Study On Purification Of Coking Sulfur Paste And Its Modification Mechanism To Asphalt

Coking Sulfur Paste?CSP?is a by-product of wet air oxidation desulphurisation progress for coke oven gas purification.Maily made up by sulfur,accompanying with impurities of water,thiocyanate and thiosulfate,polycyclic aromatic hydrocarbons?PAHs?of tar and desulfurization catalyst,CSP is a kind of industrial solid waste,which is too hard to utilize,resulting in a lot of serious pollutions.How to recycle and utilize CSP is an important research topic;China is in the rapid development period of asphalt highways.Most domestic asphalts have problems such as high wax content,high temperature sensitivity,poor water stability,and insufficient durability.It is extremely urgent to develop low-cost domestically modified asphalts that meet the road performance requirements and are inexpensive.This paper carries out research on purification of CSP and its modification mechanism to Asphalt,which realize the utilization of CSP resources,meanwhile,improve asphalt quality and reduce asphalt cost.It is of great significance to improve the efficiency of enterprise resource utilization and the extension of the industrial chain.Based on the resource utilization of CSP,this paper systematically carried out the following six aspects of research.1.Clarified the composition and properties of CSP through multi-dimensional analysis;2.Explored the basic conditions for the purification of sulfur by combination of leaching and sulfonation;3.Studied the conventional properties and rheological behavior of asphalt modified by CSP;4.Analyzed the mechanism of CSP modified asphalt through variation of content and structure of four components of asphalt;5.Evaluated and analyzed road service performance of CSP modified asphalt mixture,based on the study of the best oil-stone ratio;6.Combined with the existing coking system,studied the optimal conditions and impurity transition rules of eluting CSP with ammonia water.The main conclusions are as follows:Clarified the composition and properties of CSP1.S contained in CSP reached up to 88.53%of the total weight and substantially existed in the form of elemental sulfur,which accounted for 91.53%.The rest of S existed in the form of thiosulfate,thiocyanate and sulfates.There were also microelements in CSP,such as Fe,Br,Ca,P,Mo,Cl,whose contents were less than2.50%;Elemental sulfur in CSP was presented in the form of rhombic sulfur?S??;Impurities in CSP could be divided into three categories:water-soluble inorganic impurities?WI?,dichloromethane-soluble impurities?DI?,other impurities?OI?,accounting for 12.16%,4.2%,2.61%respectively among the whole CSP.WI consisted of NH₄SCN,?NH₄?₂S₂O₃,FeSO₄,PDS and hydroquinone accounting for58.39%,9.05%,24.67%,3.70%,3.37%respectively of the total WI.DI mainly contained polycyclic aromatic hydrocarbons,including benzenes,naphthalenes,fluorenes,phenanthrenes,anthraquinones and pyrenes.C of OI existed mainly in the form of C-C/C-H,and O of OI existed in the form of C=O and C-O;The weight loss of CSP in the heating process mainly consists of two stages,namely the organics volatilization stage of 100²70? and the sulfur gasification stage of 270³90? liquid,their weight loss rate are 3.49%and 95.09%,respectively.The residual substances are mainly in the form of sulfates of Fe and Ca,which can be converted into Fe₂O₃ and CaSO₄ after high temperature burning.Toluene Leaching Characteristics of CSP2.The optimum conditions for the leaching of CSP by toluene are 70mL:5g?L/S?,90??leaching temperature?,30min?leaching time?and 20??Cooling temperature of sulfur-toluene?,under these conditions,85.87%sulfur solubility and96.16%sulfur purity can be achieved,which can effectively remove water-soluble impurities;The product sulfur still contains organic substances such as toluene,xylene,naphthalene,phenanthrene,oxonium,biphenyl,etc.These polycyclic aromatic hydrocarbons have similar structural characteristics to S₈,resulting in inclusion and adsorption of crystal grains during sulfur crystallization,which is the main reason for their entry into sulfur products;The purity of sulfur after secondary treatment with sulfonation-water washing reached 99.5%.The impurities such as naphthalene,phenanthrene,biphenylene and oxonium were effectively removed,toluene in the product sulfur was reduced by 98.78%,xylene was decreased by91.79%,and ethylbenzene was reduced by 87.72%.Its purity reached the requirements of industrial qualified products.Properties and mechanism of CSP modified asphalt.3.WI in CSP have the advantages of reducing the penetration of the asphalt and shortening the curing time required to achieve stable performance;however,there are defects such as severe deterioration of the low-temperature ductility of the asphalt and suppression of the improvement of the temperature-sensing property of the asphalt by the sulfur.Therefore,it is necessary to remove this part of impurities in the process of preparing the sulfur-based asphalt modified;DI in CSP can promote the conversion of the asphalt to the sol-gel,enhance the temperature stability,and assist improve the softening point,enhance the high temperature performance,meanwhile,supplement the content of asphalt to a certain extent,enhance the low temperature ductility of asphalt.4.The conventional properties of CSP₂-DH are greatly affected by the ratio of CSP₂ blending and curing days.In terms of viscosity,the addition of CSP₂ promotes the penetration value of asphalt?25??,increaseshe ability to resist flow.Moreover,the higher the proportion of CSP₂,the more obvious the effect of modification and the shorter curing time required to reach steady state.40%CSP₂-DH reached the stable value of 49.6 mm on the 8th day,which was 43%lower than the asphalt DH.The rotational viscosity value?135??of the CSP₂-DH modified asphalt decreased significantly compared with asphalt DH,which is beneficial to the mixing and transportation of asphalt mixture.The viscosity did not decrease linearly with the proportion of CSP₂.When the proportion of CSP₂ was 30%,the decrease in viscosity remained unchanged.As the proportion increased to 40%,the viscosity began to rebound.The addition of CSP₂ reduces the dynamic viscosity of the asphalt?60??and meets the specifications after curing;In terms of temperature sensitivity,the PI of CSP₂-DH increased with the increase of CSP₂ blending amount and the increase of curing days.When the amount of CSP₂ blending amount increased from 10%to 40%,the PI value of CSP₂-DH increased from-1.93 to 0.21 after stabilization,which promoted the conversion of asphalt from sol to sol-gel and enhanced the temperature sensing performance.CSP₂ reduced the mixing temperature and compaction temperature of asphalt;In terms of high temperature performance,CSP₂ improves the softening point of asphalt and enhances the high temperature stability of asphalt.The softening points of CSP₂-DH and CSP₂-ZH modified asphalt reach 56.8? and 54.1?,respectively,which increased by 25.6%and 17.1%compared with asphalt DH and ZH,respectively.The higher the proportion of CSP₂,the shorter curing time required to reach steady state and the higher the softening point stability value.When the amount of CSP₂ blending amount increased from 10%to 40%,the softening point of CSP₂-DH increased from 53.2? to 60.9?;In terms of the low temperature performance,CSP₂ can improve the ductility?5??of asphalt binders at the early stage of the curing process,and the rate of ductility increase declined as the proportion of CSP₂ increased.After curing for 20 days,the ductility?5??of asphalt binders decreased,only the one with CSP₂?10%?had ductility greater than the asphalt's.Both residual oil and DOP can improve the defect of CSP₂-DH's ductility value decreasing with time.2%added amount of DOP and residual oil can increase the ductility value?5??of CSP₂-DH by 3.18 times and 3.56 times,respectively.After curing,the low temperature ductility can be further improved.In terms of adhesion,the adhesion of CSP₂-DH was slightly lower than that of DH,the percentage of peeled area was less than 10%,and the grade was grade 4.In terms of rheological properties,G',G"and G*/sin?of CSP₂-DH in the low temperature region?<50??are lower than asphalt DH,with the increase of temperature,the decreasing trend is weakened.In the high temperature region?>60??,the high CSP₂ blending can slow down the tendency of elastic characteristics to the viscous characteristics with increasing temperature and improve the high temperature resistance of asphalt.5.The mechanism of modified asphalt with CSP₂ can be divided into two parts.At the early stage of the curing process,the modification mechanism is mainly to improve the properties of asphalt by the cross-linking reaction between sulfur of CSP₂and asphalt?R-SO₂-R,C=S and C-S?,and the introduction of PAHs of tar.With the extension of curing time,the chemical combination of sulfur and dissolved sulfur in asphalt is converted to free crystalline sulfur,the crystalline sulfur is evenly distributed in the bitumen,filling the bitumen voids and leading to higher Cohesion,enhance the high temperature performance of asphalt.The study of four-component asphalt found that CSP₂ resulted in an increase in the content of asphaltenes and saturated fractions,and a decrease in colloidal and aromatic fractions.Compared with asphalt DH,40%CSP₂-DH increased the asphaltene and saturate by 121.97%and21.45%,respectively,and the resin and aromatic decreased by 33.42%and 15.23%,respectively.The CSP₂ mainly reacted with saturate and aromatic to form S=O,C=S,and S-H.With the extension of curing time,these functional groups gradually disappear.CSP₂ does not chemically react with asphaltene and resin,but the resin will undergo oxidative condensation to form asphaltenes during the mixing process.6.The optimum oil-stone ratio of 30%CSP₂-DH binder is 4.92%.At this time,the corresponding mineral void ratio meets the requirements,which is close to the optimum oil stone ratio of 5.08%obtained by the alternative formula method.Under the same conditions,the replacement ratio of CSP₂ modifier to asphalt is 1.4:1,which can reduce the amount of asphalt by 23.55%and significantly reduce the paving cost;The Marshall stability of the CSP₂-DH mixture is 38.3%higher than that of DH mixture,and the flow value is reduced by 27.6%.The addition of CSP₂ effectively improves the strength performance of the asphalt mixture.After 20 days of curing,the precipitation of crystalline sulfur filled the pores in the asphalt,the stability was improved by 45.3%compared with the asphalt,and the improvement of the strength properties of the mixture was more obvious;In terms of high temperature performance,CSP₂ effectively improves the high temperature rutting resistance of asphalt mixtures.The dynamic stability of CSP₂-DH mixture is 1.03 times higher than that of DH asphalt mixture,reaching 1847.5 times/mm,which is much higher than the standard requirement of 800 times/mm.After 20 days of maintenance,the stability of the movement was increased by nearly 10%;In terms of water damage resistance,the CSP₂-DH mixture has better water resistance resistance in the freeze-thaw split test,and the TSR value after curing is 95.5%.The residual stability of the CSP₂-DH mixture in the immersion Marshall test satisfies the technical requirements of?85%and compared with the DH mixture,the 48-hour water immersion stability increased by 31.7%before curing,and the stability after curing increased by 46.0%.In terms of low temperature crack resistance,CSP₂ reduced the splitting tensile strength of the asphalt mixture by 15%,but the deformation deformation was not much different.The extender DOP can alleviate the tendency of the splitting tensile strength after the addition of CSP₂,and can effectively improve the low temperature crack resistance of the CSP₂-DH mixture.Ammonia water eluting Characteristics of CSP7.The ammonia water?10%?originally prepared for desulfurization was used to selectively remove and recover impurities in CSP.The optimum elution conditions were 20??elution temperature?,100 r/min?stirring rate?,5 min?Single elution time?and 10 mL/g?L/g?,under this condition,the purity of sulfur reached 94.671%,the WI removal was complete,and the DI and OI contents were both reduced by 8.33%and21.8%.The addition of a surfactant and a sulfonating agent in concentrated ammonia water can enhance the removal of DI,but the surfactant also has a dissolution and removal effect on sulfur,and reduces the yield of sulfur;The ammonia water elution process can effectively remove Fe,Br,P,Cl,Ca and other elements in CSP,but has no effect on the removal of Mo element;the eluted product is analyzed by HS-GC×MS at 140?.There are still carbon disulfide and polycyclic aromatic hydrocarbons such as naphthalene,benzene and hydrazine.