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UDC 541.1.17.541.128.43.544.4
CURRENT STATE OF CATALYTIC OXIDATION OF ALKYLAROMATIC CHLOROHYDROCARBONS AND ITS DEVELOPMENT PROSPECTS
A.C.Efendi, E.M.Babayev, F.A.Yunisova, B.A.ismayilova, N.Aykan
M.Nagiev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
[email protected] Received 29.02.2016
The study of synthesizing alkylaromatic chlorohydrocarbons, as well as current state of their catalytic oxidation is considered. The posibility of catalytic oxidation of chlorotoluenes in the presence of varie-tyheterogeneous catalytic systems was shown. The effects of active components, reaction time and reaction temperature on the performance of catalysts were also investigated. The appropriate optimum reaction condition for the activity and selectivity for received catalysts was designated and under that condition the highest value of conversion chlorotoluenes was determined. Meanwhile, to neutralize ecological harmful substance very important greener and safer raw materials (benzaldehydes, maleic anhydride and their chloro analogues) have been also obtained.
Keywords: catalytic oxidation, chlorotoluenes, maleic anhydride, chlorobenzaldehyde, chloromaleic anhydrides, solid catalysts.
Introduction
Rapid development of petrochemical industry, especially derivation and conversion processes of hydrocarbons and their chloric analogues cause increasing the quantity of environmental pollutions. In the article the sources, structures, properties, analysis methods and environmental fate including bioaccumulation and toxicity studies of some groups of alkylaromatic chlorohydrocarbons are reviewed [1-3]. Chlorinated hydrocarbons comprise a large spectrum of compounds that are of enormous industrial and economic importance because of their applications and global outputs. They are used as pesticide, herbicide, industrial solvents, dielectric liquids, antimicrobial substances [4-7]. Apart from the common feature of having one or more covalent bound chlorine atoms, these compounds show a complex diversity of behaviour that is primarily characterized by their aliphatic or aromatic character and the presence of other functional groups. Nevertheless, the introduction of chlorine atom(s) into a hydrocarbon significantly influences its physicochemical and biochemical properties and the tendency to bioaccumulation and environmental persistence. Acting in combination with possible (eco) toxicological effects, these properties have pushed the chloro-chemistry into the focus of considerable debate and governmental regulatory action [8].
Protecting environment from the polluting with these compounds and their harm to human organism presents the issue of ecological importance [9, 10]. Therefore, different kinds of research have been devoted to this issue over the entire world [1, 2, 11-13]. For instance it was shown that sediments of the Spittelwasser creek are highly polluted with organic compounds and heavy metals due to the discharge of untreated wast waters from the industrial region of Bitterfeld-Wolfen (Germany) in the course of more than one century [13]. However, relatively few data have been published about the chlo-roorganic contamination of the sediment. Different (chloro)organic compounds with special emphasis on polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), and chloroben-zenes have been reported. Existing concepts for the remediation of Spittelwasser sediment include the investigation of natural attenuation processes, which largely depend on the presence of an intact microbial food web. In order to gain more insight into terms of biological activity, an analysis was made of the capacity of microflora sediment to degrade organic matter by measuring the activities of extracellular hy-drolytic enzymes involved in the biogeochemi-cal cycling of carbon, nitrogen, phosphorus and sulphur. Furthermore, the detection of physiologically active bacteria in the sediment, partic-
ularly of those known for their capability to re-ductively dehalogenate organochlorine compounds, illustrates the potential for intrinsic bio-remediation processes.
In China the occurrence of persistent toxic substances (PTS) over the entire world and possibly their disposal was studied. Organochlo-rines in atmospheric gas-phase and particular matter were collected by high-volume sampling (filters and polyurethane foams) and used GC methods. The samples were analysed for 9 persistent organic pollutants (POPs) regulated under the global POP convention, namely aldrin, chlordane (cis- and trans-isomers cC and tC), di-chlorodiphenyltrichloroethane (DDT) and metabolites (o,p'-DDT, p,p'-dichlorodiphenyldichloro-ethane (p,p'-DDD) and pp'-diclorodiphenyldi-chloroethylene (pp'-DDE), dieldrin, endrin, hep-tachlor, hexachlorobenzene (HCB), mirex and polychlorinatedbiphenyl (PCB) (congeries number 28, 52, 101, 153 and 180), and for hexachlo-rocyclohexane (HCH a-, P- and y-isomers), a PTS and now considered for regulation under the convention, too. At the coastal site additionally o,p'-DDE and -DDD, P-endosulfan, iso-drin, heptachlorepoxide and 5-HCH, and on the island site additionally p ,p '-DDT and 12 additional PCB congeners were analysed. The mean concentrations of DDT and its metabolites, HCB, HCH, and PCB at the coast were in the 100-1000 pg/m range. Higher concentrations prevailed during night-time. The currently used pesticides mirex and chlordane were found at elevated levels, i.e. 79 (6.6-255) and 36 (<6-71) pg/m3, respectively, at the coast but not over the island. The POPs pesticides aldrin, dieldrin and endrin, never registered in China, were mostly found at <10 pg/m except for endrin at the coastal site (up to 400 pg/m3) and aldrin on the island site (up to 50 pg/m ) [11]. One more research was carried out by the ZHANG [2] with his team. There were collected solid samples for analysis of 13 polychlorinated biphenyls (PCBs) in order to assess the levels of pollution, sources, area distribution, and potential risk for the environment. All methods were rigorously tested and an adequate quality control was ensured. Only one site had no PCBs residues, and the
highest total PCBs concentration in the surface soils was 32.83 ng/g. The average concentrations in the entire soil sample were 4.13 ng/g, signalling low-level pollution. Tetra-, penta-, and hexachlorinated biphenyls were dominant species in soil samples, accounting for more than 75% of £PCBs in the soil samples. PCB 118 was the most abundant congener in all the samples. The PCB 118 was about 20% of £PCBs. The soil organic matter content showed only a weak correlation with the levels of all PCB congeners, in which a better correlation was noted for the more volatile lighter PCB congeners than for the heavier homologues. To a certain extent, the sources and land use seemed to influence the levels of PCBs [2].
PAHs and PCBs were measured in the mussel Perumytiluspurpuratus (Lamarck) collected from three different sites along the coast of Valdivia and Valparaiso, South-Central and Central Chile, respectively. Pollution at these sites is considered low with PAHs originating mainly from pyrolytic sources according to the phenanthrene/anthracene and fluoranthene/py-rene ratios. Temporal variation of polycyclic aromatic hydrocarbons (PAHs) was observed in Valdivia, while site variation was observed along the Valparaiso area. Total PAH concentrations in Valdivia ranged from 29.2 to 89.5 ng/g in 2001 and from 31.0 to 48.6 ng/g in 2002 while in Valparaiso samples the total PAHs ranged from 27.3 to 253.1 ng/g and from 12.1 to 26.3 ng/g in 2001 and 2002, respectively [14]. Polychlorinated biphenyls were not found in mussels from Valdivia; however five non-planar congeners were detected in samples from Valparaiso with total concentrations between 1.0 and 16.6 ng/g in 2001 and between 3.4 and 29.0 ng/g in 2002. The pesticide heptachlor epoxide was detected in all sampling sites of Valdivia during the years 2001-2002 at concentrations ranging between 1 and 3.5 ng/g.
POP contamination of US food by measuring perfluorinated compounds (PFCs), orga-nochlorine pesticides, and PCBs in composite food samples was studied in [15], the results about meat, fish vegetable samples were shown respectively in a the Table 1, Figure 1.
Table 1. Levels of PCBs, polyfluorinated compaynds PFCs, and organochlorine pesticides in composite meat samples [ng/g wwxxxx or LOD]_
Marker Hamburger Bacon Sliced turkey Sausages Ham Sliced chicken breast Roast beef Canned Chili
Lipid percent 21.70 36.10 2.00 23.90 4.30 4.70 4.60 9.10
PCB-52 ND(0.1) ND(0.09) ND(0.04) ND(0.1) ND(0.05) ND(0.05) ND(0.04) nd(0.03)
PCB-101 ND(0.4) ND(0.3) ND(0.1) ND(0.4) ND(0.2) ND(0.2) ND(0.1) ND(0.09)
PCB-118 ND(0.2) ND(0.1) ND(0.06) ND(0.2) ND(0.07) ND(0.08) ND(0.09) ND(0.05)
PCB-153 1.2 ND(0.4) ND(0.2) ND(0.5) ND(0.2) ND(0.3) ND(0.2) ND(0.2)
PCB-138 ND(0.7) ND(0.4) ND(0.2) ND(0.6) ND(0.2) ND(0.3) ND(0.2) ND(0.2)
PCB-108 0.21 ND(0.10) ND(0.04) ND(0.1) ND(0.04) ND(0.06) ND(0.05) ND(0.4)
PFOA* 0.15 0.24 ND(0.02) 0.09 0.02 0.02 ND(0.02) ND(0.01)
PFBS** ND(0.04) ND(0.05) ND(0.02) ND(0.04) ND(0.02) ND(0.02) ND(0.02) ND(0.01)
PFHS*** ND(0.04) ND(0.05) ND(0.02) ND(0.04) ND(0.02) ND(0.02) ND(0.02) ND(0.01)
a-HCH ND(0.08) ND(0.03) ND(0.01) ND(0.03) ND(0.01) ND(0.01) ND(0.01) ND(0.01)
P-HCH ND(0.09) ND(0.03) ND(0.01) ND(0.03) ND(0.02) ND(0.01) ND(0.02) ND(0.01)
p,p-DDT 0.08 ND(0.06) ND(0.01) 0.17 ND(0.02) ND(0.01) ND(0.01) ND(0.01)
p,p-DDE 1.12 0.16 ND(0.03) 0.42 ND(0.04) ND(0.02) 0.28 ND(0.01)
o,p-DDD ND(0.03) ND(0.03) ND(0.01) ND(0.03) ND(0.01) ND(0.01) ND(0.01) ND(0.01)
p,p-DDD 0.053 ND(0.06) ND(0.01) 0.037 ND(0.02) ND(0.01) ND(0.03) ND(0.01)
Dieldrin 0.17 0.12 ND(0.02) 0.031 ND(0.02) ND(0.01) ND(0.02) ND(0.01)
Endosulfansulphate 0.17 ND(0.08) ND(0.03) ND(0.07) ND(0.03) ND(0.03) ND(0.03) ND(0.01)
Toxaphene-26 ND(0.2) ND(0.08) ND(0.04) ND(0.08) ND(0.04) ND(0.04) ND(0.04) ND(0.01)
Toxaphene-50 ND(0.2) ND(0.1) ND(0.07) ND(0.1) ND(0.06) ND(0.07) ND(0.07) ND(0.01)
a-Chlordane ND(0.04) ND(0.03) ND(0.01) ND(0.03) ND(0.01) ND(0.01) ND(0.01) ND(0.01)
Oxychlordane ND(0.2) ND(0.04) ND(0.03) ND(0.04) ND(0.03) ND(0.02) ND(0.04) ND(0.01)
trans-Nanochlor 0.05 ND(0.03) ND(0.01) ND(0.03) ND(0.01) ND(0.01) ND(0.01) ND(0.01)
c/s-Heptachlor epoxide 0.07 ND(0.03) ND(0.01) 0.052 ND(0.01) ND(0.01) ND(0.03) ND(0.01)
Pentachlorbenzene 0.06 ND(0.03) ND(0.02) ND(0.03) ND(0.02) ND(0.01) ND(0.02) ND(0.01)
Hexachlorbenzene 0.18 ND(0.1) ND(0.04) ND(0.1) ND(0.05) ND(0.03) ND(0.08) ND(0.01)
ND - practically not detected (literary data); LOD - limits of detection, * - perflyorooctanoic acid, ** - perfluorobutane sulfonate, *** - perfluorohexane sulfonic, wwxxxx - wet weight.
Fig. 1. Estimation of per capita dietary exposure to pesticides, PCBs, and PFOA using 2007 USDA food availability data, for all ages, estimating values below the LOD as zero. HCHs: a-HCH, P-HCH, 5-HCH, y-HCH, e-HCH; DDTs: op-DDT, pp -DDT, op-DDE, p,p -DDE, op-DDD, p,p -DDD; endosulfans: a-, p-endosulfane, endosulfanesulfate; toxaphenes: toxaphene-26, toxaphene-50, toxaphene-62; aldrins: aldrin, dieldrin; endrin heptachlors: heptachlor, cis-heptachlor epoxide, trans-heptachlor epoxide, transnonachlor; chlordanes: a-chlordane, p-chlordane, oxychlordane; chlorobenzenes: pentachlorobenzene, hexachlorobenzene; PCBs: PCB-28, PCB-52, PCB-101, PCB-118, PCB-138, PCB-153, PCB-150.
According to their noteworthy fuse behaviours in fats, lipids and organic solvents they are able to be bioaccumulated. Even a small quantity of them has toxic cancerous effects on organism. Their stability for chemical and biological changes gives them wide-spread ability. Due to these facts the production of these chemicals were declared prohibited by the International Global Convention in Stockholm on 23 May 2002. Although this argument it had manufactured approximately 2 million tons of polychlorinated biphenyls. In this order, diben-zo-p-dioxin, alderin, dialderin, DDT (dichlorodi-phenyltrichloroethane), hexachlorobenzene, tok-safen, chlorbutadienes and etc. can be shown. Notwithstanding, they are aimed for agricultural purpose most of them under different names in USA (Aerochlors), Japan (Kenachlor), Germany (Chlorofan), France (Phenochlor), Russia (Sovol, Sovtol), Italy (Phenchlor) are widely used as industrial substances, such as condenser oil, dielectric liquids in transformer, plastifi-cators, elastomers in the production of hydraulic liquids, lubricating oils, varnishes, glues [6, 7, 16-21].
Nowadays, variety of methods are utilised for their disposal. As a consequence, production and application of these compounds was banned. However, methods had to be developed not only to dispose materials that contain these substances, but also to remedy the numerous contaminated sites [22]. Although numerous bacteria capable of degrading environmental pollutants have been isolated, characterized and used in bioremediation processes, many compounds of environmental concern such as PCBs, dioxins, and explosives are still hardly biodegradable as well as are very harmful, immiscible in water, incombustible, thermo-, acid-, alkali-stable. The emerging methodologies of genetic engineering, although considered as highly promising for the construction of "superbugs," largely failed to create the requested recombinant hyper degraders with catabolically enzymes exhibiting novel and/or highly improved features, apart from very few exceptions. The so-called peripheral sequences of the oxidative degradation of chloroaromatic compounds in
aerobic bacteria yield central intermediates with a diphenolic structure such as catechols or hy-droxybenzoquinols. These compounds are subsequently cleaved by enzymes that use molecular oxygen and further metabolized by central pathway sequences. The broad variety of mechanisms resulting in dechlorination that occur in these peripheral or central sequences is specifically discussed [23, 24].
Studies devoted to the eco-friendly disposal of hazardous organic substances (OS) and waste through oxidation in supercritical water (SCW) are reviewed by Fedyaeva [12]. One advantage of using SCW is the possibility of complete and rapid oxidation of OS in closed systems. The oxidation rate is determined by the temperature, proportions between the reagents, bond dissociation energies, and solubility of OS in SCW, decreasing in the series aliphatic > aromatic, heterocyclic >polyaromatic compounds. The main oxidation products are carbon dioxide, nitrogen, and water; sulfur, phosphorus, and halogens are converted into the respective mineral acids. There are a number of difficulties in the implementation of particular processes on the industrial scale, which impede the achievement of an acceptable performance of installations in terms of safety and stability. These difficulties are mainly associated with heterogeneous processes on the reactor walls, such as the corrosion of constructional materials and deposition of salts, which lead with time to changes in the kinetic characteristic of the main and coupled reactions.
Catalytic oxidative conversion of mono-chlorotoluenes
It should be noted that infinite-small mole concentration of alkylaromatic chlorohydrocar-bons (10-1-10-2 mol/l) make their counteraction more difficult, and nearly impossible to effect-tuate the disposal with available methods. It will be purposeful both neutralization of them and the use of rewarding raw materials in chemical industry. Likewise synthesizing necessary inoffensive compounds such as aldehydes, anhydrides, acids and ketenes is too prior issue. The majority of the classical methods to produce those yields from the corresponding chloro-
aromatic hydrocarbons don't follow sustainable chemistry principles [14, 25-27]. Consequently, in the recent decades the aim of the research in this field has been the development of solid catalysts for the selective oxidation of chlorinated alkyl aromatic hydrocarbons in liquid or in gas phase in order to replace aforementioned classical methods by other which are simpler and cause low environmental pollution.
Chlorinated benzenes and toluenes obtained during the decomposition of polychlorin-ated aromatic hydrocarbons are also toxic and harmful compounds. There are several methods for the derivation and conversion of chloroben-zenes and chlorotoluenes [28-37]. One of supposed reaction mechanism was shown [36]:
CH3
CHO
Laccase, ABTS
pH=4.5, 1-2 hrs, Troom, convers. >90%
Cases: X=Y=Z=H; X=F/Cl, Y=Z=H; X=H, Y=NO2/Cl, Z=H; X=Y=H, Z= NO2/F/Cl.
A strain Rhodococcus specialized OCT 10 DSM 45596T, exhibiting 99.9% of 16S re-combinated dezoxinucleic acid (rDNA) identity with Rhodococcus wratislaviensis NCIMB 13082, was isolated from a soil sample. The strain completely mineralised 2-chlorotoluene, 2-bromotoluene, o-xylene, benzyl alcohol and benzoate. In contrast, 2-fluorotoluene was only partially mineralised. By GC-MS and NMR 1H analyses, 4-chloro-3-methylcatechol was identified as the central intermediate in the degradation pathway of 2-chlorotoluene. It was further degraded by enzymes of the meta-cleavage pathway. Catechol 1,2-dioxygenase and chloro-catechol 1,2-dioxygenase as the initial enzymes of the ortho-cleavage pathways were not detectable under these conditions. Furthermore, neither formation nor oxidation of 2-chlorobenzylic alcohol, 2-chlorobenzaldehyde, or 2-chloroben-zoate was observed, thereby excluding side chain oxidation activity [38].
The results of investigations into the processes involved in the heterogeneous catalytic oxidation of benzene and its derivatives at the
L.V.Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, are summarized. The mechanisms of the full and partial oxidation of benzene, toluene, and their halogen derivatives are discussed [35].
Liquid phase oxidation of para-chloro-toluene (PCT) with aqueous H2O2 had been investigated [25, 26] in the presence of vanadium silicates - VS-1 (MFI) and VS-2 (MEL). Vanadium impregnated silicalite-1 (V/Si-1) and sili-calite-2 (V/Si-2) were also included for comparison. Under identical conditions, VS-1 was considerably more active for PCT conversion than the others, however, VS-1 and VS-2 were found to be comparable for the selective formation ofpara-chlorobenzaldehyde (p-ClBZD). The effects of reaction time, Si/V molar ratio, catalyst concentration, reaction temperature and H2O2/PCT molar ratio were examined during the catalyst performance in order to optimize the conversion of PCT and selectivity forp-ClBZD. The conversion of PCT using VS-1 was increased significantly with the increase in reaction time, catalyst concentration, reaction temperature and H2O2/PCT molar ratios, however, an increase in the Si/V molar ratio of VS-1 lowered the PCT conversion and increased slightly the selectivity for p-ClBZD. A selectivity of the order of >64.0% to p-ClBZD was obtained at 13.4 wt. % conversion of PCT at 373 K. After the separation of the catalyst during the reaction from the reaction mixture, the product formation was not noticed. Recycling of the catalyst showed that the deactivation of the catalyst VS-1 was related to the stability of the vanadium ions in the framework of VS-1. The reaction pathway from PCT to p-ClBZD was thought to be via formation of para-chloro-benzyl alcohol (p-ClBZA) and proceeds probably through a homolytic mechanism.
Manganese-containing MFI-type Mn-ZSM-5 zeolites were prepared and characterized by XRD, UV-vis DRS, SEM, XPS, N2 adsorption-desorption, NH3-TPD and ICP-AES techniques. The zeolites show high catalytic activity and selectivity in the heterogeneous oxidation ofp-chlorotoluene to p-chlorobenzal-dehyde reported [27].The effects of catalyst
X
X
Y
Y
Z
Z
concentration, water addition, HBr amount, as well as reaction time and temperature of a product yield were investigated. Under the optimized conditions (catalyst 20 mg, p-chlo-rotoluene 1 mL, solvent (acetic acid) 10 mL, HBr (40 wt.%) 30 mg, H2O 3 g, oxygen flow rate 50 mL/min, time 8 h, temperature 1000C),
the Mn-ZSM-5 (Si/Mn = 48, Mn 1.7 wt.%) catalyst showed p-chlorotoluene conversion of 93.8% and p-chlorobenzaldehyde selectivity of 90.5%. The excellent catalytic activity can be attributed to the distribution of Mn species and the mild acid sites. Supposed reaction layout is given as follows:
CH
Cat. HBr
(1)
Br I
CH2
(2)
(6)
HO—CH
2
H2O
-HBr
[O]
O
CH
CH
HOAc
(4)
OAc
[O]
(5)
[O]
(7)
X-PhCH3 + [Mn(III)Br]2 -^ X-PhCH2Br +
X - halogen
Bismuth incorporated MCM-41 mesopo-rous samples were synthesized and catalysed the selective oxidation of 4-chlorotoluene efficiently even on a large scale with H2O2 as oxidant in acetonitrile [39]. Reported no bismuth was detected by ICP in the condensed reaction mother liquid, and the recycle test proved that the catalyst was stable.
Excell synthesis of o-chlorobenzaldehyde from o-chlorotoluene was carried out [40] using
3+
Mn in sulphuric acid as a mediator. Reaction conditions were optimized to obtain maximum oxidation efficiency for the aldehyde. Reuse of the spent mediator required its regeneration; however, these results were in low current efficiency.
A novel method for the catalytic oxidation of o-chlorotoluene (OCT) to o-chlorobenzaldehyde (CBD) was proposed using vanadium doped anatasemesoporous TiO2 (V/MTiO2), the catalytic reaction conditions were investigated [41]. Under the optimum catalytic reaction conditions: 10 mL of acetic acid 1000C of reaction temperature, 10 h of reaction time and 100 mg
[Mn(II)]2 (1)
of catalyst, the conversion rate of OCT could reach 95.3%, with a selectivity of 63.5%.
Photolyses of p-, m- and o-chlorotoluene in methanol gave formation quantum yields of methylanisoles of the order of 10-2, which are substantially smaller than those for chloroben-zene. The values for the para- and ortho-isomers are smaller than thase for the metal isomer. This result explained [42] in terms of the effect of the methyl substituent, which induces negative charges at the o- and p-positions. The effect of biacetyl addition was also examined and the results indicated that the triplet route is significant, as in the case of chlorobenzene. However, about half the methylanisole was formed without any dependence on the biacetyl concentration, indicating the presence of an intermediate state with a very short lifetime.
Liquid-phase selective oxidation of p-chlo-rotoluene has been investigated [37, 43-46]. The oxidation process catalyzed by Co/Mn/Br with molecular oxygen under atmospheric pressure was studied [37]. Acetic acid-water was used as the reaction medium in place of the commonly
used pure acetic acid, which inhibited the further oxidation of p-chlorobenzaldehyde and enhanced the selectivity. Moreover, it is advantageous to use acetic acid-water as the reaction medium because water is a product of the reaction and the separation of the acetic acid-water mixture thus formed is a difficult and uneconomic process. The effects of the initial water concentration, Co/Mn and Br/(Co+Mn) mole ratios, amount of the catalyst, p-chlorotoluene/ solvent volume ratio, reaction temperature, reaction time, and oxygen flow rate were investigated. The optimum reaction conditions were as follows: initial water concentration of the solvent in 10 wt.%, Co/Mn mole ratio of 0.67, Br/(Co+Mn) mole ratio 0.4, amount of the catalyst accounting for 4 wt.% of the substrate, p-chlorotoluene/solvent volume ratio 1.5, reaction temperature 1060C, reaction time 10 h, and the oxygen flow rate 10 mL/min. Under these conditions, a 14.3% yield of p-chlorobenzalde-hyde was obtained at 19.7% conversion of p-chlorotoluene with 72.4% selectivity.
The adsorption and oxidation ofp-chlo-rotoluene (PCT), p-methoxytoluene (PMT), and toluene on vanadyl pyrophosphate catalyst (VPP) were studied by in situ FTIR and EPR spectroscopy. Various amounts of strongly adsorbed ben-zaldehydes and cyclic anhydride species were observed by FTIR in dependence on the different educts after oxidation experiments. The extent of spin-spin exchange perturbation and, thus, the loss of the EPR signal intensity caused by substrate adsorption and interaction is influenced by the nature of the aromatic compound. The strength of reactant and product adsorption on the catalyst surface was found to be an important selectivity-limiting factor in the aldehyde formation. The benzaldehyde adsorption is enhanced by additional interaction of the carbonyl group with Br0nsted acid hydroxyl groups generated during oxidation reaction, which facilitates deeper oxidation. The co-adsorption of pyridine is one possibility to suppress the strong aldehyde adsorption and to improve the selectivities. Yields of benzal-dehydes and selectivities at constant conversion increase in the order PMT<toluene<PCT. Strong product adsorption favored by electron donating p-substituents causes total oxidation leading to lower aldehyde selectivities. Both the acid/ba-
sic characters of the reactants and products and their steric properties play an important role for adsorption/desorption processes [47].
The oxidations of p- and w-chlorotoluene are summarized in Table 2. The p-chloro-substi-tuted substrate, p-chlorotoluene, is much more reactive than the w-chloro-substituted counterpart [64].
Table 2. Gas-phase O2 oxidations of p- and w-chloro-toluenes, catalyst - CVD Fe/Mo/DBH_
Substrate ^-Chlorotoluene m-Chlorotoluene
Temperature (0C) 350 375 400 350 400 450
Conversion, (%) 33.7 54.4 76.5 8.2 15.8 33.2
Product selectivity, (%)
pCBA 59.4 53.4 42.3 - 24.0 26.9 38.1
mCBA 0.3 0.2 0.1 - 35.2 17.8 7.8
CB 1.4 2.4 4.1 - 18.4 9.7 5.3
MA 12.2 15.6 16.1 - 8.3 9.1 5.3
CO 6.8 7.8 11.1 - - 11.4 14.6
CO2 19.2 20.0 25.9 14.2 25.3 27.9 -
^CBA: ^-chlorobenzaldehyde, mCBA: m-chloroben-zaldehyde, CB: chlorobenzene, MA: maleic anhydride.
Degradation of toluene and 4-chloroto-luene in air mixture was studied by using electron beam generated plasma reactor. It was found that removal efficiency of toluene and 4-chlorotoluene was influenced by radiation dose, i.e. energy deposited in the gas, and their initial concentration. The by-products formed as a result of degradation of toluene or 4-chlorotoluene under electron beam radiation were identified [48]. The mechanism of their degradation was proposed. ^OH radicals play a main role in degradation process of toluene or 4-chlorotoluene. For degradation of 4-chlorotoluene, reaction of ^OH radicals with 4-chlorotoluene by hydrogen abstraction from the methyl group, followed by peroxyl radical formation, is a main reaction pathway. 4-chlorobenzaldehyde and 4-chlorobenzyl alcohol are formed according to the Russel-mechanism. For degradation of toluene, reaction pathway of ^OH radicals with toluene by hydrogen abstraction from the methyl group plays an important role. Besides it, there are the other two important reaction routes. One is reaction of ^OH radical addition and H atom abstraction from benzene ring; the other is ^OH-adduct reaction. Cresol, nitrotoluene and ring cleavage products are formed from these two reaction pathways. Since Cl is more electronegative than H, H atom abstraction from -CH3 by OH radicals from toluene (HC6H4CH3) is easier than
from 4-chlorotoluene (ClC6H4CH3), this may explain why the decomposition efficiency of toluene is slightly higher than that of 4-chlorotoluene in an air mixture under EB radiation.
Catalytic oxidations of dichlorotoluenes
Catalytic oxidation of 2,4-dichlorotoluene in the presence of cobalt stearate as a catalyst to 2,4-dichlorobenzoic acid was carried out [49]. The findings have led to the conclusion that 2,4-dichlorotoluene oxidation is kinetically regular. The procedure may be recommended for controlling the quantity of 2,4-dichlorobenzoic acid as a major drug manufacture intermediate.
Ammoxidation of 2,6-dichlorotoluene to 2,6-dichlorobenzonitrile is indeed an industrially important reaction for producing various commercially useful chemicals. In this contribution, differences in the catalytic performance of bulk, supported and promoted VPO samples are described in [50, 51]. The kinetics of the vapour-phase ammoxidation of 2,6-dichlorotoluene (DCT) to 2,6-dichlorobenzonitrile (DCBN) over a vanadium phosphorus oxide (VPO) catalyst was investigated. The main focus is on developing a mathematical model to describe the reaction kinetics of ammoxidation of DCT in a non-isothermal fixed-bed lab-scale reactor. The effect on catalytic performance of various operating parameters, including reaction temperature and contact time, as well as of DCT, NH3, O2, and H2O partial pressures, were studied. The experimental kinetic data obtained under noni-sothermal conditions were correlated by the rate equations based on the Langmuir-Hinshelwood mechanism. The derived kinetic model was validated by comparing experimental results obtained in up-scaled experiments from a miniplant with that of simulated results. The simulated values of various parameters, including the conversions of DCT and O2 and even the yields of DCBN and COX, agree well with those of experimentally measured values.The choice of P/V ratio was found to play a key role on the catalytic properties of the catalysts. Activity is observed to decrease with increase in P/V ratio of the catalysts. About 55% (Y) yield of DCBN and ca. 95% conversion (X) of DCT is obtained
over bulk VPO solids having low P/V ratios (<1). However, the catalytic performance of these bulk VPO. Solids is considerably improved when they are supported on y-Al2O3 (Y-DCBN = 70% and X-DCT >90%). In the direction of further enhancing the yield of DCBN, some selected transitional metal ions (Cr, Fe, Co and Mo) are also used as promoters for the present VPO solids. These promoted catalysts displayed superior performance compared to bulk and supported VPO catalysts. Amazingly, the yield of DCBN is significantly enhanced from 55% (on bulk VPO solids) to 80% on the promoted VPOs, which is indeed a remarkable outcome of this study.
Ammoxidation of 2,6-dichlorotoluene to 2,6-dichlorobenzonitrile was carried out at atmospheric pressure using VPO catalysts. Different catalyst supports were used and their influence on the catalytic performance has been evaluated. Nature of support has shown clear influence on the activity and selectivity behaviour of the catalysts. Higher activity (X-DCT > 90%) and selectivity (S-DCBN >75%) along with good long-term stability could be successfully achieved over TiO2 (anatase) supported VPO catalyst [52].
There were researches about some other researches touch upon photochemical and enzymatic conversion of chloro-aromatic hydrocarbons [36, 53]. In them the reaction mechanisms of the conversion were respectively given in the scheme 1 and scheme 2.
The report [54] firstly reviews the basic information on chlorotoluene including its classification, application and manufacturing technology. The report then explores global and China's top manufacturers of chlorotoluene listing their product specification, capacity, production value, and market share etc. The report further analyzes quantitatively 2009-2014 global and China's total market of chlorotoluene by calculation of the main economic parameters of each company. The breakdown data of Chlorotoluene market are presented by company, by country, and by application. The report also estimates 2014-2019 market development of Chlorotoluene Industry.
R=OMe; R=F; R=Me; R=CF3
Scheme 1. The photochemical reaction of the d6 Re(I) complex Cp*Re(CO)3 with several substituted dichloroarenes (were Cp*=C5M5, Re -Rhenium, d6 - d-orbital 6 electron).
Cl
OH
Cl Cs-tecA2 Cs-tecA1 Cl Cs-tecA3 Cs-tecA4
2,5-dichlorotoluene
H+
NADH oxygen
NAD+
OH
OH
Cs-tecB
NAD+
H+
NADH
OH
oxygen ^>2 H+
Cl
O
O=< Cl
>=O
O
4/1
2 H+ chloride
O
O
O
O
O
H+ O
H2O H+
O
O*
O*
H+
O
O*
O
2-chloro-3-methylmaleylacetate
Scheme 2. Enzymatic conversion of 2,5-dichlorotoluene to 2-chloro-3-methylmaleylacetate.
The report then analyzes the upstream raw materials, downstream clients, and current market dynamics of Chlorotoluene Industry. In the end, the report makes some proposals for a new project of Chlorotoluene Industry and a new project of Chlorotoluene Industry before evaluating its feasibility. Overall, the report provides an in-depth insight of 2009-2014 global and China Chlorotoluene Industry covering all important parameters.
Vanadium based catalysts in the gas phase oxidation reactions
Vanadium phosphates have been established as selective hydrocarbon oxidation catalysts for more than 40 years [67, 68]. This review includes a perspective on the future use of vanadium phosphate catalysts. Their primary commercially use has been the production of maleic anhydride (MA) from «-butane [55]. During this period, improvements in the yield of MA have been sought. Strategies to achieve these improvements have included the addition of secondary metal ions to the catalyst, optimization of the catalyst precursor formation and intensification of the selective oxidation process through improved reactor technology. The mechanism of the reaction continues to be an active subject of research, and the role of the bulk catalyst structure and an amorphous surface layer are considered here with respect to the various V-P-O phases present. The active site of the catalyst is considered to consist of V4+ and V5+ couples, and their respective incidence and roles are examined in detail here. The complex and extensive nature of the oxidation, which for butane oxidation to MA is a 14-electron transfer process, is of broad importance, particularly in view of the applications of vanadium phosphate catalysts to other processes:
The review deals with an analysis of the main structural and reactivity properties of mixed oxide systems containing vanadium oxide as the key component in catalysts for gasphase reactions, mainly oxidations [56]. Particular focus is placed on catalysts showing intrinsic bi-functional properties, where the combination of both acidic/basic properties and redox V-sites is a requisite for achieving optimum catalytic performance. For the selected catalytic systems, structure-reactivity correlations that have been proposed in many dozens literature were analyzed, with the aim of shedding light on the molecular-level aspects of current processes and facilitating a more rational design of future catalysts.
The methods of preparating vanadium modified molecular sieves, their characterization and applications in catalysis are discussed [67].
Recent advances (since 2000) are achieved in the application of oxovanadium complexes as catalysts or mediators for oxidations by molecular oxygen, peroxidative oxygenations (both including epoxidations), halo-genations and carboxylations of aliphatic and aromatic hydrocarbons, and/or olefins, toward the syntheses of a variety of organic compounds, such as alcohols, ketones, epoxides, aldehydes, organohalides and orcarboxylic acids. Some of these systems operate in liquid media, whereas others involve VO-catalysts immobilized on solid supports [57].
Taking into consideration all reviewed reference materials gas phase catalytic oxidation reactions of chlorotoluenes have been carried out [33, 48, 58-63] over the vanadium oxide based systems.
Oxidation of alkylaromatic chlorohydro-carbons in the presence of synthesized catalytic systems at the 600-773 K temperature, contact time 0.2-1.0 sec and consentration of inital components mole ratio CT:O2=1:1-1:30 investigated [40]. As a preliminary the activity of sthesized catalysts checked in the oxidation reaction of 2-chlorotoluene. Attained results described on the Table 3.
While synthesizing the catalysts effect of active components ratios on phase forming process was established [61].
tion reaction of p-chlorotoluene (p-ClT). The conversion of p-substituted toluene in the presence of these catalytic systems at 643 K temperature and 0.7 sec-1 contact time was 60-90%. The results are given in the Table 5. According to the table the activities of none participated on the suppliers oxide catalysts in contrast to catalytic systems based on SiO2 or Al2O3 aren't high. V-P-O/SiO2 and V-Mo-Sb/Al2O3 showed high results among the attained catalytic systems.
Influence on the oxidation reaction of active components of these catalysts was also studied. Influence of the ratio of active components V:P on the oxidation reaction at 643 K was given (Figure 2). As it can be seen from the Figure 2 at a V:P= 1:2-1:3 ratios the conversion of p-CT performs 88-92%, the yields of mono-chloromaleic anhydride (MClMA) was 3032%. Yield of p-chlorobenzaldehyde (p-CB) begins to increase at V:P=1:4-1:5 ratios. According to the obtained results usage of the catalytic systems based on V:P= 1:2-1:3 are considered purposeful for our further researches.
Mole ratio T,GC Phase forming
V Mo P
3 i i 5GG V2MoO8, VO(PO4)2, V2O5, P2O5, MoO3
3 i i 6GG V2MoO8, V9Mo6O40, VO(PO4)2, V2O5, P2O5
2 i i 6GG V2MoO8, V9Mo6O40, VO(PO4)2, V2O5, P2O5
2 2 i 5GG V2MoO8, V9Mo6O40, PVMoPO4, V2O5, P2O5
i i i 5GG V2MoO8, V9Mo6O40, VOPO4, V2O5, P2O5,MoO3
i 2 2 6GG V2MoO8, V9Mo6O40, V2O5, P2O5,MoO3
i i 2 6GG V2MoO8, V9Mo6O40, V2O5, P2O5,MoO3
i 3 i 6GG V2MoO8, V9Mo6O40, H4PVMonO40, V2O5, P2O5
Table 5. The influence of catalytic systems on the p-chlorotoluene oxidation at 673 K, p-ClT:O2=1:2Q
Catalytic systems Conversion p-ClT Yield
MClMA MA p-ClB aldehyde p-ClB acid CO2
V-P-O 64 iG 8 - - 34
V-Mo-O 7G 15 12 - 2 35
V-Sb-O 6G 16 iG - - 3G
V-P-O/SiO2 9G 32 26 iG 12 14
V-Mo-O/Al2O3 84 3G 25 12 12 iG
V-Sb-O/Al2O3 82 26 22 7 8 16
V-Mo-O/SiO2 82 26 24 6 7 12
V-Mo-Sb/Al2O3 86 3G 24 4 6 14
Table 3.Activity of catalytic systems in the oxidation
reactions of 2-chlortoluenes, Т=713 К, т =G.8 sec
Catalytic system 2-Chlorotoluene
conversion yields of anhydrides CO+CO2
V-P-O 68 27 45
V-Mo-O 68 28 46
V-Sb-O 64 30 46
V-P-O/SiO2 86 44 43
V-P-O/Al2O3 9G 46 26
V-Mo-O/SiO2 8G 64 24
V-Mo-O/Al2O3 82 70 27
V-Sb-O/SiO2 76 43 28
V-Sb-O/Al2O3 77 48 26
Mo-Co-O 6G 40 36
Mo-Co/Al2O3 7G 30 38
Bi-Co/SiO2 62 24 2G
V-Mo-Sb/SiO2 94 78 2G
On the example of receiving V-P-Mo-O-system influence of an initial components condition on a formation of active phase was given. Attained results are shown on the Table 4.
The activities of catalytic systems based on oxide synthesized and participated on the variety of suppliers were determined in the oxida-
Table 4. Phase forming of V-P-Mo-O-catalyst system
Temperature dependence of the p-chlorotoluene oxidation reaction yields on the synthesized V-P-O-systems supported SiO2 was studied. Although the oxidation reaction begins at 603 K and conversion of p-chlo-rotoluene 50%, determined yields of main products are negligible (Figure 3).
By increasing the temperature both the conversion of the p-chlorotoluene and yield of MClMA begin to rise, and at the temperature
643 K they showed the maximum (32-34%). Simultaneously the yields of maleic anhydride (MA), p-chlorobenzaldehyde and p-chloro-benzoic acid (p-ClB acid) decreased. By the further increase of temperature p-ClT conversion continuous to increase, but also yields of main products getting by its maximum begins to decrease and this happens by way of their exposing deep oxidation process that verified by increasing of CO2 yield.
Fig. 2. Influence on the p-chlorotoluene oxidation reaction of active components: 1 - conversion of p-ClT, 2 - yield of MClMA, 3 -yield of p-ClBenzald.
Fig. 3. Temperature dependence of the p-chlorotoluene oxidation reaction yields o n the synthesized V-P-O-systems supported SiO2 : 1 - ClT, 2 - MA, 3 - p-ClBenzald, 4 - p-ClB ac id, 5 - CO2, 6 - MClMA.
Conclusion
According to antecedent research materials it is determined that maleic, mono-, di-chloromaleic anhydrides, as well as chloroben-zaldehydes attained from the catalytic oxidation reactions of alkylaromatic chlorohydrocarbons are important intermediates in the preparation of biological active compounds, ethers, dyes, perfumes, pharmaceuticals, and agrochemicals [64]. From this point of view the development of heterogeneous catalysts capable of produc-ting chlorobenzaldehydes, maleic, mono-, di-chloromaleic anhydrides by the selective oxidation of alkylaromatic chlorohydrocarbons in gas or liquid phase is still actual.
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ALKILAROMATIK XLORKARBOHiDROGENLORlN KATALITIK OKSIDLO§MOSININ MUASiR VOZiYYOTi УЭ iNKl§AF PERSPEKTiVLOM
A.C.0fandi, E.M.Babayev, F.A.Yunisova, B.A.ismayilova, N.Aykan
Xlorlu alkilaromatik karbohidrogenlarin alinmasi va katalitik oksidla§masinin muasir durumu analiz edilmi§dir. G6starilmi§dir ki, xlortoluollann muxtalif heterogen katalitik sistemlar uzarinda selektiv oksidla§masinin hayata kegirilmasi mumkundur. Aktiv komponentlarin, reaksiya muddatinin va temperaturun katalizatorlarin aktivliyina va reaksiyanin selektivliyina tasiri muayyan edilmi§dir. Reaksiyalarin hayata kegirilmasi ugun optimal §arait segilmi§, hamin §araitda katalizatorun aktivliyi va selektivliyi 6yranilmi§dir. Naticada, ekoloji cahatdan tahlukali olan maddalar zararsizla§dirilmi§, elaca da geni§ tatbiq sahalari olan malein anhidridi va onun xlorlu toramalari, xlorbenzaldehid kimi ekoloji tamiz va tahlukasiz xammallar alinmi§dir.
Agar sozlar: katalitik oksidh§m3, xlortoluollar, malein anhidridi, xlorbenzaldehid, xlormalein anhidridbri, heterogen kataliz.
СОВРЕМЕННОЕ СОСТОЯНИЕ КАТАЛИТИЧЕСКОГО ОКИСЛЕНИЯ ХЛОРАЛКИЛАРОМАТИЧЕСКИХ УГЛЕВОДОРОДОВ И ПЕРСПЕКТИВА ЕГО РАЗВИТИЯ
А.Дж.Эфенди, Э.М.Бабаев, Ф.А.Юнисова, Б.А.Исмаилова, Н.Ф.Айкан
Рассматривается современное состояние получения и каталитического окисления хлоралкилароматических углеводородов, являющихся токсичными соединениями и отравляющими окружающую среду. Показаны возможности их каталитического окисления с целью получения нетоксичных соединений, имеющих широкое применение, такие как хлорбензальдегид, малеиновый ангидрид и их хлорпроизводные. Изучена активность многих гетерогенных каталитических систем в реакции селективного их окисления. Определены оптимальные условия проведения реакции окисления.
Ключевые слова: каталитическое окисление, хлортолуолы, малеиновый ангидрид, хлорбензальдегид, хлормале-иновые ангидриды, гетерогенный катализ.
