Peng Xinxin; Xia Changjiu; Lin Min; Zhu Bin; Luo Yibin; Shu Xingtian

(State Key Laboratory of Catalytic Materials and Reaction Engineering,SINOPEC Research Institute of Petroleum Processing, Beijing 100083)

Abstract: The toluene oxidative bromination reaction catalyzed by hollow titanium silicalite (HTS) zeolite in aqueous medium was investigated by employing H2O2 and HBr under mild conditions without the need for organic solvent. A high toluene conversion (90.7%) and high selectivity of mono-bromotoluene (99.0%) was achieved under the optimal reaction conditions. The UV-Raman spectroscopy was applied for the mechanism study and the result reveals that HTS is efficient for catalyzing the oxidation reaction of HBr with H2O2 to produce abundant active bromine species, which can further facilitate the toluene electrophilic bromination reaction. A two-step toluene bromination reaction mechanism involving the HTS catalyzed active bromine species “generation-conversion-utilization” process is proposed based on the UV-Raman spectroscopy analysis.

Key words: titanium silicalite; oxidative bromination; organic solvent free; H2O2/HBr; polybromine ion

1 Introduction

As a class of useful intermediates, the brominated aromatic compounds are widely used for the synthesis of pharmaceuticals, agricultural chemicals, etc. Owing to its high reactivity, molecular bromine Br2is commonly used as an electrophilic brominating reagent for bromination reaction. However, the toxic nature of Br2, the difficulty in handling as well as the low atom efficiency (half of bromine atom is converted into hydrobromic acid, HBr)have hindered its wide use.

Mild brominating reagents such asN-bromosuccinimide andN-bromoacetamide are much safer without producing HBr. Yet, this approach is limited by its low atom efficiency, moreover, Br2is indispensable for the preparation of the brominating reagents[1]. Oxidative bromination, which employs hydrogen peroxide (H2O2)or oxygen as oxidants and inorganic bromide salts or alkylammonium bromides as bromine source under acidic reaction conditions, is an alternative and promising protocol[2-3]. Through this approach, the bromide ions are oxidized and the substrates are brominated by the in situ produced bromine species. However, the reaction efficiency is relatively low, thus, the use of excessive bromide salts or H2O2is unavoidable. Although various effective homogeneous catalysts have been developed,which contain active centers of metals such as vanadium[4], molybdenum[5-6], tungsten[7-8]or nonmetals[9],the catalyst separation and recycling remain under further consideration. Another concern for bromination reaction is to minimize the usage of a large amount of organic solvent from the perspective of “green” chemistry.Since water is non-toxic, non-flammable and abundant,developing new approaches with water as solvent is of great importance[10].

Titanium silicalite is effective for activating H2O2and further catalyzing organic substrates oxidation reactions.To the best of our knowledge, the titanium silicalite/H2O2system has not yet been applied in the oxidation reaction involving bromide ions or other inorganic compounds except for NH4·H2O in ketone oximation reaction. Herein,we chose toluene as the model compound, and an organic solvent-free toluene oxidative bromination reaction system using H2O2as oxidant, HBr as bromine source and hollow titanium silicalite (HTS) as heterogeneous catalyst was proposed. Reaction conditions were investigated and UV-Raman spectroscopy characterization was applied to monitor the formation of active bromine species during the HBr catalytic oxidation reaction.

2 Experimental

2.1 Catalysts preparation and characterization

Ti(SO4)2was used as purchased from the Sinopharm Chemical Reagent Co., Ltd. without further puri fication.TiO2/S-1 and Ti-SBA-15 zeolites were prepared by impregnation of TiCl4on commercial silicalite-1 (S-1) and SBA-15 zeolite, respectively. Typically, a certain amount of TiCl4was dissolved in 15.26 g of HCl aqueous solution (10%) and stirred for 30 min.Then the liquid was slowly added into 15 g of zeolite to obtain a mixture, which was then stirred slowly for 4 h at ambient temperature. At last, the mixture was dried at 110 °C for 6 hours and calcined at 550 °C for 4 h to obtain TiO2/S-1 and Ti-SBA-15 zeolites. The S-1, SBA-15, and HTS zeolites are supplied by the Sinopec Hunan Jianchang Petrochemical Co., Ltd.

The X-ray diffraction (XRD) patterns were collected on a Philips PANalytical X’pert diffractometer with nickel- filtered Cu Kα radiation (40 kV, 250 mA). The 2θ scanning ranged from 5° to 35°, and the scanning rate was 0.4 (°)/min. The X-ray fluorescence (XRF) experiments were conducted on a Rigaku 3721E spectrometer with W radiation (40 kV). The X-ray photoelectron spectroscopy(XPS) spectra were recorded on a Thermo-Fischer-VG ESCALAB250 with Al Kα radiation, and the framework titanium content and extra-framework titanium content were integral results of the Ti 2p3/2peaks at 460.3 eV and 458.7 eV, respectively.

2.2 Toluene bromination reaction

The toluene bromination reaction was carried out in a three-necked flask equipped with a condenser and a magnetic stirrer. In a typical experiment, 0.53 g of catalyst, 0.0575 mol of toluene and 0.0575 mol of HBr(30%) were mixed and stirred. Then 0.0575 mol of H2O2(30%) was added by a peristaltic pump at a feeding rate of 0.3 mL/min to initiate the reaction. After reacting at 30 °C and atmospheric pressure for 2 h, the liquid product was collected, neutralized, and then analyzed by an Agilent 6890N GC equipped with a HP-5 capillary column.

2.3 Bromine species characterization

The UV-Raman spectra were recorded on a Raman spectrometer (LabRAM HR UV-NIR, Jobin Yvon)with a microscope. The line at 325 nm from a He-Cd laser was used as the exciting source. The laser power was kept below 1 mW. The reactants including H2O2,HBr, and HTS (n(H2O2):n(HBr)=1:1), 1% of H2O2, 0%or 2% of HTS) were mixed, reacted and injected into the quartz cell and lastly characterized by the Raman spectroscopy at ambient temperature. The Raman spectra between 170 cm-1and 1 200 cm-1(200 s accumulation)were automatically recorded as the average of duplicate measurements. HClO4was used as the internal standard substance for semi-quantitative analysis of bromine species.

3 Results and Discussion

3.1 Characterization of Ti-containing zeolites

The crystalline structures of S-1, TiO2/S-1, HTS, SBA-15, and Ti-SBA-15 zeolites were characterized by XRD measurement, with the patterns shown in Figure 1. It can be seen that both TiO2/S-1 and HTS zeolites showed characteristic peaks of the MFI topology ranging from 22° to 25°. However, the relative crystallinity of TiO2/S-1 zeolite decreased by 12% compared with S-1, which indicated the formation of amorphous Ti species after Ti impregnation. Although the peak intensity of Ti-SBA-15 zeolite slightly decreased after Ti impregnation, the morphology remained unchanged. The diffraction peaks at 0.84° (100), 1.46° (110) and 1.68° (210) shifted to 0.95°,1.62° and 1.86°, respectively, for Ti-SBA-15 zeolite as compared with SBA-15, indicating a slight shrinkage of unit cell.

Figure 1 XRD patterns of (a) S-1, TiO2/S-1 and HTS, and (b) SBA-15 and Ti-SBA-15

The bulk and surface chemical composition of TiO2/S-1, Ti-SBA-15, and HTS zeolites were determined by XRF and XPS techniques, respectively, with the results shown in Table 1 and Figure 2. The molar ratio of Si to Ti and the chemical state of Ti analysis results are listed in Table 1. It can be seen from Table 1 that the bulk n(Si)/n(Ti) ratio for three Ti-containing samples was around 20. However, the surface n(Si)/n(Ti) ratio for TiO2/S-1, Ti-SBA-15 and HTS zeolites was 39, 12 and 74,respectively. It seems that the Ti species were more likely to be enriched on the surface of Ti-SBA-15, as compared with the other two samples since itsn(Si)/n(Ti) ratio was much lower on the surface than in the bulk phase.The composition of 4-coordinated and 6-coordinated Ti species (with a binding energy equating to 459.2 eV and 460.6 eV, respectively) was also analyzed. The content of 4-coordinated Ti species on the surface of HTS zeolite was the highest among the three samples, while the Ti species existed mainly as 6-coordinated species on TiO2/S-1 zeolite as shown by the analysis results.

Table 1 Si and Ti chemical composition and Ti coordination properties of TiO2/S-1, Ti-SBA-15 and HTS samples

3.2 Catalytic performance of Ti-containing catalysts

Figure 2 XPS spectra of TiO2/S-1, Ti-SBA-15 and HTS samples

HBr can be easily oxidized by H2O2owing to the difference of their redox potential between H2O2and Br-under acidic condition. Once H2O2is introduced into the reactants, Br2is formed and the solution turns into brownish red. Toluene bromination reaction catalyzed by different Ti-containing catalysts was performed by using H2O2(30%) and HBr (30%) as the oxidant and the bromine source, respectively. The molar ratio of toluene∶HBr∶H2O2was 1∶1∶1, and the mass ratio of catalyst to toluene was 1∶10. The reactions were conducted under atmospheric pressure for 2 h, with the results shown in Table 2.

It can be seen from Table 2 that toluene conversion was 26.8% for the blank test, and the major products were ortho- and para-substituted bromotoluene (with a selectivity of 30.9% and 65.8%, respectively). There was only a small amount of multi-substituted bromotoluene and benzyl substituted by-products (with a selectivity of 3.3%). It is well-known that benzene ring substituted products are mainly formed through electrophilic mechanism involving the attacking by electrophilic reagent such as “Br+” species, while the substitution on benzyl group follows the radical mechanism. Given the less steric hindrance of para-position of toluene, it was reasonable to conceive that the para-bromotoluene was more preferred to be formed than ortho-bromotoluene.In addition, taking into consideration of by both steric hindrance and orientation effect of methyl and Br species in benzene ring substitution, multi-substituted bromotoluene is less likely to form.

Four Ti-containing catalysts including homogeneous catalyst (Ti(SO4)2) and heterogeneous catalysts (TiO2/S-1, Ti-SBA-15, and HTS) were tested for toluene bromination reaction. The results in Table 2 reveal that Ti(SO4)2, TiO2/S-1, and HTS catalysts were all effective in promoting toluene conversion except for Ti-SBA-15,the toluene conversion of which increased only by 1.7%.This is perhaps due to the Ti species aggregation on the surface of Ti-SBA-15, thus leading to insufficient active centers necessary for catalyzing the reaction to happen.Although the toluene conversion for Ti(SO4)2was 39.3%,its by-product selectivity reached 20.1%. That might be explained by homolysis of Br-Br to form Br· free radicals,which were induced by the 6-coordinated Ti4+species in aqueous solution, and could further promote the methyl substitution.

When the bromination reaction was catalyzed by TiO2/S-1 zeolite other than Ti(SO4)2, the toluene conversion was 44.8% and the by-product selectivity was 3.1%. It is noticed that HTS was the most active catalyst among these catalyst samples as the toluene conversion reached up to 54.0%, which was twice as much as the result of non-catalyzed reaction. Furthermore, the by-product selectivity was as low as 3.6%.

The catalytic performance is highly related to the state and quantity of active centers on the zeolite surface. The XPS characterization result revealed that the 6-coordinated Ti species were the dominant Ti species existing on the surface of TiO2/S-1 catalyst. Since its toluene conversion was significantly increased compared with the blank test, it is assumed that the 6-coordinated Ti species were capable of promoting toluene bromination reaction. The dominant surface Ti species of HTS consisted of both the 4-coordinated framework Ti species and the 6-coordinated extra-framework Ti species with a 4-coordinated Ti/6-coordinated Ti ratio of 1.72. The 4-coordinated framework Ti species within MFI type zeolite have long been discovered to be effective in activating H2O2and hence oxidizing organic substances[11]. Given the result that HTS is the most effective catalyst for toluene bromination reaction among the tested samples and the relatively high surfacen(Si)/n(Ti) ratio of HTS compared with TiO2/S-1,it is safe to conclude that the 4-coordinated framework Ti species is more effective in catalyzing this reaction and is the main catalytic oxidative bromination active center for HTS zeolite.

Since HTS zeolite showed the best catalytic performance among all the tested catalysts, toluene bromination re-action was further studied by employing HTS as the catalyst. The in fluence of HTS zeolite amount on toluene bormination reaction was investigated. The molar ratio of toluene∶HBr (30%)∶H2O2(30%) was set at 1∶1∶1, and the reactions were conducted at 30 °C for 2 h. The GC analytical results are shown in Table 3. It can be seen from Table 3 that the toluene conversion increased along with an increasing amount of HTS zeolite. Since the toluene conversion increased only by 1.8% asm(HTS)/m(toluene)ratio increased from 0.100 to 0.150, it is estimated that the mass ratio of HTS to toluene at 0.100 is sufficient for catalyzing the toluene bromination reaction. We also noticed that the products selectivity of the reaction catalyzed by different amount of HTS remained basically the same as the non-catalyzed reaction.

Table 2 Toluene bromination reaction catalyzed by different Ti-containing catalysts

Table 3 In fluence of HTS zeolite amount on toluene bromination reaction

Reaction conditions, such as the molar ratio of HBr to H2O2, the HBr concentration, and the reaction time, were further investigated for toluene bromination reaction catalyzed by HTS zeolite. When the molar ratio of toluene∶HBr∶H2O2was 1∶2∶1, and the mass ratio of catalyst to toluene was 1∶10, the test results are shown in Table 4. By increasing the HBr to H2O2molar ratio from 1∶1 to 2∶1, the toluene conversion increased from 54.0% to 69.1%, and a decrease in both by-products selectivity was observed. The conversion of toluene was promoted along with an increasing HBr concentration, because the toluene conversion reached 73.2%, and the by-product selectivity was 2.3% when the HBr aqueous solution with a concentration of 48% was used. Prolonging the reaction time was also useful for improving the toluene conversion.When the reaction time was extended to 18 hours, the toluene conversion reached 90.7% and the bromotoluene selectivity could be as high as 99.0%.

Excessive HBr or higher HBr concentration or even prolonging the reaction time is effective in improving the toluene conversion and bromotoluene selectivity. Furthermore, the unreacted HBr can be easily separated and recycled thanks to the liquid-liquid-solid reaction system and the insoluble nature of both toluene and brominated products in water phase. The above results suggest that HTS/H2O2/HBr system is effective in facilitating the toluene bromination reaction.

Table 4 In fluence of reaction conditions on toluene bromination reaction catalyzed by HTS zeolite

3.3 Reusability of HTS zeolite

The reusability of HTS zeolite in toluene bromination reaction was investigated by separating the HTS zeolite from liquid products through filtration and the solid was recycled for the next run of toluene bromination reaction.The molar ratio of toluene∶HBr (30%)∶H2O2(30%) was 1∶2∶1, and the reactions were performed at 30 °C for 12 h. The HTS zeolite was recycled for 7 times successively, with the GC analytical results presented in Table 5.The toluene conversion was retained to be as high as the fresh HTS catalyzed reaction till the 5threcycle. After the 7threcycle, the toluene conversion dropped from 88.1% to 42.4%. During the recycling reactions, the products selectivity only changed slightly. We assumed that the catalyst was deactivated after the 7threcycle, so we separated the catalyst and calcined it at 550 °C under atmospheric condition and then used it for further bromination reaction.The result shows that toluene conversion was recovered as the fresh one.

Table 5 Reusability of HTS zeolite in toluene bromination reaction

Figure 3 XRD patterns of fresh HTS,deactivated HTS and calcinated HTS

The samples of fresh HTS, deactivated HTS, and calcined HTS were collected for further characterization to investigate the deactivation bahavior of the catalysts. The XRD patterns were obtained, with the analysis results shown in Figure 3 and Table 6. The characteristic peaks of MFI topology between 22° to 25° were retained well for the deactivated HTS and the calcined HTS samples,although the peak intensity of deactivated HTS was slightly lower than the fresh HTS and calcined HTS samples. The difference could also be seen in the relative crystallinity.The bulk and surfacen(Si)/n(Ti) ratios of the three samples are very close based on the results of XRF and XPS analyses. However, the molar ratio of the 4-coordinated Ti to the 6-coordinated Ti on the zeolite surface decreased after deactivation and calcination. Since the toluene conversion of the calcined HTS was totally recovered, the change in coordination state of a part of Ti species was insufficient to affect the zeolite’s catalytic performance. The texture properties of the three samples were studied, with the results listed in Table 6. It can be seen that the external speci fic area of micropore volume remained unchanged after deactivation, while the BET speci fic area and mesopore volume decreased obviously.Nevertheless, these values were recovered on a par with the fresh HTS once it was calcined. This suggests that the micropores of the deactivated HTS were blocked by organic compounds, which might lead to the deactivation after 7threcycle. It also explains the reason leading to the decreased relative crystallinity of deactivated HTS zeolite.

Figure 4 XPS spectra of fresh HTS, deactivated HTS, and calcinated HTS

3.4 Characterization of bromine species

HBr is easily to be oxidized to HBrO by H2O2, and HBrO can further react with HBr to form Br2. With the existence of Br-ions, Br2is prone to generate high-order polybromine ions, such as3and even higher species (Figure 5). In order to characterize the generation of these species in the H2O2/HBr system, we employed the Raman spectroscopy to explore the evolution of bromine species in a mixture of H2O2and HBr at different reaction time with or without HTS catalyst. The Raman spectra are shown in Figure 6.

It can be seen from the spectra that except for the H2O2and HClO4peaks at 878 cm-1and 934 cm-1, respectively, 5 other peaks can be found. The fundamental frequencies of bromine species such as BrO-[12], Br[13],, and2are assigned at 620 cm-1, 308 cm-1, 170 cm-1, and 250respectively, according to references. However, the BrO-species is difficult to be detected because it is likely to transfer into Br2under strong acidic condition (Eq. 2). At the same time, Br2is also difficult to be detected since it is preferred to transfer into more stable substances, for example, high-order polybromine species (Eqs. 3 and 4).Although the fundamental frequency ofis beyond the detection range, its four overtones, including the 1stovertone (333 cm-1), the 2ndovertone (492 cm-1), the 3rdovertone (663 cm-1), and the 4thovertone (829 cm-1),fall within the detection range and the peak intensities are strong enough to be recorded distinctly. The peak intensity of Br5-is also very strong but the higher species,such asis indiscernible. In one word, the distribution of the Raman peaks suggests that Br-is oxidized and is further converted into more stable ions, and can mainly exist asandbromine species, no matter with or without the catalysis of HTS.

Figure 5 Evolution of active bromine species

Table 6 Characterization of fresh, deactivated, and calcined HTS zeolites

Figure 6 Raman spectra of bromine species generated under (a) non-catalyzed and (b) HTS catalyzed condition

Figure 7 Relative content ofand ions at different reaction time under (a) non-catalyzed and (b) HTS catalyzed condition

3.5 Reaction mechanism

An apparent difference can be drawn between spectra in Figure 6 (a) and (b). The H2O2peak is well retained even after reacting for 90 minutes in the non-catalyzed experiment, while for the HTS catalyzed one, that peak disappears after reaction for 10 minutes. It indicates that the H2O2depletion rate is much faster in the HTS catalyzed reaction system. In order to describe the difference of the reaction rate under two different conditions quantitatively, HClO4which is inert to both two reaction systems is added as an internal standard substance to calculate the relative content of both(the 1stovertone) and(fundamental frequency) ions.andions are selected for calculation because they are the major bromine species detected by the Raman spectroscopy. The relative content of bromine species is calculated according to the following equation. Relative content =m(HClO4)*A(and)/A(HClO4), wheremrefers to mass andA— the peak area. The relationship between relative content and reaction time are depicted in Figure 7.

It can be seen from Figure 7 that although the total amount of bromine species for both non-catalyzed and HTS catalyzed reaction is increasing along with the prolonging of reaction time, the relative content of bromine species of non-catalyzed reaction is much lower than that obtained after reaction catalyzed by HTS for the same reaction time. The relative intensity data of reaction time ranging from 5 to 60 minutes for Figure 7(a) and from 5 to 15 minutes for Figure 7 (b) are selected for linear fitting to correlate the relationship between the relative content of bromine species and the reaction time.Thereby, two equations are obtained. The first isR= 0.24t+34.27 for the non-catalyzed reaction, and the other isR= 3.34t+ 39.11 for the HTS-catalyzed reaction, whereRis the relative content andtis the reaction time. The slope of the two equations could be used for reaction rate comparison. It is estimated that the production rate of bromine species obtained between 5 to 15 minutes is about 14 times higher for the HTS-catalyzed reaction, as compared with the non-catalyzed reaction. This meansthat the HTS zeolite exhibits a much stronger effect in catalyzing H2O2and HBr oxidation and generating active bromine species.

Based on the above analysis, a two-step reaction mechanism including the active bromine species generation catalyzed by HTS and in situ toluene bromination is tentatively proposed. To begin with,the H2O2is activated by the framework Ti species of HTS zeolite and HBr is then oxidized to generate HBrO and Br2. But eventually these bromine species would transform and could mainly exist as highorder polybromine ions, such as Br3-, and Br5-. These conversions are reversible and the high-order polybromine ions can be converted into lower-order ones readily. Due to the excellent catalytic performance of HTS zeolite[16],these high-order polybromine ions are abundant enough and capable of supplying as much active Br+species as possible, which are derived from HBrO or Br2following the reverse reaction of Eqs. 2, 3, and 4. On the other hand,benzene ring bromination reaction occurs following the electrophilic substitution mechanism, the reaction rate of which is related to the concentration of electrophilic reagent other than the HTS zeolite. Therefore, through this HTS catalyzed active bromine species “generationconversion-utilization” process, the toluene bromination reaction can be promoted efficiently and a high toluene conversion is obtained.

4 Conclusions

The HTS zeolite catalyzed organic solvent-free toluene catalytic oxidative bromination reaction with H2O2/HBr system under mild reaction conditions was investigated.Different Ti-containing catalysts were studied for toluene bromination reaction and the HTS zeolite exhibited the best catalytic performance owing to the 4-coorinated framework Ti species. Under optimal conditions, a toluene conversion of 90.7% and a mono-bromotoluene selectivity of 99.0% were achieved. The HTS zeolite was robust enough to catalyze the toluene bromination reaction under acidic conditions for at least 5 runs, while retaining a high toluene conversion. The blockage of micropores in HTS zeolite by organic compounds was the main reason of catalyst deactivation, and the catalytic activity of HTS zeolite could be recovered by calcination.The reaction mechanism was studied by the UV-Raman spectroscopy. The HTS zeolite is effective in catalytic oxidation of HBr to form sufficient active bromine species. These species function as electrophilic agent and can react with the benzene ring of toluene to yield monobromotoluene as the main product. This study proposes a facile and promising approach for toluene bromination by using titanium silicalite zeolite as the catalyst, and also supplies a new example of inorganic compound oxidation catalyzed by titanium silicalite.

Acknowledgements: The author thanks for the financial support of SINOPEC Corporation (S413108).

Novel Catalyst for Manufacture of Cyclohexanone Via Cyclohexanol Dehydrogenation Developed by SINOPEC Nanjing Research Institute of Chemical Industry Has Passed Appraisal

On July 29, 2020 the project “Industrial application of catalyst for manufacture of cyclohexanone through cyclohexanol dehydrogenation” undertaken by the SINOPEC Nanjing Research Institute of Chemical Industry (NRICI) passed the appraisal of scientific research achievements organized by the SINOPEC Science and Technology Division. The experts attending the Appraisal Meeting have recognized that all performance indicators of the NDH6 catalyst for manufacturing cyclohexanone have reached the advanced level of similar international catalysts.

At present, the SINOPEC Nanjing Chemical Industry Company, Ltd. uses the cyclohexane method to manufcature cyclohexanone with a production capacity of 160 kt/a. Both of the benzene hydrogenation process and the cyclohexanol dehydrogenation process apply a heat-conducting oil system. The temperature of the heatconducting oil for benzene hydrogenation is 240 ℃ at the outlet, while that of heat-conducting oil used in the cyclohexanol dehydrogenation process is 230 ℃ at the initial stage of dehydergenation catalyst life cycle and increases to 260 ℃ at the final stage of catalyst life cycle.The research workers have independently developed the NDH6 catalyst for cyclohexanol dehydrogenation.Addition of cocatalyst to the NDH6 catalyst can increase the low-temperature catalytic activity to extend the operating cycle of the catalyst in the low-temperature stage (＜210 ℃), and the waste heat formed during benzene hydrogenation can be utilized to support the cyclohexanol dehydrogenation system in order to reduce the operating cost and energy consumption in the dehydrogenation process

The outcome for commercial application of the NDH6 catalyst in the 60 kt/a cyclcohexanone unit has revealed that under standard conditions the cyclohexanone conversion rate is more than 55.0%, and the cyclohexanone selectivity has exceeded 99.0%, with the catalyst operating stably. In comparison with the traditional Cu-Zn dehydrogenation catalyst, the NDH6 catalyst can increase the cyclohexanone conversion rate by 4%—5%, with the steam consumption reduced by 1.34 t/h.