Hydrogenation Upgrading Of Straw Polyol Liquefaction Products Over Acid-modified Attapulgite Supported Amorphous Alloy Catalyst

With the decrease of fossil resources,the increasingly serious greenhouse effect and the increasing public and society's call for environmental protection,it is of great significance to develop the technology of transforming renewable resources such as lignocellulose into liquid fuel and chemicals to alleviate the energy crisis and promote ecological environment protection.The liquefaction product of straw in polyols solvent is used to prepare biodegradable polymer materials such as bio-based polyurethane,which is of great significance for promoting the high-value comprehensive utilization of straw resources.Due to the different degradation mechanisms of cellulose,hemicellulose and lignin in straw,the liquefaction product usually contains some carbonyl compounds such as aldehydes,ketones,acids and esters in addition to liquefied solvents and their derivatives.As a result,the amount of catalyst consumed in the process of polyurethane foaming will be higher,and some problems will be brought,such as lower quality of polyurethane foam,much darker color,and unevenly distributed pores.Therefore,in order to improve the quality of downstream biomass-based polyurethane products,it is necessary to upgrade the liquefaction product before polyurethane foaming.The catalytic conversion of carbonyl compounds in liquefaction products by hydrogenation technology is an effective method for upgrading liquefaction product.In this paper,the liquefaction products of wheat straw were used as the research object.Through the research on the mechanism of wheat straw liquefaction,the preparation,performance evaluation and catalytic mechanism of hydroformylation catalysts for carbonyl compounds such as furfural(FUR)and butyl levulinate(BL),and application in the upgrading of wheat straw liquefaction products,the content of carbonyl compounds in the liquefaction products could be effectively reduced.The main conclusions are as follows:(1)Using wheat straw as raw material,ethylene glycol,glycerin and polyethylene glycol#400/glycerin as solvent,the liquefaction performance and behavior were compared The results show that polyethylene glycol#400/glycerol as a solvent has higher liquefaction efficiency,and the relative content of carbonyl compounds including aldehydes,ketones,acids,and esters in the crude liquefaction product reaches 10.37%.The carbonyl compounds mainly includes levulinic acid,acetic acid,glycerol acetate,hydroxyacetone,5-methyl-2(3H)-furanone,etc.Through thermogravimetric analysis and infrared spectroscopy analysis of wheat straw,wheat straw/liquefaction solvent mixture,liquefaction residue and liquefaction product,the wheat straw liquefaction mechanism is obtained:The chain hydroxyl groups of cellulose and hemicellulose are preferentially degraded under strong acid conditions,and degradation fragement is combined with the liquefaction solvent to produce an active substance containing polyhydroxyl groups;these active substances undergo oxidation reaction to generate carboxylic acid,and esterification reaction with polyol under the action of acid catalyst in the later period of liquefaction to generate esters;lignin structure has undergone certain changes,but its aromatic ring still exists.(2)The acid-modified attapulgite-supported Ni1Co1B amorphous alloy catalyst(Ni1Co1B/H+-ATP)was prepared by impregnation-reduction method.Through the liquid phase hydrogenation reaction performance evaluation of FUR,the best attapulgite types and loading content of Ni1Co1B amorphous alloy and the optimum reaction conditions for the FUR hydrogenation to furfuryl alcohol(FA)were obtained.The structure-activity relationship between composition-morphology-structure-properties of the catalyst were characterized by N2 adsorption/desorption,SEM,TEM,XRD,XPS,etc.The results showed that the specific surface area and pore structure of acid-modified attapulgite are directly related to the adsorption and activation of furfural molecules,and are the key factors for the selection of attapulgite support;H+-ATP supported 20%Ni1Co1B catalyst(20NCB/H+-ATP)has the best FUR hydrogenation performance,and reacts for 2 h under the best conditions(reaction temperature 140?,stirring speed 800 rpm,initial hydrogen pressure 3.0 MPa),the FUR conversion is 91.3%,and the FA selectivity reaches 82%;the 20NCB/H+-ATP catalyst has good thermal stability and recycling performance.The mass loss rate of the NiCoB amorphous alloy after 6 h of hydrogenation reaction is only 2 wt%,and the used catalyst has uniformly particle size,high dispersion and well amorphous structure.After six cycles of recycling,the quality of the NiCoB amorphous alloy decreased by 5.2 wt%,in contrast the FUR conversion increased by 3.9%.It is mainly due to the new Co-Ni alloy hydrogenation active site generated during the catalyst recycling process,which can restore and enhance the FUR hydrogenation activity of the catalyst.(3)Through the catalytic performance evaluation of BL hydrogenation over Cu-doped Ni1Co1B catalyst,an ideal Cu/Ni/Co molar ratio of 0.5/1/1 is obtained.The introduction of Cu is beneficial to improve the dispersion of NiCoB amorphous alloy particles and their ability to activate and convert ester groups;the acid-modified attapulgite-supported Cu0.5Ni1Co1B catalyst(Cu0.5Ni1Co1B/H+-ATP)was prepared by impregnation-reduction method,over which the BL conversion and the yield of ?-valerolactone(GVL)are as high as 99.7%and 96.3%in the optimal reaction solvent cyclohexane,respectively.This is mainly because the oxygen-containing groups of BL have stronger adsorption in alkanes and H2 activation can be enhanced in alkanes.The further introduction of Mo element into Cu0.5Ni1Co1B/H+-ATP catalyst can promote the conversion of GVL to 1,4-pentanediol(1,4-PDO).At 200? reaction,the BL conversion reaches 100%,GVL and 1,4-PDO selectivity is 78.1%and 3.3%respectively.The structure-activity relationship of Cu(M)NiCoB/H+-ATP catalyst and catalytic rection mechanism were also studied by N2 adsorption/desorption,SEM,TEM,XRD,XPS,H2-TPD and NH3-TPD.The results showed that the good stability and recycling performance of the catalyst can be due to the high dispersion of the hydrogenation active sites of the Cu(M)NiCoB amorphous alloy and its interaction with the H+-ATP carrier,as well as the synergistic effect between Cu(M)NiCoB and Cu+/Cu0 active sites and the acid active site origined from the structural hydroxyl group of H+-ATP and exposing Al3+.(4)The Cu0.5Ni1Co1B/H+-ATP catalyst was applied in the hydrogenation upgrading of liquefaction product of wheat straw obtained from different liquefaction solvents and showed good universality and recycling performance.Under the best reaction conditions(catalyst dosage of 6 wt%,reaction temperature of 100?140 ?,initial hydrogen pressure of 1.0 MPa and stirring rate of 200 rpm),the relative content of carbonyl compounds in liquefaction product reduced by 71.2%.Through GC-MS analysis,the removal mechanism of carbonyl compounds was obtained as follows:The ester compound BL was converted into GVL and polyols over Cu0.5Ni1Co1B/H+-ATP metal/acid bifunctional catalyst,and the ketone compound,hydroxyacetone and furanone were converted into polyols.Furthermore,the lumped method was used to study the kinetics of hydrogenation upgrading reaction of liquefaction product,and a genetic algorithm combined with a nonlinear programming method was used for calculation and optimization.The range of activation energy is 81.48?182.91 kJ/mol,and the pre exponential factor is 2.67×107?8.83×1020 min-1.Furthermore,the kinetic model has good reliability.The kinetic study showed that the hydrogenation upgrading of wheat straw liquefaction product can be rapidly and efficiently carried out at low temperature.The optimum temperature is 100?120 ?,and the reaction time is 60?120 min Through the kinetic analysis,the compounds transformation rule and mechanism during the hydrogenation upgrading process of straw liquefaction products were revealed.