comment form code redirect to wp_comments_post.php with blank page

There are other issues in your code or the $form_args array items, but the main ones are:

1. The blank page is due to missing hidden comment fields for replying to comments — see get_comment_id_fields(), where the fields are in the submit_field arg by default.

   So to quickly fix that, add %2$s in that arg like so:

   'submit_field' => '... <button type="submit" class="button btnprimary form-control"> submit request </button> %2$s ...',
   

   But you should actually use the submit_button arg to customize the submit button HTML, then with the submit_field arg, use something like:

   'submit_field' => '<div>%1$s %2$s</div>',
   

2. The comment textarea field needs to have its name set to comment.

   'comment_field' => '... <textarea class="form-control" placeholder="Message" ... name="comment"> ...',
   

3. Please, make sure your HTML is valid — you’ve got an unwanted </form> tag in the submit_field arg. 🙁

I hope that helps and please review the comment_form() reference for details on the other args, and other relevant details/resources.