Application Scheme for Determination of Metal Elements in Crude Oil (ICP-AES Method)

Key words :ICP-AES metal elements

Introduction: The existence of some trace metal elements in crude oil has adverse effects

on   petroleum   processing,   storage   and   transportation   process   and   environmental protection.  Therefore,  the  type  and  content  of  harmful  elements  in  crude  oil  is  an important  index  to  evaluate  the  quality  of  crude  oil.  At  present,  the  commonly  used methods  for  the  determination  of  trace  elements  in  crude  oil  are  atomic  absorption spectrometry,  atomic  fluorescence  spectrometry,  ultraviolet  visible  spectrophotometry and  so  on.  With  the   development  and  maturity  of  atomic  emission  spectroscopy, inductively coupled plasma atomic emission spectrometry (ICP-AES) has been widely used in  the  elemental  analysis  of  crude  oil  because  of  its  features  such  as  simultaneous determination of multiple elements, wide linear range, high sensitivity, small matrix effect, high  precision,  fast  and  accurate.  A  rapid  method  for  the  determination  of  14  metal elements including Barium, calcium, cadmium, cobalt, chromium, copper, iron, potassium, magnesium,  sodium,  nickel,  lead,  vanadium  and  manganese  in  pipeline  crude  oil  was established by ICP-AES.

Instruments and reagent materials

Macylab  ICP-6800S  Inductively  Coupled  Plasma  Emission  Spectrometer  (petrochemical machine);

Muffle furnace;

Quartz volumetric bottles include 100 mL and 50 mL, soaked in 10% hydrochloric acid, 10% nitric acid, rinsed with deionized water, dried in the oven for use, quartz crucible (100 mL), boiled in 10% hydrochloric acid solution, burned at 750℃ in Muffle furnace for 2 h, cooled to room temperature and stored in the dryer for use.

Standard reserve liquid containing barium, calcium, cadmium, cobalt, chromium, copper, iron, potassium, magnesium, sodium, nickel, lead, vanadium and manganese, 1000mg/L; Nitric acid (68%), excellent purity; Argon, purity greater than or equal to 99999%.

Sample handing

Weigh 30.0 g crude oil sample after mixing with electric mixer. The sample is placed in a crucible, heated on an electronic multipurpose furnace, and burned freely until the fire is extinguished. Then the residue is transferred to a high-temperature Muffle furnace and burned for a certain period of time until the residue completely becomes ash. The residue is taken out and cooled to room temperature, then 15 mLHNO3 is added and dissolved on an electric heating plate.  Heat and concentrate to  1-2 mL, cool and transfer to  50 mL volumetric bottle, dilute to scale, shake well. The sample treatment of blank test is carried out according to the above method except that the sample to be tested is not added.

Instrument Operating Condition

Through the  recommended  instrument  conditions  and  repeated  exploration  tests,  the instrument conditions were optimized as follows: radio frequency power 1150W, atomizer pressure 207.5kPa, auxiliary gas flow rate 0.5L /min, peristaltic pump speed 100 r/min. The analytical spectral line data of selected elements were shown in Table 1.

Table 1.    Elemental analysis spectral line data and series

Working curve drawing

Standard reserve solution containing barium, calcium, cadmium, cobalt, chromium, copper, iron, potassium, magnesium, sodium, nickel, lead, vanadium and manganese (1000 mg/L)  was configured into standard use solution of 100 mg/L.

Ca, V, Pb standard liquid 2.0, 4.0, 6.0, 8.0, 10.0 mL, Fe, Ni standard liquid 1.0, 2.0, 3.0, 4.0, 5.0 mL,  Mn,  Mg,  Cu, Co, Cd,  Ba, Cr standard  liquid 0.1, 0.4,  1.0,  1.4,  20  mL  in  100  mL volumetric bottle, Ca, V, Pb(2.0, 4.0, 6.0, 8.0, 10.0mg/L), Fe, Ni(L.0, 2.0, 30, 4.0, 5.0 mg/ l), Mn, Mg, Cu, Co, Cd, Ba, Cr (0.1, 0.4, 1.0, 1.4, 2.0mg/L) A series of mixed standard solutions a, b, c, d, e.

Na was removed and K standard solution 2.0, 4.0, 6.0, 8.0, 10.0 mL was used in 100 mL volumetric  bottle  and  configured   into   B  series  mixed  standard  solution  f,  g,   h,  i,  j containing Na and K(2.0, 4.0, 6.0, 8.0, 10.0 mg/L).

Testing

Under the set instrument test conditions, the metal content of the standard solution is

measured, and the working curve is drawn according to the measured results. According to the working curve, the metal element content of the sample is determined under the   set instrument test conditions.

Result and discussion

The choice of ashing conditions

Ashing time A batch of crude oil samples were selected and treated at ashing temperature of  500℃,550℃,650℃,700℃ and  ashing  time  of  20,  25,  30  and  40h,  respectively.  The results show that when the ashing time is 3 h, the ashing is complete.

When  the  ashing  temperature  is  550 ℃ ,  the  measured  value  of  each  metal  element content is basically the highest. This is because at 500℃ the sample did not complete the ash, the remaining small carbon  particles are easy to absorb  metal elements, and it is difficult to dissolve with acid; At 650℃ and 700℃ , the ashing temperature is too high, which causes the volatilization of elements and the retention of the crucible wall, so that the measured value of each metal element content is low. So the ashing temperature was chosen at 550  ℃.

When analyzing the content of metal elements in crude oil, the crucible ashing method is used to treat the sample. Quartz crucible is suitable for the melting crucible during the ashing of pipeline crude oil. The suitable ashing conditions are as follows: temperature 550  ℃, time 3 h.

The  inductively  coupled  plasma  atomic  emission  spectrophotometer  is  used  for  the determination of metal elements in pipeline crude oil. It is simple, rapid and accurate to determine  many  elements  at the  same time  by  treating  the  sample  at  one time. The detection limits of all metal elements ranged from 0 000 6 to 0.723 omg/L. The relative standard deviations of all other metal elements except cadmium were less than 7.0%, and the recoveries were between 91% and 115%.

Machine parameters

Macylab ICP-6800S Inductively Coupled Plasma Optical Emission Spectrophotometer

Product introduction

ICP-6800  series   inductively  coupled   plasma  emission  spectrometer   is  an   inductively coupled plasma emission spectrometer developed by our company after many years of technology accumulation. It is used to determine the content of trace and trace metallic elements  or  non-metallic  elements  in  various  substances  (which  can  be  dissolved  in hydrochloric acid, nitric acid, hydrofluoric acid, etc.), with high degree of automation, easy operation, stable and  reliable. At  present, the  instrument  is widely  used  in  rare  earth, geology,  metallurgy,  chemical   industry,  environmental   protection,  clinical   medicine, petroleum   products,   semiconductors,    food,   biological    samples,    criminal   science, agricultural research and other fields.

3. Working environment

Storage and transportation temperature :15℃-25℃ Storage and transportation relative humidity :≤ 70% Atmospheric pressure :86-106 kPa

Power supply adaptability :220±10v 50-60MHz Working humidity :≤ 70%

Operating temperature :15℃-30℃