Naphthalene recovery

Coal tar is the traditional feedstock for the recovery of naphthalene. The introduction of new cracking processes in the last decades has given rise to the availability of petroleum-based raw materials. In addition to coal-derived naphthalene, petroleum-derived naphthalene has been recovered since 1961 - predominantly in the USA by deall lation of the residues of ethylene production and of reforming-and cat-cracker fractions which are rich in aromatics. The worldwide production of petroleum-derived naphthalene has been declining in the last decade, representing presently only around 5% of the total, since adequate supplies of coal-based naphthalene are available. 

In other petroleum-derived naphthalene feedstocks of lower aromaticity, such as reforming residues and cat-cracker recycling oils, there is, as a result of their lower aromaticity, a higher proportion of alkylnaphthalenes thus the naphthalene content is not sufficient for direct recovery in an economic manner. Dealkylation processes must therefore be used to increase the concentration of naphthalene. 

---

The economics of naphthalene recovery from coal tar can vary significantly, depending on the particular processiag operation used. A significant factor is the cost of the coal tar. As the price of fuel oil increases, the value of coal tar also increases. The price history of naphthalene from 1975 to 1993 is given in Table 7. 

Light and heavy coal tar oil were applied dermally for the lifespan of mice or until persistent papillomas developed at the application site. Test solutions were applied three times weekly in male and female mice. Both produced skin tumors the light coal tar oil contained benzene, toluene, xylene, solvent naphtha, and was the residual oil drained from a naphthalene recovery operation the heavy coal tar oil was a mixture of creosote, anthracene oils, and the oil drained from the naphthalene recovery operation. The heavy oil was less potent compared to the effects observed in the BaP group of the study. 

Naphthalene and several tar acids are the important products extracted from volatile oils from coal tar. It is necessary to first extract the phenolic compounds from the oils and then to process the phenol-depleted oils for naphthalene recovery. 

Tar acids are produced by the extraction of the oils with aqueous caustic soda at a temperature sufficient to prevent naphthalene from crystallizing. The phenols react with the sodium hydroxide to give the corresponding sodium salts as an aqueous extract known variously as crude sodium phenate, sodium phenolate, sodium carbolate, or sodium cresylate. The extract is separated from the phenol-free oils, which are then taken for naphthalene recovery. 

Approximately 50—55% of the product from a coal-tar refinery is pitch and another 30% is creosote. The remaining 15—20% is the chemical oil, about half of which is naphthalene. Creosote is used as a feedstock for production of carbon black and as a wood preservative. Because of modifications to modem coking processes, tar acids such as phenol and cresyUc acids are contained in coal tar in lower quantity than in the past. To achieve economies of scale, these tar acids are removed from cmde coal tar with a caustic wash and sent to a central processing plant where materials from a number of refiners are combined for recovery. 

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. 

Creosote. In coal-tar refining, the recovery of tar chemicals leaves residual oils, including heavy naphtha, dephenolated carboHc oil, naphthalene drained oil, wash oil, strained anthracene oil, and heavy oil. These are blended to give creosotes conforming to particular specifications. 

Figure 22-8 shows the features of a horizontal center-fed column [Brodie, Au.st. Mech. Chem. Eng. Tran.s., 37 (May 1979)] which has been commercialized for continuous purification of naphthalene and p-dichlorobenzene. Liquid feed enters the column between the hot purifying section and the cold freezing or recovery zone. Ciystals are formed internally by indirect cooling of the melt through the walls of the refining and recovery zones. Residue liquid that has been depleted or product exits from the coldest section of the column. A spiral conveyor controls the transport of solids through the unit. 

An electrostatic precipitator is used to remove more tar from coke oven gas. The tar is then sent to storage. Ammonia liquor is also separated from the tar decanter and sent to wastewater treatment after ammonia recovery. Coke oven gas is further cooled in a final cooler. Naphthalene is removed in a separator on the final cooler. Light oil is then removed from the coke oven gas and is fractionated to recover benzene, toluene, and xylene. Some facilities may include an onsite tar distillation unit. The Claus process is normally used to recover sulfur from coke oven gas. During the coke quenching, handling, and screening operation, coke breeze is produced. The breeze is either reused on site (e.g., in the sinter plant) or sold offsite as a by-product. 

Use vapor recovery systems to prevent air emissions from light oil processing, tar processing, naphthalene processing, and phenol and ammonia recovery processes. 

Metabolites may also play a role in the association of the substrate with humic and fulvic acid components. Two illustrations are given (a) naphth-l-ol, an established fungal metabolite of naphthalene, may play a role in the association of naphthalene with humic material (Burgos et al. 1996) and (b) it has been shown that C-labeled metabolites of [9- C]-anthracene including 2-hydroxyanthracene-3-carboxylate and phthalate were not extractable from soil with acetone or dichloromethane, and required alkaline hydrolysis for their recovery (Richnow et al. 1998). 

Betzemeier et al. (1998) have used f-BuOOH, in the presence of a Pd(II) catalyst bearing perfluorinated ligands using a biphasic system of benzene and bromo perfluoro octane to convert a variety of olefins, such as styrene, p-substituted styrenes, vinyl naphthalene, 1-decene etc. to the corresponding ketone via a Wacker type process. Xia and Fell (1997) have used the Li salt of triphenylphosphine monosulphonic acid, which can be solubilized with methanol. A hydroformylation reaction is conducted and catalyst recovery is facilitated by removal of methanol when filtration or extraction with water can be practised. The aqueous solution can be evaporated and the solid salt can be dissolved in methanol and recycled. 

Benzene releases in byproduct recovery operations Naphthalene residues generated in the final cooling tower Sulfur and sulfur compounds recovered from coke oven gas Wastewater from cleaning and cooling (contains zinc, ammonia still lime, decanter tank tar, or tar distillation residues)... 

K145 residues from naphthalene collection and recovery operations... 

Using an acrylamide-gel as support, Coombe- 0 has demonstrated the quantitative assay of neomycin with a recovery of 96% in the presence of bacitracin and polymixin. In this case quantitation was achieved by densitometry after staining the gel with naphthalene black. 

Until 1959, all the phthalic anhydride was made from coal tar naphthalene, the double-benzene ring compound also shown in Figure 18—3 was easily oxidized directly to phthalic acid. But with phthalic anhydride being only a small share of coal oil, and with the demand for phthalic anhydride escalating rapidly, coal tar became an inadequate source. The frantic search for an alternative route led to the development of the recovery process for ortho-xylene from refinery aromatics streams discussed in Chapter 3 and the... 

SimplePHOX 7a proved a useful tool to force the diastereomeric reduction of olefin 31a to pseudopteroxazole precursor 31b in perfect diastereoselectivity and 90% yield with only trace amounts of over-reduced product. NeoPHOX catalyst from ligand 14b, a closely related system to 7a, furnished product 32b in 93% ee, which was then easily recrystallized to enantiopure material with 58% recovery. The R enantiomer of 33b was synthesized by the use of catalyst from ligand 8a in 90% ee and 98% yield with the fully aromatized naphthalene as 2% byproduct. A higher catalyst loading of 2 mol% of catalyst from 7a was used to produce the... 

Poro-xylene is an industrially important petrochemical. It is the precursor chemical for polyester and polyethylene terephthalate. It usually is found in mixtures containing all three isomers of xylene (ortho-, meta-, para-) as well as ethylbenzene. The isomers are very difficult to separate from each other by conventional distillation because the boiling points are very close. Certain zeoHtes or mol sieves can be used to preferentially adsorb one isomer from a mixture. Suitable desorbents exist which have boiling points much higher or lower than the xylene and displace the adsorbed species. The boihng point difference then allows easy recovery of the xylene isomer from the desorbent by distillation. Because of the basic electronic structure of the benzene ring, adsorptive separations can be used to separate the isomers of famihes of substituted aromatics as weU as substituted naphthalenes. 

Senzaki, T. and Noguchi, K. (1998) Separation and recovery of benzothiopene and naphthalene. Jpn Patent 10255415. 

Quality Assurance/Quality Control. QA/QC measures included field blanks, solvent blanks, method blanks, matrix spikes, and surrogates. Percent recovery was determined using three surrogate compounds (nitrobenzene-d5, 2-fluorobiphenyl, d-terphenyl-diQ and matrix spikes (naphthalene, pyrene, benzo[ghi]perylene) the recoveries ranged from 80 to 102%. Separate calibration models were built for each of the 16 PAHs using internal standards (naphthalene-dg, phenanthrene-dio, perylene-di2). Validation was performed using a contaminated river sediment (SRM 1944) obtained from NIST (Gaithersburg, MD) accuracy was <20% for each of the 16 analytes. 

---