Conversion Of Biomass Wastes Into Formic Acid And Acetic Acid Under Hydrothermal Conditions

In order to reduce the dependence on fossil fuels and reduce environmental pollution,it is urgent to find new clean energy.As the most abundant renewable resources on Earth,biomass has become a popular direction of energy research.The utilization of biomass wastes can improve wastes management and also benefit for the production of industrial chemicals and fuels production,so as to achieve sustainable development.Food wastes and coconut husk are two kind of valuable biomass wastes which have difficulty in their disposal.By adopting the hydrothermal oxidation technology,not only the high-water-content biomass wastes can be disposed directly without drying pretreatment but environment pollution problems caused by other disposal methods can be avoided as well.Herein,in this paper,a facile and rapid method for the conversion of these biomass wastes into formic acid and acetic acid under mild hydrothermal conditions was proposed.Specific results are as follows:First,conversion of vegetable wastes into acetic acid was studied.The results showed that the two-step hydrothermal method was effective for the production of acetic acid.The addition of NaOH solution in the first step could increase the yield of acetic acid.The optimal condition for potato acetic acid production from potato was 300 ~oC of reaction temperature,the60 s of first-step reaction time,90 s of second-step reaction time,NaOH concentration 0.5 mol/L,70%oxygen supply.The yield of acetic acid was30.5%.In addition,for the raw materials using carrots and lettuce,yield of acetic acid were 28.3%and 27.5%respectively.Second,conversion of food wastes into formic acid was studied.The results showed that adding 30 min~60 min acid pretreatment procedure before oxidation reaction can effectively improve the selectivity of formic acid and greatly increase the yield of formic acid.The optimal condition for pretreatment was:1.2 mol/L HCl,160 ~oC,30~60 min;the optimal condition for the oxidation reaction was 250 ~oC,140%oxygen supply,1mol/L NaOH,60 s.The results showed that purified starch and cellulose which are typical model compounds of food wastes could be converted efficiently to formic acid with 78%and 46%yield.The main components of food wastes,rice,flour,potato,carrots,and tissue could also be converted into formic acid with a satisfying yield of more than 40%except tissue(30%).Simulated food wastes could be converted into formic acid with yield of 42%,indicating that this method is feasible and effective for valorization of high water-content and complex composition food wastes.In addition,it was found that the formic acid yield was positively correlated with the total yield of monosaccharide after pretreatment,indicating that the final yield of formic acid mainly depends on the degree of hydrolysis of polysaccharide in pretreatment process.Finally,hydrothermal conversion of coconut husk into formic acid and acetic acid was studied.Acid pretreatment was also effective for the hydrothermal conversion of coconut husk.The optimal condition for pretreatment of coconut husk was 1.2 mol/L HCl,0.31 g/L coconut husk,160 ~oC,60 min;the optimal condition for the oxidation reaction of coconut husk was 1 mol/L NaOH,300 ~oC,120 s,140%oxygen supply.The total yield of formic acid and acetic acid was 50.2%,with formic acid yield of25.8%and acetic acid yield of 24.4%.In conclusion,this study proposed a quick and efficient approach for conversion of two kinds of biomass wastes,food wastes and coconut husk,into high value-added organic acid,formic acid and acetic acid.It provides a new idea for the utilization of the high water-content and complex composition biomass wastes.