I n d . Eng. Chem. Res. 1988, 27, 1565-1571
1565
KINETICS AND CATALYSIS Continuous-Flow Processes under Gas-Liquid Phase-Transfer Catalysis (GL-PTC) Conditions: The Reaction of Dialkyl Carbonates with Phenols, Alcohols, and Mercaptans Pietro Tundo* Istituto di Chimica Industriale dell'llniversita' di Messina Cas., Post. 29-S., Agata 98010, Messina, Italy
Francesco Trotta and Giovanni Moraglio Istituto di Chimica Macromolecolare dell'Uniuersita' di Torino, Via G. Bidone, 36-10125 Torino, Italy
Ferdinand0 Ligorati ENIChem Sntesis, Bolgiano, 20100 Milano, Italy
When dimethyl carbonate is reacted with phenols, thiophenols, and mercaptans under GL-PTC conditions (continuous flow of gaseous reactants over a solid bed supporting a liquid phase-transfer catalyst), the corresponding ethers and thioethers are produced with high rate and selectivity (no C-alkylation products or dissymmetrical carbonates). Since the process is actually catalytic (the acidity is removed from the reaction environment as COP),the reaction can be carried out indefinitively. On the contrary, the reaction of alcohols with dimethyl carbonate gives exclusively transesterification products. Selectivities are explained in terms of BA12 and BAc2 mechanisms, because the BAlz pathway is enhanced by anion activation. We previously reported (Tundo, 1979; Tundo and Venturello, 1984) on some reactions carried out under GL-PTC conditions and remarked how this new method of synthesis allows transfer of the knowledge of phasetransfer catalysis (PTC) to reactions carried out under continuous flow of reagents. Accordingly, in GL-PTC reactions both reagents and products in the gaseous phase are reversibly adsorbed over a liquid film; in turn, the latter is supported over a solid. The liquid film constitutes the phase in which the reaction occurs; moreover, since the liquid actually is a molten PT catalyst, it allows the activation of the anions or the bases present there (Tundo et al., 1982a,b). With regard to the conditions, a comparison can be made with supported liquid phase catalysis (SL-PC) (Rony, 1968; Datta and Rinker, 1985; Datta et al., 1985a,b); as in GL-PTC, a liquid catalyst is also adsorbed over a solid in SL-PC. The most important processes operating under such conditions are sulfur dioxide oxidation, aromatic alkylation, and oxychlorination. However, activated anions were never allowed to react, in classical organic synthesis, under SL-PC conditions. Owing to the higher temperatures and the different reaction conditions involved, operating under GL-PTC conditions allows us to disclose new ways of synthesis. This is the case of the reaction of anilines with dimethyl carbonate (DMC) (Trotta et al., 1987): this reaction, in place of the corresponding urethane which is usually obtained in homogeneous conditions, yields N-methylaniline with high selectivity: a weak base (potassium carbonate) is able to produce and to activate, in the presence of a PT catalyst, the PhN-COOCH3 anion. In the same way, a similar combination of catalyst and base allows the alkylation of
weak CH-acid compounds (Tundo et al., 1987). We report here the reaction of oxygen and sulfur nucleophiles (RO- and RS-) with dialkyl carbonates under GL-PTC conditions. It was reported some years ago that, operating under pressure in batch and using sodium methoxide as a base, phenol gives methyl phenyl carbonate (Merger et al., 1980) and thiophenol gives methyl phenyl thioether (Tamura et al., 1975); alcohols produce transesterification (Romano and Koch, 1984),while the reaction of mercaptans is not reported. Interesting for our purposes was the observation that, when methyl iodide (or KI) was catalytically added to the reaction mixture of PhOH and DMC, anisole was obtained instead of the transesterification product (Iori and Romano, 1980). Since anisole is presumably produced by the reaction of phenol with iodomethane, the necessary regeneration of the latter implies the reaction of I- with DMC, according to a BAlz mechanism: I-
+ (CH30)ZCO
-
CHJ
+ CH30C00-
(1)
Our intent was to investigate if anion activation, already well known to occur in GL-PTC, was enough to shift the nucleophilic reactions of oxygen and sulfur in dialkyl carbonates toward the alkylation (eq 2) rather than the usual carboxyalkylation (eq 3), according to Scheme I in which DMC is considered.
Results The reactions were carried out at atmospheric pressure and at temperatures between 160 and 180 OC (mostly at 180 "C). A liquid mixture containing the dialkyl carbonate, the compound to be reacted, and, eventually, a solvent was
0888-588518812627-1565$01.50/0 0 1988 American Chemical Society
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Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988
Table 1. Dimethyl Carbonate (DMC) a n d Diethyl Carbonate (DEC) a s Alkylating Agents of Phenol a n d Thiophenol under GL-PTC Conditions" product conversn, 70 entry carrier reagents (molar ratio) flow (liquid), mL/h DMC + PhOH (1.2) 18 PhOCH3 92.5 1 cyclohexaneb 85.5 (60.0)' DMC + PhOH (1.2) 25 PhOCHB 2 cyclohexaneb DMC + PhOH (1.2) 38 PhOCH3 74.0 3 cyclohexaneb DMC + PhOH (1.2) 90 PhOCH3 45.0 4 cyclohexaneb DMC + PhSH (1.2) 90 PhSCH3 99.5 5 cyclohexaneb DMC + PhSH (1.2) 200 PhSCH3 99.5 6 cyclohexaneb DMC + PhOH (2.0) 24 PhOCH3 94.9 (59.2)' 7d nitrogene 24 PhOCzH, 41.2 8d nitrogen' DEC + PhOH (2.0)
2' = 180 " C ;atmospheric pressure. Catalytic b e d 95 g of K2C03coated with 5 w t 70 of PEG 6000. "0 mL of cyclohexane was added to 0.1 mol of phenol and 0.12 mol of DMC. 'K2COs alone, without PEG. dK,C03 coated with 15 w t % of PEG 6000. 'Gaseous flow, 30 mL/m. Scheme I
liC
RX-
+ DMC 2 RXCH3 + CH,OCOO-
(2)
RX-
+ DMC
(3)
RXOCOCH,
+ CH,O-
1
z
f
x=o,s k , is nucleophilic attack to a saturated carbon, BAl, mechanism k , is nucleophilic attack to an unsaturated carbon, BAc2 mechanism
fed, with fixed fluxes obtained by a syringe pump, to the head of the tubular reactor containing the solid beds acting as catalysts. Owing to the temperatures and the concentrations of the components, the mixture became gaseous. Complete vaporization of high boiling compounds (phenols, mercaptans, etc.) was assured by an excess of low-boiling carbonate (DMC, bp 90.4 "C; diethyl carbonate, bp 126.8 "C) or by a solvent or by nitrogen, both used in this case as gaseous carriers of the reaction. Two types of solid beds were used: the first one (bed A) had solid potassium carbonate as solid support on which a catalyst was adsorbed; the second one (bed B) had spherical macroporous a-alumina pellets (3 mm in diameter; surface area 0.03 m2/g) as support for the base and the catalyst. Their relative quantity on this support was varied. As is known, a-alumina support is extensively used in industrial processes since it avoids preferential gaseous ways; for this reason it allowed m6re accurate experiments to be carried out, necessary for investigating the reaction mechanism. The reactions were carried out in two columns: the first one was 48 cm in length and 2.0 cm in diameter; the second column (48 cm in length and 1.4 cm in diameter) was used in the experiments carried out with macroporous a-alumina spheres (Figures 2-5). The reaction mixture was collected by cooling with a condenser placed at the column outlet. According to such conditions, the reactions of phenols, thiophenol, mercaptans, and alcohols are described below. Reaction of Phenols with Dialkyl Carbonates. We have found that, when a mixture of phenol and DMC (the more extensively studied reaction) was allowed to go through a solid bed composed - of a PT catalyst (poly(ethylene glycol) having a MW of 6000, PEG 6000) and a base, anisole was produced with high selectivity (no trace of C-alkylated products was observed (Matsuzaki and Ohsuga, 1986; Matsuzaki et al., 1985)),according to eq 4. PhOH
+ DMC
GL-PTC base
PhOH
+ C02 + CHBOH
(4)
Unlike the alkylations with alkyl halides, where a stoichiometric base is needed for neutralizing the coming acid, when dialkyl carbonates act as alkylating agents, the acidity is removed from the bed as C02;therefore, the base is not consumed and may be used just in catalytic amounts.
L
. 16:
?i3
13:
-
-
Figure 1. Anisole from phenol and DMC according to eq 4; influence of the temperature and DMC/PhOH molar ratio. Solid bed: 95 g of K&03 coated with 5 wt % of PEG 6000; atmospheric pressure; flow (liquid), 24 mL/h. ).( DMC/PhOH = 2.0; (A)DMC/ PhOH = 4.5; (m) DMC/PhOH = 7.0.
Moreover, this fact opens the way to continuous-flow conditions, with a process being actually catalytic, since the bed composition does not change with time. The reagents and the products distribute themselves on and are retained by the liquid film of the catalyst, roughly according to the boiling point of the compounds involved (compare gas-liquid chromatography). For that reason, the composition of the effluent mixture varies at the beginning of the experiments, until steady conditions are reached: in the case of phenol, for example, DMC and methanol leave the column first, then anisole, and then if present, the nonreacted phenol. All the reported data are taken at steady conditions when effluent composition becomes constant (2-8 h, based on reagent flow). High conversions of phenol into anisole are easily reached, as shown in Figure 1: conversion increases when either the temperature or the DMC/PhOH molar ratio is increased at a fixed contact time. The influence of the reagents' feeding rate is reported in Table I, operating with solid potassium carbonate as a support; here also, other experiences are shown for comparison. The effect of the reagents permanence time in the reactor is pointed out in Figure 2; here, moreover, over a bed of type B (a-alumina spheres), the DMC/PhOH molar ratio was 411. Interesting to note, bigger difference in reaction efficiency (higher conversion) among the several catalytic beds are observed for higher reaction time (lower feeding rate). In light of these results, a pilot plant was built; working at 220 "C, it produced anisole (from phenol) during 3 weeks without any stopping and, when it operated at 280 "C, it produced 4-methoxyphenol(from hydroquinone). We will report on that plant in a later paper. The results with
Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988 1567
1oc
z
0
= >
8
50
w
50
0
2,5
C
100
FLOW I n L h
X
Figure 2. Influence of flow (liquid) of the reagents in the reaction between phenol and DMC carried out on two different catalytic beds: (0) 40 g of a-alumina spheres coated with 5 wt % of KZCO, and 5 wt % of PEG 6000; ( 0 )40 g of a-alumina pellets coated with 5 wt % of K2C03 alone. Phenol/DMC, 1/4 mol/mol; T = 160 OC; atmospheric pressure.
1co
5.0
PEG 6000
Figure 4. Influence of PEG 6000 on the reaction between phenol and DMC. The pellets were coated with 5 wt % of K2C03. The reaction was carried out under the same conditions as in Figure 3.
-
lc
0
c
50 F.m
I~L/iil
Figure 5. Influence of the flow of the reagents in the reaction between phenol and DMC, carried out under the conditions in Figure 3: ( 0 ) percent of conversion of phenol (left scale); (m) PhOCOOCH,/PhOCH, ratio in the reaction products (right scale). 2.5 %
5.c
K2C03
Figure 3. Influence of K2C03 percent (on a-alumina spheres coated with 1 wt % of PEG 6000) on the reaction between phenol and DMC. Liquid flow: 46 mL/h. Other conditions are those in Figure 2.
hydroquinone were noticeable: working at atmospheric pressure, with a DMC/hydroquinone molar ratio of 1.5 and contact time of 13 s, conversions of 98.2% and 77.9% yield in the monomethyl ether were observed. This value is higher than in homogeneous conditions (alkylation with methanoi: 87% selectivity at 55% conversion (Rivetti and Romano, 1982)), with DMC (alkylation promoted by KI (Iori and Romano, 1980)), or when using CH31 as an alkylating agent (62% selectivity at 98% conversion; CH31, 1.0 molar equiv (Newman and Cella, 1974)). As with DMC, diethyl carbonate gives the corresponding ether but with a slower reaction rate (Table I, entry 8). Reported in the Experimental Section are also the reactions of @-naphtholwith DMC that produces the corresponding methyl ether. With the aim of investigating the reaction mechanism, the reaction between phenol and DMC, performed on a-alumina spheres, was carried out with and without the base or the PEG. The results are shown in Figures 3 and 4, respectively. It is clear that the reaction does not proceed in the gas phase at all. The presence of a base is strictly necessary, while the presence of PEG is less necessary. More precisely, the effect of PT catalysts varies with the time spent by the reagents in the column, being higher at lower flow rate. In order to observe the possible reaction intermediates, short reaction times were employed. These experiments
are shown in Figure 5. Although in low yield, at higher flow rates (referred to as the reacted phenol) the transesterification product PhOCOOCH, increases; its presence emphasizes that reaction 3 (RX- = PhO-) takes place in GL-PTC, as well as under homogenous conditions (Merger et al., 1980). However, as the reaction time and conversion of phenol increase, PhOCH3 takes the place of PhOCOOCH3. Reaction of Thiophenol and Mercaptans with DMC. According to eq 2, under GL-PTC conditions thiophenol gives its corresponding ether: PhSH
+ DMC
GL-PTC base
PhSCH3 + COZ + CHSOH (5)
The reaction rate is higher than for PhOH, so that, under comparable conditions, the conversion was complete (Table I, entries 5 and 6). Moreover, no trace of thiocarbonate PhSCOOCH, was detected, PhSCH, being the sole product. Higher feeding rates were not experimented owing to thermostating low accuracies. In the same way, nC8H1,SCOOCH3was not a reaction product of the reaction of n-octylmercaptan with DMC, as it yielded only the thioether (eq 6 and Experimental Section): GL-PTC
n-CsH17SH + DMC 7 IZ-C~H~~S + CCOZ H ~+ CH30H (6)
Reaction of Alcohols with DMC. Transesterification reactions were already reported under GL-PTC conditions (Tundo et al., 1983). Nowadays DMC can be synthesized economically directly from methanol, oxygen, and carbon monoxide with copper(1) salts as catalysts. So far produced by ENIChem Synthesis in Italy, it is now also industrially
1568 Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988
developed by Dow Chemical in the USA. This safe reagent is improving in applications and is trying to replace phosgene as a source for carbonic acid derivatives and dimethyl sulfate as a methylating agent (Romano et al., 1980). With the aim to develop an alternative synthetic way not based on phosgene, the synthesis of dialkyl carbonates via transesterification between several alcohols and DMC was investigated. Actually, the reaction proceeds according to eq 7 and 8, yielding selectively the transesterification products. In the case of ethanol, from thermodynamic ROH ROH
+ DMC
+ ROCOOCH:,
GL-PTC base
GL-PTC base
ROCOOCH:,
(R0)2CO + CH30H
(7) (8)
calculations made with group contribution on gaseous components, K of eq 7 plus 8 (at 453 K) is 2.45; it follows that, when a E%H/DMC molar ratio of 2.0 (as in all the reported examples) was used, the conversion defined by eq 9 cannot exceed 62%. The value of 2.45, different from conversion % = 1/,[ROCOOCHJ [(RO),CO] 100 (9) [ROCOOCH,] + [(RO),CO] [DMC]
+
+
the unity value, derives from the comparison between methanol and a primary alcohol; in fact, K9 becomes near unity (AG N 0.1 kcal/mol) in the reaction of diethyl carbonate and 1-propanol, where two primary alcohols are competing. The results obtained from the reaction of ethanol with DMC are shown in Figure 6. As in the case of phenol, the reaction is slower in the absence of PEG (Figure 6a). More interestingly, (EtO),CO is higher with respect to the monotransesterificated compound, is higher when the catalyst is present, and is higher also if slower feeding flows are used (Figure 6b). By use of the same flow rate (reaction is kinetically controlled), a comparison between the reactivities of some alcohols with DMC was carried out. As reported in Table 11, when hindrance due to the alkylic chain is increased, the conversion decreases; moreover, a firmer decrease is observed proceeding from primary to secondary to tertiary alcohols. From a preparative point of view, it should be easy to make a continuous-flow apparatus able to synthesize just one of the transesterification products: continuous-fractionating reaction mixture represents a well-known technology.
Discussion Selectivity. High reaction selectivity arises when phenols, thiophenols, mercaptans, and alcohols are reacted with DMC (or dialkyl carbonates in general), under GLPTC conditions: the first ones produce solely the 0- and S-alkyl derivatives, while alcohols give transesterification. It is well-known that in RXH
+ B z RX-+
BH+
(10)
the thermodynamic equilibrium constants, Keq,for alcohols, phenols, and mercaptans follow the order Keq(ROH)
< Keq(ArOH) < Keq(RSH)
(11)
The generated anions (with relative concentration, a t steady conditions on the catalytic liquid phase following the same order) react with DMC according to eq 2 or/and 3.
Because eq 10 involves very fast reactions, the corresponding observed kinetic constants (kobsd)will be (Frost and Pearson, 1961) kobsda
= Keqka
(12)
kobadt
= Keqkt
(13)
It is well-known that anion nucleophilic strength in SN2 displacements varies (RO- < ArO- < RS-) as Kq in eq 11 does. As a consequence of these two concomitant causes, we ought to observe a higher difference in reactivity between the different compounds, as kobsda in eq 12 is concerned. Actually we observe three cases. 1. Mercaptans and Thiophenols. Both produce only thioethers, the reaction rate being higher with thiophenol than that with mercaptans. In both cases, transesterification does not occur (Table I). 2. Phenols. Ethers are the sole products if the reaction time is long enough. The reaction does not proceed in the absence of a base (Figure 3), and it is promoted by the liquid film of a PT catalyst (Figure 4). With small reaction times, when the conversion is much lower, the transesterification product PhOCOOCH, is also observed (Figure 5). Thermodynamically, the transesterification between phenol and DMC is not favored (K, = 3 X lo4 at 453 K); this is in agreement with the right scale in Figure 5, where PhOCOOCH, at high flow is only 9% anisole. On the other hand, methyl phenyl carbonate does not decompose by heating: after 24 h a t 60 "C in the presence of a large excess of PEG 6000, methanol, and DMC, no reaction occurs; the mixture gave anisole and phenol only when sodium methoxide was added. 3. Alcohols. As already reported in the reaction of alcohols with ethers (Tundo et al., 1983), also the reaction with dialkyl carbonates produces only transesterification; eq 14 does not occur at all. With alcohols, a reaction RO-
+ DMC 3+
ROCH3 + COz + CH30H
(14)
mechanism similar to the one in homogeneous conditions is present (March, 1985): the reaction rate is controlled by the formation of the corresponding anion (primary > secondary > tertiary) and by the steric hindrance due to the alkylic chain (Table 11). Reaction Mechanism. In order to have the bed actually catalytic, either in alkylation and transesterification, the base is regenerated according to eq 15 and 16, respectively. Reactions 15 and 16 are relatively fast proBH+ + CH3OCOO-
-
CH3OH + COZ + B
BH+ + CH30- F! CH30H + B
(15) (16)
cesses and therefore do not control reaction rate. The reactivity is controlled only by the formation of the reactive anion, and in SNz displacements kobsda is given by eq 12. According to the compound involved, experimentally it follows the order kobsda(ROH)
> hobad t(RSH)
'
The fact that opposite trends in eq 17 and 18 coexist is
Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988 1569 Table 11. Transesterification of Some Alcohols with DMC under GL-PTC Conditions" alcohol conversn, % ethanol 47.2 1-propanol 28.7 27.5 1-butanol 2-butanol 1.5 2-methyl-2-propanol 0.0 "Reactions carried out on 90 g of K&03 coated with 5 wt % of
PEG 6000. T = 180 "C, atmospheric pressure; liquid flow, 10.2 mL/h. Alcohol/DMC molar ratio = 2.0.
not surprising in GL-PTC, if compared to that already observed in the alkylation with dialkyl carbonates of aromatic amines. Actually, the reaction of ArNH2 with DMC, under the same conditions, gives only transamidation and not N-alkylation (Trotta et al., 1987); vice versa, the produced carboxymethyl derivative ArNHCOOCH, yields only N-alkylation, presumably because ArN-COOCH, is an anion easier generated, rather than ArNH- from ArNH2. Both steps are highly selective, affording ArNHCH, and not ArN(CH& as final product. In order to explain this selectivity, it is necessary to understand why the BAlZpathway is preferred. It was already reported that esters react as alkylating agents in the presence of strong nucleophiles (I-, PhS-, CN-), if the reaction is performed in DMF or HMPT (McMurray, 1982). More recently, it has been found that in actual gas-phase reactions the BAlz mechanism is strongly improved with respect to the BAcz one (Fukuda and Mc Iver, 1979;Takeshima et al., 1983),as the "hard methoxide also gives dimethyl ether in the reaction with methyl benzoate: proceeding from liquid methanol to gas phase as reaction environments, kobsd &/kobsd improved by 7 order of magnitude (Comisarow, 1977). The change in reaction mechanism was attributed to the fact that, lacking polar protic stabilization of the anion, the negative charge in the gas phase is more stabilized if spread out over three atoms. These findings meet our results well, since in PTC anion activation comes just from lacking anion stabilization; alkyl aryl ethers, alkyl aryl thioethers, and dialkyl thioethers were already reported to be reaction products in GL-PTC by anion activation of phenols, thiophenols, and mercaptans, respectively (Tundo et al., 1982a). Moreover, "hard" alkoxides are still solvated by the liquid phase and therefore give only classical transesterification products. Diffusion and Adsorption. In GL-PTC the reaction occurs on the catalytic liquid film where reagents and products are reversibly adsorbed. The processes are controlled by liquid diffusion of the reagents onto the liquid film, the diffusion in gas phase being made negligible by the gaseous flow rate over the catalyst (Tundo et al., 1988). The influence of diffusion is shown in Figure 4, where, when the amount of the catalyst is increased, a proportional growth in conversion is not observed. Moreover, this trend is shown also in reactions carried out with K2C03 + PEG or just on K&03 (Figure 2); at higher feeding rates, the catalytic activities of both beds are comparable, while they differ at low flow. The difference can be attributable to the larger time the reagents have for disposal, in order to diffuse inside the liquid film where the reaction is promoted. On the other hand, the same trend is observed in the case of alcohols (Figure 6a). The fact that potassium carbonate alone is able to catalyze the reaction also means that the reaction may occur on the wide surface of the potassium carbonate minute crystals. The reaction is also controlled by adsorption and partition phenomena. Adsorption clearly improves reagents
concentration on the liquid film and consequently the reaction rate. Partition may produce selectivity toward different reagents or, in the case of a bifunctional compound, selectivity in mono- or diderivative. This is the case of the reaction of ethanol with DMC (Figure 6b), where diethyl carbonate is produced with higher conversions in the presence of PEG rather than in its absence. The boiling point of monotransesterified product (107 "C) is higher than that of DMC, and its concentration on the liquid film is higher. As a consequence, the monoderivative reacts faster with ethanol than DMC does. In the absence of a liquid film, no selectivity is observed. Moreover, the fact the hydroquinone yields its mono0-methyl derivative with the highest selectivity up to now observed in alkylation reaction can be related to a partition phenomenon too. In fact, DMC reacts faster with the reagent present in higher concentration on the liquid phase, that is with hydroquinone which has a higher boiling point (bp 285-8 "C). As previously shown, the reaction yields the monomethyl ether; this compound, owing to the relatively lower boiling point (244 "C) leaves the liquid phase easily. This is quite different from LL-PTC, where hydroquinone gives preferentially the diderivative rather than the monoderivative. In this case, partition is controlled by the lipophilicity of the compound, and p-methoxyphenol is more lipophilic than hydroquinone. In GL-PTC, partition between gas and liquid phases is controlled by the nature of the liquid phase and by the vapor tension of the compound involved (compare GLC); this is a well-known concept in heterogeneous catalysis (Satterfield, 1980).
Conclusions While dialkyl carbonates cannot be used in LL-PTC condition owing to their fast hydrolysis, anion activation in GL-PTC makes them effective alkylating agents, by a shift reaction pathway from the BAc2 mechanism to the BA1, mechanism. Moreover, the alkylation can be carried out under continuous-flow conditions since COz is meanwhile produced. Noticeably, the dialkyl carbonates are not toxic as many alkylating agents are. During the reaction, no byproducts such as inorganic salts are produced. These facts are interesting from an industrial point of view since GL-PTC processes are able to be extended on a larger scale. The new types of phenomena which control reaction selectivity (reaction mechanism and gas-liquid partition) are promising from a theoretical point of view as well. Experimental Section All the compounds employed were commercial samples (ACS grade) and used without further purification. aAlumina pellets were acquired from Industrie Bitossi, Vinci-Firenze. Phenyl methyl carbonate was synthesized according to the literature, starting from phenol and methyl chloroformate. Preparation of the Catalytic Beds. Bed A: K2C03 Coated with 5 wt % of PEG 6000. PEG 6000 (5.0 g) was dissolved in about 150 mL of dichloromethane, and then 95.0 g of potassium carbonate was added. The solvent was removed under vacuum, and the solid obtained was put in an oven for 2 h a t 120 "C. Bed B: a-Alumina Pellets Coated with 5 wt % of KzC03and 5 wt % of PEG 6000. Ten grams of potassium carbonate and 10.0 g of PEG 6000 were dissolved in 150 mL of water. a-Alumina pellets (180 g) were added, and the water was removed under vacuum; the coated
1570 Ind. Eng. Chem. Res., Vol. 27, No. 9, 1988
Chimica Fine e Secondaria” (It. Patent Appl. 20611 A/86; CNR and ENIChem Sntesis), and by Minister0 “Pubblica Istruzione”, Fondo 40%. One of us (P. T.) thanks CNR and the British Council for the stay at Department of Chemistry, Lancaster University, Lancaster, U.K. Acknowledgment is made to Prof. P. Hodge for his suggestions and hospitality. Registry NO.PEG, 25322-68-3; DMC, 616-386; DEC, 105-58-8; KZCO,, 584-08-7; PhOH, 108-95-2; PhSH, 108-98-5; PhOCH3,
L__ r n
I
*
Figure 6. Influence of the flow of the reagents on the reaction between DMC and ethanol (1/2, mol/mol). T = 180 “C; atmospheric pressure: ( 0 , 0 )95 g of K2C03coated with 5 wt % of PEG 6000; (m, 0)95 g of K&03 alone. (a) Conversion according to formula 9. (b) Percent (EtO)&O in the reaction mixture.
spheres were put in an oven a t 110 “C for one night. Execution of the Reactions. All the reactions were carried out under atmospheric pressure. The column was packed with the required amount of catalytic bed (A or B) and thermostated at the reaction temperature with continuous circulation of oil (Ultrathermostat Lauda MGW). The liquid mixture of dialkyl carbonate and the compound to be reacted were continuously sent to the reactor with a syringe pump (Sage Instruments 341 A). The reaction products were recovered at the outlet of the column by collecting the gases with a Liebig condenser; they were analyzed by gas chromatography (Varian Vista 6000) by comparison with authentic samples. Reaction of DMC with Phenol (Table I, Entry 1). The reaction was carried out at 180 “C, with 95 g of bed A containing 5 wt 70 of PEG 6000. The reaction mixture (prepared by phenol, 9.41 g; DMC, 10.5 mL; cyclohexane, 41 mL; DMC/phenol molar ratio = 1.2) was continuously sent to the reactor with a liquid flow of 18 mL/h. The collected products were analyzed by gas chromatography: after 8 h, their composition did not change, since steady conditions had been reached (conversion 92.5% ). Reaction of DMC with %-Naphthol.Fifteen grams of 2-naphthol were dissolved in 75 mL of DMC (DMC/ 2-naphthol molar ratio = 8.01, and the solution was continuously sent to the reactor at 180 “C with a liquid flow of 24 mL/h over 95 g of potassium carbonate coated with 5 wt 70 of PEG 6000. In the leaving gases only 2-methoxynaphthalene was detected. Reaction of DMC with Thiophenol (Table I, Entry 5). Thiophenol (10.2 mL), DMC (10.1 mL), cyclohexane (41 mL) were mixed (DMC/thiophenol molar ratio = 1.2) and sent on 95 g of catalytic bed, all the conditions being the same as those for 2-naphthol. Total conversion into thioanisole was observed at liquid flows of 0.40, 1.50, and 3.30 mL/min. Reaction of DMC with n -0ctylmercaptan. n-Octanethiol (17.4 mL), DMC (10.1 mL), and cyclohexane (41.0 mL) were mixed (DMC/thiol molar ratio = 1.2). Under the same conditions as the reaction of 2-naphthol, 54.2 % conversion into only methyl n-octyl thioether was observed. Reaction of DMC with Ethanol (Table 11, Entry 1 and Figure 6). The reaction was carried out in a column containing 90 g of bed A coated with 5 wt % of PEG 6000 at 180 “C. The reagent mixture (ethanol/DMC molar ratio = 2.0; 11.33/8.78 mL/mL) was sent at 180 “C at a flow of 1.02 mL/h. After steady conditions were reached, the conversion was 47.2%, computed according to eq 9.
Acknowledgment This work was supported by CNR, “Progetto Finalizzato
100-66-3; PhSCH3, 100-68-5; PhOCzH5, 103-73-1; 2-naphthol, 135-19-3; 2-methoxynaphthalene, 93-04-9; n-octylmercaptan, 111-88-6; n-octyl thioether, 3698-95-1; ethanol, 64-17-5; 1-propanol, 71-23-8; 1-butanol, 71-36-3; 2-butanol, 78-92-2.
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Received for review February 8, 1988 Revised manuscript received April 14, 1988 Accepted May 2, 1988
Catalytic Cracking of High-Nitrogen Petroleum Feedstocks: Effect of Catalyst Composition and Properties Julius S c h e m e r * and Dennis P. M c A r t h u r Unocal Corporation, Science and Technology Division, P.O. Box 76, Brea, California 92621
Eight experimental FCC catalysts have been evaluated for cracking high-nitrogen feedstocks. The data obtained from microactivity tests show a decrease in conversion with increasing nitrogen content in feedstock. At constant conversion, an increase in feedstock nitrogen content results in a decrease in gasoline yield, while coke, light hydrocarbons, and hydrogen yields increase. High-zeolite content, as well as the presence of acid sites, high surface area, and a broad pore size distribution in the catalyst matrix, is beneficial in cracking high-nitrogen feedstocks. At constant feed nitrogen content, an increase in catalytic conversion results in a decrease in percent nitrogen recovered in the liquid products. Most of the nitrogen-containing compounds in the liquid product are in the decant oil (355+ " C ) and light cycle oil (232-355 O C ) fractions.
I. Introduction The change in the quality of feedstocks processed by refiners over the last decade has led to significant changes in refinery operations. Feedstocks today are heavier, more aromatic, and contain higher levels of sulfur, nitrogen, and metals. The impact of feedstock quality upon the operation of FCC units has been reviewed in several papers (Magee et al., 1979; Ritter et al., 1981). Although the deleterious effect of nitrogen compounds on the performance of cracking catalysts has been known for several decades (Mills et al., 1950; Voge et al., 1951; Villand, 19571, only a limited number of papers has been published more recently on this subject. The correlation between nitrogen content of a FCC feedstock and its effect on cracking catalysts is discussed by Jacob et al. (1976) and Schwab and Baron (1981). Fu and Schaffer (1985) reported the effect of individual nitrogen compounds on the activity and selectivity of two commercial FCC catalysts. They found a correlation between the gas-phase proton affinity of the nitrogen-containing molecule and its poisoning effect on cracking catalysts. Young (1986) has found correlations between catalyst composition and its ability to crack feedstocks blended with different amounts of quinoline. Silverman et al. (1986) have shown that, if the surface area of the catalytic matrix is increased, the nitrogen tolerance of an FCC catalyst can be increased. Corma et al. (1987) have investigated the effect of basic nitrogen on n-heptane cracking over high-silica zeolites. In a recent publication (Scherzer and McArthur, 1986), we discussed the nitrogen resistance of several commercial FCC catalysts, used for cracking high-nitrogen feedstocks. The evaluation of commercial FCC catalysts indicated that high-zeolite-containing catalysts are suitable for cracking high-nitrogen feedstocks. Furthermore, the data obtained suggested that differences in activity and selectivity werre also due to differences in the non-zeolitic components of these catalysts. In order to establish more specific correlations between catalyst composition, their cracking properties, and the nitrogen distribution in liquid products, we have prepared
Table I. Feedstock Prooerties feed no. F-1 gravity, OAPI 22.0 1.19 s, wt % 0.30 N,wt % basic N, wt % 0.094 0.12 Conradson, C, w t 70 aniline pt, "C 19 Br no. 12.3 refraction index (at 67 "C) 1.4950 metals, ppm 4 Fe Ni 0.6 V
