Cyclopentadiene cracking

Aliphatic C-5—C-6. Aliphatic feedstreams are typically composed of C-5 and C-6 paraffins, olefins, and diolefins, the main reactive components being piperylenes cis-[1574-41 -0] and /n j -l,3-pentadiene [2004-70-8f). Other main compounds iaclude substituted C-5 and C-6 olefins such as cyclopentene [142-29-OJ, 2-methyl-2-butene [513-35-9] and 2-methyl-2-pentene [625-27-4J. Isoprene and cyclopentadiene maybe present ia small to moderate quaatities (2—10%). Most steam cracking operatioas are desigaed to remove and purify isoprene from the C-5—C-6 fraction for applications ia mbbers and thermoplastic elastomers. Cyclopentadiene is typically dimerized to dicyclopentadiene (DCPD) and removed from C-5 olefin—diolefin feedstreams duriag fractionation (19). 

Gyclopentadiene/Dicyclopentadiene-Based Petroleum Resins. 1,3-Cyclopentadiene (CPD) is just one of the numerous compounds produced by the steam cracking of petroleum distillates. Due to the fact that DCPD is polymerized relatively easily under thermal conditions without added catalyst, resins produced from cycloaHphatic dienes have become a significant focus of the hydrocarbon resin industry. 

The monomer, CPD, obtained via cracking of the dimer, DCPD, and the dimer both have extensive uses. Cyclopentadiene is probably the most widely studied conjugated, cycHc diolefin system. Eleven review articles dealing with the chemistry of cyclopentadiene have been pubHshed (1—11). An article dealing specifically with European uses of DCPD has also been pubHshed (12). The discovery ia 1951 of stable metal derivatives has given additional impetus to the study of the chemistry of cyclopentadiene. Eive review articles have been pubHshed on this subject (13—17). 

In the United States, Europe, and Japan, DCPD streams of 70—95 wt% purity are available. Estimates of recoverable DCPD production capacity in the United States for 1990 for all grades of DCPD is >127, 000 metric tons (39) and in Europe is 48,000 metric tons (40). The vast majority of this production is from hydrocarbon steam-cracking operations. Based on the total operations, more CPD is produced than indicated above, but because of the relatively small quantities available at a single location, much of the cyclopentadiene caimot be recovered profitably. Important producers in the U.S. are Dow, Exxon, LyondeU, SheU, and Texm ark in Europe, Dow and SheU and in Japan, Nippon Zeon (40). 

Cyclopentadiene was prepared by cracking dicyclopentadiene of 95% purity purchased from Aldrich Chemical Company, Inc. 

A Cj to Cg cracked naphtha cut is heated imder pressure in a soaking drum. Dimers and codimers of cyclopentadiene, methylcyciopentadiene, and isoprone are formed. This is followed by distillation, leaving a dimer concentrate bottoms. 

Since the equilibrium lies to the left at higher temperatures, cyclopentadiene can be obtained by thermolytic cleavage of the dimer and distilling the monomer prior to use (cracking distillation). 

The use of cyclopentadiene as a diene provides a route to the [2.2.1]bicycloheptane skeleton, which is of considerable theoretical interest. Cyclopentadiene, however, exists as its Diels-Alder dimer at room temperature and must be cracked thermally to... 

Transpolypentamer (TPR) is produced by the ring cleavage of cyclopentene. Cyclopentene is obtained from cracked naphtha or gas oil, which contain small amounts of cyclopentene, cyclopentadiene, and... 

ENB is normally prepared in a two-step process (Scheme 9.5). The first step involves in situ cracking of dicyclopentadiene to cyclopentadiene, and... 

Several different companies have greened various steps of the process. In VNB production by-products come from competing Diels-Alder reactions and polymerization, largely of cyclopentadiene. The reaction is usually carried out in a continuous tube reactor, but this results in fouling, due to polymerization, at the front end, where the dicyclopentadiene is cracked to cyclopentadiene at temperatures over 175 °C. Whilst fouling does not have a very significant effect on yield, over time it builds up. 

Dicyclopentadiene is the Diels-Alder reaction dimer of cyclopentadiene. It is the thermodynamically stable form of cyclopentadiene at room temperature, and is also a byproduct in the olefin cracking process. Industrially, it is isolated by distillation, and currently is readily available in North America. 

Cycloalkanes may be pyrolized in a manner similar to that for alicyclic alkanes. Cyclopentane, for instance, yields methane, ethane, propane, ethylene, propylene, cyclopentadiene, and hydrogen at 575°C. Analogous to cracking of alicyclic alkanes, the reaction proceeds by abstraction of a hydrogen atom followed by p scission. The cyclopentyl radical may undergo successive hydrogen abstractions to form cyclopentadiene. 

Diels-Alder reactions like the one illustrated opposite are cycloadditions mobilising six electrons. The dimerization of cyclopentadiene 1.1 is another Diels-Alder reaction, but also illustrates its inherent reversibility—cracking the dimer 1.2 on heating is called a retro-cycloaddition or a cycloreversion. 

For preparation of cyclopentadiene from the dimer, see G. Wilkinson, Org. Syntheses, 36, 31 (1956). The dicyclopenta-diene used as starting material was dried by passage through a 1 x 12-in. column of activated alumina prior to cracking. 

Gasoline hydrorefining is applied to remove polymerizable by-products (isoprene, cyclopentadiene, styrene and indene) from stream-cracked gasoline to prevent gum formation. Partial hydrogenation of dienes to monoalkenes and the hydrogenation of... 

For the preparation of poly(isoprene), the monomer 2-methyl-1,3-buta-diene (= isoprene = IP) is required as feedstock. This monomer can be obtained by various condensation methods that utilize four principles to create the C5 skeleton. In the more modern process IP is obtained from the C5 cracking fraction which contains various double-bond containing hydrocarbons with 5 C-atoms (e.g. among other C5-compounds the fraction contains cyclopentadiene, various pentadienes and pentenes) [478]. The preparation of pure IP by either of these two routes is cost intensive. By the direct and selective polymerization of IP in the crude C5 cracking fraction the cost intensive isolation of pure IP is avoided. Thereby production costs for IR are considerably reduced [264,265]. The selective polymerization of IP in the crude C5 cracking fraction is achieved by the application of a NdP-based catalyst system. The latest patent of Michehn claims a process in which dehydrogenation of the C5 cut is applied prior to polymerization. In this way an IP-enriched C5-fraction is obtained which does not contain a high quantity of disubstituted alkynes, terminal alkynes and cyclopentadiene. The unpurified C5-fraction is used as the feedstock for polymerization [591,592]. 

Cyclopentadiene is a product of petroleum cracking. It dimerizes exothermically in a Diels-Alder reaction to dicyclopentadiene, which is a convenient form for storage and transport. Dicyclopentadiene plus cyclopentadiene demand in the United States amounted to 270 million lb in 1998. 

Ethylene and propylene are produced primarily by the cracking of naphtha. They also are available from the fractionation of natural gas. Ethylidene norbornene is produced by reacting butadiene with cyclopentadiene. 1,4 Hexadiene is produced from butadiene and ethylene. Dicyclopentadiene is obtained as a by-product from the cracking of heavy feedstocks to produce ethylene. 

Monomeric 1,3-cyclopentadiene is obtained by the thermal cracking of cyclopentadiene dimer which is heated at about 150° in a nitrogen atmosphere in a distillation apparatus with a water-jacketed condenser. The fraction which boils below 44° is collected at 0° and is then degassed and stored in vacuo at — 78°. ... 

The procedure for preparing the dry salt, K[C5H4(CH3)], is identical with that previously described in Sec. A for K[C5H5], except that methylcyclo-pentadiene (1.210 g, 15.1 mmol) is used in place of the 1,3-cyclopentadiene. Methylcyclopentadiene (isomer mixture) is obtained from the thermal cracking at 200° of commercially available methylcyclopentadiene dimer.4 The fraction distilling between 73 and 75° is collected at 0°. The distillate is then redistilled under nitrogen at atmospheric pressure, collected at 0°, and stored at — 78° in vacuo after degassing. 

---