Hi. I’m not a programmer, so I’m looking for advice. My plan is to use Arduino to automate my distillation column. The first step would be to automate the temperature control. The temperature needs to be 55 Celsius, the idea is for the Arduino to read the temperature and adjust the speed of a water pump accordingly. The problem is that the adjustments in the water flow need to be very small. I’m probably looking at a pmw 12volt pump. Is this possible, and what would I need to make it work? Thanks in advance. 
Really? Why? Can we see photos of your distillation column? Where do you measure the temperature?
A full distillation run takes about 6 hours, all that time I have to monitor the temps and adjust them manually. It would be nice to automate that part, so I’m free to do other things while the distillation is running.
The amount of speed control you can get from PWM is very poor. You will not be able to get it to run very slowly.
For good control of a very slow motor you need to use a stepping motor. Preferably controlled by a timer interrupt pulsing the stepping motor driver.
For your first project you have a big learning curve in front of you.
Good luck.
I didn't ask why you want to automate it. I asked you for details so we can help you.
The water flow is around 500ml per minute
Thanks, can you identify some of the parts in that photo for us? Where would the pump and thermometer attach?
I would recommend a ds18b20 temperature sensor. You can get these in stainless steel probe format.
Yes, can you please answer my question, why you need fine control of the flow rate? Are you very mathematically inclined? To control a variable device in a feedback loop, a PID is the usual approach.
The incoming cold water is the hose with the black clip, the outgoing hot water is the hose with the red clip. The temp probe sits above the outgoing hot water. Above the hose with the red clip
The column is very sensitive, at the moment I’m using a manual needle valve behind a 12v dc pump.
Ok, but you said you adjust it manually. What is the minimum and maximum flow rate between which you adjust it? Between those limits, what level of control do you believe you need? 1%? 2%? 5%? 10%?
Hmmm. Cold in, warm out. So you want to adjust the pump speed until the output stream is 55C? Have I described it right?
Yes. More flow results in lower temps, lower flow will increase the temp.
You can't run the pump too slowly, then. It seems like the ability to measure the temperature depends somewhat on there being flow.
Couldn't you arrange to feed water that is already adjusted to some temperature? Instead of trying to regulate it in the tube?
I don't know much about distillation, so please forgive this dumb question. Why do you need to control the temp in the column? Could you control the temp in the vessel and have a fixed flow rate in the column?
Yes. If there is no water moving trough the column, the temp reading will be inaccurate
that was a tie. 
The distillation process is not constant, as the ethanol content in the pot decreases, the temperature in the column changes. Adjusting the water flow is the easiest way to control it. Adjusting the temp in the pot takes to long to react due to the thermal mass in the pot.