Slurry 상 Aniline 수소화 공정에 있어서 공정변수들의 최적화 연구

조홍백, 박융호

한양대학교 화학공학과

Optimization of the Process Parameters in the  Hydrogenation of Aniline in a Slurry Reactor

Hong-baek Cho, Yeung-Ho Park

Dept. of Chem. Eng., Hanyang Univ.

Introduction

Cyclohexylamine(CHA), which is obtained from catalytic hydrogenation process, is a kind of fine chemical being extensively used for organic synthesis, pesticide, plasticizer, and etc. The research concerning catalytic hydrogenation of amine group was started from the early 1920, and various reaction methods have been suggested to raise the selectivity of the desired product, CHA, and to suppress dicyclohexylamine(DCHA). The catalytic  effects of platinum group metals on the synthesis of aromatic amine were studied [1,2], and the result of work using alcohol as solvent was also published [3]. In addition, in some research a little portion of DCHA or [eqn: NH_3] was introduced prior to starting reaction to elevate CHA selectivity [4,5]

In this research a few process parameters; including the reaction time between catalyst and substrate, the impeller type, the number of times of the catalyst reuse in batch liquid catalytic hydrogenation have been studied.

Hydrogenation apparatus

Fig.1 shows the scheme of the reactor used in this work. Reactor can hold 2[eqn: l], is operated up to 100atm, heated by external electric power. And the motor for impeller is operated up to 1800 revolution per minute(RPM). By operating vacuum pump between every[eqn: N_2](g) and [eqn: H_2](g) purge, a negative pressure in the reactor could be utilized to minimize the existing ratio of unnecessary gases prior to reaction. Cooling coil was embedded inside of the reactor and in order to prevent temperature from  decreasing steeply at the time of solenoid valve's on-off,  caused by evaporation latent heat and vaporization heat, cold trap was installed and operated fit for set point in the line. The impeller shaft is designed so as to install various types of impellers and to change the impeller's level. Six types of impellers including disk turbine type(narrow), pitched blade type(straight), pitched blade type(bent; forward), pitched blade type(bent; reward), pitched blade type(folded), disk turbine type(wide), were used.

[eqn: N_2](g) and [eqn: H_2](g) lines are connected to the upper side of the reactor and gases were bubbled at the bottom side of reactor. Detecting [eqn: H_2](g) consumption was measured with a built-in flow meter. And sparger holes were drilled downward to protect solid catalyst from entering and being stacked in it.

The basic parameters and conditions in carrying out aniline hydrogenation are as follows. Operation temperature was 170℃, operation time was varied between 3 to 5 hours, pressure was 50 atm, and 5 wt% Ruthenium on activated carbon was used as catalyst. GC-FID was used to analyse the reaction product.

Experimental Procedures

Fig.1 shows the apparatus of aniline hydrogenation for this experiment. After introducing aniline 1.2[eqn: l] and the catalyst, Ru/C, 11.98g(1wt% of reactant) into the reactor, [eqn: N_2] purge was done to get rid of remaining air in the reactor and inert atmosphere could be prepared by repeating the purge operation two more time. Then [eqn: H_2]  purge was carried  out three times to remove the [eqn: N_2] in the reactor. After these preliminary procedure, [eqn: H_2] bomb pressure was checked, reaction temperature and agitation speed were set, and reaction started.

Result and Discussion

Fig.2 shows the effect of agitation intensity on CHA selectivity. At 500rpm the selectivity was the highest as 72.66% and the conversion was almost 100%. It showed that after reaction of 3 hours the CHA selectivity decreased . This implies of hydrogenolysis occurred to produce DCHA or cyclohexane(CH).

The effects of impeller type on CHA selectivity is described in Table 1. When PBT(bent);(Pitched blade type) was used the selectivity was the highest value, but the conversion was the lowest. When disk turbine type(wide) was used both CHA selectivity and conversion were high. In the case of PBT(folded) and PBT(straight), though all of the reactant was converted, CHA selectivity exhibited a little lower than that of disk turbine. When the blade width becomes wider, the concentration of DCHA decreased without change of CHA concentration. From these result it was concluded that the best impeller type is disk turbine type.

Next, the activity changes of the reused metal catalysts were studied. Since the noble catalyst is expensive , it is normally collected and reused. But its activity is decreased as it is used repeatedly. In this research the activity change over aniline hydrogenation was observed and described in Table 2. From the second reuse activity and selectivity is observed to decrease steeply. So in order to keep activity from decreasing, a little portion of new catalyst should be added to keep the reaction rate at a desired value while catalyst reuse.

Conclusion

The effect of process parameters; impeller type, agitation speed and catalyst reuse were exhibited obviously. And the further study to investigate on the effect by temperature profile and pressure variation and to determine the optimum process parameters  will be carried out.

Reference

[1] A. E. Barkdoll, D. C. England, H. W. Gray, W. Kirk, Jr., and G. M. Whitman, J. Am. Chem. Soc., 75, 1156 (1953)

[2] M. Freifelder and G. R. Stone, J. Am. Chem. Soc., 80, 5270 (1958)

[3] Merten et al, U. S. Patent 4,384,142 (May 17, 1983)

[4] Shigeo Nishimura, Tetsuo Shu and Tomoyoshi Hara, Bulletin of the Chem. Soc. Jap. Vol. 39, P 329∼323 (1966)

[5] G. M. Winans and H. Adkins, J. Am. Chem. Soc., 54, 306 (1932)

Table 1. The variation of selectivity by impeller types

Impeller type	Conv.(%)	Selectivity(mol %)
		CH	CHA	Aniline	DCHA
Disk turbine(wide)	100	2.48	94.40	0	3.09
Disk turbine(narrow)	100	1.99	94.40	0	3.61
PBT(folded)	100	2.78	92.87	0	4.74
PBT(straight)	100	3.53	92.10	0	4.24
PBT(bent); forward direction	35.62	2.34	95.94	-	1.72
PBT(bent); backward direction	29.2	0.75	90.00	-	9.04

* Operation condition; Temperature;170℃, Pressure;50atm, Catalyst;Ru/C, Reaction time;3hr,                             Agitation speed;500rpm

Table 2. The variation of selectivity  by catalyst reuse cycle

	Catalyst Type	Time (hr)	Conv.(%)	Selectivity(mol%)
				CH	CHA	DCHA
Run1	(new)	0.5	1.3	0.01	87.69	5.38
		1	40.37	0.62	87.64	11.74
		2	97	1.11	84.82	14.05
		3	100	2.01	82.06	15.92
Run2	(1 cycle)	0.5	0.14	7.14	0	7
		1	28.62	0.59	79.32	20.06
		2	52.76	0.28	75.47	24.24
		3	76.46	1.5	74.12	21.73
Run3	(2 cycle)	0.5	0.02	0	0	100
		1	14.36	0.21	65.11	34.68
		2	31.93	3.45	74.41	25.24
		3	43.03	0.93	76.50	22.57
Run4	(3 cycle)	0.5	0.50	94	0	6
		1	6.29	3.18	44.04	55.48
		2	9.75	0	42.77	52.13
		3	12.72	1.18	50.16	48.66

* Operation condition : Temperature;170℃, Pressure.;50atm, Catalyst;Ru/C,

Agitation speed;500rpm, Impeller type;Disk turbine(wide).

Fig  The apparatus of aniline hydrogenation

* Operation condition : Temperature;150℃, Pressure;50atm,  Catalyst;Ru/C, Reaction time;3hr, Impeller type;PBT(straight)