Can a portable air conditioner be used to reduce moisture in a room?
I would consider a dehumidifier which will pull moisture out of the air. I'd also check into why the wall is getting moist. Are you sure there is enough insulation in the wall, because you definitely should not have moisture condensing on or in the walls.

An air conditioner will make the room colder which you probably don't want if the weather is already turning cold. The dehumidifier will pull the moisture out of the air without cooling the air the way an air conditioner would.

For the time being the dehumidifier should pull moisture out of the room for you. The specs for the appliances (dehumidifier or air conditioner) are usually fairly accurate, most notably on larger name brands. I've found knock-off and smaller brands to be a bit sketchy when it comes to performance, so I've learned my lesson and usually go for the larger more established brand names when it comes to things like this.