Preparation of symmetrical and mixed secondary alkylamines over raney nickel and supported copper catalysts

Heterogeneous Catalysis and Fine Chemicals IV H.U. Blaser, A. Baiker and R. Prim (editors) 0 1997 Elsevier Science B.V. All rights reserved.

PREPARATION OVER

OF SYMMETRICAL

RANEY

S. Gobolos,

131

NICKEL

AND MIXED

AND SUPPORTED

M. Hegediis,

SECONDARY

COPPER

ALKYLAMINES

CATALYSTS

E. Talas and J. L. Margitfalvi

Central Research Institute for Chemistry OB 17, Hungary

of the Hungarian

Academy

of Sciences, 1525 Budapest,

Summary

Raney nickel secondary

catalyst

amines

modification

was modified

in the alkylation

selectivities

secondary

alkylamine,

commercial

around

with 0.5 wt % V or Mg to increase of ammonia

70-80

n-propanol

% were obtained

N-ethyl-N-n-butylamine

CuO-ZnO-Al203

with

or i-butanol.

at 90-95

was prepared

Due

% conversions.

from ethylamine

catalyst. The highest yield of EtNHn-Bu

at 190 oC and EtNH2/n-BuOH

the selectivity

to

to the

The mixed

and n-butanol

on a

around 76 % was obtained

molar ratio 5 or above.

Introduction Symmetrical NH-R’,

and mixed

respectively

secondary alcohol

secondary

are used as epoxy

amines are frequently on a nickel

propylamine

alkylamines hardeners

and plant

prepared by the alkylation

or copper

(n-Pr2NH),

with the general

catalyst

[l].

(i-BgNH)

can be produced

in industrial

protecting

of a primary

In this work

di-i-butylamine

formula

highly

of R-NH-R

agents. Lower

and Raliphatic

amine or ammonia

selective

preparation

and N-ethyl-N-n-butylamine

with an of di-n-

(EtNH-nBu)

is

described. Di-n-propylamine propanol

on

Ba(OH)2

propionaldehyde

catalyst

or i-butylamine

alumina

Ni/Al203

over a cobalt-containing

exane on Ni/Al203 ammonia

modified

at 370-380

Di-i-butylamine

from i-butanol

amines prepared

obtained

mixed

selectivity

secondary

on copper-containing

In this paper

amine

of Raney

in the alkylation

we report the preparation

nickel

of ammonia

amine

catalyst. The effect of reaction

temperature

on the selectivities

of symmetrical

and yields

catalyst with

of N-ethyl-N-n-butylamine

molar

discussed.

of in n-

about the alkylation

of

from i-butanol

over

on alumina

at 200 oC with a yield

from a pimary

with n-

amination

acrylonitrile

was prepared

and i-butylamine

ZnO-Al203 ratio

of ammonia

reductive

of 60

and an alcohol

were

catalysts at 190-200 oC with 30-50 % yields [ 1 l-131.

the effect of modification

of secondary

studied. In addition,

the

OC with 28 % yield [7]. 20 wt% Co - 5 wt% Ni catalyst supported

.6 [lo]. usually

by

only scare data is available

[6-lo].

was used to prepare di-i-butylamine Aliphatic

[2],

catalyst [3] or by the hydrogenation

[4,5]. However,

with i-butanol

scale by the alkylation

catalyst

and ammonia and mixed

with

n-propanol

V or Mg

and i-butanol

over a commercial or primary secondary

on the is

CuO-

amine to alcohol amines

will

be

132

Experimental The skeletal nickel catalyst (Ni) was prepared by leaching a 50 w4% Ni-Al alloy with 20 wt% NaOH-H20 solution at 50 °C as desrcibed elsewhere [14]. Modification of Raney Ni catalyst with 0.5 wt% V or Mg was carried out by adsorption using an aquoeus solution of NH4VO3 or MgCl2, respectively [15]. V an Mg modified catalysts will be referred as Ni(V) and Ni(Mg), respectively. Prior to activity test the catalysts were heated to 250 ^C at a rate of 2 ^C/min in a flow of 75 % H2 - 25 % N2 mixture and kept at 250 ^C for 3 hours. A commercial CuO-ZnO-Al203 catalyst (referred as CuZn/Al, with composition: 37 wt% CuO, 36 wt% ZnO, 27 wt% AI2O3 and particle size: 0.31-0.63 mm) treated in 75 %H2 - 25 % N2 mixture at 250 ^C for 3 hours was used in the preparation of mixed amine. The composition, the textural and surface properties of the catalysts were studied by AAS, mercury porosimetry, XRD, XPS and TG-DTA [16,17]. The amount of metallic copper on the surface of catalyst was determined by titration with N2O [18]. The characterization of bulk and surface properties of the catalysts is given elsewhere [14,16,17]. The alkylation of NH3 with n-PrOH and i-BuOH and that of EtNH2 with n-BuOH was carried out at 0.45 MPa partial pressure of ammonia, under 1.3 or 2.1 MPa total pressure and at a H2/NH3 or H2/EtNH2 molar ratio of 3 in a continuous-flow reactor charged with 20 g of skeletal or 13 g of CuZn/Al catalyst (WHSV = 0.7-1.5 h'^). The reaction products were analysed by GC using FID and a glass column (3 m x 3 mm) filled with 60/80 mesh Chromosorb P NAW containing 5 % wt% KOH and 18 wt% Carbovax 20M. The conversion of alcohol and the quantitative yields of amines were determined using i-propanol as an internal standard. Results and Discussion Conversion and selectivity data obtained in the alkylation of ammonia with n-propanol over different Raney nickel catalysts are listed in Table 1. Data given in Table I indicate that n-Pr2NH can be obatined on unmodified and vanadium modified Raney nickel catalyst with 70-72 % selectivities at 92-95 % conversions. Upon modifying the Raney nickel catalyst with Mg the selectivity of the secondary amine increased to 74-75 % at 94-97 % conversions. The increase of the reaction temperature from 225 to 245 ^C resulted in slight increase of the conversion and the selectivity to the primary amine both on unmoified and Mg modified catalysts. The introduction of V or Mg modifiers affected both the selectivity of the secondary amine and the ratio of primary to tertiary amines. The effect of NH3/n-PrOH molar ratio on the selectivites in the alkylation of ammonia with npropanol is shown in Fig. 1. The selectivity of n-Pr2NH is represented by the difference of values of the two curves shown in the figure. Upon increasing the ratio of ammonia to alcohol in the range of 1.4-2.0 the selectivity of the desired secondary amine was only slightly altered, whereas the selectivity of the primary amine increased and that of the tertiary amines decreased as expected from the thermodynamics. The effect of reaction temperature on the conversion of n-PrOH in its reaction with ammonia is shown in Fig. 2a. As seen in the figure 215 and 240 ^C is required to achieve 90 and 95 % conversions, respectively. In this reaction upon increasing the reaction

133

temperature in the range 190-250 ^C the selectivity of n-Pr2NH slightly increased at the expense of the primary amine (see Fig.2b). Table 1 Alkylation of ammonia with n-propanol over different Raney nickel catalysts (P=2.1 MPa, WHSV=1.5 h-^ NH3/n-propanol molar ratio) N^ Catalyst

Xa % 92.1 94.6 94.7 93.5 97.5

T OC

225 1 Ni 245 2 Ni 225 3 Ni(V) 225 4 Ni(Mg) 245 5 Ni(Mg) a) X = conversion of n-propanol

Selectivities, % n-Pr2NH n-PrNH2 9.2 69.8 9.5 70.7 11.3 71.7 9.3 75.3 10.0 74.4

Yield, % n-Pr^N 21.0 64.3 19.8 66.9 17.0 67.9 15.4 70.4 15.6 72.5

100

CO

0)

o 0)

CO

1.5

1.7

1.9

2.1

NHg/nPrOH molar ratio

Fig.l Effect of NH3/n-PrOH molar ratio on the selectivities in the alkylation of ammonia with npropanol over vanadium modified Raney nickel catalyst (T= 225 ^C, WHSV=1.4 h'^, H2/NH3=3, conversion of n-PrOH=93-95 %). Conversions, selectivities and yield of i-Bu2NH obtained in the alkylation of ammonia with ibutanol are summarized in Table 2. The modification of the Raney nickel catalyst with vanadium resulted in 4-5 % increase in the selectivity of secondary and primary amine, whereas the conversion only slightly decreased (compare exp.s N^l and N^2 in Table 2.).

136 EtNHn-Bu varied between 54-60 %. The incerase of the amine/alcohol molar ratio to 5 or 10, resulted in high selectivity and yield of the mixed amine (see exp.s N®6, N^7 and N^IO in Table 4).

100 Conversion, % Fig. 3 Correlation between conversion and selectivity in the alkylation of ethylamine with n-butanol over CuO-ZnO-Al203 catalyst. (Data given in Table 3 and Table 4 are used; n>5 - data obtained at n = 5 and 10 are used.) Table 4 Alkylation of ethylamine with n-butanol on CuZn/Al catalyst (P=1.3 MPa, WHSV=0.7 h"!) NO

T

na

OC

1 2 3 4 5 6 7

175 178 190 195 205 191 193 201 208 190 201

1.3 1.3 1.3 1.3 1.3 5 5 5 5 10 10

Xb % 67.1 70.3 88.4 93.9 96.9 91.1 93.5 95.6 97.1 93.1 97.5

EtNHnBu 81.8 79.2 67.3 62.6 55.9 83.3 80.4 77.5 75.1 82.4 74.1

Selectivities, % nBu2NH nBuNH2 4.9 9.9 11.4 5.2 8.2 19.0 9.1 22.2 26.3 10.2 4.1 12.1 13.4 5.2 14.9 6.4 7.5 15.9 13.3 3.9 6.1 19.2

8 9 10 11 a) n=EtNH2/n-butanol molar ratio, b) X = conversion of n-butanol, c) yield of EtNHn-Bu

Yieldc % 54.9 55.7 59.5 58.8 54.2 75.9 75.2 74.1 72.9 76.7 72.2

137

Fig.4 gives further data on the effect of reaction temperature at diffferent EtNH2/n-BuOH molar ratios. As seen in Fig. 4 the selectivity of EtNHn-Bu is significantly higher when pure ethylaraine was used instead of 70 wt% EtNH2-H20 mixture. This can be explained by the fact that water is one of the reaction products in the alkylation of ammonia or an amine with an alcohol, therefore the addition of water to the ractants thermodynamically is unfavourable [1]. Neither the concentration of ethylamine (70 or 100 %) nor the amine/alcohol molar ratio had changed the reaction temperature (190 ^C) at which the highest yield of mixed amine was obtained (see Fig. 4).

90i EtNHz, n>5

210

220

Fig.4 Correlation between the yield of EtNHn-Bu and reaction temperature in the alkylation of ethylamine with n-butanol over CuO-ZnO-Al203 catalyst. (Data given in Table 3 and Table 4 are used; n>5 - data obtained at n = 5 and 10 are used.) Conclusions Raney nickel modified with Mg or V can be used for the highly selective preparation of symmetrical amines by the alkylation of ammonia with n-propanol or i-butanol. Upon modifying the Raney nickel catalyst with 0.5 wt % V or Mg, 4-5 % increase in the selectivity to secondary amines was observed and the selectivities reached 70-80 % at 90-95 % conversions. In the alkylation of ammonia with an alcohol symmetrical secondary amines can be obtained with 70 % yield over Mg or V modified Raney nickel catalyst at 220-240 ^C and ammonia/alcohol ratio of 1.5. In an industrial application 2-4 % increase of the selectivity results in an important finantial benefit. It was shown that pure (100 %) ethylamine and 70 % EtNH2 in water can be used for the preparation of N-ethyl-N-butylamine over a commercial CuO-ZnO-Al203 catalyst.