Sabbatical from work as a non-student I have already finished my studies and work in a private  company. I would like to know that I could do my sabbatical as a researcher in a university. Is there any specific procedures or limitation for it?
Generally you would need to contact the university and/or some specific research group to see if they could accommodate you. I think that this is rare enough that you won't find a lot of places with policies designed for it, so you would need to work through individual contacts. 

Some research groups may be able to hire outside researchers, but many have funds intended only for supporting students. 

If you can go visit some nearby university and make contact with a researcher or department head you would learn more. 

You might also need to worry about what your company permits you to do outside the company. Some will want to impose restrictions. Others not. 

It would be different if you can bring research funding from your company with you. Universities are usually pretty happy about outside funding.