Technology

Process yields marketable biomass fractions Battelle-Geneva Laboratories'

process separates, upgrades

all three main components of

Ikjnocellulosic materials

without expensive chemicals

The first phase in development of a new process for fractionating ligno-cellulosic biomass into its main con­stituents—pentose, cellulose, and lignin—is drawing to a close at Bat­telle-Geneva Laboratories. A second phase leading to design of a pilot plant likely will be getting under way soon.

Work on the process is being car­ried out by researchers A. Johansson and J. P. Sachetto and section man­ager A. Roman in the industrial technology center of the Swiss labo­ratories. Their work to date has aimed at establishing the basic reaction pa­rameters for a process to upgrade biomass—composed, for example, of mixed agricultural and forest resi­dues.

For dealing with biomass made up of residues, the researchers point out, processes should not be very sensitive to scaleup so that relatively small units can be constructed near local sources of raw material supply or specialty pulp demand. For an eco­

nomically viable operation, they say, a process ideally should be such that all three of the main components of lignocellulosic materials—cellulose, hemicellulose, and lignin—can be separated and upgraded indepen­dently, without the need for expen­sive chemicals and large amounts of energy.

The Battelle researchers think they have such an approach. In their pro­cess, the hemicelluloses are obtained as pentose monomers. The cellulose, almost lignin-free, can be hydrolyzed further into glucose. And the lignin could be used either as a fuel or as feedstock for production of phenol and monoaromatics.

The process uses phenols as a sol­vent. The researchers point out that phenols have long been known as good solvents for lignin, particularly in the presence of acid catalysts. But when phenol is used as a lignin sol­vent under acidic conditions, it is lost rapidly through copolymerization with lignin and possibly with furfural formed from the hemicellulose in the raw materials.

Although phenols are used as de-lignification solvents in the Battelle-Geneva process, resinification is avoided, the researchers say. The delignification is carried out at 100 °C and atmospheric pressure. Under these conditions, the phenols are to­tally miscible with the water phase, forming a homogeneous liquid phase

into which the lignin is dissolved, with simultaneous hydrolysis of the hemi­cellulose.

The remaining fibrous cellulose fraction is separated by filtration and the liquid phase allowed to cool. During cooling, the phenolic portion with the dissolved lignin separates spontaneously from the aqueous phase containing the pentoses. The aqueous phase can be recirculated to increase concentration before further treatment of the pentoses. The phe­nols are separated from the hydro­phobic fraction and recirculated.

The remaining lignin fraction, which is free of sugars, can be used as a fuel. Alternatively it can be hydro-cracked to produce phenol for make­up in the process. Hydrocracking, the researchers say, offers a straightfor­ward way of upgrading the lignin fraction. Not only does it provide an autonomous source of phenol for makeup but it produces excess amounts of phenols and monoaro­matics of commercial value.

A major objective of the Geneva lab has been to develop a process that makes use of existing industrial equipment for a full-scale operation, thus holding down scaleup and equipment costs. Corrosion tests have been carried out so that materials of construction can be specified.

On this basis, investment cost has been worked out for a plant size of 100,000 tons of pure cellulose pulp per year—not an optimal size, it being on the small side, but sufficient as a basis for comparison. The plant would treat about 220,000 tons of raw ma­terial per year. By-products would consist of 44,000 tons per year of pentose (in about 15% aqueous solu­tion) together with a net production of about 7000 tons per year of phenol and 14,000 tons per year of liquid fuel oil.

Total investment cost for a bat­tery-limits plant is estimated at $34 million, including a hydrocracking unit. Annual production costs for raw material, chemicals, and labor would come to $14 million, assuming a price of $50 per ton for raw material and reasonable chemical losses in the op­eration. The total energy balance shows a small surplus production of energy.

James Krieger, Washington

Process upgrades biomass using phenol as solvent

Phenol Separation I—+-Pentose

Biomass » B Digestion

Cellulose ^ fraction

w Lignin fraction

38 C&ENMay31 , 1982

Filtration Separation

Washing

Lignin processing

Phenol makeup

Phenol

Aqueous phase