N-methylformamide prepration, help needed

i have 40% methylamine in water, i'm trying to move the methylamine as a gas, the system is build like the apparatus in the picture, now in the beginning at temp around 75 degrees(celsius), everything goes well, a white gas form above the formic acid (99%), then after about 15 minutes it's disappear, the bubbles slow and raise in the temp will not help.
please anyone has any idea?

what is the duration of the process for 500ml 40% methylamine and 250ml formic acid?

what the temputere range this thing should work with?

- i have ice cold water in the left condencer.

thanks!