In-situ synthesis of hydrogen peroxide for green production of nylon

Cyclohexanone oxime is a key precursor for the production of caprolactam, a commodity chemical used in the synthesis of polyamide nylon 6
.
The traditional route of cyclohexanone oxime production involves the reaction of cyclohexanone with hydroxylamine sulfate, producing ammonium sulfate (a low-value fertilizer with limited applications) as the main by-product
.
Alternative routes are hampered by the need to maintain a consistently low reaction pH or low selectivity to the desired product
.
Hydrogen peroxide (H2O2) has suitable oxidizing ability, and its reaction product is water, which is very suitable as an environmentally friendly selective oxidant for green chemical synthesis
.
The preparation of nylon 6 monomer cyclohexanone oxime is a very good example
.
Compared with the traditional oximation process, EniChem confirmed that the use of H2O2 as an oxidant, titanium-silicon molecular sieve catalyzed H2O2 ammoxidation to prepare cyclohexanone oxime can greatly simplify the production process, while obtaining high conversion and high selectivity, greatly reducing low-value The generation of by-products and waste makes the entire production process greener and more economical
.
At present, more than 70% of the cyclohexanone oxime with an annual output of more than 6 million tons in the world is prepared by hydrogen peroxide ammoxidation
.

Although H2O2 plays an increasingly important role in the development of green chemistry, the existing industrial anthraquinone preparation methods are not "green" enough: this preparation method has complex processes, high investment costs, and organic solvents may pollute the environment , the use of large amounts of precious metal catalysts, high storage/transportation costs and the need for additional dilution for use have significant disadvantages
.
If the in-situ method can be used to directly generate H2O2 to complete the catalytic ammonia oxidation and other reactions, it can greatly save energy consumption and equipment investment, not only make the whole process more economical and green, but also play an extremely important role in the development of new green chemicals and chemical synthesis.
meaning
.

A glimpse of the results

Recently, Graham Hutchings, Richard J.
Lewis of Cardiff University, Cardiff Catalysis Institute, and Liu Xi, Chen Liwei of Shanghai Jiaotong University School of Chemistry and Chemical Engineering In-situ Center for Material Science and other units collaborated to make breakthroughs.
The titanium-silicon molecular sieve-supported gold-palladium alloy catalyst was specially designed to achieve a one-step process of high concentration directly from hydrogen, oxygen, ammonium bicarbonate and cyclohexanone under the conditions close to industrial hydrogen peroxide ammoxidation (same type of reactor and reaction conditions).
Selectively prepare cyclohexanone oxime, and obtain nearly 100% cyclohexanone selectivity, nearly 100% ammonia selectivity and 67% hydrogen selectivity, and its cyclohexanone oxime yield is comparable to that of industrial hydrogen peroxide ammonia oxidation.
The rate is the same, which verifies a new way of coupling in-situ H2O2 synthesis and ammonia oxidation to realize green chemical production
.

In this work, the researchers demonstrate the central role of AuPd alloy and titanium-silicon molecular sieve (TS-1) as a bifunctional catalyst: AuPd alloy with optimized metal ratio and loading can be efficiently generated under heating and weak alkaline environment H2O2, and TS-1 can effectively use the in-situ generated H2O2 to complete the ammonia oxidation reaction
.
Single-component Au has no catalytic activity for this reaction, single-component Pd shows a certain conversion rate but relatively low selectivity, and the catalyst with simple physical mixing also has no catalytic activity, but once the AuPd alloy is formed, the reaction activity is greatly improved.
improvement
.
The supported AuPd alloy has excellent catalytic activity to catalyze H2/O2 to H2O2, but no ammonia oxidation catalytic ability; while TS-1 can catalyze the formation of cyclohexanone oxime when commercial H2O2 solution is used as the oxidant, but the selectivity is poor
.
The simple physical mixing of the two catalysts yields excellent catalytic performance, which proves that the in-situ generation of H2O2 can be used to efficiently and conveniently complete the catalytic preparation of this important polymer monomer
.

core innovation

1.
A breakthrough design of titanium-silicon molecular sieve-supported gold-palladium alloy catalyst to achieve direct hydrogen, oxygen, ammonium bicarbonate and cyclohexanone under conditions close to industrial hydrogen peroxide ammoxidation (same type of reactor and reaction conditions).
One-step high-selectivity preparation of cyclohexanone oxime;

2.
The AuPd alloy with optimized metal ratio and loading can effectively generate H2O2 under heating and weak alkaline environment, while TS-1 can effectively use the in-situ generated H2O2 to complete the ammonia oxidation reaction

Industrial Applicability

In order to verify its industrial applicability, the researchers designed a special fixed fluidized bed reactor to evaluate the reactivity and lifetime of the catalyst in an industrial-like facility
.
Experiments show that the catalytic activity has remained stable for a long time of 40 hours or 250 hours, and there is no obvious decline
.
In cooperation with Japan's UBE Corporation (UBE Corporation, one of the main manufacturers of nylon), the researchers conducted an economic evaluation of this catalytic system and found that if the catalytic life of the precious metal is only 0.
75 years, the in-situ generation of H2O2 to prepare cyclohexanone oxime The cost of the catalyst is close to the existing industrial production cost.
If the catalyst life is extended to 2.
3 years, its preparation cost will be reduced by 13% compared with the existing industrial cost
.
This economic assessment does not take into account the additional cost savings associated with ex-situ production of H2O2 and transport, dilution,
etc.
Considering the reaction's high conversion, high selectivity, low by-product formation, and high utilization of H2 and NH3, the entire production process is more sustainable and environmentally friendly
.
Through advanced catalyst design, detailed experiments and sufficient microstructure characterization, the researchers successfully combined in-situ H2O2 synthesis with existing chemical production for the first time, and proved scientifically and technically that the use of in-situ H2O2 synthesis can be achieved.
Feasibility and economy of the new route of green chemical industry
.