Click to enlarge the image

.1              Evaporation

Evaporation is for non-volatiles where volatile liquids are separated from non-volatile solutes. The properties of the liquid and the solute determine parameters such as temperature, pressure and time to apply. On laboratory scale the rotary evaporator is the most common. Other evaporator techniques are falling film evaporator, wiped film evaporators and spinning cone evaporators. Considerable savings can be made by using multi-stage evaporation and falling film evaporation (Xiu & Zeng, 2008). Evaporation differs from distillation in that the vapour usually is a single component, and even when vapour is a mixture, no attempt is made to separate the vapour into fractions.

.2              Extraction

Extraction is a technique where you transfer one or more compounds from one phase to another. Compounds can be extracted from both liquid and solid phase. Depending on which compounds are wanted, their properties and from what they are extracted there are several parameters to be taken into consideration and special techniques that can be performed. The solubility of the solute in the extraction solvent is the most important parameter.

Liquid-liquid extraction is mostly used by organic chemist to separate products from by-products and unreacted starting material after a chemical reaction. The liquids involved have to be immiscible in order to form two layers upon contact. Extraction is often referred to as washing. However, the washing really refers to the removal of impurities from the target compound i.e. water by extraction with saturated sodium chloride solution while the extraction removes the target compound from an impure matrix.

Solid-liquid extractions are used in industries to extract valuable natural compounds from different plants. To optimise recovery of the wanted compounds the extraction solvent must diffuse into the solid sample in order to reach the solute. The solute has to be soluble in the extraction solvent to diffuse out of the sample into the bulk solution. Elevated temperatures shorten the extraction times and improve yields. However, higher temperatures might lead to degradation of the solute. To increase the extraction efficiency an applied pressure can keep the solvent in liquid state at higher temperatures and increase the rate of which the solvent permeates through the sample due to the extra applied pressure. Where the solvent reaches a supercritical stage as a result of applied temperatures and pressures it obtains gas-like properties of diffusion, viscosity, and surface tension, and liquid-like density and solvation power and the extraction method is then called supercritical fluid extraction, SFE. (Azmir, o.a., 2013)

.3              Chromatography

Chromatographic separation is based on differences in the migration velocities of components of a mixtures passing through a stationary phase that typically consists of solid particles packed as a bed in a chromatography column. The velocity depends on the components level of interaction with the mobile and the stationary phases. Partitioning between solid phase and solute may for example come from adsorption, ion-exchange, ligand-exchange, ion-exclusion and/ or size exclusion. In large scale production distillation and crystallization are most efficient since chromatography in comparison is more costly in general. In the design of chromatography processes for complex mixtures a stepwise combination of different separation modes is often the most efficient and a number of biomass separations by chromatography have been investigated. (Hellstén, Siitonen, Mänttäri, & Sainio, 2012), (Hellstén, Lahti, Heinonen, Kallioinen, & Mänttäri, 2013), (Hellstén, Heinonen, & Sainio, Size-exclusion chromatographic separation of hydroxy acids and sodium hydroxide in spent pulping liquor, 2013)

Simulated Moving Bed (SMB) chromatography is used commercially to separate fructose and glucose and there is a lot of potential using this technology to separate even other biomass fractions. The advantage of SMB is the ability to purify larger quantities using less solvents, less stationary phase and less energy than batch chromatography. One more technology that could be considered is Counter Current Chromatography (CCC). Chromatography are, for example, investigated for recovery compounds in black liquor

.4              Distillation

In practice, distillation may be carried out by either of two principal methods. The first method is based on the production of a vapour by boiling the liquid mixture to be separated and condensing the vapours without allowing any liquid to return to the still. There is then no reflux. The second method is based on the return of part of the condensate to the still under such conditions that this returning liquid is brought into intimate contact with the vapours on their way to the condensate. Either of these methods may be conducted as a continuous process or as batch process. (McCabe, Smith, & Harroitt, 1985)

.5              Crystallisation and Precipitation

Crystallisation is a unit operation frequently used for isolation and purification of materials in processes ranging from bulk chemicals to specialty chemicals and pharmaceuticals, on scales from thousands of tons down to grams per day. Commercial crystallisers may operate either continuous or batch wise. Crystallisation is important in industry as compared to other separation techniques, e.g. distillation or membrane processes, crystallisation requires less energy. The handling and storage of a material is easier with a crystalline material as compounds often are more stable in its crystalline form. This reduces costs and hence affects the industry.

A precipitate is an insoluble solid that emerges from a liquid solution. The emergence of the insoluble solid from solution is called precipitation. Often the precipitate emerges as a suspension. Precipitates can form when two soluble salts react in solution to form one or more insoluble products. The insoluble product separates from the liquid and is called a precipitate. Precipitates can also form when the temperature of a solution is lowered. The lower temperature reduces the solubility of a salt, resulting in its precipitation as a solid. (chemicool)

.6              Flocculation

Flocculation is an important separation step in many processes that depends on physical, chemical and biological factors. The floc formation depends on the ability of compounds or micro-organisms to stick to each other and to other particles. Flocculation in pulp and paper mills needs case specific sludge treatment as each pulp mill has unique sludge’s. (Hakkarainen & Sillanpää, 2007)