Study On The Preparation Of Trialkylamine With Catalytic Amination

Fatty alkyl tertiary amines including mono-, di-, and tri-alkyl tertiary amines (RNMe2, R2NMe and R3N, respectively), as important intermediates for cationic surfactants, amphoteric compounds and important organic intermediates, have extensive applications. These derivatives of tertiary amines can be used in the fields of textile printing and dyeing, health care, daily chemical, petroleum chemical, metal processing and so forth. Catalytic amination of fatty alcohols is a major process for the preparation of these amines at present. Studies on catalysts, synthetic processes for mono-alkyl tertiary amines and their cationic quaternary ammonium salts have been performed for a long time, and have been reported widely. Up to now, very few articles were reported about the synthesis of tri-alkyl tertiary amines and catalysts and their quaternary ammonium salts.Tri-alkyl tertiary amines contain a bulky group (three long alkyl-chains) with a steric-hindrance. Therefore, more active catalysts than those used for the preparation of mono-and di-alkyl tertiary amines are required. The reaction mechanism has particularity, too. Therefore, the work in this paper is centered on the study of the synthesis of tri-long-alkyl tertiary amines, more effective amination catalysts, reaction mechanism and a new type of quaternary ammonium salts.A series of diatomite-supported catalysts with different Ni:Cu ratios were prepared by co-precipitation method from copper nitrate, nickel nitrate and sodium carbonate and tested by the amination of n-octanol with ammonia to trioctylamine under atmospheric pressure. The best element ratio was optimized and a detailed reaction mechanism was proposed. The third element Zn and Mg were added into the optimal catalyst and their effects on the performance of catalyst were investigated (Chapter2). TPR (temperature programmed reduction) were carried out to investigate reduction temperatures of catalysts, and XPS (X-ray photoelectron spectroscopy) spectra were measured to investigate surface compositions and valence state of catalyst elements (Chapter3). H2-TPD and NH3-TPD (temperature programmed desorption) were used to research adsorption and desorption properties of catalysts (Chapter4). XRD (X-ray diffraction) was used to analyze surface crystalline phase of catalysts particles. TEM (transmission electron microscopy) was carried out to observe morphology of catalysts. BET (N2adsorption-desorption isotherm) was measured to test specific surface areas, pore volume and pore size distribution of catalysts (Chapter5). A new type of containing hydroxyethyl group quaternary ammonium salts were synthesized from trioctylamine, monolauryltertiary amine and didecyltertiary amine. The structures of the quaternary ammonium salts were characterized and the surface activities were measured (Chapter6). The main results and conclusions in this paper are as follows:The results of amination reaction showed that the catalyst containing only Cu or only Ni had low activity and selectivity. The coexistence and synergism of Ni and Cu were essential for the generation of effective activity and selectivity. The optimum Ni/Cu molar ratio was1.25:1. The conversion of alcohol was higher than99%, and the content of trioctylamine in amination products reached over97%. A detailed reaction mechanism was proposed. The amination of octanol with ammonia is a consecutive reaction, via the formation of octylamine and dioctylamine, to form trioctylamine. The reaction from dioctylamine to trioctylamine is the rate-determining step of the formation of trioctylamine. The effects of the third element Mg and Zn on catalyst performances were investigated. The catalyst adding Mg had high activity and selectivity. The catalyst adding Zn had high activity, but the selectivity droped to about90%.The results of H2-TPR indicated that the catalysts containing NiO and CuO had decrease in the reduction temperature compared with the catalysts containing NiO or CuO only that might be brought about by a strong synergism due to the coexistence of Ni and Cu. The reduction temperature of the optimum catalyst was the lowest,170.6℃, the same as the catalyst reduction temperature in amination reaction. The addition of Zn and Mg had obvious influences on the catalyst reduction that the reduction temperatures increased and the reduction degrees decreased.The results of XPS revealed that the surface Ni/Cu ratio of the optimum catalyst was3.2:1, indicating that Ni was easily concentrated on the catalyst surface and Cu was easily concentrated on the catalyst bulk. The reduction of Cu and Ni of the catalysts was not completed at the reduction condition of H2at170℃for40mins. The contents of Cu0and Ni0were about70%and9%, respectively. This result indicated that the optimum catalyst performance was the synergism of a particular ratio of Cu0/Cu2+and Ni0/Ni2+. Zn was concentrated on the catalyst surface and Mg was concentrated on the catalyst bulk when Zn or Mg was added into the optimal catalyst. The contents of Ni0decreased because of the concentration of Zn on the catalyst surface, resulting in the decrease of the selectivity of the catalyst.The results of H2-TPD showed that Ni had strong hydrogen absorption capacity and that of Cu was weak. The function of Cu in catalysts was mainly dehydrogenation and the function of Ni was hydrogenation. Ni and Cu must be concurrence in catalysts that catalysts had dehydrogenation and hydrogenation simultaneously. There was larger steric-hindrance to prepare trialkylamines, the hydrogenation ability of the catalyst for trialkylamines should be stronger than the catalyst for monoalkyl tertiary amines. Therefore, Ni was main active component for trialkylamines and Cu was main active component for monoalkyl tertiary amines. The hydrogen absorption capacity of the catalyst adding Zn or Mg increased.The results of NH3-TPD indicated that there were two adsorption states of NH3on the surface of catalysts that were possibly the adsorption related to the cleavage of N-H bond and the ligand adsorption by the lone pair of electrons of N atom. The first adsorption was weak and was the active adsorption state for amination reaction. The second adsorption was strong and difficult to desorb under the condition of amination reaction that was disadvantageous for amination reaction. The catalyst adding Mg had no the ligand adsorption and had no harmful effect on the amination reaction. But the catalyst adding Zn appeared the ligand adsorption peak taking some active site so that the amination reaction was attected.The characterization results of catalysts structure by XRD, TEM and BET were accordant. The catalyst particles were small by TEM, the diffraction peaks were small by XRD indicating the presence of small particles and the specific surface areas were larger. Only NiO diffraction peaks were observed in the optimal catalyst and the catalyst adding Zn or Mg and the diffraction peaks of CuO, MgO and ZnO disappeared, which means that the three oxides were highly dispersed on the carrier and NiO. The optimal catalyst had smaller nanoparticles and the dispersion was better than other catalysts, so the amination reaction was better, too.A new type of containing hydroxyethyl group quaternary ammonium salt-trioctylhydroxyethylammonium chloride (TQA) was synthesized from trioctylamine, hydrochloric acid and ethylene oxide, and was compared with monolauryldimethylhydroxyethylammonium chloride (MQA), didecylmethylhydroxyethylammonium chloride (DQA). The structures of the quaternary ammonium salts were characterized and confirmed by FT-IR,’H-NMR and element analysis. The surface activities were measured and were compared with the conventional quaternary ammonium salt without hydroxyethyl group. The results indicated that the containing hydroxyethyl group quaternary ammonium salts exhibit higher surface activities. The compounding properties of cationic and anionic surfactants of MQA and LAS were studied. The interfacial tension, emulsifying power, wetting force and detergency were improved obviously at the mass ratio of LAS/MQA=9:1. The cationic and anionic surfactants of MQA and LAS had obvious synergism.