getting 'category_id' link in the SEF URLS'
 
like http://www.example.com/my-sample-product.html?category_id=27
 
how to remove the part after '?' from the urls?

Have done this on my site, will see if I can find you the amended code

thanks Benshanks, looking forward for it.

Did you found solution for that? I'm seeing duplicate content error in Google webmaster tools because of this.

Is that available in English please?

open file block/block_product_list.php, find string 392.
old: $details_query = get_query_string($details_parameters, array("page", "sort_ord", "sort_dir"), "", false);
new: $details_query = get_query_string($details_parameters, array("page", "sort_ord", "sort_dir", "category_id"), "", false);

thanks kaktyc1