This is how SCM works

With the prices of Oil flowing down, the refineries have reduced their output. Reliance in India is a major refinery that has also taken a massive cut. They use chlorine as part of their process. Reduction of refining has meant a reduced demand for chlorine. A huge quantity of chlorine that would otherwise be used up in the refining process was thus diverted to the open market.

With an excess of chlorine in the open market the prices of chlorine went down. In order to control the prices, the manufacturers of chlorine reduced their production. This is a simple standard story till here. Chlorine manufacturing has a by product - caustic soda. This is used by a lot of industries to make many other products. With reduced chlorine production, the caustic production also reduced. However the caustic demand was still the same. This caused the caustic price to jump up.

Thus while we have oil prices coming down, the prices of caustic products and its allied industries have gone up. Every product in the supply chain has some connections and not every connection is direct. Complicated relationships may cause surpirsing behaviour in the movement of prices of seemingly unrelated commodities.