Membrane Sleeve Spray Drying for Respirable Powder Recovery
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Solution Overview
Problem
Conventional spray drying systems are inadequate for producing small quantities of dry, solvent-free powder with particle sizes suitable for respirable aerosols, as they suffer from high process losses, limited scalability, and inefficient solvent vapor removal, particularly for pharmaceutical agents requiring particle sizes below 5 µm.
Innovation Solution
A counter-current spray drying system with a vertical tube reactor and a permeable membrane sleeve that separates the descending aerosol flow from the ascending air flow, allowing diffusive solvent removal while preventing convective mixing, along with a recirculation loop for solvent stripping and a tangential air flow to enhance drying efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional spray drying systems are used to produce small quantities of powder, then the production scale matches preclinical development needs, but the process losses are too high and yield is insufficient
Solution Approach 1:
A membrane sleeve is introduced as an intermediary component between the aerosol stream and the drying gas flow. The membrane allows selective permeation of solvent vapors while preventing direct contact between the aerosol particles and the drying gas, thereby minimizing particle losses and maximizing product recovery yield.
Solution Approach 2:
The system employs a thin membrane sleeve that flexibly surrounds the aerosol stream. This thin film structure provides a large surface area for solvent vapor removal while maintaining minimal resistance to aerosol flow, enabling efficient drying with high particle recovery.
2Productivity
If heated drying gas is used to quickly evaporate solvent, then drying speed increases, but particle temperature rises and may damage labile compounds
Solution Approach 1:
The membrane sleeve acts as a thermal barrier that mediates between the heated drying gas and the aerosol particles. It allows solvent vapor to pass through while preventing excessive heat transfer to the particles, maintaining their temperature within safe limits for labile compounds.
Solution Approach 2:
The system changes the drying mechanism from direct thermal heating to controlled vapor permeation. By adjusting the membrane properties and drying gas flow rate, the process achieves efficient solvent removal without relying on high temperatures that would damage sensitive pharmaceutical agents.
3Ease of operation
If cyclones or filters are used to separate particles from process stream, then particle collection is achieved, but product yield is considerably lower than 60%
Solution Approach 1:
The membrane sleeve serves as a continuous intermediary that facilitates gentle particle separation throughout the drying process. Particles are collected at the end of the process stream with minimal losses, achieving yields exceeding 90% compared to conventional cyclone or filter methods.
4Object-generated harmful factors
If absorptive material is used to remove solvent vapors, then solvent removal is achieved, but the material becomes contaminated with dried substances and requires frequent changing
Solution Approach 1:
The membrane sleeve is positioned as an intermediary barrier that prevents dried substances from contacting the absorptive material. Solvent vapors permeate through the membrane for removal, while the particle-laden aerosol stream remains separated, eliminating contamination of the absorptive material and reducing maintenance requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system achieves high yield (>80%) of dry, solvent-free particles with controlled particle sizes (1-5 µm) and extended residence time, reducing aerosol losses and enabling the processing of labile agents at ambient temperature, while maintaining the integrity of the drying process.
Implementation Method 1
The membrane is permeable in order to admit diffusion of vaporized solvent from the process stream to the ascending air stream
Implementation Method 2
a membrane sleeve essentially surrounding the peripheral area of said process tube, separating the descending process stream from the ascending air stream. The membrane sleeve is permeable in order to admit diffusion of vaporized solvent
Implementation Method 3
a counter-current spray drying system with a vertical tube reactor and a permeable membrane sleeve that separates the descending aerosol flow from the ascending air flow, allowing diffusive solvent removal
Implementation Method 4
a spray generating device, capable of generating said aerosol droplets of solution
Implementation Method 5
extended residence time at ambient temperature, thereby being able to process normally labile agents
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
The invention relates to a spray drying system and a method for its operation that provides a composition of dry. or essentially solvent free, particles from a solution of an agent. The system comprises a generally vertical tube reactor arranged for counter-current removal of solvent from a process flow fed with aerosol droplets of solution descending from the top said reactor with an ascending gas flow. The reactor includes a perforated process tube for transportation of the process flow from the outlet of an aerosol generating device to a dry particle collecting device. A membrane sleeve essentially surroundes the peripheral area of said process tube and separates the descending process stream from the ascending gas stream. Vaporized solvent is transported from the process stream to the ascending gas stream. A reactor housing is sealingly covering said process tube and membrane sleeve and is provided with means for introducing and/or removing the process fluids.