An Oklahoma-based company plans to spend up to $900 million to build a plant that converts Alberta propane into a more valuable product used to make plastics. Williams says the facility will be the first in Canada to make polymer-grade propylene. The gas will be transported on railcars to U.S. Gulf Coast petrochemical producers, but the company is also exploring ways to develop a market within Alberta. Much of the propane Williams will use is a byproduct of the oilsands upgrading process. David Chappell, president of Williams’ Canadian division, says processing the gas in Alberta is better for the economy…