C4 cracker stream

Today, more butadiene (BD) is produced from butene (another C4) through steam cracking of naphtha gas oil (a byproduct of ethylene/propylene production). Through extractive distillation of this C4 cracker stream, the butadiene is obtained. Com-... 

Today more butadiene is produced from butene (another C4) through steam cracking of naphtha gas oil from ethylene/propylene production (it is a byproduct of eth-ylene/propylene production). Through extractive distillation of this C4 cracker stream, the butadiene is obtained. Commonly the yield achieved forBD is dependent on the quality of the feedstocks used for ethylene production. Usually the heavier the feedstock, the greater the BD production. Reportedly, the lighU feedstock only yields about one-fifth the yield of butadiene compared to the heavy feedstock. 

The Hj/400°FVT streams from each system are sent to separate flash drums where the bulk of the Cj and lighter material is removed. The virgin and cat cracker streams from the flash drums go to separate debutanizers while the Powerformer stream goes to an absorber-deethanizer followed by a debutanizer. The Q and lighter overhead streams from the virgin and cat cracker debutanizers are sent to this absorber- deethanizer for final deethanization. In the flow scheme shown this tower does not have a separate lean oil. It is called an absorber-deethanizer because the Powerformer stream serves in part to absorb the Cj and C4 components in the streams from the debutanizers. A separate lean oil stream is added in cases where higher Q and Q recoveries are justified. 

A typical C4 hydrocarbon stream coming from a gas oil or naphtha cracker, like that shown in the last chapter in Figure 5-4, might have the following composition ... 

The C4 stream from steam crackers, unlike its counterpart from a refinery, contains about 45% butadiene by weight. Steam crackers that process significant amounts of Hquid feedstocks have satellite faciUties to recover butadiene from the stream. Conventional distillation techniques are not feasible because the relative volatihty of the chemicals in this stream is very close. Butadiene and butylenes are separated by extractive distillation using polar solvents. 

The overhead stream from the debutanizer or stabilizer is a mix of C, s and C4 s, usually referred to as LPG (liquefied petroleum gas). It is rich in olefins, propylene, and butylene. These light olefins play an important role in the manufacture of reformulated gasoline (RFG). Depending on the refinery s configuration, the cat cracker s LPG is used in the following areas ... 

The first serious notice of C4 hydrocarbons came with the development of refinery cracking processes. When catalytic cracking became popular, refiners were faced with disposing of a couple of thousand barrels per day of a stream containing butane, butylenes, and small amounts of butadiene. Their first thought was to burn it all as refinery fuel, but then they developed the alkylation process. With that, they could undo some of the molecule shatter that took place in the crackers and reassemble some of the smaller pieces as alkylate, a high-octane gasolinerblending component. 

When butadiene is produced in olefins plants or in refinery crackers, they come mixed with relatively large volumes of the other C4 family. Sometimes the other C4S need not be separated from each other, for example if they are going to be used for allcylation plant feed. In that case, the butadiene can be separated from the other C4S by extractive distillation. This process uses a solvent that will preferentially dissolve butadiene, ignoring the other components in the stream. 

Describe how youd use the following processes to handle the C4 stream in the heavy liquids cracker in Figure 5-3 ... 

The petrochemical products from olefins plants are ethylene, propylene, C4 s (butanes, butylenes, and butadiene) and a stream containing the BTXs, Refinery cat.crackers produce propylene and C4S. They produce some ethylene, but often it is not recovered. 

In 2000 two major petrochemical companies installed process NMR systems on the feed streams to steam crackers in their production complexes where they provided feed forward stream characterization to the Spyro reactor models used to optimize the production processes. The analysis was comprised of PLS prediction of n-paraffins, /xo-paraffins, naphthenes, and aromatics calibrated to GC analysis (PINA) with speciation of C4-C10 for each of the hydrocarbon groups. Figure 10.22 shows typical NMR spectral variability for naphtha streams. Table 10.2 shows the PLS calibration performance obtained with cross validation for... 

For comparative purposes the typical weight percentage yields for a DCC unit, an FCC unit and a steam cracker are shown in Table 8.1. Propylene yields from the DCC unit are considerably higher than those from an FCC nnit. The DCC mixed C4s stream also contains increased amounts of bntylenes and iso-C4s as compared to an FCC. These high olefin yields are achieved by deeper cracking into the aliphatic components of the initially prodnced naphtha and life cycle oil (LCO). 

Hydroformylation of Other Lower Olefins and Dienes - Lower olefins such as 1-butene or 1,3-butadiene are hydroformylated with acceptable rates using Rh/tppts catalysts according to the RCH/RP process. Hoechst AG Werk Ruhrchemie has developed an attractive new process350 for the hydroformylation of raffinate II, a mixture of 1-butene, cis- and /rbutane derived from the C4 stream of naphtha crackers (after removal of 1,3-butadiene... 

The various sources of isobutylene are C4 streams from fluid catalytic crackers, olefin steam crackers, isobutane dehydrogenation units, and isobutylene produced by Arco as a coproduct with propylene oxide. Isobutylene concentrations (weight basis) are 12 to 15% from fluid catalytic crackers, 45% from olefin steam crackers, 45 to 55% from isobutane dehydrogenation, and high purity isobutylene coproduced with propylene oxide. The etherification unit should be designed for the specific C4 feedstock that will be processed. 

C4 raw cuts of stream crackers typically contain butanes (4-6%), butenes (40-65%) and 1,3-butadiene (30-50%), as well as some vinylacetylene, 1-butyne, propadiene and methylacetylene. First, acetylenes are selectively hydrogenated and the 1,3-butadiene is extracted resulting in butene cut (or raffinate I). Isobutylene is next removed to produce raffinate II which contains linear butenes and some residual 1,3-butadiene. The latter needs to be removed to achieve maximum butene yields. The methods and catalysts for this process are chosen according to the final use of butenes. The demand for polymer-grade... 

A comparative study of nanocomposites (16% Nafion-silica and commercial SAC-13) has been performed by Hoelderich and co-workers169 in the alkylation of isobutane and Raffinate II. Raffinate II, the remaining C4 cut of a stream cracker effluent after removal of dienes, isobutane, propane, and propene, contains butane, isobutylene, and butenes as main components. High conversion with a selectivity of 62% to isooctane was found for Nafion SAC-13 (batch reactor, 80°C). Both the quality of the product and the activity of the catalysts, however, decrease rapidly due to isomerization and oligomerization. Treating under reflux, the deactivated catalysts in acetone followed by a further treatment with aqueous hydrogen peroxide (80°C, 2 h), however, restores the activity. 

Direct dehydroisomerisation (DHI) of n-butane into isobutene over bifunctional zeolite-based catalysts represents a potential new route for the generation of isobutene utilising cheap n-butane feedstock. Isobutene is used worldwide for production of methyl tert-butyl ether (MTBE) and polyisobutylene. It is currently obtained via extraction from refinery/cracker C4 streams or via conversions of isobutane (in one step) or n-butane (in two steps).1,2 Isobutene can also be produced via the isomerisation of n-butenes,3 although there is no evidence that this is practised commercially.2,3... 

Application To produce high-purity butadiene from a mixed C4 stream, typically a byproduct stream from an ethylene plant using liquid feeds (liquids cracker). The BASF/Lummus process uses n-methylpyrrolidone (NMP) as the solvent. 

Application To produce propylene and ethylene from low-value, light hydrocarbon streams from ethylene plants and refineries with feeds in the carbon number range of C4 to C8, such as steam cracker C4/C5 olefins, cat-cracker naphthas, or coker gasolines. 

The various components of LPG streams are used in a variety of processes. Propane, butane and isobutane are used as cracker feedstock for the production of olefins which is discussed in later chapters. In addition n-butane is used for the production of 1,3-butadiene. This compound can also be extracted from the C4 cracked gases by extensive distillation coupled with a selective absorption process. 

A cracker C4 stream contains all of the possible C4 hydrocarbons which are listed in Table 5.2. Of these commercial interest focuses on butenes, isobutene, 1,3-butadiene and butanes. Efficient separation is impossible by distillation alone and complete separation is by a combination of distillation, selective hydrogenation and selective absorption. If butadiene is not required this ean be hydrogenated and the butenes and butane separated by distillation. 

Table 5.2 Typical Composition of a Naphtha Cracker C4 Stream...

The final product of interest is butane. This can be separated and either sold as LPG or recycled as a cracker feedstock. All of the C4 stream can be recycled for cracking. However, olefins and especially dienes and the C4-aceylenes rapidly form coke and the C4 stream is generally fully hydrogenated to butane. 

Table 7.2 presents the data for a plant which extracts propylene and pyrolysis gasoline, but recycles the rest of the products. Of the byproducts the mixed C4 stream is recycled to the feed-side of the cracker furnaces, with the hydrogen and methane recycled to the fuel-side. The same quantum of operating allowances for feed and fuel are included in the statistics. 

After separation of the mixed olefins the product work up is similar to that in a steam cracker using LPG feedstock. Small amounts of carbon dioxide are removed and the hydrocarbon gases are dried before passing to a de-ethaniser column. The C2- fraction is passed to an acetylene removal unit before methane is removed from the C2 stream. This comprises 98-i-% ethylene, the remainder being ethane. The C3+ stream is split between the C3 fraction (98% propylene) and C4+. The work up of the C4 stream to produce linear butenes (not shown in the figure) is likely to be less problematic than the corresponding C4 stream from steam crackers, which is highly complex and cannot be separated by fractionation alone. The process produces little product above C5. 

One possible starting material for the production of Cio alcohols is the above-mentioned Raffinate-2, a C4 feedstock derived from mixed C4 streams of steam crackers. After butadiene has been removed from the mixed stream, Raffinate-1 is obtained. The isobutene content of Raffinate-1 is removed by conversion to MTBE (methyl t-butyl ether), leaving behind a stream rich in mixed butenes which do not react in the MTBE process this is designated Raffinate-2. Accordingly, in the USA and western Europe MTBE plants are the main consumers for Raffinate-2. 

CDTech uses catalytic distillation to convert isobutene and methanol to MTBE, where the simultaneous reaction and fractionation of MTBE reactants and products takes place [51], A block diagram of this process is shown in Figure 3.31. The C4 feed from catalytic crackers undergoes fractionation to extract deleterious nitrogen compounds. It is then mixed with methanol in a BP reactor where 90% of the equilibrium reaction takes place. The reactor effluent is fed to the catalytic distillation (CD) tower where an overall isobutene conversion of 97% is achieved. The catalyst used is a conventional ion-exchange resin. This process selectively removes MTBE from the product to overcome the chemical equilibrium limitation of the reversible reaction. The MTBE product stream is further fiactionated to remove pentanes, which are sent to gasoline blending, whereas the raffinate from the catalytic distillation tower is washed with water and then fractionated to recover the methanol. 

Figure 3.34 shows a schematic of the Ethermax process by Hiils AG and UOP [61]. Feed for the process includes methanol or ethanol and hydrocarbon streams containing reactive tertiary olefins such as isoamylene and isobutylene. Typical hydrocarbon streams are FCC light gasoline, steam cracker C4 hydrocarbons, or product from a butane dehydrogenation unit. In the production of MTBE, the feed first passes through an optional water wash system (1) to remove resin contaminants. The majority of the reaction is carried out in a... 

Feed Olefinic C4 streams from steam cracker or fluid catalytic cracking (FCC) units can be used as feedstock for the recovery of butene-1. 

Mixed C4 streams, containing butadiene, butenes, and butanes, are co-produced in steam-cracking processes. These streams contain valuable components, which can be either processed in situ or extracted purely. A typical composition of a steam-cracker C4 cut is shown in Fig. 3.1. Maximizing its value is a major objective for most petrochemical companies. Therefore, a variety of techniques exists for upgrading the C4 streams by removal of pure C4 components and conversion of low-value streams to higher-value products. 

The iGi stream can be originated from several sources (Peters et al., 2000) ( ) as coproduct of butadiene production from steam cracker C4 fractions, ( ) as product of selective hydrogenation of butadiene in mixed C4 fractions from steam crackers Hi) as iC4 in the C4 fraction of FCC units (iv) as coproduct of the dehydrogenation of isobutane, and (v) as coproduct of dehydration of t-butanol. 

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