Process for preparing ethylene oxide addition products

Abstract

A process for preparing ethylene oxide addition products comprises (i) purging a tank reactor with an inert gas to displace any oxygen; (ii) charging the tank reactor with a starting compound capable of adding on or inserting ethylene oxide; (iii) charging the tank reactor with a catalyst while avoiding catalyst depositions on the reactor inner wall above the liquid level of the starting compound in the reactor; and (iv) introducing ethylene oxide, wherein a portion of said ethylene oxide reacts in a liquid phase with the starting compound, and the remaining ethylene oxide together with the inert gas forms a gas phase above the liquid phase, wherein the partial pressure of the ethylene oxide in the gas phase constitutes more than 50% of the total gas phase pressure. The process allows for safely preparing ethylene oxide addition products at greater reaction rates, involving greater partial pressure of ethylene oxide.

Description

[0001] Process for Preparing Ethylene Oxide Addition Products

[0002] The present invention relates to a process for preparing ethylene oxide addition products.

[0003] Addition products of ethylene oxides onto alcohols, amines, acids or esters are important industrial products which find a variety of uses, especially as nonionic surfactants.

[0004] The ethoxylation is typically performed batchwise, for example in stirred autoclaves or loop reactors, at temperatures between 80 and 200 °C. Alternatively, the liquid reaction mixture can also be dispersed into an ethylene oxide-containing gas phase. Typically, a compound with the nucleophilic site - for example an alcohol, a carboxylic acid, an ester or an amine - is initially charged together with the catalyst and then the desired amount of ethylene oxide is injected, which generally establishes a pressure of up to 20 bar depending on the temperature. Suitable catalysts are basic compounds, for example alkali metal alkoxides, or Lewis acids.

[0005] The process involves a liquid reaction mixture and an ethylene oxide-containing gas phase, which may be afflicted with the problem of inadequate mass transfer at the phase interface and hence reduced conversion.

[0006] For safety reasons owing to the flammability of ethylene oxide, the process is typically performed under inert atmosphere, such as nitrogen or another inert gas. The partial pressure of the ethylene oxide reactant is preferably limited by dilution with the inert gas, to a gas phase concentration of 50% or less. This ensures safety against explosion-like polyaddition of the ethylene oxide.

[0007] Dilution of the ethylene oxide reactant with an inert gas, however, reduces the ethylene oxide equilibrium concentration of the liquid phase due to lower ethylene oxide partial pressure in the gas phase. The lower ethylene oxide equilibrium concentration of the liquid phase induces a decreased reaction rate.

[0008] US 2009 / 326283 discloses a method for the production of alkylene oxide addition products comprising (I) charging a tank reactor with a starting compound plus a diluent gas, wherein a portion of said alkylene oxide reacts in a liquid phase with said starting compound, and the remaining alkylene oxide together with said diluent gas forms a gas phase, (II) continuously drawing off said liquid phase from the bottom of the reactor, and recycling to the top of the reactor via a Venturi noezzle, and (ill) metering said gas phase comprising alkylene oxide into the Venturi nozzle via a vacuum line.

[0009] The invention seeks to provide a process for preparing ethylene oxide addition products that can be safely accomplished at greater reaction rates, involving greater partial pressure of ethylene oxide. It has been found that the objective can be achieved if suitable precautions are taken to manage the risks of explosion.

[0010] The invention relates to a process for preparing ethylene oxide addition products, comprising:

[0011] (I) purging a tank reactor with an inert gas to displace any oxygen;

[0012] (II) charging the tank reactor with a starting compound capable of adding on or inserting ethylene oxide;

[0013] (ill) charging the tank reactor with a catalyst while avoiding catalyst depositions on the reactor inner wall above the liquid level of the starting compound in the reactor; and (iv) introducing ethylene oxide, wherein a portion of said ethylene oxide reacts in the liquid phase with the starting compound, and the remaining ethylene oxide together with the inert gas forms a gas phase above the liquid phase, wherein the partial pressure of the ethylene oxide in the gas phase constitutes more than 50% of the total gas phase pressure.

[0014] Inertization of the Reactor

[0015] The tank reactor is inertized, i.e., purged with an inert gas to displace any oxygen and other gases that may be detrimental to the addition reaction. Preferably, the tank reactor is purged with an inert gas and evacuated several times. This is done by means known to the skilled person for this purpose, such as vacuum pumps or the like. Alternating application of reduced pressure and purging with inert gas removes air and traces of water.

[0016] Nitrogen, argon, methane or carbon dioxide may be used as inert gases. For reasons of its better availability and thus of its low price, nitrogen is the preferred inert gas.

[0017] Preferably, oxygen is displaced to below 1.0 vol.-%, preferably below 0.3 vol.-%, in particular to below 0.05 vol.-%.

[0018] The step (I) of purging the tank reactor with an inert gas to displace any oxygen can be performed before or after the sequence of steps (ii) and (ill), however it is generally preferred that the tank reactor is first purged with an inert gas.

[0019] By applying the above order, oxygen and other gases detrimental to the addition reaction, are prevented from dissolving in the starting material and re-entering the gas phase in the course of the reaction.

[0020] Reactor Design

[0021] Generally, thorough mixing of the contents of the reactor should be ensured in all the reaction phases. To this end, an agitator, an external circulation system or a combination of both may be adopted.

[0022] The reactor preferably comprises an agitator which is preferably freely suspended in the reactor. This means that the agitator does not rest on a bearing which is inside the reactor. The movement on a bearing may generate frictional heat, and dispensing with such a bearing allows for avoiding hot surfaces.

[0023] Generally, the agitator comprises a rotatable shaft which extends through an opening in a reactor lid and is sealed by a mechanical seal, such as a double mechanical seal, which is continuously cooled.

[0024] The mechanical seal typically comprises a rotating ring and a mating ring having contact surfaces that slide against each other to form a seal. The rotating ring is affixed to the rotatable shaft, while the mating ring is installed in a gland, i.e., a device which holds the stationary ring in a cavity within the mechanical housing structure and connects it to a chamber surrounding the seal, that is adapted to abut the rotating ring. The rotating ring is typically pressed against the stationary ring either by a spring or a bellows system. Heat generated at the seal face, the surface of the mating ring that slides against the rotating ring, can be removed by channeling a coolant fluid entering the mating ring to a position adjacent to and in close proximity with the interior surface area of the mating ring to substantially reduce the surface temperatures that occur on the seal face.

[0025] Preferably, the mechanical seal is of the forced circulation type. In this case, a fluid is constantly circulated through the seal, cooling and lubricating the surfaces of the seal. The flow and temperature of the circulating fluid are suitably continuously monitored so as to control the seal temperature.

[0026] As a further means to increase the mixing intensity, an external circulation system or a combination of an agitator and an external circulation system may be adopted. Via the external circulation system, liquid phase is withdrawn from the bottom of the reactor and introduced into the gas phase of the reactor. The liquid phase may be introduced at the top of the reactor or sprayed or atomized into the gas phase of the reactor. The external circulation system generally comprises a pump, and preferably may contain at least one heat exchanger.

[0027] The external circulation loop is suitably put into operation once a minimum liquid filling level has been attained. To this end, a discharge valve at the bottom of the reactor is opened and the liquid phase is pumped in circulation and introduced into the gas phase of the reactor.

[0028] The ethylene oxide addition reaction is highly exothermic. The temperature within the reactor is kept at the desired level or adjusted to the desired level by cooling. Cooling is generally carried out via the reactor wall and / or by means of heat exchanger surfaces arranged internally in the reactor and / or externally in the pumped circulation, e.g. on cooling coils, cooling cartridges, plate, tube bundle or mixer heat exchangers. These should be configured such that cooling can also be carried out effectively at the start of the metering phase, i.e., at a low level of fill. Internal cooling means, especially cooling coils, are suitably located in close proximity to the reactor wall, in particular so as not to interfere with the movement of the agitator, if present

[0029] Suitable cooling media for passing through the cooling means are not particularly limited and include water, mixtures of water and glycol, and / or oil. Preferably, the cooling media is a mixture of water and glycol in a weight ratio of 5:1 to 1 :5.

[0030] The heat exchanger means may also be used at the start of the reaction for heating the contents of the reactor to the reaction temperature.

[0031] The reactor generally comprises a thermally insulating jacket. It has been found advantageous if the jacket comprises a closed cell insulating material. Unlike fiber insulating materials, the closed cell insulating material does not allow for ethylene oxide to spread quickly within the thermally insulating jacket in case of a reactor leakage, thereby preventing hot spot formation within the thermally insulating jacket and thus on the inner wall of the reactor.

[0032] A preferred closed cell insulating material is foam glass. Minimizing the Risk of Sparks

[0033] A possible cause of ethylene oxide gas phase explosions is the generation of sparks due to friction in and around moving machinery within the reactor. For safety reasons, the generation of sparks should thus be avoided.

[0034] Suitably, the tank reactor is electrically grounded to earth. It is also preferred to provide adequate electrical grounding to earth, either directly or indirectly, of metal parts of the tank reactor and preferably all piping, instrumentation and process equipment in those areas that are in contact with ethylene oxide-containing gas phase.

[0035] It is even more preferred, preferably in combination with electrical grounding, to minimize or to eliminate potential differences between connecting flange sets of this equipment, piping and instrumentation by electrical interconnections, such as by providing at least one metal wire cable strongly attached and electrically connected to both of the flanges of at least one connecting flange set, preferably of all connecting flange sets.

[0036] It is understood that the agitator is assembled by use of fasteners, such as nuts and bolts. Said fasteners need to be secured adequately to avoid loosening of agitator components such as agitator blades, which may lead to undesired generation of friction and / or sparks.

[0037] Avoiding Hot Surfaces

[0038] To perform the process, the tank reactor is first charged with the starting compound and the catalyst. In this connection it has been found that the way the tank reactor is charged with the catalyst is considerably more important than had previously been thought.

[0039] Explosions can be initiated by hot surfaces. If a film or deposit of catalyst is deposited on the metal surface reactor inner wall, this can cause a local exothermic polymerization reaction of ethylene oxide when getting into contact with the deposition. The result is that the metal surface gets hotter. As it gets hotter, any material coming into contact with the surface also gets hotter and becomes insulated from the cooling effect of the wall. Without cooling, the locally increased temperature can cause an auto ignition of the gas phase ethylene oxide with a resultant explosion.

[0040] It has now been discovered, and this discovery forms a basis for the present invention, that if a direct contact of ethylene oxide-containing gas phase with the catalyst in the absence of liquid phase is avoided, numerous advantages accrue. One feature of the present process is the added safety involved. Consequently, the partial pressure of the ethylene oxide in the gas phase can be increased while keeping the likelihood of explosion minimal.

[0041] According to the invention, the tank reactor is charged with a catalyst while avoiding catalyst depositions on the reactor inner wall above the liquid level of the starting compound in the reactor. This includes avoiding or minimizing splashing or foaming. Splashing can fling dissolved catalyst or catalyst particles into areas of the reactor inner wall where they will not be flushed away by the liquid phase during agitation. In order to avoid splashing, the catalyst should not be charged from the reactor top, in particular when the catalyst is in the solid state.

[0042] Foaming is also undesirable because the foam may contain catalyst, dissolved or in the form of small particles. The higher the foaming rises in the reaction vessel, the more small catalyst particles may be deposited, as a thin film, when the foaming recedes. Since this thin film remains above the liquid level of the reactor, the catalyst particles in the film are exposed to the ethylene oxide-containing gas phase.

[0043] In an embodiment, the catalyst is introduced into the tank reactor below or at the liquid level of the starting compound in the tank reactor. In case the catalyst is in the solid state, the catalyst is preferably introduced at the liquid level (in other words, the wet-dry line) of the starting compound in the tank reactor, i.e., immediately above the liquid level. In case the catalyst is in the liquid state, the catalyst is preferably introduced below the liquid level, i.e., subsurface.

[0044] In another embodiment, the starting compound is metered into the tank reactor via a starting compound feed conduit, the catalyst is metered into the tank reactor intermittently or at least temporarily concurrently with the starting compound via the starting compound feed conduit, and the conduit is flushed with neat starting compound or solvent after the introduction of the catalyst is completed. This embodiment is particularly preferred when the catalyst is in the liquid state. Thereby, spills of the catalyst on the agitator or further internals such as coils are washed away. Introduction of the catalyst concurrently with the starting compound may be effected by inline mixing, i.e., by injecting the catalyst into the starting compound stream.

[0045] In yet another embodiment, if liquid catalyst is charged via a separate catalyst line from the reactor top, spilling on reactor internals, especially internal coils has to be avoided by design of the inlet pipe. Alternatively, the catalyst line can be washed with a washing liquid such as water to wash off any spills.

[0046] In a further embodiment, a homogeneous mixture of the catalyst and the starting material is prepared outside the reactor in a pre-conditioner or mix-melt tank and subsequently charged to the tank reactor. In this case, catalyst encrustation on reactor internals which may lead to hot spot formation is of substantially reduced concern.

[0047] Different catalysts can be used and may be charged into the reactor by one or more of the above-described methods.

[0048] In general, the presence of particle contaminants such as rust particles in the reactor should be avoided. The iron oxides contained in rust particles, e.g., may cause a decomposition or polymerization reaction of ethylene oxide. Thus, the tank reactor is typically made of stainless steel. However, feed and discharge conduits for charging or discharging the reactor are typically made of carbon steel. Rust particles may form on the surfaces of carbon steel. In order these particles being carried into the reactor, adequate rust filters are preferred at the joints between carbon steel and stainless steel in the conduits, e.g., at connecting flanges. Hence, the process preferably comprises removing particle contaminants from all fluid streams metered into the reactor. The particle contaminants are in particular rust particles. Removal of the particle contaminants is suitably achieved by the use of adequate filters.

[0049] Charging Ethylene Oxide to the Reactor

[0050] Metering of the ethylene oxide into the reactor may occur through nozzles, in particular nozzles in the bottom of the tank reactor or through a distributor ring immersed in the liquid. The introduction of stirring energy into the liquid phase causes mixing, during which a small amount of the ethylene oxide is dissolved in the liquid phase; the remaining amount forms a gas phase above the liquid with the gas used for inertization.

[0051] In the inventive process, an amount of ethylene oxide is metered into the tank reactor such that the partial pressure of the ethylene oxide in the gas phase constitutes more than 50% of the total gas phase pressure. During the ethylene oxide addition reaction, ethylene oxide is consumed. To keep the ethylene oxide partial pressure at a suitably high level, further ethylene oxide is continuously metered into the reactor until a desired degree of ethylene oxide addition has been reached.

[0052] Preferably, the partial pressure of the ethylene oxide in the gas phase constitutes more than 55% of the total gas phase pressure, in particular more than 60% of the total gas phase pressure, most preferably more than 70% of the total gas phase pressure.

[0053] The composition of the gas phase may be monitored by withdrawing aliquots of the gas phase in regular intervals and analyzing the aliquots via gas chromatography. Alternatively, the composition of the gas phase may be determined by measuring the gas pressure in the reactor, calculating the partial pressure of the ethylene oxide therefrom, taking into account the inert gas pressure before the beginning of the reaction.

[0054] The process of the invention is typically conducted discontinuously. Once an adequate degree of ethylene oxide addition has been achieved, the reaction product is withdrawn from the reactor.

[0055] Starting Compounds

[0056] Typical examples of starting compounds capable of adding on or inserting ethylene oxides are alcohols, acids such as carboxylic acids, esters such as alkyl carboxylates or polyol carboxylates, and amines.

[0057] Preferred are alcohols are compounds of the formula (I)

[0058] R1-OH (I) wherein R1is a linear or branched hydrocarbon radical having 1 to 22 carbon atoms, preferably 8 to 18 carbon atoms, and 0 or 1 to 3 double bonds. Typical examples are, in addition to the lower aliphatic alcohols methanol, ethanol and the isomeric butanols and pentanols, the fatty alcohols, specifically caproic alcohol, capryl alcohol, 2 -ethylhexyl alcohol, capric alcohol, lauryl alcohol, isotridecyl alcohol, myristyl alcohol, cetyl alcohol, palmoleyl alcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, linolyl alcohol, linolenyl alcohol, elaeostearyl alcohol, arachyl alcohol, gadoleyl alcohol, behenyl alcohol, erucyl alcohol and brassidyl alcohol, and technical-grade mixtures thereof, which are obtained, for example, in the high-pressure hydrogenation of technical-grade methyl esters based on fats and oils, or aldehydes from the Roelen oxo process, and as a monomer fraction in the dimerization of unsaturated fatty alcohols.

[0059] Technical-grade fatty alcohols having 12 to 18 carbon atoms, for example coconut fatty alcohol, palm fatty alcohol, palm kernel fatty alcohol or tallow fatty alcohol may be used.

[0060] Preferred acids are carboxylic acids of the formula (II)

[0061] R2-COOH (II) wherein R2is a linear or branched acyl radical having 1 to 22 carbon atoms and 0 or 1 to 3 double bonds. Typical examples are in particular the fatty acids, specifically caproic acid, caprylic acid, 2-ethylhexanoic acid, capric acid, lauric acid, isotridecanoic acid, myristic acid, palmitic acid, palmoleic acid, stearic acid, isostearic acid, oleic acid, elaidic acid, petroselic acid, linoleic acid, linolenic acid, elaeostearic acid, arachic acid, gadoleic acid, behenic acid and erucic acid, and technical-grade mixtures thereof, which are obtained, for example, in the pressure cleavage of natural fats and oils, in the reduction of aldehydes from the Roelen oxo process, or the dimerization of unsaturated fatty acids.

[0062] Technical-grade fatty acids having 12 to 18 carbon atoms, for example coconut fatty acid, palm fatty acid, palm kernel fatty acid or tallow fatty acid may be used. It will be appreciated that it is also possible to ethoxylate functionalized carboxylic acids, for example hydroxycarboxylic acids such as ricinoleic acid or citric acid, or dicarboxylic acids such as adipic acid.

[0063] Suitable esters include use esters obtained from carboxylic acids with alcohols having 1 to 22 and preferably 1 to 4 carbon atoms or polyols, especially glycerol, trimethylolpropane or pentaerythritol. When they are full esters, the ethylene oxide groups are inserted into the carbonyl ester bond.

[0064] Suitable amines include compounds of the formula (III)

[0065] R3-NH-R4(III) wherein R3and R4are each independently hydrogen, alkyl groups having 1 to 18 carbon atoms or hydroxyalkyl groups having 1 to 4 carbon atoms. Typical examples are methylamine, dimethylamine, ethylamine, diethylamine, methylethylamine, and the different propyl, butyl, pentyl and fatty amines of analogous structure.

[0066] In general, the molar ratio between ethylene oxide and the starting compounds may be 1 :1 to 200: 1 , preferably 1 : 1 to 50:1 and especially 1 :1 to 20: 1.

[0067] If the starting compound is liquid, the reaction may be carried out in the absence of extraneous solvents. However, if extraneous solvents are necessary or desired, suitable extraneous solvents include non-protic solvents such as ethers, which are not susceptible to ethylene oxide addition. Catalysts

[0068] The ethylene oxide addition reaction takes place in the presence of catalysts which may be of homogeneous or heterogeneous nature. Suitable homogeneous catalysts include alkali metal hydroxides and alkali metal alkoxides, especially sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium tert-butoxide and potassium tert-butoxide.

[0069] Suitable heterogeneous catalysts include double metal cyanide (DMC) catalysts, which are known in the art. DMC catalysts have a very high activity in ethylene oxide addition reactions and render possible the preparation of, e.g., polyether polyols under optimum conditions at very low catalyst concentrations (100 ppm or less), so that in general it is no longer necessary to separate off the catalyst from the finished product.

[0070] Suitable heterogeneous catalysts moreover include cyanide-free metal salts, such as metal halides, metal pseudohalides, metal nitrates, metal sulfates and metal carboxylates. Preferably, the cyanide-free metal salts are transition metal salts.

[0071] Suitable heterogeneous catalysts include zinc chloride, zinc bromide, zinc iodide, zinc nitrate, iron(ll) sulfate, iron(ll) bromide, iron(ll) chloride, cobalt(ll) chloride, cobalt(ll) thiocyanate, nickel(ll) chloride, nickel(ll) nitrate, zinc acetate, zinc acetylacetonate, zinc benzoate and chromium oleate.

[0072] Mixtures of various metal salts can also be employed.

Claims

Claims1 . A process for preparing ethylene oxide addition products, comprising:(i) purging a tank reactor with an inert gas to displace any oxygen;(ii) charging the tank reactor with a starting compound capable of adding on or inserting ethylene oxide;(ill) charging the tank reactor with a catalyst while avoiding catalyst depositions on the reactor inner wall above the liquid level of the starting compound in the reactor; and(iv) introducing ethylene oxide, wherein a portion of said ethylene oxide reacts in a liquid phase with the starting compound, and the remaining ethylene oxide together with the inert gas forms a gas phase above the liquid phase, wherein the partial pressure of the ethylene oxide in the gas phase constitutes more than 50% of the total gas phase pressure.

2. The process according to claim 1 , wherein the tank reactor comprises an agitator with a rotatable shaft which extends through an opening in a reactor lid and is sealed by a mechanical seal which is continuously cooled.

3. The process according to claim 2, wherein the mechanical seal is of the forced circulation type.

4. The process according to claim 2 or 3, wherein the temperature of the mechanical seal is continuously monitored.

5. The process according to any one of the preceding claims, comprising withdrawing liquid phase from the bottom of the reactor and introducing the liquid phase into the gas phase of the reactor via an external circulation loop.

6. The process according to any one of the preceding claims, comprising purging the tank reactor with an inert gas and evacuating the tank reactor several times.

7. The process according to any one of the preceding claims, wherein oxygen is displaced to below 1.0 vol-%.

8. The process according to any one of the preceding claims, wherein step (ill) comprises charging the catalyst into the tank reactor below or at the liquid level of the starting compound in the tank reactor.

9. The process according to any one of the preceding claims, wherein the starting compound is metered into the tank reactor via a starting compound feed conduit, the catalyst is metered into the tank reactor intermittently or at least temporarily concurrently with the starting compound via the starting compound feed conduit, and the conduit is flushed with neat starting compound after the introduction of the catalyst is completed.

10. The process according to any one of the preceding claims, wherein a homogeneous mixture of the catalyst and the starting material is prepared outside the reactor in a pre-conditioner tank and subsequently charged to the tank reactor.11 . The process according to any one of the preceding claims, wherein the tank reactor comprises a thermally insulating jacket, the jacket comprising a closed cell insulating material.

12. The process according to any one of the preceding claims, comprising removing particle contaminants from all fluid streams metered into the reactor.

13. The process according to claim 12, wherein the particle contaminants are rust particles.

14. The process according to any one of the preceding claims, wherein the tank reactor is made of stainless steel.

15. The process according to any one of the preceding claims, wherein the tank reactor is electrically grounded to earth.