We provide trusted solutions for ethylene dichloride production

EDC podcast transcript

KG: Hello. Good morning, good afternoon, and good evening. Welcome to another Servomex podcast. Today we will be discussing ethylene dichloride – EDC, sometimes also referred to as the 1,2-dichloroethane process – the description of the process, the applications in this process, and what are the things that we should consider in terms of the measurement challenges.

My name is Karen Gargallo, I am the application manager based in the UK Technical Centre. The application team is responsible for helping our customers develop solutions for their application challenges, process control, safety and so on. I’m joined today by two of my colleagues who are the experts in this EDC process.

MinWoo Lim is the application development engineer in the Asia Pacific region, based in South Korea, and Stephen Firth is business development manager, based in the UK Technical Centre. So, Steven?

SF: Hello, yes, I’m business development manager – I cover mainly Europe and Asia, in this particular iteration. I’ve been with Servomex a little over 25 years. I did start off in applications, infrared applications, working on infrared product range, but I’ve since diversified into oxygen and sampling systems over the remaining few years.

KG: Thanks, Stephen. I think your background on sample system and science, especially in this process will be very beneficial in our discussion today. MinWoo?

MWL:  Hello, I’m Mr. Lim, MinWoo. Based in Asia Pacific and China application support. I work on their application support, as their application inquiries, in Asia Pacific and China also, researching over the market in Asia. Also, considering what the Asian market is, what is the increasing market in Asia, working every time.

KG: Okay, thanks MinWoo. I do urge you, I think, to listen to podcasts related to vinyl chloride monomer process, which is already available on our website, EDC and VCM processes go hand in hand in the production of PVC or polyvinyl chloride, which is the third-most widely produced polymer worldwide.

The advantage, of course, of PVC is that it is very chemically resistant and a versatile component that it is used in the manufacture of construction materials and the PPE, such as medical gloves, overshoes, and also in the construction of sporting venues, you know, the chairs that you can see in sporting venues.

So now that we’ve seen the importance of PVC, in the VCM podcast our colleagues, Maria and Matt, explain, of course, the importance of VCM and have touched on EDC. So, MinWoo, maybe give us some details please on how EDC is actually produced.

MWL: Yeah, EDC production is that almost plant using to chlorination reactor and oxy chlorination reactor. Chlorination reactor, using the chlorine and ethylene, combine it in the reactor and produce the EDC. Oxy chlorination using ethylene and oxygen and HCl, three components combine in reactor and produce the EDC also. And produce the crude EDC in the chlorination reactor and oxy chlorination reactor, and go to the EDC clean-up fractionator for the production of pure EDC. EDC clean-up fractionator is used to remove the light ends with caustic scrubber and heavy ends also. After clean-up fractionator, pure EDC goes to the pyrolysis for VCM production. Pyrolysis is production of the VCM and go to the quenching system and HCL splitter and VCM clean up fractionator for the purification of VCM. After purification of VCM, go to the VCM storage tank. All of the VCM production, this plant have five major plant for direct chlorination, oxy chlorination, purification of EDC, thermal cracking of EDC, and purification of VCM.

KG: Okay, so you’ve mentioned that there are two main methods on how EDC is produced: direct chlorination and oxychlorination.

Looking at the components that are required, and also produced in this to reactors, I think for Steven is that, of course ,reactors, you know, high-pressure obviously, high-temperature, so some conditioning is needed. What considerations do we think about in the reactor stages of this process?

SF: Okay, yeah. So, basically, there are two reactors on most EDC plants. There’s the simple chlorination reaction, which is where ethylene and chlorine are reacted together. They’re usually quite dry, so the initial measurements are straightforward. The sample, the EDC that’s produced, also has a little bit of chlorine and a little bit of moisture due to a little bit of overreaction that you always get. And that means it’s quite a corrosive mixture, so you’ve got to be careful what components you put into contact with the sample. It’s not unusual to use Monel or Hastelloy as part of the sampling system. And then, rather than using Viton O-rings, you’d either use PTFE or specialist Chemraz-type O-rings to keep everything there.

The oxychlorination reaction is a much more brutal place, basically ethylene oxygen, hydrogen chloride, lots of chlorination products. And there, it’s even more important to use the correct materials for your sampling system and for your gas analyzer as well. So they’re the two major issues.

Further down, when you clean up your EDC, that’s not too bad, but again, at the other side of the pyrolysis furnace, again, quite a lot of corrosive products.

The other thing to bear in mind is the fact that, as Karen has mentioned, the EDC and the VCM are highly toxic, and highly carcinogenic, so it’s really important to ensure that the sampling system is leak-tight, and the testing of the sampling system, the testing is complete, so that there are no leaks effectively, which is clearly an unwanted issue on these sorts of plants.

KG: Thanks Stephen. So, with the chlorination reactor and oxychlorination reactor, of course, for process control, reactor efficiency, we need to make process control measurements. You mentioned, of course, ethylene and chlorine are needed as inlet components to the reactor. So most likely measurements are needed for those.

And, in addition, for the oxychlorination reactor, you have ethylene, oxygen, and also HCl. But I know with chlorination reactions, and in addition to the corrosive nature, we also, of course have flammables that are present and also produced in the reactors. What other measurements, apart from process control, should we also consider when flammable samples are present?

MWL: The oxygen measurement is critical in the chlorination reaction and oxy chlorination reactor also. There is an efficiency drop if too little O₂ is present, but too much O₂ can create an explosive mixture in the reactor. For the maximum process safety, multiple OxyExact process O₂ analyzers, in the safety voting system, are used.

KG: I think it’s a very good point you mentioned about safety, and the requirement of a voting system to make chlorination or other oxidation-type reactions safe and efficient. With the nature of the oxygen measurement, what considerations in terms of the technique, and also the analyzers, must we think about, and of course our customers think about for this very critical application?

MWL: Yes, so we need to consider the material, because the chlorination is using chlorine. If water and chlorine combine it produces HCl, and HCl is critical to the 316SS material critical impact to hydrogen chlorination. We consider and recommend the Hastelloy pipework in the chlorination reactor. If the customer is using the OxyExact analyzer, we recommend the Hastelloy pipework.

KG: Do you have anything to add, Stephen, on other considerations for the analyzer with safety applications?

SF: The chlorination reaction is relatively straightforward. The oxychlorination is really, really carefully controlled. That’s the one where they put the two-out-of-three voting system. The oxygen level needs to be controlled to a very small range, effectively, to get maximum efficiency. The other thing they need at this particular point is fast response. It’s not unusual to be asked for sampling systems or an analyzer measurement for oxygen of below 30 seconds, is quite a common requirement on this.

So, the actual analyzer needs to respond quickly, but the sampling system itself needs to develop the sample to the analyzer at a rapid rate. It’s also important that the sampling systems are totally independent, so there’s no single point of failure within them. You tend to find that there are three totally separate sampling systems for the three oxygen analyzers, and then any other analyzers – usually the infrareds for the ethylene or the UV for the chlorine – are totally separate as well. But the three oxygens are the key ones on this particular point.

But yeah. Speed of response, materials of construction are really critical for this particular application.

KG: Good. So we’ve covered the oxygen for safety and also for process control. Based on our discussions so far, in addition to the oxygens, there are also infrared and UV measurements – of course the UV is for the chlorine – we have the ethylene.

Apart from gas phase measurements with the presence of corrosive components, I would think, of course, that water’s probably another important measurement that we have to consider, because water with anything corrosive or chlorinated actually makes it highly corrosive. So, the EDC cleanup section, which you have both mentioned, most likely reduces the chances of corrosives in the process.

But with regard to the measurements in the section, what are the measurements or the analysis that we have to consider?

MWL: Yeah. The problem customers face in EDC application is the corrosiveness, therefore Hastelloy material is recommended for the place where the sample flows. This process requirement to measure is “water in EDC” process. This means that basically, in the pure EDC process, even after they’re removing the moisture from the EDC, a similar amount of material, water, may generally remain. It usually contains up to 2-5 ppm H₂O in this process. H₂O and EDC can cause corrosion of the 316SS pipe. And so monitoring of the H₂O in EDC is required. The SpectraExact 2500 is optimized for the H₂O in EDC application, and is installed on many sites. Also, the 2500 can choose the Hastelloy pipe work material option.

KG: So, you’ve mentioned the requirement to measure water in EDC, and also the use of the SERVERTOUGH SpectraExact 2,500. I want to, if we can, look into a bit more detail on why the 2500 is ideal for this important measurement in the process. You mention, of course, the possibility of choosing either Monel or Hastelloy, but are there other advantages of the SpectraExact for such a, such a measurement? Maybe Steven can add something?

SF: Yeah, the water in EDC measurement is a liquid measurement. You have your sample coming in at pressure, and the idea, as MinWoo has mentioned, is to minimize the amount of moisture in the sample. It is usually measured as a trend; they’re not really interested in the particular value. They’re just interested in maintaining the level below, effectively, the corrosion point.

The big advantage from a 2500’s point of view is the sample cell is separate from the electronics, so we can put a highly flammable liquid through the sample cell and still maintain safety by having a separate cell. We’re also able to monitor the temperature of the liquid and provide sample temperature compensation, because the actual reading varies with temperature. By being able to provide that compensation, we ensure that everything’s taken at a constant temperature, so we get a constant output.

KG: Thank you, Steven. And with gas phase measurements, the calibration, I would think, is much more straightforward. I’ve also, of course, talked to customers that would question how the calibration of a liquid phase analyzer would differ from a gas phase analyzer. And, of course, the challenges of doing a liquid phase calibration. Can you maybe give us a bit more background on how the customer would calibrate a water in EDC analyzer?

SF: Calibration is obviously really important for a gas phase system, and it’s relatively straightforward. You have your zero gas, your span gas, and you can introduce these, in turn, into the sample cell, and it’s relatively straightforward. With a liquid it’s a little more complicated.

The zero is not too bad from the point of view… the zero is basically dry EDC, and Servomex can supply calibration vessels. You can have your EDC from Merck, or one of the normal suppliers, and dry that with a molecular sieve, and that will give you a really good zero. The Servomex sampling systems are designed such that we can use gas pressure to force the dry liquid through the sample system, and then give you your zero.

The way to do the span is to make use of the cross-interference of the water to carbon dioxide. And then we can use a gas bottle of carbon dioxide – it’s normally around the 8% level – to give you the equivalent of a 50 ppm moisture EDC, and this makes the calibration relatively straightforward. So  you use the liquid to give you the zero point and then, while the liquid is still in the cell, you add in the CO₂ through the, normally, the End Bosses which are normally purged for safety, and in this case, we’re just going to use them briefly for the calibration. And that gives you your span point, making sure that you don’t need to use water and EDC.

The problem with EDC is it’s very hydroscopic. So even if you make up a sample of 50 ppm in the lab, by the time you get that to the actual analyzer, it’s liable to be 60, 70, 80 ppm, and not a good way of doing the calibration.

So the use of zero EDC, the dry EDC for your zero, and then the CO₂ surrogate for the span makes the calibration much more straightforward and much easier for the site to make use of.

KG: Yeah, very good point, Steven. I know that some sites, of course, are not too keen on using laboratory techniques, like [indistinct] hydrators, which they have used in the past and they have to take multiple grab samples until they get stable measurements that are representative of the water in the sample. So actually having surrogate [indistinct] calibration, you see a less hazardous component such as CO₂ is a big advantage to our customers when they need to measure water in EDC in this process.

So, now that we have cleaned and produced the EDC products, what then follows is what we then do with our products. The main usage of EDC is in the production of vinyl chloride monomer, or VCM, which is then a precursor of course, to the production of polyvinyl chloride, or PVC. I think it’s also worth just discussing how VCM is made, because the production of HCl in the VCM process is actually recycled and also used as the HCl feed to the oxychlorination reactor.

So, we now have the EDC, what is then the next station to process so that we can make the VCM? I think MinWoo, you mentioned earlier something with regards to obviously cracking the EDC to get the VCM. Can you give us a bit more information about the process, please, and the important measurements we have to do?

MWL: If this plant is for production of pure EDC, this plant requires the VCM production through pyrolysis, and pyrolysis activation about the thermal cracking of the EDC. EDC is cracking to VCM and HCl production. This process is… go to quenching and HCl splitter and VCM fractionator process, passing it for purification of VCM. And we can get the pure VCM material. And this pure VCM material can use the PVC production. This pyrolysis in the plant is very important in the VCM production. This pyrosis is a process requiring the combustion efficiency measurement, and this will be using the FluegasExact 2700 for the combustion efficiency check, and also we can use the Laser 3 Plus Combustion O₂ and Combustion CO measurement.

KG: Okay, so I think for our listeners, with the term thermal cracking, that means of course we use heat to crack the bonds of the EDC, so then you get more useful products for further down in the process. I think we mentioned, of course, we produced from the pyrolysis reaction and thermal cracking of EDC, vinyl chloride, which is of course needed for the production of PVC and HCl. So, again, chlorinated components are present in the process.

The FluegasExact, of course, uses Zirconia and also the combustible measurement, but some customers also require something that gives them faster response. I’ve seen customers looking for alternatives, and one of them is the leases. Why do you think, Steven, that some customers would, say, opt for the Laser 3 Plus, which can be an in situ analyzer, over, say, the FluegasExact?

SF: There are a couple of reasons. Depending on the size of the furnace, the laser will go across the process. Firstly, it basically reacts at the speed of light, so the reaction time for a laser is usually a few seconds, compared to a typical Zirconia of 20 to 30 seconds, something like that, so you’re going to get a faster speed of response, that’s the first thing you’re going to get.

The second thing is because you’re going across the process, you get a measurement that is slightly different, but goes across all of that process. It gives you more accurate measurement of the oxygen and what’s happening in the process and enables more control of the actual process.

Perhaps more critically, the CO measurement you get from a laser is a pure CO measurement. So, for safety, especially with natural gas feeds and hydrogen feeds, being able to measure the CO independent of any other flammable gas is really important, because it’s the first sign of runaway in combustion and that’s the first sign of a potential explosion, And there’s been a number of those over the years where the CO has run away and then exploded, so CO becomes really important.

And also, the advantage of the Servomex CO laser is that you can do a CO and methane measurement – so you get a CO measurement and the methane measurement in the same unit. Now the methane measurements are really only used on start-up, when you want to light the furnace – you put, usually, natural gas into the furnace and light it. If there’s a failure to light, then the furnace fills with natural gas, which is obviously undesirable. And the laser will give you a warning that the methane level is increasing significantly and very quickly, and is an additional safety requirement. So that’s why people tend to be looking at lasers in place of the 2700s for the combustion control.

KG: Ah, thanks to you. I think it’s a very good point that with combustion-type processes, pyrolysis, thermal cracking, it’s just not the control that we have to consider, but also of course, safety, especially when you have methane in the natural gas feed and, of course, the combination with any leakage in the furnace can cause a dangerous condition. So again, control and safety are very important in a combustion control process.

So now we have the vinyl chloride and the HCL. If we talk about HCl, the acid hydrochloric acid, or even hydrogen chloride gas, it sounds dangerous, toxic. We need, of course, to make this important measurement, so again, what consideration with HCl do we have to think about?

SF: Basically, as MinWoo has pointed out, the EDC is cracked to produce vinyl chloride in HCl. Now, the hydrogen chloride doesn’t want to be emitted, but it is recycled into the oxychlorinator, so it’s typical to put a simple hydrogen chloride measurement on the process line.

Surprisingly, HCl is relatively straightforward to measure. The only slightly difficult thing about it is, in combination with water, you get hydrochloric acid, which is quite an aggressive, corrosive mixture. So, from that point of view, it is all about the materials of construction and the fact that the 2500 can keep that toxic mixture away from the electronics, so that prevents any issues with the gas leaking out into the electronics and causing a problem.

The other thing on the 2500s is that we’re able to purge the areas around the windows to keep them clear of any leakage gas, whether its flammable or toxic, and it means that that’s swept away and prevents any buildups, so you don’t get a buildup of flammable gas, which could be an issue from an explosion point of view, or toxic gas, which could be an issue from a service point of view. So that’s quite an important safety precaution that’s built into the Servomex 2500 to keep the service engineers, the maintenance engineers in good shape.

So the HCL goes one way, and then the VCM, which is highly carcinogenic and toxic goes the other way. Again, everything is sealed, so that’s really important, to keep the sampling system leak-tight. And then that will be either stored or it will be used to produce PVC directly, depending on what’s happening.

VCM, apart from its wonderful properties of being highly toxic, is explosive. So it’s really important to use the traditional oxygen inerting systems within that part of the plant to ensure that the oxygen level is maintained at a relatively low level, typically four or five percent is what they want to do, to prevent any explosions within the VCM production line.

KG: Thanks, Steven, this is a good point, on the design of the SpectraExact, of course, not just for this process, but any process where you have toxic or flammables, the design of the cell is deliberate, so that for any reason, window breakage or whatever, that the hazardous nature of the sample will not of course, affect on-site personnel or service engineers and so on.

We’ve discussed the safety aspect in the inerting in the storage tanks for VCM, because it’s all so flammable that an oxygen measurement is needed. As with any safety application, making sure that the oxygen is low, or low enough to not constitute an explosive, mixture is extremely important. With the levels of oxygen that we need, which products would be suitable for such an important safety measurement? MinWoo?

MWL: Yeah, for the safety reason, we can recommend the SERVOTOUGH [OxyExact] 2200, because the SERVOTOUGH 2200 can use the voting system. Voting system means that customer installs dual products. SERVOTOUGH 2200 can install to one control unit and six, or three, or two transmitter units installed. It is means that if one transmitter has a fault, the customer can use another transmitter unit. But, if customer uses the Oxy 1900, and the Oxy 1900 [has a] fault, they cannot measure the oxygen level in the process. If suddenly increase, the O₂ level, without O₂ measurement, we have a high flammable risk. Therefore, we recommend SERVOTOUGH 2200 for the safety reason. But customers normally use the Oxy 1900 because of cost impact. But, every time, we meet the customer and recommend SERVOTOUGH 2200. All of the Sales team, CSR team also, can recommend to customer for safety reason the SERVOTOUGH 2200, because of voting system.

KG: Thank you, MinWoo. So, you mentioned a couple of Servomex Paramagnetic products, the OxyExact 2200 and the Oxy 1900. We started a discussion on how we make EDC, considerations in the process, the important measurements and Steven, of course, his background in sampling systems, not just, of course, the analyzers, but also the sampling systems critical in the EDC/VCM process.

Hopefully we’ve given you some information on why it is important to produce EDC and VCM, why we need to make important measurements in the process for control, safety, and quality measurements. And I want to thank MinWoo for his contribution to this podcast, and of course, Steven,

MWL: Thank you for inviting me to the today’s podcast. Today was a very beneficial time for me, so thanks, Steven, and thanks Karen.

SF: Yeah, thank you for listening to this podcast, and I hope you found it useful. Thank you.

KG: Thank you from me, Karen, for listening to the podcast and please look forward to the next in the series.