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[*] posted on 18-2-2015 at 08:39


I like this shape, made from HDPE. Should replace metal shaft with Teflon or glass for use in nitration mixtures- Spin in direction that causes fluid to be drawn in from top & bottom, expelled from sides (clockwise as seen from above).

image.jpg - 27kB




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[*] posted on 19-2-2015 at 01:00


So whats wrong about magnetic stirrer?
http://en.m.wikipedia.org/wiki/Magnetic_stirrer
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[*] posted on 19-2-2015 at 01:04


That's a cool design, basically the style used in (most?) Compressors today, though wide open like that it obviously wouldn't compress much, and the thin blades would minimize risk of cavitation. Good idea!
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[*] posted on 19-2-2015 at 08:03


Quote: Originally posted by ecos  
So whats wrong about magnetic stirrer?
http://en.m.wikipedia.org/wiki/Magnetic_stirrer


How hard do you want to strike nitroglycerin between hard plastic and glass surfaces? It's not terribly sensitive when wet, but still I would not.




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[*] posted on 19-2-2015 at 13:59
Homemade Overhead Stirrer


Thanks for the ideas. For now I am going to try and use what I have lying around though.

It isn't beautiful, but it is a good working homemade variable speed overhead stirrer with lots of power and speed. Total cost ca. $26.60 ($10 for second hand 18V cordless drill, ca. $15 for 10mm diameter Teflon rod & $1.60 for mounting hardware). Often times drills in nearly perfect shape like this can be found very cheap or free because the batteries need replacing. It is often more cost effective to simply buy a whole new drill kit than to replace just the battery or batteries. I discovered that cordless drills have very good speed control; all that is required is a way to precisely control the trigger position. The trigger position controls the position of a variable resistor in the pulse width modulator trigger module. The drill also has a high and a low speed setting on the gear head. A c-clamp was found in the junk pile which was originally designed to hold a half ton truck cap on. The c-clamp works very nicely for setting and maintaining trigger position and speed. The trigger mechanism (pulse width modulator) was removed from the drill. A section of regular household extension cord (3m long) was spliced in as an extension between the trigger mechanism (pulse width modulator) and the drill. The useless cells were removed from the battery pack and the pack casing was mounted to the vertical member of the stirrer stand; the drill can be easily attached and removed in this way. The drill is rated as 18V, but works fine from 12V providing all the speed and power needed. The pulse width modulator is rated for 9-24V and 12A. A computer power supply rated for 12V and 12A was used to supply power to the PWM. The stirring blade or paddle is put in the 2L flask lengthwise then turned sideways and threaded to the rod. A much larger paddle can be put through the neck of the 2L flask in this way. Two stirring blades were made which can both be threaded to the end of the rod together if desired. The Teflon rod has a slight bend to it, so I will be looking for something better such as a steel rod coated with Teflon or HDPE. I would imagine that HDPE plastic tubing could be used to coat or slide over a straight steel rod. A tight friction fit where the rod and paddle are threaded together could make a decent seal and prevent acid from reaching the steel rod. It is very easy to form a vortex, even at about medium speed, but the bent shaft makes higher speeds unstable. The blade is also not balanced which could be a problem at high speed. When both blades are attached together they can be installed so that there is better balance.

BTW, the "Teflon sled runner" that I obtained from a scrap yard is actually HDPE (determined by density). Checking density is a good way to help determine what type of plastic one has if it is found as salvage and the identity is uncertain.

A plastic shield could be attached to the shaft, close to the chuck, to prevent most acid vapors from reaching the drill. An exhaust fan with the inlet positioned just above the flask neck would also help prevent acid vapors from reaching the drill.


1.jpg - 259kB 2.jpg - 230kB 3.jpg - 227kB 4.jpg - 422kB 5.jpg - 439kB 6.jpg - 454kB 7.jpg - 208kB 8.jpg - 448kB


[Edited on 20-2-2015 by Hennig Brand]




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[*] posted on 20-2-2015 at 15:39


Looking at the common stainless steels, it appears as though none are ideally suited for contact with nitration acid though 304 is fair according to several compatibility tables. I picked up an 18 inch long piece of 3/8 inch diameter 304 SS from a local machine shop for about $3. The end of the SS rod was threaded with a die. The HDPE stirring paddles were drilled and tapped and made balanced by cutting off the bottom lip that the Teflon rod was threaded into earlier. With the relatively straight rod and balanced blade the stirrer can be run at high speed now with only minimal vibration.

The 304 SS will corrode in the mixed acid, but the rate should be very slow especially at the low temperatures of a nitric ester nitration. HDPE is also not an ideal material for nitration mixtures, but it too should degrade relatively slowly especially at the low temperatures of a nitric ester nitration. Also, the contact time is normally fairly brief since nitric ester nitrations are normally relatively rapid.

Here are a few pictures. The flask is 2L and contains water. The last picture is of the stirrer running at about 80% of full speed.

1.jpg - 466kB 2.jpg - 418kB 3.jpg - 440kB 4.jpg - 448kB


[Edited on 20-2-2015 by Hennig Brand]




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[*] posted on 22-2-2015 at 05:53


HDPE and PP should withdraw H2SO4/HNO3 at cold temperature...
but upon heating they might loose integrity by softening-melting.

Oxydation and nitration will only occure at high temperature.
The presence of colourizers and charge agents might lower the resistance...so better use transparent colorless plastic.

Aluminium and Iron will withdraw concentrated HNO3 alone but maybe not in admixture with H2SO4: there exists a passivation effect of HNO3 towards those metals (probably due to surfacial special oxyd layer formation) ....passivation of iron stops as soon as in contact another metal like copper.

[Edited on 22-2-2015 by PHILOU Zrealone]




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[*] posted on 22-2-2015 at 08:11


Yeah, using uncolored white HDPE would probably be best, you are right.

I have used the same HDPE as a stirrer blade in an ETN synthesis here: http://www.sciencemadness.org/talk/viewthread.php?tid=7209&a...

At the time I thought it was Teflon, since that was what I was told it was. In retrospect it would have been very easy to tell the difference since the densities are very different. The HDPE appears to be unaffected after being used twice, for about 3 hours total contact time, in a nitration acid made by adding ammonium nitrate to sulfuric acid. I didn't check the weight of the HDPE before and after, however, which would have been informative (something to keep in mind this time around perhaps).


Also, HDPE appears to be what the dark gray bushing used on the receiver flask was made of here: http://www.sciencemadness.org/talk/viewthread.php?tid=15676&...

The HDPE plastic bushing has been exposed to nitric acid vapors for several hours at this point with only slight blistering if any observed on the end exposed. Once again, taking the weight before and after would have been a good idea.


Here is some compatibility ratings taken from, http://hayata.com/products/chemicalCharts/mo.htm. There are many other sites giving similar ratings. "Ratings of chemical behavior listed in this chart apply at a 48-hr exposure period."

................................................Stainless Steel 304.....Stainless Steel 316
Chemical....................................Compatibility.............Compatibility
Nitrating Acid (<15% HNO3)........ C-Fair .....................D-Severe Effect
Nitrating Acid (>15% H2SO4)....... C-Fair ....................C-Fair
Nitrating Acid (<1% Acid)............ C-Fair.................... A-Excellent
Nitrating Acid (<15% H2SO4)....... C-Fair.................... C-Fair
Nitric Acid (20%)........................ A-Excellent............. A-Excellent
Nitric Acid (50%)........................ A-Excellent............. A-Excellent
Nitric Acid (5-10%) .....................A-Excellent.............. A-Excellent
Nitric Acid (Concentrated)............ A-Excellent.............. A-Excellent


[Edited on 22-2-2015 by Hennig Brand]




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[*] posted on 22-2-2015 at 09:09


Found a decent compatibility table with lots of information for nitration acids in contact with different stainless steels at various concentrations and temperatures. From this table it looks as though 316SS is actually better than 304SS is some cases, though both appear to be very good at low temperatures.

The pdf containing the compatibility tables is attached below. The ratings include a general corrosion rate as well.

"
0 = resistant to general corrosion (mass loss rate <0.1 g/h · m² corresponding to a corrosion rate < 0.11 mm thickness reduction/year)
1 = slight susceptibility to general corrosion, suitable for some applications (0.1 – 1.0 g/h · m² corresponding to 0.11 – 1.10 mm thickness reduction/year)
2 = low resistance to general corrosion, unsuitable for virtually all applications (1.0 – 10.0 g/h · m² corresponding to 1.1 – 11.0 mm thickness reduction/year)
3 = no resistance to general corrosion (>10.0 g/h · m² corresponding to > 11.0 mm thickness reduction/year)
The following warning is provided for the major forms of localised corrosion
L = risk of pitting, crevice corrosion or stress-corrosion cracking, even in resistance class 0
"

A jpg of the nitration acid part of the table was made as well. Column 4 and 5 refer to 304 and 316 stainless steels respectively.

Stainless Steels & Nitration Acids Compatibilities.jpg - 175kB

Attachment: Material Compatibility Tables.pdf (213kB)
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[*] posted on 23-2-2015 at 06:03


Yeah in most places I've worked HDPE is generally referred to as Teflon, few know the difference because it's not particularly important for most uses.
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[*] posted on 23-2-2015 at 06:54


I particularly like the specifications of those last 3 corrosion resistant grades- N08904 and similar. Did a quick Google search.

1.4465 X1CrNiMoN 25-25-2 SEW400

1.4539 X1NiCrMoCu 25-20-5 10088-2 N08904

1.4565 X2CrNiMnMoNbN 25-18-5-4 SEW400 S34565


Plenty of suppliers for N08904 tube and bar stock on line, nothing for smaller pre fabricated vessels/reactors. Anyone experienced with the metallurgy of this class of stainless, can they be MIG welded and the weld retain the desired corrosion resistance? I suck at TIG!




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[*] posted on 23-2-2015 at 06:58


Nobody here has done it on an amateur scale so I thought I'd bring it up: What about stirring with compressed air?

Clean dry air from a small air compressor (maybe for a fish tank?) and a sizeable CaCl2 drying bottle is blown at low pressure through a glass tube attached to a 2-neck flask through a thermometer adapter. There are no moving parts to contact anything and create a dangerous friction situation, and the sparging effect can help reduce the buildup of dissolved nitrogen oxides. A reflux condenser is fitted to help mitigate the escape of nitric acid. The rather closed nature of the setup also allows waste fumes to be conveniently routed out of the room.

If you rig it right, the air tube could also be used to deliver the glycerin, with the application of a female T-joint (one ground glass and two hose barbs) fixed to the bottom of a pressure-equalizing addition funnel, to deliver the glycerin into the airstream.

This setup would clearly only work for nitration baths using mixed acids. The viscosity of cold H2SO4 and a nitrate salt would probably make air-stirring ineffective.




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[*] posted on 23-2-2015 at 08:17


Kind of like this?



image.jpg - 314kB




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[*] posted on 23-2-2015 at 08:41


Hi Bert,

I start to feel that you like this figure a lot :)
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[*] posted on 23-2-2015 at 10:19


Quote: Originally posted by Bert  
Kind of like this?


Yes, I saw this several posts back. I believe it is also the method many manufacturers used industrially. I have not seen anyone actually use this technique in an amateur laboratory though.

It may be worthwhile investigating since amateur stirring setups are usually rigged and may involve running heavy brushed motors on cobbled-together stands, teetering over pools of high explosives/flammable liquids as they spark away, wobbling occasionally to strike the stirrer against glass...

Air stirring is also cheap. I have a fishtank pump for air sparging that cost me $7, and the tubing usually comes free with the pump.




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[*] posted on 23-2-2015 at 12:07


Bert, I was interested in those other special super low corrosion rate stainless steels as well. The local fabrication shop here has offered to try and order me whatever I want if I give them some numbers. For now they have 2' of 3/8" 316 waiting for me to pick up. It is a little more expensive than 304, but not that much (ca. 20% more).

I was thinking of using a bushing (Teflon or HDPE) that would fit in the neck of the flask. This could allow the drive shaft to pass through and still maintain a decent seal. A Teflon or HDPE bearing, which could be as simple as a hole in a block of either plastic, could be positioned above the flask and could be part of a frame or flask housing/compartment, positioned below the drill (motor and gear head assembly), built to take strain off of the drill bearings and gears and provide protection for the delicate glass and possibly sensitive explosive contained within from falling objects, etc. If the stirrer blade is designed and positioned properly one should be quite certain that it will not contact the sides of the vessel while stirring.

I have seen it stated in the literature that compressed air was used in the past at least on the small scale. I don't think normal sized pet store aquarium air pumps would put out the volume and pressure needed for the 2L flask, with about 1L of fairly viscous contents, I am using. Seems to me those pumps put the air out in little pulses as well, not really in a continuous stream like from an air compressor with pressurized storage tank.

The other big advantage of the overhead stirrer, probably the most important, is the ability to provide good mixing to very viscous mixtures. I think it is going to be fantastic for solid nitric ester nitrations. A glycerine nitration with mixed acid would put very little load on the drill which is also a good thing.

Even a common household fan could often be used to prevent the buildup of flammable gases and vapors and keep the concentration in air below the flammability and/or explosive limits.


[Edited on 24-2-2015 by Hennig Brand]




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[*] posted on 26-2-2015 at 00:22


Do you have a drill press, by any chance? With the stirrer in the drill running at low speed, lower and lock it into place, and when you're done, raise it up and release. When making NC I've always just put it in a jar and slowly rotated it periodically to make sure everything was getting evenly nitrated, and I've gotten decent results, but having something like that slowly spinning the mixture would help a great deal, I'm sure.
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[*] posted on 26-2-2015 at 18:17


A drill press is an option. I like how most drill presses are more robust than cordless drills and have the motor and most other sensitive parts not directly over the chuck. Cordless drills do have a lot of nice features though, such as an adjustable torque limiter, basically infinite speed control (PWM), and an easy to use keyless chuck. Cordless drills aren't really designed for continuous duty, but I think the loads are small enough for my purposes and will be fine.

Regarding stainless steel corrosion in nitration acids, the corrosion rate of a rotating shaft will be much higher than for a storage tank, of a given SS, holding the same acid at the same temperature. Of the common stainless steels 316 is definitely a better choice than 304, but I am still going to try out the 304 shaft for low temperature nitric ester reactions. I found a couple of well known alloys (stainless type steels) that are much more corrosion resistant than 316. They are, of course, less commonly available and more expensive as well.

Hastelloy
http://en.wikipedia.org/wiki/Haynes_International

Alloy 20
http://en.wikipedia.org/wiki/Alloy_20

Attached is a data page for Alloy 20. It discusses welding and other processes as well. I am not a welder, but I am fairly certain that most if not all the stainless steels can be welded. From reading it seems that all types/methods of welding are used dependent on the application. TIG is of course know as the "Cadillac of Welding" if I remember correctly. I have seen welding rods that were stamped "316", and rods of other alloy compositions can be obtained as well.

A big problem that can occur when welding stainless steels is "weld decay". It is common to see stainless steels with a line of corrosion running beside the weld a small set distance from the weld. I made the attached pdf regarding weld decay from the following webpage, which seems to have done a good job of explaining the phenomenon. I hope they don't mind my including it here too much.

http://www.corrosionclinic.com/types_of_corrosion/weld_decay...

There are techniques to prevent weld decay, such as heat treatments and also some alloys, particularly those with low carbon content, are much less susceptible as well.



Attachment: Alloy 20 Data Sheet.pdf (139kB)
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Attachment: Weld Decay Explained.pdf (440kB)
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[Edited on 27-2-2015 by Hennig Brand]




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[*] posted on 27-2-2015 at 18:51


We only use 316L SS for the internal wetted parts of our pharmaceutical tanks after we double weld the seams and dress and sand them then we have to polish them to .4 RA (mirror finish) after its given the ok by the inspector its passivated internally to smooth the surface off even more, then you get the tank back in 6 months to a year to referb it cause the dumb factory workers use metal mixing poles and scratch the inside up :mad:. nuxy.
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[*] posted on 3-3-2015 at 18:46
304 Stainless Steel and HDPE Held Up Well In Nitration Acid


I will just give a brief description here and possibly later something more thorough with more pictures in an ETN thread. A mixed acid was made from 600g of ammonium nitrate, 900mL of 91% sulfuric acid and was used to nitrate 150g of erythritol in a 2L flask. Mixing was provided for nitration, dilution and washing stages by the previously built overhead stirrer. The HDPE blade and 304 SS shaft were in contact with the mixed acid for about 2 hours and there appears to be no visible damage whatsoever. The tool marks, which are visible in the picture, are the result of my sloppy work earlier during construction. The temperature of the nitration never went above 15C which is ideal from a corrosion prevention perspective.

Addition of the 150g of erythritol was done over the course of about 30 minutes. No supplemental cooling was used. The ambient temperature was about -5C, which is a different situation entirely from performing the reaction in the summer with an ambient temperature of +30C for instance. Using this type of mixed acid and coarse crystals of erythritol (about the size of granulated white sugar) this reaction is very easy to control; very slow and gentle if a little care is used. Supplemental cooling or slower erythritol addition would be required in a hotter environment.

It is very possible, and would not be much more difficult, to make a pound of ETN at a time with this arrangement. A 3L or larger flask should be used, however, and a 20L pail should be used for dilution and washing as well.


3.jpg - 432kB 6.jpg - 327kB

9.jpg - 197kB 13.jpg - 231kB


[Edited on 4-3-2015 by Hennig Brand]




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[*] posted on 3-3-2015 at 23:52


Impressive batch and a very cool stirrer system ;) What was your yield if you don't mind me asking? I've never scaled an ETN synthesis to this level and it would be interesting to know how it looks in terms of process yield.



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[*] posted on 4-3-2015 at 06:28


Thanks, I know that you like making equipment too. If I know you though, construction would likely have been a little neater. :)
Still drying the product, but I will take a dry crude weight before recrystallization and post it here. I lost at least a small amount during filtering. Regular coffee filters aren't really practical at this scale, so a cloth filter (piece of old undershirt) placed in a large colander was used. During filtering, it is the material which builds up on the membrane that does most of the filtering not the filter membrane itself. When I first started filtering some fines went right through the filter, but once a small amount built up over the larger holes almost none passed through (only clear liquid could be seen passing). The correct procedure would have been to collect what passed through the filter until the filtrate was clear and then pass the filtrate which was collected up until then back through the filter to collect any fines that initially passed through. The yield still looks pretty good and it won't be long until it is dry.




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[*] posted on 4-3-2015 at 11:07


I'm not a fan of loose wire bundles...that much is true :D
But then again I certainly do lack the capacity and determination for achieving perfection. Preferences may vary wildly and in the end functionality is the real judge of success, I guess...
Btw, are you drying your batch before recristallisation? I've found this practice to be unworthy and a waste of time in case etn is involved. One can just squeeze the batch more or less dry between paper towels or other suitable absorbant media and then go on dissolving it in preheated alcohol of choice. Works like a charm and is a great time saver...not to mention the slightly raised safety of handling a damp batch...and it will not spill so easily as it sticks together in the damp state.

[Edited on 4-3-2015 by markx]




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[*] posted on 4-3-2015 at 11:47


It's a work in progress. :D
What I thought I was seeing, a long time ago, was that even small amounts of water significantly reduced the methanol's ability to dissolve the crude ETN (ETN has very low solubility in water). Even slightly damp crude ETN can hold a surprisingly large amount of water. Also, knowing the dry weight makes it easier to accurately determine the amount of solvent needed for the recrystallization to follow. It is something to consider though, since it is a pain to dry the crude product, which is very fine and not as crystalline, clumpy and with more hydroxyl groups left unnitrated as well as at least a small amount of acid contamination which all make drying more difficult. The recrystallized material is always much easier to dry I find.


[Edited on 4-3-2015 by Hennig Brand]




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[*] posted on 5-3-2015 at 14:33



The following solubility data was taken from, Characterization of Erythritol Tetranitrate. Part I: Physical Properties by Matyas et al.

Table 1. Solubility of ETN in water.

Temperature [Degrees Celsius].......... 5........ 20........ 40..... 60........80
Solubility [mg] ETN in 100 mL water... 1.53.... 3.02..... 9.33...26.9... 39.9




"A risk-free world is a very dull world, one from which we are apt to learn little of consequence." -Geerat Vermeij
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