Synthesis of 1,4-Diazabicyclo [2,2,2] Octane with Alkaline Earth

Article pubs.acs.org/OPRD

Synthesis of 1,4-Diazabicyclo [2,2,2] Octane with Alkaline Earth Phosphate Catalysts Work from the Organic Reactions Catalysis Society Meeting 2016 James E. Wells,† Frederick C. Wilhelm,∥ James F. White,*,‡ and Nance K. Dicciani§ †

Air Products and Chemicals, Broomall, Pennsylvania 18105, United States 3RiversCatalysis, LLC, Richland, Washington 99352, United States § Honeywell, Fort Washington, Pennsylvania 19034, United States ‡

ABSTRACT: Here we report on the discovery and development of a new catalyst based on strontium hydrogen phosphate for efficient production of DABCO, 1,4-diazabicyclo [2,2,2] octane. It was brought from initial lab scale discovery to commercial use in less than 1 year. It provides significant value for production of DABCO via much higher selectivity and nearly double the productivity of the silica−alumina material used as the previous commercial catalyst. The value is not only in higher observed productivity but also in large savings in feedstock costs derived from the improved reaction selectivity and also a much longer effective useful lifetime than the previous silica−alumina.

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INTRODUCTION Organic aliphatic amines are an important chemical commodity worldwide. They have a myriad of uses including in the manufacture of pesticides, pharma products, agricultural agents, rubber chemicals, plasticizers, dyestuffs, plastics, surfactants, and as process chemical ingredients. All up to a carbon number of around 10 or 12 are very or at least somewhat water-soluble and possess strong disagreeable ammonia-like odors. The methyl, ethyl, and propyl amines are the most widely used by industry. Alkyl amine basisities (Kb) are generally in the range of 0.6 × 10−4 to about 10 × 10−4. The commercial manufacture of alkyl amines general involves one of several processes. Mainly these are heterogeneous catalytic amination of alcohols by ammonia gas with either a solid acid such as alumina, silica−alumina, or a catalyst containing metals such as Ni, Co, Ru, Pt, or Pd on a suitable support. The ratio of mono-, di-, and trialkyl amine can normally be regulated by control over conditions, especially the amount of excess ammonia as the thermodynamically favored form is usually the trialkyl, especially for methyl, ethyl, and n-propyl amines. Another version of the alcohol amination is reaction of monoor dialkyl amine with alcohols forming the trialkyl amine. In this way, amines with different carbon number alkyl groups can be made. A third process involves high pressure catalytic reduction of nitriles with hydrogen over a metal containing catalyst, most often Fe or Ni, and sometimes Pd or Pt. Again the process outcome can be controlled by at least the ratio of H2/Nitrile and also the presence of added ammonia. In certain cases, alkali metal hydroxides are also included to improve selectivity. Reductive catalytic alkylation of aldehydes or ketones with amines or ammonia is a common technique and allows formation of mixed alkyl amines. The catalysts are usually composed of Pt, Ru, or Ni on a suitable support, often activated carbon. Often the Pt or Ru catalysts are used in a sulfide modified form. © XXXX American Chemical Society

The Ritter reaction of HCN with olefins followed by treatment with sulfuric acid and then base hydrolysis is used for manufacture of amines where the nitrogen is next to tert-alkyl functions and is thus used to make t-butyl amine from isobutylene. Amination of olefins with a suitable solid acid, often a zeolite, can also lead to alkyl amines, but one of the earliest commercial processes, the reaction of ammonia with alkyl halides is not any longer used commercially, mainly due to issues around the coproduct HCL. Alkyl amines are reactive with a very wide variety of organic and inorganic reagents, often producing commercially useful products. These are too numerous for this discussion, and the reader is referred to the two chapters by M. C. Turcotte and his coauthors in Kirk-Othmer’s Encyclopedia of Industrial Chemistry (2001, Vol. 2, p 369 and 2004, Vol. 2, p 537) for more details. This paper is essentially about a significant advance in the manufacture of DABCO, which is a special case of a very useful bicyclic structured tert-alkyl amine.

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BACKGROUND

1,2-Diazabicyclo [2,2,2] octane, trademarked DABCO, is a versatile organic dinitrogen Lewis base1 with a variety of uses. Besides being a unique Lewis base, it is a common component of catalysts for producing polyurethane foams2−5 and is used in various organic transformations6,7 including Sonogashura coupling8 and the Morita−Baylis−Hilman reaction.9 It has been used as a zeolite templating agent,10 also an antioxidant, and is used in some pharma applications and as an improver for chemical pulp bleaching to name a few.11,12 Although the actual basicity of DABCO is not really high, its pkb is about 5.4, and its activity as an organic base catalyst is higher than many other Received: March 22, 2016

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DOI: 10.1021/acs.oprd.6b00096 Org. Process Res. Dev. XXXX, XXX, XXX−XXX

Organic Process Research & Development

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supported tungstopyroposphate. Other Texaco and Jefferson Chemical patents38 claim a variety of solid catalysts and process temperatures for production of DABCO, aminoethyl and hydroxyethyl piperazine and related materials with low to moderate yields. These are perhaps significant as they show a path toward AEP and HEP which are conceptually ideal precursors to DABCO as well as some additional ways to prepare DABCO although at less than ideal yield, space time yield (STY) and selectivity. Bayer claims DABCO yields of 30% up to 55% in a unique homogeneous process39 by heating various DABCO precursors such as HEP with lauric acid under reflux at 280 to 305 °C and distilling the product mixture. Swedish workers40 showed that heating a wide variety of polyamines and the mixtures to above 300 °C in the presence of hydrogen halides produces DABCO in yields of 9−20%. BASF showed that alumina catalysts produce DABCO in a gas phase process from N,N′-dihydroxyethylpiperazine with yields between 30% and 46%.41 Air Products (Houdry) workers found a unique process42 that produces DABCO in a one-step gas−liquid phase process when piperazine and ethylene oxide are reacted at atmospheric pressure over alumina, aluminum phosphate, and calcium or iron phosphates. DABCO yields of 50−60% based on piperazine are reported. Alumina seems to the preferred catalyst for this transformation. Ethyl Corp. showed that a variety of amine feeds including HEP, ethanolamine, diethanolamine, and 1,4-bis(hydoxyethyl)piperazine can be converted to DABCO over titania or zirconia catalysts.43 In particular, a high surface area version of TiO2 (Harshaw Ti 0720, surface area of 150−180 M2/g) as 1/8″ tablets was used with a variety of feeds, sometimes with addition of ammonia, to produce DABCO in up to 50% yield based on amine fed. Actual reported yields were from 0.7% to 50.9% depending on feed type and temperature. Perhaps the most unusual and interesting of the later reported DABCO synthesis is from D. Zhao et al.44 in 2008. These workers report yields of DABCO up to 68% with ca. 73% selectivity from ethylenediamine or monoethanolamine at low temperatures (90 °C) in certain ionic liquids. It is unknown if the effective lifetime of any of these alternate catalysts is adequate for commercial use, and indeed it is not clear if any of the catalysts of these newer reports are being used commercially today. However, one thing clear from the literature is that nearly any acidic material can produce at least some DABCO from a suitable feed such as HEP, AEP, or even ethylenediamine, ethanolamine and diethanolamine, triethanolamine, and the like. Clearly some catalysts are better than others, but unfortunately there does not seem to be a definitive study available that links catalyst performance with catalyst surface properties. This might be a suitable challenge for future study. It is also curious to these authors that, although many different types of acidic materials are claimed in patents and the literature, some seem curiously absent; for example niobia based solid acids, and there is only a single reference to various common Keggin type heteropoly phosphor- and silico-molybdates and tungstates,37 which are known solid acids. Ion exchange resins are also curiously absent. However, there is one 1978 ref 45 from Texaco workers that specifically states that there is no reaction for some related amine reactions with Amberlyst 1546 probably because the required reaction temperatures are higher than the thermal stability limit of the resins.

organic nitrogen bases because of its structure which projects the nitrogen lone pairs into space essentially free of steric hindrance.2 The structure of DABCO is shown in Figure 1.

Figure 1.

The molecule has been known for over 75 years, but its commercial manufacture has been plagued with difficulty in the form of poor selectivity especially when traditional feeds such as ethanolamine, ethylenediamine, diethylenetriamine, piperazine, and ethylene glycol plus ammonia are used in manufacture. Air Products, DABCO’s trademark owner and primary commercial manufacturer, entered into Air Product’s chemical product portfolio in the mid to late 1950s after a group of Houdry staffers noticed a solid white material collecting at the exhaust of a lab scale catalyst calciner.13 The calcination underway involved an alumina supported catalyst that in some way incorporated ethylenediamine and/or ethanolamine in the composition. The white material was identified as 1, 4-diazabicyclo [2, 2, 2] octane, and thus its intentional manufacture was explored and an initial process scheme developed by E. C. Herrick.14 The Herrick process utilized a silica−alumina catalyst and yielded somewhere around 12% (by volume based on reactor liquid condensate) using ethanolamine as feed. The really unique feature of the Herrick patent is the use of a paraffin solvent wash and final sublimation in the recovery scheme to yield a highly pure crystalline DABCO product. This and other early Houdry-Air Products patents15−21 do not show dramatic or very impressive catalyst performance, with claimed DABCO weight yields from total feed ranging from about 8% to near 40%, a significant improvement over prior art. For example, in 1942 O. Hromatka22,23 reported DABCO yields of around 2−3% and in the mid-1950s J. Ishigura and co-workers report “acceptable yields”,24,25 which considering the state of the art at that time was believed to be somewhere less than the 8−10% range.13 More recent work by M. Selvaraj et al.26 claim DABCO yields in the high 80% range over mesoporous solid acids (MCM-41 derivatives) from ethanolamine and similars, while J. Armour et al.27,28 claim combined DABCO plus piperazine yields of 81− 89% from ethylenediamine over surface modified pentasil style zeolites. The relative amounts of DABCO and piperazine are not clear from the data reported. N. Srinivas et al.29 report DABCO yields between about 27% and up to nearly 79% from ethanolamine over various Si/Al ratio modified pentasil zeolites. Other workers have also reported DABCO formation with zeolite catalysts but invariably at low yields.30−34 The exception is work by BASF that showed 95% DABCO selectivity at >95% conversion with a mixture of piperazine and ethylenediamine feed over a TS-1 type zeolite.35 In 1988 and 1991 Texaco-workers obtained patents for conversion of hydroxyethylpiperazine (HEP) to DABCO. The 1988 patent by Vanderpool et al.36 claims DABCO selectivity between 77% and 92% at HEP conversions from 54% to 100% over zirconia or titania doped with phosphorus and another by Zimmerman and Knifton37 claim HEP conversions from 17% to 100% and DABCO selectivities from 54% to 90% over titania B



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One of the continuing issues with the Air Products DABCO process at the time of this project was that a relatively significant amount of byproducts were formed even when the ideal HEP or AEP feeds were being used. These byproducts consisted mainly of piperazine, dimers, trimers, and various poorly defined high molecular weight materials. Piperazine has some byproduct market value, and eventually certain of the high molecular weight materials were sold as corrosion inhibitors. Other byproducts and “tars” presented a significant waste disposal burden. The DABCO mole selectivity of the commercial silica−alumina used at the time at near 100% HEP feed conversion was only around 40%. Low selectivity means less than ideal reactor productivity, that is low STY. Obviously there was room for significant improvements. Of course there was always some interest in finding a better catalyst that could be “dropped into” the existing plant so there were various R&D efforts over time that tried to find such a material, and there was a continuing catalyst improvement program for many years prior to the instant one. Sometime in the late 1970s or early 1980s, a modification of the existing silica− alumina catalyst was developed and commercialized. It served to slightly improve catalyst life but was not patented.13 This modification was used for a few years and eventually discontinued for various practical reasons. It can be said that despite many years of low level R&D no breakthrough improvements were discovered. So there were financial and other incentives to discover and implement a significantly improved catalyst with high DABCO yield, excellent life, and much improved selectivity and productivity. One of the other incentives for new catalyst development was to reduce the difficulty in recovery and purification. As previously noted, the original commercial catalyst and also the improved version of the late 1970s or early 1980s produced not only DABCO but piperazine and a number of higher molecular weight products. These increased the complexity and costs of recovery resulted in a significant waste disposal burden and, perhaps more important, raised overall feedstock costs. In addition a significantly improved catalyst might be able to operate at a higher space rate, effectively increasing plant capacity at little or no capital cost. This paper reports on the development of a very simple and long-lived catalyst family that was brought from an initial bench scale discovery through all necessary small scale piloting and life tests, catalyst scale up and then to full commercial operation within only about nine months. The key to successful implementation in such a short time scale was extremely good and totally seamless energetic teamwork by staff contributors from the basic discovery, catalyst scale up, piloting, engineering,

Since its initial commercial production in the 1950s DABCO was a key profit product at Air Products. It was not only an easily marketable material, but the early commercialization time allowed Air Products’ Houdry Division to expand its product portfolio into the relatively lucrative (at the time) market for a wide variety of DABCO based polyurethane catalysts. DABCO production was plagued for many years with a relatively low selectivity and STY catalyst with a limited lifetimethat is, the initial silica−alumina catalyst that was used basically since production began. Since the catalyst was rather inexpensive, its use continued for many years. In some ways its commercial longevity was based on the discovery and validation that aminoethylpiperazine (AEP) and especially hydroxyethylpiperazine (HEP) were much preferred feeds compared to smaller molecules like the ethanolamine and diethanolamines that were the earliest feed type.13 Figure 2 illustrates the intramolecular cyclization reactions from AEP and HEP that lead to DABCO. It should be obvious

Figure 2.

that there are many alternate intermolecular pathways that can lead to dimers, polymers, tars, C−N bond breaking, and other nonselective products. Table 1 illustrates the structures of the key compounds and some of the properties as well as the theoretical weight yield of DABCO that would be available from their complete and 100% selective conversion to DABCO. The theoretical weight yields are less than 100% since the conversions of both AEP and HEP involve loss of one mole of either ammonia or water. Table 1. Compounds of Interest and Some Properties

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for DABCO selectivity and that known to be exhibited by common solid phosphates. This realization led to multiple conversations regarding the best path forward. Finally agreement was reached that an experimental catalyst discovery plan should focus on materials that have only one type of acidity. In particular the focus would be on surfaces with single types of Bronsted acidity. This focus was developed in part because most common acids were known to be active but not very selective for DABCO production. We theorized that single type Bronsted solid acid structures might be easier to construct or acquire than single type Lewis acids and that since the commercial Si/Al catalyst possessed significant Lewis nature and was not very selective, Lewis acids should not be part of the initial new search. The plan was to include Lewis acids if the Bronsted acids did not lead to any improvements. This plan initially resulted in a fairly short list consisting of mainly hydrogen and pyro phosphates, ortho arsenates, hydrosulfates, and similar anions with various +1, +2, and +3 cations. The two-person discovery team then set about procuring or preparing such materials for reaction performance testing.

and DABCO production plant areas. Another key was the fact that Air Products’ management recognized very early on the potential value of the discovery to the business and did not excessively manage the development process. Instead they strongly supported the development by pretty much giving free reign plus all the needed resources and encouragements to the assembled technical team. Initially there was only one Houdry Division Technical staff assigned to the new program tasked with developing a new catalyst. Eventually another staff was assigned to assist. An initial plan to fully characterize the various known DABCO catalysts for surface and physical properties was formulated. This classical approach was deemed the best way to finally understand the chemistry and then use this fundamental knowledge to uncover a new catalyst. This approach had not really been attempted in prior work. The most important catalyst features were assumed to be surface acidity distribution, surface area, and porosity, so these were measured via the usual techniques accepted at the time; that is, BET, Hg, and N2 porosity and acidity by NH3 desorption and also calorimetry using organic amine probes such as N-butyl amine. Actual reactivity testing was conducted as described below in the Experimental Section using aqueous solutions of hydroxyethyl piperazine (HEP) and aminoethyl piperazine (AEP), same as the commercial plant feeds. Catalyst characterization focused mainly on the commercial catalyst and its modified counterpart as well as certain catalysts from the literature that were reaction tested such as gamma-alumina, AlPO4, boron phosphate, other commercial silica−aluminas, and a few others. Simultaneously, a program of catalyst exploration was mounted and a broad range of possible new solid acid catalysts were tested. This included homemade versions of silica−aluminas, phosphate doped oxides, some apatite47 type minerals, Cr2O3/Al2O3, various X and Y zeolites, natural clinoptolite and chabazite zeolite that had been converted to the proton form, and a significant array of various mixed oxides. These were also analyzed for BET area and porosity and some also for acidity. This effort lasted many months and included reactivity testing of all of the catalysts which were initially subjected to the physical and surface characterization. There were no suitable high through-put screening tools available at the time this work began in the early 1980s so all catalysts were tested one at a time. None of the initial new catalyst candidates that were tested led to any real performance improvements. Also there was no direct and obvious correlation between catalyst performance and any of the characterization data. The only feature that all of the catalysts had in common was that they had a wide range of surface areas and the active ones also possessed a broad collection of surface acidity of many different strengths and types, that is, both Lewis and Bronsted. However, these early characterizations of surface acidity, physical properties, and DABCO synthesis performance produced two important insights. First, it seemed that high surface area and pore size/volumes exhibited by the commercial catalysts, and indeed most of the other catalysts tested over the years contributed little or nothing positive. This was not so surprising since pore diffusion can be slow, not allowing the catalyst pellet interiors to contribute much positive effect. This can be considered a good insight, and we began to feel that any solid having the “correct” acidity and high selectivity might also have low surface area and pore volume, leading to a situation where the most useful activity is at the particle surface. Second, there was the probable correlation between the acidity required

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EXPERIMENTAL SECTION Experimental methods and materials have been described in US Patents.48,49 In general the phosphate catalysts were prepared by precipitating a metal nitrate solution (e.g., Sr, Ba, Ca, Cu, or Ca and the like) with a solution of ammonium or sodium mono or dihydrogen phosphate. This was accomplished by combining the solutions with gentle heating and good stirring. Sulfate and arsenate catalysts were made by precipitating metal nitrate solutions with sulfate or arsenate containing solutions instead of phosphate. The resulting precipitate slurry was then vacuum filtered on a Buchner filter using Whatmann qualitative filter paper. The collected precipitate was washed on the filter under vacuum with distilled or deionized water and dried in an air oven at about 110−120 °C. After drying, the precipitate was broken or formed into small pieces (approximately 0.12−0.25 in.). In a few cases the powder was mixed with water into a stiff paste and formed into pellets and then dried again. In some cases the particles were then converted substantially to pyrophosphate form by heating in a flowing air and steam mixture from 300 °C up to 750 °C for several hours. The steam content was usually around 20% by volume. Catalyst phases were determined by IR spectroscopy or X-ray diffraction and the composition of metals and phosphorus, sulfur, or arsenic by dissolving a portion of the dried precipitate in HCL or HNO3 and analyzing the resulting solutions by ICP. Coated catalysts (a core−shell configuration) were prepared when the dried precipitate was not hard enough to form physically stable granules. The coating was done by the powder coating method described in US 3,956,377 on low surface area silica−alumina (alundum)50 0.125 in. spherical particles. The freshly prepared coated catalysts were air-dried at 110 °C before testing. In all coated cases the resulting particles comprised 25% by weight of active catalyst in the shell coating and 75% by weight of inert alundum core. The catalysts were tested by loading 20 cc of the catalyst into a 0.75 in. I.D. 316 stainless steel reactor tube approximately 15 in. long. The reactor tube was positioned in a vertical clamshell style tube furnace with the catalyst bed centered within the furnace to ensure a uniform bed temperature. Inert quartz particles were used below and above the bed as bed support and as a preheat zone, respectively. The initial life test was done in a reactor of the D



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Table 2. Initial Results with Hydrogen Phosphate Catalysts for HEP Conversion to DABCO run no.

catalyst type

catalyst form

control 1 2 3 4

Si/Al* SrHPO4b SrHPO4c SrHPO4b Sr/Ba(HPO4) Sr/Ba = 1/3.5

granular granular granular granular granular

5

Sr/Ba(HPO4) Sr/Ba = 2/1

6

95% SrHPO4 −5% Sr(H2PO4)2e

25% coated spheres 25% coated spheres

feed type

space rate v/v/h

run temp., deg C

feed % conv.

DABCO yield, mol. %

DABCO selectivity, mol. %

HEP HEP HEP HEP Crude HEP HEP

0.21 0.21 0.21 0.21 0.21

360 360 360 370 360

100 99.3 99.3 95.4 99.9

39.8 83 93.7 82.6 97.3d

39.8 83.6 94.4 86.6 97.4d

0.21

380

99.1

67.8

68.4

HEP

0.21

380

98.3

63.5

64.6

a

Commercial catalyst. bMainly beta SrHPO4 with small amt. of apatite-like Sr5(OH) (PO4)3 via X-ray diffraction and IR spectroscopy. cFresh is nearly pure beta SrHPO4 with broad IR bands, used is nearly pure beta SrHPO4 but sharp IR bands. dBased on feed analysis for HEP, catalyst is essentially all monohydrogen phosphate form. eFrom XRD and IR analysis on fresh catalyst.

the new catalysts was done in the manner described above in the Experimental Section. The target was any catalyst that provided better conversion and selectivity results than the silica−alumina control. Surprisingly, one of the first few catalysts tested, a SrHPO4, yielded remarkable results as can be seen in Table 2. Compared to the control silica/alumina commercial plant catalyst the SrHPO4 catalyst exhibited very significantly improved performance in terms of HEP conversion and DABCO yield and selectivity. These results were so much better than the plant catalyst that it became easy to engage management in approving a wider ranging and dedicated effort at validating and scaling the SrHPO4 catalyst. This approval enabled the assembly of a technical and business team to pursue commercialization of the new catalyst. Of course testing of other, related compositions was continued and most of the results are presented in Table 4. Additional runs on the SrHPO4 catalyst with repeat catalyst preparations gave essentially the same results as those in Table 2, thus validating the earliest test data on that composition. XRD and IR data suggested that beta crystal form of SrHPO4 is an amazingly active and selective catalyst for HEP conversion to DABCO. It was also found that equivalent results could be obtained from either alpha or beta SrHPO4. Also revealed is that barium can participate in basically the same catalytic chemistry. It is clear that, even at same liquid feed space rate as the control and about the same HEP conversion, the productivity of the SrHPO4 catalyst is considerably better than the silica/alumina control plant catalyst. Calculated as space time yield (STY, moles Dabco/liter of catalyst-hour) the control catalyst value is about 0.79, while the STY for the SrHPO4 catalyst ranges from 1.64 to 1.83 in these tests. That is about a 2-fold increase in productivity, a remarkable improvement. This improvement arises mainly from the improvement in DABCO selectivity, that is, significantly more efficient feed utilization. With this dramatic catalyst improvement in hand, a life test was clearly in order. A life run was begun with a slightly different catalyst form. It was different in two ways: (1) it was a pyrophosphate, and (2) it was in the form of 0.125″ × 0.25″ formed extrudates. The feed was HEP, but the liquid feed space rate was increased to 0.3 from 0.2. This was done as an attempt to make changes in conversion and selectivity over time easier to detect. The results are shown in Table 3, below. Over the course of 78 days of continuous operation, no loss in conversion was observed. However, there was a small improvement in DABCO wt % yield and also in piperazine yield. This is a result of slightly improved selectivity. Note the small increase in

same design and size. and the later pilot life test was done in a larger version of the same design holding about 1 L of catalyst. The experimental reaction feed, consisting of hydroxyethylpiperazine (HEP) or N-aminoethylpiperazine (AEP) and deionized (DI) water, was conducted into the reactor tube at atmospheric pressure via a conventional syringe pump at between 6.5 and 7.0 mL/h. The typical feed composition was 60% organic and 40% deionized (DI) water. A liquid feed rate of 7 mL/h translates to an organics space velocity of close to 0.21 L feed/liter catalyst/hour. The various Houdry-Air Products patents suggest space rates in the range of 0.1−0.5, and the production plant was typically operated in this range. To begin a catalyst evaluation, the reactor was first heated under flowing dry nitrogen to 300−400 °C, over a period of 15− 30 min followed by stopping the nitrogen and starting the organic plus water liquid feed at the desired reaction temperature. Liquid effluent samples were collected periodically in a preweighed and ice-cooled receiver for analysis. Reactor offgases were generally minimal and thus not analyzed. The liquid samples were weighed for material balance calculation and then analyzed by conventional GC methods. Conversions, selectivity, and weight yields were calculated from the recovered liquid analysis and product weights. In general, the material balances for the best catalysts were near 100%, but most of the poorer catalysts had lower material balances suggesting that significant amounts of nonselective and not analyzable heavies were formed. Although the collected product liquids often were colored yellow or orange-brown, some of the heavies appeared to remain on the catalysts as evidenced by a brown, gray, or black substance (coke) observed on the catalyst as it was unloaded. No attempt was made to characterize heavy materials or coke. Surface pH of catalysts was determined by use of either wetted pH papers or mostly by the use of Hammett indicator dyes in the usual fashion.51−53 Surface pH of the best catalysts was in the range of 4−5. Point of zero charge and iso-electric measurements were not made.

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RESULTS AND DISCUSSION After agreeing on the plan to explore single site type acidity materials as outlined in the introduction, the discovery team set about acquiring or making samples that should fit the desired catalyst type. Specifically these were a series of mono- and dihydrogen phosphates, sulfates, and arsenates of various common cations. Most were made via precipitation of a metal nitrate solution with a solution of the intended anion. Testing of E



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development and validation of an economically effective process to scale up and manufacture catalyst with the same or better properties as the best of the lab scale materials. Another issue is the plant process engineering and techno-economics to show that there is a real benefit to changing to a new catalyst and that making a change is compatible with existing production plant process equipment and especially the recovery section, and if changes are needed, to engineer and build them before the new catalyst is installed. The team went about conducting these activities. One big benefit to the effort was that Air Products’ Houdry Division had at the time an excellent catalyst development pilot lab and also some good reaction pilot facilities, both of which had very experienced and skilled technical staffs as part of the team. It might seem that scaling the precipitation of SrHPO4 and forming the resulting washed and dry powder into formed pellets (extrudates) suitable for commercial fixed bed catalyst use would be straightforward. This turned out not to be so as the precipitation of such materials can be fairly complex.56,57 The questions around what is the most effective Sr2+ and HPO4−1 precursors and their concentrations, the order and rates of combination, how to efficiently wash, what are the QC/QA targets, and finally how to form the product into something hard and durable enough for commercial operation all had to be addressed. Much of these details and results were kept as trade secrets, but it is enough to say here that addition of the phosphate component to the strontium component with good stirring worked well. Forming the washed and dried SrHPO4 into 0.125″ diameter extrudates presented some serious challenges which were finally overcome largely by selection of an effective and catalytically inert additive that resulted in a very hard, durable pellet with catalytic performance equivalent to the best of the lab scale preparations. The initial plant catalyst charge was successfully produced by Houdry’s catalyst plant in Paulsboro, NJ. Eventually, a commercial catalyst producer was selected and qualified. A longer term life test was conducted using pilot scaled catalyst. This test was conducted with a reactor holding approximately 1 L of beta SrHPO4 catalyst 0.125″ formed pellets and run with plant HEP feeds for approximately 3 months. Essentially no change in performance (HEP conversion, DABCO and piperazine yield, and product selectivity) was observed. The pilot life test data essentially matched that of runs 4 and 6 of Table 4. Post run XRD and IR examination of the catalyst revealed some small amount of pyrophosphate formation (amount not quantified). The physical hardness of the catalyst also increased slightly and surface area was but little changed. These data provided the final incentive for approving the commercial use of the new catalyst. The time from initial lab discovery to first successful commercial plant operation was approximately nine months, considered a remarkable achievement.

Table 3. Initial Strontium Pyrophosphate Life Test catalysta run time LHSV v/v/h FEED bed temp., deg. C HEP conv., % DABCO yield wt % piperazine yield wt %

Sr2P2O7 0.125″ × 0.25″ 1 day 0.3 HEP 360 99+ 40.5 13.5

78 daysb 0.3 HEP 368 99+ 43 18.5

a

Catalyst of example no. 4, U.S. Patent 4,405,784, is essentially all pyrophosphate when fresh. bSrHPO4 present after 78 days

run temperature by 8 °C which is a minor change and probably of little consequence unless it was responsible for the increased HEP cracking to piperazine. Note that XRD and IR analysis of the spent catalyst indicated some minor conversion of the initial pyrophosphate to monohydrogen phosphate. The relative amounts of pyrophosphate and monohydrogen phosphate could not be determined, and thus it is also unknown to what extent the SrHPO4 form present contributes to the overall performance or when in the run it began to form. There appeared to be very little “coke” on the catalyst at the end of the 78 day life test based on its rather light color. A slight increase in pellet side crush strength (ASTM D4179) was found at the end of run, but little change in BET surface area was detected. A fairly wide range of alternate phosphate, sulfate catalysts, and an arsenate catalyst were tested as well. Most of these are shown in Table 4. HEP or AEP were fed at feed space rate of 0.21 and at the indicated temperatures. Table 4 clearly shows these several features and results. 1. Sr and Ba monohydrogen phosphates are remarkably active and selective catalytic materials for preparation of DABCO from HEP. 2. Essentially pure strontium pyrophosphate and dihydrogen phosphates are slightly less active than beta SrHPO4 for HEP conversion but considerably less selective for DABCO than Sr monohydrogen phosphate. 3. Both alpha and beta forms of SrHPO4 are good catalysts for DABCO formation (the data that supports this is not shown for simplicity). 4. Contrary to expectations derived from other reports,54,55 the coated versions of the catalysts are generally less effective and selective than the bulk forms of the same catalyst. This observation remains a mystery; possibly due to a low exotherm from the cyclization since coated catalysts are most effective where large exotherms are seen. 5. AEP feed is more difficult to convert to DABCO than HEP on these kinds of catalysts and often leads to higher piperazine than HEP. The reason for this is speculated to be due to the thermodynamics of releasing NH3 (heat of formation kJ/m = −46.2) with AEP cyclization vs releasing water (heat of formation kJ/m = −285.8) with HEP feed. That is, making water as a byproduct is more favorable that making ammonia. 6. Sr and Ba hydrogen phosphates are more efficient catalysts than other +2 and also +3 cation forms, for example, Ca, Zn Cu, Mg, La, Ce, Ni, and Co. To commercialize a catalyst from a lab scale discovery, multiple key activities must be accomplished. These include appropriate life tests with physical and chemical measurements of the catalyst before and after life tests and, very importantly, the

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CONCLUSIONS A new and highly active and selective catalyst for manufacture of DABCO was discovered, developed, and successfully implemented in an existing commercial plant with few changes in plant equipment or overall process. The catalyst consists of strontium hydrogen phosphate (SrHPO 4 ) and its possible admixtures with strontium dihydrogen phosphate (Sr(H2PO4)2), strontium pyrophosphate (Sr2P2O7), and an apatite-like strontium hydroxyl phosphate (Sr5(OH)(PO4)3). Barium may also be part of the compositions, F



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Table 4. Additional Catalyst Testing: Phosphate and Other Catalysts with Single Acid Site Types run no.

catalyst

form

feed

test temp., °C

mol. % conversion

DABCO yield, wt. %

piperazine yield, wt. %

DABCO selectvity, wt. %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 32 33 34 35 36 37 38 39 40 41 42 42 44 45 46 47 48 49 50

SiO2/Al2O3a AlPO4b AlPO4b SrHPO4c SrHPO4d SrHPO4c SrSO4 BaSO4 SrHAsO4 SrHAsO4 SrHPO4c SrHPO4c,e SrHPO4/Sr(H2PO4)2f SrHPO4/Sr(H2PO4)2f SrHPO4c SrP2O7 SrP2O7 Sr(H2PO4)2 Sr(H2PO4)2 Sr(H2PO4)2 Sr/BaHPO4 Sr/Ba = 1/3.5 Sr/BaHPO4 Sr/Ba = 2/1 Sr/BaHPO4 Sr/Ba = 2/1 CaHPO4/Ca(H2PO4)2f CaHPO4/Ca(H2PO4)2f Nd2(HPO4)2 Nd2(HPO4)2 Ce2(HPO4)3 Ce2(HPO4)3 La2(HPO4)3 La2(HPO4)3 La/SrHPO4 La/Sr = 1/15 La/SrHPO4 La/Sr = 1/15 CoHPO4 CoHPO4 NiHPO4 NiHPO4 CuHPO4i ZnHPO4 Al2(HPO4)3 Al2(HPO4)3 CaHPO4 MgHPO4 BaHPO4 ZnHPO4 Sr(H2PO4)2 Sr(H2PO4)2 Sr(H2PO4)2 Sr(H2PO4)2

granule granule granule granule granule granule granule granule 25% coated 25% coated granule granule 25% coated 25% coated granule granule granule granule granule 25% coated granule 25% coated 25% coated 25% coated 25% coated granule granule granule granule granule granule granule granule granule granule granule granule granule granule granule granule granule 25% coated 25% coated 25% coated granule granule 25% coated 25% coated

HEP HEP AEP HEP HEP HEP HEP HEP HEP AEP AEP HEP HEP AEP AEP HEP HEP AEP AEP HEP HEP HEP AEP HEP AEP HEP AEP HEP AEP HEP AEP HEP AEP HEP AEP HEP AEP HEP HEP HEP AEP HEP HEP HEP AEP HEP AEP HEP AEP

360 400 375 360 360 370 360 360 340 360 400 360 380 400 400 360 400 320 320 320 360 380 400 380 380 340 360 340 360 340 360 360 380 360 380 360 380 340 380 380 380 360 380 380 400 320 320 320 320

100 100 83 99.3 99.3 95.4 36.4 31.2 36.2 43.5 99 98.6 98.3 77 99 98.6 99.2 95.5 99.6 98.9 99 99.1 56.8 91.2 90.2 98.4 96.2 99.9 92.6 98.8 95.2 99.2 96.1 98.7 91.9 82.4 56.7 99.4 94.7 98.3 88.4 99.6 99.9 37.4 57.9 95.5 99.6 98.9 91.1

39.8 28.4 33.9 83 93.7 82.6 2.1 14.3 4.6 1.2 30 76 63.5 18.8 29 30.7 41 24.7 6.7 22 83.8g 67.8 13.8 56.2 34.4 18.2 7.5 32.3 7.8 16.2 25.5 58.7 27.4 40 19.4 36.2 6 17.6 45.9 39.7 17.1 59.2 47.2 23.2 12.2 24.7 6.7 22 11

not reported 6 26.7 not reported not reported not reported 27.3 2.9 6.2 1.6 21 7.8 14.7 16.4 21 9 9 4.4 0.6 3.6 7h 5.5 9.1 5.8 9.9 5.4 2.1 8.4 7.9 4.2 3.3 5.3 14.6 8.4 17.4 5.6 7.8 4.2 6.7 9.4 25.8 23.5 15.8 1 11.3 4.4 0.6 3.6 18.3

39.8 28.4 40.8 83.5 94.4 86.6 5.7 45.8 14.0 2.8 30.3 77.0 64.6 25.2 29.3 31.0 41.3 25.9 6.7 22.2 84.6 68.4 24.3 61.6 23.7 28.9 26.7 29.4 25.7 29.1 26.4 27.6 25.3 27.4 24.2 22.9 14.9 29.2 24.9 25.9 23.3 27.7 26.3 9.8 14.5 29.8 31.1 30.9 28.5

a

Commercial silica/alumina. bData from Example II of US 3,297,701. cBeta form of SrHPO4, precipitated by H3PO4 + NaOH. dBeta form of SrHPO4, precipitated by NH4H2PO4. eAfter multiple hrs. of use, analysis indicates some SrP2O7 (pyrophosphate) formed. fMixed phases, % each is uncertain. g97.3 mol % based on feed analysis. h10.6 mol % based on feed analysis. iCatalyst analysis after run shows minor amounts of CuP2O7 and Cuo metal.

Possibly this involves some sort of phosphate ester or amide intermediate instead of a typical acid catalyzed pathway. Piperazine is a marketable coproduct, but the formation of other nonselective products is substantially diminished compared to the older commercial Si/Al catalyst. The overall result is

substituting in part for strontium. The catalyst has demonstrated long life, good physical durability, and very little decline in DABCO yield or selectivity during up to 2 years of commercial use. The reason for the remarkable performance of SrHPO4 is not known. However, speculation is that it operates by a substantially different mechanism than the old silica−alumina. G



Article

(18) Swanson, R. W. U.S. Patent 3,146,236 to Air Products and Chemicals, 1964. (19) Swanson, R. W. U.S. Patent 3,148,190 to Air Products and Chemicals, 1964. (20) Mascioli, R. L. U.S. Patent 2,977,364 to Air Products and Chemicals, 1961. (21) Mascioli, R. L. U.S. Patent 3,166,558 to Air Products and Chemicals, 1965. (22) Hromatka, O. Ber. Dtsch. Chem. Ges. B 1942, 75, 1302− 1310.10.1002/cber.19420751107 (23) Hromatka, O. Chem. Abstracts 1944, 38, 2627. (24) Ishiguro, J., et al. J. Pharm. Soc. (Japan) 1955, 75, 1110, 1162, 1318, 1367, and 1370. (25) Ishiguro, J., et al. J. Pharm. Soc. (Japan) 1955, 75, 674−677. (26) Selvaraj, M.; et al. Microporous Mesoporous Mater. 2004, 74, 157− 162. (27) Armour, J. N., et al. U.S. Patent 5,741,906 to Air Products and Chemicals, 2000. (28) Armour, J. N., et al. U.S. Patent 6,084,096 to Air Products and Chemicals, 2000. (29) Srinivas, N.; et al. Microporous Mesoporous Mater. 2002, 51, 43− 50. (30) Segawa, K.; et al. Stud. Surf. Sci. Catal. 1996, 101, 267. (31) Anand, R.; Rao, B. S. Catal. Commun. 2002, 3 (10), 479−486. (32) Selvaraj, M.; et al. Microporous Mesoporous Mater. 2004, 74, 143− 155. (33) Anand, R.; Jyothi, T. M.; Rao, B. S. Appl. Catal., A 2001, 208 (1− 2), 203−211. (34) Budnik, R. A.; Sander, M. R. Eur. Patent 158, 1985; p 139. (35) Frankenkron, M.; Stein, B. U.S. Patent 6,562,971 to BASF. (36) Vanderpool, S. H.; Brader, W. H.; Yeakley, E. L.; McConnell, T. T. U.S. Patent 4,757,143 to Texaco Chemical Company, 1988. (37) Zimmerman, R. L.; Knifton, J. F. U.S. Patent 5,037,838 to Texaco Chemical Company, 1991. (38) Brader, W.H. U.S. Patents 3,056,788 (1962), 3,120,526 (1964), 3,157,657 (1964), 3,285,917 (1966), 3,342,820 (1967), 3,386,800. Brader, W. H.; Rowton, R. L. 3,172,891, 1965, 3,297,701. Brader, W. H.; Cour, T. H. 3,231,573, 1962. Muhlbaur, H. G.; Lichtenwalter, M. 3,285,920, 1967. Brennan, M. E.; Moss, P. H.; Yeakey, E. L. 4,409,657. Brennan, M. E.; Speranza, G. P. 4,338,443. (39) Spielberger, G.; Koln-Flittard, G. E. U.S. Patent 3,080,371 to Bayer, 1963. (40) Matel, P. M. T.; Tornquist, J. T.; Steinjner, O. R. U.S. Patent 3,242,183 to the Authors, 1966. (41) Bosch, H. G.; Baer, K.; Schneider, K. U.S. Patent 4,017494 to BASF, 1977. (42) Oakes, M. D.; Upson, L. L.; Ziv, M. H. U.S. Patent 3,772,293 to Air Products and Chemicals, 1973. (43) Shubkin, R. L.; Hargus, D. C. U.S. Patent 4,725,681 to Ethyl Corp., 1988. (44) Zhao, D.; et al. Catal. Commun. 2008, 9, 1725−1727. (45) Brennan, M. E.; Moss, P. H.; Yeakley, E. L. U.S. Patent 4,095,022 to Texaco Development Corp., 1978. (46) Amberlyst 15 is a well-known sulfonic acid based ion exchange product of Rohm & Haas Corp. (now DOW). (47) From Wikipedia http://en.wikipedia.org/wiki/Apatite: “Apatite is a group of phosphate minerals, usually referring to hydroxyapatite, fluorapatite, and chlorapatite, named for high concentrations of OH−, F−, and Cl− ions, respectively, in the crystal. The formula of the most common end members is written as Ca10(PO4)6(OH,F,Cl)2”. The mineral samples used in this program were of undefined composition but did have an acidic surface pH. (48) Wells, J. E.; Eskinazi, V. U.S. Patent 4,521,600 to Air Products and Chemicals, 1985. (49) Wells, J. E. U.S. Patent 4,514,567 to Air Products and Chemicals, 1985. (50) Alundum is product of The Norton Company (now Norpro-St, Gobain). (51) Hammett, L. P.; Deyrup, A. J. J. J. Am. Chem. Soc. 1932, 54, 2721.

a substantial increase in commercial plant reactor productivity with minimal capital investment. Other benefits include substantially reduced feed costs, reduced waste disposal burden, and reduced recovery and purification costs. The only possible downside was the reduced availability of the mixture of dimer, trimer, and similar materials that constituted a corrosion inhibitor byproduct. Further studies of the phosphate family of catalysts yielded new technology and IP for Air Products for a variety of other amine condensations.41,58−63 Finally, the commercial development and implementation of this catalyst was completed in the amazingly short time of only about nine months.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. J.E.W. is retired from Air Products and Chemicals, Broomall. F.C.W. was retired from Air Products and Chemicals, Zionsville. N.K.D. is retired from Honeywell. ∥ F.C.W. is deceased.

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ACKNOWLEDGMENTS Thanks to Air Products and Chemicals for permission to publish and especially to Ed Donley, a retired Air Products CEO, and to Kathy Hayes for facilitating the permission process. Thanks also goes to the many team members whose tireless efforts made the development and implementation of the SrHPO4 catalyst a reality. In particular this includes Maurice Mitchell, Nance Dicciani, Susan Laager, Victoria Eskinazi, Harry Ladenheim, Linda Snyder, Pradip Rao, Richard Jenkins, Stanley Gussow, James Sykes, Ron Stansbury, Tom Wiggins, Rocco Mascioli, and William Wong. We apologize to those who may have been omitted due to any memory lapses.

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REFERENCES

(1) Cecchi, L.; et al. Eur. J. Org. Chem. 2006, 21, 4852−4860. (2) Farkas, A.; et al. Ind. Eng. Chem. 1959, 51, 1299. (3) Yang, H.; Tian, R.; Li, Y. Front.in Chem. China 2008, 3, 279−287. (4) Salsibury, W. C. U.S. Patent 4,048,105 to McCord Corp., 1975. (5) Foote, J. F. U.S. Patent 3,265,641 to Pittsburgh Plate Glass, 1966. (6) Ho, T. L. Synthesis 1972, 12, 702. (7) Baghernejad, B. Eur. J. Chem. 2010, 1 (1), 54−60. (8) Luque, R.; Macquarrie, D. J. Org. Biomol. Chem. 2009, 7 (8), 1627− 1632. (9) Baylis, A. B.; Hilman, M. E. D. Ger. Pat. 2155113, 1972. (10) Ullman’s Encyclopedia of Industrial Chemistry, Vol. A2; VCH, 1998; p 16. (11) Tene Baum, L. E. In Heterocyclic Compounds-Pyridine and its Derivatives, Part I; Klingsberg, E., Ed.; Interscience: New York, 1960. (12) Ullman’s Encyclopedia of Industrial Chemistry, Vol. A22; VCH, 1993; p 339. (13) Personal communications with Houdry/Air Product’s staffs during the late 1970s. (14) Herrick, E. C. U.S. Patent 2,937,176 to Houdry Process Corporation, 1960. (15) Krause, J. H. U.S. Patent 2,985,658 to Houdry Process Corporation, 1961. (16) Farkas, A.; Krause, J. H. U.S. Patent 2,977,363 to Houdry Process Corporation, 1961. (17) Farkas, A.; Oakes, M. D. U.S. Patent 3,123,607 to Air Products and Chemicals, 1964. H



Article

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