As noted already, given the string provided, your code will set num to 68. Here are a few pointers:
If you just want to remove the first character and don't need to match it, you can use:
recipe = recipe.Substring(1);
The Split method will create a new array with 8 elements, so there is no reason to initialize rElements with an array. Instead you can use:
var rElements = recipe.Split(' ');
If you need to convert all of the string entries in the rElements array into integers you can do this:
var numArray = rElements.Select(e => int.Parse(e)).ToArray();
Of course, if you need to check each one, you can use a loop with either TryParse or a try/catch. Putting it all together, you get:
var recipe = "搾68 00 00 37 00 45 00 00";
recipe = recipe.Substring(1);
var rElements = recipe.Split(' ');
var numArray = rElements.Select(e => int.Parse(e)).ToArray();