The refining method of palladium is mainly a combination of chloropalladium acid precipitation and ammonia complexation. (2) The direct reduction method may use two reducing agents of formic acid and hydrazine hydrate. China Metal Palladium Product Standard ( GB1420-89 ) /% species Pd Pt Rh Ir Au Cu Fe Ni Al Pb Si Total impurity HPdt-1 99.99 0.003 0.002 0.002 0.002 0.001 0 0 0 0.001 0.003 0.01 HPd-2 99.95 0.02 0.02 0.02 0.02 0.005 0.01 0.01 0 0.005 0.005 0.05 HPd-3 99.9 0.03 0.03 0.03 0.05 　 0.01 0.01 0 0.01 0.01 0.1
Semi-welded plate evaporator has wide plate gaps, wide channel openings and laser welding, which enable them to perform vacuum and low pressure evaporation processes in both water-based and organic-containing systems.
Evaporator can be considered the point of heat capture in a refrigeration system and provides the cooling effect required for any particular application.There are almost as many different types of evaporators as there are applications of heat exchanger. However,evaporators are divided in to two categories such as (i)direct cooler evaporators that cool air that,in turn,cools the product and(ii) indirect cooler evaporators that cool a liquid such as brine solution that, in turn, cools the product. Normally, the proper evaporator comes with the system. However, there may be an occasion when designing a system, so one will need to determine the requirements and select the proper evaporator from a manufacturer's catalog or manual.
In practice,the following evaporators are commonly used for cooling,refrigerating,freezing,and air conditioning applications:•liquid coolers,•air coolers, and/or gas coolers.
Shell and tube type heat exchangers are the more common form of evaporation units for water cooling and chilling applications.
Evaporator,Semi Welded Evaporator,Rising Film Plate Evaporator,Milk Evaporator Heat Exchanger Jiangsu Baode Heat-Exchanger Equipment Co.,LTD , https://www.baodehex.com
The solution containing palladium 40-50g/L is oxidized by chlorine or, for example, hydrogen peroxide, and a deep red (NH4)2PdCl6 crystal is precipitated by adding ammonium chloride with a theoretical excess of 10%-15%:
H 2 PdCl 4 +2NH 4 Cl+Cl 2 ====(NH 4 )2PdCl 6 ↓+2HCl
It was isolated by filtration after an impurity base metals, palladium salts of boiling water method for the reduction of palladium soluble alkylene ammonium chloride:
(NH 4 )2PdCl 6 +H 2 O====(NH 4 ) 2 PdCl 4 +HCl+HClO
The oxidative precipitation was repeated 2-3 times to completely separate the ruthenium metal. Palladium solution is heated to 80 ° C plus ammonia to complex palladium:
H 2 PdCl 4 +4NH 4 OH====[Pd(NH 3 ) 4 ]Cl 2 +4H 2 O+2HCl
Control pH8~9, filter out other precious metal impurity precipitates, light-colored [Pd(NH 3 ) 4 ]Cl 2 solution is acidified to pH 0.5-1 with hydrochloric acid at room temperature to form yellow [Pd(NH 3 ) 2 ]Cl 2 precipitation:
[Pd(NH 3 ) 4 ]Cl 2 +2HCl====[Pd(NH 3 ) 2 ]Cl 2 ↓+2NH 4 Cl
After filtration, it is complexed with ammonia water, acidified with hydrochloric acid, and repeated 2-3 times to obtain pure dichlorodiamine chromium palladium salt. The combined method can refine 80-99% crude palladium into 99.99% pure palladium with a direct yield of 97%-98%.
The preparation of pure metal palladium has a satin burning method and a direct reduction method.
(1) Calcination method Pure (NH 4 ) 2 PdCl 6 or [Pd(NH 3 ) 2 ]Cl 2 is placed in a porcelain crucible and capped, dried in a dedicated muffle furnace, and then heated to 500-600 ° C. The metal palladium is calcined, but part of the palladium is oxidized to form PdO. It needs to be hydrogen-reduced at 500-600 ° C in a tube furnace. After cooling to 100 ° C, it is protected by an inert atmosphere to room temperature to obtain sponge metal palladium: 
Reduction of metal palladium by direct recovery from weakly basic palladium-containing pure solution with formic acid:
H 2 PdCl 4 +HCOOH=====Pd↓+4HCl+CO 2 ↑[next]
The fine palladium powder produced by the reduction of formic acid adsorbs a large amount of gas, and requires high-temperature hydrogen reduction and cooling under an inert atmosphere to obtain metal palladium.
The metal palladium is produced by reduction of hydrazine hydrate directly from the palladium ammine complex.
Restore from solution:
2Pd(NH 3 )4Cl 2 +N 2 H 4 ·H 2 O=====2Pd↓+4NH 4 Cl+3N 2 ↑+H 2 O
Restore in suspension:
2Pd(NH 3 )2Cl 2 +N 2 H 4 ·H 2 O====2Pd↓+4NH 4 Cl+N 2 ↑+H 2 O
The metal palladium produced by the reduction of hydrazine hydrate is relatively dense, with less adsorbed gas and no need for high temperature hydrogen reduction.
The Chinese metal palladium product standard (GB1420-89) is shown in the table.