USB Blaster disapears from the hardware setup of the quartus prime programmer when I connect a com port with the teraterm using an FTDI usb to I2C adapter.

I use Win7 64b, and have multiple USB Blasters (one a Terasic dongle, another a Terasic board with embedded USB Blaster), an FTDI USB serial dongle, and a couple other serial dongles all connected at the same time. I don't observe this issue, and never have. See the screenshot from the device manager panel, above.

I am using TeraTerm v4.99 and I usually have it open all the time, no problems.

I would make sure the 'VCP' box is not checked on your Altera device driver Advanced Panel, just in case. It would not normally be checked.

I suspect you have a USB VID/PID collision between your Altera devices and your FTDI serial controllers, so windows is loading the wrong driver.

You might try forcibly removing the drivers (uninstall) for the Altera dongles and your serial dongle, and then plug them in one at a time and point to the correct driver directories.