Energy giant Shell (NYSE:SHEL) on Friday said it expects to record a post-tax impairment hit of up to $2 billion mainly linked to its Singapore and Rotterdam plants, while also saying trading in its key gas division will decline on the quarter.This comes after Shell on Tuesday announced it would temporarily suspend on-site construction at its 820,000 metric tons a year biofuels facility in Rotterdam amid current market conditions. The decision has led the oil company to project it will book a non-cash post tax impairment between $600 million and $1 billion for the Rotterdam hub when it…