Technically, yes. The MacBook will be able to detect the Power Bank and receive charge, but will be limited to charging at a rate of 18w. Most MacBooks require between 30w-96w in order to charge at the correct rate, depending on the MacBook you have. 

Although it is technically able to SLOWLY charge your MacBook, it is not recommended to be used in this manner. Over time, this may even affect the battery consumption rate. Again, highly not recommended.