<?php
$string = <<<STR
2234323,23,23,44,433;3,23,44,433;23,23,44,433;23,23,44,433;4534453,23,23,44,433;
3,23,44,433;23,23,44,433;23,23,44,433
7545455,23,23,44,433;3,23,44,433;23,23,44,433;23,23,44,433
STR;
$string = preg_replace('/;?\R/', ';', $string); // I don't know if this is actually necessary for your real project
var_export(
preg_split('/;(?=\d{7}\b)/', $string)
);