An Integrated Process for the Synthesis of Solid Hydroxylamine Salt

Jan 4, 2015 - Key Laboratory of Green Chemical Technology and High Efficient Energy Saving of Hebei Province, School of Chemical Engineering, Hebei Un...
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An Integrated Process for the Synthesis of Solid Hydroxylamine Salt with Ammonia and Hydrogen Peroxide as Raw Materials Yuanyuan Xu, Zhihui Li, Liya Gao, Dongsheng Zhang,* Xinqiang Zhao, Shufang Wang, and Yanji Wang* Key Laboratory of Green Chemical Technology and High Efficient Energy Saving of Hebei Province, School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, People’s Republic of China S Supporting Information *

ABSTRACT: An integrated process was designed for the synthesis of hydroxylamine salt with ammonia and hydrogen peroxide as raw materials; that is, hydroxylamine is produced from a combination process of cyclohexanone ammoximation and cyclohexanone oxime hydrolysis, whereby cyclohexanone and its corresponding oxime, which is circulated, act as the “reaction carrier”. Solid hydroxylamine salt was obtained through the integrated process, which corresponds to an overall yield of 64.2% with respect to ammonia. Moreover, the “reaction carrier”, as well as the catalyst employed, can be recycled in the process. In addition, many studies17−20 showed that hydroxylamine can be formed by acid hydrolysis of cyclohexanone oxime (reaction 2). However, cyclohexanone oxime was usually prepared by the condensation of cyclohexanone with hydroxylamine.21 From this point of view, it was unacceptable to synthesize hydroxylamine through the above oxime hydrolysis reaction. Recently, the discovery of titanium silicalite-1 (TS-1) opened new green catalytic processes with hydrogen peroxide as an oxidant.22,23 Soon after, this success prompted an important TS-1-catalyzed reaction, which produces cyclohexanone oxime from cyclohexanone, H2O2, and NH3 (reaction 3).14,24−26 Considering this, a flash idea came into our mind. Could these two reactions, that is, reactions 2 and 3, be combined to synthesize hydroxylamine as shown in Scheme 1?

1. INTRODUCTION Hydroxylamine and its salts are versatile chemicals, which play key roles in diverse applications ranging from semiconductor manufacture to pharmaceutical synthesis, as well as in large-scale production of cyclohexanone oxime for nylon manufacture.1−5 Currently, there are several ways to produce hydroxylamine. These are the Raschig process,6 the hydroxylamine−phosphate− oxime (HPO) process,7 the catalytic hydrogenation of nitric oxide,8 and acid hydrolysis of nitroalkanes. Almost all of the processes are based on chemical reduction of higher oxidation state compounds of nitrogen. However, there are some drawbacks with these processes, such as the formation of unwanted byproducts, mainly nitrous oxide and ammonium sulfate.9 For these reasons, new routes have been proposed for making hydroxylamine. Langer10 and Lewdorowicz9 suggest generating hydroxylamine by electrochemical process. However, such a process is technically complicated and expensive.11 Mantegazza et al.12,13 proposed a direct catalytic process for the production of hydroxylamine, using ammonia (NH3) and hydrogen peroxide (H2O2) as raw materials (reaction 1). It has received considerable attention for its potential economic advantage and eco-efficiency.14−16 Nevertheless, a large excess of ammonia is required, and the molar ratio of NH3/H2O2 is usually above 10, preferably from 30 to 50. The yield of hydroxylamine (99% cyclohexanone oxime selectivity (SCyo−O). All of the TS-1 samples exhibit catalytic activity for the ammoximation. However, TS-1## shows somewhat lower cyclohexanone conversion as a result of low Ti content in the zeolite.32,39,41 Obviously, TS-1 is an excellent catalyst for the formation of oxime, capable of giving a maximum cyclohexanone conversion of 99.1%. Consequently, various amounts of TS-1 catalyst were screened as shown in Figure 1a. Cyclohexanone conversion first increases and then remains around at 99%. Better results can be achieved at 0.6 g of TS-1 catalyst. Thus, 0.6 g of TS-1 catalyst with a Ti content of 6.62 wt % was used for further optimization. 1070

DOI: 10.1021/ie5044665 Ind. Eng. Chem. Res. 2015, 54, 1068−1073

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Industrial & Engineering Chemistry Research

commercially available cyclohexanone oxime. The melting point (88.4−88.8 °C) of the synthesized sample was very close to that of the commercial one (88.2−88.7 °C), and identical infrared spectra were observed for the two samples (see Figure S2 in the Supporting Information). Step II: Acid Hydrolysis of Cyclohexanone Oxime. In the acid hydrolysis process (reaction 2), the above-prepared cyclohexanone oxime was used as raw material, and hydrochloric acid was chosen as acid catalyst. Various parameters were investigated to optimize the process. The results are displayed in Figures 3 and 4. Initially, various reaction temperatures and times were screened. As depicted in Figure 3, the conversion of cyclohexanone oxime depended greatly on the reaction temperature, increasing with rising temperature from 20 to 60 °C. When further increasing the temperature, the conversion increases slightly. Concerning the reaction time, cyclohexanone oxime conversion increases first, passing through a maximum at 1 h, and then decreases by prolonging reaction time. Hence, the optimum reaction temperature and time are 60 °C and 1 h, respectively. Next, the influence of the amount of water and hydrochloric acid was studied as indicated in Figure 4. For the influence of water, a better result can be obtained at 15 mL (833 mmol) of H2O. With increasing the molar ratio of HCl/cyclohexane oxime, cyclohexanone oxime conversion first increases, and then

equal amounts of NH3 and H2O2 (see reaction 3), it is clear that a little excess of NH3 and H2O2 would favor cyclohexanone oxime formation. As shown in Figure 2a and b, the conversion of cyclohexanone increases steadily and then remains around 99% with increasing molar ratio of NH3/cyclohexanone or H2O2/cyclohexanone. The suitable molar ratio of cyclohexanone:NH3:H2O2 is 1:1.2:1.3. For the variation of cyclohexanone conversion versus temperature (Figure 2c), a bellshaped curve is observed. High yield of cyclohexanone oxime is obtained at 70 °C. However, the conversion is reduced obviously with the temperature above 80 °C. This may be due to easier vaporization and decomposition of reactants, particularly NH3 and H2O2.30,39 As for the influence of reaction time, the yield of cyclohexanone oxime can be improved by having a longer reaction time.15,35 The optimum reaction condition is at 70 °C for 1.5 h. Under this reaction condition, cyclohexanone was almost completely converted into cyclohexanone oxime, corresponding to 99% cyclohexanone conversion and 99% oxime selectivity. Consequently, the ammoximation reaction was performed under the optimal condition. At the end of the reaction, the TS-1 catalyst was filtered and collected for further treatment. The resulting mixture was cooled in an ice bath to get solid cyclohexanone oxime. To further verify the above synthesized solid, a portion of the solid was crystallized twice from ethanol, and then characterized by comparison with a sample of

Figure 3. Effect of reaction temperature (a) and time (b) on cyclohexanone oxime conversion. Reaction conditions: (a) Cyclohexanone oxime, 15.0 mmol; hydrochloric acid, 2 mL (HCl, 23.2 mmol); H2O, 833 mmol; 1 h. (b) Cyclohexanone oxime, 15.0 mmol; hydrochloric acid, 2 mL (HCl, 23.2 mmol); H2O, 833 mmol; 60 °C.

Figure 4. Effect of the amount of water (a) and HCl/cyclohexane oxime molar ratio (b) on cyclohexanone oxime conversion. Reaction conditions: (a) Cyclohexanone oxime, 15.0 mmol; hydrochloric acid, 2 mL (HCl, 23.2 mmol); 60 °C, 1 h. (b) Cyclohexanone oxime, 15.0 mmol; H2O, 833 mmol; 60 °C, 1 h. 1071

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Industrial & Engineering Chemistry Research remains around 99%. The HCl/cyclohexane oxime molar ratio of 2.3 is enough for the present hydrolysis process. 3.2. Preparation of Solid Hydroxylamine Hydrochloride (NH2OH·HCl). Under the above optimal conditions, the integrated process was carried out, and all of the cyclohexanone oxime prepared in the ammoximation (step I) was employed in the hydrolysis process (step II). After completion of the hydrolysis process, the reaction mixture was cooled and extracted with toluene. The obtained acidic aqueous phase was evaporated to dryness under reduced pressure. Some 2.9 g of white solid NH2OH·HCl was obtained. An overall yield with respect to NH3 is 64.2% as shown in Table 2 (run 1), which is much higher than

Table 4. Effect of the Usage of TS-1 on Ammoximation of Cyclohexanonea

run

mCyo−O (g)

1 2 3

5.8 5.5 6.1

b

mHy−H (g)

yHy−H (%)c

2.9 2.6 3.1

64.2 57.5 68.6

SCyo−O (%)

99.1 98.2 97.8 95.4

99.9 99.8 99.7 99.7

Reaction conditions: cyclohexanone, 62 mmol; H2O, 833 mmol; NH3, 65 mmol; H2O2, 80 mmol; 1.5 h, 70 °C.

reaction, it could be separated by a simple filtration, followed by drying and calcinations. The regenerated catalyst then was tested under the same reaction conditions as for the fresh one. The results are given in Table 4. There is no clear decrease in the catalytic activity. Even after four runs for the reaction, the conversion would still be 95.4%. It proved that the TS-1 catalyst was stable enough to be recycled in the ammoximation.

step II a

XCyo (%)

a

Table 2. Experimental Results of the Integrated Process under Optimal Condition step I

run 1 (fresh) 2 3 4

4. CONCLUSIONS In summary, an integrated process was realized for the synthesis of hydroxylamine with ammonia and hydrogen peroxide as raw materials; that is, hydroxylamine is produced from a combination process of cyclohexanone ammoximation and cyclohexanone oxime hydrolysis, whereby cyclohexanone and its corresponding oxime, which is circulated, act as the “reaction carrier”. The integrated process was carried out under the optimized conditions. Solid hydroxylamine hydrochloride was obtained, which corresponds to an overall yield of 64.2% with respect to ammonia. Moreover, the “reaction carrier” can be circulated through the process. Titanium silicalite catalyst was stable enough to be recycled multiple times.

a

The amount of cyclohexanone oxime. bThe amount of hydroxylamine hydrochloride. cThe yield of NH2OH·HCl = the actual amount (mol) of NH2OH·HCl/the initial amount (mol) of NH3. Reaction conditions: cyclohexanone, 62 mmol; NH3, 65 mmol; H2O2, 80 mmol; 70 °C; 1.5 h for step I; and cyclohexanone oxime, HCl/cyclohexane oxime molar ratio 2.4, 60 °C, 1 h for step II.

previously reported (using NH3 and H2O2 directly as raw materials). Furthermore, two additional runs (runs 2 and 3) were made using the same parameters to check the reproducibility of the results. No significant deviations were found from the values reported in Table 2. Additionally, the chemical composition of the solid sample (run 1) was characterized by elemental analysis (Table 3).

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ASSOCIATED CONTENT

S Supporting Information *

XRD patterns of the TS-1 zeolites samples and FT-IR spectra of cyclohexanone oxime samples. This material is available free of charge via the Internet at http://pubs.acs.org.

Table 3. Chemical Compositions of the Synthesized NH2OH·HCl NH2OH·HCl

N (wt %)

H (wt %)

O (wt %)

self-synthesized sample commercially available sample

17.28 17.37

5.91 5.92

24.37 24.36

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AUTHOR INFORMATION

Corresponding Authors

*Tel./fax: +86 22 60200445/60204061. E-mail: zds1301@ hebut.edu.cn. *E-mail: [email protected].

Most elemental compositions obtained conform reasonably well to the commercially hydroxylamine hydrochloride. Moreover, the synthesized solid was used (as hydroxylamine) in the reaction of cyclohexanone ammoximation under suitable conditions;15 99% of cyclohexanone was converted to cyclohexanone oxime. As a result, the solid prepared is indeed hydroxylamine hydrochloride (NH2OH·HCl) in the present research. 3.3. Recycling of the Reaction Carrier. In the integrated system, it is interesting to see the recycling of the “reaction carrier”, that is, cyclohexanone and its corresponding oxime. After completion of the hydrolysis process (step II), the resulting mixture was extracted with toluene. The obtained organic phase was collected and separated by vacuum distillation to get cyclohexanone. The recycling cyclohexanone was used in the ammoximation reaction (step I), and better result was obtained, corresponding to 99.4% yield of cyclohexanone oxime under ideal conditions, which opens a bright future for industrial application. 3.4. Reusability of TS-1 Catalyst. In addition, the reusability of the TS-1 catalyst was investigated in the ammoximation (step I). Because TS-1 was a solid catalyst in the liquid-phase

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for the financial support of the National Natural Science Foundation of China (21236001, 21106029, and 21176056), the National Natural Science Foundation of Tianjin (12JCQNJC03000), and the National Natural Science Foundation of Hebei Province (B2012202043).

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