The survey describes industrial processes for theproduction of light olefins emphasizing on C4 hydrocarbons.Value chains in the petrochemical andthe oil refining industry are strongly interrelatedwith regards to olefin production. An account isgiven on the production and the consumptionvolumes of the various C4 hydrocarbons on a globalbasis, including an outlook for alternative, petrochemicaland bio-based processes for the productionof C4 olefins.
An Overview of Industrial Processes for the Production of Olefins – C 4 Hydrocarbons Michael Bender [1] www.ChemBioEngRev.de ª 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ChemBioEng Rev 2014, 1, No. 4, 136–147 136 Abstract The survey describes industrial processes for the production of light olefins emphasizing on C 4 hy- drocarbons. Value chains in the petrochemical and the oil refining industry are strongly interrelated with regards to olefin production. An account is given on the production and the consumption volumes of the various C 4 hydrocarbons on a global basis, including an outlook for alternative, petro- chemical and bio-based processes for the produc- tion of C 4 olefins. Keywords: Butadiene, Butylene, Hydrocarbons, Industrial processes, Olefins Received: June 25, 2014; accepted: June 30, 2014 DOI: 10.1002/cben.201400016 1 Production and Consumption of Butenes Today, light olefins are produced by a number of processes in the petrochemical and oil refining industry. Worldwide, a vol- ume of 1 billion t of various hydrocarbon feedstock is used to generate approx. 400 million t of light olefins per year. The residual product volume (ca. 600 million t) is composed of higher hydrocarbons, mainly of gasoline fractions (Fig. 1). Approx. 60 % of the global feedstock volume is processed in fluid-catalytic cracking (FCC) units in oil refineries. The re- mainder of 40 % is used in steam cracking in ethylene plants. Ethylene is almost exclusively generated in these plants, in sim- ilar amounts from steam cracking of naphtha and gas oil and of ethane and liquefied petroleum gas (LPG), respectively. At present, increasing volumes of ethylene are also produced by modified FCC processes, such as deep catalytic cracking (DCC). In difference to ethylene, only half of the global propyl- ene volume is generated by steam cracking, mostly of naphtha and gas oil. The other half of the global propylene production rests on conventional FCC units in oil refineries. About a tenth of the global propylene is generated in dedicated processes, in particular by olefin metathesis of 2-butene and ethylene, as well as by propane dehydrogenation (PDH). In difference to the former two light olefins, C 4 hydrocar- bons are mainly generated in FCC units as a by-product of gas- oline production. Only a quarter of the global C 4 hydrocarbon volume stems from steam cracking of naphtha and gas oil. Marginal volumes of C 4 olefins are currently produced by bu- tane dehydrogenation (BDH). While volume growth rates of the light olefins are close to the growth of the gross domestic product (GDP) at 4 to 5 % a –1 , the world gasoline demand is expected to grow by only 1 % a –1 . Thus, growth in global feedstock for olefin production can be expected to be slower by 1 to 2 % than olefin growth rates, i.e., at approx. 3 % a –1 . Four different C 4 olefins are industrially relevant, namely 1-butene, 2-butene, isobutene, and butadiene. These olefins are generated and further processed jointly with n- and isobutane in a complex network of industrial processes. In some cases the C 4 olefins are purified and used in substance, but in the major- ity of all cases C 4 olefins are further processed when contained in C 4 fractions, the so-called raffinates (Fig. 2). Steam cracking of naphtha and gas oil yields a butadiene- rich C 4 fraction, the so-called crude C 4 . Butadiene is produced in substance from this product stream by extraction, yielding a by-product stream of the remaining C 4 components, the so- called raffinate 1. Raffinate 1 is rich in isobutene, but also con- tains significant amounts of the n-butene isomers. In some cases the valuable butadiene is not recovered, but crude C 4 is processed by selective hydrogenation of the butadiene, yielding additional volumes of n-butenes in the raffinate 1 product stream. Steam cracking of ethane or LPG yields only small amounts of C 4 olefins that cannot be recovered economically. These volumes are often hydrogenated fully to butanes, which are re- cycled back into the cracker furnaces as so-called co-crack. In- stead, 1-butene that is required, e.g., as a co-monomer for the manufacturing of linear low density polyethylene (lldPE), can be produced from ethylene by dimerization. ————— [1] Dr. Michael Bender BASF SE, Ludwigshafen, Germany. E-Mail: [email protected]
Transcript
An Overview of Industrial Processes for the Productionof Olefins – C4 Hydrocarbons
The survey describes industrial processes for theproduction of light olefins emphasizing on C4 hy-drocarbons. Value chains in the petrochemical andthe oil refining industry are strongly interrelatedwith regards to olefin production. An account is
given on the production and the consumptionvolumes of the various C4 hydrocarbons on a globalbasis, including an outlook for alternative, petro-chemical and bio-based processes for the produc-tion of C4 olefins.
Today, light olefins are produced by a number of processes inthe petrochemical and oil refining industry. Worldwide, a vol-ume of 1 billion t of various hydrocarbon feedstock is used togenerate approx. 400 million t of light olefins per year. Theresidual product volume (ca. 600 million t) is composed ofhigher hydrocarbons, mainly of gasoline fractions (Fig. 1).
Approx. 60 % of the global feedstock volume is processed influid-catalytic cracking (FCC) units in oil refineries. The re-mainder of 40 % is used in steam cracking in ethylene plants.Ethylene is almost exclusively generated in these plants, in sim-ilar amounts from steam cracking of naphtha and gas oil andof ethane and liquefied petroleum gas (LPG), respectively.
At present, increasing volumes of ethylene are also producedby modified FCC processes, such as deep catalytic cracking(DCC). In difference to ethylene, only half of the global propyl-ene volume is generated by steam cracking, mostly of naphthaand gas oil. The other half of the global propylene productionrests on conventional FCC units in oil refineries. About a tenthof the global propylene is generated in dedicated processes, inparticular by olefin metathesis of 2-butene and ethylene, as wellas by propane dehydrogenation (PDH).
In difference to the former two light olefins, C4 hydrocar-bons are mainly generated in FCC units as a by-product of gas-oline production. Only a quarter of the global C4 hydrocarbonvolume stems from steam cracking of naphtha and gas oil.Marginal volumes of C4 olefins are currently produced by bu-tane dehydrogenation (BDH).
While volume growth rates of the light olefins are close tothe growth of the gross domestic product (GDP) at 4 to 5 % a–1,the world gasoline demand is expected to grow by only 1 % a–1.
Thus, growth in global feedstock for olefin production can beexpected to be slower by 1 to 2 % than olefin growth rates, i.e.,at approx. 3 % a–1.
Four different C4 olefins are industrially relevant, namely1-butene, 2-butene, isobutene, and butadiene. These olefins aregenerated and further processed jointly with n- and isobutanein a complex network of industrial processes. In some cases theC4 olefins are purified and used in substance, but in the major-ity of all cases C4 olefins are further processed when containedin C4 fractions, the so-called raffinates (Fig. 2).
Steam cracking of naphtha and gas oil yields a butadiene-rich C4 fraction, the so-called crude C4. Butadiene is producedin substance from this product stream by extraction, yielding aby-product stream of the remaining C4 components, the so-called raffinate 1. Raffinate 1 is rich in isobutene, but also con-tains significant amounts of the n-butene isomers. In somecases the valuable butadiene is not recovered, but crude C4 isprocessed by selective hydrogenation of the butadiene, yieldingadditional volumes of n-butenes in the raffinate 1 productstream.
Steam cracking of ethane or LPG yields only small amountsof C4 olefins that cannot be recovered economically. Thesevolumes are often hydrogenated fully to butanes, which are re-cycled back into the cracker furnaces as so-called co-crack. In-stead, 1-butene that is required, e.g., as a co-monomer for themanufacturing of linear low density polyethylene (lldPE), canbe produced from ethylene by dimerization.
C4 olefin recovery in oil refineries, mainly from FCC units,and in small volumes in delayed coking units, directly yieldsraffinate 1. These product streams can be further processedjointly with similar streams from ethylene plants. The usual
processes for olefin production yield C4 hydrocarbons in differ-ent ratios. Steam cracking almost exclusively yields C4 olefins,while FCC units are operated such that the total C4 olefin con-tent and the isobutane content of the raffinate 1 stream are in astoichiometric one-to-one balance. This ratio is required to fur-ther process these components into alkylate gasoline. n-Butanedoes not react under the alkylation process conditions. Otherratios of C4 hydrocarbons are obtained, e.g., in the upcomingdehydrogenation processes (Tab. 1).
Beyond butadiene production, raffinates are further proc-essed to a number of different products. Raffinate 1 is used tomanufacture methyl tert-butyl ether (MTBE) and ethyl tert-bu-tyl ether (ETBE) by acid-catalyzed, selective etherification ofisobutene with methanol and ethanol, respectively. Both MTBEand ETBE are large-scale products used as important additivesto the gasoline pool.
Alternatively, C4 olefins can be catalytically converted withisobutane in raffinates yielding alkylate gasoline, another im-portant additive to the gasoline pool. Additional isobutenevolumes can be generated from n-butenes by acid-catalyzedskeletal isomerization. As an example for this process typeCDTech’s ISOMPlus process can be named. ISOMPlus operatesa ferrierite catalyst at 340 to 440 �C to generate isobutene fromn-butenes by rearranging the molecular carbon skeleton [13].
Isobutene can be recovered in substance by acid-catalyzedcleavage of MTBE or iso- and tert-butanol, respectively. Isobu-tene is consumed in substance, e.g., for the production of poly-isobutene (PIB).
1-Butene can be isomerized by acid catalysis or by hydroiso-merization to 2-butene. N-olefins can be produced in substanceby catalytic distillation. They are used for some specific, mostlychemical production processes.
2 The Growing Market for Butenes
Worldwide, approx. 30 million t of isobutylene are generatedper year, mainly in oil refineries, where it is directly processedinto MTBE, ETBE, and alkylate gasoline. Much smaller vol-umes are chemically processed into elastomers such as PIB orinto chemical intermediates such as methacrylic acid and itsderivatives (Fig. 3).
The growth rate of global isobutylene volumes is largely driv-en by growth of its two main products. Historically, alkylategasoline and MTBE volumes have grown rapidly by approx.4 % a–1. MTBE volumes but were stagnant in the recent pastdue to the MTBE ban in the U.S. and other regions. Mean-while, ETBE has started to substitute these volumes and growthof the two ethers combined is expected to continue at historicpace, supporting an expected growth rate of approx. 4 % a–1 forglobal isobutylene volumes in future. Similar to isobutylene,1-butene is generated by three quarters in FCC units. Only aquarter of the global 1-butene volume is generated in ethyleneplants, mostly from naphtha and gas oil. Small volumes areproduced on purpose by dimerization of ethylene, e.g., by theAlphabutol process of the Institute Francais du Petrol (IFP).These volumes are often used as co-monomer for the polyeth-ylene (lldPE) production (Fig. 4).
Figure 1. Global volumes by process type: Total hydrocarbonfeedstock supply to light olefins production (a); ethylene, pro-pylene, and butenes (b, c, and d). Own estimates were based onsources [1–6].
Most of the 1-butene is consumed in the production of alky-late gasoline, while only one quarter is used in the productionof chemicals and polymers. After isomerization to 2-butene1-butene volumes are also consumed to produce propylene bymetathesis with ethylene. Similar to isobutylene volumes of1-butene will grow mainly along with alkylate gasoline.Thesupply and demand situation for 2-butene is very similar to1-butene. 2-Butene is also produced mainly in refineries and isconverted by approx. three quarters into alkylate gasoline. TheFCC process yields a 2-butene to 1-butene ratio much closer to
thermodynamic equilibrium than that of the steam crackingprocess. Thus, FCC units have a larger share in global 2-buteneproduction than in 1-butene production (Fig. 5).
Since most of the global C4 hydrocarbon volumes are pro-duced in oil refineries this raises the question of why such asmall part of these volumes become available to the petrochem-ical industry. As already explained above, C4 hydrocarbons inrefineries are mainly used as a feedstock for the gasoline pool,either directly as a C4 additive in cooler periods of the year orin warmer periods as alkylate gasoline or as tert-butyl ether
Figure 2. Network of petrochemical and refinery processes for the generation and conversion of C4 hydrocarbons; Starting from raw ma-terials a number of crudes are produced first that are used as feedstock for the primary generation of olefins. C4 olefins are further pro-cessed from their raffinates and in some cases are recovered in substance before being used as a chemical feedstock.
Table 1. Composition of raw C4 hydrocarbon streams generated in different petrochemical and refinery processes; the red boxes indi-cate the difference in butane to butene ratios between steam cracking and fluid catalytic cracking.
C4 Boilingpoint [�C]
Yield [wt %]
SC, lowseverity
SC, highseverity
FCCcracker
n-ButaneBDH
EthanolETB
n-ButeneODH
MTO[ZSM-5]
1,3-Butadiene –4.4 28 49 0.2 9–13 90 58 –
Isobutene –6.9 32 22 24 – – – ~ 30*
cis-Butene-2 +3.7 7 5 11 37–41 10 8 ~ 60
trans-Butene-2 +0.9 7 6 15
Butene-1 –6.3 20 14 15 – 1.3
Isobutane –11.7 2 1 37 – – – < 10**
n-Butane –0.5 4 3 12 ~ 50 – 4
Source [7] [7] [8] [9] [10] [11, 12]
(XTBE, Fig. 6).When blending C4-based components in thegasoline pool, two main aspects are important: on the onehand, blending alkylate gasoline and XTBE leads to an increaseof the octane number and, thus, of the gasoline quality; on theother hand, alkylate gasoline limits the so-called Reid vaporpressure of gasoline more effectively than XTBE components.In difference, blending bioethanol into the gasoline pool leadsto a significant increase of the Reid vapor pressure. This in-crease can be compensated for by co-blending alkylate gasolinebetter than by blending with XTBE components.
Consequently, the strong growth of bioethanol volumes ingasoline is, hence, coupled to an equally strong growth of theglobal alkylate gasoline demand. At the same time total gaso-line production is almost stagnant, whereby available C4 hydro-
Figure 3. Global isobutylene volumes and growth; a) volumesby production process, estimated from global capacities andtypical C4 yields (see Fig. 1 and Tab. 1); b) volumes by use, esti-mated from [14–17].
a)
Steamcracking
23%
Fluid-catalyticcracking, total
73%
Butene-1 by source18 Mmto / +4 % p.a.
Ethylenedimerisation
4%
b)
Polyethylene(hdPE / lldPE)
9%
Polybutene-1,3%
Propylenevia metathesis
10%
Alkylategasoline
73%
Butene-1 by use18 Mmto / +4 % p.a.
Chemicals6%
Figure 4. Global butene-1 volumes and growth; a) volumes byproduction process, estimated from global capacities and typi-cal C4 yields (see Fig. 1 and Tab. 1); b) volumes by use, estimatedfrom [18, 19].
a)
Methyl EthylKetone,
6%
Propylenevia metathesis
24%
Alkylategasoline
70%
2-Butene by use14 Mmto / +4 % p.a.
b)
Fluid-catalyticcracking, total
86%
Steam cracking,14%
2-Butene by source14 Mmto / +4 % p.a.
Figure 5. Global butene-2 volumes and growth; a) volumes byproduction process, estimated from global capacities and typi-cal C4 yields (see Fig. 1 and Tab. 1); b) volumes by use, estimatedfrom [20, 21].
XTBE2%
Butane7%
Bioethanol10%
Gasolinefractions
75%
Gasoline, total∼1,000 Mmto / ∼1 % p.a.
Alkylate gasoline
7%
Figure 6. The global gasoline pool, volumes by component. In-dividual components and their physical properties relevant togasoline blending are summarized in Tab. 2 [22, 23].
carbon volumes, mostly from FCC units do not grow asstrongly as their two main gasoline products (Fig. 7).
No significant change of this situation can be expected mid-term. Refinery operators will have only little incentives to shiptheir C4 hydrocarbons to consumers in the petrochemical in-dustry. Long term, the demand situation for alkylate gasolinecould ease, if bioethanol is substituted by biobutanol as a com-
ponent for the gasoline pool, a trend still in its in-fancy. Biobutanol boosts the octane number of gas-oline, but unlike bioethanol, without increasing itsReid vapor pressure. This would relieve the de-mand for alkylate gasoline as a low-vapor pressureblending component and, thus, could make C4 ole-fins from refineries available for the petrochemicalindustry.
Since all three butenes are expected to grow byabout 4 % a–1, it will be interesting to see how thecorresponding volumes will be produced. Withmuch lower growth rates in gasoline volumes FCCunits will not be able to satisfy this growing demandalone. Also, with ethylene plants being convertedfrom liquid to gas feedstock butene availability fromsteam cracking will also decrease, potentially leavingbehind a supply gap in C4 olefins.
3 Alternative Sources for Butenes
When turning our view to alternative processes for manufac-turing C4 olefins dehydrogenation of the corresponding butaneis the first process that must be mentioned. Iso- and n-butanecan be dehydrogenated to raffinate-2 and raffinate-1-compati-ble product streams, respectively (Fig. 8). Butadiene-rich crudeC4 streams can be generated from n-butenes by oxidative dehy-drogenation and can be further processed conventionally bybutadiene extraction. Butanes are available as feedstock in largeamounts from natural gas, from crude oil distillation, or as aresidual stream from raffinate processing in oil refineries andpetrochemical plants.
Industrial processes for dehydrogenation of light paraffinsare available from various licensors (Tab. 3). Due to thermody-namics of the dehydrogenation reaction operating tempera-tures are high at around 600 �C and the processes are operatedat relatively low pressure. Most of the processes use a combina-tion of platinum and tin as the active ingredient of the dehy-drogenation catalyst while support materials are different fordifferent licensors. As an exemption the Catofin process usesan alumina-supported chromium oxide catalyst.
Dehydrogenation processes typically operate at partial con-version of the paraffin feedstock between 50 and 60 %. Underthese conditions the processes reach C4 olefin selectivities ofabout 90 %. The remainder of the converted feedstock (~10 %)forms coke deposits on the catalyst surface. These deposits areused in some process types like in the Catofin and in the Ole-flex process to generate internal process heat by combustionduring catalyst regeneration. In contrast, the STAR process usessteam injection into the reactant stream to minimize coke de-posits by internal steam reforming. Depending on the cokemanagement concept cycle times between two catalyst regener-ation steps vary between a few minutes and several hours percycle for the various process types.
Table 2. Individual components and their physical properties relevant to gaso-line blending [22, 23]
Component Blend octane number(RON + MON)/2
Reid vapor pressure[psi]
Net energy[%]
Crude gasoline 88 6–11 100
Ethanol 112 18–22 65
Isobutanol 102 4–5 82
Alkylate gasoline 95 4–5 95
C4 raffinate 86–104 50–70 ~ 105
MTBE 110 8 80
ETBE 111 4 83
b)
a)
Alkylate gasoline, total∼∼65 Mmto / ∼4 % p.a.
Figure 7. Volumes and growth rates of the two main blendcomponents for the gasoline pool; a) bioethanol [24]; b) alkylategasoline [14].
Figure 8. Dehydrogenation reaction of n-butane (left) and isobutane (right).
Endothermal dehydrogenation allows only partial conver-sion of ethane, propane, and of butane feedstock in the techni-cally relevant range of operating temperatures up to 800 �C(Fig. 9). Heat of reaction can be introduced into the reactionvolume in three different ways (Fig. 10): the reaction volumecan be heated externally, e.g., by gas burners. Alternatively, thereactant gas flow can be preheated to temperatures highenough above the kinetic onset temperature to carry heat intothe reaction volume by its heat capacity. The heat capacity ofthe reactant gas stream may be further increased by steam dilu-tion to increase the amount of heat introduced. Thirdly, heat ofreaction can be generated internally by selective combustion ofthe hydrogen that is released by the dehydrogenation reaction.Oxygen that is mixed into the reactant gas stream reacts withthe hydrogen on the dehydrogenation catalyst.
Variable economics of olefin-producing processes also de-pend on by-product yields. As can be seen in Tab. 4 (yellowboxes), when steam cracking propane and butanes, about onequarter of the feedstock is converted into light gas, mainly syn-thesis gas and methane. However, when dehydrogenating theseparaffins, the resulting light-gas yield is much lower. Hence, C3
and C4 dehydrogenation offer an incentive when compared tosteam-cracking of these two paraffins.
In contrast, steam cracking of ethane generates only smallvolumes of low-valued light gas more comparable to light-gasyields in C3 and C4 dehydrogenation. Thus, the potential dehy-drogenation of ethane would not offer the same incentive overethane cracking as the dehydrogenation of higher paraffinsdoes over their respective steam cracking.
For the on-purpose production of butenes the dehydrogena-tion of butanes is advantageous over all the other processes de-scribed above, because it does not generate by-products in largeamounts.
Catalytic cracking of methanol is an interesting way to producelight olefins in so-called ‘‘methanol-to’’ (MT) processes (Fig. 11).
The multitude of possibilities to produce methanol from car-bon-containing raw materials via synthesis gas grants a flexibleaccess to light olefins from all four raw material sources – natu-ral gas, crude oil, coal, and biomass.
While ExxonMobil’s original methanol-to-gasoline (MTG)process was dedicated primarily to gasoline production frommethanol, later developments like UOP’s methanol-to-olefin
Table 3. Industrial processes for the dehydrogenation of butanes to butenes [25–27].
Process parameters UOP oleflex Uhde STAR process Clariant Catofin Linde-BASF process
Reactor Moving bed, radial flow,adiabatic
Fixed-bed, isothermal plus adiabaticreactor
Fixed-bed, adiabatic Fixed-bed, isothermal
T [�C] 580–650 570–590 560–650 550–650
p [bar] 2 5 0.3–0.5 >1
Cycle time 5–10 d 7 h 6–20 min ~ 9 h
X(C4¢) per pass [%] 50 ~35 60–65 C3¢:30
S(C4†) [%] n-C4†: 81;i-C4†: 91
> 91–93 90 C3†:90
Catalyst Pt-Sn on Al2O3 Pt-SN Zn/Ca aluminate Cr2O3 : Al2O3 Pt-Sn support
0
25
50
75
100
400 500 600 700
Con
vers
ion
[%]
Temperature [°C]
Butane
Propane
Ethane
Figure 9. Thermodynamically limited conversion of light para-ffins in endothermal dehydrogenation. The gray area indicatesthe catalytically relevant range of operating temperatures;from: [27].
high Tin
z, t
Q⋅
Low Tin
Q⋅
Q⋅
Low Tin
Q⋅
ΔRH = CP,gas ⋅ΔT
preheated reactant gas
ΔRH = ΔRHcomb.
H2 combustionin-situ
ΔRH = ΔRHcomb.
external gas firing
Adiabatic AutothermalIsothermal
Figure 10. Heat management concepts for endothermal dehy-drogenation processes; from [27].
2 CH3OH → CH3OCH3 + H2O → HCx + 2 H2O
Figure 11. Two-step reaction of methanol to hydrocarbons inmethanol-to processes.
(MTO) and Lurgi-Air Liquide’s methanol-to-propylene (MTP)processes were aimed at producing light olefins (Tab. 5). How-ever, the main purpose of these processes is not the productionof C4 olefins but mainly of propylene and ethylene. Rather,some modifications of these processes are available that furtherupgrade the primary yield of the latter two olefins by catalyticcracking of the small C4 olefins volumes that are co-generatedin the MT process. Industrial operating conditions allow for aprimary C4 hydrocarbon yield of ca. 10–12 %, most of it as C4
paraffins. Hence, an industrial MT process for producing C4
olefins is not readily available yet.
4 Economics of Olefin-producingProcesses
The cost structure of all MT processes depends indirectly onthe raw material that is used to produce the methanol feed-stock. Coal is relatively cheap per gram of carbon that ends inmethanol compared to natural gas. However, its specific in-vested capital per ton of methanol product is significantly high-
er as can be seen from Fig. 12. Generating synthesis gas fromcoal requires more equipment than from natural gas due to ex-tensive processing of solids.
Depending on costs related to specific investment cheap coalmay not always be so cheap. The investment for a worldscale
Table 4. Industrial processes for the generation of light olefins and liquid hydrocarbons: product yields in percent of feedstock andglobal volumes in Mmto [1–6, 28].
Figure 12. Economy of scale of petrochemical processes for theproduction of light olefins based on alcohols as feedstock [33].
MT plant based on coal may be higher by about $ 1.5 billionthan for one based on natural gas. For the first ten years, thisinvestment penalty would result in higher costs of approx.300 million $ a–1 (depreciation and capital costs at typical rates)or around 150 $ t–1
methanol. These added costs are higher thanthe variable cost advantage of coal versus cheap natural gas,i.e., at 4 $ MMBtu–1. Hence, under these conditions a coal-based MT process will not be competitive versus one based onnatural gas. However, when coal is cheap, i.e., at 60 $ t–1, andnatural gas is expensive, i.e., at 12 $ MMBtu–1, coal-based MTprocesses become cost competitive (Fig. 13).
Economics of different petrochemical processes for the pro-duction of light olefins can be compared based on their contri-
bution margin 1 (CM1). For the present paper CM1 was calcu-lated based on published product yields for the variousprocesses and on U.S. market prices for feedstock and prod-ucts, respectively. All other cash expenses were neglected fornow. CM1 represents a rough estimate for the operating cash-flow and, thus, compares profitability between different pro-cesses.
At current US market prices steam cracking of ethane yieldsby far the highest CM1 margin, followed by propane dehydro-genation and by the two olefin-generating MT processes. CM1margins of all other processes are significantly lower. For mostof the processes CM1 margins are driven by the product mix,while for ethane cracking it is driven mainly by low feedstockcosts.
Regional differences, in general, play a major role in the se-lection of suitable processes to produce light olefins and otherbasic petrochemicals (Fig. 14). Differences in feedstock pricesresult from geological differences in raw material abundance.In contrast, regional differences in market prices and productdemand result from differences in population and economicpower. Regions rich in raw material like the Middle East, theformer GUS countries, Australia, or Latin America possess acomparatively small population and generate a low absoluteGDP. Petrochemicals that are produced in these regions arepredominantly exported, while countries poor in raw materials,but rich in population and with a strong GDP like Europe orAsia are net importers of these goods.
As an exception, the U.S. currently enjoy significant raw ma-terial resources and at the same time a strong demand for theseproducts in a large population with a strong economy. In addi-tion, U.S. petrochemical producers increasingly export theirproducts globally.
Figure 13. Economics of different petrochemical processes forthe production of light olefins; the values represent estimates ofcontribution margins 1, i.e., revenue minus variable costs. All es-timates are based on U.S. market prices for raw materials, feed-stocks and products.
Popula�on
GDP
Coal reserves
Oil reserves
Natural Gas reserves
North America
South America
Europe
frmr. GUS states
Africa
Middle East
Asia Pacific
Australia
Figure 14. Regional differences in population, GDP and raw material abundances; the global figures have been composed from individ-ual Wikipedia entries by country for population, GDP and for the raw material reserves, respectively. Full scale of each graph represents a60 % share of the region in the respective global figure.
Due to these regional differences it is necessary to take trans-port costs for raw materials and for petrochemical products in-to account when deciding on investments into petrochemicalprocess equipment and on the location of the individual invest-ment (Tab. 6).
High specific costs are related to the transport of hydrocar-bon equivalents in particular for liquefied natural gas (LNG)and for liquefied petroleum gas (LPG). However, methanol andbiomass, such as corn, also come with relatively high transportcosts when calculated by the ton of hydrocarbon equivalent.For LNG and LPG, costs are high mainly due to an extensiveinfrastructure transport of methanol, and biomass is expensivebecause they contain large amounts of water that must betransported alongside. Due to cheap infrastructure, crude oiland gasoline but also coal can be transported relatively cheap.
The differences in specific transport costs require petro-chemical processes that are based on natural gas, ethane, andLPG to be operated in the region of raw material abundance,e.g., in the Middle East, but also in the United States. Ethanecracking is currently big in these two regions. In contrast, oil-or coal-based processes are often operated in the region wherepetrochemical products are to be marketed, e.g., in Europe orin Asia. Olefin production in these two regions relies predomi-nantly on naphtha cracking and in Asia industrial MT plantsthat use coal-based methanol feedstock have been installedworldwide for the first time.
5 Butadiene – A very special case
Butadiene represents a peculiar case in the world of C4 olefins.It is mainly used as a monomer in the production of variouselastomers. Elastomers are predominantly used in the tire in-dustry and, hence, its consumption pattern depends on theglobal car industry. Its global volumes are somewhat smallerthan for the other three C4 olefins, mostly because it is exclu-sively used in petrochemical production, while the other C4
olefins are consumed mainly in gasoline products (Fig. 15).Butadiene prices vary with large amplitudes over time
(Fig. 16). Changes in demand and supply occur in sync overthe economic cycle, leading to hefty price changes in both
directions. These amplitudes are much larger than for the otherolefins, making decision timing for new investments into buta-diene production very difficult.
At present butadiene is only produced by steam cracking ofnaphtha. Butadiene yields in FCC units are very low. Butadieneinterferes negatively in the acid-catalyzed alkylate gasoline pro-duction. Therefore, butadiene is removed from FCC raffinatesby selective hydrogenation. With increasing amounts of ethanecracking, butadiene may be produced in future by ethylene di-merization followed by oxidative dehydrogenation.
In addition to steam cracking butadiene could be producedfrom coal or biomass via butanediol as an intermediate. Start-
Table 6. Overseas shipment costs for different raw materials and petrochemical products; cost figures have been collected from [34–38].
Commodity Shipment cost[US $ t–1]
Energy content[MMBtu t–1]
Shipment costs[US $ MMBtu]
Shipment costs[US $ t–1
H2C eq.]
Liquefied natural gas (LNG) 140 53.4 2.64 160
Liquefied petroleum gas (LPG) 100 (Panama)150–200 (Cape Horn)
47.3 2.11–4.22 100–200
U.S. crude oil 11–17 39.7 0.28–0.43 10–20
U.S. gasoline 10–12 41.2 0.41–0.49 10–12
U.S. coal 10–20 ~ 27 0.37–0.74 20–40 (via MTX)
U.S. methanol 30–60 19 1.58–3.16 70–140
U.S. ethanol 30–60 25.6 1.17–2.34 50–80
U.S. corn 30–60 ~ 15 2.00–4.00 109–174 (via EtOH)
b)
a)
ABS polymers12%
nitrile rubber4%
SBD blockcopolymers
6%
Butadiene10 Mmto / 4.5% p.a.
polybutadiene26%
SB latex12%
SB.elastomers
28%
Other4%
FCC, total1%
Other (ODH)4%
Steam cracking,Naphtha & GO
78%
Steam cracking,Ethane & LPG
17%
Butadiene10 Mmto / 4.5% p.a.
Figure 15. Global butadiene volumes and growth; a) volumesby production process; b) volumes by use; estimates based on[39, 40].
ing with coal-based Reppe chemistry, butadiene could be ob-tained by catalytic dehydration of butanediol, originally a pro-cess that was operated in the 1940s to produce synthetic rub-ber. A somewhat more conventional way to butadiene wouldbe the dimerization of ethanol [41] after Lebedev or after Os-tromislensky. Bioethanol can be produced routinely from bio-mass by fermentation. However, ethanol dimerization has notbeen optimized for industrial yields. These processes were oftenoperated in war times or in isolated national economies. Hence,their profitability is often not competitive in today’s world mar-ket.
Beyond steam cracking of liquids, additional butadiene canbe generated by oxidative dehydrogenation (ODH) of n-bu-tenes (Fig. 17).
Product streams of these processes can be processed furthersimilar to crude C4, i.e., by extraction of the butadiene. ODHprocesses were developed by several companies and some ofthese processes are available on a license basis (Tab. 7).
At butene conversion between 75 and 90 %, the selectivitiesto butadiene range at 90 % or higher. Different mixed-metaloxide catalysts are operated, resulting in space time yields be-tween 500 and 1000 kg m–3h–1. Feedstream compositions of thedifferent processes vary with regard to their content in oxygen,steam, and butene.
CM1 margins for ODH processes are difficult to obtain due tothe large amplitudes in butadiene prices. For a representativebutadiene price of 2000 $ t–1, the CM1 margin would amount toapprox. 400 $ t–1, when assuming typical U.S. prices for raffinatefeedstock. These estimates show that ODH processes will playan important role in the global butadiene supply in the future.
6 Outlook – Biochemical Processesfor C4 Olefin Production
In the past, technical developments resulted in a number of fer-mentative processes for the production of industrial chemicals.With a 10% share in the global gasoline pool, bioethanol has al-ready arrived in the group of very large industrial chemicalproducts. In recent years, several start-up companies have be-gun to develop fermentation processes for the production ofhigher industrial alcohols such as isobutanol and butanediol.Typical yields of these processes range from 0.3 to 0.5 talcohol
per ton of sugar or corn starch [46] (Tab. 8).
Catalytic dehydration of the corresponding industrial mono-alcohols easily yields ethylene [47] and isobutylene [48], whilethe same reaction on 1,4-butanediol does not easily producebutadiene [49] (Fig. 18).
Figure 16. Prices for butadiene (red curve) versus those for eth-ylene (blue), propylene (velvet), and naphtha (black) between2010 and 2013; amplitudes in butadiene prices are much largerthan for the latter three materials [40].
O2, H2O, , + H2O
Figure 17. Oxidative dehydrogenation (ODH) of n-butenes tobutadiene.
Table 7. Survey of four different ODH processes; additional ODH processes were developed by BP Chemicals, Mitsubishi Chemicals andNippon Zeon.
Phillips O/X/D Petro/Tex Oxo/D SK Energy ODH BASF ODH
Table 8. Fermentative yields of different industrial alcohols(column 1 and 2, from: [46]) and CM1 margins of different ole-fins obtained from these alcohols by catalytic dehydration (col-umn 3 and 4). It is assumed for simplification that the dehydra-tion process yields 100% olefins. *Prices [$ t–1]: 2000 (i-butylene)and 2500 (butadiene).
Bio-alcohol Yield Olefin frombio-alcohol
CM1 [$ t–1]
Ethanol 0.45 t t–1corn Ethylene ~ 110
Isobutanol 0.35 t t–1sugar Isobutylene* –500 – +500
1,4-Butanediol 0.5 t t–1sugar Butadiene* ~ 300
In any case, it can be concluded that the comparatively sim-ple dehydration of bio-based industrial alcohols can generatepositive CM1 margins and, depending on market prices, maybecome as profitable as conventional petrochemical processes.
However, prices of bio-based raw materials for the fermenta-tive production of alcohols may undergo drastic changes thatcould easily undermine process profitability on the long run.After a long period of relatively stable prices soft commoditieshave recently experienced price hikes that doubled or eventripled market prices for certain carbohydrates (Fig. 19).
Despite of these uncertainties additional efforts will be spentin future developments of production processes for petrochem-icals on the basis of biomass can be expected. Hopefully, someof these processes will also grant access to bio-based C4 olefins.
7 Conclusion
Today, a number of processes for the gen-eration, the conversion and the separa-tion of C4 olefins in petrochemicals andin oil refineries are already available onindustrial scale. At present the majorityof global C4 olefin volumes are generatedand further processed in oil refineriesmaking blend components for the gaso-line pool. Their availability for petro-chemical production purposes hinges ontheir valuation relative to their alternativeproduction by petrochemical processes.
In future, butane dehydrogenation will yield increasing vol-umes of C4 olefins. Smaller volumes of butadiene will be gener-ated by oxidative dehydrogenation of butenes obtained by de-hydrogenation before. MT processes may also be tuned for C4
olefin production depending on further process development.Bio-based routes to C4 olefins are still in their infancy. Their
success will largely depend on the development of market pri-ces for biomass raw materials and on a potential solution of theconflict of food versus fuel.
The author has declared no conflict of interests.
Michael Bender received hisPh.D. in Physical Chemistry in1997 from the Ruhr-Universi-tat Bochum, having worked inthe group of Prof. Freund. Hetook his first position withBASF as catalyst researcher inthe same year. From 2001 to2009, he held business posi-tions with BASF as productmanager and business man-ager for petrochemical cata-lysts. In 2009, Dr. Bender be-came a R&D group leader and
was promoted to Senior Expert in Catalyst Research withBASF SE, Ludwigshafen, in 2013.
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