Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 38-40
38
may then be directly related to catalyst performance under hydrotreating conditions. Registry No. THF, 109-99-9; cobalt molybdate, 12640-46-9. Literature Cited
Furimsky, E. Cat. Rev. Sci. Eng. 1080, 22(3),371. Furimsky, E. Fuel Process Techno/. 1982, 6 , 1. Furimsky, E. I n d . Eng. Chem. Prod. Res. Dev. 1983, preceding paper in this issue.
Received for review November 30, 1981 Accepted August 30, 1982
Benson, S. W. "Thermochemical Kinetics": Wiley: New York, 1968: Chapter 4.
Selective Dehydrochlorination of Ethylene Chlorohydrin over Acid-Proof Basic Catalysts Recovering Dry Hydrogen Chloride Isao Mochlda, Hldekl Watanabe, Hlroshl FuJHsu,and Kenjlro Takeshlta Research Institute of Industrial Science, Kyushu University, Kasuga 8 16, Japan
Catalytic ellmination of hydrogen chloride from chlorohydrins into corresponding epoxides was investigated by a gas chromatographic pulse technique to find a selective catalysis which allows the recovery of hydrogen chloride produced at the same time. MImzHCI(CH,)!$iO,, immobilized 2-methyllmidazde on silica gel, was found to catalyze at 250 OC the dehydrochlorination of ethylene chlorohydrin into ethylene oxide at a selectivity as high as 85 % at a conversion level of 20% without any catalytic deactivation for many pulses, although the same catalyst failed with propylene chlorohydrin, giving acetone as the major product. The catalytic active site is assumed to be the free base of the catalyst which can be produced thermally to allow the recovery of hydrogen chloride.
Introduction It has been established that basic substances promote the selective dehydrochlorination of ethylene chlorohydrin (ECH) into ethylene oxide (EO), whereas acidic substances promote the formation of acetaldehyde (AA)as described by eq 1 (Mochida et al., 1972). The selective synthesis of ~
IHZEH?
-ti+
OH CH z-CH
I I OH Cl
CY=CH2
3H
2
----
Table I. Dehydrochlorination of ECH reacselection total tivity temp, conv, of EO, % "C %
cat. MImz HClfCH
2-)9
Si 0,a
CHCY3
II C
( A A J (1)
MImzHClCH,PhfCH, j,SiO," KOH/SiO,
225 250 300 250 300
200
a Catalyst, 600 mg; pulse size, 5 pL.
&
mg; pulse size, 2 pL.
- yyp2 -c,-
CL! iti2
I 21
A- tl
b
PQ)
EO from ECH with recovery of hydrogen chloride from the reaction is the most useful method from a practical viewpoint; however, if basic substances such as sodium hydroxide are used, they react with the hydrogen chloride to form the corresponding salts, and thus they and hydrogen chloride are lost. We report here the acid-proof basicity of hydrochlorinated 2-methylimidazole bound to silica gel (MImzHClfCH2j$3i02)(Mochida et d.,1980),which is of use in the above dehydrochlorination. Hydrochlorinated imidazole was found to liberate hydrogen chloride at elevated temperatures to exhibit basicity, which promotes the selective dehydrochlorination in a similar manner to DBU (1,5-diazabicyclo-[5,4,0]-undec-5-ene)-HCl supported on silica gel as previously reported (Mochida et al., 1981). Experimental Section Material. The catalyst of immobilized 2methyimidazole on silica gel, abbreviated as MImzHClfCH2j$3i02,was prepared using chloropropyltrimethoxysilane according to Burwell et al. (Burwell, 1974; Leal et al., 1975), who intended to use Imz-SiOz as an
4.9
23.4 34.0 3.1 4.3 10.1
92.2 87.4 70.6
trace trace 81.7
* Catalyst, 100
immobilizing ligand. The catalyst prepared using [ [ p (m)-(chloromethyl)phenyl]ethyl]trimethoxysilane in a similar manner was abbreviated as MImzCH2Ph(CH2hSi02. KOH/Si02 was prepared by impregnating the base on the gel from its aqueous solution. The amounts of KOH supported on silica gel, and of MImzHCl in forms of MImzHClfCH2@i02 and MImzHC1CH2PhfCH2hSi02were 0.33, 1.56, and 1.71 mmol/ g, respectively. The immobilized 2-methylimidazole catalysts are illustrated in Figure 1. Procedure. The dehydrochlorination of ECH was studied with a microcatalytic gas chromatographic pulse technique (Mochida and Yoneda, 1967; Kokes et al., 1955), using polyethylene glycol (2 m, 80 "C) t o measure the conversion of ECH, and VZ-7 (2 m, room temperature (r.t.)) to quantify EO and AA. The dehydrochlorination of 1-hydroxy-2-chloropropane (PCH) was studied in a similar manner using polyethylene glycol (2 m, 80 O C ) to measure the conversion of PCH and polyethylene glycol (4m, r.t.1 and VZ7 2 m, r.t.1 to analyze propylene oxide (PO), propionaldehyde (PA), and acetone in the products. Results and Discussion Catalytic activities of MImzHClfCH2j$3i02 and MImzHC1CHZPhfCH2j-&3iO2 in the first pulse at several
0196-4321/83/1222-0038$01.50/00 1983 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 1, 1983
39
Table 11. Dehydrochlorination of PCH
a
cat.
reaction temp, "C
total conv, %
MImzHClfCHk-f,SiO, a MImzHCIC~,PhflH,jzSiO,a KOH/SiO,
250 300
35.3 19.6 19.8
Catalyst, 600 mg; pulse size, 5 pL.
200
selectivity, 3'%
PO 2.6
7 .o
100
PA
acetone
18.6
78.7 74.2
18.8 trace
Catalyst, 100 mg; pulse size, 2 ML.
A
1
Mlmz HCI- CH2-PhfCH~f2Si02
Mlmz HC[+CH&SiO,
Figure 1. The structure of imidazole catalysts.
-s
In
A P
A
*
*I 5
10
7.5
Pulse Size(,ul)
Figure 3. Effects of pulse size in the dehydrochlorinationof ECH over fresh MImzHCl+CHzj8SiO2:(0) conversion of ECH; (A) Selectivity of EO; amount of catalyst, 600 mg; reaction temperature, 250 O C ; pulse interval, 30 min.
Pulse Number
Figure 2. Dehydrochlorination of ECH over MImzHClfCHzj$3iOz: (0) conversion of ECH; (A), selectivity of EO; amount of catalyst, 600 mg; pulse size and interval: 5 ML,30 min; reaction temperature, 250 OC.
reaction temperatures are summarized in Table I, where that of KOH/Si02 is also included for comparison. The MImzHClfCH2)sSi02exhibited a considerable activity of 24% conversion at 250 "C where the selectivity for EO was as high as 87 % The major byproduct was AA. The selectivity was noted to be comparable to that of KOH/Si02. The higher reaction temperature of 300 "C further increased the activity; however, the selectivity decreased significantly to 71% . The lowering of the temperature to 225 "C decreased markedly the activity to only 5% with some increase of selectivity. In contrast, the activity of MImzHClCH2PhfCH2j$3i02was very low even at 300 "C. The activity and selectivity of MImzHClfCH2j$i02 in the successive pulses are illustrated in Figure 2, where the reaction temperature and the pulse size were fixed at 250 "C and 5 pL, respectively. The interval time between pulse injections was rather strictly held to be 30 min. The conversion and the selectivity stayed unchanged for eight pulses or more, indicating the catalytic ability of the anchored 2-methylimidazole. In contrast, the activity of KOH/Si02 decreased by each pulse to be almost zero after 5 pulses, reflecting the stoichiometric nature of the reaction. The influences of pulse size on the activity and selectivity of MImzHClfCH2)sSiOzin the first pulse are shown in Figure 3, where the reaction temperature was 250 "C. Although the selectivity remained as high as 87% regardless of the pulse size, the activity sharply decreased with the increase of pulse size until 7.5 pL, leveling off at larger sizes. The pulse size was proportional to the partial pressure of the reactant when the size was below 7.5 pL; however, the larger size increased the width of the pulse shape at the constant pressure because of the heating capacity of the evaporator. Based on such pulse profiles,
the decrease of the activity shown in Figure 3 indicates the zero order of the reaction in the feed. Dehydrochlorination of 1-Hydroxy-2-chloropropane. The dehydrochlorination reactivities of PCH over MImzHClfCH2)sSi02and the reference catalyst are summarized in Table 11. The reaction is expected to produce PO and PA, but no acetone can be produced directly from the reactant as illustrated in eq 2, although CH 3-C
II
-CH,
acetone
.
PCH
CH,-CH,-CH
II 0
PA
the produced epoxide can be isomerized into acetone as well as PA. In contrast to the result that PO was quite selectively produced over KOH/Si02, the major product over the 2-methylimidazole catalysts was acetone with minor formation of PA and PO, although EO was selectively produced in almost the same extent on both catalysts. Acetone is excluded from the primary product as described above, indicating that PCH may be fairly selectively converted over the catalysts into PO, which may be further transformed fairly selectively into acetone by the acidic nature of the hydrochlorinated catalysts. It should be noted that MImzHC1CH2PhfCH2j$3i02showed some activity against PCH at 300 "C. The higher reactivity of PCH was suggested. Product selectivity depends on the stability of the first stage products, EO or PO, in the second reaction. Burwell (1974) and Leal et al. (1975) proposed the dehydrochlorination of MImzHCl+CH2f3Si02with ethylene oxide at 0 "C. Ethylene oxide produced catalytically may be able to survive during the short contact time of the catalytic reaction. In contrast, highly reactive propylene oxide suffers the successive transformation over the same catalyst at a similar contact time. The amount of free base (MImztCHzj3SiOz)in the MImzHCl+CHzj3SiOzafter the heat treatment at the re-
40
Ind. Eng. Chem. Prod. Res. Dev. 1903, 22, 40-44
action temperature, which was quantified by the titration with hydrochloric acid, was 3.2% of the total imidazole group of the catalyst. The dehydrochlorinated product in a pulse of ECH corresponds to 1.9% of the total 2methylimidazole group, that is 60% of the free base, indicating that the free base produced thermally from MImzHCl can be the active site for the reaction and the recovery of dry hydrogen chloride can be achieved. Thus, the reaction scheme over MImzHCl catalysts can be summarized by eq 3. The thermal decomposition of the hy, & T
/-
"ILr-2P"
~
7 7
z
drochloride may allow the recovery of hydrogen chloride and can be a rate-determining step, leading to the zero order in the reactant. Thus, the pulse intervals are strongly
influential in the catalytic activity. A reactor accompanied with the catalyst regeneration unit instead of a continuous flow one should be designed for a practical purpose. Registry No. ECH, 107-07-3; HCl, 7647-01-0; EO, 75-21-8; PCH, 78-89-7; PO, 75-56-9; PA, 123-38-6; acetone, 67-64-1.
Literature Cited Burwell, R., Jr. CHEMTECH 1974, 370. Kokes, R. J.; Tobln. H.; Emmett, P. H. J. Am. Chem. SOC. 1955, 77, 5860. Leal, 0.:Anderson, D.; Bowman, R.; Basolo, F.; Burwell, R., Jr. J Am. Chem. SOC. 1975, 9 7 , 5125. Mochida, I.; Yoneda, Y. J. Catal. 1967, 7 , 386. Mochida, I.: Anju, Y.; Koto, A.; Seiyama, T. Bull. Chem. SOC.Jpn. 1972, 4 5 , 1635. Mochida, I.; Watanabe, H.; Fujltsu, H.; Takeshita, K. J , Chem. SOC.,Chem. Commun. 1980, 793. MochMa, I.; Watanabe, H.; Uchino, A.; Fujitsu. H.: Takeshita, K.; Furuno, M.; Sakura, T.: Nakajima, H. J. Mol. Catal. 1981, 72,359.
Received for review December 21, 1981 Accepted September 27, 1982
Effects of Phosphorus on Nickel-Molybdenum Hydrodesulfurizat ion/H ydrodenitrogenation Catalysts of Varying Metals Content Carl W. Fitr, Jr.,' and Howard F. Rase' DepaHment of Chemical Engineering, The University of Texas, Austin, Texas 78712
Five Ni-Mo catalysts were studied having varying amounts of Mo and P and a constant Ni/Mo ratio. A catalyst with low metals and medium phosphorus content was found to be best for hydrodesulfurization while a highmetaldhigh-phosphorus catalyst gave the best performance and lowest hydrogen consumption for nitrogencontaining feeds. The phosphorus-containing catalysts were less susceptible to coking and produced a more
hydrogen-rich coke.
Hydrotreating catalysts based on Co-Mo or Ni-Mo deposited on a y-alumina carrier are not only fascinating systems but they are also essential in the commercial production of low-sulfur products from petroleum and coal-derived liquids. It is not surprising, therefore, that studies aimed a t both further understanding of these rather complex catalysts and improving their performance continue to stimulate interest in laboratories throughout the world. One area of interest, common to all catalysts, has been the use and performance of promoters in improving activity, selectivity, and catalyst life. One such promoter for Co-Mo and Ni-Mo catalysts, phosphorus, has been investigated and recommended over a period of three decades and is now used in a number of merchant catalysts. The investigation reported here had as its purpose the study of the effect of phosphorus on activity and selectivity in relation to metals content of a group of similarly prepared Ni-Mo/A1203 catalysts. Interesting differences were observed, and some insights on the mode of phosphorus interaction were realized.
Previous Observations Because of the commercial interest in improving hydrotreating catalysts, the patent literature is a major source of information on discoveries and observations on phosPhillips Petroleum Co., Bartlesville, OK 74004.
phorus as a promoter. As early as 1953 Haresnape and Morris (1953) of the Anglo-Iranian Oil Co. claimed that adding phosphorus in the form of cobalt phosphomolybdate or (NH4)3P04.12M003increased the hydrodesulfurization (HDS) activity. The relative activity for a catalyst containing 2.85% COO,15.6% Moo3, and 1.14% P205was 115 compared to an activity of 100 for a similar catalyst with no phosphorus. The promoting effect of phosphorus in improving hydrogenation activity was confirmed in a patent by Housam and Lester of British Petroleum Co. (1959) for both Co-Mo/Al,O, and Ni-W/ Al,O, catalysts. A single-step impregnation procedure using phosphoric acid was proposed by Colgan and Chomitz (1966) of American Cyanamid. Phosphoric acid was found to act as a stabilizing and solubilizing agent, allowing a high concentration of metal to be impregnated uniformly. They recommended a phosphoric acid to molybdenum mole ratio of about 0.4:1, yielding about 1to 5 wt % phosphorus on the catalyst. Larger amounts of phosphorus tend to mask the active areas and reduce the activity of the catalyst. A catalyst containing 14.5% MOO,, 3.5% NiO, and 3.8% H P 0 3 was shown to have an HDS activity of 127 and an HDN activity of 149 when compared to a similar catalyst without phosphorus. Phosphorus also provides increased strength and heat stability. According to Hilfman of UOP (1971), the function of phosphorus is to inhibit the formation of nickel aluminate
0196-4321/83/1222-0040$01.50/0 0 1983 American Chemical Society
