| Steam explosion(SE) began with beaver board production in 80 years ago. In recent decades biomass conversion research, it was found that SE is conducive to lignocellulose hydrolysis fermentation process as a pretreatment technology with some advantages include low energy consumption, little pollution and environmentally friendly property. These inspire people that this pretreatment technology might provide vast potential promising application.However, for a long time, we have not enough knowledge in steam explosion mechanisms, the SE process technology and the SE device design have always remained in traditional pump boiling technology stage, whose screen index is severity factor, simulating explosion process by flow boiler valve opening. All of these cause that SE pretreatment effects remain in boiling effect level and SE application scale is constrained greatly. In the 21 st century, this technology is seriously in doubt because of few theory research advances, and some experts even propose replacing SE pretreatment with hot liquid water pretreatment and steam pretreatment, which has already less meaning of existence.Based on the careful analysis and understanding of explosion nature, this study proposes Instant Catapult Steam Explosion(ICSE) technology and its device design, redefines the meaning of steam explosion. By the studies on physical property, surface property, physicochemical property and microstructure morphology analyses, we compared pretreatment effect between ICSE and the other pretreatment technology, explored biomass conversion mechanism under ICSE pretreatment, found some data and phenomena which could reflect steam explosion real meaning.The author’s study was perfectly reflected in this doctoral dissertation, including:(1)Based on the studies and calculation in gas kinetics and engineering thermodynamics in steam explosion process, we thought that steam explosion is closely related with conversion time and conversion energy as an energy rapid conversion process. In the explosion time derivation process, we proposed a steam explosion model which is constructed by piston and cylinder, called ICSE technology model. We confirmed the technology indexes which accurately reflect its essence: explosion time and explosion power density, definitude technology features which are explosion shock wave and conversion of heat into power. The calculation results show that explosion time have 123-fold between ICSE and traditional device. The test results show that material temperature is 55~60℃ after ICSE, which is considerably below boiling and flowing processes, achieves a conversion of heat into power.(2) We proposed a whole set of test equipment and production equipment design projects and prototypes, summarized the features of explosion unit, drew up the design considerations of explosion outlet seal device. We detected explosion time and the whole machine indicators of ICSE prototypes. The result show that the whole explosion process is less than 12 ms, which coincides with the calculated result and achieves the design expectation.(3) We studied the ICSE technology influence on lignocellulose physicochemical property. By testing the content change of lignin, cellulose and hemicellulose in silage corn straw after ICSE pretreatment, this study measured each technology factor influence on ICSE effect. Experiments show high pressure and short time would minimize lignin content in ICSE, which could not be explained by severity factor. In severity factor theory, severity factor will all increase by pressure and time. which could not differentiate high pressure short time and low pressure long time. It is denied further that severity factor was used to indicate the process measurement. Moreover, we found that acid-soluble lignin has a step point at 2.4MPa in part, and hemicellulose has a step point at 140~160s in three pressure sections. To synthesize the three elements change rule, 2.4MPa/140 s is one of the best combination of ICSE technology.(4) We studied the ICSE technology influence on lignocellulose hydrolysis character. By difference steam pressure and holding time parameter combinations using in straw ICSE test, we study the hexose and pentose concentration changing rules in the hydrolysate under stand saccharification condition, validate and optimize ICSE process parameters. The study shows that ICSE has an optimal effect area in promoting hexose enzyme hydrolysis, which is located in center of 2~2.4MPa steam pressure and 140~160s holding time. Pentose concentration increases with holding time extending, achieves an ideal level in the scope of 1.8~2.0MPa steam pressure.(5) By a study that compares ICSE with boiling flow and alkali retting, we explored the mechanism that ICSE acts on biomass physical property, surface energy property and microstructure. In this study, we conducted solid surface energy test, settlement characteristics test, BET surface area and pore-size distribution test, and analysis of SEM morphology. Among them, solid surface energy test shows unusual results: ICSE could increase solid surface energy to 71.1m J/m2, has a 20.3% increase compared with boiling flow and a 25.7% increase compared with alkali retting, has a 10.0569 m J1/2/m hydrophilic index, has changed solid surface property obviously. Settlement characteristics test shows that ICSE samples settle all, boiling flow samples have a 0.69:1 floating rate, alkali retting samples have a 2.13:1 floating rate. SEM morphology analysis show that ICSE process changes organization structure drastically, fracture and crush cell wall completely. BET surface area and pore-size distribution test shows ICSE could increase solid surface energy to 3.4471m2/g, has a 57.4% increase compared with boiling flow and a 263.0% increase compared with alkali retting, pore-size and pore-volume increase. These tests reflect that ICSE could improve effectively biomass solid surface energy and hydrophilic index, increase biomass surface area and compatibility with water, reveal the superiority of ICSE over the other pretreatment technology.(6) We studied the mechanism of ICSE changing biomass physicochemical property by XRD, FTIR and TGA test. XRD test shows that ICSE achieves a 29.4% decrease in degree of polymerization compared with boiling flow and a 26.1% decrease compared with alkali retting, decrease 8 peaks than original sample, has the biggest change in microstructure. FTIR test shows that ICSE sample’s spectrum occurs much more obvious displacement than the other samples’, declares that ICSE could change more obviously in organic functional groups. TGA test shows that ICSE achieves a 19.7% increase in maximum weight loss rate compared with boiling flow and a 21.2% increase compared with alkali retting, a 31.8% decrease in pyrolysis residue mass fraction compared with boiling flow and a 26.4% decrease compared with alkali retting. |
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