lots of questions there. the answer is that people do hire newly-graduated people as consultants. you do have knowledge in your field which can be relevant. you have also been taught how to think and express yourself, which is another valuable skill. some big consulting firms will also hire you as part of their teams, at a junior level, just as they would consider any graduate. a firm that specialises in the chemical sector will normally have a strong interest in recruiting people who can understand the technical issues that might be raised in an assignment. of course, the other side of the coin is that you do need to think about what happens next, in say 2 or 3 years. how will this experience help you to build your career for the future? or will you end up in a dead-end, older but no wiser than you are today?
on the patent question, i am not an expert, but usually companies will want to claim patent rights themselves. the only way around this is to negotiate at the time of signing the agreement, if you really have something they find very valuable. but having your name as a co-inventor on a patent is no bad thing in itself, even if they have all the rights.