<?php
$data = array(array(17,99), array(17,121), array(99,77), array(45,51), array(45,131), array(131,56), array(14,256), array(233,231), array(14,15));
$result = array();
foreach ($data as $innner_array) {
    $intersect_array = array();
    foreach ($result as $key => $result_inner_array) {
        $intersect_array = array_intersect($innner_array, $result_inner_array);
    }
    if (empty($intersect_array)) {
        $result[] = $innner_array;
    } else {
        $result[$key] = array_unique(array_merge($innner_array,     $result_inner_array));
    }

}
var_dump($result);
?>

array(5) {
  [0]=>
  array(4) {
    [0]=>
    int(99)
    [1]=>
    int(77)
    [2]=>
    int(17)
    [3]=>
    int(121)
  }
  [1]=>
  array(4) {
    [0]=>
    int(131)
    [1]=>
    int(56)
    [2]=>
    int(45)
    [4]=>
    int(51)
  }
  [2]=>
  array(2) {
    [0]=>
    int(14)
    [1]=>
    int(256)
  }
  [3]=>
  array(2) {
    [0]=>
    int(233)
    [1]=>
    int(231)
  }
  [4]=>
  array(2) {
    [0]=>
    int(14)
    [1]=>
    int(15)
  }
}