WO2020103006A1

WO2020103006A1 - Process for preparing primary amines from alcohols

Info

Publication number: WO2020103006A1
Application number: PCT/CN2018/116575
Authority: WO
Inventors: Feng Niu; Vitaly ORDOMSKY; Stéphane STREIFF; Andrei Khodakov; Zhen YAN; Bright KUSEMA
Original assignee: Rhodia Operations; Universite Lille 1 - Sciences Et Technologies; Le Centre National De La Recherche Scientifique; Centrale Lille
Priority date: 2018-11-21
Filing date: 2018-11-21
Publication date: 2020-05-28

Abstract

A process for preparing a primary amine by reacting an alcohol with ammonia in the present of a metal catalyst comprising metal nanoparticles, wherein the metal nano-particles comprises at least one transition metal in elemental form and/or at least one transition metal compound and carbonaceous species are deposited on the metal nan-oparticles.

Description

Process for preparing primary amines from alcohols

TECHNICAL FIELD OF THE INVENTION

The invention relates to a process for preparing amines from alcohols in the presence of a metal catalyst. The catalyst notably comprises cobalt, ruthenium or nickel nanoparticles deposited over with carbonaceous species.

BACKGROUND

Owing to the importance, a number of routes for aliphatic primary amines synthesis have been developed till now, including Hofmann alkylation, Buchwald-Hartwig and Ullmann reactions, hydroamination, reduction of nitriles, and reductive amination. Among the well-established and important synthesis ways, by far the most utilized approach is the alcohols amination, mostly be the reaction of alcohols and ammonia. Compared with aliphatic acids, esters, alkenes, ethers, and other reactants, alcohols and ammonia are inexpensive and readily starting materials for direct one-pot amination. Most importantly, selectively catalytic synthesis of primary amines directly from alcohols and ammonia with elimination of water, under relatively mild conditions, without producing waste is a highly economic and environmental friendly process.

The amination of alcohols over different catalysts under hydrogen can be achieved via the so called "Borrowing Hydrogen" methodology, which consists dehydrogenation and hydrogenation processes. With the help of suitable dehydrogenation-hydrogenation catalysts, such as supported Ni, Cu, Pd, Ru, Co, Mo and metal oxides catalysts, alcohols can react directly with ammonia to form desired amines. Although homogeneous and heterogeneous catalysts are widely used for amination of alcohols under hydrogen, they suffer from some drawbacks such as limited substrate scope, the need for high temperature (>200℃) , high pressure of NH ₃, high H ₂ pressure, different undesired side reactions during amination, such as disproportionation of amines, aldehyde condensation and formation of nitriles. The most challenging in alcohols amination is selectively synthesis of primary amines, as they are more nucleophilic than ammonia and compete with it in reaction with electrophiles such as alkyl halides or aldehydes, producing secondary or tertiary amines, leading to the formation of mixtures of products, which are hard for separation.

Catalysts deactivation due to coke formation is an important technological and economic problem of great and continuing concern in the practice of industrial catalytic processes. Deactivation issues greatly impact research, development, design and operation of commercial processes. The mechanisms of solid catalysts deactivation can be result from poisoning, fouling, thermal degradation and sintering, vapor formation, vapor-solid and solid-solid reactions, and attrition or crushing, which are caused by chemical, mechanical and thermal aspects. Among them, poisoning is the strong chemisorption of species (reactants, products, or impurities) on catalytic sites which block some sites for catalytic reaction.

Although catalyst deactivation is undesired, some poisons may be added purposefully to selectively block some active surface sites, thus, ether to moderate the activity and/or to improve the selectivity of non-treated catalysts. In addition to other deactivation mechanisms, deposition of carbonaceous species on the surface of the catalyst appears to be one of the main reasons of catalyst deactivation. Before the present invention, people can’t find application of selective deactivation for improving the selectivity to primary amines.

SUMMARY OF THE INVENTION

The present invention therefore pertains to a process for preparing a primary amine by reacting an alcohol with ammonia in the present of a catalyst comprising metal nanoparticles, wherein:

- the metal nanoparticles comprise at least one transition metal in elemental form and/or at least one transition metal compound,

- carbonaceous species are deposited on the metal nanoparticles.

For the first time, different types of carbonaceous species were induced purposefully on the surface of metal nanoparticles through alcohol pre-treatment process under high temperature to improve the selectivity to primary amines in gas or liquid phase amination. By using pre-treated catalyst, selectivity of primary amine can be significantly improved up to 2-3 times in comparison with the parent catalyst.

According to the present invention, the amination process to obtain a primary amine is simple, efficient and thus suitable for commercial industrialization.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is an image of TG analysis of Co/γ-Al ₂O ₃ (CP-250-1) ;

Fig. 2 is an image of TG analysis of pretreated Ru/γ-Al ₂O ₃ and Ni/γ-Al ₂O ₃;

Fig. 3A-3D are TEM-EDX images of Co/γ-Al ₂O ₃ (CP-250-1) ;

Fig. 4 is a FTIR spectroscopy image of Co/γ-Al ₂O ₃ (CP-250-1) ;

Fig. 5 is a TPH-MS image of Co/γ-Al ₂O ₃ (CP-250-1) ;

Fig. 6 is an image of temperature-conversion curve for amination of 1-butanol with ammonia over non-treated Co/γ-Al ₂O ₃;

Fig. 7 is an image of effect of NH ₃/1-butanol molar ratio towards conversion and selectivity for amination of 1-butanol with ammonia over non-treated Co/γ-Al ₂O ₃;

Fig. 8 is an image of selectivity-conversion curve for amination of 1-butanol with ammonia over non-treated Co/γ-Al ₂O ₃;

Fig. 9 is an image of BA selectivity-conversion curve for amination of 1-butanol with ammonia over Co/γ-Al ₂O ₃ before and after 1-butanol treatment;

Fig. 10 is an image of selectivity-conversion curve for 1-butanol amination over Ru/γ-Al ₂O ₃ before and after 1-butanol pre-treatment.

Fig. 11 is an image of selectivity-conversion curve before and after 1-butanol pre-treatment over Co/γ-Al ₂O ₃ for liquid amination of 1-butanol;

Fig. 12 is an image of selectivity-conversion curve before and after 1-butanol pre-treatment over Co/γ-Al ₂O ₃ for liquid amination of 1-octanol;

Fig. 13 is an image of selectivity-conversion curve before and after 1-butanol pre-treatment over Co/γ-Al ₂O ₃ for liquid amination of benzyl alcohol;

Fig. 14 is an image of selectivity-conversion curve before and after 1-butanol pre-treatment over Co/γ-Al ₂O ₃ for liquid amination of furfuryl alcohol;

Fig. 15 is an image of selectivity-conversion curve before and after 1-octanol pre-treatment over Co/γ-Al ₂O ₃ for liquid amination of 1-octanol;

Fig. 16 is an image of selectivity-conversion curve before and after 1-hexanol pre-treatment over Co/γ-Al ₂O ₃ for liquid amination of 1-octanol;

Fig. 17 is an image of selectivity-conversion curve for 1-octanol amination over Ni/γ-Al ₂O ₃ before and after 1-butanol pre-treatment.

DETAILED DESCRIPTION

One of the key challenges in amination reactions is selectivity towards primary amines, which are much more valuable in comparison with secondary and tertiary amines is not ideal enough. The inventors of the present invention found the selectivity can be increased if the metal nanoparticles comprised in the catalyst are deposited with certain amount of carbonaceous species.

The metal nanoparticles of the catalyst comprise at least one transition metal in elemental form and/or at least one transition metal compound.

As used herein, metals of group IB, IIB, IIIB, IVB, VB, VIB, VIIB and VIIIB are often referred to as transition metals. This group comprises the elements with atomic number 21 to 30 (Sc to Zn) , 39 to 48 (Y to Cd) , 72 to 80 (Hfto Hg) and 104 to 112 (Rf to Cn) .

Preferably, the transition metal is selected from the group consisting of nickel, cobalt, copper, chromium, platinum, palladium, rhodium, ruthenium, iridium, silver, gold, cerium, bismuth, rhenium and mixures thereof, more preferably selected from the group consisting of nickel, cobalt, ruthenium and mixtures thereof and most preferably cobalt.

The catalyst may be a supported metal catalyst. In this case, the catalyst comprises a supporting material on which the metal nanoparticles are dispersed.

In some embodiments, the supported metal catalyst comprises one and only one transition metal in elemental form.

In some embodiments, the supported metal catalyst comprises at least two transition metals in elemental form.

Transition metal compound is preferably selected from the group consisting of: metal oxides, salts of metal and any combination thereof. Said salts could be chosen in the group consisting of halide, nitrate, nitrite, carbonate, bicarbonate, sulphate, sulphite, thiosulfate, phosphate, phosphite, hypophosphite, formate, acetate and propionate.

In a particular embodiment, the supported metal catalyst comprises at least one transition metal in elemental form and its corresponding transition metal oxide.

The supporting material of metal nanoparticles may be those well known to the person skilled in the art, which is selected from the group consisting of zeolites, Kieselguhr, silica, alumina, silica-alumina, clay, titania, zirconia, magnesia, calcia, lanthanum oxide, niobium oxide, carbon and any combination thereof, preferably from the group consisting of alumina, carbon and zeolites and more preferably alumina or carbon and most preferably alumina.

The metal loading of the supported catalyst is in a range of 1 to 30 wt. %, preferably 5 to 20 wt. %, mostly preferably 5 to 15 wt. %.

The average diameter of the metal nanoparticles is from 1 to 100 nm and preferably from 3 to 20 nm, which is measured using transmission electron microscopy (TEM) .

For TEM analysis, a JEOL 2100 with Filament LaB6 having an acceleration voltage of 200 kV equipped with a camera Gatan 832 CCD was used. As support, square 230 mesh TEM support grids (copper) were used. The magnification factor had a range of '10,000～' 600,000. For 50 nm: magnification factor was 40,000～50,000; for 20 nm: 60,000～120,000; for 10 nm: 250,000; for 5 nm: 400,000; for 2 nm: 500,000～600,000. Samples of 0.1 wt. %nanoparticles in methanol suspension were measured. The obtained results were analyzed using the DigitalMicrograph software. For each sample, two pictures were taken and a total of 100 nanoparticles were analyzed for obtaining the described size distribution. From this size distribution, the average particle size of the nanoparticles was obtained. The software used to measure the size of the nanoparticles was ImageJ thereby approximating the particles to be spherical. After setting the scale, the maximum diameter of the particles was manually measured one by one to a total number of particles measured of 100. Every particle has been measured 3 times to obtain an average size.

As used herein, the carbonaceous species refer to substances consisting of or containing elemental carbon or its compounds.

The elemental carbon can be graphite, carbon black, carbon nanotubes, carbon nanohorns or carbon nanofibers.

The carbon compounds may notably be long chain hydrocarbons, carboxylic acid, amorphous polymeric carbons.

Preferably, the long chain hydrocarbons can be C ₃-C ₃₀ aliphatic hydrocarbons and preferably C ₅-C ₃₀ aliphatic hydrocarbons. Said aliphatic hydrocarbons may comprise one or more carbon-carbon double bonds or triple bonds.

Preferably, the carboxylic acid can be C ₃-C ₃₀ aliphatic carboxylic acid and preferably C ₅-C ₃₀ aliphatic carboxylic acid. Said aliphatic carboxylic acid may comprise one or more carbon-carbon double bonds or triple bonds.

Preferably, the amorphous polymeric carbons are polymerization by alcohols used for treating the catalyst, long chain hydrocarbons or carboxylic acid above mentioned.

The weight ratio of the carbonaceous species deposited on the metal nanoparticles is from 1 to 10%, preferable 1 to 5%, based on the total weight of the catalyst, which is measured by thermogravimetric analysis (TGA) .

For example, Thermogravimetric analysis (TG) can be carried out using a Mettler Toledo SMP/PF7458/MET/600W instrument. The analyses are performed on pre-treated catalyst in air at a temperature ranging from room temperature to 800℃. The weight loss is considered as weight ratio of carbonaceous compounds deposited on the catalyst.

Before being used in amination reaction, the catalyst may be reduced by any convenient means, for example treating them at the desired temperature with a reducing gas such as hydrogen or carbon monoxide or mixtures containing them, of 200 to 500℃, preferable 200 to 450℃ for 1 to 20 hours, preferably 3-15 hours.

The carbonaceous species deposition may be realized by contacting the catalyst comprising metal nanoparticles with an alcohol at a temperature from 150 to 400℃, preferable 150 to 300℃, mostly preferable 200 to 300℃ for 0.1 to 8 hours, preferably 0.2 to 7 hours, most preferably 0.25 to 3 hours.

It was found that the metal catalyst treated by this method leads to high selectivity of the desired primary amine.

The alcohol used for treating the catalyst can be a lower aliphatic monohydric alcohol. Preferably, the alcohol is a C ₁-C ₁₀ aliphatic monohydric alcohol, more preferably propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, and decanol, mostly preferably primary alcohol such as 1-butanol, 1-hexanol, 1-octanol.

This treatment can be performed under a nitrogen atmosphere.

The alcohol used for treating the catalyst can be introduced in gas or liquid form and preferably gas form.

In one preferred embodiment, the treatment of the catalyst is performed in a fixed bed reactor, in which the alcohol used for treating the catalyst is introduced with the help of N ₂ carrier gas. For example, the N ₂ carrier gas is saturated with alcohols beforehand. In this embodiment, the gas pressure in the reactor is of at least 1 bar, preferably from 2 bar to 20 bar, more preferably from 3 bar to 6 bar.

The alcohol used as starting material of amination reaction can be aliphatic alcohol or aromatic alcohol, which is optionally substituted by one or several functional groups. The functional groups are selected from the group consisting of alkyl, alkenyl, alkynyl, alkoxy, alkylated amino, carboxyl, ester, cyano, nitro and halogen.

The alcohol used as starting material may preferably comprise 1 to 5 hydroxyl groups and preferably 1 to 3 hydroxyl groups.

The alcohol used as starting material preferably may comprise 1 to 30 carbon atoms and preferably 1 to 10 carbon atoms.

Preferably, the aliphatic alcohol is an aliphatic monohydric alcohol, which is selected from the group consisting of methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol and 1-decanol. The primary amines obtained accordingly are methylamine, ethylamine, 1-propylamine, 1-butylamine, 1-pentylamine, 1-hexylamine, 1-heptylamine, 1-octylamine, 1-nonylamine, 1-decylamine.

Preferably, the aromatic ring of the aromatic alcohol has 1 or 2 five-membered or six-membered ring.

The aromatic ring as used herein can be a hydrocarbon or heterocyclic ring, and may be selected from the group consisting of benzene, pyrene, furan, thiophene, terthiophene, pyrrole, pyridine, terpyridine, pyridine oxide, pyrazine, indole, quinoline, purine, quinazoline, bipyridine, phenanthroline, naphthalene, tetralin, biphenyl, cyclohexylbenzene, indan, anthracene, phenanthrene, fluorene, and azulene.

Ammonia can be introduced in gas or liquid form in the process according to the present invention. It was, found that in view of selectivity and yield it is desirable that the NH ₃ is introduced in gas form at a pressure of at least 7 bar, preferably in the range of 7 bar to 30 bar, more preferably in the range of 10 bar to 20 bar.

The amination can be conducted under usual process parameters well known to a person skilled in the art. In view of yield and selectivity of the process it is, however, preferred to conduct the amination at a temperature of at least 80℃, preferably in a range of 100℃ to 200℃, more preferably 100℃ to 180℃, most preferably 140℃ to 180℃.

A reductant can be optionally introduced into the reaction medium. Preferred reductant is H ₂. The pressure of H ₂ during the reaction can be selected according to the requirements by the skilled person. It was, however, found that in view of selectivity and yield it is desirable that the H ₂ is used at a pressure of at least 1 bar, preferably in a range of 1 bar to 30 bar, more preferably 2 bar to 20 bar, and most preferably 3 bar to 6 bar.

The reaction time is also not particularly limited and can be selected by the skilled person according to the desired yield and purity of the desired primary amine product. For example, the reaction can be conducted for at least 1 hour, preferably at least 4 hours, such as about 4 to 24 hours.

The molar ratio of ammonia to alcohols is in a range of 2 to 100, preferably 7 to 50 and more preferably 17.

The amination of alcohols can be conducted in both gas phase and liquid phase. The gas phase amination can performed in a continuous fixed-bed reactor system under atmospheric pressure of alcohols with ammonia. A nitrogen flow was saturated with liquid alcohols, leading to a gaseous alcohol feeding into the reactor.

The liquid phase amination can performed in a reactor charged with alcohol and metal catalyst. The reactor was sealed and evacuated by applying vacuum followed by charging NH ₃ and H ₂ into the reactor. The reactor was then placed on a hot plate equipped with a magnetic stirrer. After the reaction, the reactor was cooled down to room temperature.

It was furthermore found that the process according to the present invention can be conducted as one-pot process. It is rather possible to charge the reactor with alcohols, ammonia, the metal catalyst and optionally H ₂ and then conduct the reaction.

The following examples are given by way of non-limiting illustration of the present invention.

EXAMPLES

Example 1. Catalyst synthesis and pretreatment

1.1 Synthesis of Co, Ru and Ni heterogeneous catalyst

The Co/γ-Al ₂O ₃ (14.5 wt%Co) catalyst was prepared by incipient wetness impregnation (IWI) of γ-Al ₂O ₃ with aqueous solutions of cobalt nitrate (Co (NO ₃) ₂·6H ₂O) . The impregnated sample was dried in air under 80℃ overnight and calcined in an air flow (～10 ml/min) up to 400℃ with a heating ramp of 2℃/min from RT to 400℃.

Ru/γ-Al ₂O ₃ (10.0 wt%Ru) catalyst was prepared through incipient wetness impregnation (IWI) of γ-Al ₂O ₃ with aqueous solutions of ruthenium (III) chloride hydrate (RuCl ₃·xH ₂O) . The impregnated sample was air-dried at 80 ℃ followed by calcination in air flow (～10 ml/min) at 350 ℃ (2 ℃/min form RT to 350 ℃) for 2 h.

Ni/γ-Al ₂O ₃ (10.0 wt%Ni) catalyst was prepared through incipient wetness impregnation (IWI) of γ-Al ₂O ₃ with aqueous solutions of nickel (II) nitrate hexahydrate (Ni (NO ₃) ₂·6H ₂O) . The impregnated sample was dried in air under 80℃ overnight and calcined in an air flow (～10 ml/min) up to 400℃ with a heating ramp of 2℃/min from RT to 400℃.

1.2 Pre-treatment of Co, Ru and Ni catalyst in alcohols

30-100 mg of the prepared Co, Ru or Ni catalyst was charged in fixed bed reactor and reduced at 400℃ (200℃ for Ru) in hydrogen flow 1 ml/min during 10 h with subsequent cooling down to 250℃ or 300℃ in the flow of N ₂, afterwards the catalyst was pretreated in the flow of N ₂ as a carrier gas with saturation by alcohols (1-butanol, 1-octanol or 1-hexanol) under atmospheric pressure for 0.25-3 h. After pretreatment the reactor was cooled down in pure N ₂ flow and the catalyst was transferred in Ar atmosphere to batch reactor for liquid phase test or used for catalytic test in gas phase in the same reactor. The Co/γ-Al ₂O ₃ as-pretreated by 1-butanol was denoted as CP-250-t (t=0.25 h, 0.5 h, 1h and 3h) as shown in Table 1.

Table 1

Pretreated Co/γ-Al ₂O ₃	Time/h
CP-250-0.25	0.25
CP-250-0.5	0.5
CP-250-1	1
CP-250-3	3

TG analysis (Fig. 1) of CP-250-1 shows burning of carbon species at about 300℃ in air flow. The decrease of the weight corresponds to about 5 wt%of carbon on the surface of the catalysts after butanol pretreatment. Thermogravimetric analysis (TG) was carried out using a Mettler Toledo SMP/PF7458/MET/600W instrument. The gas flow rate of air (100 mL·min ^-1) , sample loading (about 20mg) and the heating rate (5℃·min ^-1) were kept constant in all experiments. The analyses were performed on 1-butanol pre-treated catalyst in air at a temperature ranging from room temperature to 800℃, with the objective of determine the weight loss related to deposition of carbonaceous compounds.

Fig. 2 shows TG analysis of Ru/γ-Al ₂O ₃ and Ni/γ-Al ₂O ₃ pre-treated by 1-butanol at 250℃ for 1h.

Identified from the TG results, carbonaceous species are also successfully deposited on the surface of Ru (250℃, 1 h or 3h 1-butanol pretreatment) and Ni (250℃ or 300℃, 1 h 1-butanol pretreatment) catalysts by alcohols pre-treatment process.

TEM-EDX images (Fig. 3A-3D) of CP-250-1 show localization of Co and C on the catalyst after pretreatment.

FTIR spectroscopy (Fig. 4) indicated the presence of aliphatic carbon species on the surface of the catalyst which may be explained by polymerization of alcohols:

FTIR spectroscopy were recorded at room temperature using a Thermo Nicolet 460 spectrometer equipped with a DTGS (CsI) and processed using the Nicolet OMINCTM software at 64 averaged scans at a 2 cm ^-1 of resolution and an optic velocity of 0.4747cm/s.

The methane TPH-MS profile (m/z=15) , resulting from the decomposition of different types of carbonaceous species, was conducted to help the further determination of the carbon types deposited on the surface of the catalysts. As shown in Fig. 5, for the fresh catalyst, there was no obvious methane signal detected, which indicates that no carbon species were left on the surface of the fresh catalyst. After pre-treatment, it is obvious that four main peaks corresponding to methane signal are identified at～240 ℃, 330 ℃, 490 ℃, and 525 ℃, indicating four major types of carbon species deposited on the active surface sites of the pre-treated catalyst based on their reactivity with hydrogen. The shoulder-like peak at～240 ℃ is attributed to long chain hydrocarbons and some other side products like dibutylether, butylbutyrate and 2-etyl -3-hydroyhexanal, which have strong adsorption on the surface of the catalyst. The peak placed at～330 ℃ is corresponding to carboxylic acid species. The shoulder-like peak at～490 ℃ and the sharp peak at～525 ℃ are indentified to amorphous polymeric and elemental carbons containing graphite, carbon black, carbon nanotubes, carbon nanohorns or carbon nanofibers, respectively. The temperature and methane peak positions referring to different types of carbonaceous species are in good agreement with most reported literatures based on the identification of reference compounds.

Temperature-programmed hydrogenation (TPH) coupled with mass spectroscopy (MS) was carried out using an AutoChem II 2920 V3 0.2 Micromeritics apparatus. The amount of the catalyst was about 80 mg. TPH-MS was performed from room temperature to 800 ℃ with a temperature ramp of 5 ℃/min using a mixed gas of H ₂/Ar (5 vol%H ₂) . The hydrogenation of carbonaceous species: C _ads+2H ₂→CH ₄ (m/z=15, instead of 16 to avoid interference from ionized oxygen coming from water vapor) was monitored using a Balzers Omnistar mass spectrometer.

Example 2. Catalytic gas phase amination reaction

30 mg treated/non treated catalyst prepared by Example 1 was used for amination test. A nitrogen flow was saturated with liquid 1-butanol at 70℃, resulting in a gaseous alcohol feeding into the reactor. The total flow rate was varied from 10 to 25 ml/min, thus the calculated gas hourly space velocity (GHSV) was from 20 to 50 L/g·h. The amination temperature was 140℃ according to the conversion of alcohol. The NH ₃/BuOH molar ratio was 7.

The catalytic activity of the catalysts was evaluated in gas phase amination of 1-butanol (BuOH) with ammonia, which was performed in a continuous fixed-bed reactor system under atmospheric pressure with online gas chromatographic detection of reaction products.

The influence of reaction temperature, BuOH/NH ₃ molar ratio and the relationship between conversion of alcohol and selectivity of primary amine were firstly investigated for reference non treated catalyst Co/γ-Al ₂O ₃. No 1-butanol conversion was observed during the experiment without catalyst. The conversion of 1-butanol increases as the reaction temperature increases from 100 to 160℃ as shown in Fig. 6. The conversion is almost 100%when the temperature reaches 140 ℃, which indicates that Co/γ-Al ₂O ₃ is active catalyst for gas phase amination of 1-butanol. 140℃ has been chosen for further investigation of the selectivity modification after catalyst pre-treatment under 1-butanol.

The influence of NH ₃/BuOH molar ratio on the activity and selectivity of cobalt catalyst was also studied under the reaction condition of 120℃, a GHSV of 20 L/g·h as shown by Fig. 7. As the molar ratio increases from 7 to 50, the conversion drops dramatically to nearly 0. The selectivity of BA increases from ～10%to ～85%. The decrease in 1-butanol conversion might be due to the competitive adsorption of excessive ammonia since the slowest and decisive step during amination of 1-butanol appears to be the dehydrogenation of 1-butanol. Likewise, the increase of BA selectivity is the result of preferential amination by ammonia and not by BA. From the economic point of view, it is better to use lower amount of ammonia during amination reaction. So here, the NH ₃/BuOH molar ratio was kept 7 in the present experimental investigation.

2.1 Amination over non treated Co/Al ₂O ₃ catalyst

Selectivity to BA decreases while DBA and TBA increase with increasing 1-butanol conversion (Fig. 8) . As the 1-butanol conversion reaches to almost 100%, the distribution of amine products for BA, DBA and TBA is about 1: 3: 1, , in good agreement with previous results. Likely, under the condition of higher alcohol conversion, , more primary amine will be produced and adsorbed on the surface of the cobalt catalyst, causing the condensation reaction and giving second and tertiary amines, which largely lowers the selectivity of primary amine.

The reaction proceeds according to the scheme with the main products: primary, secondary and tertiary amine:

The reactants and products were analyzed using an online gas chromatograph (Shimadzhu GC-2014 with a flame ionization detector) equipped with a six-port valve and a HP-5 column (length 30 m, , diameter 320μm, film thickness 0.32μm) . Helium was used as a carrier gas with a split ratio of 50. The conversion of 1-butanol using CH ₄ as standard gas is defined as:

The selectivity of primary amine (BA) is calculated as:

A _i refers to the area of peak exported from GC; f _i are the different response factors; M _i refers to the molecular masses of different compounds; n _Ci refers to amount of carbon atoms in the molecule.

2.2 Amination over pretreated Co/Al ₂O ₃ catalyst

As shown by Fig. 9, after 1-butanol pre-treatment, there is a large modification towards the BA selectivity. As the pre-treatment time increases from 0.25 h to 3 h, the selectivity increases followed by a slight decrease compared with the selectivity for non-treated catalyst under same conversion. After exposing to 1-butanol for 1 h, the selectivity effect reaches the highest level. Even under high conversion (80%) , there is almost 45%selectivity enhancement compared with the non-treated catalyst. These results showed that after catalyst pre-treatment by 1-butanol, the selectivity of primary amine could be largely modified due to the active surface modification through carbon deposition. The selectivity of 1-butylamine increases from 35 to above 70%in gas phase at 80%conversion of 1-butanol over Co/Al ₂O ₃ after catalyst treated at 250℃ in 1-butanol flow.

2.3 Amination over pretreated Ru/γ-Al ₂O ₃

Fig. 10 shows selectivity-conversion curve for 1-butanol amination over Ru/γ-Al ₂O ₃ before and after 1-butanol pre-treatment.

The results show that Ru/γ-Al ₂O ₃ treated by 1-butanol is also effective for synthesis of primary amines in gas phase amination of 1-butanol.

Example 3. Catalytic liquid phase amination reaction

To show the selectivity effect of primary amines universally, the pre-treated cobalt catalyst by alcohols was tested in liquid amination of different alcohols.

3.1 Catalytic liquid amination process

The liquid amination of different alcohols with NH ₃ was also investigated using 1-butanol pre-treated Co/γ-Al ₂O ₃. The catalytic tests were carried out in 30 mL stainless steel autoclaves geared with a pressure gauge and a safety rupture disk. In a given experiment, the reactor was charged with a known amount of alcohol and a known amount of 1-butanol pre-treated cobalt catalyst (～100 mg) . The reactor was sealed and evacuated by applying vacuum followed by charging NH ₃ (～7 bar) and H ₂ (～3 bar) into the reactor. The reactor was then placed on a hot plate equipped with a magnetic stirrer for 4-24 h at 180℃.

After the reaction, the reactor was cooled down to room temperature and the mixture was analyzed on an Agilent 7890 GC equipped with a HP-5 capillary column with 5 wt%phenyl groups using biphenyl as the internal standard.

3.2 Selectivity effect after catalyst pre-treatment by 1-butanol

Fig. 11 to 14 shows the selectivity-conversion curve before and after 1-butanol pre-treatment over Co/γ-Al ₂O ₃ for liquid amination of different alcohols.

As shown by Fig. 11 to 14, before catalyst pre-treatment by 1-butanol, under high alcohol conversion, the selectivity of primary amines (butylamine, octylamine, benzylamine and furfurylamine) was always very low. This is similar as the results of gas phase amination. The selectivity effect could be controlled by adjusting the pre-treatment time from 1 h to 3 h as shown in Fig. 12 and Fig. 13 for 1-octanol and benzyl alcohol amination. 3h was the suitable condition for selectivity modification according to the results.

3.3 Selectivity effect after catalyst pre-treatment by other alcohols

Apart from the catalyst pre-treatment by 1-butanol, we also pre-treated Co/γ-Al ₂O ₃ by 1-hexanol or 1-octanol to see if there is also some selectivity enhancement. The procedure of catalyst pre-treatment by different alcohols was the same as 1-butanol pre-treatment.

Fig. 15 and Fig. 16 show the selectivity-conversion curve before and after different alcohols pre-treatment over Co/γ-Al ₂O ₃ for liquid amination of 1-octanol.

After catalyst pre-treatment by different alcohols, there was also some modification of the primary amine selectivity under same conversion for amination of 1-octanol, identifying the similar carbon deposition process, which increased the primary amine selectivity.

3.4 Amination over pretreated Ni/γ-Al ₂O ₃

Fig. 17 shows selectivity-conversion curve for 1-octanol amination over Ni/γ-Al ₂O ₃ before and after 1-butanol pre-treatment.

The results show that Ni/γ-Al ₂O ₃ treated by 1-butanol is also effective for synthesis of primary amines in liquid phase amination of 1-octanol.

Claims

A process for preparing a primary amine by reacting an alcohol with ammonia in the present of a catalyst comprising metal nanoparticles, wherein:

-the metal nanoparticles comprise at least one transition metal in elemental form and/or at least one transition metal compound,

-carbonaceous species are deposited on the metal nanoparticles.
The process according to claim 1, wherein the average diameter of the metal nanoparticles is from 1 to 100 nm and preferably from 3 to 20 nm.
The process according to claim 1 or 2, wherein the transitional metal is selected from the group comprising Co, Ni, Ru and mixtures thereof.
The process according to any one of claims 1 to 3, wherein the metal catalyst further comprises a supporting material.
The process according to any one of claims 1 to 4, wherein the supporting material is selected from alumina, carbon and zeolites and more preferably alumina or carbon and most preferably alumina.
The process according to claim 4 or 5, wherein the metal loading is in a range from 1 to 30 wt. %, preferably 5 to 20 wt. %, mostly preferably 5 to 15 wt. %.
The process according to any one of claims 1 to 6, wherein the metal nanoparticles deposited by carbonaceous species are prepared by contacting the metal nanoparticles with an alcohol at a temperature from 150 to 400℃, preferable 150 to 300℃, mostly preferable 200 to 300℃.
The process according to claim 7, wherein the metal nanoparticles deposited by carbonaceous species are prepared by contacting the metal nanoparticles with an alcohol for 0.1 to 8 hours, preferably 0.2 to 7 hours, most preferably 0.25 to 3 hours.
The process according to claim 7 or 8, wherein the alcohol is 1-butanol, 1-hexanol or 1-octanol.
The process according to any one of claims 7 to 9, wherein nitrogen gas is charged.
The process according to any one of claims 1 to 10, wherein the carbonaceous species are C ₃-C ₃₀ aliphatic hydrocarbons.
The process according to any one of claims 1 to 10, wherein the carbonaceous species are C ₃-C ₃₀ aliphatic carboxylic acids.
The process according to any one of claims 1 to 10, wherein the carbonaceous species are amorphous polymeric carbons polymerized by alcohols used for treating the catalyst, C ₃-C ₃₀ aliphatic hydrocarbons or C ₃-C ₃₀ aliphatic carboxylic acids.
The process according to any one of claims 1 to 13, wherein the weight ratio of the carbonaceous species is from 1 to 10%, preferable 1 to 5%, based on the total weight of the catalyst.
The process according to any one of claims 1 to 14, wherein the alcohol reacting with ammonia is an aliphatic alcohol or aromatic alcohol, which is optionally substituted by one or several functional groups.
The process according to any one of claims 1 to 15, wherein the alcohol reacting with ammonia comprises 1 to 5 hydroxyl groups and preferably 1 to 3 hydroxyl groups.
The process according to any one of claims 1 to 16, wherein the alcohol reacting with ammonia comprises 1 to 30 carbon atoms and preferably 1 to 10 carbon atoms.
The process according to any one of claims 1 to 17, wherein the alcohol reacting with ammonia is an aliphatic monohydric alcohol, which is selected from the group consisting of methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol and 1-decanol. mostly preferably from the group consisting of 1-butanol, 1-octanol and 1-hexanol.
The process according to any one of claims 1 to 17, wherein the alcohol reacting with ammonia is an aromatic alcohol having 1 or 2 five-membered or six-membered aromatic ring.
The process according to claim 19, wherein the alcohol is selected from the group consisting of benzyl alcohol, furfuryl alcohol and 2, 5-hydroxymethylfurfural.
The process according to any one of claims 1 to 20, wherein the molar ratio of ammonia to the alcohol is in a range of 2 to 100, preferably 7 to 50 and more preferably 17.
The process according to any one of claims 1 to 21, wherein the preparation of a primary amine is conducted at a temperature of at least 80℃, preferably of 100℃ to 200℃, more preferably of 100℃ to 180℃, most preferably of 140℃ to 180℃.
The process according to any one of claims 1 to 22, wherein the reaction is conducted in the presence of H ₂.
The process according to any one of claims 1 to 23, wherein the reaction is conducted at a NH ₃ pressure of at least 7 bar, preferably in the range of 7 bar to 30 bar, more preferably in the range of 10 bar to 20 bar.