Study On The Catalytic Cracking Characteristics Of Fractions Of Low Temperature Coal Tar From Northern Shaanxi

Coal tar is a bulk product produced during the clean and efficient use of coal resources.Its clean and efficient use not only minimizes waste of resources,but also is the key to clean coal technology.The structure of coal tar is complex,and its catalytic conversion to benzene,toluene,xylene and naphthalene?BTXN?is one of its effective ways.In this paper,using low temperature coal tar from northern Shaanxi as raw material,finely cut coal tar?CT?using rotary film rectifier?VTA?to obtain>200°C fraction?CT200F?and<200°C fraction?LCT?;ZSM-5,HY,USY and?molecularare selected as catalysts.Catalytic cracking experiments were carried out on CT,LCT and CT200F by rapid pyrolysis instrument-gas chromatography-mass spectrometer?Py-GC/MS?in different atmospheres?He,CH₄,H₂?and different temperatures?400⁸00°C?,and the distribution of their catalytic cracking products was investigated.The catalytic cracking experiments were carried out with six typical compounds(naphthalene,phenanthrene,pyrene,C₂₂2 alkane,phenol and naphthol)as the model compounds in the coal tar.The formation of the target product BTXN under different catalytic conditions was investigated.The mechanism of catalytic cracking of coal tar to produce light aromatic hydrocarbons was discussed.The main contents and results could be as follows:?1?He atmosphere,800°C:the total relative content of BTXN in the thermal cracking products of CT,LCT and CT200F was 12.66%,4.83%and 15.85%,respectively.ZSM-5 is very efficient for CT and CT200F translate into BTXN,and the BTXN content increased by about 1 time.?2?He atmosphere,at 800°C:ZSM-5 has better selectivity for toluene and xylene than other catalysts,while Y-type zeolite has lower selectivity.under HY catalysis,naphthalene has the highest selectivity,CT was 39.86%,33.86%in LCT,and 39.06%in CT200F.It is known that HY is more advantageous for the catalytic preparation of naphthalene.?3?CT200F under CH₄ and H₂ atmosphere conditions:There's no BTX here,while naphthalene is produced under different atmospheric conditions,the content of naphthalene in He and CH₄ atmosphere is significantly higher than H_2.?4?In He atmosphere,naphthalene can form benzene and toluene under different catalyst conditions,but toluene will undergo further dealkylation reaction to form benzene,wherein the effect of?molecular sieve is significant;?molecular sieve can be more effective under He atmosphere.The degree of conversion of phenanthrene and anthracene to naphthalene with a smaller number of rings,but the further conversion of naphthalene is inhibited under USY conditions.Under the condition of usy,the conversion of phenanthrene and pyrene to naphthalene was weaker than that of?-zeolite,but the further conversion of naphthalene and other pyrolysis fragments was enhanced,and the light-weight of naphthalene and naphthalene was finally formed into toluene and benzene.The effect of zsm-5 on catalytic cracking of polycyclic aromatic hydrocarbons?PAHs?is poor.?5?In the CH₄ atmosphere,ZSM-5 and HY are not conducive to the catalytic cracking reaction of linear alkanes;under USY conditions,linear alkanes mainly undergo chain scission reaction to form olefin compounds with reduced carbon number;under?molecular sieve conditions,the low molecular compound can be further reacted to form a?2 to 4 ring?polycyclic aromatic hydrocarbon.?6?The H₂ atmosphere condition is not conducive to the catalytic cracking of CT200F to form monocyclic aromatic hydrocarbon compounds such as benzene,toluene and xylene,regardless of the type and nature of the catalyst.