Recovery or Destruction —
New Developments for Industrial Wastes
R.D. FOX, Group Leader
K.J. HIMMELSTEIN, Senior Research Engineer
The Dow Chemical Company
Midland, Michigan 48640
INTRODUCTION
The chemical process industries have long practiced the recovery of products and
byproducts from the various solid, liquid and gaseous effluents of their manufacturing
processes. In the past the feasibility of carrying out these recovery steps as part of the
manufacturing process has been determined largely on the basis of economics. Only if the
operations required for recovery could result in the desired return on the investment was the
recovery process ultimately incorporated in the overall design.
In recent years, a new dimension has been added to the measurement of chemical
recovery feasibility. Concern for the environment and its improvement has brought about
the need in the chemical industries for improved manufacturing processes and equipment
and for a higher degree of purification of their effluents.
The treatment of industrial wastes to remove soluble organic chemicals has always
involved decisions requiring a comparison of systems providing recovery with those based
on destruction, and selection of an optimum method. The recent escalations in the value of
organic chemicals and their shortage, as well as the rising costs of energy and shortages of
fuels, make recovery considerations even more important.
The Dow Chemical Company has for many years been committed to maximizing
product recovery and effluent purification while minimizing energy consumption.
Recovery of organic chemicals from aqueous effluents requires some method of physical
separation of the chemicals from the bulk of the waste. One of the most efficient methods
available for the separation of organic chemicals from wastewater is adsorption, especially
on activated carbon.
Activated carbon is unique among adsorbents in its capability to adsorb a wide variety
of industrial organic molecules from both liquids and gases. It can remove them with a
loading or organic per unit weight of carbon typically in the range of 0.1 to 1.0. The removal
is quite efficient, easily producing an effluent with 1 ppm organic in a properly designed
system. Only in cases where the molecule is very small or very large does activated-carbon
fail to perform adequately, and it has long been used to purify water, wastewater and air.
In aqueous applications, recovery of the adsorbed chemicals has received little
attention. Most activated-carbon adsorption systems, in dealing with the problem of what
to do with the saturated or spent carbon, either discard the spent carbon or reactivate it in a
special thermal regeneration furnace, burning off the adsorbed chemicals in a controlled
atmosphere. The latter is more efficient from a carbon usage standpoint but still involves
carbon losses of 5-10% per cycle. This cost can be prohibitive when considered for industrial
waste purification.
Industrial wastes are typically high strength, containing large concentrations of
organic chemicals. Activated carbon thus saturates quickly, and cycle times are short,
requiring frequent carbon regeneration. If thermal regeneration is used, carbon makeup
costs are prohibitively high; as a result, industrial waste treatment systems have been unable
to fully utilize the capabilities of activated carbon.
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