R help - Jul 2017 - How to replace match words whith colum name of data frame?

I have two data frame. I want to use "chemical_df" to match
"concept_df "


concept_df <- data.frame(concept=c("butan acid ", "nano
diamond particl", "slurri
composit", "composit ph polis", " inorgan particl ", 
"grind liquid", "liquid formul", "nanoparticl",
"size abras particl", "agent malic acid"))

chemical_df <- data.frame(chemical=c("basic", "alkalin",
"alkali", "acid",  " ph ", "hss"))

Here is my match code:

library(magrittr)
match_df <- NULL
for (i in 1:length(chemical_df$chemical)) {
match_df<-data.frame(category=concept_df[grep(chemical_df$chemical[i],
concept_df$concept), ] ) %>%
rbind(match_df)
 }

But I don't want this result:
          concept                                category
        1 butan acid                          butan acid
        2 nano diamond particl
        3 slurri composit
        4 composit ph polis             composit ph polis
        5 inorgan particl
        6 grind liquid
        7 liquid formul
        8 nanoparticl
        9 size abras particl
        10 agent malic acid              agent malic acid

I desire to get :
          concept                               category
        1 butan acid                         chemical
        2 nano diamond particl
        3 slurri composit
        4 composit ph polis             chemical
        5 inorgan particl
        6 grind liquid
        7 liquid formul
        8 nanoparticl
        9 size abras particl
        10 agent malic acid             chemical

Is any way to solve it?


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