ISSN 2070�0504, Catalysis in Industry, 2010, Vol. 2, No. 4, pp. 387–392. © Pleiades Publishing, Ltd., 2010.Original Russian Text © V.A. Lomonosov, A.S. Panasyugin, O.L. Smorygo, V.A. Mikutskii, A.N. Romashko, S.F. Tikhov, V.S. Sadykov, 2010, published in Kataliz v Promyshlennosti.

387

INTRODUCTION

The problem of neutralizing VOCs (volatile organiccompounds) in ventilation emissions of the printing,footwear, and paint industries and other industriesassociated with the use of solvents is still of great inter�est and demands the improvement of purification sys�tems. Progress in neutralizing VOC emissions fromstationary industrial sources was achieved with thelarge�scale implementation of catalytic methods [1,2]. For relatively high concentrations of VOCs (1–10.00 g/m3) and large volumes of treated gas, the cat�alytic annealing of VOCs on block�type catalysts [3,4], which allows us to treat streams of gases with high(up to 105 h–1) loads on the catalyst at low pressure dif�ferentials, is preferred. Block catalysts (ceramic andmetal) with a cellular structure ensure intensive heatand mass exchange between the gas stream and cata�lyst surface [5]. In using catalysts with a cellular struc�

ture, higher loads are therefore possible in processeswith external diffusion resistance [6, 7].

The choice of block catalyst technology is deter�mined by the initial composition of the neutralizedmedium, the composition of the intermediate andfinal products, and the process temperature. The tech�nology and the composition of the catalyst mustensure not only the required levels of purification, butalso the high stability (deactivation stability) of thecatalyst during the interaction of the active compo�nent and the reaction medium.

Selecting the support material and operationalloads on the catalyst in designing devices for waste gasneutralization is a rather complicated problem. Whena close macroporous structure is used, metal andceramic supports have various thermophysical andcorrosion properties that considerably influence thelength of their service life. Selecting the operationalloads on the catalyst (the admissible level of which

CATALYSIS AND ENVIRONMENTALPROTECTION

Pd/γ�Al2O3 Catalysts on Cellular Supportsfor VOC Vapor Neutralization

V. A. Lomonosova, A. S. Panasyuginb, O. L. Smorygoc, V. A. Mikutskiic, A. N. Romashkoc, S. F. Tikhovd, and V. S. Sadykovd

a Belarussian State University, ul. Nezavisimosti 4, Minsk, 220030 Belarusb NIILOGAZ Laboratory, Belarussian National Technical University, ul. Ya. Kolasa 24, Minsk, Belarus

c Powder Metallurgy Institute, National Academy of Sciences of Belarus, ul. Platonova 41, Minsk, 220005 Belarusd Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of Sciences,

pr. Lavrent’eva 5, Novosibirsk, 630090 Russia@

Abstract—The results from investigating the influence of temperature, concentration, and flow rate on thecatalytic oxidation of vapors of volatile organic compounds (VOCs) in the presence of Pd/γ�Al2O3 catalyst oncellular supports are presented. The activity of Pd/γ�Al2O3 catalysts on ceramic and metal block supportswith a cellular structure during the catalytic neutralization of VOC (ethanol, ethyl acetate) vapors under lab�oratory conditions was determined, and the most stable catalyst for the preliminary study of a large batch waschosen. A pilot unit was created to test a large batch of cellular block catalyst in neutralizing VOC vaporsunder conditions of flexographic production. It was established that a high rate of conversion (> 99 %) wasachieved for VOC concentrations of 0.5 g/m3 at volume rates of up to ~104 h–1, and for VOC concentrationsof 5.0 g/m3 at volume rates of up to ~5 × 105 h–1. The change in the activity of the catalysts on metal (nickelalloyed by aluminum) and ceramic cellular supports in service was investigated. After 300–500 min of oper�ation, virtually complete deactivation of catalyst on a metal support was observed, accompanied by the for�mation of nickel oxide and acetate. Pilot unit tests with catalyst on cellular supports having a volume of 14.5 lin neutralizing the ventilation emissions of flexographic production confirmed the possibility of more than90% conversion at VOC concentrations of ~ 0.1 g/m3 and more than 97% at VOC concentrations of over1 g/m3. A consistently high conversion of VOC was observed during a 100 h test of the pilot unit. A system forrecovering the heat released during VOC oxidation lowers the operating costs of the pilot unit.

Keywords: Pd/γ�Al2O3 catalyst on cellular ceramic and metal supports, oxidation of ethanol/ethyl acetatemixtures, conversion, stability in a reaction medium, pilot tests in neutralizing emissions of flexographic pro�duction.

DOI: 10.1134/S2070050410040148

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depends on the flow temperature) is also complicated:at high temperatures of the stream, it becomes possibleto raise the volume rates and thus reduce the loadingon the block catalyst, but the operating costs (theenergy expended on heating the gas stream) simulta�neously rise. It is therefore important to determine thelowest temperature of the stream at which toxic com�pounds in the required range of concentrations areeffectively neutralized. No less important is the choiceof the block support, which does not affect catalyststability (i.e., it does not lead to its deactivation duringoperation).

In this work, we investigated the activity and stabil�ity of Pd/γ�Al2O3 catalysts on ceramic and metal blocksupports with a cellular structure during the catalyticneutralization of VOC (ethanol, ethyl acetate) vaporsunder laboratory conditions to select the most stablecatalyst for the preliminary study of a large batch. Oursecond task was to create a pilot unit and test a largebatch of cellular block catalyst in neutralizing VOCvapors under the conditions of flexographic produc�tion.

EXPERIMENTAL

Preparation of Block Catalysts and Methods of Investigation

Cellular materials (foamed ceramics and foamedmetal) with cells around 2 mm in size and obtained byduplicating the structure of foamed polyurethane(FPU) were used as the supports for the catalyst. Fea�tures of the porous structure, microstructure, andmorphology of the surface of such supports aredescribed in detail in [8–10].

Supports based on mullite�corundum ceramicswere obtained through the multiple impregnation ofFPU�blanks with ceramic suspension and the removalof excess suspension by centrifugation. The materialswere sintered in air at 1400°C. The obtained ceramicsupport (Fig. 1a) had an overall porosity of 85%(±2%). The suspension from which the mullite�

corundum ceramics were prepared consisted of clay,kaolin, aluminum oxide, and pegmatite. After theimpregnation and sintering of the FPU, the ceramicswere approximately 50% mullite, 30% free aluminumoxide (corundum), 10–12% microcline, and up toseveral percent free silicon oxide (cristobalite) andglass phase.

Foamed metal supports were obtained through theelectrolytic deposition of nickel on an FPU�blankwith subsequent sintering at 1150°C in an endogasmedium (a mixture of CO, H2, and N2 obtained by thepartial oxidation of methane) [11], thermodiffusionaluminizing, and oxidative heat treatment in air at1100°C. The surface of the foamed nickel supportafter thermodiffusion treatment was protected fromthe effects of the external medium by layered inter�metal coating and a layer of α�Al2O3 [5]. The porosityof the obtained metal supports (Fig. 1b) was 95%(±0.5%).

Samples of the metal and ceramic catalyst supportswere prepared in the form of cylinders 20 mm long and15 mm in diameter. We can see from Fig. 1 that theemployed technologies allowed us to fully preserve theopen interlocked macroporosity, ensuring low hydrau�lic losses during the propagation of high�speed gasstreams.

The metal and ceramic cylinders of the secondarysupport were thrice impregnated with a mixture of92% humidity boehmite gel (synthesized earlier by thehydrothermal method in [12]) and freshly prepared90% humidity aluminum dihydroxynitrate (in a solidresidue ratio of 1 : 1). After drying at 110°C andannealing at 500°C, a layer of γ�Al2O3 with a content(support wt %) of 6.1 ± 0.2 for foamed ceramics and5.0 ± 0.1 for foamed metal was formed on the struc�tural elements of the supports. The specific surface ofthe deposited γ�Al2O3 was 220–250 m2/g.

The active component (Pd) was coated through theimpregnation of the samples in an excess of palladiumchloride solution of 0.5 g/l concentration. After dryingto constant weight at 110°C, the impregnated samples

(a) 2 mm 2 mm(b)

Fig. 1. Structures of cellular (a) ceramic and (b) metal supports.

CATALYSIS IN INDUSTRY Vol. 2 No. 4 2010

Pd/γ�Al2O3 CATALYSTS ON CELLULAR SUPPORTS 389

were annealed in air at 500°C and then reduced in dis�sociated ammonia (a mixture of N2 + 3H2 [11] at55°C). The Pd content of the obtained block catalystswas ~0.003 g/sm3.

The surface morphology and features of theobtained catalysts’ macroporous structure were stud�ied on a CamScan 4 electron scanning microscope.XFA of the catalyst on block supports after operationwas performed on a DRON�4 diffractometer.

Catalytic oxidation of VOC was investigated in atubular flow reactor (inner diameter of quartz tube, 20mm) at the NIILOGAZ laboratory of BNTU. Adiaba�ticity was ensured by the external glass�fiber insulationof the tube in the zone of sample placement and ther�mocouples. The apparatus ensured a controlledexpenditure of gas of up to 1000 l/h through a catalystof 15 mm diameter and 40 mm height, allowing us tostudy the activity of the catalysts at volume rates of upto 105 h–1. The air stream was saturated with VOCvapors by running it through a scrubber. Air saturatedwith a VOC mixture of ethanol and ethyl acetate (typ�ical components in emissions of flexographic produc�tion) was used as the model medium. The air streamwas saturated with VOC vapors by running it throughthe scrubber, which contained ethanol and ethyl ace�tate in a volume ratio of 6 : 1. Our investigations wereperformed at two concentrations of VOC, g/m3: 0.5 ±0.1 and 5.0 ± 0.5.

Before feeding it into the thermally insulated reac�tor with the catalyst, the vapor–air mixture was heatedin a glass tube with nickel�chromium winding. Thecomposition of the gas was determined on a Tsvet�100gas chromatograph. The chromatograms were inter�preted using the Mul’tikhrom 1.39 software. The tem�perature of the gas stream at the inlet and at the outletfrom the catalyst was controlled by thermocouples.

Investigations of the dependence of the degree ofconversion on the rate of incoming flow at various tinletand VOC concentrations were performed in thestepped temperature rise mode. Samples were taken 5min after flow stabilization. Each curve was obtainedon an individual sample of block catalyst.

A pilot unit for the catalytic combustion of VOCvapors with a nominal capacity of ventilation emis�sions of 100 m3/h was built for purposes of industrialtesting. Tests of the unit were conducted to see howwell it would purify ventilation emissions from theflexographic equipment of OOO Unifleks (Minsk).

RESULTS AND DISCUSSION

Laboratory tests included:

more precise determination of the effect of temper�ature at the inlet to the reactor in the catalytic oxida�tion of VOCs at various concentrations and flow rates;

determining the stability of the catalysts on cellularceramic and metal supports.

It is known that the reactions of ethanol and ethylacetate oxidation are exothermic (specific combustionheat, 1370.7 and 2246.4 kJ/mol, respectively [13]).Under certain conditions, such processes are thereforepossible in the autothermal mode. At an ethanol : ethylacetate ratio of 6 : 1, adiabatic heating should occur at~120 and ~12°C for concentrations of 5 and 0.5 g/m3,respectively. The temperature at which VOC oxidationbegins on the prepared block catalysts was determinedfrom the dependence of the gas stream temperature atthe outlet from the catalyst on the time when there is acontrolled change in the temperature at the inlet andat different volume rates. Figure 2 shows a typicaldependence demonstrating the change in toutlet on thetime at a controlled linear rise of tinlet up to 400°C anda volume rate of v0 = 104 h–1; tinlet is shown by thedashed line on the plot, while toutlet is shown by solidline for two concentrations of VOCs.

From Fig. 2 it is obvious that toutlet begins to deviatenotably from tinlet at 210–220°C for concentrations of0.5 g/m3 and at 190–200°C for concentrations of5 g/m3. VOCs that burn rapidly when the ignition tem�perature is reached are apparently adsorbed on thesecondary γ�Al2O3 support at low temperatures. Later,after a constant flow temperature tinlet is established,toutlet stabilizes. As the VOC concentration rises from0.5 to 5.0 g/m3, the stationary (for a >0.5–4 experi�ment) range of temperatures at the inlet and outlet(Δt = toutlet – tinlet) increases from ~ 10 to ~ 100°C(Fig. 2). It was revealed that under stationary condi�tions, the block catalyst temperature is determined notonly by the VOC concentration but by the flow rate aswell. At high concentrations of VOCs and v0 ≈ 105 h–1,the difference between the catalyst temperature andtinlet was ~500°C; after heating of the flow entering the

600

10 20 30 40

500

400

300

200

100

0Time, min

Temperature, °C

Concentration of VOCs 0.5 g/m3

Concentration of VOCs 5.0 g/m3

Fig. 2. Dependence of the gas stream temperature at theoutlet from the ceramic catalyst on time upon a controlledchange in the temperature at the inlet (dashed line) anddifferent concentrations of VOCs, g/m3 (curves).

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reactor ceased, oxidation continued in the autother�mal mode.

The character of the dependences was similar forall of the investigated ranges of concentrations andvolume rates. With metal supports, combustionoccurred at higher inlet temperatures, due apparentlyto the former’s greater thermal conductivity and, con�sequently, greater losses of heat when warmed.

Figure 3 presents the dependences of the degree ofconversion on the rate of incoming flow for various tinletand VOC concentrations. From Fig. 3a it is obviousthat in the stationary mode at VOC concentrations of5 g/m3 and v0 < 5 × 104 h–1 the degree of conversionhovers at a level of ~100%. With an increase in the vol�ume rate, the degree of VOC conversion drops to ~92–95%. At low VOC concentrations, the degree of con�version falls below 99% at v0 ≈ 104 h–1 (Fig. 3b).At high volume rates, the degree of low�concentrationVOC conversion falls to a level of less than 20% in thestationary modes. At VOC concentrations of ~ 5 g/m3

and elevated volume rates, the autothermal mode ofreaction becomes possible, due to the heat releasedduring ethanol and ethyl acetate oxidation. The possi�ble thermal effects were considered in designing thepilot unit.

The catalysts on different supports exhibited simi�lar activity during brief (1–2 h) tests. Differences wererevealed during longer tests: the activity of the catalyston ceramic supports stabilized after 35 h and remainedrather high (Fig. 4a), while the catalyst on metal sup�ports was almost completely deactivated after 5–6 h oftests (Fig. 4b). Along with a decline in VOC conver�sion, the composition of the oxidation products alsochanged. According to the results from a gas chro�matographic analysis of the gaseous mixture at theoutlet of the reaction unit, traces (<0.01 g/sm3) of ace�tic acid (the content of which increased as the catalystdeactivated) were detected.

Changes were observed in the catalyst after it wasremoved from the reactor: following an 8�h cycle ofoperation in vapors of ethanol/ethyl acetate, the base

of the catalyst’s metal support was grey�green and brit�tle. XFA of the catalyst’s surface layer after 3–4 h oftests revealed reflexes in the regions of 2Θ = 12.98;21.19; 22.36, and 22.45°. These were identified asnickel acetate hydrate ((CH3COO)2Ni · 4H2O), whileweak reflexes in the region of angles 2Θ = 43.25;37.24, and 62.80° corresponded to NiO. After morethan 8 h of catalyst operation, the intensity of thereflexes corresponding to nickel oxide increased incomparison to the reflections corresponding to aceticnickel. We concluded that deactivation and thereduced strength of catalyst based on cellular metalnickel were associated with formation of acetate andoxide of nickel. It is important that preliminary ther�modiffusion aluminizing does not allow us to avoidcatalyst deactivation. A catalyst on a cellular ceramicsupport was chosen for subsequent pilot tests, due toits high level of stability.

A general comparison of the hydraulic, textural,and mechanical properties of cellular and honeycombsupports was performed in [14]. It was shown that atcomparable pressure differentials and coefficients ofpermeability, the cellular supports are distinguished bygreater turbulization of the gas stream. In the reactionof CO oxidation, the catalysts on cellular supportsproved to be more efficient than those on honeycombsupports [14]. The main advantage of cellular blocks isdue largely to the turbulization of the gas stream at thecomparatively low hydraulic resistance of the catalyticlayer [19].

Pilot tests of a block catalyst (Pd/γ�Al2O3 on a cel�lular support) were performed on a pilot unit for theneutralization of VOCs in ventilation emissions (nom�inal capacity of the unit, 100 m3/h; volume rate, 104 h–

1). The total volume of the block catalyst was 14.5 l.The basic scheme of the unit is presented in Fig. 5. Airfrom the ventilation system travels along a heat�insu�lated channel into the heating system (a block ofTENs) through a tubular heat exchanger and then to ablock cellular catalyst with dimensions of 300 × 3000 ×150 mm in the form of layered plates measuring 150 ×

0 2 4 6

100

95

90

85

80Deg

ree

of

VO

C c

on

vers

ion

, %

8 10

(a)

2 4 6

100

80

60

20

Volume rate × 104 1/h0 8 10

(b)

405.0 g/m3 VOC, 270 °C5.0 g/m3 VOC, 230 °C5.0 g/m3 VOC, 215 °C

5.0 g/m3 VOC, 270 °C5.0 g/m3 VOC, 230 °C5.0 g/m3 VOC, 215 °C

Fig. 3. Dependence of VOC conversion (CVOC) using catalyst with a cellular ceramic support on the volume rate of flow at dif�ferent temperatures, °C at the inlet to the reactor (curves), and concentrations of VOCs, g/m3: (a) 0.5, (b) 5; stationary mode.

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Pd/γ�Al2O3 CATALYSTS ON CELLULAR SUPPORTS 391

150 × 25 mm. After neutralization, the gas is expelledfrom the heat exchanger.

A command system controls the power of theheater with allowance for the thermal effect of the oxi�

dation reactions. The unit’s heating system is powerfulenough to heat the gas stream to 300°C.

As can be seen from the data presented in the table,the degree of conversion in the unit depends stronglyon the initial concentration of VOCs in the gas Stream.The total degree of conversion in the table was calcu�lated as the ratio of the change in the percentage of theconcentration of ethanol and ethyl acetate after thestream is fed through the catalyst (ΣCinlet – ΣCoutlet) tothe total concentration at the inlet (ΣCinlet). At lowVOC concentrations, heating to high temperatures isrequired to achieve a high degree of conversion.On the whole, our tests allowed us to establish thateven at low total concentrations of ethanol and ethylacetate (<0.2 g/m3) and v0 = 104 h–1, the block cellularcatalyst conversion of VOCs was more than 90% attinlet = 290°C. As the concentration was increased to1–2 g/m3, conversion of more than 97% was observedat tinlet = 250°C. Consistently high conversion of VOCscontinued over ~102 h of tests on the pilot unit. Ourrecommended conditions for industrial operation areas follow: volume rate of flow, 104 h–1; temperature atblock catalyst inlet, 250–300°C, depending on theconcentration of VOCs.

CONCLUSIONS

The effect of the temperature at the inlet, the con�centration of the oxidizable compounds, and flow vol�ume rate on the conversion of VOC (ethanol/ethylacetate) vapors in the reaction of catalytic oxidationusing Pd/γ�Al2O3 catalyst on cellular supports (blockcatalyst Pd content, 0.003 g/sm3) was investigated.Comparative tests of the catalyst on cellular metal andceramic supports over a range of concentrations of0.5–5.0 g/m3 were performed. It was established thathigh degrees of conversion (>99%) are achieved for aVOC concentration of 0.5 g/m3 at volume rates of upto ~104 h–1 and a VOC concentration of 5.0 g/m3 atvolume rates of up to ~5 × 105 h–1. Catalyst deactiva�tion accompanied by the formation of oxide and ace�

0 500 1000 1500

100

95

90

85

80Deg

ree

of

VO

C c

on

vers

ion

, %

2000 2500

(a)

100 300 400

100

80

60

20

Time, min0 500 700

(b)

40

Ceramic support, 280 °CCeramic support, 260 °CCeramic support, 245 °C

Metal support, 280 °C

Metal support, 260 °C

Metal support, 245 °C

3000 600200

Fig. 4. Change in VOC conversion over time at gas temperatures of (�) 245, (�) 260, and (�) 280°C at the inlet to the reactor forcatalysts on (a) ceramic and (b) metal supports (VOC concentration, 0.5 g/sm3; volume rate, 104 h–1; stationary mode).

1

2

3

4

5

Fig. 5. Basic scheme of the VOC neutralization pilot unit.1 heat exchanger; 2 body; 3 thermocouples; 4 block cata�lyst; 5 heating block.

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tate of nickel was observed when a metal support wasused. A pilot unit of VOC vapor neutralization wasprepared to test the block catalyst on cellular supports(catalyst volume, 14.5 l). The conversion of VOCs onthe unit was verified in neutralizing ventilation emis�sions of flexographic production.

Compared to traditional granulated catalysts, theproposed catalyst is characterized by low hydrauliclosses at high rates of flow and a low content of theactive component (palladium). The proposed tech�nology for depositing Pd/γ�Al2O3 catalyst on cellularsupports is simple and can be applied on an industrialscale in the mass production of cellular materials. Thedesign concepts tested on the pilot unit can be used tocreate industrial plants for the purification of ventila�tion emissions.

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VOC conversion in ventilation emissions of flexographic production

No. tinlet, °C v0, h–1Concentration*, g/m3

, %at entry at exit

1 220 1.0 × 104 0.0568 0.2680 0.0055 0.0192 92.4

2 230 1.8 × 104 – 0.3560 – 0.0257 92.8

3 230 1.5 × 104 0.0673 0.3090 0.0059 0.0232 92.3

4 240 2.0 × 104 – 0.3190 – 0.0298 90.7

5 260 1.0 × 104 0.0332 0.1022 0.0128 0.0093 83.7

6 290 1.0 × 104 0.0332 0.1022 0.0078 0.0054 90.3

7 250 1.0 × 104 0.0987 0.5120 0.0070 0.0290 94.1

8 250 1.0 × 104 0.121 0.7680 0.0053 0.0338 95.6

9 250 1.0 × 104 0.233 0.9060 0.0058 0.0226 97.5

10 250 1.0 × 104 0.316 1.188 0.0050 0.0188 98.42

11 250 1.0 × 104 0.349 1.625 – 0.0174 99.12

12 250 1.5 × 104 0.375 1.857 – 0.0473 97.88

* Numerator, ethyl acetate; denominator, ethanol.

KVOCΣ

SPELL: 1. boehmite