Study On Bio-Oil/Char Production From Kitchen Food Waste By Hydrothermal Treatment

Kitchen food waste generated during purchase,preparation and consumption of meals are usually composed of carbohydrate,protein,and lipid.Incineration of kitchen waste would lose amount of energy cause of the high moisture and low heating value in kitchen waste.Landfill of kitchen waste would bring pathogenic bacteria contamination cause of the high organic matter concentration.The special consumers'behavior and cooking habits in china lead to high lipid and salt concentration in kitchen waste,which gives great challenges to biological treatment;besides,the biological treatment still has some problems about inefficient,high request for the feedstocks,high residuum after treatment and so on.Hydrothermal treatment of kitchen waste with high efficiency,good adaptability for feedstocks,unnecessary for dehydration,valorization of products etc.has attracted a lot of interest.This research focused on kitchen waste and the typical components,studied the mechanization of hydrothermal reaction and the effects of key parameters.The denitrification and viscosity breaking of oil products with addition of acid,alkaline,heavy metal were researched;the upgrading process of heavy oil products in supercritical water and the demulsification of water-in-oil emulsion products were also studied.The hydrochar were activated for porous structure,and the activation route were deduced.Finally,technological process,heat balance,and economic analysis of hydrothermal treatment on kitchen waste were designed and studied.The main contents of this paper are as follows:?1?Hydrothermal treatment of real kitchen waste was performed in a batch reactor.The effects of key parameters including reaction temperature,residence time,and water recycle,and the characteristic of products were studied.The optimal parameters of hydrothermal treatment on kitchen waste were recommend as follow:300?³20?of reaction temperature,20 min⁴0 min of residence time,8 MPa¹1 MPa of reaction pressure.Under optimal parameters,the yield of bio-oil products was higher than 43%,the HHV was higher than 37 MJ/kg,the viscosity was lower than 1.2 Pa·s,the concentration of Gas oil fraction was higher than 50%,the concentration of Residuum fraction was lower than 15%;the characteristics of bio-oil indicted the potential of fuel utilization.Water recycle can enhance the yield of bio-oil,content of C and H elements,energy recovery,and content of low boiling-point fractions.?2?The typical model components of carbohydrate,protein,and lipid were selected as feedstocks to study the effects of components on hydrothermal reaction.Yield prediction model based on interaction of components was established,the interaction of carbohydrate and protein was in-depth studied,and the route of hydrothermal reaction with different model components was deduced.The interaction of carbohydrate and protein can significantly increase the bio-oil yield and decrease the bio-char yield.During hydrothermal process,the hydrolysis of kitchen waste was the first step to generate oligomers or monomers;then the polymerization,restructuring,condensation,dehydration,decarboxylation of the intermediate products were performed to form abundant hydro-products.?3?Hydrothermal treatment of real kitchen waste with addition of acid,alkaline,heavy metal were researched,and the denitrification and viscosity breaking of bio-oil products were the main objective.The results show that acid addition with an appropriate rate can effectively decrease the N content and viscosity;simultaneously it can also enhance the fluidity of bio-oil.The N content of bio-oil with acid addition can be as low as 0.58%.When the rate of acid additives and feedstock was 2.5 mol/kg,the static and dynamic viscosity of bio-oil were both close to 0.1 Pa·s,which were lower than that of non-additives.On contrast,the effects of alkaline and heavy metal additives on denitrification were weak,and the effects on yield,C recovery,content of low boiling-point fractions,and residuum were negative.?4?Upgrading process of heavy bitumen in supercritical water?SCW?and the demulsification of water-in-oil emulsion products were also studied.The results show that SCW upgrading reaction can enhance the quality of bio-oil,including viscosity,molecular weight,H/C ratio,residence carbon and content of asphaltene.After hydrothermal reaction,the products of oil,char,water were mixed in the reactor,and stayed in water-in-oil emulsion.With the increase of hydrothermal temperature,the water content of water-in-oil emulsion decreased,and the maximum diameter of water droplets increased.The chemical demulsification can remove the water droplets in emulsion;when the hydrothermal temperature was 440?,the water removal efficiency of chemical demulsification can reach92.3%,and the water content after demulsification was as low as 2.5%.?5?Hydrothermal treatment of D-xylose,cellulose,lignin,and wood at reaction temperature of 200?²60?and residence time of 2 h⁸ h were set up as L₁₆?4⁵?orthogonal test.Then,the hydrochar was activated to produce porous materials,and the activation route were deduced.When the reaction temperature was 260?,the HHV of all hydrochar were26.96 MJ/kg²8.75 MJ/kg;the elementary composition of hydrochar was close to lignite.After KOH activation,the microspheres in hydrochar derived from D-xylose,cellulose,and wood were decomposed,and the surface of activated char was smooth with porous structures.In the activation process,the microspheres tended to be coalesced first,then destructed to form micropores.The BET surface area,total pore volume,and total metal uptake capacity were significantly improved on activated char deriving from carbohydrates,especially from cellulose,as high as 1430 m²/g,0.767 cm³/g,and 168.7 mg/g,respectively.On the contrast,the high stability of lignin derived chars inhibits the thermal and chemical destruction in the activation process,which suppresses the formation of micropores.The carbohydrates/cellulose were more suitable for KOH activation to produce microporous materials than the lignin-based materials.?6?Technological process,heat balance,and economic analysis of hydrothermal treatment on kitchen waste were designed and studied.The pre-heating process has the strongest influence on the dosage of high temperature stream.During the design of reactor,the pre-heating process should be improved,which can decrease the dosage of high temperature stream and operating costs.The calculation results of heat balance show that 2.56 ton of high temperature stream was used when treating 1 ton of kitchen waste particles,corresponding to640 Yuan of stream cost;meanwhile,0.43 ton of bio-oil was produced,which valued at 1070Yuan.Regardless of other operating costs,the value of bio-oil products can cover the stream cost,which indicting the preliminary feasibility of hydrothermal treatment on kitchen waste.