A method includes, controlling a first process using a first process control system. The method also includes controlling a second process using a second process control system. The method further includes controlling the first and second process control systems together. In addition, the method includes optimizing at. least one process objective using both the first and second process control systems. The first process can be a natural gas liquids production process, and the second process can be a liquefied natural gas production process. The process objective could include at least one of : profit, natural gas liquids quantity, natural gas liquids quality, liquefied natural gas quantity, and liquefied natural gas quality.