Soap dispensers typically have a pump mechanism that dispenses liquid soap, while lotion dispensers usually have a trigger that releases a pre-measured amount of lotion.
Regarding refilling, soap dispensers can be refilled with any liquid soap, while lotion dispensers must be refilled with the same type of lotion that was originally used.
Finally, lotion dispensers are often designed to be more comfortable to hold and use than soap dispensers. So, they are typically smaller in size and have a more ergonomic shape.