| Pretreatment is a prerequisite and core step in lignocellulose biorefinery processes by definitively affecting transformation efficiency,emission and technical-economic indexes of upstream and downstream processes.As an important part of dry milling biorefinery processing(DMBP),dry acid pretreatment(DryAP)is combined with subsequent biodetoxification and high solids content simultaneous saccharification and fermentation to form an efficient biorefinery transformation system.This system minimizes energy consumption,fresh water input,and waste water generation and almost achieves the technical and cost indexes of corn ethanol and organic acids production.In this thesis,the study is focused on several technical bottlenecks of DryAP including high strength steam requirement,reactor corrosion by acid catalyst and long term storage of pretreated material and obtains reasonable solutions to these problems.Key technological breakthroughs of DryAP have been realized and technical foundation and application value of DMBP have been consolidated in this study.Meanwhile,DryAP has been extended to the field of heavy metal pollution government and important progress has been achieved.In the first part of this thesis,the steam heat source strength of pretreatment was studied and evaluated in detail.Pretreatment is an energy-intensive process and its main heat source is from high temperature steam.The intensity factors of steam such as temperature and stress directly determine the manufacture and operation costs of steam generation unit and reactor unit and significantly affect inhibitors generation during pretreatment.The main objective of this chapter was to explore the effect of different heating steam pressure supplied as heat source on DryAP efficiency.The pretreatment unit consists of a 20 L pretreatment reactor and a steam generator.The effect of different heating steam pressure varying from 1.5,1.7,1.9 to 2.1 MPa on physical property,composition,enzymatic hydrolysis and SSF performance of pretreated corn stover was tested.Meanwhile,a CFD model was established to simulate the steam holdup during DryAP in pretreatment reactor.The results show that the pretreatment efficiency of the pretreated corn stover heating by lower pressure steam is satisfying.This study gives an important scientific basis for steam supply strength during pretreatment and provides a solid basis for engineering design of the steam boilers used in distributed pretreatment.The second part of this thesis was aimed to reduce reactor corrosion during pretreatment operation and the corrosion degree was quantitatively measured.As a core technical barrier during dilute acid pretreatment,steam explosion pretreatment and hydrothermal pretreatment operations which are based on low pH conditons,reactor corrosion degree directly affects investment cost,operation cost and technical feasibility of pretreatment reactor.Low-corrosive pretreatment is essential for efficient biorefinery processes.Iron ion release from inner wall of micro-pretreatment reactor was measured for the accurate quantitation of the corrosion degree in this study.The experiment was conducted in a micro-pretreatment reactor and several important operation parameters of pretreatment on reactor corrosion were examined,including solid/liquid ratio,acid concentration,and acid catalysis species.The results show that higher solid/liquid ratio and lower acid concentration can significantly reduce reactor corrosion.Corrosion degree of sulfuric acid is comparable to that of formic acid and methylsulfonic acid,while hydrochloric acid is most corrosive to the pretreatment reactor.In sulfuric acid pretreatment,reactor metal material corrosion was reduced approximately 85%when the solid/liquid ratio increased from the conventional value of 1:10 to the high value of 1:0.5 at the same acid concentration.High solids content DiyAP was confirmed to reduce pretreatment reactor corrosion significantly.This study provides an important technical support for industrialized application of DryAP.The third part of this thesis was focused on the long-term storage of dry acid pretreated lignocellulose feedstock.Long time preservation of lignocellulose biomass without microbial contamination and sugar loss is crucially important.A three months' outdoor storage of dry acid pretreated corn stover was tested in this chapter.The compositions of the pretreated corn stover after long term storage were stable and a slight increase in hydrolysis yield and ethanol fermentability were obtained.Additional merits including antimicrobial contaminant environment from low pH and high inhibitor content,as well as the mild and slow hydrolysis of hemicellulose in the storage were found in pretreated material.This study reported an important solution from the perspective of biorefinery processes technology to feedstock storage and guaranteed continuous feedstock supply in biorefinery processes.The fourth part of this thesis was an attempt to expand DryAP to the field of heavy metal pollution government based on characteristics of DryAP including low energy consumption and zero waste water generation.At present,phytoremediation is a primary technology utilized for the government of heavy metal pollution.However,how to use heavy metal contaminated plants rationally without secondary pollution to the environment is a common concern in the field of heavy metal pollution government.In this chapter,paddy was selected as a model crop for phytoremediation.Rice straw was used to do DryAP and biodetoxification for subsequent ethanol fermentation with no wastewater generation.Meanwhile,contaminated rice grain was used to produce ethanol by conventional dry processes.The results showed that both contaminated rice straw and rice grain could obtain satisfied performance during biorefinery processes and no secondary pollution was generated.This pretreatment method can not only solve the secondary pollution problem in phytoremediation,but also obtain some biochemicals such as ethanol during biorefinery processes for economic and environmental benefits.Overall,several technical issues of DryAP were solved by reducing high strength steam supply,realizing a demotion of pretreatment reactor material corrosion and long term storage of pretreated material.Meanwhile,DryAP has been extended to the field of heavy metal pollution government,which significantly increases the industrial application potential of DryAP and whole DMBP and provides an important technical support for the application of DMBP in the industrial production. |
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