Light hydrocarbon aromatization catalysts

Life Testing of Light Hydrocarbon Aromatization Catalysts... 

In the moving bed processes, the preheated feed meets the hot catalyst, which is in the form of beads that descend by gravity to the regeneration zone. As in fluidized bed cracking, conversion of aromatics is low, and a mixture of saturated and unsaturated light hydrocarbon gases is produced. The gasoline product is also rich in aromatics and branched paraffins. 

Selectivity to desired products including light hydrocarbons, gasoline, or diesel fuel depends upon the catalyst employed, the reactor temperature, and the type of process employed. Products of the F-T synthesis are suitable for further chemical processing because of their predominantly straight chain structure and the position of the double bond at the end of the chain. By-products formed on a lesser scale include alcohols, ketones, acids, esters, and aromatics. 

The aromatization of liquefied petroleum gases (LPG) has been investigated for more than a decade due to its economical and strategic importance for the exploitation of natural gas reserves and valorization of light hydrocarbons obtained from petroleum refining. Commercially, these reactions using gallium modified ZSM-5 zeolite catalysts are known as Cyclar process, developed jointly by UOP and BP [1]. 

Light hydrocarbons (Ci to C4) and aromatics (mainly Ce to Ce) were produced by ZSM-5 due to the the conversion of olefins and paraffins. Thus,these results provide evidence for cracking of olefins, paraffins and cyclization of olefins by ZSM-5 at 500 C. The steam deactivated ZSM-5 catalyst exhibited reduced olefin conversion and negligible paraffin conversion activity. 

The Cyclar process converts C3 and G paraffins to aromatics via a bifunctional zeolitic catalyst (25). Typical aromatic yields in Table 3.11 are 70 wt-%, with 6 wt-% hydrogen yields. The light hydrocarbon products can be used as fuel for the plant. Cyclar can be considered for remote locations as an alternative to flaring LPG, or when refrigerating LPG for shipment is not economical. 

Conversion is limited to about 10 per cent Selectivity exceeds 90 mole per cent in linear mono-olefms, whose internal double bond is statistically distributed along the chain, with less than 10 per cent in the alpha position. The catalyst is placinnm on alumina promoted by lithium and arsenic. The main co-products are diolefms (2 to 3 per cent), aromatics (3 to 4 per cent), light hydrocarbons and hydrogen, which is more than 96 per cent volume pure. 

In the aromatization process of light hydrocarbons, the deposition of coke on the catalyst proceeds rapidly in comparison with other processes such as naphtha... 

Catalyst life estimation tests were also conducted on four different catalysts used for aromatization of light hydrocarbons in this system, namely H-ZSM-5, Zn/H-ZSM-5, Ga/H-ZSM-5 and H-Ga-silicate. Based on the results of characterization of the spent catalysts, the primary cause of deterioration of catalyst activity is the elimination of active metal from the zeolite framework. 

Catalysts tend to be deactivated in the process of plastics pyrolysis because of coke deposition on their surface. The deactivation of HZSM-5, HY, H-zeolite and silica-alumina was compared by Uemichi et al. [86]. In the case of PE pyrolysis and HZSM-5 added as catalyst, no deactivation occurred due to the low coke deposit, and high yields of light hydrocarbons (mainly branched hydrocarbons and aromatics) were achieved. In the case of PS, however, coke production increased dramatically, so HZSM-5 was deactivated very quickly. Silica-alumina catalyst was deactivated gradually and slowly with the increase of cracking gas, while HY- and H-zeolite molecule sieve catalysts were deactivated very quickly. Walendziewski et al. [87] studied the catalytic cracking of waste... 

---