function tag_to_category ($post_id = 0) {
     if (!$post_id) return;
     $post_tags = get_the_tags($post_id);
     foreach ($post_tags as $tag) {
		$cat_id = wp_create_category($tag->name);
    	$result =  wp_set_post_terms( $post_id, $cat_id, 'category', true );
     }
}

add_action('save_post','tag_to_category');