ISSN 2070�0504, Catalysis in Industry, 2013, Vol. 5, No. 3, pp. 204–208. © Pleiades Publishing, Ltd., 2013.Original Russian Text © V.Z. Kuz’min, I.A. Kayumov, I.I. Safarova, D.Kh. Safin, V.A. Shepelin, 2013, published in Kataliz v Promyshlennosti.

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INTRODUCTION

Butyl rubbers are the most widely produced of thespecial�purpose rubbers, while the production of bothbutyl and halobutyl rubbers is growing year by year. Thisresults in a need for continuous expansion of the produc�tion of their monomer namely, high�purity iso�butylenewith concentrations of no less than 99.95 wt %.

Traditional methods for the production of iso�butylene�containing fractions are hydrocarbon feed�stock pyrolysis, catalytic cracking, and dehydrogena�tion. The concentration of iso�butylene in C4 hydro�carbon fractions can vary from 15–16 wt % on averagein catalytic cracking fractions to 42–46 wt % in thedehydrogenation of iso�butane [1].

Due to the close boiling temperatures of C4 com�ponents in hydrocarbon fractions, existing industrialmethods of the recovery of iso�butylene are based onits preliminary chemical reaction with differentreagents.

Among the primary iso�butylene recovery methodsindustrially proven around the world are those basedon the synthesis, separation, and subsequent decom�position of tert�butanol, alkyl tert�butyl ethers, andespecially methyl tert�butyl ether (MTBE), now pro�

duced at many petrochemical plants, on sulfocationitecatalysts [1, 2].

There is no clear guide as to the preferability of onemethod or another, since each has its advantages anddisadvantages.

The hydration of iso�butylene on sulfocationitecatalysts is characterized by a relatively low reactionrate, the presence of a phase interface caused by themutual insolubility of water and hydrocarbons, andhigh energy consumption due to the need to concen�trate alcohol�containing solutions. The high degree ofiso�butylene recovery from the hydrocarbon fraction(98–99%) and the high purity of the obtained mono�mer (99.99 wt % of the basis) are incontestable advan�tages of this method.

The recovery of iso�butylene from hydrocarbonfractions through the synthesis, separation, anddecomposition of MTBE is characterized by lowerenergy consumption, but this method is also imper�fect. Its disadvantages are associated with the use ofhigher temperatures, the need for dilution with vaporat the stage of MTBE decomposition [3], the presenceof the methanol–iso�butylene azeotrope mixture, andthe formation of dimethyl ether (DME) at the stage of

CATALYSIS IN CHEMICAL AND PETROCHEMICAL INDUSTRY

Developing the Technology for Producing Highly Concentrated iso�Butylene

V. Z. Kuz’mina, I. A. Kayumovb, I. I. Safarovaa, D. Kh. Safinc, and V. A. Shepelina

aOAO Nizhnekamskneftekhim, Nizhnekamsk, Tatarstan, 423574 RussiabOOO EITEK Research and Production Company, Nizhnekamsk, Tatarstan, 423575 Russia

cNizhnekamsk Chemical Engineering Institute, Nizhnekamsk, Tatarstan, 423570 Russiae�mail: kvzsk@mail.ru; kaumov_irek@mail.ru; tretre@rambler.ru; Safin_D@cos.ru; ShepelinVA@nknh.ru

Abstract—The technology used at Russian plants for the recovery of polymerization�grade iso�butylene isbased on synthesizing tert�butanol through the hydration of iso�butylene incorporated into raw hydrocarbonfractions with the subsequent separation and decomposition of tert�butanol. The hydration of iso�butylene isperformed in reactive extraction reactors with countercurrent initial reagents on a molded sulfocationite cat�alyst. In this paper, a version of the process performed in a flow reactor at near�stoichiometric ratios ofreagents is proposed in the context of modernizing the existing technology. The dependence of iso�butyleneconversion and the amount of by�products (dimers, sec�butanol) on the type of hydrocarbon feedstock andthe process parameters is studied. The iso�butane–iso�butylene fraction (IIF) and the butylene–iso�butylenefraction (BIF) are used as feedstocks. It is shown that iso�butylene conversion is lower for the BIF feedstock,and the concentration of by�products is higher than for the IIF feedstock. A tert�butanol synthesis flowsheetis proposed that includes flow and reactive extraction reactors and allows us to increase the capacity of anexisting plant with a simultaneous reduction in the process’s overall energy consumption due to the produc�tion of a highly concentrated tert�butanol solution at the outlet of the flow reactor, and to obtain iso�butylenewith a purity of no less than 99.99 wt %.

Keywords: iso�butane–iso�butylene fraction, butylene–iso�butylene fraction, tert�butanol, reactive extrac�tion reactor, flow reactor, hydration, sulfocationite catalyst

DOI: 10.1134/S2070050413030070

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DEVELOPING THE TECHNOLOGY FOR PRODUCING HIGHLY CONCENTRATED 205

MTBE decomposition, which considerably compli�cate the problem of purifying iso�butylene.

The problem of selecting the technology for recov�ering iso�butylene from the corresponding C4 fractionsarises when building a new plant. However, existingplants must often be modernized to increase theircapacities. The only industrially proven technology forthe production of polymerization�grade iso�butyleneat Russian plants is the one developed at the Instituteof Synthetic Rubber Monomers (Yaroslavl, Russia) [1]on the basis of the hydration of iso�butylene onmolded sulfocationite catalyst in a reactive extractionreactor at high (10� to 15�fold) mass excesses of waterwith respect to hydrocarbons.

One way of modernizing the existing technologyfor iso�butylene recovery, which is based on hydrationon sulfocationite catalysts in order to lower energyconsumption, is to perform the process in flow reac�tors at near�stoichiometric iso�butylene : water ratios,since this enables the production of more concen�trated tert�butanol aqueous solutions.

The authors of [4, 5] showed that tert�butanol solu�tions with concentrations of up to 86.6 wt % can beobtained by hydrating iso�butylene on a macroporoussulfocationite in three sequential stages while addingtert�butanol to the reaction system to increase themutual solubility of water and hydrocarbons. Differentversions of a process based on this approach have beenproposed. In our opinion, those in which the reactorblock is in the form of two serially arranged reactorsand the process is performed without supplying themwith additional tert�butanol [6], or in the form of a sin�gle reactor with several reaction zones and a prelimi�nary supply of tert�butanol at the inlet of the first reac�tion zone [7, 8], are most promising. The primarytypes of hydrocarbon feedstocks for the production ofpolymerization�grade iso�butylene are iso�butane–iso�butylene fractions obtained following the dehy�drogenation of iso�butane and the pyrolysis of buty�lene�containing C4 fractions separated from butadi�ene�1,3. The selection of a feedstock for each pro�ducer is governed by the accessibility or availability ofone production process or another. The pyrolysis ofthe butylene–iso�butylene fraction after preliminaryseparation of butadiene�1,3 and the concentration ofiso�butylene is used only in the production of highly con�centrated iso�butylene at OAO Nizhnekamskneftekhim.The process is performed in the countercurrent regimein a cascade of reactive extraction reactors. The expe�rience gained in operating the industrial unit showsthat the contribution from secondary alcohol forma�tion and olefin oligomerization side reactions whenusing BIF as a hydrocarbon feedstock is higher thanwith IIF, even though the small quantities of excesswater used in the process suppress the alkene oligo�merization side reaction because BIF containsbutene�1, trans�, cis�butenes�2, and butadiene�1,3 inaddition to iso�butylene.

In synthesizing tert�butanol from BIFs on highlyactive macroporous cationites at small quantities ofexcess water (10–20 mol %), the contribution fromthe side reactions of the formation of dimers and sec�ondary butyl and butenyl alcohols can grow.

In this work, we studied the dependence of theamount of by�products formed in the synthesis of tert�butanol on the type of the initial hydrocarbon feed�stock and the parameters of the process performed ina flow reactor at low molar excesses of water withrespect to iso�butylene. Based on the obtained experi�mental data, we consider one possible arrangement ofthe tert�butanol synthesis flowsheet for increasing thecapacities of an existing plant.

EXPERIMENTAL

Our iso�butylene hydration experiments were per�formed on a laboratory�scale unit with a 500�cm3 flowreactor loaded with a sulfocationite catalyst inamounts of 110 g. Lewatit K 2620 macroporous cat�ionite (Lanxess/Bayer) and KU�2FPP molded cata�lyst (TU 2174�011�05766801–2003, OAO Nizhne�kamskneftekhim), a composite of polypropylene andsulfonated styrenedivinylbenzene copolymer, wereused as catalysts. The total static exchange capacity ofthe catalysts was 5.2 and 2.8 mmol/g, respectively. Thespecified temperature was maintained by supplying aheat transfer agent from a thermostat into the reactor’sjacket through a flexible hose. The initial reagents weretransported with dosing pumps. A water–tert�butanolmixture and a C4 fraction forced with water from anintermediate vessel were fed in as separate flows.

The initial hydrocarbon fractions were IIF andBIF, the average compositions of which are given inTable 1.

To improve the mutual solubility of hydrocarbonsand water, we used a tert�butanolwater azeotrope frac�tion with a water content of 11–12 wt %. Experimentswere performed at temperatures of 70, 80, and 90°Cwith feedstock hourly space velocities (HSVs) of 0.96and 1.4 h–1. To keep the mixture components in the

Table 1. Average compositions of initial C4 fractions

ComponentsConcentration, wt%

IIF BIF

Propane 0.58 –

Propene 0.08 –

iso�Butane 57.97 3.57

n�Butane 0.79 6.11

Butene�1 – 29.18

iso�Butene 40.21 54.18

Butenes�2�cis�, trans� 0.30 6.50

Butadiene�1,3 – 0.35

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KUZ’MIN et al.

liquid phase, the system pressure was held within arange of 17–20 atm, depending on the temperature.

To obtain more reliable results, we took two reac�tion mass samples every 30 min in each experiment.Depending on the feedstock HSV, the first sample wastaken no earlier than 1.5–2 h after the unit reached thespecified operational regime. Reaction mixture sam�ples 5–6 cm3 in volume were transferred to glassampoules placed into special metallic containers. Thecomposition of the reaction mixtures was determinedby three different methods on a Kristall�5000 Lyukschromatograph using capillary columns withdeposited Al2O3/Na2SO4 and CP WAX 57 CB phases.Reaction mixture components were identified on aDSQ chromatography mass spectrometer (ThermoElectron) using a capillary column with deposited CPWAX 52 CB phase.

RESULTS AND DISCUSSION

The experimental data for our series of iso�butylenehydration experiments with Lewatit K 2620 sulfoca�tionite are given in Table 2. The experiments were per�formed at an initial reagent C4 fraction : tert�butanolazeotrope : water mass ratio of 1 : 0.8 : 0.1. This

reagent ratio ensured a small molar excess of waterwith respect to iso�butylene and the homophasicity ofthe reaction mixture.

In all cases, the conversion of iso�butylene in BIFwas lower than in IIF; this is explained by the higherpolarity of butenes, relative to iso�butane, and thusbetter adsorption of butenes on the sulfocationitecatalyst. Together with water and tert�butanol, butenesensure a greater drop in the catalytic activity of thecatalyst and in the rate of iso�butylene hydration aswell.

As the reaction temperature rises, a regular increasein the amount of such by�products as C4 alkene dimers(Fig. 1) and sec�butanol (Fig. 2) is observed for bothfeedstock types.

The dimerization of alkenes is typical of both IIFand BIF, but is greater for BIF: the concentration ofdimers in a BIF tert�butanol concentrate is 0.3–0.5 wt %,2–3 times higher than for IIF.

The content of secondary alcohols in the case ofIIF changes slightly under different process conditionsand is 0.003–0.007 wt %. This is explained by the verylow concentration of butenes in the initial hydrocarbonfraction. Considerable growth in the concentration ofsecondary alcohols is observed for BIF, and its highest

Table 2. Conversion of iso�butylene for different initial C4 fractions at varying process parameters

Temperature, °C HSV, h–1Conversion of iso�butylene, %, for the initial C4 fractions

IIF BIF

70 0.96 59.8 51.9

80 0.96 53.0 47.1

90 0.96 46.2 42.9

70 1.4 50.9 49.7

80 1.4 47.2 44.5

90 1.4 42.9 40.9

0.1

065 70

0.2

0.3

0.4

0.5

0.6

75 80 85 90 95T, °C

0.1

065 70

0.2

0.3

0.4

0.5

0.6

75 80 85 90 95T, °C

C, wt % C, wt %

BIF

IIF IIF

BIF

(a) (b)

Fig. 1. Temperature dependence of the dimer concentration (wt %) for IIF and BIF feedstocks at HSVs of (a) 0.96 and (b) 1.4 h–1.

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DEVELOPING THE TECHNOLOGY FOR PRODUCING HIGHLY CONCENTRATED 207

value is 0.11 wt % within the studied range of conditionsat a temperature of 90°C and HSV of 0.96 h–1.

Since the existing technology for synthesizing tert�butanol in the reactive extraction regime is based onusing KU�2 FPP molded cationite as a catalyst, wealso performed experiments on this catalyst. In com�parison to the process on a macroporous cationite,hydration on KU�2 FPP molded cationite with the useof IIF is characterized by increased formation ofiso�butylene dimers despite the lower catalytic activityof molded cationite, relative to macroporous resins.The concentration of C8 hydrocarbons at the outlet ofthe reactor is thus 5–6 wt % even at 70°C, dependingon the HSV. Increasing the feedstock HSV leads toslower formation of dimers, but this has a negativeeffect on iso�butylene conversion. The concentrationof C8 hydrocarbons thus falls from 5.98 to 2.27 wt %,and iso�butylene conversion drops from 51 to 39% whenthe feedstock HSV is increased from 0.96 to 1.4 h–1.

The increased formation of dimers is probably dueto the radically different distribution of water andhydrocarbons over the molded catalyst grains. KU�2FPP catalyst has heightened hydrophobicity and thusa lower affinity for water, and it adsorbs hydrocarbonsmuch better due to the polypropylene it contains. Theconcentration of iso�butylene in catalysts grains turnsout to be rather high, and the dimerization reactionbegins to compete with hydration. As a consequence,there is an intense accumulation of dimers along withthe formation of tert�butanol. We would expect thatthe oligomerization reaction intensifies with risingtemperature for BIF containing butenes and 1,3�buta�diene in addition to iso�butylene. Not only does thislead to a considerable drop in the process’s selectivity,it also results in the rapid deactivation of the catalystdue to its resinification. Molded cationite is thereforenot suitable for use when synthesizing tert�butabol inflow reactors with small molar excesses of water.

The obtained experimental data confirm ourassumptions regarding an increase in the yield of by�products when butylene fractions are used as iso�buty�lene�containing feedstock. At the same time, if wecompare hydration in a flow reactor and the industrialprocess performed in a reactive extraction reactorwhen using BIF as feedstock and macroporous sulfo�cationites as catalysts, the total amount of by�productsis comparable in these processes, and they contain thesame compounds.

In our opinion, the integrated use of reactiveextraction and flow reactors is the optimum variantwhen increasing the capacity of existing plants for theproduction of highly concentrated iso�butylene. Thebasic flowsheet of the reactor block for such an inte�grated process is shown in Fig. 3.

Such organization of production requires one morereactor and distillation column in addition to theexisting process equipment. An iso�butylene�contain�ing fraction is first fully or partially fed into flow reac�tor 1, which is a tube or column reactor with one orseveral catalyst beds [6, 7] in which most of theiso�butylene reacts with water to produce tert�butanol.After separation from a water–alcohol solution in col�umn 2, hydrocarbon fraction VI is sent to reactiveextraction reactor 3, where the residual iso�butylene isrecovered. Waste hydrocarbon fraction VIII and tert�butanol aqueous solutions V and IX are processed fur�ther by the existing process flowsheet.

The use of such a flowsheet allows us to maintain ahigh degree of iso�butylene recovery from the initialBIF, to obtain a concentrated tert�butanol solution atthe outlet of the reactor even at the first stage, and toreduce the amount of water fed into the reactiveextraction reactor at the second stage and thus reducethe energy consumption at the stage of tert�butanolconcentration.

0.02

065 70

0.04

0.06

0.08

0.10

0.12

75 80 85 90 95T, °C

065 70

0.02

0.04

0.06

0.10

75 80 85 90 95T, °C

0.08

C, wt % C, wt %

BIF

IIF

BIF

IIF

(a) (b)

Fig. 2. Temperature dependence of sec�butanol concentrations (wt %) for BIF and IIF feedstocks at HSVs of (a) 0.96 and (b) 1.4 h–1.

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CONCLUSIONS

Diene�free C4 fractions of different origins can beused for the production of polymerization�grade iso�butylene via the synthesis and subsequent decomposi�tion of tert�butanol. The rate of the reaction betweeniso�butylene and water changes along with the yield ofby�products, depending on the composition of the ini�tial hydrocarbon feedstocks. More specifically, weobserve the increased formation of oligomers and sec�ondary C4 alcohols and a drop in the rate of iso�buty�lene hydration when butylene�containing fractions areused. It follows that the reactor’s feedstock capacity inthe case of BIF is slightly lower than for IIF, and anincrease in the concentration of by�products has a

negative effect at the stages of the purification of inter�mediate process flows and the end product. The typeof hydrocarbon feedstock does not determine theselection of a reactor block’s structure.

Incorporating an additional flow hydration reactorinto the process chain is the optimum solution inmodernizing existing plants for the production ofpolymerization�grade iso�butylene and increasingtheir capacity. Integrating the two types of reactorallows us to maintain the high degree of iso�butylenerecovery typical of the reactive extraction process, toreduce the overall energy consumption of the processby obtaining a concentrated tert�butanol solution atthe outlet of the flow reactor, and to produce high�purity (no less than 99.99 wt %) iso�butylene at thesame time.

REFERENCES

1. Pavlov, S.Yu., Vydelenie i ochistka monomerov dlya sin�teticheskogo kauchuka (Separation and Purification ofSynthetic Rubber Monomers), Leningrad: Khimiya,1983.

2. Kirpichnikov, P.A., Beresnev, V.A., and Popova, L.M.,Al’bom tekhnologicheskikh skhem osnovnykh proizvodstvpromyshlennosti sinteticheskogo kauchuka (Handbookof Process Flowsheets of Primary Synthetic RubberProduction Plants), Leningrad: Khimiya, 1976.

3. Aleksandrova, I.V., Synthesis of iso�butylene by thecatalytic decomposition of methyl tert�butyl ether,Cand. Sci. (Eng.) Dissertation, Tobolsk: Tobolsk Ind.Inst., 2012.

4. Korenev, K.D., Kapustin, P.P., Ukhov, N.I.,Zavorotnyi, V.A., and Korol’kov, B.V., Neftepererab.Neftekhim., 1993, no. 7, pp. 27–29.

5. Korenev, K.D., Korol’kov, B.V., and Zavorotnyi, V.A.,Neftepererab. Neftekhim., 1993, no. 12, pp. 31–33.

6. RF Patent 2255931, 2005.7. RF Patent 2451662, Byull. Izobret., 2012, no. 15.8. RF Patent 2453526, Byull. Izobret., 2012, no. 17.

Translated by E. Glushachenkova

IX

1

2

3

I

II

III

IV

V

VI

VII

VIII

Fig. 3. Basic flowsheet for the reactor block of a combinedtert�butanol synthesis plant with flow and reactive extrac�tion reactors: (1) flow reactor, (2) distillation column,(3) reactive extraction reactor; (I) BIF, (II) and (VII)water, (III) mixture of hydrocarbons, tert�butanol, andwater, (IV), (V), and (IX) tert�butanol aqueous solutions,(VI) and (VIII) C4 hydrocarbons.