The Melt Static Crystallization (MSC) was first used for the purification of coal tar derivatives such as naphthalene or anthracene.
Over the years, LITWIN has developed a lot of new applications of MSC to purify fine chemicals, petrochemicals, food as well as pharmaceuticals intermediates.
More than 60 industrial plants based on the modern version of the PROABD® MSC are in operation worldwide.

ADVANTAGES OF PROABD® MELT STATIC CRYSTALLIZATION (MSC) PROCESS
 
Final Purities up to 99.9+%, high yield
The PROABD® MSC process can achieve over 99.9+% purity or simply the specified commercial product quality. Yields over 95 % can be reached if not limited by the eutectic point or by product solubility at the final temperature of crystallization. Combined with a distillation unit, the purification can be optimized especially for isomer separation.

Low operating costs
The energy consumption of MSC plants is remarkably lower than dynamic crystallization, taking into account the same performance criteria such as purity and yield.

Low maintenance costs
Crystallization is carried out in a closed vessel without any mechanical equipment in contact with the product. As a semi-batch process operating statically, PROABD® MSC operation and maintenance manpower is reduced to less than 0.2 man/day.

Process flexibility
PROABD® MSC is a fully automated semi-batch process. Cycles are running one after the other when the product volume in the feed tank is sufficient.
When the feed flow rate decreases, every cycle will wait until the required volume is available to start up its own sequence of process step. Therefore, the crystallization unit tunes itself automatically to any feed flow rate change. By slight modifications of the operating parameters, the PROABD® MSC process allows the increase of the final purity without any additional equipment.
New market trends highlight this particular advantage of the PROABD® Melt Static Crystallization. Therefore, it is not rare that industrial operating plants are producing chemicals with a higher purity than the designed one.

Easy scale up
The modular system of the crystallizer allows the scale up from single element up to several hundred thousand tons per year capacity.

EXTRACT OF PRODUCT LIST
 
• Benzene and benzene derivatives
• Paraxylene and derivatives
• Toluene and derivatives
• Naphthalene and naphthalene derivatives
• Nitrated and/or chlorinated derivatives of aromatic compounds
• Phenols
• Paracresol, metacresol, xylenols
• Non aromatic cyclic compounds
• Anthracene
• Isocyanates
• Peroxides
• Organic acids
• Aromatic products
• Aliphatic products
• Alcohols, cetones

and other products…
 
PROCESS DESCRIPTION

The PROABD® MSC is a semi-batch process based on the specific phases equilibria of chemical mixtures.
The product is purified in a crystallizer, a vessel equipped with heat exchange surfaces specially designed for cooling and heating the product according to the process steps. Specific internals are used to enable a liquid-solid separation.  The heat exchange is controlled with high accuracy to initiate the growth of crystals with a low specific area.

THE PROCESS STEP BY STEP

FEEDING
The crystallizer is filled with the crude product from the feed tank.

PRECOOLING
The product is precooled down to the crystallization point by an appropriate thermal fluid circulation in the crystallizer. The thermal loop is cooled by a refrigerant according to the considered temperature level.

CRYSTALLIZATION
The feed product is exposed to a further controlled cooling and the crystallization starts. The geometry of internals as well as the product immobility enable an optimal and uniform crystal growth finally contributing to establish a crystalline network comparable to a column packing. Crystals are obtained with low specific surface area.
During this step, impurities are concentrated in the liquid phase surrounding the pure crystals.
The crystal rate (crystal mass vs. total feed mass) can be limited by:
• an eutectic point,
• the final temperature level.
The density of the crystalline network must be optimized to obtain a predetermined permeability during next steps of the process sequence.

DRAINING
The liquid fraction (reject) containing the concentrated impurities flows out of the crystallizer by gravity.  This liquid fraction can be concentrated at a lower temperature level if needed. In this case, the reject is purified by the same sequence of operation in a concentration stage. Proceeding this way results in a higher yield.

FINAL PURIFICATION
At the end of draining, the crystals are surrounded by a residual liquid film called "retentat" having the same impurities concentration as the reject drained off during previous draining step.
Final purification consists in the purification of this liquid film, that can be performed by two process ways:
• Sweating: it consists of a partial melting induced by a controlled heating of the crystallizer content. The pure liquid resulting from this melting mixes with the residual film surrounding the crystals and flows out by gravity. So the purity of the film surrounding the crystals, and consequently of product contained in the crystallizer increases progressively.
• Washing: it is a repeated feeding and draining of a product of higher purity than the liquid film surrounding the crystals.  The film purity is increasing sequentially.

MELTING AND DISCHARGE
When the targeted purity is reached, the crystallizer content is melted and drained. Generally, the specified purity can be met by one or two stages. For specific products, the number of stages may be higher.

CONTACT

contact.proabd@litwin.fr