Development Priorities of Cooling Water Treatment Agents
                        By Cheng Zhangjin
China National Chemical lnformation Centre
China is extremely short of water resources.  The  pollution  of  water
sources in China is getting more serious. With the  rapid  development
of the  national  economy,   the  water  consumption  in  industry  is
increasing fast and making the shortage of  water  resources  all  the
more prominent. The water consumption in urban areas was 46.9  billion
m3 in 1995, in which the consumption in industry was 32.8  billion  m3
(accounting for around 70%), and the amount of cooling  water  used  in
industrial production accounted for 80% of the total water consumption
in industry. Increasing the recycle rate and  reducing  the  discharge
amount of cooling water is therefore the focus in water conservation.
The introduction  of  large  chemical  fertilizer  units  in  the  70's
promoted the development of cooling water recycle technologies.  While
assimilating most of foreign water treatment technologies, China  also
developed its own technologies of special features in  the  80's.   To
promote the development of water treatment technologies  to  a  higher
level and accelerate their application in commercial production,   the
State Science Commission allocated special funds in  the  90's  to  24
major debottlenecking research projects of water treatment agents  and
arranged a group of projects for commercialization of research results
. All these projects have already passed technical appraisal.
scale inhibition and dispersion agents
Organic scale inhibition and  dispersion  agents  used  most  often  in
recycle cooling water include polycarboxylic acids (polyacrylic  acid,
polyacrylic amine and polymaleic acid), copolymers with sulfonic  acid
group, phosphonates and phosphonic  carboxylic  acids  also  with  the
property of corrosion inhibition. The development of  copolymers  with
sulfonic acid group is in full swing in China in the recent years.  It
caught the special attention in foreign countries in the  80's. However,
China was unable to make research and development at that time due  to
the lack of AMPS.  Many  domestic  producers  developed  tertiary  and
quaternary copolymers of AMPS in the 90's, and copolymers  with  other
sulfonic acid monomers (such as ethylene sulfonic acid  and  propylene
sulfonic acid) started commercial production.
The development of phosphorus-containing polymers is focused once again
in China. Phosphorus-containing copolymers of acrylic acid and acrylic
esters, and tertiary copolymers with carboxyl group,  sulfonic  group,
phosphate group and a non-ion group have been  developed.   Phosphorus
-containing copolymers have applied for patent,  and  the  fomer  State
Science Commission has already constructed a 1 000 t/a commercial unit
.
corrosion inhibitors
Corrosion  inhibitors  can  be  divided  into  organic  varieties   and
inorganic varieties.
Phosphonic organic varieties still hold the leading position  in  China
and have been the focus for research and development for  many  years.
Divinyl triamino pentamethyl phosphonic acid was  developed  in  1997.
The product has excellent property of scale and  corrosion  inhibition
when used in water with high alkali content and extra hardness.
Phosphorus-free organic varieties have been the target  of  development
for long  years  because  the  products  can  eliminate  environmental
pollution caused by phosphorus-containing varieties and facilitate the
control of bacteria and algae in cooling water. Due to factors such as
high production cost and poor corrosion inhibition, however, they  are
still at the research stage and have seldom been used in cooling water
systems.
Inorganic varieties  mainly  include  those  of  nitrites,   chromates,
polyphosphates, silicon series, molybdenum series and tungsten series.
Polyphosphate varieties are used  most  often.   With  more  stringent
requirements in environmental protection,  the  development  of  water
treatment agents causing little environmental pollution has  been  put
on the agenda.  Silicon  and  molybdenum  varieties  are  ideal  water
treatment agents because they cause little harm  to  the  environment.
They will become hot spots for development in the next few years.
biocides
The biocide used most often is oxidative chlorine. Chlorine dioxide has
more advantages than  chlorine,   and  its  consumption  is  therefore
increasing in both domestic and foreign markets.
Non-oxidative biocides developed by China include bromochloro hydantoin
, amide compounds with active bromine, quaternary phosphonium salts and
isothiazolinone. In 1997 China led the world  in  developing  dimethyl
hexadecyl ethylamine. The effect of the product is 5 - 7 times  higher
than traditional varieties and a 400 t/a  capacity  has  already  been
formed.
multi-functional water treatment agents
Multi-functional water treatment agents refer  to  those  with  one  or
several functions  of  corrosion  inhibition,   scale  inhibition  and
bacteria elimination. Their research is still lagging behind in  China
due to the lack of basic theory. Only one  university  is  engaged  in
their research and has so far  developed  modified  natural  polymeric
flocculating agent CG-A. Breakthrough is expected to be  made  in  the
field in the next 10 years, and a new page will be written  about  the
mechanism of water treatment agents at that time.  

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