Study On The Behavior Of Fe²⁺/Fe³⁺-subcritical Water Catalytic Pyrolysis Of Organic Matter In Oil Shale

Energy is the foundation and pillar of the progress of human civilization.With the rapid development of the world economy,conventional oil and gas resources have been depleted.As an unconventional oil and gas resource with huge reserves,oil shale has attracted the attention of researchers all over the world.China has abundant oil shale reserves,ranking second in the world.The vigorous development and utilization of oil shale resources are of great significance to guaranteeing China's socialist modernization.This paper takes the subcritical water in-situ extraction technology of oil shale as the research direction,and in view of the fact that most of the oil shale in the formation is still at a relatively low temperature in the in-situ extraction of oil shale,the oil shale in the formation has a limited degree of expansion during pyrolysis,and the subcritical water method takes a long time.The feasibility of low-temperature subcritical water pyrolysis of organic matter from oil shale was investigated,and the extraction process and product characteristics changes were analyzed in detail;The catalyst-subcritical water method for in-situ oil shale mining technology is proposed,the synergistic effect of Fe²⁺/Fe³⁺and subcritical water is studied,and the catalytic mechanism of Fe²⁺/Fe³⁺is revealed;the influence of oil shale swelling amount on the extraction effect is clarified.The specific research content is as follows:(1)Use 300?low-temperature subcritical water to extract organic matter in oil shale,discuss the production rules of shale oil and residual bitumen;use gas chromatography-mass spectrometry,gas chromatograph,X-ray diffractometer and the nitrogen isotherm adsorption/desorption analyzer analyzed the composition change law of the extracted products;finally,the cracking process and characteristics of oil shale in low-temperature subcritical water were described in detail.The results show that during the low-temperature subcritical water extraction process at 300?,the cracking efficiency of kerogen in the oil shale and the migration rate of bitumen products are very low.When the extraction time reaches 250 h,the kerogen inside the oil shale can be fully cracked,and the highest shale oil extraction yield can be obtained at the same time,but a large amount of bitumen still remains in the oil shale.The main components of shale oil and residual bitumen are n-alkanes,n-alkanoic acids,n-alkane-2-ones and isoprenoids.Both the decarboxylation reaction and the decarbonylation reaction of the extracted product under low temperature conditions are difficult to occur.With the extension of the extraction time,the secondary cracking of the extracted products intensifies,resulting in the increase of low molecular weight n-alkanes in shale oil and C₂-C₆ hydrocarbons in gas products.With the cracking and release of kerogen and the decomposition of carbonate minerals,pores and fissures in the oil shale gradually develop.The extracted waste water solution contains a large amount of cyclohexanone derivatives,isoprenoids and phenol derivatives.(2)The catalyst-sub critical water method for in-situ oil shale mining technology is proposed,and two transition metal salt catalysts FeCl₂ and FeCl₃,which are efficient,inexpensive and environmentally friendly,are selected.The synergistic effect of Fe²⁺/Fe³⁺and subcritical water was studied,revealing the catalytic mechanism of Fe²⁺/Fe³⁺.The research results show that subcritical water can carry Fe²⁺and Fe³⁺into the massive oil shale and expand its catalytic range.Fe²⁺and Fe³⁺can promote the cracking of kerogen,the migration of bitumen products and the decomposition of carbonate minerals.The optimal concentration of FeCl₂ and FeCl₃ are both 0.08 mol/L.Under the catalyzed condition of FeCl₂ or FeCl₃,the maximum extraction yield of shale oil can be obtained in only 40 h,while it takes 70 h under non-catalyzed condition.The catalytic effect of FeCl₃ is better than FeCl₂.Analysis of the characteristics of the extracted products shows that the main components of shale oil are n-alkanes,isoprenoids,n-alkane-2-ones and aromatics.FeCl₂ did not significantly affect the change trends of the relative content of the main components in the shale oil and residual bitumen with the extraction time.With the increase of FeCl₂ concentration,the relative content of asphaltenes in shale oil and the relative content of high molecular weight n-alkanes(C₂₈-C₃₅)in shale oil and residual bitumen gradually increase.The addition of FeCl₂ leads to an increase in the content of oxygen-containing organic matter and nitrogen-containing organic matter in the waste water solution,and also promotes the production of CO₂.Fe element will eventually be enriched in the oil shale matrix,but will not enter the shale oil,which indicates that adding FeCl₂ will not increase the burden of the later shale oil refining process.The ¹³C NMR analysis of kerogen showed that FeCl₃ could promote the breaking of heteroatom bonds in kerogen and the ring-opening reaction of aromatic structure,while inhibiting the condensation reaction of kerogen.The breaking of the heteroatom bond triggers the chain cleavage reaction network of kerogen,which increases the cleavage rate of kerogen.At the same time,FeCl₃ can also effectively promote the decomposition of residual bitumen and carbonate minerals and destroy the mineral structure in the oil shale,creating more heat and mass transfer channels,thereby increasing the migration rate of bitumen products.(3)The effect of oil shale expansion on the behavior of transition metal salt-sub critical water catalytic extraction of organic matter from oil shale is studied.As the radial expansion of oil shale increases,the extraction yield of shale oil gradually increases,while the extraction yield of residual bitumen gradually decreases,and the sum of the two gradually increases.When the expansion of oil shale increases,the internal pores and fissures of oil shale also increase,the infiltration capacity of subcritical water and transport capacity of residual bitumen both increase accordingly.When the expansion of oil shale is less than 0.15 cm,the addition of FeCl₃ has almost no effect on the yield of shale oil.When the radial expansion of oil shale is greater than 0.30 cm(33%of the free expansion),the FeCl₃ catalytic effect can be manifested significantly.The relative content of low-molecular-weight compounds in shale oil and residual bitumen shows a decreasing trend with the increase of oil shale expansion.The research in this article fills the gap in the field of catalytic hydrothermal cracking of oil shale,and provides a certain theoretical basis and technical support for the efficient in-situ exploitation of oil shale.