Is it possible to obtain the richter grade of an earthquake with the data of an accelerometer?
The Richter Number is a measure of total energy released in an earthquake.  To calculate it, even roughly, you need to know the epicenter of the earthquake (that needs at least three measurements from three locations) and the length and intensity of the shaking to determine the energy contained in the waveform.  All you seem to have with your accelerometer is the peak intensity of the shaking at a single point.  So the answer is no.