Synthesis of Alkyl Halides from alcohol?

This reaction goes by a typical SN1 mechanism, and the yields are generally quantitative. The product is very volatile, however, with a BP near room temp. Your low yield means that you lost product to evaporation somehow. There are lots of places it could happen: When adding the acid, if it gets too warm. When doing the sep funnel work, if you don't keep everything cold. When distilling, if there's a leak in the apparatus or if the collecting vessel isn't kept cold and nearly closed. If you put or collected your product in a beaker at any time, that would allow it to evaporate.