Raschig Process Research Articles

A New Strategy for the Synthesis of Monomethylhydrazine Using the Raschig Process

A new strategy for the development of monomethylhydrazine (MMH) using the Raschig process is discussed in this publication. The determination of optimal conditions for the synthesis of MMH required the development of a kinetic model. In order to validate the results of the calculation, a device for synthesis under pressure (13 bar) by direct injection of the stoichiometric monochloramine, synthesized using microreactor technology, into monomethylamine (MMA) was developed. The experimental data, in accordance with the theoretical results of the kinetic model, make it possible to establish a new process for the synthesis of monomethylhydrazine.

A new strategy for the synthesis of monomethylhydrazine using the Raschig process. 2: Continuous synthesis of stoichiometric monochloramine using the microreactor technology

After having established in a previous paper that the synthesis of stoichiometric monochloramine is hazardous due to the high exothermicity of the reaction and the risk of decomposition of the solution from 36 °C, it appeared that the best solution for this synthesis is to use microreactor technology. A series of experiments carried out using a Doehlert experimental design provided access to a mathematical model describing, for an initial fixed composition ratio [NH4+]0/[OCl−]0, the evolution of the yield as a function of temperature, the flow rate of the reagents and the number of sodium hydroxide equivalent. Thus, the optimal conditions for the synthesis of stoichiometric chloramine using microreactor technology were established.

A new strategy for the synthesis of monomethylhydrazine using the Raschig process. 1. Study of the stability of monochloramine

In this paper, we describe a new strategy developed for the synthesis of MMH using the Raschig process. For the first time, it consists in synthesizing chloramine under stoichiometric conditions which leads to a more economical process because it avoids the additional steps of extraction due to the presence of excess reagents. However, monochloramine is not very stable and, therefore, it is necessary to study its stability. The various batch tests show that the reaction must be strictly controlled. As shown from DSC analyses on stoichiometric chloramine solutions, a risk of decomposition is present from 36 °C. Thus, controlling the temperature rise requires efficient cooling in the synthesis reactor or synthesis at low temperature, in order to avoid any sudden decomposition of the synthesis solution.

Synthesis of N‐Aminopyrrolidine by the Raschig Process: Kinetic and Mechanistic Study of the Monochloramine‐Pyrrolidine Interaction

ABSTRACT1‐Pyrrolidinamine (NAPY) belongs to a family of large compounds, namely the alkylhydrazines, used as precursors for different targets in fine chemicals, such as pharmaceuticals and cosmetics. Different synthetic methods are described in the literature; however, many of them are not adaptable on a large scale. The Raschig process appears to be the most relevant method for preparing hydrazines at the industrial scale: hydrazines are obtained by two successive reactions. The first involves the formation of monochloramine from sodium hypochlorite and excess ammonia. The second consists of reacting, in a basic medium, the monochloramine previously synthesized with excess amine to provide the corresponding hydrazine. It is a clean and selective method, distinguished by its nonpolluting aspect, its low cost, and the feasibility of continuous transposition to industrial scale. However, it presents some disadvantages linked to the low hydrazine concentrations in the synthesis solutions. The optimization of the synthesis parameters is therefore essential and requires a detailed kinetic and mechanistic study of the reaction of NAPY formation by the chloramine/pyrrolidine interaction. The kinetics of the NAPY formation reaction were studied in alkaline medium, at first at a temperature of 25°C. Excess pyrrolidine was used with respect to NH2Cl, in order to minimize the influence of side reactions. Owing to the high reaction rates, the essays were carried out in a dilute medium, using reagent concentrations ranging between 1 × 10−3 and 4 × 10−2 M. The ionic strength of the medium was established by NaOH concentration (0.1 M). Then, the influence of the temperature was studied between 15 and 45°C for NH2Cl and PY concentrations, respectively, equal to 2 × 10−3 and 0.01 M, in order to check the conformance to the Arrhenius law. Finally, the characterization of the reaction mixture permitted establishment of a global reaction scheme, including two main secondary reactions.

Kinetic modeling of the synthesis of N-aminopiperidine via the Raschig process: Reaction optimization and continuous process

N-aminopiperidine (NAPP) belongs to a large family of compounds, namely the cyclic alkylhydrazines, used as precursors for different targets in fine chemicals, such as pharmaceuticals and cosmetics. The formation of NAPP via the Raschig process by reacting piperidine (C5H10NH, PP) with monochloramine (NH2Cl) involves many side-reactions because of the reactivity of the latter. An exhaustive kinetic model, which reflects the rate of NAPP formation and that of side-reactions occurring during the synthesis of NAPP, was established. Additionally, a comparative study of theoretical and experimental concentration-time curves permitted to verify the accuracy of the model in a diluted medium. Moreover, the established kinetic model allowed to define the optimal conditions for NAPP synthesis in a concentrated medium, by varying the reactants concentrations, [PP]/[NH2Cl] ratio, pH and temperature. Hence, the application of the kinetic model enabled to optimize the reaction in view of its transfer to a continuous process.

Kinetic and mechanistic study of N-aminopiperidine formation via the raschig process

Formation of N-aminopiperidine (NAPP) in the reaction of monochloramine with piperidine was studied by varying the reagents concentrations, pH and temperature. The study was carried out in diluted solutions, recording simultaneously monochloramine concentration by UV spectrophotometry at 243 nm and hydrazine concentration at 237 nm after treatment with formaldehyde. The presence of two competitive reactions: formation of NAPP and a complex parallel reaction limiting the yield of hydrazine, was established. Reaction products were characterized by GC/MS analysis. The rate constant of NAPP formation and activation parameters were determined, k1 = 56 × 10−3 M−1 s−1 (25°C) and k1 = 9.3 × 106 exp(−46.5/RT) M−1 s−1, respectively.

Evolution of the Liquid–Vapor Equilibrium Properties of Several Unsymmetrical Amines: Determination of Their Binary Isobaric Diagrams and Applications to the Distillation

This work deals with the synthesis, extraction, and purification of a new exocyclic hydrazine with cosmetic applications, N-aminopyrrolidine (NAPY). The final extraction and purification steps of the useful product are often linked to distillation operations. The optimization of these separation conditions requires then the knowledge of the thermodynamic properties of the liquid–vapor equilibria. The synthesis reactions are carried out by the Raschig process, which is based on the reaction of a large excess of amine with chloramine in aqueous medium and without any use of solvent. The distillation step involves the liquid–vapor equilibria in the ternary system NAPY + pyrrolidine + water and, first of all, requires the knowledge of the water + pyrrolidine binary system. For a better understanding of the behavior of aqueous mixtures of amine, three liquid–vapor binary diagrams of water + amine type were investigated by ebulliometry. The three binary isobaric diagrams water + pyrrolidine, water + butylamine, and water + diethylamine were established under atmospheric pressure. The evolution of the thermodynamic properties of these amines according to the nature of the substituent will be then deduced by comparison of these experimental diagrams. This study will thus lead us to a better understanding of the molecular interactions in the liquid phase.

Kinetic and Mechanistic Study of N-Aminopiperidine Formation via the Raschig Process

Kinetic and Mechanistic Study of N-Aminopiperidine Formation via the Raschig Process

Synthesis of hydroxyethylhydrazine by the Raschig process and comparison with synthesis by the alkylation process

AbstractThe Raschig synthesis of hydroxyethylhydrazine (HEH) is studied, that is, the reaction of monochloramine on ethanolamine. The formation of HEH is monitored by UV spectrometry, and the influence of temperature and pH is studied. The primary reaction is an SN2‐type mechanism, whereas the main secondary reaction is the oxidation of HEH by monochloramine. This reaction is also monitored by UV spectrometry, and the oxidation product is identified by GC–MS analysis, showing the formation of hydroxyethylhydrazone. The reaction mechanisms and the rate constants were determined, and the results permit establishing the main reactions occurring during HEH synthesis. These reactions were validated in a concentrated medium, with the systematic study of the influence of the molar ratio p ([HEH]0/[NH2Cl]0) and the final sodium hydroxide concentration and temperature. A comparison is made with the other synthesis process already published, that is, the alkylation of hydrazine by either chloroethanol or epoxide. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 331–344, 2011

Extraction of Hydrazine by Selective Precipitation: Process Flow-sheet

This study relates to an improved process devoted to the preparation of an endocyclic hydrazine, the pyrazolidine (PYRZ, C3H8N2), in order to develop a versatile and flexible method, more suitable for an industrial scale and which can be implemented in batch or continuously process, according to the desired tonnage. This synthesis way is based on a transposition of the Raschig process, by the action of sodium hypochloride on 1,3diaminopropane at room temperature, then recovering of the hydrazine formed. The overall process of synthesis, extraction and purification of pyrazolidine was established and optimized and a process flow-sheet was proposed.

Techno‐Economic Analysis of Hydrazine Hydrate Technologies

AbstractThe increasing demand of current world production for hydrazine hydrate emphasizes the need to focus on the techno‐economic analysis of the existing technologies. Three processes, namely the Raschig process, urea process, and peroxide‐ketazine process, are chosen for technical analysis followed by cost estimation and economic assessment. The technical part involves the development of flow sheets, process design, carrying out of calculations as well as estimation of raw materials, labor, utilities, and process equipment by sizing and other sub‐components. The economic part comprises the estimation of working capital, fixed capital investment, total capital investment, and total production costs. Economic parameters like net profits, rate of return, payback period, and break‐even point are also estimated to perform economic analysis. The results obtained from technical analysis and economical feasibility studies show that the peroxide‐ketazine‐based hydrazine hydrate technology has clear advantages in terms of raw material consumption and economic competitiveness.

Interaction between substituted chloramines and liquid ammonia using the indirect Raschig process

In this paper, different hydrazines are synthesised by the indirect Raschig process. This consists of introducing a substituted chloramine (R 1 R 2 NCI) into liquid ammonia under pressure to obtain the corresponding hydrazine (R 1 R 2 NNH 2 ). The experimental results, in disagreement with those reported in the literature, lead us to propose a new mechanistic scheme involving a chlorine transfer reaction. Thus, the formation of chloramine (NH 2 CI) and the amine (R 1 R 2 NH) occurs first. Chloramine reacts immediately with the substituted amine, in agreement with the direct Raschig process, to produce the hydrazine. Under these conditions, the nature of the hydrazine is kinetically controlled by the excess amine. It is then possible to synthesise different hydrazines from the same substituted chloramine. This mechanism is validated by the following syntheses: unsymmetric dimethylhydrazine (UDMH), N-aminopiperidine (NAPP) and N-amino 3-azabicyclo[3.3.0]octane (NAZA).

Synthesis of 1‐amino‐2‐methylindoline by Raschig process: Kinetics of the oxidation of 1‐amino‐2‐methylindoline by chloramine

AbstractThe synthesis of 1‐amino‐2‐methylindoline by the Raschig process was undertaken in aqueous solution. The principal side reaction that occurs in the medium is the oxidation of 1‐amino‐2‐methylindoline formed by chloramine. To increase the yield of 1‐amino‐2‐methylindoline, its oxidation by chloramine was studied by GC and HPLC at various concentrations of reactants and for a pH interval ranging between 9.9 and 13.5. The reaction is bimolecular and exhibits a specific acid catalysis. In alkaline medium, 1‐amino‐2‐methylindole is the principal product. The enthalpy and entropy of activation were determined at pH 12.89. In unbuffered solution, the interaction was autocatalyzed by the ammonium ions formed, which indicates a competitive oxidation of neutral and ionic forms of 1‐amino‐2‐methylindoline by chloramine. A mathematical treatment based on one implicit equation allows a quantitative interpretation of all the phenomena observed over the above pH interval. It takes both acid–base dissociation equilibrium and alkaline hydrolysis of chloramine into account. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 515–523, 2002

Synthesis of 1‐amino‐2‐methylindoline by Raschig process: Parallel reactions, modeling, and optimization

AbstractThe reaction between chloramine and 2‐methylindoline was studied at pH 12.89, T = 40°C, and for different initial concentrations of reactants. The interaction includes two concurrent bimolecular mechanisms leading to 1‐amino‐2‐methylindoline and 2‐methylindole. The rate laws were determined at the first moments of the reaction by using a differential method. By considering the totality of the reactions that occur in the medium, an appropriate mathematical model was developed. It permits to follow the evolution of the system over time and to calculate the final yields of reaction products. An optimization in terms of the initial contents of 2‐methylindoline and chloramine was performed. It indicated that the maximum yield of 1‐amino‐2‐methylindoline does not exceed 56%. The results show the limit of the Raschig process for the synthesis of indolic hydrazines in aqueous medium. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 575–584, 2002

Kinetics of dehydrohalogenation ofN-chloro-3-azabicyclo[3,3,0]octane in alkaline medium. NMR and ES/MS evidence of the dimerization of 3-azabicyclo[3,3,0]oct-2-ene

The formation of 3-azabicyclo[3,3,0]oct-2-ene in the course of the synthesis of N-amino-3-azabicyclo[3,3,0]octane using the Raschig process results from the following two consecutive reactions: chlorine transfer between the monochloramine and the 3-azabicyclo[3,3,0]octane followed by a dehydrohalogenation of the substituted haloamine. The kinetics of the reaction were studied by HPLC and UV as a function of temperature (15 to 44°C), and the concentrations of NaOH (0.1 to 1 M) and the chlorinated derivative (1 to 4×10−3 M). The reaction is bimolecular (k=103×10−6 M−1 s−1; ΔH0#=89 kJ mol−1; and ΔS0#=−33.6 J mol−1 K−1) and has an E2 mechanism. The spectral data of 3-azabicyclo[3,3,0]oct-2-ene were determined. IR, NMR, and ES/MS analysis show dimerization of the water-soluble monomer into a white insoluble dimer. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 129–136, 1998.

Elaboration d'alkylhydrazine par transfert de phase

This work concerns the preparation of monomethylhydrazine by Raschig's process, using phase transfer between an aqueous medium and terbutylmethylether. In a first step the influence on the yield of the ratios [NaOH]/[NH 2Cl], [MMA]/[NH 2Cl] and the amount of NH 2Cl was studied. Then the feasibility of a continuous process was checked in a pilot unit built in the laboratory. The yields at 15 °C are good and comparable with those obtained at 70 °C by synthesis according to the classical Raschig process. The byproducts resulting from degradation phenomena are located in the organic phase.

Mathematical treatment of kinetics governing the synthesis of N,N-dialkylhydrazines by the Raschig process

N,N-dialkylhyrdrazines R 2NNH 2 can be prepared by the controlled oxidation of an amine R 2NH by chloramine. The synthesis is carried out under stoichiometric conditions owing to the existence of side reactions which limit the yield. An appropriate mathematical treatment of the reaction kinetics allows complete characterization of the final state from one implicit equation and analytical expressions. The formulae established when R is the methyl group reveal the pilot parameters of the synthesis and permit study of the limiting cases.

Formation of Hydrazine from Ammonia in a Source of Electrons in a Selected Energy Range (SESER)

THE formation of hydrazine from ammonia in a gas discharge is a synthetic route which is more direct than the Raschig process used industrially1. In the Raschig process the reaction mixture for optimum yields of hydrazine consists of ammonia and sodium hypochlorite in the ratio of about 40:1. On reaction this yields a mixture of about 0.2% hydrazine in aqueous solution with sodium hypochlorite, excess ammonia, ammonium chloride and nitrogen. Conversions of ammonia to hydrazine of up to 6 weight% have been obtained in a gas discharge but the yields of hydrazine per unit energy input are then unacceptably low2. The principal reason for this, at high power input, is the electron-induced decomposition of hydrazine and its precursor and arises from the unfavourable electron energy distribution3. Typically, this is a Maxwellian distribution with a mean energy of ∼ 1 eV which produces up to five times as many electrons which can decompose hydrazine4 (energy >3.9 eV) and its precursor as those which can decompose ammonia4 (energy >4.5 eV). One way of overcoming this problem would be to use a device producing electrons with a more favourable energy distribution, that is, more electrons with energy >4.5 eV and less with energy in the region 3.9 to 4.5 eV, which can only dissociate hydrazine.

Phenol Now Made in America by German Raschig Process

Phenol Now Made in America by German Raschig Process