtain a middle-boiler stream 22 and a third bottoms stream 23. The middle-boiler stream 22 is directed to buffer tank 5.

[0095] The third bottoms stream 23 is directed to finishing tower 24 to obtain pure TAA as a distillate stream 25, and a bottoms stream 26 containing high-boilers.

[0096] Example 1

[0097] The process was simulated via CHEMASIM (an open source version of which is available as OPEN CHEMASIM™; see H. Hasse, B. Bessling, R. Bbttcher, OPEN CHEMASIM™: Breaking Paradigms in Process Simulation; Editor(s): W. Marquardt, C. Pantelides, Computer Aided Chemical Engineering, Elsevier, Volume 21, 2006, Pages 255-260, https: / / doi.org / 10.1016 / S1570-7946(06)80055-6).

[0098] The examples were calculated based on a feed stream having a typical composition of a reaction product from the reaction of acetone and ammonia on a fixed bed HY zeolite catalyst as follows. All mass flows are reported as relative mass flows, based on 100 pbw / h of the feed stream.

[0099] * pbw / h = parts by weight per hour

[0100] In a process as depicted in Fig. 1, the feed stream was introduced in acetone separation column 9 via line 8. The distillate stream 25 from finishing tower 24, i.e., the TAA product, had the following composition: The combined recycle stream 10, 19 and 22 had the following composition:

[0101] The bottoms stream 20 had a mass flow of 1.51 pbw / h and contained 87.9 wt.-% of TMDP and was discharged from the process. Water withdrawn via line 17 was partially discharged?

[0102] The TAA recovery yield was 99.2 %, based on TAA contained in the feed ((21.94 pbw / h * 99.4 wt.-%) : (100 pbw / h * 22.0 wt.-%)). Reference Example 1

[0103] A reaction product stream had the following composition:

[0104] The reaction product stream was subjected to purification in a distillation train of four distillation columns connected in series. The distillate streams of the first three distillation columns were combined to a recycle stream. The distillate stream of the fourth distillation column constituted the TAA product. No heteroazeotrope phase separation was applied.

[0105] The TAA product stream had the following composition:

[0106] The combined recycle stream had the following composition:

[0107] The TAA recovery yield was 85 %, based on TAA contained in the feed ((18.72 pbw / h * 99.78 wt.-%) : (100 pbw / h * 22.0 wt.-%). In example 1, the TAA product stream had a content of TMDP of only 219 ppm (0.0219 wt.-%), whereas in the reference example the TAA product stream had a content of TMDP of 406 ppm (0.0406 wt.-%).

Claims

Claims1. A process for preparing triacetone amine, the process comprising(i) reacting acetone and ammonia in the presence of a catalyst to yield a reaction product comprising TAA, acetone, mesityl oxide and TMDP;(ii) directing the reaction product to an acetone separation tower to obtain an unreacted acetone stream; and a first bottoms stream;(iii) directing the first bottoms stream to an azeotrope separation tower to obtain an azeotrope distillate stream containing aqueous azeotropes of mesityl oxide and TMDP; and a second bottoms stream;(iv) directing the second bottoms stream to a middle-boiler separation tower to obtain a middle-boiler stream; and a third bottoms stream;(v) directing the third bottoms stream to a finishing tower to obtain pure TAA as a distillate stream, and a bottoms stream containing high-boilers;(vi) subjecting the azeotrope distillate stream to phase separation to obtain an organic phase and an aqueous phase; directing the organic phase to a TMDP separation tower to obtain a recyclables distillate stream containing mesityl oxide, and a bottoms stream containing TMDP; and(vii) recycling the unreacted acetone stream, the middle-boiler stream and the recyclables distillate stream at least partially to step (i); and discarding the TMDP bottoms stream.

2. The process according to claim 1, wherein the first bottoms stream contains 2 wt.-% of acetone or less.

3. The process according to claim 1 or 2, wherein in the azeotrope separation tower a sufficient amount of water is available to permit formation of aqueous azeotropes of essentially the total amount of mesityl oxide and TMDP contained in the first bottoms stream.

4. The process according to any one of the preceding claims, comprising recycling the aqueous phase at least partially to the azeotrope separation tower.

5. The process according to any one of the preceding claims, wherein the catalyst is a heterogeneous catalyst, preferably zeolite.

6. The process according to any one of the preceding claims, wherein the acetone separation tower is operated at a pressure of 0.8 to 1.5 bara.

7. The process according to any one of the preceding claims, wherein the azeotrope separation tower is operated at a pressure of 0.2 to 0.5 bara.

8. The process according to any one of the preceding claims, wherein the middleboiler separation tower is operated at a pressure of 0.05 to 0.07 bara.

9. The process according to any one of the preceding claims, wherein the finishing tower is operated at a pressure of 0.004 to 0.008 bara.

10. The process according to any one of the preceding claims, wherein the TMDP separation tower is operated at a pressure in the range of from 0.1 to 0.5 bara.

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