Hydroxypropyl celluloses(HPC) were homogenously synthesized by the reaction of cellulose with propylene oxide in NaOH/urea aqueous solution.Water-soluble HPC with molar degree of substitution(MSNMR) in the range of 0....Hydroxypropyl celluloses(HPC) were homogenously synthesized by the reaction of cellulose with propylene oxide in NaOH/urea aqueous solution.Water-soluble HPC with molar degree of substitution(MSNMR) in the range of 0.52~0.78 was prepared from microcrystalline cellulose,cotton linters,and spruce sulfite pulp.The structure of the HPC samples was characterized by means of FT-IR,NMR,gas chromatography(GC),and size exclusion chromatography(SEC) analyses.Three types of cellulose samples with different molecular weights were found to dissolve well in the NaOH/urea solvent with no obvious differences in reactivity and regioselectivity.The relative reactivity of hydroxyl groups in the glycosyl unit was in the following order:O-6>O-2>O-3.In addition,the results of the study indicated that the tandem reaction during hydroxypropylation could be ignored.展开更多
In this study,waste cotton fabric was used as cellulose raw material and pretreated in aqueous NaOH/urea solution system to investigate the effect of NaOH/urea pretreatment solution on the hydrolysis of cotton fiber.T...In this study,waste cotton fabric was used as cellulose raw material and pretreated in aqueous NaOH/urea solution system to investigate the effect of NaOH/urea pretreatment solution on the hydrolysis of cotton fiber.The cotton fiber was pretreated with different conditions of aqueous NaOH/urea solution,and the pretreated cotton fiber was hydrolyzed under the same conditions as the original cotton fiber.The results of characterization analysis showed that water retention value of pretreated cotton fiber was higher than that of unpretreated sample.Moreover,the cotton fiber presented both a convoluted structure and a coarser surface,XRD results suggested that the crystallinity degree of cellulose decreased dramatically,more cellulose II appeared,and the hydrogen bond is broken.Among the different pretreatment conditions,the pretreatment effect was the best when the reaction temperature was 0°C,the solid-liquid ratio was 2:50,and the NaOH/urea ratio was 7:12.The hydrolysis experiments of pretreated and unpretreated cotton fibers showed that when the hydrothermal temperature was 230°C,the heat preservation was 2 h,and the hydrochloric acid concentration was 5 wt.%,the glucose yield reached 29.99%.H+could catalyze the hydrolysis of cotton fiber more effectively due to damage to crystal structure and hydrogen bonds.展开更多
In order to study the combustion characteristics,NOx emission and NH3 slip in a new trinal-sprayed precalciner,the simulations of combustion and aqueous urea solution based selective non-catalytic reduction(SNCR)proce...In order to study the combustion characteristics,NOx emission and NH3 slip in a new trinal-sprayed precalciner,the simulations of combustion and aqueous urea solution based selective non-catalytic reduction(SNCR)process were conducted by computational fluid dynamics in this precalciner,the effects of different injection heights,different injection flow rates and stratified injection under different flow rates on SNCR process were studied.The results showed that the flow field was symmetrically distributed in the precalciner,and the flue gas from the rotary kiln formed the recirculation region on both sides of the cone body,which increased the residence time of the solid particles.The temperature was mainly between 1100 K and 1250 K in the middle and upper column of the precalciner,which met the demand of the pulverized coal combustion and raw material decomposition.The concentration of NO at the outlet of the precalciner was 559 ppm,moreover,different injection heights and different injection flow rates had a strong influence on NOX removal efficiency and NH3 slip.The aqueous urea solution should be injected at SNCR-1 to prolong the residence time of NH3,and injection flow rate had an optimal flow rate but not the higher the better.When the injection flow rate under stratified injection was 0.019 kg/s,which could play a better optimization role on NO removal efficiency on the basic of the injection flow rate.In consideration of cost effective,a stratified injection with an injection flow rate of 0.019 kg/s and an injection height of 20 m,25 m and 30 m was suggested as a compromise of a satisfactory NOx reduction rates and reasonable NH3 slip.Under this condition,numerical simulation result showed that NOx concentration at the outlet of precalciner was 297.27 mg/Nm3 and NH3 slip was 4.67 mg/Nm3,meeting emission standard.展开更多
文摘Hydroxypropyl celluloses(HPC) were homogenously synthesized by the reaction of cellulose with propylene oxide in NaOH/urea aqueous solution.Water-soluble HPC with molar degree of substitution(MSNMR) in the range of 0.52~0.78 was prepared from microcrystalline cellulose,cotton linters,and spruce sulfite pulp.The structure of the HPC samples was characterized by means of FT-IR,NMR,gas chromatography(GC),and size exclusion chromatography(SEC) analyses.Three types of cellulose samples with different molecular weights were found to dissolve well in the NaOH/urea solvent with no obvious differences in reactivity and regioselectivity.The relative reactivity of hydroxyl groups in the glycosyl unit was in the following order:O-6>O-2>O-3.In addition,the results of the study indicated that the tandem reaction during hydroxypropylation could be ignored.
基金supported by the National Natural Science Foundation of China[Nos.51703153 and 21802101].
文摘In this study,waste cotton fabric was used as cellulose raw material and pretreated in aqueous NaOH/urea solution system to investigate the effect of NaOH/urea pretreatment solution on the hydrolysis of cotton fiber.The cotton fiber was pretreated with different conditions of aqueous NaOH/urea solution,and the pretreated cotton fiber was hydrolyzed under the same conditions as the original cotton fiber.The results of characterization analysis showed that water retention value of pretreated cotton fiber was higher than that of unpretreated sample.Moreover,the cotton fiber presented both a convoluted structure and a coarser surface,XRD results suggested that the crystallinity degree of cellulose decreased dramatically,more cellulose II appeared,and the hydrogen bond is broken.Among the different pretreatment conditions,the pretreatment effect was the best when the reaction temperature was 0°C,the solid-liquid ratio was 2:50,and the NaOH/urea ratio was 7:12.The hydrolysis experiments of pretreated and unpretreated cotton fibers showed that when the hydrothermal temperature was 230°C,the heat preservation was 2 h,and the hydrochloric acid concentration was 5 wt.%,the glucose yield reached 29.99%.H+could catalyze the hydrolysis of cotton fiber more effectively due to damage to crystal structure and hydrogen bonds.
基金This work was supported by the general institute of building materials research of china(No.2017YFC0210801)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘In order to study the combustion characteristics,NOx emission and NH3 slip in a new trinal-sprayed precalciner,the simulations of combustion and aqueous urea solution based selective non-catalytic reduction(SNCR)process were conducted by computational fluid dynamics in this precalciner,the effects of different injection heights,different injection flow rates and stratified injection under different flow rates on SNCR process were studied.The results showed that the flow field was symmetrically distributed in the precalciner,and the flue gas from the rotary kiln formed the recirculation region on both sides of the cone body,which increased the residence time of the solid particles.The temperature was mainly between 1100 K and 1250 K in the middle and upper column of the precalciner,which met the demand of the pulverized coal combustion and raw material decomposition.The concentration of NO at the outlet of the precalciner was 559 ppm,moreover,different injection heights and different injection flow rates had a strong influence on NOX removal efficiency and NH3 slip.The aqueous urea solution should be injected at SNCR-1 to prolong the residence time of NH3,and injection flow rate had an optimal flow rate but not the higher the better.When the injection flow rate under stratified injection was 0.019 kg/s,which could play a better optimization role on NO removal efficiency on the basic of the injection flow rate.In consideration of cost effective,a stratified injection with an injection flow rate of 0.019 kg/s and an injection height of 20 m,25 m and 30 m was suggested as a compromise of a satisfactory NOx reduction rates and reasonable NH3 slip.Under this condition,numerical simulation result showed that NOx concentration at the outlet of precalciner was 297.27 mg/Nm3 and NH3 slip was 4.67 mg/Nm3,meeting emission standard.
