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Servomex delivers solutions to meet your TDI process needs
Servomex is an expert in the supply of analyzers and systems designed to meet all requirements of the TDI process, including process control, quality, and emission monitoring. Our turnkey solution for TDI gas analysis overcomes common process challenges such as gas cross-sensitivity, the highly toxic nature of the process, and detection of low levels of chlorine within the TDI product.
The synthesis of TDI is both complicated and hazardous. It starts with the nitration of toluene to dinitrotoluene, then the reaction of diaminotoluene and phosgene, proceeding to the distillation of the toluene diamine mixture, and finally the differentiation of the TDI product to produce the required useful isomers. The process combines a range of toxic, flammable, and corrosive components, including hydrogen, chlorine, and carbon monoxide.
The TDI process requires high levels of gas analysis for both process control and product purity throughout all three processes. A wide range of impurities and emissions must be accurately measured, including methane (CH4), oxygen (O2), water (H2O), carbon monoxide (CO), chlorine (Cl2), phosgene, and hydrogen chloride (HCl). This requires a highly flexible analytical solution that delivers safe and reliable measurements throughout the complex production process.
A highly flexible, high-performance analytical solution for a wide range of gases, the SERVOTOUGH SpectraExact 2500 uses Infrared and Gas Filter Correlation sensing technologies to deliver the real-time online monitoring needed in the harsh process conditions of TDI production. Fully certified for continuous measurement of flammable samples, the resilience and flexible measurement architecture of the SpectraExact 2500 meets a range of challenges, including overcoming gas cross-sensitivity, and successful detection of chlorine levels in the toxic environment.
We have a wide range of experience in supplying analytical systems for the TDI production process, delivering the accurate, reliable, and stable solutions your process needs.
Our deep applications knowledge allows our experts to advise you on the best solution for your process requirements, with gas analysis solutions to meet your specific plant conditions.
Servomex offers an extensive portfolio of accurate and reliable gas analysis technologies, providing you with the measurement technique that best suits each analysis point in your TDI production process.
All our gas analyzers are supported by a worldwide network of service personnel, delivering reliable analytical performance at optimum levels from day one, and backed by wide-ranging after-sales support products.
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Find out how we support TDI production with our range of products and solutions. This selection of resources has the information you need, ready to download now.
Our expert process solutions eliminate the need to use toxic 100% phosgene, for safer control of purity and quality
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October 2024
July 2024
Find out how our gas analysis solutions help overcome the challenges of your toluene diisocyanate process with this expert podcast. We examine the main measurement points and the key role of our SpectraExact 2500 photometric analyzer.
RJ: Hello and welcome to this Servomex podcast on the gas analysis requirements of the toluene diisocyanate process, TDI for short. My name is Rhys Jenkins and I’m the spectroscopic product manager for Servomex, for IR process products. Today I’m joined by my colleague Maria to discuss the TDI process and to focus on which Servomex products are best fitted to its measurement needs.
In particular, we will be discussing the new Servomex infrared analyser, the SpectraExact 2500, which is suitable for both gas and liquids. Hi Maria. Can you give a brief overview of who you are and your role at Servomex?
MM: Hello Rhys, and hello everyone. My name is Maria Mokosch, and I am a senior application development engineer at Servomex.
RJ: Thank you, Maria. So before we talk about Servomex analysers and solutions, can you give me a very quick overview on the TDI process itself?
MM: Sure. In a nutshell, toluene diamine (or TDA) and phosgene are combined in the presence of a solvent to produce toluene diisocyanate or TDI, which is then used to produce polyurethane. Polyurethane is used in the manufacture of a large number of products such as fibres, elastomers, foams and surface coatings, which are then used in other applications. The overall process also includes the production of phosgene and as a by-product, hydrochloric acid.
RJ: Okay, so what are the main challenges in doing gas analysis within these processes?
MM: The main challenges are that this process uses and produces components which are extremely toxic, flammable, and corrosive. These gases and liquids need to be safely sampled from the process and then analysed. Leaks and any unsafe conditions must be avoided so that site personnel are kept as safe as possible. Servomex provides analysers for a number of measurements within the overall process. Today, we are going to focus on the main gas measurements within that process: phosgene, and gases and phosgene, orthodichlorobenzene (or ODCB), moisture, and hydrochloric acid. For these gases, Servomex can provide analysers to cover quality control, process control, and emissions, and safety, at various points in the process.
RJ: So that’s a lot of different measurements. How many different analyser types would be required?
MM: Apart from oxygen, we can cover all of these measurements with the same analyser series, the SpectraExact 2500, which is a highly stable and very sensitive analyser, designed specifically for infrared process measurement in the most arduous conditions. The technology used is single-beam dual-wavelength, which is a well-known infrared technique. You have a measurement and a reference filter which allows you to remove common mode effects from the measurement, such as tools, ageing, and contamination of the cell. This leads to a highly stable measurement with a long calibration interval. For toxic processes, a long calibration interval has the advantage of reducing the servicing requirements, which then also reduces, obviously, the risk to site personnel as well as reducing the costs.
RJ: Now, phosgene was one of the gases you mentioned, and the phosgenation process that converts TDA and phosgene into the TDI is a vital part of the overall process. But phosgene is also an extremely toxic gas with very low exposure limits. To handle such a gas and to calibrate an analyser, it must be a very risky process. So, what levels of phosgene can the SpectraExact 2500 handle?
MM: Indeed, the SpectraExact 2500 was specifically designed to measure toxic, flammable, and corrosive gases in hazardous areas. The integrity of the measurement cell is vital to the measurement. We separate gas or liquid by optics and include purged volumes between measurement cell and the enclosure as optics. It is designed in such a way to ensure that toxic and corrosive gases cannot go into the analyser enclosures and build up, so they can either damage the analyser or cause toxic hazards during operation.
As you mentioned earlier, for very toxic gases such as phosgene, we must be extremely careful. Therefore, we use much-enhanced leak test specifications for the cell assembly. Using these segregation and high-integrity methods, we can measure phosgene up to 100% and to below 5 ppm with the SpectraExact 2500. Our technical centre, based in the UK, is capable of undertaking calibrations with phosgene up to 1%. Obviously, we take health and safety precautions when undertaking such a calibration.
For measurement ranges greater than 1%, a theoretical response can be derived using actual filter profiles. This so-called theoretical calibration method may also be applied to lower ranges, thus eliminating the requirement for labour-intensive toxic calibrations and minimising the potential exposure to toxic gases. In addition, we can use a surrogate calibration with a gas which absorbs at the same wavelength as phosgene. We then correct for the differing absorption characteristics. All of these methods are backed by 30 years of experience and know-how, with many analysers installed globally.
RJ: So, Maria, you’ve covered phosgene in some detail. But what are the other measurements on the TDI process that the SpectraExact 2500 can do?
MM: Throughout the TDI production process, there are many measurements with the SpectraExact 2500. After the HyCO process, we measure methane or moisture impurities in carbon monoxide, which is then used in the production of phosgene. We also measure trace carbon monoxide and hydrogen before the TDA process. In the production of phosgene, we also monitor ppm levels of moisture in the chloride feed. The SpectraExact 2500 can perform many measurements within the TDI manufacture itself, from ppm chlorine and carbon monoxide measurements, to the measurement of moisture in the solvent, orthodichlorobenzene, as well as many more. I would also like to quickly mention the Servomex OxyExact and Oxy analysers, which are used within the TDA process to measure oxygen and carbon monoxide after the HyCO process.
RJ: Well, thank you Maria. Quite a lot to go through there. Quite a detailed explanation with some interesting chemical names to trip us up as well as we go. But again, thank you for that very brief overview of the applications of the SpectraExact 2500 in the TDI process and its suitability for a wide range of gases and concentrations, especially when dealing with the highly toxic, flammable, corrosive gases.
MM: Thank you, Rhys, for the invitation and the opportunity to talk about TDI, which is one of Servomex’s star applications for the SpectraExact 2500.
RJ: Finally, I’d like to remind the listeners to either contact your local Servomex representative or go to www.servomex.com for more information. We have brochures and fliers on the TDI process and we can go into more detail on the analyser specifications. So all that remains is to say thank you for listening, and I hope you have a very good day. Bye-bye.
Ethylene Dichloride (EDC), sometimes referred to as 1,2-dichloroethane, is a vital component in the manufacture of polyvinyl chloride (PVC), the third most widely produced polymer worldwide. The production of EDC involves many intricacies, and its measurement faces many challenges.
EDC production predominantly employs two methods: direct chlorination and oxychlorination. In direct chlorination, ethylene and chlorine are reacted, producing EDC with traces of chlorine and moisture due to slight overreactions. This makes the resultant mixture corrosive, necessitating careful selection of components that come into contact with the sample.
The oxychlorination reaction is more complex, involving ethylene, oxygen, hydrogen chloride, and various chlorination products. This reaction requires meticulous control, especially of the oxygen level, to ensure maximum efficiency. Speed of response is crucial, with a typical requirement being below 30 seconds.
Post-production, the EDC undergoes a cleanup process to reduce corrosive components. This is crucial as water, combined with other corrosive or chlorinated components, can make the mixture highly corrosive.
The SERVOTOUGH Spectra Exact 2500 plays a pivotal role in EDC production, especially in measuring water in EDC. Given the hydroscopic nature of EDC, maintaining moisture levels below the corrosion point is vital. The analyzer’s design ensures that the sample cell remains separate from the electronics, preventing potential contamination from corrosive or toxic samples.
For combustion control, lasers like the Laser 3 Plus offer advantages such as rapid response and the ability to measure across the entire process. This provides a more accurate representation of what’s happening in the process, ensuring better control.
Safety is paramount in EDC production. Given the toxic and carcinogenic nature of EDC and Vinyl Chloride Monomer (VCM), it’s crucial to ensure that the sampling system is leak tight. Regular testing of the sampling system is essential to prevent any leaks, which could pose significant risks on these plants.
Moreover, the production of VCM from EDC involves thermal cracking, which uses heat to break down the bonds of EDC. This process produces vinyl chloride and HCl. The HCl is recycled and used as feed for the oxychlorination reactor. Given the toxic nature of HCl, especially when combined with water to form hydrochloric acid, it’s crucial to use the right materials for the sampling system and gas analyzer.
The production of EDC and its subsequent use in PVC manufacturing is a complex process that requires precision, control, and utmost safety. With the right tools, techniques, and safety measures in place, the industry can ensure efficient production while minimizing risks.
Toluene Diisocyanate, commonly referred to as TDI, is an organic compound with immense industrial significance. Predominantly, two of its six possible isomers are harnessed to manufacture a plethora of materials. These range from flexible polyurethane foams, which find applications in upholstery, mattresses, and automotive seats, to adhesives, sealants, and surface coatings.
The production of TDI is intricate, involving the amalgamation of various toxic, flammable, and corrosive components. These include hydrogen, chlorine, and carbon monoxide. Given the volatile nature of these components, the process necessitates a gas analyzer that is adept at continuously measuring flammable samples. Enter the SERVOTOUGH Spectra Exact 2500 – a state-of-the-art analytical solution tailored for a broad spectrum of gases.
The Spectra Exact 2500 isn’t just another gas analyzer. It offers real-time online monitoring, capable of both single and multi-component analysis. Harnessing non-dispersive IR and UV technology, it is perfectly suited for the demanding conditions of TDI production.
A pivotal step in TDI production is treating toluene diamine with phosgene. Here, the Spectra Exact 2500 plays a crucial role. It undertakes quality and process control measurements, gauging parts per million chlorine and percentage carbon monoxide amidst the phosgene backdrop. A challenge arises as carbon monoxide exhibits phosgene cross-sensitivity. However, the Spectra Exact 2500, with its advanced Gas Filter Correlation technology, ensures precise analysis of carbon monoxide, even in intricate background matrices.
Following this, the resultant TDI isomer mixture in solution undergoes further processing. The Spectra Exact 2500 meticulously monitors phosgene quality and purity, while also keeping an eye on impurities like hydrogen chloride, carbon monoxide, and moisture. It also tracks the ortho-dichlorobenzene byproduct for water and isocyanate groups. As the process progresses, phosgene and hydrogen chloride are segregated and reintroduced into the process.
Distillation is the next step, purifying the mixture. Here, the hydrogen chloride byproduct is again scrutinized for phosgene and solvent impurities. The Spectra Exact 2500’s design is noteworthy, boasting high-integrity sample cells with a helium leak test option, making it ideal for measuring toxic samples.
Finally, as the purified TDI product is readied, the Spectra Exact 2500 undertakes the vital role of measuring phosgene emissions in the stack. Its design ensures that the sample cell remains isolated from the electronics, safeguarding the analyzer from potential contamination by corrosive or toxic samples. This robustness, combined with its flexible measurement architecture, ensures it can tackle a myriad of challenges, from detecting chlorine levels to overcoming cross-sensitivity issues.
The Spectra Exact 2500 is not just an instrument; it’s a testament to Servomex’s commitment to innovation and excellence. With its unparalleled performance, it stands as a beacon of reliability in the complex and toxic environment of TDI production, reflecting Servomex’s global expertise in addressing intricate TDI application challenges.
If you’re still not convinced we can deliver what you need, then let one of our experts reassure you. Our proven technologies provide the best-fit solutions for measurements across the TDI production process – speak to us to see how we can help.