Chemicals I Have Known (and Made) - Acrylonitrile

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The last chemical I wrote about, hydrogen peroxide, I described as a cute, cuddly chemical. The next chemical I was involved with was anything but cuddly. Acrylonitrile, or Acrylo as we called it, is an organic chemical that is used to make acrylic plastics and fibers. By itself, it has toxicity as it will release cyanide within the body. But the process to make the chemical is also very nasty, and especially so where we made it in Memphis. A little background first, though.

 

I received a promotion and gained the title of Production Supervisor in the Acrylo process. This was a big enough process that it had two production supervisors. I was placed in charge of planning the annual shutdown, which required intense logistical planning. I served as a backup to the real process supervisor. He was a Memphis native who had come up from the hourly wage roll to his exempt role position. He actually was a classmate of Elvis Presley when they were both in junior high school, but he did not have any good stories about their shared time. So I had the advantage of being able to learn about supervision while only occasionally really taking charge.

chemical plant

The Acrylo process is a huge process, more like an oil refinery than a standard chemical plant. It had six huge reactors where the chemicals propylene, ammonia, and oxygen (from air) are mixed with a catalyst in fluidized bed reactors. These reactors were about 12′ in diameter, and some 40′ tall. The reaction itself creates significant heat, so the reactors are full of tubes containing water which turn into steam that helps to drive the later separation processes. Once the chemicals have reacted, the off-gases are sent into an absorbing tower. This tower was over 100′ tall, and about 15′ in diameter. After the gases are absorbed in water, it is necessary to separate out the other reaction products. The primary one is hydrogen cyanide, which I wrote about earlier. There were two distillation towers used to separate and purify the hydrogen cyanide, which was then sent by pipeline to the other part of the plant that produced cyanide as its primary product. I remember that one of the pumps that transferred the cyanide developed a leaky seal, and since it was several months before the scheduled shutdown, the solution was to barricade off a section of the process with good old yellow and black warning rope, guaranteed to be a barrier against all chemicals. NOT! In fact, even beyond the tape, you could taste the cyanide, and this is how I became sensitive to cyanide and was able to easily pass the sniff test during my annual physical at the plant. It does not smell like bitter almonds, rather, it is an unpleasant sensation that grabs at the back of the throat.

 

Once the cyanide was removed, the crude acrylonitrile had to be separated out of the ammonia-laden water. There were a total of five distillation towers, each with a different purpose, until finally the refined acrylonitrile was pure enough to go into the storage tanks. One of the distillation towers actually concentrated another byproduct, acetonitrile, which is used as a solvent. Eventually though, the ammonia-laden water was neutralized with sulfuric acid, and had to be disposed of. Now every other commercial acrylo plant in the US was in a location where the waste stream could be injected into the earth in a deep well. In Memphis with its extensive aquifer system near the Mississippi River, this was not a viable option. So when the plant was built in the 1960’s, and energy was extremely cheap, the solution implemented was to incinerate this stream. We had three huge stacks that could be used to “thermally oxidize” the solution, and release nitrogen, water, and sulfur dioxide to the atmosphere. We were the 2nd largest sulfur dioxide emitter in western Tennessee. Only the Tennessee Valley Authority’s coal-fired power plant was a larger source. As you can imagine, when the dual energy shocks of the 1970’s came, burning a water waste stream put a larger and larger burden on profitability. So much so that when our plant suffered a major freezing incident one winter, that proved to be the final straw that led to the plant’s closure and eventual dismantlement. Chemical plants really, really do not like cold, freezing weather. And seeing 12″ diameter burst water pipes start to leak when they finally thaw is not something I ever want to witness again.

 

But before the process was closed, there were some really wild times I had. One in particular involved a one ton cylinder of sulfur dioxide. Now pure sulfur dioxide was used as a polymerization inhibitor in the vapor space in the columns where cyanide was purified. So we had tubing running from the cylinder up to the tops of the distillation towers. Even though sulfur dioxide boiled at 14ºF, it took a little extra push to ensure that enough gas flowed up to where it was needed. So we had a simple plywood enclosure where we kept the cylinder, and we had steam coils underneath the cylinder. Such a complex system couldn’t ever go wrong, could it? Well, it did go wrong, and the fusible plug in the cylinder that kept it from over-pressurizing, that plug melted and began to release the content of the cylinder to the atmosphere. That was one of the days where the other Process Supervisor wasn’t there, and I was in charge. I had to direct the evacuation of the adjacent laboratory and technical building, but what saved us was one operator who was able to get onto a forklift with breathing air, and pulled the cylinder out, where it could be sealed by hammering a wooden plug into the hole where the fusible plug had been. We prevented releasing the entire cylinder contents, which could have affected a large area, including US 51 highway which ran parallel to the plant.

 

To this day I don’t remember what we did to get another cylinder in and fix the tubing that had torn away when the cylinder was pulled out, but I do remember that we didn’t create a huge environmental incident.

 

When we finally did get into our planned shutdown, the biggest job was the replacement of our 100+’ tall absorbing tower. We got cranes in that were able to lift the entire tower – the big crane to lift from the top, a smaller crane to guide the bottom section. Then the process was reversed so that the new column was installed. We did this on a weekend when most of the lab people and other technical engineers weren’t around. My job? To run the video camera that captured the move. Somewhere there was a VHS tape that documents the replacement of this absorbing tower, which was used for about one year before the entire process was shut down.

 

Propylene is the main reactant to make acrylo. It has properties very similar to its chemical cousin, propane. So you know those long cylindrical tanks that hold propane? We had four big tanks that held the propylene. One thing that most folks don’t know about chemical piping is that there is almost always a little bit of leakage that comes out of valves and flanges. And for whatever reason, propylene attracts wasps. So going up on the storage tanks was a bit of an adventure. It was necessary to keep watch in order to knock down wasp nests before they got too big.

 

One other similarity to a refinery was that the residual gases from all of the columns was released through a flare stack. This stack was 175′ tall at its tip, and one of the tasks for the shutdown was to inspect the flare. I, being a novice supervisor, didn’t always think about my decisions. We had an intern who had his own pilot’s license, and was clearly unafraid of heights. So he asked, and I gave permission, for him to do the inspection on his own, and trusted him to do it safely. If he had an accident, my career would have been over at that time. But he completed the inspection, and came down safely. It was only years later after I gained more experience that I realized what a risk I took with his life and with my own career in my company.

 

The equipment for this process was huge. We used air as an ingredient. So it was a 2500 horsepower air compressor that fed the reactors. That was one impressive motor that ran that compressor.

 

Of all of the chemical processes I worked with, this one was by far the “dirtiest”. We emitted tons per day of sulfur dioxide. We sometimes had cyanide leakage. We had another wastewater stream that did go to the sewer system, that we had to monitor for compounds that had the nitrile (or cyanide) functional group – the CN on the end of the molecule. Before I worked in the process, they had tried to see if they could use the ammonium sulfate waste stream as a fertilizer for soils that needed acidification. They had a section of ground near the plant set up to receive the waste, and monitored the soil to see how it worked. Spoiler alert – it didn’t work.

 

One thing that I appreciated in my time in this process was that we had a Superintendent who believed that his supervisors should know what we were expecting workers to do. So all of us had to put on self-breathing air packs (like scuba tanks), put on chemical-proof suits, and disassemble and reassemble a flange with its bolts. It did show me how exhausting working in that type of environment was. When I took off the suit, I was drenched in sweat. But in my mind, I thank my old supervisor’s supervisor for giving me a taste of what it really is like to work in such an environment.

 

In the Memphis plant where I worked, there were four large chemical processes. I’ve shared the stories of three of them. One more to go.

 

Posted first on my blog https://evenabrokenclock.blog

Comments

James Travil Added Oct 3, 2018 - 7:45pm
Wow, that's pretty frightening to work so closely with some of those chemicals Clock. Interesting read though. I sure hope that they paid you well for the hazards involved! 
Ward Tipton Added Oct 4, 2018 - 1:22am
The best my Dad could do was boiling the Nitroglycerin out of his dad's dynamite. 
 
As for my personal experience with chemicals ... "No comment" says it about as good as anything else would. 
Mark Hunter Added Oct 4, 2018 - 3:57am
If there's one thing I learned from being on the hazmat unit, it's that people just don't understand how hazardous the processes are that bring us our modern society.
FacePalm Added Oct 4, 2018 - 5:42am
Unless i missed it, the thing that's missing from the article is what "acrylonyitrile" is actually used for; "making acrylic plastics and fibers" doesn't really say much...nor how the process what discovered, and if it was by accident, like silly putty.
 
Did working at such a plant ever make you long for simpler chemical applications/processes, like those of George Washington Carver and his peanuts?
 
That said, i've heard that one can make REAL money by creating molds - that is, for making parts for assembly, not, say, on bread.
Ward Tipton Added Oct 4, 2018 - 7:25am
I used to love silly putty ... and Sunday comic strips ... That gal from Lil Abner never looked better ;) 
opher goodwin Added Oct 4, 2018 - 9:48am
Wow! My daughter is a chemical engineer working with pretty much the same chemicals. Small world.
Even A Broken Clock Added Oct 4, 2018 - 10:34am
James - The thing is that once you have become used to dealing with chemicals, through classwork, you lose some of the fear associated with them. Not the respect, though.
 
Do you know what chemical is the most hazardous one in a chemical plant? The one that causes the most deaths? It's nitrogen. Nitrogen purges are used to prevent flammable atmospheres from forming inside of storage tanks, and for instrument purges into reaction vessels and distillation towers. Thus when people go into vessels, if the oxygen levels have not been verified as being adequate, people go in alive, but come out dead.
Even A Broken Clock Added Oct 4, 2018 - 10:38am
Ward - you reminded me of one of my high school classmates who got into the "boom" aspects of chemistry. I remember some of the classmates spread ammonia tri-iodide on the stairways of our high school. The excess ammonia dried out, and when the classes changed, people got exposed to contact iodine, which made a bang and released a cloud of iodine vapor. Now if people tried that, we'd have homeland security to deal with for sure.
 
Dang. Now I've revealed my high school hijinks. I'll never get put onto the Supreme Court.
Even A Broken Clock Added Oct 4, 2018 - 10:41am
Mark - hazmats are not anything to play around with, that's for sure. And there are a bunch of them, on the highways and especially on the rails. Did you ever learn about candy stripers? That was the nickname for hydrogen cyanide rail cars, that were white but had a red stripe running parallel to the ground, and one running around the circumference of the car. A very unique visual decoration on the car.
Even A Broken Clock Added Oct 4, 2018 - 10:44am
Face - if you remember acrylic yarn, and acrylic sweaters that were popular in the 70's and 80's, that is pure polyacrylonitrile. The main plastic using acrylo is abbreviated as ABS for acrylonitrile-butadiene-styrene for the individual monomers. That is used a lot for water piping, both within houses and for drain piping.
 
The actual process was called the Sohio process, for the Standard Oil of Ohio company. They developed the technology and licensed it to other companies.
Even A Broken Clock Added Oct 4, 2018 - 10:44am
Opher - you've gained an appreciation for what folks go through, that's for sure.
Dino Manalis Added Oct 4, 2018 - 12:29pm
 You're an expert on chemicals and able to alert people how to keep dangerous substances away from terrorists!
Neil Lock Added Oct 4, 2018 - 2:49pm
The take home message I got from this article was: learn from your mistakes. And that's well and good. I worry, though, if over-regulation to prevent people making mistakes may stifle innovation - even stop major advances being made?
Katharine Otto Added Oct 4, 2018 - 4:10pm
Clock,
I enjoy reading these articles, even if they are somewhat over my head.  I think about how large and dangerous these operations are.  I believe acrylic is still used a lot in yarn and clothing.  I'm a knitter who has to look carefully to find natural fibers like wool and cotton.  And isn't acrylic also used in paint?  You say it can release cyanide in the body?  Do you mean if ingested, or if worn as clothing?  
 
Also, isn't sulfur dioxide a component of acid rain?  
 
Thanks for the insights into at least part of the chemical industry.
Even A Broken Clock Added Oct 4, 2018 - 4:35pm
Dino - no, not really. Since I'm retired, there's naught I can do about terrorism.
Even A Broken Clock Added Oct 4, 2018 - 4:40pm
Neil - I do think I learned but it took a while. Probably the best learning exercise I had came from process hazards reviews, where you go through a systematic process of trying to figure out what could go wrong, and what protections you have in place to prevent an incident. I'll give you an example. For protection against over-pressurization of vessels, you will have relief valves or rupture disks. But for materials that can polymerize, the vent lines leading up to these devices are stagnant, and the monomer vapors can polymerize. Therefore  you ensure that you have a purge installed on the space leading to the relief device. All well and good. But what if you find in a shutdown, that the inlet is still plugged with polymer? That says you need to increase your inspection frequency in order to prevent polymer buildup. That's a good example of what might come from one small piece of a hazards review.
Even A Broken Clock Added Oct 4, 2018 - 4:49pm
Katharine - acrylonitrile is the main source of acrylic yarn. The trend towards more natural fiber has caused a market share loss for polymers like acrylics. What's important to keep in mind is that natural fibers are also polymers, just polymers that living organisms have crafted instead of man.
 
By the time the monomers have polymerized, they have lost their toxicity. Acrylic fiber is not toxic, but the unreacted monomer can be toxic.
 
And yes, sulfur dioxide was the main culprit in acid rain. In fact, the greatest reduction in acid rain has come with the installation of scrubbers on coal fired power plants. Of course, you can't cure one problem without causing another one. Since they use scrubbers and lime solutions to absorb the sulfur dioxide in the stacks, they also pick up the fly ash, and end up with the coal ash sludge that caused the pollution in North Carolina when the ponds were overwhelmed with floodwaters from Florence.
Mark Hunter Added Oct 4, 2018 - 7:21pm
The candy stripers are one of the first things they warned us about, Clock!
Michael B. Added Oct 5, 2018 - 3:27am
@ EABC - Interesting post. Chemicals are much like women in that I'd rather do them than work with them. Come to think of it, women and computers also have an inversely-proportional relationship; on one hand, I'd rather work ON them than WITH them, and on the other hand, I'd rather work WITH them than ON them, lol.
 
I don't miss chemicals one bit. I think I told you about being stung by H2O2, which was yet another reminder to treat chemicals with a certain amount of respect. This post reminded me of a couple of my favorite chemical warfare stories, like the time an Indian bitch who was allegedly a PhD created a toxic cloud of vapors from unreacted acrylates that resulted in several people going home sick and me with an almost homicide-inducing headache. My favorite one of all time is when some moron, who was being "supervised" by an even bigger moron, poured NMP into a system that normally used DI water and IPA, which made the plastic components look like something out of Chernobyl...just in time for a hot job for a particularly important customer!
Ward Tipton Added Oct 5, 2018 - 7:12am
Two chemists walk in to a bar. The first one says "I will have H20" ... the second says "I will have H20 too" ... he died. 
Even A Broken Clock Added Oct 5, 2018 - 10:18am
Mark - I'm glad to hear that they (hydrogen cyanide rail cars) were discussed. Were one to crash and leak, the best thing to do is ignite the liquid and vapors. The characteristics of HCN are that a vapor cloud will not explode (flame wave front > speed of sound), it results in a deflagration (flame wave front < speed of sound). Therefore the best thing to do is let it burn out totally and not put out the fire.
 
Of course, if the car were next to a car of chemicals that could explode, then there would be a real dilemma.
Even A Broken Clock Added Oct 5, 2018 - 10:22am
Michael - I actually could follow your acronyms, but have to ask about the reaction that ensued. If you had de-ionized water and iso-propyl alcohol, why would n-methyl pyrollidine cause an ignition?
Even A Broken Clock Added Oct 5, 2018 - 10:22am
Ward - you earned a rim shot on that one.
Mark Hunter Added Oct 5, 2018 - 2:38pm
By nature firefighters don’t like to let things burn, but over the years we’ve learned our lessons.
Michael B. Added Oct 8, 2018 - 2:51pm
@ EABC - The NMP attacked the polymers that several of the components in the system were constructed of.
Even A Broken Clock Added Oct 9, 2018 - 12:37pm
Thanks, Michael. I hadn't considered that possibility. That NMP is a pretty good solvent.

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