Study On Preparation Of The Long-chain Ethers As Diesel Additives From Biomass By Catalytic Pyrolysis Combined With Transfer Hydrogenation And Etherification

Diesel engines are widely used in the military,engineering,marine and other transportation sectors,and the demand for diesel is increasing,but the environmental pollution caused by diesel combustion is also more serious.Countries around the world have introduced increasingly strict emission regulations to limit vehicle emissions,such as particulate matter(PM),CO,NO_x,etc.Numerous studies at home and abroad have shown that the addition of long-chain ethers into diesel can significantly reduce pollutant emissions,and its physical and chemical properties are similar to those of diesel,eliminating the need for modifications to the feed and combustion systems.Compared to petroleum,biomass is the only renewable resource containing O element,which is an ideal raw material for the preparation of long-chain ethers.However,there are still many problems in the production process of biomass-based long-chain ethers,such as long process routes,low selectivity and yield of product,harsh reaction conditions,high costs,etc.Solving the above problems is of great significance to realize the high-value use of biomass,optimize the energy structure of China and achieve carbon peaking and carbon neutrality goals.To address the above problems,the work designed and implemented a green and efficient production process for biomass-based long-chain ether as a diesel additive based on the fuel design concept,and further investigated its low-temperature oxidation performance.The pyrolysis properties of seven agricultural holocelluloses and two forestry holocelluloses were studied by TGA and Py-GC/MS.It was found that agricultural holocelluloses were more suitable for the preparation of ketones,aldehydes and furans with the carbonyl group,with the highest target product content of 51.4%obtained by fast pyrolysis of corn stalk holocellulose.A quadratic relationship existed between the cellulose to hemicellulose mass ratio(CE/HCE)in holocellulose and the content of dehydrated sugars or levoglucosan.When the CE/HCE exceeded 1.7,the content of dehydrated sugars and levoglucosan in the products from holocellulose pyrolysis increased rapidly,which was not conducive to the production of the target product.The steam-exploded pretreatment showed that the conditions,low pressure and short time,were favorable to the removal of lignin.When the steam explosion pressure was 2 MPa and the holding time was 3 min,the lignin removal reached a maximum of 65.08%,and the lignin and holocellulose contents were 7.9%and 76.67%,respectively.The catalytic effect of Fe-Ce mixed metal oxides on pyrolysis gas of steam-exploded holocellulose(SE)was systematically investigated by a two-stage fluidized/fixed-bed reactor and a DFT calculation.The Fe/Ce molar ratio below 0.6 favored the formation of Fe-Ce solid solution and oxygen vacancies,thus improving the catalytic ketonization activity of the SE pyrolysis gas,among which the Fe/Ce(0.3)showed the highest catalytic activity for the production of carbonyls,with carbon yields of up to 25.55%.The optimization of the process conditions(carrier gas flow rate and WHSV)can further increase the carbon yield of carbonyls to 28.91%.DFT results showed that the formation energy of oxygen vacancies on the surface of Fe-Ce mixed metal oxides increased and it was detrimental to adsorb levoglucosan and acetic acid with an increasing Fe/Ce molar ratio.After 200 min of continuous operation,the Fe/Ce(0.3)remained highly active and there was little carbon deposition and adsorption of metal carboxylates on the catalyst surface.The effects of catalyst type,catalyst mass ratio,reaction temperature and reaction time on the transfer hydrogenation and etherification reaction of 2-butanone,the main component of bio-oil from catalytic pyrolysis of SE,were investigated.When the 2-butanone/isopropanol mixture was 50 m L(2-butanol concentration of 4 M),the Cu/Char dosage was 0.5 g,the H-Beta dosage was 0.5 g,the initial nitrogen pressure was 2 MPa,the reaction temperature was 120℃and the reaction time was 12 h,the conversion of 2-butanone reached 100%and the selectivity of sec-butyl isopropyl ether reached the maximum of 83.13%.The optimum experimental conditions were applied to the transfer hydrogenation and etherification reaction of bio-oil from catalytic fast pyrolysis of SE.The conversion of the bio-oil gradually increased with increasing reaction time,from 31.77%at 1 h to 36.28%at 12 h and the mass yield of long-chain ethers increased from 53.94%at 1 h to 62.86%at 12 h.The catalyst remained highly active after 5 repeated runs.Mass and energy analyses of the processing technique from biomass to long-chain ethers as diesel additives showed that approximately6.2 t of dry-based corn stalk was required to produce 1 t of long-chain ethers and 28.7%of the energy in the corn stalk was transferred to the long-chain ethers.The low-temperature oxidation characteristics of the long-chain ethers were investigated through a variable compression ratio diesel engine.The physical and chemical properties of the long-chain ethers were analyzed and their blending conditions with n-heptane were also investigated.The effects of compression ratio and blending ratio on the low-temperature oxidation characteristics(in-cylinder pressure,in-cylinder temperature and net heat release rate)and CO emissions of the synthetic fuel were investigated.The results showed that long-chain ethers were only suitable for combustion blended with diesel in a low ratio.As the compression ratio increased,the maximum in-cylinder pressure and the maximum in-cylinder temperature of long-chain ethers increased.At the same compression ratio,the maximum in-cylinder pressure and maximum in-cylinder temperature of long-chain ethers were greater than those of n-heptane.Under the critical compression ratio,both n-heptane and long-chain ether showed low-and high-temperature exothermic peaks,and the low-and high-temperature exothermic peaks of long-chain ether were significantly higher than those of n-heptane,and the crankshaft angle corresponding to the exothermic peaks were also earlier than that of n-heptane.Therefore,the compression ignition activity of long-chain ethers was better than that of n-heptane.At the critical compression ratio,the CO emissions of long-chain ethers were reduced by 77.2%compared to n-heptane.At the same compression ratio,the maximum in-cylinder pressure and maximum in-cylinder temperature increased as the long-chain ethers blending ratio increased.When the blending ratio of long-chain ethers increased from 0 to 30%(LE30),the critical compression ratio of the fuel decreased from7.35 to 6.90,and the maximum in-cylinder pressure and temperature for the critical compression ratio increased from 21.35 bar and 1077.28 K for n-heptane to 22.94 bar and1220.52 K for LE30,respectively.At the critical compression ratio,the blending ratio has less influence on the low-and high-temperature exothermic peaks,while the higher the blending ratio,the earlier the low-and high-temperature exothermic phenomena appeared.In conclusion,the compression ignition activity of the fuel blend increased as the blending ratio of long-chain ethers increased.At the critical compression ratio,the CO emissions of LE30were reduced by 44.97%compared to n-heptane.