How to make a regular expression to search for words in a text?

Question

PHP

I do so

$keywords_post = '#[email protected]_fc,#[email protected]_fc,#instagram,#[email protected]_fc,#[email protected]_fc,#[email protected]_fc,#[email protected]_fc,#[email protected]_fc,echo,sky';
$keywords_post = str_ireplace(',', "|", $keywords_post);

if(preg_match("#{$keywords_post}#i", mb_strtolower($a_post->response->items[$it]->text)))

finds ordinary words separated by commas, but not with hashtags. How to fix?