Study On The Structure-reactivity Relationship Of Heavy Organics And A Novel Reactor

Heavy organics(for example,coal,biomass,oil shale,heavy tar,pitch,some waste polymers)can be characterized as a complex mixture containing various alkanes,cycloalkanes,aromatic hydrocarbons and so on.With the worldwide exhaustion of petroleum,the conversion of heavy organics to fuels and chemicals has earned popularity.Besides,the situation that China is rich in the reserve of coal but poor in the reserves of petroleum and natural gas,emphasizes the urgency for China to develop the clean and efficient conversion technology of heavy organics.However,the present utilization of heavy organics in China is still highly pollutant and wasteful,mainly because the structure and structure-reactivity relationship of heavy organics are too complex to control their reactions with the current knowledge.Therefore,this dissertation studied the structure and structure-reactivity relationship of heavy organics from the following 4 aspects:(1)The conventional structural research of heavy organics in the viewpoint of compounds or chemical structural models,is respectively too complex or too simplified to quantify the structure and structure-reactivity relationship of heavy organics.However,considering that the types of covalent bonds are much less than those of compounds in heavy organics and the essence of chemical reaction is the transformation of covalent bonds,it should be reasonable for depicting heavy organics' structures in the viewpoint of bonding structure,namely the abundance information of various covalent bonds in heavy organics.This idea also may be the foundation for the better understanding of structure-reactivity relationship of heavy organics,but the relative work was rarely reported.Therefore,the chapter 2 checked the validity of 25 coal chemical structural models using the experimental C%-fa(aromaticity)regulation.The quantity of main covalent bonds in the relatively valid models was counted and then converted to the bonds' concentrations(g-1 coal).Meanwhile,based on a newly proposed method to calculate the bond's concentration via ultimate analysis and 13C NMR parameters,the bonding characteristics of coals were studied.It was found that the data of 28%coal chemical structural models cannot fit the experimental C%-fa regulation.The concentrations of main covalent bonds of the models and coals vary regularly with coalification(C%),indicating that during coalification the changes of coals' bonding structures are more essential than those of coals' chemical structures.Regarding the coals' bonding structures as the baseline,the structural models underestimate the abundance of the bonds related to aromatic carbons,whereas overestimate the abundance of the bonds related to aliphatic carbons.(2)It is well known that many conversion technologies of heavy organics refer to pyrolysis,which obeys the free radical mechanism,namely the thermal decomposition of heavy organics to generate free radicals and the couple of free radicals to generate products.Therefore,the research to correlate the bonding structure(proposed in chapter 2)with free radical reaction of heavy organics should be the key for studying the structure-reactivity relationship of heavy organics in a micro level.Many literatures have applied electron spin resonance(ESR)to study the radicals' behavior during the conversion of heavy organics,but many controversies remain.The most important question "whether the ESR spectroscopy can detect free radicals in reaction"(equivalent to the question"whether the ESR-detectable radicals can be directly correlated to the decomposition of bonding structure"),still lacks comprehensive summary.The chapter 3 reviewed the ESR research on heavy organics from 3 aspects,including the origin of ESR signals,the analysis methods of spectra as well as the research approaches.The correctness for correlating bonding structure to ESR-detectable radicals was analyzed.It was concluded that the ESR-detectable radicals are those wrapped in solid structure,and thus are hard to correlate with the rupture of bonding structure directly.Further,the study on structure-reactivity relationship of heavy organics in the viewpoint of "bonding structure vs.ESR-detectable radicals" will not be appropriate.(3)Considering that nowadays no appropriate device can detect free radicals in the thermal conversion of heavy organics,the chapter 4 selected the quantity of solvent-donated H(RH)in hydrogenolysis of oil shales to correlate with the bonding structures of oil shales.This is because that in the selected hydrogenolysis experiments the free radicals generated from oil shales can be capped by solvent H as timely as possible,thus RH covers the information of free radical reaction.As for quantifying the relationship between bonding structures and RH,the reported and referable approaches(for example,correlation analysis,kinetic models,computational chemistry),usually behave poorly in predicting experimental results due to some simplification in modelling.While recently it is found in literatures that the machine learning models,particularly the Artificial Neural Network(ANN),not only can quantify the relationship between structural parameters and reaction results of heavy organics accurately,but can also provide some scientific knowledge about the structure-reactivity relationship of heavy organics via some tactics.Therefore,the chapter 4 applied ANN models to quantify the relationship between the bonding structures,hydrogenolysis conditions and RH of oil shales.The detailed behaviors of various covalent bonds during reaction were discussed according to the sensitivity analysis.It was found that ANN has the capability of predicting RH accurately,when using the bonding structures and hydrogenolysis conditions of oil shales as ANN inputs.The free radicals generated from the rupture of Cal-Cal,Cal-Car,Cal-O,Car-O,Cal=O bonds in oil shales will be capped by solvent H;the large steric hinderance of aromatic structure represented by Car-Car bonds can inhibit H donation from solvent;the structures of Cal·,Car·,O·generated from the rupture of Cal-H,Car-H,O-H bonds tend to couple with other radicals,or be capped by solvent H after the condensation of local structures;while the ·H and ·OH from Cal-H,Car-H,O-H bonds can cap the free radicals from oil shales,decreasing the quantity of donated H from solvent.(4)The imperfection of the experimental reactors in literatures may mislead the research on structure-reactivity relationship of heavy organics.The so-called imperfection usually involves two problems,the severe volatiles reaction and incomplete collection of products,but the reactors proposed so far are still inefficient for simultaneously overcoming the above 2 problems.It is necessary to develop new reactor and experimental method.The chapter 5 introduces a newly designed reactor which can inhibit volatiles reaction and collect all products simultaneously.The quantity and quality of coal pyrolysis products from the new reactor are closer to those from primary pyrolysis of coal,compared to those from the conventional reactors,which indicates that the new reactor is more appropriate for the research on structure-reactivity relationship of heavy organics.