Microcatalytic System for Gas Oil Cracking Mai V. Chen,' William P. Burgess, and Roland H. Daniels Mobil Research and Development Corporation, Central Research Division, Princeton, New Jersey 08540
The fixed bed microcatalytic system reported earlier (Chen and Lucki, 1971) has been modified and automated. The automated system is used to do repeated cycles of crackinghegeneration. Thus, the cyclic nature of the catalytic cracking process can be simulated by this unit. The test procedure is programmed by an electric timer to actuate six control circuits over a 60-min cycle allowing unit operation substantially unattended. The circuit is particularly suited for studies of long term stability of cracking catalysts.
intrsatmion A primary objective in testing new laboratory cracking c&alysts has bcen to search for improvement in yield and octane of gasoline from gas oil as well as improvement in activity and stability of the catalyst. The speed of catalyst evaluation has always been influenced by the necessary :nimmum amount of catalyst needed for testing its perfor~ i a n cThe ~ . development of a microcatalytic system for gas o:l cracking (Chen and Lucki, 1971) reduced the quantity of c:rtalvst required to as low as 0.1 cm3, and with the aid of gas ckrromatographv and mass spectroscopy, the test provides such information as activity, yield, and octane of gasoline. The obvious drawback of such a test is that it produced only a miniscule amount of product and offered limited ability to tec3tingaging properties of new catalysts. A variety of laboratory steaming tests (Letzsch et al., 1976; Magee and Blazek. 1976) has been developed to duplicate the mrformance of equilibrium catalysts produced in commercial uqits. However, experience has shown that no single laboratory deactivation procedure can be used to predict accurately the performance of an equilibrium catalyst. Apparently, the unlv way to obtain an equilibrium catalyst is to run a unit for 3 wfficitwt length of time under commercial operating conditions (Letzsch Pt a]., 1976). This costly and time-consuming urocediire has seldom. if ever, been adopted by any labora;'lrv We &scribe here a modified microcatalytic system which Iias been automated for unattended operation of many cracking-regeneration cycles. Studies on the long term staLXtv of commercial cracking catalysts using this system will LE reported later E)~sctpillptiomaf Tebk lJnit A schematic diagram of the unit is shown in Figure 1. Refrwing to the originall microcatalytic system (Chen and Lucki, 4971 the major modifications consist of the following. (1)An eicctrically operated three way valve &in. Hoke Select0 Mite) operated through a Hoke Electro Mechanical Valve Actibastor (Motid 01 12LlF) at the top of the reactor selects either the liquid feed stream or a gas stream. (2) An electrically opi~r,itedthree-way valve is located a t the bottom of the re:vim which directs the cracked products and the flushing to 3 conitlen:,er a t -4 O F during the cracking cycle, and TU\ comtraibtmn e a s s to a vent or to a carbon monoxide burner kr &>terminationduring the regeneration cycle. (3) Two np: voitagt, circuits are connected to the thermocouple meci t o control the temperature of the reactor. These bucking ~olltagesallow thp reactor to be controlled at temperatures 150 t o 450 "F a k r o . ~the set point of the temperature controller nhich is normally wt for the cracking cycle. (4) There are two dectricaily oymated on/off valves on the helium and air lines. ( 5 : 'I'hese 16 a 6jCB-rnin electric timer (Sealectro Corp., Sealec142
lnd. Eng. Chern.. Prod. Res. Dev., Vol. 16, No. 3, 1977
troswitch) containing a six-node actuator capable of turning on or off six circuits at specified times. These six circuits individually control the position of the three-way valves, the electrically operated on/off valves, the feed pump, and the bucking voltage circuits. Each may be set to go on or off for 1 to 59 min. A typical timing sequence is schematically shown in Figure 2. Before the test, the reactor is heated to the desired temperature and the carbon monoxide burner is maintained at 1000 O F . The catalyst is then pretreated in the reactor with a 35-min regeneration cycle, i.e., have the electric timer set at the 20 min mark (see Figure 2). The catalyst is subjected to aidwater a t the reaction temperature for 10 min, after which the reactor temperature is raised to 1030 O F for 10 minutes; the catalyst is then subjected to high temperature (1300 O F ) air/water for 15 min to complete the regeneration. Finally, the catalyst is purged with helium and allowed to cool to the reaction temperature in 5 min. The test cycle is carried out in the following steps with the timer starting on the 0-minute mark: (1)0-5 min-2.5 g of oil (Light East Texas Gas Oil) is pumped over 5 g of catalyst a t the predetermined reaction temperature; (2) 5-20 min-the catalyst is purged for 15min a t the same temperature with 16 cm3/min of helium; (3) 20-30 min--the catalyst is regenerated for 10 min at the same temperature with 10 cm3/min of air with a controlled partial pressure of water; (4) 30-40 minregeneration temperature is raised to 1030 OF; (5) 40-55 min-regeneration temperature is raised tu 1300 O F ; (6) 55-60 min-reactor is cooled to reaction temperature in helium (16 cms/min). During cracking and purging the reactor effluent passes through the three-way valve to a two-stage product collection system. It is cooled to -4 O F to condense the liquid products and then to a liquid nitrogen trap to condense all the condensables. Each material balance may consist of I to 24 cycles of crackinghegeneration. The collected liquid is weighed and analyzed on a %in. X 10-ft SE-30 Silicon gum rubber column. The gas products, collected in the liquid nitrogen trap, are weathered to room temperature into a constant volume evacuated bomb and its volume is measured (Chen and Lucki, 1971). The gases are then analyzed on a % in. X 16-ft Porapak Q column to determine the C1 through C6 paraffins and olefins. The average molecular weight of the gases is calculated and the liquid and gas analyses are combined to yield a mass balance before coke determination. During the regeneration period, the combustion gases are either vented or sent through a carbon monoxide burner and converted to COn and water with secondary air injected at the inlet of the carbon monoxide burner. The procedure for coke determination has been described earlier (@henand Lucki, 1971).
Table I. Experimental Results Average temperature of reaction, OF Cat./oil, wtlwt WHSV, h-1 Reaction time, min Catalyst weight, g Syn. crude recovered, wt % of feed Gass recovered, wt % of feed Coke recovered, wt % of feed Mass recovered, wt % of feed Product distribution Coke Gas
780 211 6 5.25 6.02 82.47 10.52 1.62 94.61 1.7 0.06 0.24 0.12 1.9 1.3 4.5 2.1
2.9 0.27 0.57 0.41 3.3 2.4 6.8 3.1
0.8
52.5 34.8 65.2 74.7
C1 CZ' CZ c3= c3
i-C4
C4= n -C4 Cs+ Gasoline to 430 OF Gas oil 430 O F + Conversion thru C5+ Choline Raw octane of gasolineb to 430 OF, R
+0
835 850" 211 2/1 6 6 5.22 5.00 6.02 181 77.25 78.51 19.06 16.05 2.87 1.38 99.18 95.97 Wt 96 of feed. no loss basis
882 2/1
6 5.24
6.02 67.66 28.26 3.3? 89.94
1.4
c.
