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Wiped Film Evaporators (WFE) or Rolled Film Systems

Traditional Wiped Film evaporators have been around for a long time. There are a number of manufacturers which offer equipment acceptable in the low vacuum range, where the distillation conditions might not be challenging. Designing robust wiper systems which perform reliably without damaging the evaporator surface in long term operating campaigns is the most challenging engineering feature associated with Wiped Film Evaporation design. The UIC Distillation Division addressed this issue years ago and concluded a "Rolled Film Evaporator" offered a multitude of operational advantages over the traditional wiper approach. Rolled Film Evaporator advantages include:

• Consistent wiped film thickness distributed over the evaporator surface
• Provides a homogeneous material layer across the evaporator with mixing action
• Promotes higher distillation rates as the roller's extended surface increases the evaporator's theoretical surface area by 15% - 25%
• Minimizes wiper maintenance and wear-and-tear on the evaporator with a simple roller mechanism which rarely fails
• No bottom seals are necessary which minimizes the potential for vacuum leaks.

This special wiper system is used in the UIC rolled Film evaporators and Short Path Evaporators. This roller wiped film system has proven it has tremendous advantages in many applications over the years. The roller system consists of a cylindrical "basket", composed of guide rods on which rollers are fixed. The rollers are made of a glass fiber reinforced PTFE compound. The roller wiped film system is driven by a motor from outside the distillation chamber. The centrifugal force presses these rollers into the liquid film flowing downwards. Since there is no mechanical load on the evaporation surface, scratches and "fouling" are avoided. The roller wiped film system guarantees a uniform, laminar mixing of the thin film on the entire evaporator surface. Due to overlapping of the rollers and wiping on the unheated areas, so-called "dead-zones" are avoided. At the same time, the liquid thin film on the rollers is continuously renewed. This results in a very low residence time of the evaporating feed on the evaporator surface. Build-up or caking of material on the evaporator surface and on the rollers, which might happen with other wiping systems, is completely avoided with the UIC designed roller wiped film system.

The large clearance between rollers and guide rods facilities a "floating roller" which assures an even distribution of the feed material on the evaporator without causing damage to the evaporator. The necessity for a bottom bearing for the wiper basket is precluded by the floating action of the roller, so problems related to product penetrating into the lower bearing, or vacuum leaks through the bearing are eliminated.

Rolled Film Evaporators

The Rolled Film Evaporator is used in conjunction with an external condenser. The Rolled Film Evaporator serves as an excellent degasser, or for stripping slightly volatile compounds including water, alcohols, aromatic and aliphatic solvents, esters and other similar chemical compounds. Rolled Film Evaporators are often employed upstream of higher vacuum short path evaporators to remove volatile compounds and facilitate higher feed rates in the short path equipment. The normal operating conditions of Rolled Film Evaporators are similar to other vacuum tight Wiped Film Evaporators, and distillation may be conducted at atmospheric equivalent boiling points as high as 500°C, with vacuum levels as low as 1.0 - 5.0 mbar, provided the external condenser and the vacuum set are designed complimentary to the volatility of the material.

Laboratory Distillation Systems

Laboratory Distillations Systems can be as simple as a borosilicate glass, single stage rolled film or short path unit with an evaporator surface area of 0.01 mˆ2, to a more sophisticated multi-stage system incorporating wiped film evaporators as the initial stage with subsequent short path stages. The more complex laboratory units are often fabricated with 316 stainless steel or high nickel alloys for use under extremely corrosive conditions.

Below is a table indicating typical single stage laboratory units and their respective capacities. Also indicated for reference are some photographs of standard laboratory units.

Laboratory Single Stage Distillation Units
Unit Specifications	RFL 1	RFL 4	RFL 6
Nominal Processing Rate (kg/hour)	0.01-0.02	0.04-1.00	0.04-5.0
Evaporator Surface Area (square meters)	0.018	0.043	0.06
Condenser Surface Area (square meters)	0.05-0.10	0.20-0.40	0.30-0.60
Operating Pressure (square meters)	Atmospheric to 1.00 mbar
Length (mm)	1,000	1,000	1,000
Diameter (mm)	400	500	700
System Weight (approximate kg)	50	65	125

Commercial Distillation Systems

Commercial Standard Single Stage Rolled Film Distillation Units
Unit Specifications	RF 20	RF 50	RF 100	RF 200	RF 400	RF 800	RF 1200	RF 1600
Nominal Processing Rate (kg/hour)	30	75	150	300	600	1,200	1,800	2,400
Evaporator Surface Area (square meters)	0.20	0.50	1.00	2.00	4.00	8.00	12.00	16.00
Condenser Surface Area (square meters)	2.00	5.00	10.00	20.00	40.00	80.00	120.00	160.00
Operating Pressure (absolute mbar)	Atmospheric to 1.0 mbar (optimum)
Length (mm)	1,550	2,400	3,000	4,750	5,500	7,200	7,500	8,200
Diameter (mm)	130	160>	280	340	500	800	1,200	1,500
System Weight (approximate kg)	100	150	400	1,000	1,500	3,500	6,500	10,000

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