Method for producing formic acid by using orthophosphoric acid to acidifying sodium formate

The invention belongs to comprehensive utilization of waste material in phosphrous industry and organic aicd production industry. The process of preparing formic acid comprises following steps: adding a certain amount of orthophosphoric acid into reaction autoclave, adding reaction protective agent, with the weight being 1- 10%. of that of sodium formate, adding dried sodium formate with its water content being less than 0.85 at constant speed, putting reaction material into distilling still after thorough reaction, heating throgh barrier wall, the distillation time is in 2 hours, condensing and purifying the formic acid steam and getting formic acid. The material left in distillation still is sodium orthophosphate, which is reused as raw material for microcosmic salt production or produced into waterless microcosmic salt for sale.