Phosgenation Process Research Articles

How To Get Isocyanate?

Isocyanate, a pivotal chemical intermediate to synthesize polyurethane with widespread applications in household appliances, automobiles, and construction, is predominantly produced via the phosgene process, which currently holds a paramount status in industrial isocyanate production. Nonetheless, concerns arise from the toxicity of phosgene and the corrosiveness of hydrogen chloride, posing safety hazards. The synthesis of isocyanate using nonphosgene methods represents a promising avenue for future development. This article primarily focuses on the nonphosgene approach, which involves the formation of carbamate through the reaction of nitro-amino compounds with carbon monoxide, dimethyl carbonate, and urea, among other reagents, subsequently leading to the thermal decomposition of carbamate to get isocyanate. This paper emphasizes the progress in catalyst development during the carbamate decomposition process. Single-component metal catalysts, particularly zinc, exhibit advantages such as high activity, cost-effectiveness, and compatibility with a wide range of substrates. Composite catalysts enhance isocyanate yield by introducing a second component to adjust the active metal composition. The central research direction aims to optimize catalyst adaptation to reaction conditions, including temperature, pressure, time, and solvent, to achieve high raw material conversion and product yield.

A novel and green synthesis of methylcyclohexane diisocyanate: Reaction properties, deactivation and regeneration of Rh/γ-Al2O3 catalyst in benzene ring selective hydrogenation

Methylcyclohexane diisocyanate (HTDI) is the core raw material for the synthesis of high-grade polyurethane. Aiming at the problems existing environmental pollution and safety risks in the phosgene process, a novel and green synthesis route of HTDI was proposed. We studied the catalytic hydrogenation of dimethyl toluene dicarbamate (TDC) benzene ring to methyl cyclohexyldicarbamate (HTDC) in this novel route. The effects of metal active components, supports and metal Rh loadings on the catalytic performance were investigated. It was found that the supported Rh/γ-Al2O3 catalyst had excellent catalytic activity and selectivity. The yield of HTDC was close to 100 % at 100 °C under 3 MPa hydrogen pressure. However, the catalyst was deactivated seriously after the reaction. The organic matter adsorbed on the catalyst surface and covered the active metal was the main reason for the catalyst deactivation. Fortunately, the deactivated catalyst could be regenerated by solvent washing and high temperature calcination.

Simulation and optimization of the thermally coupled reactive distillation column for producing toluene diisocynate

AbstractToluene diisocyanate is an important chemical intermediate prepared by phosgenation reaction with two steps named cold and thermal phosgenation, respectively. The thermal phosgenation reaction is a complex reactive distillation process with high energy consumption and multiple targets of reaction and separation, so it is of great significance to optimize the step. The reactive distillation model of the thermal phosgenation was established for an industrial installation by aspen plus, and the effects of the different parameters of temperatures, residence times, etc., were investigated firstly; then a thermally coupled reactive distillation column was presented to perform the thermal phosgenation process, and the optimal operation and configuration parameters were obtained by simulation. The results showed that the proposed process can save the heat and cold energy with 7.29% and 32.78%, respectively, and reduce the total annual cost by about 17.11%.

Thermolysis and analysis of TDI char by supercritical methanol using TGA, DSC, IR and SEM

TDI's synthetic plant generates about 5 mass % of tar by phosgenation process, which has been currently a bottleneck needed to be broken through for the worldwide TDI companies. At present, the reduction fraction of TDI tar is up to 48% relative to the mass of tar and renders the residue of solid crust known as TDI char. In this study, a suasive and effective reduction method has been found, the supercritical methanol is executed to depolymerize the TDI char, and in short, the char can be readily methanolyzed at supercritical state of methanol. With the outstanding depolymerization capability than various existing approaches, the destruction fraction can achieve 81 mass % at supercritical point. A best value as high as 95 mass % is first discovered at 270 °C, exceeding the efficiency at supercritical state. Characterizations of the intrinsic properties of raw char and char remnant after methanolysis have been implemented by TGA, DSC, FT-IR and SEM-EDS. For industrial applications, the diverse methodologies for recovering TDI or related components by alkaline hydrolysis, distillation, vacuum distillation and thermolysis are also discussed and compared with methanolysis in order to recognize the optimal abatement technique.

Green non<italic>-</italic>phosgene process for manufacturing isocyanates

Isocyanates are the core feed-stocks for the synthesis of polyurethane. At present, the industrial production of isocyanates mainly bases on the phosgene process, which is extremely toxic and yields large amounts of corrosive HCl. Non - phosgene process for isocyanates production is always one of the most important missions for green chemistry and related contents, and its implementation will bring about the revolutionary change for the polyurethane industry. This review focuses on the development of two-step route for aliphatic isocyanates in our lab as well as the existing problems, i.e., catalytic synthesis of N- substituted carbamates using various carbonyl sources, then thermal cracking target on isocyanate, especially for our strategy to the formation and depolymerization of the polymer derived from the thermal cracking process. Based on our research, a three-step non - phosgene process for isocyanate production is proposed, which provides a promissing technology for industrial application.

Industrialization and Expansion of Green Sustainable Chemical Process: A Review of Non-phosgene Polycarbonate from CO2

The world’s first non-phosgene polycarbonate process from CO2 has been developed and industrialized by Asahi Kasei Corporation (Japan). Hitherto, all polycarbonates (PCs) have been produced using CO as a raw material. Among them, most PCs have been produced by so-called the “phosgene process” using highly toxic phosgene (COCl2) and large amounts of solvents (probable human carcinogen CH2Cl2 and water). The phosgene process has many environmental and safety problems. However, technological barriers have hindered realizing the non-phosgene PC process. The Asahi Kasei Process has not only solved the problems of the phosgene process but also contributed to sustainability (reduction of CO2 emission, materials saving, and energy saving). High-quality PC and high-purity monoethylene glycol (MEG) are produced in high yields, respectively, without waste and wastewater, starting from CO2, ethylene oxide (EO), and bisphenol A (BPA). In the monomer (diphenyl carbonate: DPC) production process, innovative reactive dis...

The Heat Is On Isocyanates In Paint

Love them or hate them, isocyanates are hard to beat. They make durable vehicle finishes that give new cars a shine that lasts for years. They also make industrial paints that are chemical resistant, flexible, and impervious to breakdown from the sun’s ultraviolet rays. When reacted with polyester or acrylic resins, isocyanates cross-link to form a polyurethane. In coatings systems that also include pigments and other additives, polyurethanes are the industry benchmark for high performance. But isocyanates have a dark side too. Reactive isocyanate oligomers are pulmonary and skin sensitizers until they fully cure, so they must be handled with care. Getting the most out of them often means that newly painted cars must cure in energy-hungry ovens. In addition, the oligomers are typically made with petro­chemical raw materials in a hazardous phosgenation process that can hardly be called green. But coating materials suppliers are moving to put a kinder ...

ChemInform Abstract: Fixation of CO2 into Cyclic Carbonates Catalyzed by Ionic Liquids: A Multi‐Scale Approach

AbstractReview: [117 refs.

Simple and effective method for producing [11C]phosgene using an environmental CCl4 gas detection tube

Carbon-11-labeled phosgene is an important labeling precursor for PET molecular probes. Despite the usefulness of [(11)C]phosgene, some difficulties, especially in the formation of [(11)C]phosgene process from [(11)C]CCl(4), hamper its use. The present article shows a simple preparation method for [(11)C]phosgene. [(11)C]CCl(4) was obtained using the conventional method by passing a mixture of [(11)C]CH(4) and Cl(2) through a heated quartz tube. The [(11)C]CCl(4) was transformed to [(11)C]phosgene simply by passing through a pretreatment tube of a Kitagawa gas detection system for the working-environmental CCl(4) concentration measurement at room temperature with a flow rate of 50 ml/min. This tube successfully transformed [(11)C]CCl(4) to [(11)C]phosgene at room temperature. [(11)C]Phosgene was obtained at nearly 80% radiochemical yield (EOB) in a short synthesis time with high reproducibility. A high yield and reliable [(11)C]phosgene production method using a gas detector tube system for working-environmental CCl(4) concentration measurement was developed.

Green and Sustainable Chemistry in Practice: Development and Industrialization of a Novel Process for Polycarbonate Production from CO2 without Using Phosgene

This review focuses on the world’s first process succeeded in development and industrialization by Asahi Kasei Corp. for producing an aromatic polycarbonate (PC) using CO2 as starting material.1 The carbonate group of PC links directly to the residual aromatic groups of the bisphenol. Until Asahi Kasei’s new process is revealed, all of carbonate groups of PC in the world were derived from CO as starting material. Furthermore, more than about 90% of PC has been produced by so-called “phosgene process”, and the PC contains Cl-impurities. It needs to use not only highly toxic and corrosive phosgene made from CO and Cl2 as a monomer, but also very large amounts of CH2Cl2 and water, and needs to clean a large amount of waste water. The new process enables high-yield production of the two products, Cl-free and high-quality PC and high-purity monoethylene glycol (MEG), starting from ethylene oxide (EO), by-produced CO2 and bisphenol-A. PC produced by the new process has many excellent properties compared with conventional PCs. The new process not only overcomes drawbacks in the conventional processes, but also achieves resource and energy conservation. The reduction of CO2 emissions (0.173 t/PC 1 t) is also achieved in the new process, because all CO2 is utilized as the component consisting main chains of the products. The newly constructed commercial plant of Chimei-Asahi Corp. (Taiwan), a joint venture between Asahi Kasei Corp. and Chi Mei Corp., has been successfully operating at full-production since June 2002. The initial capacity (PC:50,000 t/y) is now increased to 150,000 t/y. A typical example of the Green and Sustainable Chemistry (GSC) contributing to society and mankind has been realized.

Phosgene-free approaches to catalytic synthesis of diphenyl carbonate and its intermediates

Diphenyl carbonate (DPC) is considered as a substitution for phosgene to synthesize polycarbonate resins. Conventional production of DPC involves reactions of phosgene and phenol. However, the phosgene process has drawbacks such as environmental and safety problems associated with using highly toxic phosgene as the reagent, which results in the formation of chlorine salts, and copious amounts of methylene chloride as the solvent. For these reasons, environmentally friendly processes for DPC production without using phosgene have been proposed and developed in the past decades. So far, the most promising alternatives appear to be the transesterification of dimethyl carbonate (DMC) and phenol, the direct oxidative carbonylation of phenol, and transesterification of dialkyl oxalates and phenol. This paper attempts to review recent literature concerning process design and catalytic chemistry for these phosgene-free approaches. The advantages and disadvantages are discussed for each reaction. Strategies to overcome potential problems are provided. The perspectives to improve catalytic efficiency of phosgene-free process are proposed.

A novel non-phosgene polycarbonate production process using by-product CO2as starting material

Asahi Kasei Corp. has succeeded in the development of a new green process for producing an aromatic polycarbonate based on bisphenol-A (hereafter usually abbreviated as PC) without using phosgene and methylene chloride. The new PC production process is the world's first to use carbon dioxide (CO2) as a starting material. Until Asahi Kasei's new process was revealed, all of the PC in the world has been produced using carbon monoxide (CO) made from cokes or lower hydrocarbons and oxygen as a starting material. Furthermore, more than about 93% of the PC has been produced by the so-called “phosgene process” which uses phosgene made from CO and chlorine (Cl2) as a monomer. However, the phosgene process inherently involves a number of environmental and economic shortcomings in addition to the high toxicity of phosgene itself and the high carcinogenic probability of methylene chloride itself. Asahi Kasei's new process enables high-yield production of the two important products for our citizens’ lives, high-quality PC and high-purity monoethylene glycol (MEG), starting from ethylene oxide (EO), carbon dioxide (CO2) and bisphenol-A. This new technology not only overcomes the environmental and economic problems existing in the phosgene process, but also achieves resource conservation, and energy conservation. Furthermore, the new process contributes to the earth environment by the reduction of CO2 emissions (173 tons per thousand tons of product PC). Commercial application of the new process was carried out at the 50,000 ton year−1 PC plant of Chimei-Asahi Corporation, a joint venture between Asahi Kasei Corporation and Chi Mei Corporation, which was newly constructed in Taiwan and has been successfully operating since June 2002. In recognition of the outstanding advance in ecological and sustainable performance that this technology represents, Japan's Minister of Economy, Trade and Industry conferred the Green and Sustainable Chemistry Award of 2003 on us. Furthermore, the Chairman of Japan Chemical Industry Association also conferred the 35th Japan Chemical Industry Association Award of 2003 on us as an outstanding chemical technology. An outline of this new non-phosgene PC process embodying the spirit of Green and Sustainable Chemistry is given here.

Developments in the production and application of dimethylcarbonate

Manufacturing methods of dimethylcarbonate (DMC) are examined, in particular those which have been industrially exploited. Apart from the old phosgenation process, two processes based on the oxy-carbonylation of methanol went on stream: the copper chloride catalysed, one step liquid-phase process, by EniChem, and the palladium catalysed, two steps gas-phase process, via methylnitrite, by UBE. Two further technologies are attractive for full-scale development in the next future: the gas-phase direct methanol oxy-carbonylation and the alkylenecarbonate transesterification process. In the last few years, the use of DMC in the chemical industry has considerably grown, due to its chemical properties and its non-toxicity, an outstanding example being represented by the non-phosgene production of aromatic polycarbonates. Other very promising fields of large scale DMC application are as solvent and as oxygenate in reformulated fuels.

Interfacial synthesis and characterization of random and segmented block bisphenol A–tetrabromobisphenol A copolycarbonates

AbstractThe chain sequence architecture of bisphenol A–tetrabromobisphenol A copolycarbonates depends on the process employed to prepare them. An interfacial process involving a single‐step phosgenation produces a segmented block copolymer, contrary to previous assumptions. An interfacial two‐step phosgenation process allows the preparation of random copolycarbonates. In each process the control of the pH of the acqueous phase of the two phase reaction mixture is required to achieve complete comonomer conversion to copolymer and to obtain the desired sequence architecture. The chain sequence architecture of these copolycarbonates can be estimated by examination of their Fourier transform infrared spectra. The relative bandwidth of the carbonate stretching band is roughly proportional to the copolycarbonate number average sequence length, allowing the facile distinction between block and random copolymers. The number average sequence lengths of these copolycarbonates were quantified by carbon‐13 NMR spectroscopy. These analyses showed that the one‐step phosgenation process yields segmented block copolycarbonates having number average sequence lengths from about 4 to 9, and the two‐step phosgenation process produces random copolycarbonates having sequence lengths from 1.6 to 2. The distribution of the aromatic carbon triads of these random copolymers shows them to have an alternate‐segmented block architecture, which is consistent with the synthesis conditions, rather than a statistically random distribution of comonomer segments. Dynamic mechanical analysis of two of these copolycarbonates shows a dependence of their low temperature secondary transitions on the copolymer sequence structure. A segmented block copolycarbonate, having a number average sequence length of about 4, displays two distinct peaks in its tan δ curve at temperatures corresponding to those transitions observed in the respective homopolymers. The tan δ curve of a random copolycarbonate shows a single low temperature secondary transition midway between those of the homopolymer. © 1994 John Wiley & Sons, Inc.

The interfacial polycondensation of tetrabromobisphenol‐A polycarbonate. I. Model reaction and mechanism studies

Abstract2,2′,6,6′‐Tetrabromobisphenol‐A (TBBPA), a sterically hindered bisphenol, is known to give only low‐molecular‐weight polymers using the interfacial phosgenation process. The low reactivity is attributed to the bulkiness and electron‐withdrawing character of bromine substituents at the ortho positions. From the formation of carbamate products in model compound (2,4,6‐tribromophenyl chloroformate, TBPC) reactions with trialkylamines, the trialkylamine catalyst was found to act as a terminator by the degradation of the chloroformate‐trialkylamine complex. The generation of carbamate occurs through the decomposition of the acyl ammonium salt proceeding via nucleophilic displacement by Cl− at the carbon attached to the positive nitrogen center. The relative catalytic abilities of trialkylamines and pyridine derivatives were determined in the homogeneous (dichloromethane) and interfacial (dichloromethane/water) systems. From the results of model reactions with TBPC and sodium tribromophenolate, 4‐dimethylaminopyridine (DMAP) was found to be the best catalyst.

On the mechanism of isocyanate preparation by the phosgenation reaction

A new mechanism of the transformation of amine hydrochlorides into isocyanates during the phosgenation process was proposed on the basis of radioisotope exchange between p,p'-diamino-1,2-diphenylethane dihydrochloride (36Cl) and phosgene. The reaction proceeds through a transition complex of amine hydrochloride and phosgene, formed on the surface of the hydrochloride crystals.