Configuration of a Polymerization Reactor

Hi Miherko, thanks for your thourough explanation, I will discuss this tomorrow with a colleague and be right back!

Excellent answer in #1! I've seem many reactors for making acrylic polymers, and all had centered, verticle agitation shafts. The small "kicker" blade at the bottom is useful when making a half-size or less batch, and should be set fairly close to the bottom to permit agitation with minimum volume. There are generally 2 sets of large blades and a smaller set on the bottom. Cooling is also an important factor, and is much better in stainless steel vessels than glass. Baffles can also contain cooling plates for more cooling capacity, but can be somewhat difficult to clean when there is reactor fouling.

Hi Doc,

After my experience of mixing liquids, centred is the ideal to get a good Wortex and a good homogeneisation of your different ingredients, liquids and solids dissolved, at different temperature. I saw a 13,000 imperial gallon tank, completely automated or computerized to make emulsions. The shaft was on the centre. However, I am not knowing everything for everyone; Try it and prove to yourself what is good for that process or operation. I already did with a plastic tank, round and square, inside just water and plastic beads, to see better way the movement of the liquid. It was a learning experience. Also, the impeller is very iportant to modify, bevel it. Wish you good luck, Gil.

Hi folks, At our company we are having some issues now with a new "guru" that has been hired to take care of the reactors area. At this point a 1,000 liters (aprox 250 Gallons) new reactor will be built, and this guy insists in introducing changes into our "classic" design in order to make it more "efficient" as he says. We believe this guy is a freak, but he managed to do some sweet talking to our GM and he probably will follow his advices. (No need to say this is a family business!) The process that will take effect inside this reactor (BTW: top and bottom are dome-shaped) is the polimerization of a suspension of MMA (Methyl Methacrylate). This guy is wanting to displace the propelling shat to an off center position and to use no baffles. He also wants to use slightly pitched blades at each side of the shaft in order to keep the fluid in motion. The whole process will be automated and the "feeding" of the reactor will also be automated, as SS vessels containing the different components will be placed in upper levels for weighting, blending and preheating. Solenoid valves will do the job of pouring the juices into the reactor by gravity. A serpentine will control temp of reaction by heating / cooling down it´s content. Once the process if finished, a valve at the bottom opens deriving this production into a centrifuge to separate waist fluid from polymer particles. Waist fluid is then treated with an Enzyme to obtain some more polymer; and final fluid waste passes to a treatment plant. As we believe the changes proposed by this person are wrong we asked for a meeting wit BB (big boss) to explain our point of view. The more opinions we can get about this will certainly be appreciated as we will save a lot of time and $. The points we insist more about are that an off center impulsor will create whirls and an erratic movement pattern of the particles in the process of building up, consequently resulting in a product that will not be reproduced batch after batch due to the heterogeneous movement inside the reactor. May sound weid, but this is part of the reality we have to deal with here! Best regards!! the monomer, having two parameters to control: 1- agitation (*) and 2- temperature of reaction. (*) In this case: how crucial would you think the centred position of the impeller (centered / off-center) is? ON the other hand,

It would be nice if you could get this guy to set up a small scale clear plastic model of the reactor he is proposing, and a similar clear plastic reactor like you favor, and do some mixing studies. You can add colored liquid or a suspension of your PMMA beads to see how they behave. Perhaps an equipment vendor has software to model the reactor dynamics. Something this radically different should definitely be modeled on either small scale or by software before spending a lot of money.

Hi Doc,

I don't want to add more to your problems but "off-centre shaft" system will create many problems. Turbulent mixing of liquids creates foams and bubbles because you have surfactant. Speed of mixing, impeller size, number, and shape, volume of liquid per impeller level, and size, shape, position of impellers in the tank, and orientation of buffles are to be seriously establish for good to excellent homogeneization for your system. Foam reduces the volume of your tank, foam is volume plus inconvenience, efficiency of the system is lost. "Off-centre shaft" creates different type of mixing in certain part of the vessel, having inefficiencies or dead areas, which can create inequality in temperature distribution without talking about the reaction and it's completion.

Follow the principle that the liquid is mixed by the shaft and around to create a small Wortex. More you are further from the shaft more your mixing efficiency is reduced. The impellers are extentions of the shaft in horizontal direction. Vertically is different. Also, we have different mixing at the impeller level and in between the impellers. Mixing is simple but still complicated.

When you have buffles, the speed of agitation is become important factor. Again, watch turbulence and foam. I would like to add to the pictured vessel's impellers that it must be 75 to 85% of the diametre of the tank. From the shaft the impeller is in vertical position, and the exterior half end is beveled to 45 degree for more efficient mixing.

Your 1,000 litre tank is small for real production 750 litre of emulsion. For me is a "pilote" vessel and I am another "guru" in mixing liquids for over 54 years but I don't negotiate. Wish you good luck in your negotiation of choice, Gil.

Thank you one more time for sharing your knowledge and experience with us (me and the followers of this thread)! Baffles were eliminated from the interior of the tank as the particles of polymer tended to precipitate (or to get attached) between the back-side of the baffle and the inner wall of the reactor, forming actual "stones" of polymer that only could be removed using a hammer and a chisel, with the risk of damaging the reactor. Finally, these "stones" increased the turbulence during the process (it lasts about 8 hours), also decreasing the quality of the product. Best regards!

Fluid traveling rapidly over a baffle creates a lot of shearing force, which can destabilize particles. I have seen rate of agitation affect grit formation and coagulum build-up. Slower rpm gave cleaner reactor.

Hi Doc,

I think everyone call the bottom of any tank a "dish-bottom". You should talk with an experienced tank maker, Gil.