Method for preparing isopropanol in high yield and purity

Abstract

1. A method for producing isopropanol by catalytic hydrogenation of acetone, comprising: (a) feeding a feed stream from top to bottom into an adiabatic reactor, the feed stream consisting of a gas stream containing hydrogen and a liquid stream containing fresh acetone; (b) passing the feed stream of step (a) through a fixed catalyst bed contained in the reactor, thereby obtaining a reactor outlet effluent consisting of a liquid phase and a gas phase, the catalyst bed being operated in a trickle flow regime and comprising at least one metallic copper-based catalyst; (c) separating the effluent from the reactor by separating the liquid phase from the gas phase; and (d) recycling a portion of the liquid phase obtained in step (c), wherein the portion, designated the recycle stream, is reintroduced into the liquid stream of step (a) such that the ratio of the mass flow rates of the recycle stream and fresh acetone, designated the recycle ratio, satisfies formula (I).

Description

[Technical Field]

[0001] The present invention relates to a method for preparing isopropanol in high yield and purity. [Background technology]

[0002] Isopropanol, commonly called isopropyl alcohol (IPA), is widely used in many fields, for example as a solvent and reagent in laboratory reactions and on an industrial scale, as a disinfectant in hygiene products, as a preservative in cosmetics, as an additive in paints, dyes and inks, and as an antifreeze agent in fuels.

[0003] The alcohols are used in most of the applications listed above at high purity, often exceeding 99.0%.

[0004] One of the industrially used methods for producing isopropanol involves the reduction of acetone in the presence of hydrogen and a metal catalyst.

[0005] One of the industrial solutions used for this type of reaction is the use of fixed-bed reactors operated in heterogeneous phase, in which the reagents, acetone, and hydrogen enter the reactor inside which the catalyst is fixed. The catalyst, which is generally composed of metal particles, can be dispersed on an inert or reactive support to increase the catalyst surface area, thereby improving its activity and its selectivity, and minimizing costs. In fact, by implementing this operating solution, small amounts of the often expensive metal active component are used.

[0006] The reduction of acetone to isopropanol is an exothermic reaction characterized by an equilibrium enthalpy equal to -13.4 kcal / mol. If not controlled, high temperatures can be reached in the reactor, which can lead to side reactions of both the reagents and the product, resulting in the formation of undesired products. Acetone has a low boiling point and is prone to evaporation. Its excess gaseous presence can create a hotter reaction zone, even near the catalyst bed, where the by-product formation process is accelerated by the presence of the catalyst. Furthermore, the contact of these by-products with hydrogen and the catalyst also leads to the formation of additional undesired products, further reducing the selectivity of the reaction. The main by-products of the acetone hydrogenation reaction are methyl isobutyl ketone (MIBK), methyl isobutyl carbinol (MIBC), and 2-methyl-2,4-pentanediol (HEG). The aldol condensation between two acetone molecules gives diacetone alcohol (DAA) as the first by-product, which can react with hydrogen near the catalyst bed to give 2-methyl-2,4-pentanediol (HEG), or, since the reaction temperature is generally higher than 60 °C, can dehydrate to give mesityl oxide (MOX). The oxide is highly reactive and reacts very rapidly with hydrogen to give methyl isobutyl ketone (MIBK), which is subsequently reduced to methyl isobutyl carbinol (MIBC). Meanwhile, the formed isopropanol can self-react in the presence of a high-temperature zone to form diisopropyl ether (DIPE). The main by-products and the secondary reactions mentioned above leading to their formation are illustrated in the following diagram (I).

[0007] [ka]

[0008] To reduce the formation of undesired products, the catalytic hydrogenation reaction can be carried out at a temperature value comprised between 60°C and 90°C, with 60°C being the minimum trigger temperature.

[0009] By operating at these temperatures, the catalytic hydrogenation of acetone requires a very long time to reach completion and the use of a large amount of catalyst, which makes the process uneconomical. As a result, to operate at low temperatures and obtain the high purity isopropanol required for various industrial applications with low amounts of unreacted acetone and in an economically advantageous manner, it is necessary to implement either expensive purification processes, which lead to lower process yields and higher total production costs, or various reactor solutions, which may not be applicable on an industrial scale due to their complexity.

[0010] The literature includes patents describing various methods for optimizing the isopropanol synthesis process starting from the catalytic hydrogenation of acetone.

[0011] In EP 1070698 and EP 2207762, Ineos describes a two-stage technical solution for reducing by-products in the acetone reduction reaction. The solution consists of two reactors in series operated at different temperatures and pressures. In the first reactor, most of the acetone present in the reaction mixture is reduced, while in the second reactor, which can be considered a finisher, the reaction is generally carried out at a temperature lower than the operating temperature of the first reactor in order to increase its yield and reduce the formation of by-products. In particular, in EP 2207762, a cooling system is provided between the first reactor and the finisher, allowing the temperature in the initial part of the finisher to be between 60°C and 90°C, preferably between 60°C and 80°C.

[0012] In EP 1444184, Shell describes a multi-tube reactor for optimizing both acetone conversion and hydrogenation reaction yield. The multi-tube system allows for better control of the reaction heat. The catalyst used is based on nickel oxide or Raney nickel.

[0013] Mitsui, in European Patent No. 0379323, describes the hydrogenation of acetone to isopropanol in a trickle-flow reactor, primarily using nickel-based catalysts, as fully illustrated in the examples. A trickle-flow reactor is a multiphase system consisting of a fixed-bed catalyst across which a stream of reactants, both liquid and gaseous, is simultaneously present. The gas phase can flow upward or downward depending on the type of application. However, the liquid phase primarily flows or "trickles" downward in a top-down direction over the solid catalyst. The same term "trickle" describes the operating characteristics of intermittent liquid flow over the solid catalyst in the form of a film, trickle, or droplets.

[0014] In the specification of EP 0361755, Mitsui deals with the hydrogenation of acetone in a general, by-product-free process for the production of phenol. As reported in the examples of EP 0379323, the hydrogenation reaction is described as being carried out in a fixed-bed reactor in the presence of Raney Nickel as a catalyst.

[0015] Finally, in European Patent No. 2202214, Mitsui discloses that by performing an acid treatment (washing with an acidic aqueous solution) on a Raney nickel catalyst before carrying out the hydrogenation reaction of acetone, the conversion rate of ketones and the selectivity of the resulting alcohol can be improved by reducing the amount of trace impurities that bind to the catalyst system.

[0016] In the examples of the cited patents, the catalysts used to carry out this type of reaction are nickel-based or Raney-nickel type catalysts. Raney-nickel type catalysts are usually activated in situ by adding soda, starting with a nickel-based catalyst. In the activation process, a water wash is applied to the catalyst bed to neutralize the reaction environment and eliminate alkalinity. The presence of an alkaline environment is detrimental to this type of transformation, as it increases the formation of by-products such as diacetone alcohol (DAA), for example, due to the self-condensation of acetone itself. The unsaturated by-products are reduced in this case by excess hydrogen, as reported in Scheme I. This is clearly supported by the solution presented by Mitsui in EP 2202214, in which the Raney-nickel catalyst is acid-treated before reduction to improve yield and reaction selectivity.

[0017] In addition to being economically expensive, all of these treatments introduce a certain amount of water into the reaction environment, which must then be removed from the final mixture. It is known that the removal of water in a mixture of isopropanol and possibly unreacted acetone is not a simple and standardized process, since the mixture forms different azeotropes depending on the concentration of the components.

[0018] In addition, nickel-based catalysts are highly polluting to the environment and toxic to humans, requiring special disposal procedures.

[0019] The solutions described by Ineos in EP 1070698 and EP 2207762 furthermore use complex and economically unfavorable reactor systems consisting of several reactors in series carrying out the same reaction.

[0020] Therefore, it is important to identify an economically advantageous method that can maximize the conversion, selectivity, and yield of the acetone reduction reaction and obtain high-purity isopropanol by using a simplified reactor and catalyst system. Summary of the Invention

[0021] Therefore, the main object of the present invention is to provide an economically advantageous process for producing isopropanol from catalytic hydrogenation of acetone, which can provide the alcohol in high yield and purity and is directly applicable to various industrial fields without using expensive purification processes or complex reactor solutions which are uneconomical and cannot be applied at industrial level.

[0022] As reported by Mitsui in European Patent No. 0379323, one simple and economical reactor system used for the reaction to produce isopropanol starting from acetone is known to be characterized by a reactor with a fixed catalyst bed operated in the trickle flow regime with an equicurrent feed from top to bottom consisting of a gas stream containing hydrogen and a liquid stream consisting of acetone in the presence of a metal catalyst, preferably a nickel-based catalyst as described in the examples.

[0023] However, Mitsui only defines the operating conditions that allow operation in the trickle flow regime, but does not describe the quality of the isopropanol obtained, the amount of by-products present therein, or elaborate on the possibility of optimizing the process by recycling the reactor effluent in a controlled manner, thereby maximizing its productivity.

[0024] Through several experimental tests conducted in a trickle-flow reactor, which mainly uses an economical copper-based catalyst that does not require a difficult disposal procedure and recycles a portion of the effluent from the hydrogenation reactor, it has been surprisingly found that an operating zone exists that can simultaneously maximize the conversion, selectivity, and therefore the reaction yield by recycling the effluent in a specific manner. Thus, a method for synthesizing isopropanol in high yield and high purity using an economically advantageous and industrially applicable process has been obtained. [Brief explanation of the drawings]

[0025] [Figure 1] Figure 1 reports the trends in the reaction yield (IPA yield) and acetone conversion values ​​as a function of the recycle ratio (RR) obtained for several hydrogenation tests at a pressure of 21 bar, with a temperature measured at the start of the catalyst bed comprised between 120 and 122 °C and a mass flow rate of fresh acetone divided by the mass of catalyst in kg (WHSV) of 1.86 h-1. [Figure 2] Figure 1 reports the trends in the reaction yield (IPA yield) and acetone conversion values ​​as a function of the recycle ratio (RR) obtained for several hydrogenation tests at a pressure of 21 bar, with the temperature measured at the start of the catalyst bed being between 83 °C and 92 °C and the mass flow rate of fresh acetone divided by the mass of catalyst in kg (WHSV) being 1.00 h-1. DETAILED DESCRIPTION OF THE INVENTION

[0026] All terms used in this patent application, unless otherwise indicated, are to be understood in their ordinary meaning as known in the art to which they apply.

[0027] In this patent application, the acronym "HPLC" means high performance liquid chromatography.

[0028] The terms "recycled effluent," "effluent recycle," "recycle stream," and "recycle stream" mean a material stream that is initially removed from a mainstream, then undergoes a series of chemical-physical treatments before being reintroduced into the same stream from which it was removed.

[0029] The term "fresh acetone" means acetone that is introduced directly into the reactor and does not come from a recycled effluent.

[0030] The term "recycled acetone" means acetone derived from recycled effluent.

[0031] The abbreviation exp stands for the exponential function that relates a value to an increasing power, with Euler's number as the base, the first 10 digits being 2.718281828, and the exponent being the number obtained from the expression in parentheses.

[0032] The term WHSV refers to -1 This means the weight hourly space velocity, measured in Hz, and is defined as the hourly mass flow rate of the fresh acetone stream, i.e., not considering recycled acetone, divided by the mass of catalyst.

[0033] The temperature of the hydrogenation reaction, denoted T, is defined as the temperature in degrees Celsius measured in the direction of the reagent stream, i.e., from top to bottom, by a probe placed at the beginning of the catalyst bed present in the reactor. This temperature corresponds to the temperature of the oil passing through the jacket of the preheater (P) located before the reactor (R).

[0034] The term mass flow rate refers to the amount of reagent associated with a flow rate measured in kg / h.

[0035] Abbreviation m R means the value of the mass flow rate of the recycle stream measured in kg / h.

[0036] Abbreviation m A means the value of the mass flow rate of fresh acetone measured in kg / h.

[0037] The abbreviation RR stands for the mass flow rate of the recycled effluent, m R is the mass flow rate of fresh acetone m A The recycle ratio obtained by dividing by the

[0038] The term selectivity (S, %) means the ratio of the number of moles of isopropanol produced to the total number of moles of acetone reacted multiplied by a percentage.

[0039] The term conversion (C, %) means the ratio of the number of moles of acetone reacted to the total number of moles of fresh acetone multiplied by a percentage.

[0040] The term "about" means a value within a statistical range of an order of magnitude, preferably within a 10%, more preferably 5%, and advantageously 0.1% increase or decrease from the value indicated by measurement. Such ranges may also be within the experimental error inherent in the standard measurement method used to measure or determine a given magnitude.

[0041] Unless otherwise reported, in the context of the present invention, the specification that a method comprises one or more steps means that the steps mentioned must absolutely be part of the method, but does not mean that other implicit steps not directly mentioned may alternatively also be part of the method itself.

[0042] Unless otherwise stated, in the context of the present invention, the specification that a flow, i.e., a stream, comprises one or more components means that the listed components must absolutely be part of it, but does not mean that other implicit components not directly listed could alternatively be part of it.

[0043] Unless otherwise indicated, in the context of the present invention, ranges of values ​​given for a particular parameter, e.g., weight or volume of a component of a mixture, temperature range, include the upper and lower limits of said range, as well as all intermediate values ​​included therebetween.

[0044] Therefore, the main object of the present invention is a process for producing isopropanol from catalytic hydrogenation of acetone, comprising: a) feeding an adiabatic reactor from top to bottom with feed streams consisting of a gas stream containing hydrogen and a liquid stream containing fresh acetone; b) passing the feed stream of step (a) through a fixed catalyst bed contained within a reactor, thereby obtaining a reactor outlet effluent consisting of a liquid phase and a gas phase, said catalyst bed being operated in a trickle flow regime and comprising at least one metallic copper-based catalyst; c) separating the effluent from the reactor by separating the liquid and gas phases; d) recycling a portion of the liquid phase obtained in step (c), said portion designated as recycle stream, in a manner such that the ratio of the mass flow rates of the recycle stream designated as recycle ratio (RR) to fresh acetone satisfies the following formula:

number

[0045] The acetone hydrogenation reaction is typically carried out in an adiabatic reactor operated in the trickle-flow regime equipped with inlets and outlets for the introduction and removal of reagents and products, tubes for sampling the liquid phase, and a mobile electron probe useful for observing the thermal profile of the reaction.

[0046] In a preferred embodiment, the reactor is a tubular steel reactor sized so that catalyst can be dosed on an industrial scale without encountering problems with wall effects.

[0047] The reactor contains a catalyst bed, the length of which is between 1 / 3 and 2 / 3 of the total length of the reactor, preferably about 1 / 2 of the total length. A sheath of approximately 2 mm thickness is placed over the entire length of the catalyst bed, and inside the sheath is a mobile electron probe that detects the thermal profile of the catalyst bed itself. The catalyst bed is packed between two layers of catalytically inert material. In a preferred embodiment, the inert material consists of glass beads.

[0048] The reactor is fed from top to bottom with co-current feed streams consisting of a hydrogen-containing gas stream and a fresh acetone-containing liquid stream, as described in step (a).

[0049] In a preferred embodiment, fresh acetone is charged to a tank before entering the reactor and then suitably mixed using an HPLC pump first with the recycle stream of step (d) and then with a gas stream containing hydrogen, both of which are dropped in by suitable thermal mass flow controllers.

[0050] The gas stream comprises hydrogen and may contain other inert gases such as nitrogen, helium and argon. Particularly preferred is an embodiment in which the gas stream consists solely of hydrogen.

[0051] Due to the adiabatic nature of the reactor, the feed streams of step (a) are both preheated by a preheater and an electric belt located upstream of the reactor itself. The preheater is heated by oil present in its outer jacket, and its temperature is set to the same value as the temperature measured at the beginning of the catalyst bed. Alternatively, the electric belt, located in the tube connecting said preheater with the reactor itself, is preferably heated to a temperature comprised between 3°C and 5°C higher than the temperature measured at the beginning of the catalyst bed. The temperature values ​​of the preheater and the thermal belt are set to reach the desired temperature value at the beginning of the catalyst bed.

[0052] The hydrogenation reaction then occurs in a reactor where the feed stream from step (a) contacts the fixed catalyst bed from step (b), said catalyst bed being operated in a trickle flow regime and comprising at least one copper-based catalyst.

[0053] In a preferred embodiment, the at least one copper-based catalyst may comprise a compound selected from copper oxide, copper chromite, and mixtures thereof.

[0054] In a particularly preferred embodiment, the at least one copper-based catalyst comprises copper oxide.

[0055] Other compounds or chemical elements may be present in small amounts in the copper-based catalyst, said compounds may be selected from alkali metal oxides and / or alkaline earth metal oxides, transition metal oxides, aluminum trioxide, silicon dioxide and mixtures thereof.

[0056] In a preferred embodiment, the copper oxide-containing catalyst may contain calcium oxide, manganese dioxide, and silicon dioxide.

[0057] In another preferred embodiment, the copper oxide-containing catalyst may contain zinc oxide and aluminum trioxide.

[0058] In a further embodiment, the copper oxide-containing catalyst may contain aluminum trioxide.

[0059] The effluent leaving the reactor of step (c), consisting mainly of unreacted isopropanol and acetone and hydrogen, is separated by separating the liquid and gas phases.

[0060] In a preferred embodiment, the liquid phase of the leaving effluent is separated from the gas phase in a phase separator cooled to a temperature comprised between -10°C and 0°C, preferably between -10°C and -5°C.

[0061] The effluent from the reactor passes through a condenser at the same temperature as the phase separator before entering the phase separator.

[0062] A portion of the liquid effluent from the separator, designated as the recycle stream, is reintroduced into the liquid stream of step (a) as reported in step (d), so that the ratio of the mass flow rates of the recycle stream, designated as the recycle ratio (RR), to fresh acetone satisfies the following formula:

number

[0063] In a preferred embodiment, the hydrogenation reaction is carried out at a temperature T measured at the beginning of the catalyst bed comprised between 70° C. and 140° C. Operating at temperature values ​​below 70° C. will not lead to completion of the reaction due to the proximity of the trigger limit, while operating at temperature values ​​above 140° C. will significantly increase the amount of residual acetone present in the recycle stream.

[0064] In a particularly preferred embodiment, the reaction is carried out at a temperature T comprised between 80°C and 125°C.

[0065] In a preferred embodiment, the mass flow rate of fresh acetone divided by the mass of catalyst (WHSV) is 0.90 h -1 ~3:00h -1 The reaction temperature is between 0.01 and 0.05°C. Lower values ​​lead to higher spot temperatures on the catalyst bed, increasing the catalyst deactivation rate and consequently increasing the amount of residual acetone present in the recycle stream. Higher values ​​do not allow the reaction kinetics to go to completion, again increasing the amount of residual acetone present in the effluent leaving the reactor.

[0066] In a particularly preferred embodiment, the mass flow rate of fresh acetone divided by the mass of catalyst (WHSV) is 1.00 h -1 ~2:00h -1 is included between.

[0067] In a preferred embodiment, the molar ratio of fresh acetone to hydrogen is comprised between 1.1 and 2.0. Operating at a molar ratio of fresh acetone to hydrogen lower than 1.1 results in low conversion and promotes an increase in the spot temperature on the catalyst bed, which accelerates the catalyst deactivation process. On the other hand, operating at a molar ratio of fresh acetone to hydrogen higher than 2 results in an increase in the amount of unreacted hydrogen, which results in worsening process costs.

[0068] The plant is always kept under pressure to promote complete condensation of acetone and light components formed during the reaction. The optimum pressure value applied in the present invention is determined by the excess hydrogen and is less than 30 bar.

[0069] In a preferred embodiment, the pressure of the plant is comprised between 18 bar and 25 bar, advantageously between 20 bar and 21 bar. Operation at higher pressures favors the formation of isopropanol, but increases the process costs of plants operated in the trickle flow regime.

[0070] In a particularly preferred embodiment, the hydrogenation reaction is carried out at a mass flow rate of the fresh acetone stream divided by the mass of the catalyst (WHSV) of 0.90 h -1 ~2:00h -1 , maintaining the molar ratio of fresh acetone to hydrogen at a value equal to 1.6 and maintaining the temperature measured at the start of the catalyst bed at a value comprised between 80°C and 122°C, at a pressure of 21 bar.

[0071] The reaction effluent, after separating excess hydrogen, is sent to a tank that is periodically emptied.

[0072] Sampling, useful for determining the progress of the reaction, can be carried out in a pressurized cylinder placed after the phase separator, and the samples taken are subsequently analyzed by gas chromatography using techniques known to those skilled in the art to determine the yield, selectivity of the reaction, acetone conversion, and major impurities.

[0073] Surprisingly, it has been found that by operating at different temperature values ​​and mass flow rate of fresh acetone divided by the mass of catalyst fed (WHSV), and maintaining the ratio of the mass flow rates of the recycle stream to fresh acetone, i.e., the recycle ratio (RR) value, within the range defined by equation (I), a process for synthesizing isopropanol can be obtained that gives isopropanol in a yield of greater than 99.00%, with a selectivity of greater than 99.80%, and that is capable of reaching acetone conversion values ​​of greater than 99.30%, while simultaneously minimizing the formation of reaction by-products.

[0074] As an example, from Figures 1 and 2, which illustrate the trends of acetone yield and conversion as a function of recycle ratio (RR) in different tests carried out under different operating conditions, it is clear that these magnitudes reach a maximum value simultaneously only in a certain range of recycle ratios, the range bounded by the dotted line. Values ​​below the line are outside the scope of the present invention, and some of these are reported in the experimental section as comparative examples. In particular, the temperature values ​​measured at the beginning of the catalyst bed, which are between 120°C and 122°C, 1.86 h -1 In Figure 1, which reports the yields and conversions of various tests carried out at WHSV values ​​of 1000 kJ / h and a pressure of 21 bar, it can be seen that, according to formula (I), optimum values ​​of these parameters exist for recycle ratios comprised between 5 and 15. The values ​​of the temperature measured at the beginning of the catalyst bed comprised between 83 °C and 92 °C, and the temperature at 1.00 h -1 2, where the reaction was carried out at a WHSV value of 1000 and a pressure of 21 bar, there is an optimum for these parameters, according to equation (I), at recycle ratios comprised between 3 and 10. To make the graph clearer, selectivity values ​​are not reported and are all above 99.80% for the examples according to the invention reported above the dotted line.

[0075] In particular, operating at a recycle ratio (RR) within the range of formula (I) can achieve acetone conversion values ​​of greater than 99.30%, yields of greater than 99.00%, and selectivities of greater than 99.80% to isopropanol, with a methyl isobutyl carbinol (MIBC) content of less than 1500 ppm, a methyl isobutyl ketone (MIBK) content of less than 100 ppm, a 2-methylpentane-2,4-diol (HEG) content of less than 1500 ppm, and levels of other impurities of less than 1000 ppm, with the proviso that the sum of all impurities is less than 2500 ppm, preferably less than 2000 ppm. The other impurities, the sums of which are reported in Tables 1, 2, 3, and 4 of the Experimental Section, respectively, are preferably selected from methanol, n-propanol, methylcyclopentane, 2-methyl-1-propanol, diisopropyl ether (DIPE), cyclohexane, 2-methyl-1-butanol, and diacetone alcohol (DAA).

[0076] On the other hand, as shown in the comparative examples reported in the experimental section, operating the reaction at values ​​of the ratio of the mass flow rates of the recycle stream to fresh acetone, i.e., recycle ratio (RR) values, outside the range defined by equation (I) results in acetone conversion values ​​of less than 99.00%, isopropanol selectivity values ​​of less than 99.80%, and isopropanol yield values ​​of less than 99.30%. In some comparative examples, high selectivity values, for example, around 99.70%, are obtained, but the respective yield and conversion values ​​are reduced by about 1 percentage point. This demonstrates that operation outside the range defined by equation (I) does not maximize selectivity, conversion, or yield. In addition, operating under these conditions results in isopropanol with a total impurity content of more than 2000 ppm on average, and often more than 2500 ppm.

[0077] Thus, it is always possible to define a range of recycle ratios at different operating conditions of temperature and fractional hourly feed rate (WHSV) of fresh acetone and try to maximize the yield, conversion and selectivity of the reaction.

[0078] The Examples section below describes in detail the method of the present invention, by way of non-limiting example only. [Example]

[0079] Example 1 60 g of BASF Cu-0560 copper is charged into a 70 cm long, 1.57 cm (3 / 4 inch) internal diameter tubular steel reactor to form a catalyst bed approximately 35.5 cm long.

[0080] The reactor is then continuously fed from top to bottom with a stream consisting of hydrogen and acetone such that the molar ratio of hydrogen to fresh acetone is equal to 1.6.

[0081] The WHSV of the supplied acetone is 1.86h -1 is equal to.

[0082] The temperature measured at the start of the catalyst bed is 89.1° C. and the operating pressure of the plant is 21 bar.

[0083] A portion of the liquid effluent from the reactor produces a recycle stream, which is added as feed to the starting fresh acetone. The recycle stream, calculated to operate at a recycle ratio (RR) value equal to 3, which satisfies the conditions of equation (I), provides isopropanol in a yield of 99.00% and a selectivity of 99.80%. The acetone conversion is around 99.30%.

[0084] Examples 2 to 4 Following the procedure described in Example 1, several acetone hydrogenation tests were carried out, operating at temperature values ​​measured at the beginning of the catalyst bed, as shown in Table 1, comprised between 100°C and 101°C, and keeping unchanged the values ​​of the hydrogen to fresh acetone molar ratio, WHSV, and plant operating pressure.

[0085] When operating at recycle ratio (RR) values ​​between 2 and 9 that satisfy equation (I), the reaction occurs with yields greater than 99.25% and selectivities greater than 99.80%. Acetone conversions are greater than 99.40% (Table 1).

[0086] [Table 1]

[0087] Examples 5 to 9 Following the procedure described in Example 1, several acetone hydrogenation tests were carried out, operating at temperature values ​​measured at the beginning of the catalyst bed, as shown in Table 2, comprised between 120°C and 122°C, and keeping the values ​​of the hydrogen to acetone molar ratio, WHSV, and plant operating pressure unchanged.

[0088] When operating at recycle ratio (RR) values ​​between 5 and 16, which satisfy equation (I), the reaction occurs with selectivities greater than 99.85% and yields greater than 99.25%. Acetone conversions exceed 99.35% (Table 2).

[0089] [Table 2]

[0090] Examples 10 to 17 Following the procedure described in Example 1, -1 Several acetone hydrogenation tests were carried out using a WHSV value equal to 0.015 g / L and operating at temperature values ​​measured at the beginning of the catalyst bed as shown in Table 3, comprised between 83°C and 92°C.

[0091] As can be seen from the results reported in Table 3, by operating at recycle ratio (RR) values ​​between 2 and 12, satisfying equation (I), selectivity values ​​above 99.80%, acetone conversions of 99.70% or greater, and yields above 99.50% are obtained.

[0092] [Table 3]

[0093] Comparative Examples 18 to 36 Following the procedure described in Example 1, -1 ~3.72h-1 Several acetone hydrogenation tests were carried out using WHSV values ​​between 80°C and 121°C, with the temperature measured at the beginning of the catalyst bed being the values ​​shown in Table 4 between 80°C and 121°C, and by maintaining the recycle ratio value outside the upper and lower limits of the range given by equation (I). It was found that when operating with a recycle ratio that did not satisfy equation (I), acetone conversion values ​​of less than 99.00% were obtained. The selectivity of the reaction was 99.80% or less, and the yield was less than 99.00%. In particular, it was found that all these values ​​decreased simultaneously, or that only the selectivity remained acceptable, around 99.70%, resulting in conversion and yield values ​​of less than 98.00%. The yields, conversions, and selectivities of the tests carried out are reported in Table 4.

[0094] [Table 4]

Claims

1. A method for producing isopropanol by catalytic hydrogenation of acetone, comprising the steps of: a) feeding an adiabatic reactor from top to bottom with feed streams consisting of a gas stream containing hydrogen and a liquid stream containing fresh acetone; b) passing the feed stream of step (a) through a fixed catalyst bed contained within the reactor, thereby obtaining a reactor outlet effluent consisting of a liquid phase and a gas phase, the catalyst bed being operated in a trickle flow regime and comprising at least one metallic copper-based catalyst; c) separating the effluent from the reactor by separating the liquid and gas phases; d) recycling a portion of the liquid phase obtained in step (c), The portion, designated as the recycle stream, is divided into two portions, the mass flow ratio of the recycle stream, designated as the recycle ratio, and fresh acetone being determined by the following formula: [Equation 1] (In the formula, m Ｒ is the mass flow rate of the recycle stream; m Ａ is the mass flow rate of fresh acetone, WHSV is the hourly mass flow rate of the fresh acetone stream divided by the mass of the catalyst in kg; T is the temperature in degrees Celsius measured at the beginning of the catalyst bed present in the reactor. and reintroducing the sulphur dioxide into the liquid stream of step (a) so as to satisfy A method comprising:

2. 2. The process of claim 1, wherein the temperature measured at the beginning of the catalyst bed varies within a range of values ​​from 70°C to 140°C.

3. 3. The method of claim 2, wherein the temperature is varied within a range of values ​​from 80°C to 125°C.

4. The hourly mass flow rate of the fresh acetone stream divided by the mass of the catalyst (WHSV) is 0.9 h －１ ~3.0h －１ The method according to any one of claims 1 to 3, wherein the value of

5. The value obtained by dividing the hourly mass flow rate by the mass of the catalyst (WHSV) is 1.0 h －１ ~2.0h －１ 5. The method of claim 4, wherein the value of the saturation voltage Vs is varied within a range of:

6. 6. The process according to any one of claims 1 to 5, wherein in step (a), the molar ratio of fresh acetone to hydrogen is comprised between 1.1 and 2.

0.

7. 7. The method according to any one of claims 1 to 6, wherein the feed stream of step (a) is obtained by mixing the gas stream with the liquid stream consisting of fresh acetone and the recycle stream of step (d).

8. 8. The process of claim 7, wherein the feed stream of step (a) is preheated to a temperature value 3° C. to 5° C. higher than the temperature T measured at the beginning of the catalyst bed before entering the reactor.

9. 9. The method of any one of claims 1 to 8, wherein the stream of step (a) consists of hydrogen.

10. 10. The method of any one of claims 1 to 9, wherein in step (b), the at least one metallic copper-based catalyst comprises a compound selected from copper oxide, copper chromite, and mixtures thereof.

11. 11. The method of claim 10, wherein the at least one metallic copper-based catalyst comprises copper oxide.

12. The process according to any one of claims 1 to 11, wherein step (c) is carried out at a temperature comprised between -10°C and 0°C.

13. 13. The process according to any one of claims 1 to 12, wherein the hydrogenation reaction is carried out at a pressure comprised between 15 bar and 25 bar.

14. The hydrogenation reaction was carried out at a mass flow rate of the fresh acetone stream divided by the mass of catalyst per hour (WHSV) of 0.90 h －１ ~2.00h －１ 14. The process according to claim 1, wherein the temperature is varied in the range comprised between 80°C and 122°C, the molar ratio of fresh acetone to hydrogen is maintained at a value equal to 1.6, and the temperature measured at the start of the catalyst bed is maintained at a value comprised between 80°C and 122°C, and the process is carried out at a pressure of 21 bar.

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