Xylene commercial

Per Cent Benzene.—Fraction B contains about 46 per cent of benzene, the rest being toluene and some xylene. Commercially it is termed 50 per cent benzene because 50 per cent of it distils below 100°. Fraction C contains the higher hydrocarbons xylene and mesitylene, etc., and practically no benzene or toluene. If treatment with alkali and acid has not been previously carried out these fractions are now subjected to such treatment to remove phenols and basic compounds and are then again fractionated to obtain the pure hydrocarbons. Most of the phenols are present in fraction D. This fraction is often not collected separately, but becomes part of the residue which is combined with the middle oil. The middle oil contains often as much as 50 per cent of naphthalene, which crystallizes out if the oil is cooled, and is separated by means of a centrifuge. The oil thrown off from the centrifuge yields a little benzene, toluene and... 

Many types of solvents are used in marine eoatings and in their associated cleaning materials as shown in Table 14.26.1. Almost all solvents used at shipyards are VOC and approximately one in three solvents contain HAPs. Of the H APs reported, several are included on the list of 17 high priority chemicals targeted by U.S. EPA for the 33/50 program. These ineluded xylene (commercial), toluene, and the ketones. Commercial grade xylene represents the major portion of the volatile HAPs reported. 

Synthesis of polyoxyethylene sterol was first reported by Scotney and Truter [6] in 1971. They simply mixed cholesterol and the appropriate amount of ethylene oxide in a sealed vial during 4 months. Later workers have applied more sophisticated methods to synthesize better defined products. Khachadurian et al. [7] synthesized both polyoxyethylene and methoxypolyoxyethylene derivatives of cholesterol. The former reaction was carried out in dichloromethane using boron trifluoride as catalyst. Derivatives with a methoxy terminal were prepared by condensing methoxypoly(oxyethylene)methanesulfonate with cholesterol in xylene. Commercially available products are produced by the reaction of sterol with ethylene oxide, resulting in a product with a distribution in the number of ethylene oxide (EO) units in the hydrophilic group. Meissner et al. also described the synthesis of sterol sulfate and sulfonate with oxy-ethylene spacers [8], The synthesis of sterol surfactants has been covered in a review by Folmer [9]. There are only a few producers of polyoxyethylene... 

Commercially, xylene is obtained by the catalytic reforming of naphthenes in the presence of hydrogen see toluene) or was formerly obtained from coal tar. The material so-produced is suitable for use as a solvent or gasoline ingredient, these uses accounting for a large part of xylene consumption. If xylene is required as a chemical, separation into the iso-... 

Hydrazine hydrate of 95-100 per cent, concentration is a commercial product. The 40-60 per cent, solution may be concentrated to 80-85 per cent, strength by distillation with xylene in an all-glass apparatus. 

Decarbonylation of aromatic aldehydes proceeds smoothly[71], Terephthalic acid (86), commercially produced by the oxidation of p-.xylene (85), contains p-formylbenzoic acid (87) as an impurity, which is removed as benzoic acid (88) by Pd-catalyzed decarbonylation at a high temperature. The benzoic acid produced by the decarbonylation can be separated from terephthalic acid (86) based on the solubility difference in water[72]. 

Complex Formation. AH four Cg aromatic isomers have a strong tendency to form several different types of complexes. Complexes with electrophilic agents ate utilized in xylene separation. The formation of the HE-BF —MX complex is the basis of the Mitsubishi Gas—Chemical Company (MGCC) commercial process for MX recovery, discussed herein. Equimolar complexes of MX and HBr (mp — 77°C) and EB and HBr (mp — 103°C) have been reported (32,33). Similatly, HCl complexes undergo rapid formation and decomposition at —80°C (34). 

There are several commercial processes that produce xylenes via disproportionation or transalkylation. These include UOP s Tatoray and PX-Plus,... 

In 1997, UOP announced the PX-Plus process which also uses a selectivated catalyst to convert toluene to para-rich xylenes. Pina commercialized a TDP process known as the (T2PX) process in 1984 (70). It uses a proprietary catalyst to react toluene at 42—48% conversion with selectivities to benzene of 42 wt % and to xylenes of 46 wt %. The xylenes produced are at equiUbrium. Typical commercial operating conditions of 390—495°C, H2 partial pressure of 4.1 Mpa, H2/hydrocarbon molar ratio of 4 1, and LHSV of 1—2/h. Pina s first commercial implementation occurred in 1985 at their Port Arthur refinery. 

Ciyst lliz tion. Low temperature fractional crystallization was the first and for many years the only commercial technique for separating PX from mixed xylenes. As shown in Table 2, PX has a much higher freezing point than the other xylene isomers. Thus, upon cooling, a pure soHd phase of PX crystallizes first. Eventually, upon further cooling, a temperature is reached where soHd crystals of another isomer also form. This is called the eutectic point. PX crystals usually form at about —4° C and the PX-MX eutectic is reached at about —68° C. In commercial practice, PX crystallization is carried out at a temperature just above the eutectic point. At all temperatures above the eutectic point, PX is stiU soluble in the remaining Cg aromatics Hquid solution,... 

MX Separation Process. The Mitsubishi Gas—Chemical Company (MGCC) has commercialized a process for separating and producing high purity MX (104—113). In addition to producing MX, this process gready simplifies the separation of the remaining Cg aromatic isomers. This process is based on the formation of a complex between MX and HF—BF. MX is the most basic xylene and its complex with HF—BF is the most stable. The relative basicities of MX, OX, PX, and EB are 100, 2, 1, and 0.14, respectively. 

The three major commercial Hcensors of xylenes isomerization processes are Engelhard, UOP, and Mobil. Several other companies have developed and used their own catalysts. These companies include Mitsubishi Gas—Chemical, Toray, ICI, Amoco, and Shell. AH of these processes are discussed herein. 

In 1993, UOP commercialized an improved Pt-based catalyst, 1-210. This catalyst is based on a molecular sieve, but not an alurninosihcate zeoHte. UOP claims that yields ate about 10% better than those for 1-9 catalyst. EB to xylenes conversion is about 22—25% with a Cg aromatics per pass loss of about 1.2—1.5%. As discussed below, UOP s Isomar process can also use zeoHte catalysts which convert EB to benzene rather than to xylenes. UOP has hcensed over 40 Isomar units. 

Zeolite and Molecular Sieve-Based Process. Mobil has commercialized several xylene isomerization processes that are based on ZSM-5. Amoco has developed a process based on a medium-pore borosiUcate molecular sieve. 

Mobil s Low Pressure Isomerization Process (MLPI) was developed in the late 1970s (123,124). Two unique features of this process are that it is Operated at low pressures and no hydrogen is used. In this process, EB is converted to benzene and diethylbenzene via disproportionation. The patent beheved to be the basis for the MLPI process (123) discusses the use of H-ZSM-5 zeoHte with an alumina binder. The reaction conditions described are start-of-mn temperatures of 290—380°C, a pressure of 273 kPa and WHSV of 5—8.5/h. The EB conversion is about 25—40% depending on reaction conditions, with xylene losses of 2.5—4%. The PX approach to equiHbrium is about 99 ndash 101%. The first commercial unit was Hcensed in 1978. A total of four commercial plants have been built. 

The majority of xylenes, which are mostly produced by catalytic reforming or petroleum fractions, ate used in motor gasoline (see Gasoline and other MOTORFUELs). The majority of the xylenes that are recovered for petrochemicals use are used to produce PX and OX. PX is the most important commercial isomer. Almost all of the PX is converted to terephthaUc acid and dimethylterephthalate, and then to poly(ethylene terephthalate) for ultimate use in fibers, films, and resins. 

Manufacture. For the commercial production of DPXN (di-/)-xylylene) (3), two principal synthetic routes have been used the direct pyrolysis of -xylene (4, X = Y = H) and the 1,6-Hofmaim elimination of ammonium (HNR3 ) from a quaternary ammonium hydroxide (4, X = H, Y = NR3 ). Most of the routes to DPX share a common strategy PX is generated at a controlled rate in a dilute medium, so that its conversion to dimer is favored over the conversion to polymer. The polymer by-product is of no value because it can neither be recycled nor processed into a commercially useful form. Its formation is minimised by careful attention to process engineering. The chemistry of the direct pyrolysis route is shown in equation 1 ... 

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

Commercial production of acetic acid has been revolutionized in the decade 1978—1988. Butane—naphtha Hquid-phase catalytic oxidation has declined precipitously as methanol [67-56-1] or methyl acetate [79-20-9] carbonylation has become the technology of choice in the world market. By-product acetic acid recovery in other hydrocarbon oxidations, eg, in xylene oxidation to terephthaUc acid and propylene conversion to acryflc acid, has also grown. Production from synthesis gas is increasing and the development of alternative raw materials is under serious consideration following widespread dislocations in the cost of raw material (see Chemurgy). 

The need for a continuous countercurrent process arises because the selectivity of available adsorbents in a number of commercially important separations is not high. In the -xylene system, for instance, if the Hquid around the adsorbent particles contains 1% -xylene, the Hquid in the pores contains about 2% xylene at equiHbrium. Therefore, one stage of contacting cannot provide a good separation, and multistage contacting must be provided in the same way that multiple trays are required in fractionating materials with relatively low volatiHties. 

Such a concept was originally used in a process developed and Hcensed by UOP under the name UOP Sorbex (59,60). Other versions of the SMB system are also used commercially (61). Toray Industries built the Aromax process for the production of -xylene (20,62,63). Illinois Water Treatment and Mitsubishi have commercialized SMB processes for the separation of fmctose from dextrose (64—66). The foUowing discussion is based on the UOP Sorbex process. 

Since 1971 mainly adsorptive separation processes are used to obtain high purity -xylene (55,84—86). A typical commercial process for the separation of -xylene from other Cg aromatics produces about 99.8% purity -xylene at greater than 95% recovery. 

Raw Materials. Eor the first decade of PET manufacture, only DMT could be made sufficiently pure to produce high molecular weight PET. DMT is made by the catalytic air oxidation of -xylene to cmde TA, esterification with methanol, and purification by crystallization and distillation. After about 1965, processes to purify cmde TA by hydrogenation and crystallization became commercial (52) (see Phthalic ACID AND OTHER... 

Large-scale recovery of light oil was commercialized in England, Germany, and the United States toward the end of the nineteenth century (151). Industrial coal-tar production dates from the earliest operation of coal-gas faciUties. The principal bulk commodities derived from coal tar are wood-preserving oils, road tars, industrial pitches, and coke. Naphthalene is obtained from tar oils by crystallization, tar acids are derived by extraction of tar oils with caustic, and tar bases by extraction with sulfuric acid. Coal tars generally contain less than 1% benzene and toluene, and may contain up to 1% xylene. The total U.S. production of BTX from coke-oven operations is insignificant compared to petroleum product consumptions. 

More recently, a commercial process has been introduced for the manufacture of methyl isocyanate (MIC) which involves the dehydrogenation of /V-m ethyl form am i de [123-39-7] in the presence of palladium, platinum [7440-06-4], or mthenium [7440-18-8], at temperatures between 50—300°C (31). Aprotic solvents, such as ben2ene [71-43-2], xylenes, or toluene [108-88-3], may optionally be used. A variation of this synthesis employs stoichiometric amounts of palladium chloride [7647-10-1], PdCl2. 

The first of the benzene polycarboxyUc acids to become a commercial product was phthabc acid, mosdy in the form of the anhydride. The anhydride is obtained by the catalytic vapor-phase air oxidation of o-xylene or naphthalene. The lUPAC name of phthabc anhydride is 1,3-isobenzofurandione... 

Naphthalene (qv) from coal tar continued to be the feedstock of choice ia both the United States and Germany until the late 1950s, when a shortage of naphthalene coupled with the availabihty of xylenes from a burgeoning petrochemical industry forced many companies to use o-xylene [95-47-6] (8). Air oxidation of 90% pure o-xylene to phthaUc anhydride was commercialized ia 1946 (9,10). An advantage of o-xylene is the theoretical yield to phthaUc anhydride of 1.395 kg/kg. With naphthalene, two of the ten carbon atoms are lost to carbon oxide formation and at most a 1.157-kg/kg yield is possible. Although both are suitable feedstocks, o-xylene is overwhelmingly favored. Coal-tar naphthalene is used ia some cases, eg, where it is readily available from coke operations ia steel mills (see Steel). Naphthalene can be produced by hydrodealkylation of substituted naphthalenes from refinery operations (8), but no refinery-produced napthalene is used as feedstock. Alkyl naphthalenes can be converted directiy to phthaUc anhydride, but at low yields (11,12). 

Initial production of the dimethyl terephthalate started with the oxidation of -xylene to terephthaUc acid using nitric acid both companies reportedly used similar technology (43—45). Versions of the nitric acid oxidation process, which has been abandoned commercially, involved the use of air in the initial oxidation step to reduce the consumption of nitric acid (44,46,47). The terephthaUc acid was then esterified with methanol to produce dimethyl terephthalate, which could be purified by distillation to the necessary degree (48). 

Herm/es/Djnamit JS obe/Process. On a worldwide basis, the Hercules Inc./Dynamit Nobel AG process is the dorninant technology for the production of dimethyl terephthalate the chemistry was patented in the 1950s (67—69). Modifications in commercial practice have occurred over the years, with several variations being practiced commercially (70—72). The reaction to dimethyl terephthalate involves four steps, which alternate between liquid-phase oxidation and liquid-phase esterification. Two reactors are used. Eirst, -xylene is oxidized with air to -toluic acid in the oxidation reactor, and the contents are then sent to the second reactor for esterification with methanol to methyl -toluate. The toluate is isolated by distillation and returned to the first reactor where it is further oxidized to monomethyl terephthalate, which is then esterified in the second reactor to dimethyl terephthalate. 

Eigure 3 is a flow diagram which gives an example of the commercial practice of the Dynamit Nobel process (73). -Xylene, air, and catalyst are fed continuously to the oxidation reactor where they are joined with recycle methyl -toluate. Typically, the catalyst is a cobalt salt, but cobalt and manganese are also used in combination. Titanium or other expensive metallurgy is not required because bromine and acetic acid are not used. The oxidation reactor is maintained at 140—180°C and 500—800 kPa (5—8 atm). The heat of reaction is removed by vaporization of water and excess -xylene these are condensed, water is separated, and -xylene is returned continuously (72,74). Cooling coils can also be used (70). 

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