I believe that this is possible if your phone has an unlocked bootloader, and you can modify it. I don’t know how to do this, but you can find help with stack overflow. You can also check how developers installing Android on Windows phones do it. This site talks about installing Android on an SD card for their dual-boot mode.
This is probably more work than it costs. Another option, if you intend to use it on the same exact phone model, and they are rooted: use Titanium Backup to backup all applications and settings, and then restore them to another phone. This can be done for SD or Dropbox.
check in more detail in this post i got this answer from this post