Novel Technique for Coating of Fine Particles Using Fluidized Bed and Aerosol Atomizer

Round 1

Reviewer 1 Report

Zhang et al. present an attractive novel approach for coating Geldart A particles in a fluidized bed. This interesting work certainly deserved publishing in Process. I have just two suggestions for the authors for further strengthening the paper:

1. In the introduction, the authors solely focus on the coating of particles by spraying a liquid. Especially for small particles, gas phase coating techniques (chemical vapour deposition, atomic layer depositions, …) might be a good alternative for a number of applications. It would be good if the authors mention this briefly.
2. The discussion of the yield is quite relevant for a chemical process, and an important aspect when scaling up. Even the largest values given now seem quite low. Could the authors give an indication of typical industrial values, and briefly discuss the expected effect of scaling up on the currently determined values?

Author Response

Dear reviewer,

Thank you very much for your suggestions. In view of your two questions, I have made changes in the corresponding positions of the article. Please see th attachment.

1. In the introduction section, you suggest to give a brief introduction to other coating technologies. I have added the introduction of electro plating, chemical and physical vapor deposition in lines 9-11 of the article. The corresponding applications are also mentioned here.

2. As for the yield of the modified process, due to the structure of aerosol generator and fluidized bed, the current yield of this process is really low. The explanation and improvement in this aspect are added to the conclusion of this paper. You can see the text added in lines 468-471.

Thank you again for your advice. If you have more questions, please don't hesitate to let me know.

Sincerely

Rongyi

Reviewer 2 Report

My background includes coatings technology and powder synthesis for additive manufacturing, powder coatings, paints, thermal spray and cold spray processes.

This paper discusses a technique for the combined use of a Wurster fluidized bed and a novel aerosol atomizer to coat particles primarily for the chemical, food and pharmaceutical industries which have different requirements.

So my first comment concerns the very first sentence which states that "Most coating processes are using core particles of a diameter larger than 200 μm, otherwise 9 agglomerates will be formed. This study contributes to the development of a new coating process 10 for fine particles with diameter around 50 μm".

I want to point out that the cold spray and thermal spray processes routinely use particles that are ~44um average, so the opening statement in the abstract is quite misleading and is false depending on the industry. So the paper needs to clarify this by stating up front that their process is specific to certain industries and not make general statements that do not apply to other industries that use powder particles.

Secondly, the use of an aerosol  atomizer is not unique and the technique that is discussed in the article is very similar to spray drying process. "Spray drying involves the atomization of a liquid feed into very small droplets within a hot drying gas leading to flash drying of the droplets into solid particles. The particles are then separated from the drying gas, using a cyclone and/or a filter bag, as a final spray-dried product. Spray drying is one of the most remarkable technologies currently to be applied to pharmaceuticals. It is a continuous process that converts, in a single step, a liquid feed into a powder and is an ideal process when precise attributes such as particle size, morphology and stability are required". [https://www.europeanpharmaceuticalreview.com/article/27768/spray-drying-pharmaceutical-industry/]

However, there is a distinction in that the article uses an aerosol atomizer to coat the particles whereas spray drying is used to form agglomerates of particles, in some cases much finer particles (i.e.  <1um or in the nano-scale).

There are other techniques, such as electroplating, chemical and physical vapor deposition and others that can completely encapsulate particles within the specified range discussed in the paper, but may not be conducive to food or drugs, which emphasizes the reason to be specific about what industries are to be targeted. In summary, the paper needs to clarify this by stating up front that their process is specific to certain industries and not make general statements that do not apply to other industries that use powder particles. 

Author Response

Dear reviewer,
Thank you very much for your suggestions. In response to your questions, I have made changes in the corresponding position of the article. Please see the attachment.

1. In the introduction section, you suggest to give a brief introduction to other coating technologies. I have added the introduction of electro plating, chemical and physical vapor deposition in lines 9-11 of the article. The corresponding applications are also mentioned here.
In addition, thank you very much for the comparison of aerosol generator and spray drying process, which is our next research direction.
Thank you again for your advice. If you have more questions, please don't hesitate to let me know.
Sincerely
Rongyi