Phosgene is an essential reagent utilized in the synthesis of numerous chemicals which go to make polymers, agrochemicals, and pharmaceuticals, within other uses. What differentiates phosgene and makes phosgenation a business with excessive barriers to access is its notably toxic nature. For this reason, there is no transportation of gaseous phosgene, even though a strong variant, Bis(trichloromethyl)carbonate, higher known as triphosgene, is commercially sold and even dispatched across excessive seas.
Phosgene manufacturers are adept at managing the dangers, it poses to minimize dangers especially to employees. There is a significant body of work on secure working conditions, quickly spot even small exposures, and offer fast treatment in the rare cases when it does take place. In all sites phosgene is at once used up in the downstream phosgenation section and in no longer stored. If downstream operations are close, so is upstream manufacturing. This keeps the overall plant hold-up of the chemical to a least.
Anotable thing about the phosgene industry is the level of knowledge-sharing even between corporations that compete in the marketplace. This was enough evident ta the currently-held 13th India International Phosgene Safety Conference in Vadodara (a detailed report will follow in the next issue), which noticed overseas and Indian specialists sharing industry best practices.
One of the main worries presented at the event was the widespread use of triphosgenefor making ready numerous active pharmaceutical ingredients (APIs) and fine chemicals. India’s annual intake of triphosgene is in the range of 10-kt, all sourced from China, and the worry is that many of the learnings for safely handling and the use of phosgene has not reached triphosgene users – a vulnerability which can have deadly consequences.
Diisocyanates dominate usage
The single largest use for phosgene globally is the production of diisocyanates, of which toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI) are the two most essential. Other smaller quantity diisocyanates consist isophoronediisocyanate (IPDI), and hexamethylene diisocyanate (HMDI). Together, those four account for approximately 80% of the global phosgene requires reckoned at 14.5-mt in 2025.
Phosgene is likewise wanted for the manufacturing of numerous smaller volume monoisocyanates, however for some of these non-phosgene routes exist and amplifying more preferred. Methyl isocyanate (MIC), responsible for the horrendous Bhopal accident of 1984, is an example of a exceedingly small volume isocyanate, and is used to make numerous carbamate pesticides and herbicides.
For TDI & MDI, the phosgene-based route is right here to stay, and their manufacturers are, to no wonder, amongst the largest manufacturer (and customers) of phosgene. In India, GNFC is the main manufacturer of TDI – with plants at Bharuch (capacity: 10-ktpa) and Dahej (50-ktpa), each with its own phosgene unit. While there’s no MDI manufacturing as yet, BASF does manufacture monomeric and polymeric MDI at Dahej, from a ‘splitter’ that makes use of crude MDI imported from BASF’s overseas plants as feedstock (this doesn’t need phosgene).
Non-phosgene routes to polycarbonate (PC)
Phosgene is also one of two raw materials required to make PC (the other is bisphenol-A, BPA). While there is as yet no potential for PC in India, Deepak Chem Tech Ltd., part of the Deepak Group, is in the process of putting in place an incorporated unit with a capacity to manufacture 150-ktpa of PC. When commissioned in about 2 years, this unit will emerge as the largest phosgene manufacturing and consumption centre in India.
But globally PC is no longer a main phosgene need driver. Numerous PC manufacturers together with SABIC, Covestro, Asahi and Mitsubishi Chemical/Mitsubishi Gas Chemical have independently evolved non-phosgene PC technologies, primarily based on the trans-esterification of diphenyl carbonate (DPC) with BPA. These optional routes have received some market share nowadays.
Phosgene for fine chemicals
Today, an enormous chunk of phosgene is manufactured in India for making numerous fine chemicals in smaller volumes. These consist chloroformates (made by the reaction of phosgene with alcohols); carbonate esters such as dimethyl/diethyl carbonates (used as to make pharmaceuticals and agrochemicals); and quite a range of ketones manufactured by Friedel-Crafts acylations with phosgene. The Pharmaceuticals and Intermediates Business of Atul Ltd., for example, uses phosgene to manufacture chloroformates, isocyanates and organic ureas, that go to make numerous APIs, technical agrochemicals and speciality chemicals. Paushak Ltd., a part of the Alembic Group, claims to be the largest manufacturer of phosgene-based speciality chemicals in India, along with chloroformates, carbamoyl chlorides, carbamates, and many others. It has phosgene producing ability of 14,400-tpa, that’s being enlarged. Precisely
Excellent protection record
From a production perspective, the target at all phosgene manufacturers – in India and overseas – is on building strong tactics and protection systems that minimize the risks to the maximum volume viable. A top-notch deal of thought is going into the design of phosgene plants, its construct-up, start-up, continuous operation, and periodic maintenance. Every component of the plant – its popular design, format & siting, materials of building, piping & valve selection, instrumentation, relief devices, secondary containment, and mitigation systems – are all exactly documented and refined periodically to reflect operator experiences.
Numerous secondary technical measures are utilised to detect on leaks as soon as viable and to combat escaped phosgene. These consist, e.g., continuously operating alarm systems for monitoring room air and ambient air; systems for combating escaped phosgene by way of chemical response (e.g., steam-ammonia curtains inside the case of gaseous emissions); jacketed pipes; and whole containments for phosgene processing plants or plant units.
Thanks to all kind of, and diligent operations, the track record of safety in the global phosgene industry has enhanced. Since 2021, there was only one fatality at a plant in Hungary, but that is still one too much. Analyses of phosgene exposures globally disclose that 28% were caused by human errors and another 22% due improper decontamination of equipment for maintenance. These are being addressed by using improving training at the shop-floor stage, including a reiteration of the basics.
Progressive corporations in India have also invested in laying out clean standard operating techniques (SOPs) for routine maintenance tasks and for disposing used equipment as scrap.
Eternal vigilance is the prices to pay for staying in the phosgene business, and the industry’s current record suggests that it’s doing most things proper.
Triphosgene usage
But the phosgene industry has a vulnerability – an Achilles Heel, if you will. For Numerous of the smaller volume fine chemicals manufactured in multi-purpose centers, an option to phosgene that has come to be favoured (in India and China) is triphosgene. Being strong, it’s convenient for small-scale phosgenations, and is broadly used in research, development, and industry for the manufacturing of APIs, agrochemicals, and fine chemicals.
But triphosgene too is poisonous and branding it as “secure phosgene” or “more secure phosgene” is misleading. While secure managing is feasible so long as the properties and chemical reactivity of this compound are understood and considered, its solid-state ought to no longer lead to the misconception that there is no risk. The toxicity profiles of phosgene and triphosgene also differ, with the latter having a biphasic mortality pattern – an acute poisonous impact and a second mortality height after 11-14 days. While badges broadly used to discover phosgene exposure work for triphosgene as well, they may be only calibrated for the former.
Not all triphosgene from China is the same; they come with variable quality tough to characterize with the aid of simple analytical strategies. Much of the supplies to Indian consumers is via trade channels, and frequently users are uncertain of the origin of the chemical that has possibly withstood weeks of tour via ship and road under uncontrolled conditions of temperature.
Ambit of law
Though triphosgene use is presently unregulated in India, speakers at the conference had been clear that it does come under the ambit of the Chemical Weapons Convention, an international treaty that goals to alter the manufacture, trade and use of ‘dual cause’ chemicals. Compliance with the convention demand registration and reporting of utilization with the concerned authorities on an everyday basis.
With triphosgene use becoming more regulated, it is crucial to make sure that concepts related toits use will be an extended version of that for phosgene. A beginning could be made if users of triphosgene participate in industry forums that share worldwide best practices for phosgene!
