MYSQLI escape string

[eluser]jzmwebdevelopement[/eluser]
I am currently updating a section of code that uses mysql currently the escape string is structured like this:

Code:

$product_name = mysql_real_escape_string(trim($_POST['product_name']));

and works fine.

My issue is when I change the above string to

Code:

$product_name = mysqli_real_escape_string($database, (trim($_POST['product_name'])));

and declare the following:

Code:

$database = $this->load->database();

above it I get the error that its NULL

How do I escape a string with CI?