Method for producing 2-aminopropane-1-ol from hydroxyacetone by reductive amination

Abstract

The invention relates to a method for producing 2-aminopropane-1-ol from hydroxyacetone by reductive amination using ammonia water and a co-solvent. The method comprises the following steps: mixing hydroxyacetone and ammonia water at a temperature of not more than 20 DEG C to obtain an oxazoline intermediate product; and adding either a solvent alone or a solvent and a second ammonia water to the oxazoline product in the presence of a nickel catalyst and hydrogen, and hydrogenating at a temperature of not more than 90 DEG C and a pressure of not more than 12 barggage to obtain 2-aminopropan-1-ol.

Description

Field of the invention

[0001] The present invention relates to a process for the preparation of 2-aminopropan-1-ol from hydroxyacetone by reductive amination using aqueous ammonia and a co-solvent. Description of the background art

[0002] There are several known processes for the preparation of 2-aminopropan-1-ol, also known by the name DL-propanolamine, DL-2-aminopropan-1-ol. 2-aminopropan-1-ol can be prepared from propylene oxide via chloropropanol using ammonia in various routes, or from commercial monoisopropylamine by fractionation and separation from other isomers, or from glycerol, or from nitroethane, or from alanine, or from 2-methylaziridine. However, the manufacture of 2-aminopropan-1-ol is still challenging on an industrial scale, in particular on an industrial scale as a commodity chemical. The various routes for the preparation of 2-aminopropan-1-ol are plagued by low yields, unavailability of starting materials or harsh reaction conditions.

[0003] The conditions used in the prior art are not industrially feasible on very large scale. In particular, some routes as developed by T. Tregner et al. require anhydrous ammonia and produce 2-aminopropan-1-ol with low selectivity. T. Tregner et al. (Chem. Biochem. Eng. Q., 31(4), 455-470 (2017)) teach that the reaction will be carried out at a temperature of 130-210 °C, which is very high.

[0004] The reductive amination of hydroxyacetone gives 2-aminopropan-1-ol from commercially available starting materials as taught in US 2007 / 0287868 A1 : .

[0005] However, this route requires hydrogenation at high pressure, i.e. 1100 psi of hydrogen (35 bar).

[0006] In US 3448153 A anhydrous ammonia is used, which has the disadvantage that unwanted intermediates are produced. Granted patent GB 1554176 A of BASF discloses the use of aqueous ammonia in the presence of hydrogen, but hydrogenation is carried out at high pressure of 200 bar.

[0007] There is a need to develop a process for the preparation of 2-aminopropan-1-ol at low cost and an industrial scale process requiring lower temperatures and lower pressures. SUMMARY

[0008] According to an embodiment, the present invention is a process for the preparation of 2-aminopropan-1-ol by reductive amination, the process comprising the steps of: a. mixing hydroxyacetone and aqueous ammonia at a temperature not exceeding 20 °C to obtain an oxazoline intermediate product; and b. adding a separate solvent or a solvent and a second aqueous ammonia to the oxazoline product in the presence of a nickel catalyst and hydrogen and hydrogenating at a temperature not exceeding 90 °C and a pressure not exceeding 12 bar gauge to obtain 2-aminopropan-1-ol. BRIEF DESCRIPTION OF DRAWINGS

[0009] Reference will be made to embodiments of the invention, examples of which can be illustrated in the accompanying drawings. These drawings are intended to be illustrative and not restrictive. Although the invention will be generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

[0010] Figure 1 is a schematic flow representation showing possible chemical pathways for the reaction of ammonia and hydroxyacetone and the role of water in preventing the generation of polymeric material.

[0011] Figure 2 is a chromatogram showing the gas chromatography results of the product of Example 3.

[0012] Figure 3 is a chromatogram showing the gas chromatography results of the product of Example 7.

[0013] Figure 4 is a chromatogram showing the gas chromatography results of the main cut after fractionation of the product of Example 6.

[0014] Figure 5 shows the gas chromatography results of the main cut after fractionation of the product of Example 6 1 H NMR spectrum.

[0015] Figures 6 to 9 shows the C NMR spectral data of the reaction mixture of 2-aminopropan-1-ol prepared according to Example 3. 13 C NMR spectrum.

[0016] Figures 10 to 11 shows the H NMR spectral data of the reaction mixture of 2-aminopropan-1-ol prepared according to Example 3. 1 H NMR spectrum.

[0017] Figure 12a is a schematic flow chart showing the chemical reactions taking place in the process of the invention.

[0018] Figure 12bThis is a schematic depiction of an embodiment of the method of the present invention.

[0019] Figure 13 The gas chromatography results of the hydrogenation reaction in Example 7 are shown.

[0020] Figure 14 The gas chromatography results of the oxazoline intermediate of Example 8 are shown.

[0021] Figure 15a and Figure 15b The mass spectrometry and NMR results of the oxazoline product of Example 8 are shown.

[0022] Figure 16 The gas chromatographic results of the hydrogenation reaction in Example 9 after filtration are shown.

[0023] Figure 17 The results of gas chromatography after hydrogenation using a recovered skeletal nickel catalyst following filtration are shown.

[0024] Figure 18 The effect of the gas-induced impeller on the hydrogenation reaction of Example 11 is shown.

[0025] Figure 19a The effects of pressure and temperature on the hydrogenation reaction of Example 12 are shown.

[0026] Figure 19b The effects of pressure and temperature on the hydrogenation reaction are shown with and without a gas-induced impeller.

[0027] Figure 20 The hydrogenation data for the reverse addition in the reaction of Example 13 are shown. Invention Details

[0028] In the following detailed description, embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, and it should be understood that other embodiments may be utilized and changes may be made without departing from the scope of the invention. To avoid unnecessary detail that would enable those skilled in the art to practice the embodiments described herein, certain information known to those skilled in the art may be omitted in the description. Therefore, the description and figures are to be regarded as illustrative rather than restrictive, and all such modifications are intended to be included within the scope of the teachings of the invention. It should be understood that, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” include plural indicators. It should be emphasized that, when used in this specification, the terms “comprises” or “comprising” are used to specify the presence of the stated features, integers, steps, or components, but do not exclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

[0029] According to an embodiment of the present application, there is provided a process for the preparation of 2-aminopropan-l-ol by reductive amination, the process comprising the steps of: a. mixing hydroxyacetone and aqueous ammonia at a temperature not exceeding 20 °C to obtain an oxazoline intermediate product; and b. adding a separate solvent or a solvent and a second aqueous ammonia to the oxazoline product in the presence of a nickel catalyst and hydrogen and hydrogenating at a temperature not exceeding 90 °C and a pressure not exceeding 12 bar gauge to obtain 2-aminopropan-l-ol.

[0030] In step a) or phase I (also known as imination), the oxazoline intermediate product (also known as imine herein) can be prepared in the presence of a solvent, such as methanol (to accommodate the recycle stream in a continuous mode) with >90% conversion of hydroxyacetone (also known as acetol). The imine can be stable at temperatures >10 °C. Step b) or phase II, also known as hydrogenation step, can be carried out at 5 bar gauge to 10 bar gauge to obtain ~90% yield of 2-aminopropan-l-ol in a batch time of about 3 to 4 hours.

[0031] According to an embodiment, the nickel catalyst is selected from skeletal nickel, Raney ® nickel, sponge nickel, recycled nickel catalysts, and any other type of nickel catalyst. According to an embodiment of the process, the temperature in step a) and step b) is a value between 4 °C to 20 °C and 40 °C to 90 °C, respectively, and the hydrogen pressure in step b) is a value between 5 bar gauge and 12 bar gauge. Higher temperatures help to speed up the reaction kinetics, for example at about 85 °C, the batch time is reduced by about 50%.

[0032] According to an embodiment of the above process, in step b), the solvent is selected from methanol, ethanol, propanol, any other C1-C5 alcohol, and combinations thereof.

[0033] According to an embodiment of the process, the ratio of hydroxyacetone: solvent is a value between about 1 :0.8 to 1 :2. Preferably, a ratio of 1 : 1 of hydroxyacetone: solvent is required to achieve ~90% yield of 2-aminopropan-l-ol, lower solvent concentrations reduce the 2-aminopropan-l-ol yield, and significantly higher solvent concentrations do not show any improvement in the 2-aminopropan-l-ol yield.

[0034] According to an embodiment of the process, the total ratio of hydroxyacetone: aqueous ammonia required in the process is a value between about 1 :3 to 1 :5. The total ratio is the ratio used in both step a) and step b).

[0035] The process of the present application allows for the addition of the aqueous ammonia in its entirety in a single batch in step a) itself or in two batches between step a) and step b). Thus, in step b), when the separate solvent is added, the entire amount of aqueous ammonia is added in step a) such that the ratio of hydroxyacetone:aqueous ammonia is a value in the range of about 1 :3 to 1 :5. In a preferred embodiment, the ratio is a value between 1 :3.5 and 1 :4.

[0036] Alternatively, in step b), when the second aqueous ammonia is added along with the solvent, the amount of aqueous ammonia added in step a) is such that the ratio of hydroxyacetone:aqueous ammonia is at least about 1 :0.5 and then the remaining amount of the second aqueous ammonia added in step b) is the same as required for the total ratio to be a value in the range of about 1 :3 to 1 :5. In other words, the first aqueous ammonia must maintain a minimum ratio of 1 :0.5, more preferably 1 :1, for the reaction to continue forward. The remaining portion, i.e., the second aqueous ammonia, is added such that the final ratio of 1 :3 to 1 :5 is achieved. As during the hydrogenation, the required hydroxyacetone:aqueous ammonia is about 1 :3 to 1 :5, preferably 1 :3.5 to 1 :4, to achieve a 2-aminopropan-1-ol yield of ~90%. According to an embodiment of the process, the aqueous ammonia has a concentration between 22% to 30%.

[0037] According to an embodiment of the process, the 2-aminopropan-1-ol product is further purified by filtration, vacuum distillation or a combination thereof. Any suitable method can be used to further purify the 2-aminopropan-1-ol.

[0038] According to an embodiment of the process, in step b), the nickel catalyst is recovered by washing with water and thereafter reused. The nickel catalyst can be recovered up to 3 times without any top up. Thereafter, an intermediate top up of ~10% to 20% is required. The catalyst can be recovered up to 10 times and the average 2-aminopropan-1-ol yield is about >80%.

[0039] According to an embodiment of the process, the mixing is carried out by a gas induced impeller. When the mixing is carried out by a gas induced impeller, the hydrogenation reaction time of step b) is less than 4 hours.

[0040] According to an embodiment of the process, when about 85% conversion of hydroxyacetone to oxazoline product is achieved in step a), in step b), the solvent is added to the oxazoline product.

[0041] Acetol or hydroxyacetone can be prepared by a range of known prior art methods. Commercially available acetol can be prepared via dehydrogenation of 1,2-propanediol (PG) using metal oxides at high temperature (350-400 °C) with >96% yield in a process developed by Jefferson Chemical (USA) (Chemical & Engineering News, 20th December 1965, page 38). The reductive amination process of acetol described in US 2007 / 0287868 Al uses acetol synthesized via a different route, i.e. from glycerol.

[0042] The process of the present invention is developed as an industrially viable process for the production of 2-aminopropan-1-ol at low pressure of 1-15 bar of H2. The process of the present invention uses aqueous ammonia and a C1-C5 alcohol as a co-solvent. The alcohol solvent allows for the dissolution of hydrogen gas and thus, when compared to other prior art processes which use a pressure of 35 bar or 1100 psi and water as the solvent, the pressure can be reduced. The solubility of hydrogen in water is less than in alcohol. As the solubility of H2gas in alcohol is much greater in the reaction than in water, the pressure of the system is much lower compared to the prior art. Lower pressure is always beneficial for industrial applications as the equipment considerations for high pressure processes are significantly more complex and expensive. The process of the present invention can be carried out at a lower temperature of 50-90 °C compared to the prior art which is at a temperature of 85-210 °C, making the process of the present invention even more industrially viable.

[0043] The use of aqueous ammonia or ammonium hydroxide in the process of the present invention is easier to handle compared to gaseous ammonia and also gives a good selectivity of 2-aminopropan-1-ol, i.e. about 80% selectivity, which is significantly higher than the prior art processes. Further, as described below, anhydrous ammonia can lead to the undesirable formation of polymeric materials.

[0044] Figure 12a is an embodiment of the process of the present invention, showing a schematic flow chart of the chemical reactions taking place in the process of the present invention, wherein stage I is imination, wherein hydroxyacetone [I] is reacted with about 25% ammonia water at about 5-10 °C to produce oxazoline [II]. The next stage II is called hydrogenation, wherein oxazoline [II] is reacted with solvent methanol, ammonia water and hydrogen gas at a pressure of about 10 bar in the presence of Raney nickel to produce 2-aminopropan-1-ol [III]. Figure 12b A schematic showing an embodiment wherein the ammonia water is added in two batches.

[0045] Figure 1is a schematic representation of the chemical reaction showing the possible by-products and the role of water in the formation of hydroxyacetone acetal amine and thus preventing the production of by-product I, by-product II and by-product III and polymer material. Water is assumed to prevent by-products. The intermediate hydroxyacetone imine formed in the reductive amination can dimerize (e.g. compound I and compound III) or trimerize (e.g. compound II) in the absence of water to form polymers. However, in the presence of water, hydroxyacetone acetal amine can be formed which prevents polymerization. Thus, the present invention does not encourage the use of anhydrous ammonia instead of aqueous ammonia for the preparation of 2-aminopropan-1-ol. Furthermore, the process of the present invention can be carried out as a batch process or as a continuous process, i.e. a trickle bed reactor or a continuous stirred tank reactor (CSTR), or even a CSTR cascade (e.g. two CSTR systems in series, etc.) using the reaction conditions described herein.

[0046] The following experimental examples illustrate the present invention, but do not limit the scope of the present invention: Example: 1 - Sponge nickel catalyst preparation 2.0 kg of 25% NaOH was taken in a 5 liter glass beaker fitted on a magnetic hot plate stirrer. 130 g of Ni-Al (50%:50%) alloy powder was slowly charged into the beaker at 50°C-60°C in 1 h. The temperature eventually rose to 80°C. The contents of the beaker were stirred at 50°C-60°C for another 4-5 hours. The catalyst thus obtained was washed with deionized water until its pH became neutral.

[0047] Example: 2 - Reductive amination process of acetone alcohol 200 g of acetone alcohol / hydroxyacetone (abbreviated as HA herein) was added drop wise to a 1 liter round bottom flask containing 590 g of 28% aqueous ammonia solution at below 10°C. The mixture was stirred at below 10°C for 1 hour. The progress of imine conversion was checked by gas chromatography to assess >90%.

[0048] The above reaction mixture was transferred to a 2 liter autoclave. 400 g of methanol along with 20 g of sponge nickel catalyst as prepared above was added to the reaction mixture at room temperature. The reactor was flushed with hydrogen gas and hydrogen pressure of about 6-10 bar was applied. Although the experiments herein use methanol for testing, the skilled person is well aware that any other C1-C5 alcohol can be substituted therein.

[0049] The reaction mixture was heated to 60°C ± 10°C for about 4-8 hours while maintaining the hydrogen pressure. The progress of the reaction was monitored by gas chromatography (abbreviated as GC herein). After >96% complete conversion of imine, the temperature of the reactor contents was brought down to room temperature. The selectivity of 2-aminopropan-1-ol was about 80%. The catalyst was isolated by filtration.

[0050] After filtration of the catalyst, the crude 2-aminoprop-1-ol (abbreviated as 2AP in this document) was separated into a 28.5 w / w% solution, which also contained 1.9% 1,2-propanediol and other impurities, as shown in Table 1 below: Table 1:

[0051] Ammonia, methanol, and water were distilled off under vacuum to obtain crude 2-aminoprop-1-ol, which was further purified by high-vacuum distillation.

[0052] Examples: 3 to 6 Except for some changes in reaction parameters provided in Table 2 below, the process of Example 2 was followed in Examples 3 to 6: Table 2:

[0053] Figure 2 This is a chromatogram showing the gas chromatography results of the product of Example 3.

[0054] In Example 5, the temperature was maintained at 40°C for 5 hours, 50°C for 5 hours, and 80°C for 5 hours. Similarly, in Example 6, the temperature was maintained at 60°C and then at 70°C for 4.5 hours each.

[0055] Figure 3 This is a chromatogram showing the gas chromatography results of the reaction mixture of Example 6.

[0056] At the end of the process in Example 6, the fractionation of the reactor contents provided the following results, as shown in Table 3: Table 3: Fractionation of 2-aminoprop-1-ol

[0057] Figure 4 The chromatogram shows the gas chromatography results of the main fraction (2AP product fraction) after fractionation of the product in Example 6, showing 2-aminoprop-1-ol with 92% purity. Figure 5 The main fraction after fractionation of the product in Example 6 is shown. 1 ¹H NMR spectroscopy confirmed the high purity of 2-aminoprop-1-ol obtained in the main fraction.

[0058] Figures 6 to 9 The reaction mixture prepared according to Example 3 is shown. 13 C10 NMR spectral data. The spectral data confirm that 2-aminoprop-1-ol is formed as the major product.

[0059] Figures 10 to 11 The reaction mixture prepared according to Example 3 is shown. 1 1H NMR spectral data. The spectral data confirm that 2-aminoprop-1-ol is formed as the major product.

[0060] Next, large-scale experiments will be conducted to test the method at an industrial level.

[0061] Example 7: Conversion of hydroxyacetone to 2-aminoprop-1-ol Hydroxyacetone (50 kg) was transferred to a reaction vessel and cooled to 10 °C. Then, 25% ammonia (183 kg, 4 mol equivalent) was slowly added with gentle stirring while maintaining the internal temperature below 10 °C. After the addition was complete, the temperature was maintained below 10 °C with stirring, and the consumption of hydroxyacetone was monitored by gas chromatography. After 2 hours, the intermediate was transferred to a hydrogenation reactor (750 L), and skeletal nickel (9.5 kg, dry basis, Procat) was loaded under nitrogen. The reactor was equipped with a gas-induced impeller. Finally, methanol (50 kg) was loaded into the reactor, and the reaction mixture was hydrogenated at 10 bar hydrogen pressure while maintaining the temperature at 80 °C. After 6 hours, the catalyst was filtered off, and the crude 2-aminoprop-1-ol solution was first subjected to distillation to remove water, methanol, and ammonia. The crude 2-aminoprop-1-ol solution was separated by filtration of the catalyst to give pure 2-aminoprop-1-ol in 84.9% yield (see Table 4a). In this embodiment, all ammonia is loaded in one batch in step a). [Note: 50 kg batch of hydroxyacetone + 4 equivalents of ammonia, 9.5 kg catalyst, 80°C, 6 h; a hydroxyacetone:ammonia ratio of 1:4 also works]. Figure 13 The GC results of the hydrogenation reaction in Example 7 are shown. Table 4 shows... Figure 14 The GC results demonstrate the industrial feasibility of this process. The reaction is scalable and reproducible in a typical hydrogenation reactor.

[0062] Table 4:

[0063] Table 4a below shows a further scaled-up experiment in which the yield of 2-aminoprop-1-ol was 84.9%.

[0064] Table 4a:

[0065] Table 5 below shows the gas chromatographic results of the reactions in Table 4, where the percentage yield of the oxazoline product at the end of step a) was measured to be 87.91% and 87.41% after 1 hour and 2 hours, respectively. Furthermore, the 2AP selectivity at the end of step b) with a small amount (3.28% selectivity) of 1,2-propanediol (PDO) was measured to be 86.55% after 6 hours.

[0066] Table 5:

[0067] Example 8: Conversion of hydroxyacetone to oxazoline In this embodiment, ammonia was loaded in two batches during steps a) and b). Hydroxyacetone (85 kg) was loaded into the reaction vessel and cooled to 10°C. Then, 25% ammonia (78.1 kg, 1 mol equivalent) was slowly added, and the internal temperature was maintained at 10°C–12°C with gentle stirring. The addition of ammonia was completed over 4 hours, and mixing continued for another 2 hours while maintaining the internal temperature <10°C. The conversion process was monitored by gas chromatography. Figure 14 The gas chromatographic results of the oxazoline intermediate in Example 8 are shown. In step a), a acetone alcohol:ammonia ratio of 1:1 is sufficient to achieve a conversion of acetone alcohol to the oxazoline intermediate of approximately >90%. The amount of ammonia will be reduced. Table 6 below shows oxazoline yields of 87.91% and 87.41%.

[0068] Table 6:

[0069] Table 7 shows Figure 14 The GC experimental results show that, as can be seen from the data, a acetone alcohol:ammonia ratio of 1:1 is sufficient to achieve a conversion of acetone alcohol to the oxazoline intermediate of approximately >90%. The resulting oxazoline solution was then used in the next hydrogenation step of Example 9.

[0070] Table 7:

[0071] Figure 15a and Figure 15b The analysis of the oxazoline intermediate of Example 8 using mass spectrometry (MS) and nuclear magnetic resonance (NMR) is shown. As confirmed by NMR and MS, the oxazoline intermediate is formed with high selectivity.

[0072] Example 9: Hydrogenation of oxazoline to 2-aminoprop-1-ol The oxazoline solution was transferred to a 750-liter hydrogenation reactor equipped with a gas-induced impeller. Then, an additional 25% ammonia solution (168.1 kg) was transferred to the reactor under nitrogen atmosphere. The hydrogenator was loaded with skeletal nickel (17 kg, dry basis) and methanol (85 kg). The hydrogenator was inerted with nitrogen, and the container was filled with hydrogen to achieve a pressure of 10 bar. The reaction was heated to 85 °C ± 5 °C, and the hydrogen pressure was maintained at 10 bar. The reaction progress was monitored by gas chromatography until a conversion of approximately >90% was achieved. Table 8 below shows the selectivity of 2-aminoprop-1-ol at the end of 2 hours and 3 hours as measured by gas chromatography, which were 84.21% and 88.62%, respectively.

[0073] Table 8:

[0074] After 3.5 hours, the desired conversion was achieved, and the container temperature was lowered to ambient temperature. The catalyst was separated by filtration using a Nutsche filter, and the filtrate was transferred for distillation. Ammonia, water, and methanol were distilled off from the crude 2-aminoprop-1-ol mixture under vacuum to obtain crude 2-aminoprop-1-ol, which was further purified by high-vacuum distillation.

[0075] Table 9:

[0076] Figure 16 Table 9 shows the gas chromatographic results of the hydrogenation reaction in Example 9 after filtration. Figure 16 The results in Table 9 demonstrate that high-purity 2-aminoprop-1-ol was achieved by separating ammonia into two additions in steps a) and b), respectively. [Note: The hydrogenation of oxazoline to 2AP was completed within 3.5 h, T = 85℃-90℃, H2 = 10 psi] Example 10: Hydrogenation of oxazoline to 2-aminoprop-1-ol using recycled skeletal nickel From Example 9, the nickel catalyst separated after filtration was thoroughly washed with water (25 liters × 4 washes) and used for this batch according to the procedure described in Example 9. The conversion rates of hydrogenation using the recovered skeletal nickel are given in Table 10 below: Table 10:

[0077] The results above indicate that the catalyst can be recovered without any significant loss of catalytic activity. Therefore, similar catalytic activity can be achieved by replenishing 10%-20% every 3-4 cycles. Figure 17Table 11 shows the gas chromatography results of hydrogenation using the recovered skeletal nickel catalyst after filtration. The results also indicate that the catalyst can be recovered without any significant loss of catalytic activity.

[0078] Table 11:

[0079] Example 11: Effect of Gas-Induced Impeller on Hydrogenation Rate The hydrogenation process was evaluated to understand the role of the gas-induced impeller in the hydrogenation reaction kinetics. The reaction was carried out according to Examples 2-6, except that the hydrogenation reaction was carried out using a gas-induced impeller and the temperature was varied while the pressure was set to 10 bar H2. Figure 18 The effect of a gas-induced impeller on the hydrogenation reaction of Example 11 is shown. The hydrogenation reaction at 82°C and 10 bar gauge pressure is advantageous when a gas-induced impeller is used instead of a conventional impeller because the reaction time is reduced. The gas-induced impeller increases the mixing of hydrogen in the reaction mixture and thus increases gas-liquid mass transfer. This effect has a significant impact on the hydrogenation rate. At 75°C, the conversion of hydroxyacetone to 2-aminoprop-1-ol was 73% (conventional impeller) vs. 80.9% (gas-induced impeller) after 3 hours. When the temperature was increased to 82°C and a gas-induced impeller was used, the conversion further increased to 88.7% after 3 hours. However, at 87°C, there was no significant difference between the conventional impeller and the gas-induced impeller (see [link to relevant documentation]). Figure 19a (Far right).

[0080] Example 12: To investigate the effects of pressure and temperature on the yield of 2-aminoprop-1-ol and the consumption of oxazoline during the hydrogenation reaction. Figure 19a The effect of pressure at different temperatures on the yield of 2-aminoprop-1-ol and the consumption of oxazoline is shown. Figure 19a It is evident that achieving >90% conversion at 75°C takes approximately 5 hours. However, achieving the same conversion at 87°C requires approximately 3 hours. Temperature plays a crucial role in the hydrogenation duration. Temperature has a critical impact on reaction kinetics. Increasing the hydrogen pressure from 10 bar gauge pressure to up to 20 bar gauge pressure does not significantly affect the reaction profile. However, hydrogenation at a pressure of 7 bar gauge pressure results in a reduced reaction yield. Increasing the temperature above 90°C leads to a reduced yield due to the potential degradation of 2-aminoprop-1-ol. Therefore, for the scale-up production of 2-aminoprop-1-ol, a process involving a pressure of 10 bar gauge pressure and a reaction temperature of 87°C is likely preferred. Table 12 shows the conversion of hydroxyacetone to 2-aminoprop-1-ol using a gas-induced impeller at different temperatures and pressures after 3 hours.

[0081] Table 12:

[0082] Oxazoline consumption was slow at 75 °C and independent of pressure changes from 10 bar to 20 bar. A higher temperature of 87 °C accelerated the reaction kinetics and ensured minimal oxazoline in the reaction mixture over a reaction time of approximately 4–5 hours. For all pressures, using a fresh catalyst at 87 °C, yields of 2-aminoprop-1-ol were observed to be approximately 91 wt%–92 wt%.

[0083] Figure 19b The effect of temperature on the yield of 2-aminoprop-1-ol and the consumption of oxazoline is shown with and without a gas-induced impeller. The gas-induced impeller shows an effect at 75°C, but this effect disappears at higher temperatures of 87°C, as shown from... Figure 19b As seen in the yield values ​​in Table 13.

[0084] Table 13:

[0085] Example 13: Reverse addition of hydroxyacetone to form oxazoline and 2-aminoprop-1-ol In the reverse addition process for the formation of oxazoline, 25% ammonia (78.1 kg) was loaded into the reaction vessel and cooled to 10°C. Hydroxyacetone (85 kg) was then slowly added, and the internal temperature was maintained at 10°C–12°C with gentle mixing. The addition of hydroxyacetone was completed over 2 hours, and mixing continued for another 3.5 hours, maintaining the internal temperature <10°C. The progress of the conversion was monitored by gas chromatography (Table 14). After completion, the oxazoline was used in the next step for hydrogenation according to Example 7. The results showed that the order of addition (i.e., whether acetone alcohol could be added to ammonia or vice versa) did not significantly affect the reaction.

[0086] Table 14:

[0087] Figure 20 Table 15 shows the hydrogenation data for the reverse addition in the reaction of Example 13.

[0088] Table 15:

[0089] The results showed that the order of addition (i.e., whether acetone alcohol can be added to ammonia or vice versa) did not significantly affect the reaction.

[0090] The method of this invention is an improved method for preparing 2-aminoprop-1-ol by reductive amination, wherein ammonia and C1-C5 alcohol solvents are used at a lower pressure than that used in prior art methods. The process developed in this invention yields a conversion of >96% and a selectivity of 78%-93% (Table 13) for 2-aminoprop-1-ol, as measured by external standards. The remainder consists of <4% unconverted hydroxyacetone imine, 1,2-propanediol, 2,4-dimethyl-2-oxazoline-2-methanol (which is the product of the condensation of 2-aminoprop-1-ol with hydroxyacetone), as determined by GC / MS, and higher molecular weight impurities. The formed impurities are readily separated by fractionation, as shown herein.

[0091] The embodiments described above are non-limiting. Although the invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A process for the preparation of 2-aminopropan-l-ol by reductive amination, the process comprising the steps of: a. mixing hydroxyacetone and aqueous ammonia at a temperature not exceeding 20 °C to obtain an oxazoline intermediate product; and b. adding a separate solvent or the solvent and a second aqueous ammonia to the oxazoline product in the presence of a nickel catalyst and hydrogen and hydrogenating at a temperature not exceeding 90 °C and a pressure not exceeding 12 bar gauge to obtain 2-aminopropan-l-ol.

3. The process of claim 1, wherein in step b) the solvent is selected from the group consisting of methanol, ethanol, propanol, any other Ci-C5 alcohol, and combinations thereof.

2. The process of claim 1, wherein the nickel catalyst is selected from the group consisting of Raney® nickel, Raney® Ni, sponge nickel, recycled nickel catalyst, and any other type of nickel catalyst. ® Raney® nickel, Raney® Ni, sponge nickel, recycled nickel catalyst, and any other type of nickel catalyst.

4. The process of claim 1, wherein the ratio of hydroxyacetone: aqueous ammonia required in the process in total is a value in the range of about 1 :3 to 1 :

5.

5. The process of claim 1, wherein the ratio of hydroxyacetone: solvent is a value in the range of about 1 :0.8 to 1 :

2.

6. The process of claim 1, wherein in step b) when a separate solvent is added, the amount of aqueous ammonia added in step a) is such that the ratio of hydroxyacetone: aqueous ammonia is a value in the range of about 1 :3 to 1 :

5.

7. The process of claim 1, wherein in step b) when the second aqueous ammonia is added with the solvent, the amount of aqueous ammonia added in step a) is such that the ratio of hydroxyacetone: aqueous ammonia is at least about 1 :0.5, and the remaining amount of the second aqueous ammonia added in step b) is the same as the amount required for a total ratio in the range of about 1 :3 to 1 :

5.

8. The process of claim 1, wherein the 2-aminopropan-l-ol product is further purified by filtration, vacuum distillation, or combinations thereof.

9. The process of claim 1, wherein in step b) the nickel catalyst is recovered by washing with water and thereafter reused.

10. The process of claim 1, wherein the mixing is by a gas-induced impeller.

11. The process of claim 10, wherein when mixing is by the gas-induced impeller, the reaction time for hydrogenation in step b) is less than 4 hours. ​

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