I have no idea how much energy is expended in the conversion....

I have no idea how much energy is expended in the conversion. That is the domain of the experts developing the tech. However the fact that they have trialled the process and successfully transported a batch (no idea how much) from Australia to Japan, suggests they are on a track to viability. You may be correct and it may be uneconomical or unsafe,(it is apparently highly toxic to marine life), although as we know the Japanese are not particularly worried about what they put in the ocean). time will tell. But it is encouraging that solutions are being sought.